U.S. patent application number 14/118826 was filed with the patent office on 2014-07-17 for enhanced local access in mobile communications using small node devices.
This patent application is currently assigned to NTT DOCOMO, INC.. The applicant listed for this patent is NTT DOCOMO, INC.. Invention is credited to Hiroyuki Ishii, Sayandev Mukherjee, Sean A. Ramprashad.
Application Number | 20140198655 14/118826 |
Document ID | / |
Family ID | 47259869 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140198655 |
Kind Code |
A1 |
Ishii; Hiroyuki ; et
al. |
July 17, 2014 |
ENHANCED LOCAL ACCESS IN MOBILE COMMUNICATIONS USING SMALL NODE
DEVICES
Abstract
A hybrid user equipment and small-node device data offloading
architecture is provided. In this hybrid architecture, the
small-node device includes a backhaul link to a telecommunication
network and/or the Internet. The user equipment can send and
receive data through the small-node device using the backhaul
link.
Inventors: |
Ishii; Hiroyuki; (Palo Alto,
CA) ; Ramprashad; Sean A.; (Palo Alto, CA) ;
Mukherjee; Sayandev; (Palo Alto, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NTT DOCOMO, INC. |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Assignee: |
NTT DOCOMO, INC.
Tokyo
JP
|
Family ID: |
47259869 |
Appl. No.: |
14/118826 |
Filed: |
May 31, 2012 |
PCT Filed: |
May 31, 2012 |
PCT NO: |
PCT/US12/40288 |
371 Date: |
February 28, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61492321 |
Jun 1, 2011 |
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61500426 |
Jun 23, 2011 |
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61502023 |
Jun 28, 2011 |
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61503975 |
Jul 1, 2011 |
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61505955 |
Jul 8, 2011 |
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61512132 |
Jul 27, 2011 |
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61533382 |
Sep 12, 2011 |
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Current U.S.
Class: |
370/235 |
Current CPC
Class: |
H04W 76/14 20180201;
H04W 76/15 20180201; H04W 28/08 20130101; H04W 28/0289 20130101;
H04L 47/12 20130101; H04W 52/383 20130101; H04W 52/242 20130101;
H04W 36/0069 20180801 |
Class at
Publication: |
370/235 |
International
Class: |
H04L 12/801 20060101
H04L012/801 |
Claims
1. A small-node device for offloading data traffic in a cellular
telecommunications system, comprising:
a-macro-base-station-to-the-small-node-device (BS2D) communication
section configured to receive a first control-plane message from a
base station over a BS2D communication link; a
small-node-device-to-user-equipment (D2UE) communication section
configured to transmit user-plane data to a user equipment over a
wireless D2UE communication link established responsive to the
first control-plane message; and a backhaul communication section
configured to receive the user-plane traffic data from a server
over a backhaul link.
2. The small-node device of claim 1, wherein the BS2D communication
link has a master-slave relationship between the base station and
the small-node device.
3. The small-node device of claim 1, wherein the BS2D communication
section is further configured to receive a second control-plane
message from the base station, and wherein the D2UE communication
section is configured to release the D2UE communication link
responsive to the second control-plane message.
4. The small-node device of claim 1, wherein the D2UE communication
section is further configured to transmit the user-plane data in a
radio resource allocated by the base station.
5. The small-node device of claim 1, wherein the D2UE communication
section is further configured to transmit the user-plane data in a
radio resource allocated by the small-node device.
6. The small-node device of claim 1, wherein the D2UE communication
section is further configured to transmit the user-plane data using
radio bearers assigned by the base station.
7. The small-node device of claim 1, wherein the BS2D communication
section is further configured to receive a third control-plane
message from the base station, and wherein the D2UE communication
section is further configured to transmit a pilot signal to the
user equipment responsive to the third control-plane message to
enable the user equipment to measure a radio link quality of the
D2UE communication link using the pilot signal.
8. The advanced user equipment of claim 1, wherein the D2UE
communication section is further configured to transmit the
user-plane data to the user equipment using time slots that are
time division multiplexed with time slots used by the user
equipment to receive additional user-plane data from the base
station.
9. The small-node device of claim 1, wherein the BS2D communication
section is further configured to receive a fourth control-plane
message from the base station, and wherein the D2UE communication
section is configured to reconfigure the D2UE communication link
responsive to the fourth control-plane message.
10. The small-node device of claim 1, wherein the D2UE
communication section is further configured to receive third
user-plane data from the user equipment over the D2UE communication
link, and to upload the third user-plane data to the server over
the backhaul link.
11. The small-node device of claim 1, wherein the backhaul
communication section is configured to connect to the server via at
least one of serving gateway, PDN gateway, or the base station.
12. A mobile station (user equipment) configured to receive
offloaded data from a small-node device in a cellular
telecommunication system, comprising: a
macro-base-station-to-the-user-equipment (BS2UE) communication
section configured to receive both control-plane data and first
user-plane data from the base station over a wireless BS2UE
communication link; and a small-node-device-to-the-user-equipment
(D2UE) communication section configured to receive second
user-plane data from a server through the small-node device using a
wireless D2UE communication link, wherein the BS2UE communication
section is further configured to receive a first control-plane
message from the base station over the BS2UE communication link,
and wherein the D2UE communication section is further configured to
establish the D2UE communication link responsive to the first
control-plane message.
13. The mobile station of claim 12, wherein the BS2UE communication
link is an LTE link.
14. The mobile station of claim 12, wherein the D2UE communication
link uses a carrier frequency that is different from a carrier
frequency used in the BS2UE communication link.
15. The mobile station of claim 12, wherein the BS2UE communication
section is further configured to receive a second control-plane
message from the base station, and wherein the D2UE communication
section is configured to release the D2UE communication link
responsive to the second control-plane message.
16. The mobile station of claim 12, wherein the D2UE communication
section is further configured to receive the second user-plane data
in a radio resource allocated by the base station.
17. The mobile station of claim 12, wherein the D2UE communication
section is further configured to receive the second user-plane data
in a radio resource allocated by the small-node device.
18. The mobile station of claim 12, wherein the D2UE communication
section is further configured to receive the second user-plane data
using radio bearers assigned by the base station.
19. The mobile station of claim 12, wherein the BS2UE communication
section is further configured to receive a third control-plane
message from the base station, and wherein the D2UE communication
section is further configured to receive a pilot signal transmitted
by the small-node device and to make measurement for a radio link
quality of the pilot signal, wherein a radio resource for the pilot
signal is indicated in the third control-plane message.
20. The mobile station of claim 12, wherein the D2UE communication
section is further configured to transmit third user-plane data to
the server through the small-node device using the D2UE
communication link.
21. The mobile station of claim 12, wherein the BS2UE communication
section is further configured to receive a fifth control-plane
message from the base station, and wherein the D2UE communication
section is configured to reconfigure the D2UE communication link
responsive to the fifth control-plane message.
22. A macro base station for controlling a user equipment (UE) and
a small-node device in a cellular telecommunications network,
comprising: a macro-base-station-to-the-UE (BS2UE) communication
section configured to exchange user-plane and control-plane data
with the UE using a wireless BS2UE communication link; a
macro-base-station-to-the-small-node-device (BS2D) communication
section configured to exchange control-plane data with the
small-node device using a BS2D communication link; and a D2UE
control unit configured to control an establishment and also a
release/reconfiguration/handover of a small-node-device-to-the-UE
(D2UE) communication link through a first control-plane message
transmitted to at least one of the UE and the small-node device
using a respective one of the BS2UE and BS2D communication
links.
23. The macro base station of claim 22, wherein the D2UE control
unit is further configured to determine a radio resource allocation
for the D2UE link using a second control-plane message transmitted
by the BS2UE communication section to the UE using the BS2UE
communication link and by the BS2D communication section to the
small-node device using the BS2D communication link.
24. The macro base station of claim 22, wherein the D2UE control
unit is further configured to identify the user-plane data to be
exchanged between the UE and the small node device using the D2UE
communication link by assigning a radio bearer for the D2UE link
using a fourth control-plane message transmitted by the BS2UE
communication section to the UE and using a fifth control-plane
message transmitted by the BS2D communication section to the
small-node device.
25. The macro base station of claim 22, wherein the BS2UE
communication section is further configured to receive a
measurement report from the UE using the BS2UE link, and wherein
the measurement report includes measurements of a radio link
quality for the D2UE communication link, and wherein the D2UE
control unit is configured to determine at least one of the
establishment, the release, the reconfiguration, handover, and the
radio resource allocation responsive to the measurement report.
26. A method of communicating using a small-node device in a
cellular telecommunication system, comprising: at the small-node
device, receiving a first control-plane message from a base station
over a base-station-to-the-small-node-device (BS2D) communication
link; at the small-node device, establishing a
the-small-node-device-to-a-user-equipment (D2UE) communication link
responsive to the first control-plane message at the small-node
device, receiving downlink user-plane data from a server over a
backhaul link; and from the small-node device, transmitting the
downlink user-plane data over the D2UE communication link
27. A method of communicating using a user equipment in a cellular
telecommunication system, comprising: at the user equipment,
receiving a first control-plane message from a base station over a
macro-base-station-to-the-user-equipment (BS2UE) communication
link; at the user equipment, establishing an
small-node-device-to-the-user-equipment (D2UE) communication link
responsive to the first control-plane message; at the user
equipment, receiving downlink user-plane data from the small-node
device over the D2UE communication link.
28. A method of communicating using a macro base station for
controlling a user equipment (UE) and a small-node device in a
cellular telecommunication system, comprising: at the macro base
station, exchanging user-plane data and control-plane message with
the UE using a wireless macro-base-station-to-the-UE (BS2UE)
communication link and exchanging control-plane message with the
small-node device using a
macro-base-station-to-the-small-node-device (BS2D) communication
link; at the macro base station, controlling an establishment and
also a release/reconfiguration/handover of a
small-node-device-to-UE (D2UE) communication link through a first
control-plane message transmitted to at least one of the UE and the
small-node device using the respective one of the BS2UE
communication link and the BS2D communication link, at the macro
base station, identifying user-plane data to be exchanged between
the UE and the small-node device using the D2UE communication
link.
29. A small-node device for offloading data traffic in a cellular
telecommunications system, comprising:
a-macro-base-station-to-the-small-node-device (BS2D) communication
section configured to receive a first control-plane message and a
second control-plane message from a base station over a BS2D
communication link; a the-small-node-device-to-a-user-equipment
(D2UE) communication section configured to establish a wireless
D2UE communication link with the user equipment responsive to the
first control-plane message, wherein the D2UE communication section
is further configured to transmit at least one pilot signal to the
user equipment responsive to the second control-plane message and
to exchange user-plane data with the user equipment over the D2UE
communication link; and a backhaul communication section configured
to exchange the user-plane data with a server using a backhaul
link.
30. The small-node device of claim 29, wherein the D2UE
communication section is further configured to transmit the at
least one pilot signal according to at least one of a transmission
periodicity, a frequency-domain resource, a time-domain resource, a
code-domain resource, and a transmission power as determined by the
second control-plane message.
31. The small-node device of claim 29, wherein the BS2D
communication section and the D2UE communication section are
configured to synchronize a base-station-to-user-equipment
communication link and the D2UE communication link.
32. A mobile station (user equipment) configured to receive
offloaded data from a small-node device in a cellular
telecommunication system, comprising: a
base-station-to-the-user-equipment (BS2UE) communication section
configured to receive both control-plane data message and first
user-plane data from the base station over a wireless BS2UE
communication link; and a small-node-device-to-the-user-equipment
(D2UE) communication section configured to receive second
user-plane data from a server through the small-node device using a
wireless D2UE communication link, wherein the BS2UE communication
section is further configured to receive a first control-plane
message from the base station over the BS2UE communication link,
and wherein the D2UE communication section is further configured to
establish the D2UE communication link responsive to the first
control-plane message, and wherein the D2UE communication section
is further configured to receive at least one pilot signal from the
small-node device over the D2UE communication link and to measure a
radio link quality for the D2UE communication link using the
received at least one pilot signal, and wherein the BS2UE
communication section is further configured to transmit the radio
link quality to the base station over the BS2UE communication
link.
33. The user equipment of claim 32, wherein the D2UE communication
section is further configured to receive the at least one pilot
signal according to at least one of a transmission periodicity, a
frequency-domain resource, a time-domain resource, a code-domain
resource, and a transmission power as determined by the second
control-plane message.
34. A small-node device for offloading data traffic in a cellular
telecommunications system, comprising:
a-base-station-to-the-small-node-device (BS2D) communication
section configured to receive a first control-plane message from a
base station over a BS2D communication link; a
small-node-device-to-user-equipment (D2UE) communication section
configured to transmit user-plane data to a user equipment over a
wireless D2UE communication link established responsive to the
first control-plane message; and a backhaul communication section
configured to receive the user-plane data from a server over a
backhaul link; wherein the D2UE communication section further
configured to make measurements for at least one of a processing
load, a radio resource usage, a data rate, a path loss in the
second link, a radio link quality, a block error rate, a
transmitted signal power, a received signal power, an interference
power, and a user equipment count for the D2UE communication link;
and wherein the BS2D communication section further configure to
transmit the measurement results to the base station.
35. A macro base station for controlling a user equipment (UE) and
a small-node-device in a cellular telecommunications network,
comprising: a macro-base-station-to-the-UE (BS2UE) communication
section configured to exchange user-plane data and control-plane
message with the UE using a wireless BS2UE communication link; a
macro-base-station-to-small-node-device (BS2D) communication
section configured to exchange control-plane message with the
small-node device using a BS2D communication link; and a control
unit configured to control an establishment and also a
release/reconfiguration/handover of a small-node-device-to-UE
(D2UE) communication link through a first control-plane message
transmitted to at least one of the UE and the small-node device
using the respective one of the BS2UE communication link and the
BS2D communication link, wherein the control unit is further
configured to identify user-plane data to be exchanged between the
UE and the small-node device using the D2UE communication link, and
wherein the control unit further configured to make measurement for
at least one of a D2UE connection count, a radio resource usage, a
data rate, a success rate of connection establishment, a success
rate for handover, a radio link failure count, a handover count,
and a connection re-establishments count for the D2UE communication
link.
Description
TECHNICAL FIELD
[0001] This application is directed to the operation of the
Physical and Link Layer in mobile communication protocols.
BACKGROUND
[0002] One option to increase capacity in a wireless network is to
increase the density (number of devices per unit area) of deployed
base stations or remote antenna units. If the density of the
deployed base stations or remote antenna units increases, cell
capacity increases due to frequency reuse effects. However, there
are some difficulties that come with increasing the deployment
density, especially if such deployed units must be able to operate
as conventional base stations on their own. These difficulties
include: [0003] 1) As the deployment density increases, the number
of handovers increases because the user equipment changes its
serving unit (base station) quite frequently. As a result, quality
of connectivity/mobility is expected to be degraded. Thus, the
deployed unit for increasing cellular capacity should have
high-quality interworking with the macro base station. [0004] 2)
The conventional macro base stations transmit some required
signals, such as pilot signals, synchronization signals, broadcast
signals, paging signals, and so on, all of which have the potential
to cause interference problems. Such interference limits the number
of deployed base stations and thus lowers cellular capacity. [0005]
3) Furthermore, radio resources for the required conventional macro
base station signals are typically static. Thus, dynamic and
efficient interference coordination through dynamic allocation of
the radio resources is difficult, which also limits the number of
the deployed base stations and associated cellular capacity. [0006]
4) Network operators need to assign cell ID or other cell-specific
parameter to each cell. For example, the root sequences for random
access channels in LTE uplink (UL) are an example of such
cell-specific parameters. Such cell planning for the cell ID, the
root sequences and the like is cumbersome, which also limits the
number of the deployed base stations and associated cellular
density [0007] 5) The required cell capacity is region-specific.
For example, a significantly large capacity is required in urban
areas whereas a relatively small enhancement of cell capacity may
be sufficient in suburban or rural areas. To efficiently satisfy
such divergent density needs, the deployed unit should be easily
installed with low cost/complexity [0008] 6) If the cost of each
deployed unit is high, the total system cost is quite high as the
deployment density increases. Thus, the deployed unit cost should
be relatively low to feasibly increase cell capacity.
[0009] Various architectures have thus been proposed to increase
wireless network capacity. For example, distributed base stations
using the Remote Radio Head (RRH) technology communicate with a
base station server using optical fiber. Because the base station
server performs the baseband processing, each RRH distributed base
station thus acts as a power amplifier with regard to its base
station server. As the density of the RRH distributed base stations
is increased, the baseband processing complexity is increased at
the base station server. Thus, the number of RRH cells
corresponding to each distributed RRH base stations is limited due
to this baseband complexity.
[0010] Another alternative for increasing wireless network capacity
involves the use of picocells or femtocells. Unlike the RRH
approach, baseband processing is distributed across the
pico/femtocells. But there is no high-quality interworking between
picocells/femto cells and macrocell base stations. Thus,
connectivity and mobility may not be sufficient because
conventional intra-frequency or inter-frequency handover between
picocells/femtocells and macrocell base stations is required.
Furthermore, the picocells/femtocells are indeed base stations and
thus they transmit the signals mentioned above such as pilot
signals, synchronization signals, broadcast signals, paging
signals, and so on. As a result, as the deployment density for
pico/femtocells is increased, interference problems, difficulties
in dynamic and efficient interference coordination, cell planning
problems, and related issues cannot be solved.
[0011] Yet another alternative for increasing wireless network
capacity is the use of conventional WiFi. But there is no
interworking between WiFi nodes and macrocell base stations. Thus,
connectivity and mobility is limited for a dual macrocell and WiFi
user. Moreover, the use of WiFi in macrocell networks introduces
the complications of multiple IP addresses being assigned to a
single user.
[0012] Accordingly, there is a need in the art for improved
architectures and techniques for increasing wireless network
capacity.
SUMMARY
[0013] The invention focuses on the Physical (PHY) and Link Layer
design of systems such as 3GPP's Long Term. Evolution (LTE). The
design uses a Device to UE (D2UE) and Macro to UE (BS2UE)
architecture wherein some functions are maintained by the BS2UE
link and others are supported by the D2UE link. Therefore,
according to the invention, it is possible to provide a radio
communication system for enabling high capacity, high connectivity,
low costs and low planning complexity.
[0014] In accordance with a first aspect of the disclosure, a
small-node device for offloading data traffic in a cellular
telecommunications system is provided that includes:
a-macro-base-station-to-the-small-node-device (BS2D) communication
section configured to receive a first control-plane message from a
base station over a BS2D communication link; a
user-equipment-to-the-small-node-device (D2UE) communication
section configured to transmit user-plane data to a user equipment
over a wireless D2UE communication link established responsive to
the first control-plane message; and a backhaul communication
section configured to receive the user-plane traffic data from a
network server over a backhaul link.
[0015] In accordance with a second aspect of the disclosure, a
mobile station (user equipment) configured to receive offloaded
data from an small-node device in a cellular telecommunication
system is provided that includes: a
macro-base-station-to-the-user-equipment (BS2UE) communication
section configured to receive both control-plane data and first
user-plane data from the base station over a wireless BS2UE
communication link; and a small-node-device-to-the-user-equipment
(D2UE) communication section configured to receive second
user-plane data from a server through the small-node device using a
wireless D2UE communication link established responsive to the
first control-plane message.
[0016] In accordance with a third aspect of the disclosure, a macro
base station for controlling a user equipment (UE) and a small-node
device in a cellular telecommunications network is provided that
includes: a macro-base-station-to-the-UE (BS2UE) communication
section configured to exchange user-plane and control-plane data
with the UE using a wireless BS2UE communication link; a
macro-base-station-to-the-small-node-device (BS2D) communication
section configured to exchange control-plane data with the
small-node device using a BS2D communication link; and a D2UE
control unit configured to control an establishment of a
small-node-device-to-the-UE (D2UE) communication link using a first
control message transmitted to at least one of the UE and the
small-node device using a respective one of the BS2UE and BS2D
communication links.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an example architecture for an enhanced local area
radio access system using small-node devices.
[0018] FIG. 2 annotates the data paths in the system of FIG. 1 for
a given one of the small-node devices.
[0019] FIG. 3 illustrates the control-plane and user-plane data
flows for small-node device of FIG. 2.
[0020] FIG. 4 illustrates a modification of the architecture of
FIG. 2 in which the backhaul links from the small-node devices
route through the Internet.
[0021] FIG. 5 illustrates an architecture that combines the
features shown for the embodiments in FIGS. 1 and 4.
[0022] FIG. 6 illustrates a modification of the architecture of
FIG. 5 to include a gateway between the small-node devices and the
core network/Internet.
[0023] FIG. 7 illustrates a modification of the architecture of
FIG. 5 in which the backhaul links from the small-node devices
route through a network access gateway.
[0024] FIG. 8 illustrates a modification of the architecture of
FIG. 5 in which the backhaul links from the small-node devices
route through the base station.
[0025] FIG. 9 illustrates a modification of the architecture of
FIG. 6 in which the backhaul links from the small-node devices
route through a center small-node device.
[0026] FIG. 10 illustrates time slots for the D2UE link and the
user equipment's BS2UE link.
[0027] FIG. 11 is a block diagram for an example small-node
device.
[0028] FIG. 11A is a more-detailed block diagram for a small-node
device embodiment.
[0029] FIG. 12 is a block diagram for an example user
equipment.
[0030] FIG. 13 is a block diagram for an example base station.
[0031] FIG. 14 is a flowchart for a D2UE connection establishment
method.
[0032] FIG. 14A is a flow diagram for the steps shown in FIG.
14.
[0033] FIG. 15 is a flow diagram for the release of a D2UE
connection.
[0034] FIG. 16 is a flow diagram for the reconfiguration of a D2UE
link.
[0035] FIG. 17 is a flow diagram for a D2UE link handover.
[0036] FIG. 17A is a flowchart for a user equipment measurement
technique to detect the presence of closer neighbor small-node
devices.
[0037] FIG. 18 is a flowchart for a call admission control method
for the D2UE link.
[0038] FIG. 19 (a) illustrates a mobile station interfering with a
neighboring base station.
[0039] FIG. 19 (b) illustrates a mobile station that is not
interfering with a neighboring base station.
[0040] FIG. 20 illustrates a plurality of small-node device arrayed
about a base station.
[0041] FIG. 20 is a flowchart for a user equipment traffic
measurement method.
[0042] FIG. 21 is a flowchart for a D2UE connection establishment
method.
[0043] FIG. 22 illustrates the time, frequency, and code
relationship for a plurality of D2UE pilot signals.
[0044] FIG. 22A shows a D2UE link that is synchronized with a
BS2UE, link.
[0045] FIG. 22B shows a D2UE link that is offset in time with
regard to the BS2UE link.
[0046] FIG. 22C illustrates multiple cells each having a plurality
of small-node devices.
[0047] FIG. 22D illustrates a timing relationship between the D2UE
links in a plurality of macrocell coverage areas and the
corresponding BS2UE links.
[0048] FIG. 22E shows the D2UE pilot signals from a plurality of
small-node devices.
[0049] FIG. 22F illustrates a pilot signal physical layer
format.
[0050] FIG. 22G illustrates a timing relationship between a
plurality of pilot signals formatted as shown in FIG. 22F.
[0051] FIG. 22H is a graph of the received signal power for the
pilot signals of FIG. 22G.
[0052] FIG. 23 is a flowchart for a D2UE establishment method that
is responsive to path loss measurements.
[0053] FIG. 24 is a flowchart for a D2UE handover method.
[0054] FIG. 25 is a flowchart for a D2UE link release method that
is responsive to path loss measurements.
[0055] FIG. 26 illustrates a modification of the architecture shown
in FIG. 2 to include a D2UE measurement data collection
section.
[0056] FIG. 27 is a table of D2UE measurement items
[0057] FIG. 27A illustrates the status report transmission in a
small-node device network.
[0058] FIG. 28 is a table of traffic measurement items.
[0059] FIG. 29 illustrates a measurement period corresponding to
active data transmission on the D2Ue link.
DETAILED DESCRIPTION
[0060] A cellular network device is disclosed that enables a user
to offload traffic from a macrocell base station without the
drawbacks discussed earlier. The cellular network devices
opportunistically offload traffic from the macro base stations and
are denoted as small-node devices hereinafter. The small-node
devices allow offloading of data traffic that would ordinarily have
to be carried by the link between the macrocell base station and
the UE (which may be denoted as a Macro2UE link). When a small-node
device is deployed, the offloaded data may then be carried over a
small-node device to UE link (which may be denoted as a D2UE link).
The small-node device is analogous to a femto or pico base station
in that the small-node device may control the radio resource
allocation and transport format selection for the D2UE link.
However, a mobile station receives both user-plane and
control-plane signaling from a femto/pico base station, which
conducts RRC procedures for a link between the mobile station and
the femto/pico base station. In that regard, a femto/pico base
station is indeed acting as a conventional base station to the user
equipment. Thus, a mobile station needs to make conventional
handover from a femto/pico base station to another femto/pico base
station or from a macro base station to a femto/pico base station
and vice versa. If there are numerous such handovers, the quality
of connectivity/mobility is degraded. This is because it is
impossible for the user equipment to communicate with a femto/pico
base station simultaneously with the macro base station, and
conventional intra-frequency or inter-frequency handover is needed.
In other words, it is because conventional carrier aggregation
operations cannot be conducted between two different nodes, such as
a macro base station and a femto/pico base station. In contrast, a
mobile station can transfer data with the small-node device
disclosed herein while simultaneously transferring data with a
macro base station. A macro-base-station-to-mobile-station
connection is maintained while the data offloading is conducted in
a small-node-device-to-mobile station connection. As a result, high
quality connectivity/mobility can be maintained even if the density
of deployment is increased.
[0061] Furthermore, a femto/pico base station must transmit a
cell-specific reference signal (CRS), a primary synchronization
signal (PSS), a secondary synchronization signal (SSS), and
broadcast signals. The transmission of the CRS/PSS/SSS/broadcast
signals is problematic as density of deployment is increased due to
the resulting inter-cell interference. In contrast, the small-node
device disclosed herein need not transmit CRS/PSS/SSS/broadcast
signals because the mobile station gets its control-plane signaling
from the macro base station. The small-node device is thus
exchanging user-plane data with the mobile station and does not
suffer from inter-cell interference as density of deployment is
increased.
[0062] To perform this offloading of data traffic, the small-node
devices have a backhaul link, which is connected to the Internet or
the core network so as to communicate with a server in the Internet
or the core network. The backhaul link to the small-node device is
not limited to a wired connection to the Internet, but may be a
wireless connection to the Interne, such as a WiFi or cellular
connection. The server transfers some of data to the user equipment
(which would otherwise be transferred using the base station)
utilizing the backhaul link and the D2UE connections. The D2UE
connections are controlled by the macro base station (which will be
referred to merely as a "base station" hereinafter). More
specifically, basic radio resource control, such as connection
establishment, handover, connection release, call admission control
and the like, for the D2UE connections is controlled by the base
station. Furthermore, the BS2UE connections between UE and the base
station are maintained while the D2UE connections are configured.
As a result, high quality interworking between base-station-to-UE
(BS2UE) and D2UE connections is readily achieved. Moreover, a
number of functions that are essential in conventional base
stations may be omitted in the small-node devices. For example, the
small-node devices need only support functions for D2UE,
connections. Therefore the cost and complexity of the small-node
devices can be kept low. For example, the operation of complicated
functions such as the Radio Resource Control (RRC) connection state
control and Non-Access Stratum (NAS) control is performed by the
base station. Thus, some or most of the functions for conventional
Macro2UE links such as transmitting broadcast channels,
transmitting pilot and synchronization signals, controlling
connections and the like, may be omitted in the D2UE
connection.
[0063] A small-node device is configured to support
small-node-device-to-user-equipment (D2UE) transfer of data. The
small-node device supports a base-station-to-small-node-device link
(a BS2D link) and the D2UE link is controlled by the base station
via the BS2D link. A UE as disclosed herein also supports a
base-station-to-user-equipment link (a BS2UE link) and a D2EU link.
Its D2UE link is controlled by the base station via the BS2UE link
as well. Control signaling for the D2UE connections can be
transmitted to the UE via the BS2UE connection. In an analogous
fashion, control signaling for the D2UE connections can be
transmitted to the small-node device via the BS2D connection. In
some embodiments, a D2UE connection may be similar to a D2D
(UE-to-UE or small-node-device-to-small-node-device)
connection.
[0064] To achieve high quality connectivity, more important
functions such as the RRC connection state control and also NAS
control are maintained by the base station using the BS2UE
association. More specifically, control for the radio interface in
the D2UE connections is conducted by the BS2D and the
macrocell-base-station-to-user device (BS2UE) associations. The
control includes at least one of connection establishment,
connection management, connection reconfiguration, handover,
connection release, radio resource selection management, power
control, link adaptation, call admission control, radio bearer
assignment, traffic measurement, radio measurement control, bearer
management, security association and so on.
[0065] In some embodiments, D2UE connections are maintained by a
time domain duplex (TDD) physical layer design. In such
embodiments, in the band(s) used for D2UE transmissions, the user
equipment and the small-node device time-share the use of radio
resources on the band(s). In alternative embodiments, D2UE
connections may be maintained by a frequency domain duplex (FDD)
physical layer resource sharing instead of TDD. D2UE and BS2UE
transmissions can operate in different bands exploiting Carrier
Aggregation Functions. The carrier aggregation functions correspond
to functions, in which the transmitter can transmit signals and the
receiver can receive signals in more than one carrier
simultaneously. In this fashion, D2UE transmissions can operate in
one band, and BS2UE transmissions can operate in another band,
simultaneously in time.
[0066] Alternatively, D2UE and BS2UE transmissions can operate in
different bands exploiting time division multiplexing functions,
wherein the D2UE transmission occur only at selected times and the
BS2UE transmissions occur at the remaining time.
The System Architecture
[0067] Various small-node device embodiments will now be discussed
in further detail. Turning now to the drawings, FIG. 1 shows a
plurality of small-node devices or units 500.sub.1through 500.sub.3
within a cellular communication system. This system also includes a
base station 200 as well as user equipment (UE) 100.sub.1,
100.sub.2, and 100.sub.3. As used herein, components having the
same base element number (e.g., 100.sub.1 and 100.sub.2) have the
same configuration, function, and state unless otherwise specified.
Evolved Universal Terrestrial Radio Access (E-UTRA)/Universal
Terrestrial Radio Access Network (UTRAN) (also denoted as Long Term
Evolution (LTE)) is applied in the system of FIG. 1 but it will be
appreciated that a wide variety of other wireless protocols such as
WiMAX, WiFi, or LTE Advanced may also be implemented in the
system.
[0068] Base station 200 is connected to a higher layer station, for
example, an access gateway apparatus 300. In turn, access gateway
300 is connected to a core network (CN) 400. Access gateway 300 may
also be referred to as MME/SGW (Mobility Management Entity/Serving
Gateway). A server 600 may also be connected to the core network
400.
[0069] User equipment 100 communicates with small-node devices 500
by a device-to-user-equipment (D2UE) communication. The D2UE
communication between user equipment 100 and small-node devices 500
may be provided in a Time Division Multiplexing manner (TDD).
Alternatively, the D2UE communication between the user equipment
and the small-node devices 500 may be provided in a Frequency
Division Multiplexing (FDD) manner. The D2UE link may be an LTE
link or a simplified LTE link. However, it will be appreciated that
other protocols besides LTE such as LTE Advanced, WiMax, WiFi, or
other suitable protocols may be used to implement the D2UE
links.
[0070] Small-node devices 500 communicate with base station 200
using a base-station-to-small-node-device (BS2D) link. For example,
the BS2D link may comprise a wired X2 interface link.
Alternatively, the BS2D link may be a wired or wireless link that
is different from an X2 link. Alternatively, the BS2D link may be
an enhancement of an X2 interface. The enhancement of the X2
interface link accommodates a master-slave relationship between the
base station 200 and small-node device 500. To provide greater
capacity, small-node devices 500 are connected to the core network
400 through backhaul links in some embodiments. Each of these
backhaul links may be an Ethernet link, a WiFi link, a cellular
network link, and may be wired or wireless. Data plane traffic can
thus flow between core network 400 and small-node device 500
without burdening base station 200. In this fashion, the user
equipment can access data from server 600 without the data passing
through base station 200. In other words, small-node device 500
communicates with the user equipment 100 utilizing the D2UE
communication for data off load purposes. In other embodiments,
small-node devices 500 may be connected to base station 200,
instead of the core network 400. In this case, data plane traffic
flows in base station 200, but data processing in the base station
200 can be minimized, because data processing in lower layers such
as physical layer or MAC layer is handled by small-node device 500.
In contrast, control plane information as well as data plane
traffic (e.g., real time data such as VoIP) can continue to flow to
UE 100 via base station 200, access gateway 300, core network 400,
and server 600. FIG. 2 is an annotated version of the system of
FIG. 1 to show a BS2UE connection or link 720, a D2UE connection
710, a backhaul connection 750, a BS2D connection 730, and a
backhaul connection 740.
[0071] FIG. 3 illustrates data flow in the communication system of
FIG. 1. In that regard, there must be an entity that decides what
data will be offloaded through the small-node devices as opposed to
a conventional exchange between the user equipment and the base
station. Because the base station receives radio link quality
reports from the user equipment and/or the small-node devices, the
base station is a natural choice for the data partition decision
(i.e., deciding what data should be offloaded). However, other
network nodes can also make this decision. With regard to FIG. 3, a
decision has been made to offload some data but also have other
data not be offloaded. The non-offloaded data is designated as Data
#1, which is transferred from the access gateway apparatus 300 to
the base station 200 in backhaul connection 740 and then
transmitted to user equipment 100 in BS2UE connection 720 in
downlink (DL), and vice versa in uplink (UL). This data flow is
thus be transmitted in a conventional fashion. In addition to Data
#1, offloaded Data #2 is transferred from core network 400 to
small-node device 500 in backhaul connection 750 and then
transmitted to user equipment 100 in D2UE connection 710 in DL, and
vice versa in UL. Control-plane signaling is transmitted in BS2D
connection 730 so that base station 200 can control communication
in D2UE connection 710. Control signaling is transmitted also in
BS2UE connection 720 so that base station 200 can control the
communication in D2UE connection 710. The control signaling in
BS2UE connection 720 may be radio resource control (RRC) signaling.
More specifically, Data #1 may include RRC signaling, NAS
signaling, voice packets and the like, and Data #2 may be best
effort packets, FTP data, Web browsing packets and the like. That
is, it may be determined by data bearers what kinds of data are
transferred as Data #1 or Data #2. As a result, connectivity can be
maintained by BS2UE connection 720, and U-plane data offload can be
simultaneously achieved in D2UE connection 710.
[0072] FIG. 4 illustrates an alternative embodiment in which
small-node devices 500 may be connected to a server 610 via
Internet 410. In this case, core network 400 may be regarded as a
network controlled by a network operator. Core network 400 may
include MME, S/P-GW, a node for billing system, HLS (database for
customers) and the like.
[0073] FIG. 5 illustrates another alternative embodiment that may
be considered as a mixture of the FIG. 1 and FIG. 4 embodiments. In
this embodiment, small-node devices 500 may be connected to server
600 via core network 400 or server 610 via the Internet. Small-node
device 500 may be connected to network equipment, which in turn is
connected to server 600 via core network 400 or server 610 via the
internet. The network equipment may be an S-GW or a P-GW or other
nodes in the core network. Alternatively, the network equipment may
be a node in the internet. In another alternative embodiment, a
gateway 310 is provided between core network 400/Internet 410 and
small-node devices 500 as shown in FIG. 6.
[0074] Backhaul connection 750 may be varied as shown in FIG. 7
such that it couples between access gateway 300 and small-node
devices 500. Alternatively, backhaul connection 750 may couple
between base station 200 and small-node devices 500 as shown in
FIG. 8. In yet another alternative embodiment, backhaul connection
750 may couple between a center-node small-node device 510 and
small-node devices 500 as shown in FIG. 9. Center-node small-node
device 510 in turn couples to Internet 410 and core network 400
through a gateway 310 (which is optional) or directly to these
networks. Should center node small-node device 510 be included, a
layer sharing protocol may be implemented in which center node
small-node device 510 implements the RLC/PDCP layer whereas the
remaining small-node devices handle the Physical/MAC layers. Other
layer sharing methods may be implemented. For example, center node
small-node device 510 may implement the PDCP layer whereas the
remaining small-node devices implement the Physical/MAC/RLC layers.
It may be determined by data bearers whether data should be
offloaded through the small-node devices. It may also be determined
by data bearers whether data should flow via the small-node devices
and the Internet 410, or via the small-node devices and core
network 400, or via the small-node devices and base station 200.
Data bearers may be logical channels or logical channel types.
[0075] The carrier frequency in D2UE connection 710 may be
different from that in BS2UE connection 720. Alternatively, the
carrier frequency in D2UE connection 710 may be the same as that in
BS2UE connection 720.
[0076] In the following examples, it is assumed without loss of
generality that the carrier frequency in the D2UE connection is 3.5
GHz and that TDD is applied to the D2UE connection. Furthermore, it
is also assumed that the carrier frequency in the BS2UE connection
between base station 200 and user equipment 100 is 2 GHz, and that
the carrier frequency in the BS2D connection between base station
200 and small-node device 500 is 2 GHz. To begin the configuration,
user equipment 100 may transmit an RRC connection request to base
station 200. In response, base station configures BS2UE connection
720. Alternatively, base station 200 may send a paging signal to
user equipment 100 such that user equipment 100 sends an RRC
connection request corresponding to the paging signal to base
station 200. In response, base station 200 configures BS2UE
connection 720 as well as a connection between user equipment 100
and server 600 via base station 200, access gateway 300, and core
network 400.
[0077] Similarly, base station 200 configures BS2D connection 730
between base station 200 and small-node devices 500. This
configuration can be permanent or established analogously to the
BS2UE connection. In some embodiments, a small-node device 500 has
the ability to power-down or enter a sleep state when not in use.
In such embodiments base station 200 is configured to send
small-node device 500 a wakeup signal using BS2D connection 730 as
supported by an X2 or other suitable protocol. In some other
embodiments, the protocol design may be LTE interface. Furthermore,
the small-node device may be able to use power-saving modes, such
as stand-by modes, equivalent to user equipment. In this case,
exiting such power-saving modes may be done in the same fashion as
the user equipment 100 and possibly in response to signals expected
or sent by the base-station 200. The signals may be a paging signal
or a control signaling such as MAC control signaling or physical
layer signaling.
[0078] As discussed above, BS2D connection 730 may be always
configured between base station 200 and small-node device 500. In
such a permanently-configured embodiment, small-node device 500 may
be in a discontinuous reception mode in BS2D connection 730 when
D2UE connection 710 is not configured between small-node device 500
and user equipment 100. In this case, small-node device 100 may not
transmit signals or may transmit signals extremely infrequently
when D2 UE connection 710 is not configured between small-node
device 500 and user equipment 100. For example, even when D2UE
connection 710 is not configured between small-node device 500 and
user equipment 100, small-node device 500 may transmit only pilot
signals infrequently so that user equipment 100 can detect
small-node device 500. The periodicity of the pilot signals may be
for example 100 ms or 1 second or 10 seconds. Alternatively, even
when D2UE connection 710 is not configured between small-node
device 500 and user equipment 100, small-node device 500 may
transmit pilot signals based on a request from base station 200 so
that user equipment 100 can detect small-node device 500.
[0079] After establishment of links 720 and 730, base station 200
may use control signaling in BS2UE connection 720 to command user
equipment 100 to configure D2UE connection 710. Furthermore, base
station 200 may use control signaling in BS2D connection 730 to
command small-node device 500 to configure D2UE connection 710.
Configuring the D2UE connection 710 may also be denoted as
establishing the D2UE connection 710.
[0080] Furthermore, base station 200 controls D2UE connection 710.
For example, base station 200 may order for user equipment 100 and
small-node device 500 to re-configure or re-establish D2UE
connection 710. Similarly, base station 200 may command equipment
100 and small-node device 500 to release the D2UE connection 710.
Moreover, base station 200 may command user equipment 100 to
handover the D2UE connection to another small-node device. More
specifically, base station 200 may command user equipment 100 to
conduct the handover to another small-node device in a carrier in
which communication in D2UE connection 710 is conducted. The base
station 200 may control the above procedures utilizing RRC
signaling in BS2UE connection 720 and/or in BS2D connection
730.
[0081] Base station 200 may maintain the connections between user
equipment 100 and server 600 utilizing BS2UE connection 720 when
D2UE connection is dropped.
[0082] Base station 200 may also control the radio resource for
D2UE connection 710. The details of the radio resource control for
D2UE connection 710 are discussed further below. Alternatively,
small-node device 500 may control the radio resource for the D2UE
link. In yet another alternative embodiment, both base station 200
and small-node device 500 may control the radio resource for the
D2UE link. The following discussion will assume without loss of
generality that base station 200 performs this radio resource
management.
[0083] Base station 200 may also configures one or more radio
bearers for the communications. Control signaling for configuring
the radio bearers is transmitted to user equipment 100 in BS2UE
connection 720. Similarly, control signaling for configuring the
radio bearers is transmitted to small-node device 500 in BS2D
connection 730.
[0084] The radio bearer may be denoted as a logical channel. Base
station 200 also configures radio bearers for BS2UE connection 720
and radio bearers for D2UE connection 710. The radio bearers for
BS2UE connection 720 may be the same as the ones for the D2UE
connection 710. Alternatively, the radio bearers for the BS2UE
connection 720 may be different from those used for D2UE connection
710. For example, radio bearers for packets of non-real-time
services, such as web browsing, e-mail, and FTP, may be configured
in D2UE connection 710. Conversely, radio bearers for packets of
real-time services, such as VoIP and streaming, may be configured
for BS2UE connection 720. Alternatively, the radio bearers for
packets of non-real-time services are configured for both D2UE
connection 710 and in BS2UE connection 720 such that packets of
non-real-time services may be transmitted preferentially in D2UE
connection 710. In yet another alternative, the radio bearers for
the packets of real-time services are configured both in D2UE
connection 710 and in BS2UE connection 720 such that the real-time
services packets may be transmitted preferentially in BS2UE
connection 720. Such prioritization or priority for the packets may
be configured by base station 200. In that regard, base station 200
may configure which connection: D2UE connection 710 or BS2UE
connection 720 that should be preferentially utilized in the
communications for each radio bearer.
[0085] Control plane (C-plane) signaling, such as Non Access
Stratum (NAS) signaling and Radio Resource Control (RRC) signaling,
may be transmitted in BS2UE connection 720. For example, RRC
signaling includes signaling messages for RRC connection
establishment, initial security activation, RRC connection
reconfiguration, RRC connection release, RRC connection
re-establishment, radio resource configuration, measurement
reports, handover command, and so on. A radio bearer for C-plane
signaling may be denoted as a signaling radio bearer, C-plane
signaling may be transmitted also in the D2UE connection 710.
Alternatively, one part of a radio bearer data may be transmitted
in the D2UE connection 710 and the other part of the radio bearer
data may be transmitted in the BS2UE connection 720.
[0086] The small-node device may transmit common channels/signals,
such as Primary Synchronization signals (PSS), Secondary
Synchronization signals (SSS), Common Reference Signals, and
Broadcast channels in D2UE connection 710. Alternatively,
small-node device 500 may not transmit any common channels/signals
or may transmit common channels/signals extremely infrequently. For
example, small-node device 500 may transmit pilot signals
infrequently so that user equipment 100 can detect the small-node
device. The periodicity of the pilot signals may be for example 1
second or 10 seconds. Alternatively, small-node device 500 may
transmit pilot signals based on a request from base station 200 so
that user equipment 100 can detect small-node device 500.
[0087] User equipment 100 conducts communication in D2UE connection
710 and communication in BS2UE connection 720 simultaneously. In
one embodiment, user equipment 100 communicates over D2UE
connection 710 and over BS2UE connection 720 simultaneously
utilizing carrier aggregation functions. In that regard, user
equipment 100 may have two radio frequency (RF) interfaces to
conduct communication in D2UE connection 710 and communication in
BS2UE connection 720 simultaneously. Alternatively, user equipment
100 may conduct communication in D2UE connection 710 and
communication in BS2UE connection 720 in a time division
multiplexing manner as shown in FIG. 10. Two sets of time slots,
Duration #A and Duration #B, are shown in FIG. 10. User equipment
100 may communicate in BS2UE connection 720 in the time slots
corresponding to Duration #A and may communicate in D2UE connection
710 in the time slots corresponding to Duration #B.
[0088] The time duration for the D2UE connection may be larger than
the one for the BS2UE connection so that the data offload effects
can be increased. For example, the length of Duration #A may be 8
msec whereas the length of Duration #B may be 1.28 sec. The time
duration for BS2UE connection 720 (Duration #A in FIG. 8) may
correspond to an on-duration in a DRX control over BS2UE connection
720. The time duration for D2UE connection 710 may correspond to an
off-duration in the DRX control over BS2UE connection 720. The
off-duration means a sleep mode in DRX control, in which user
equipment 100 does not have to monitor physical control channels
transmitted from base station 200 over BS2UE connection 720. In
case that user equipment 100 uses time division multiplexing with
regard to connections 710 and 720, it does not have to support a
capability of simultaneously communicating over these connections,
i.e. user equipment 100 can switch the RF interface from BS2UE
connection 720 to that for D2UE connection 710 and vice versa. As a
result, cost/complexity of user equipment 100 can be reduced.
[0089] Base station 200 may control the radio resource for D2UE
connection 710. The radio resource may be configured selectively in
the time domain, frequency domain, and code domain resource. For
example, base station 200 may configure D2UE connection 710 to use
a non-overlapping spectrum with regard to any other D2UE
connections such as by controlling a carrier center frequency. As a
result, interference problems caused by other D2UE connections can
be mitigated. Similarly, base station 200 may configure the time
resource in D2UE connection 710 so that it does not overlap with
the time resource utilized in other D2UE connections.
Alternatively, base station 200 may configure the code resource in
D2UE connection 710 so that it does not overlap with the code
resource utilized in other D2UE connections. As a result,
interference problems caused by other D2UE connections can be
mitigated.
[0090] In an alternative embodiment, some parameters of the radio
resource for D2UE connection 710 may be configured by base station
200 and the other parameters may be configured by small-node device
500. For example, the frequency domain resource for D2UE connection
710 may be configured by base station 200 and the time domain
resource for D2UE connection 710 may be configured by small-node
device 500. Alternatively, the center carrier frequency for the
D2UE connection 710 may be configured by base station 200 and the
other frequency domain resource (such as an identification number
of resource blocks or the number of resource blocks) and the time
domain resource for D2UE connection 710 may be configured by
small-node device 500.
[0091] Alternatively, base station 200 may configure several sets
of the radio resource for D2UE connection 710, and small-node
device 500 may configure one out of the several sets of the radio
resource for D2UE connection 710.
[0092] The base station 200 transmits control signaling to user
equipment 100 in BS2UE connection 720 so that it configures the
radio resource for D2UE connection 710 as described above.
Furthermore, base station 200 transmits control signaling to
small-node device 500 in BS2D connection 730 so that it configures
the radio resource for the D2UE connection 710 as described
above.
[0093] Base station 200 controls transmission power for DL in D2UE
connection 710. More specifically, base station 200 may configure
the maximum transmission power for DL in D2UE connection 710.
Furthermore, base station 200 controls transmission power for UL in
D2UE connection 710. More specifically, base station 200 may
configure the maximum transmission power for UL in D2UE connection
710.
[0094] Base station 200 may set the maximum transmission power for
DL or UL in D2UE connection 710 based on the number of the user
equipment in the cell where the small-node device provide radio
communication service. For example, the base station sets the
maximum transmission power to be higher in case that the number of
the user equipment in the cell is relatively small. Conversely, the
base station will set the maximum transmission power to be lower if
the number of the user equipment in the cell is large. As a result,
an interference level in the carrier used in D2UE connection 710
can be reduced by making the maximum transmission power low in a
high density deployment. In case that there is not a lot of user
equipment, coverage area of D2UE connection 710 can be increased by
making the maximum transmission power high.
[0095] Alternatively, base station 200 may set the maximum
transmission power in D2UE connection 710 based on the frequency in
which communications in the D2UE connection are conducted. More
specifically, in case that the frequency in which the
communications in the D2UE connection are conducted is relatively
close to a frequency utilized by another system, interference level
with the other system can be reduced by making the maximum
transmission power low. Conversely, should the other system not be
relatively close in the frequency domain, coverage area of the D2UE
connection can be increased by making the maximum transmission
power high.
[0096] User equipment 100 has a capability of making measurements
and detecting the nearest small-node device so that the data
throughput in the D2UE connection can be maximized and the
interference caused by the D2UE connection can be minimized.
Furthermore, the user equipment has a capability of reporting
results of the measurements and the detected nearest small-node
device to the base station. In turn, the base station controls the
D2UE connection based on the results and the detected nearest
small-node device as reported by the user equipment. For example,
when the identity of the nearest small-node device changes, the
base station may order for the user equipment to stop
communications with the currently serving small-node device and
start new communication with the newly-detected nearest small-node
device.
[0097] A block diagram of an small-node device 500 is shown in FIG.
11. In this embodiment, small-node device 500 includes a BS2D
communication section 502, a D2UE communication section 504, and a
backhaul communication section 506. BS2D communication section 502,
D2UE communication section 504, and backhaul communication section
506 are all connected to each other.
[0098] BS2D communication section 502 communicates with base
station 200 utilizing BS2D connection 730. More specifically, BS2D
communication section 502 receives control signaling for D2UE
connection 710 from base station 200 and transmits control
signaling for D2UE connection 710 to base station 200. The control
signaling includes signaling for
establishing/configuring/re-configuring/re-establishing/and
releasing D2UE connection 710. Signaling for D2UE connection
handover may also be included in the control signaling. In some
embodiments, the control signaling may be an RRC layer signaling in
LTE. The control signaling is transmitted to the D2UE communication
section 504. The control signaling may include parameters for at
least one of physical layer, MAC layer, RLC layer, PDCP layer, or
RRC layer for D2UE connection 710. The control signaling may
include information for the radio bearers.
[0099] Furthermore, the control signaling may include radio
resource control information for D2UE connection 710. As described
above, the radio resource control information for D2UE connection
710 may include radio resource information that can be utilized by
D2UE connection 710 or may include radio resource information that
cannot be utilized by the D2UE connection. The radio resource may
include at least one of a time domain resource, a frequency domain
resource, and a code domain resource. The radio resource control
information may also be transmitted to the D2UE connection.
[0100] Furthermore, the control signaling may include link
adaptation information for the D2UE connection. More specifically,
the link adaptation may be one of power control and adaptive
modulation and coding. The power control information may include
information on the maximum transmission output power in the D2UE
connection.
[0101] In some embodiments, the control signaling may include
measurement results for D2UE connection 710. More specifically,
BS2D communication section 502 may transmit measurement results,
which are obtained by D2UE communication section 504. The
measurement results include radio link quality in UL for the D2UE
link such as path loss between the small-node device and the user
equipment, received signal-to-interference ratio (SIR) in UL for
the D2UE link, UL inference power, and so on. The measurements for
user equipment may concern the currently-connected user equipment
over the D2UE connection or may concern a user equipment that is
not currently connected to the small-node device using the D2UE
connection. Alternatively, the measurement results include a radio
link quality between the reporting small-node device and other
small-node devices.
[0102] D2UE communication section 504 communicates with user
equipment 100 utilizing D2UE connection 710. More specifically;
D2UE communication section 504
establishes/configures/re-configures/re-establishes/and releases
D2UE connection 710 between small-node device 500 and user
equipment 100. This management of D2UE connection 710 may be based
on the control signaling transmitted by base station 200.
[0103] D2UE communication section 504 may conduct a link adaptation
for D2UE connection 710, such as power control and adaptive
modulation and coding. Furthermore, D2UE communication section 504
transmits data to user equipment 100 and receives data from user
equipment 100 utilizing the D2UE connection 710. As described
above, data for some of the radio bearers may be transmitted in
D2UE connection 710.
[0104] Hereinafter, data transferred from the user equipment 100 to
server 600 (or server 610) is called "uplink data" and data
transferred from the server 600 (or server 610) to user equipment
100 is called "downlink data," D2UE communication section 504
transmits the downlink data to user equipment 100 using D2UE
connection 710. The downlink data is transferred from server 600
via core network 400 and backhaul communication section 506. D2UE
communication section 504 receives the uplink data from user
equipment 100 over D2UE connection 710. The uplink data is then
transferred to server 600 via backhaul communication section 506
and core network 400. D2UE communication section 504 also conducts
measurements for D2UE connection 710. More specifically, D2UE
communication section 504 make measurements of the radio link
quality for D2UE connection 710 between small-node device 500 and
user equipment 100. The radio link quality may be at least one of
pilot signal received power, path loss, signal-to-interference
ratio, channel state information, channel quality indicator, and
received signal strength indicator for UL in D2UE connection 710.
The radio link quality may be calculated using the pilot signal
transmitted by the currently-connected user equipment. The path
loss is between small-node device 500 and the user equipment. The
measurements may include the interference power level in the
frequency band over which the D2UE communication operates. In some
embodiments, D2UE communication section 504 may make measurements
of the radio link quality between small-node device 500 and other
small-node devices. D2UE communication section 504 reports the
measurement results to base station 200 via BS2D communication
section 502 and BS2D connection 730.
[0105] Backhaul communication section 506 is connected to core
network 400 via a backhaul link. The backhaul link may be a wired
connection or a wireless connection or a mixture of a wired
connection and a wireless connection. The wireless connection may
be a connection provided by a WiFi (Wireless LAN) or cellular
system.
[0106] Backhaul communication section 506 transmits to D2UE
communication section 504 the downlink data, which is transferred
via the backhaul link from core network 400. Backhaul communication
section 506 transmits to the core network the uplink data (which is
transferred from the D2UE communication section 504) via the
backhaul link.
[0107] One of ordinary skill in the art will readily appreciate
that the functional blocks shown in FIG. 11 would comprise
appropriate hardware and software. For example, FIG. 11A shows an
example instantiation of these blocks. As seen in FIG. 9A,
small-node device 500 includes an RF interface 530 for the D2UE
link. Data from the UE would be received over the D2UE link at an
antenna 520 that couples to RF interface 530. RF interface 530
includes a duplexer to enable both receive and transmit
functionality at antenna 520. Baseband data to be transmitted to
the UE is received at RF interface 530 from a baseband processor
535. A SERDES serializes the baseband data followed by a conversion
to analog form in a digital-to-analog converter (DAC). The
resulting analog signal is then processed by a quadrature modulator
to modulate the desired carrier frequency. After passing through a
bandpass filter and a power amplifier (PA), the resulting RF signal
is then ready for transmission to the UE. Reception of data from
the UE is similar except that the PA is replaced by a low noise
amplifier (LNA) and the quadrature modulator is replaced by a
quadrature demodulator. The resulting analog baseband data is then
converted to digital form in an analog-to-digital converter (ADC)
before being de-serialized in the SERDES.
[0108] In embodiments in which the BS2D link is a wireless link,
small-node device 500 may include another RF interface analogous to
RE interface 530 to service the BS2D The embodiment of FIG. 11A,
however, uses a wired BS2D link. To service such a link, small-node
device 500 includes a suitable interface card or circuit such as an
Ethernet interface 540. Control signaling exchanged between the
small-node device and the base station passes couples through
Ethernet interface 540 to baseband processor 535.
[0109] In FIG. 11A, the backhaul link is also a wired Ethernet link
that is received by an Ethernet interface 550. Downlink data from
the backhaul link thus passes from the Ethernet interface to the
baseband processor, which in turn is controlled by a host
microprocessor 560. Backhaul communication section 506 of FIG. 11
thus maps to Ethernet interface 550 as well as the supporting
functions carried out by baseband processor 535 and host
microprocessor 560. Similarly, BS2D communication section 502 maps
to Ethernet interface 540 and the supporting functions performed by
baseband processor 535 and host microprocessor 560. Finally, D2UE
communication section 505 maps to antenna 520, RF interface 530,
and the supporting functions performed by baseband processor 535
and host microprocessor 560.
[0110] A block diagram for an example user equipment 100 embodiment
is shown in FIG. 12. User equipment 100 includes a BS2UE
communication section 102 and a D2UE communication section 104,
which are connected to each other. BS2UE communication section 102
communicates with base station 200 utilizing BS2UE connection 720.
As described above, data for some of radio bearers may be
transmitted in BS2UE connection 720. For example, control signaling
such as RRC signaling, NAS signaling, and MAC layer signaling may
be transmitted in BS2UE connection 720. Furthermore, packets for
Voice over IP (VoIP) may also be transmitted in BS2UE connection
720. BS2UE communication section 102 may transmit/receive data for
all radio bearers to and from the base station 200 if D2UE
connection 710 is dropped or not available. Furthermore, BS2UE
communication section 102 receives control signaling for D2UE
connection 710 from base station 200 and transmits control
signaling for D2UE connection 710 to base station 200. Such control
signaling is the same or analogous to that described above for
small-node device 500 of FIG. 11.
[0111] The control signaling is analogous because it includes
signaling for
establishing/configuring/re-configuring/re-establishing/and
releasing D2UE connection 710. Signaling for D2UE connection
handover may also be included in the control signaling. The control
signaling may be an RRC layer signaling in LTE. Alternatively, the
control signaling may be a MAC layer signaling in LTE. In yet
another alternative embodiment, some of the control signaling may
be an RRC signaling and others may be a MAC layer signaling. The
control signaling is transmitted to D2UE communication section 104.
The control signaling may include parameters for at least one of
physical layer, MAC layer, RLC layer, PDCP layer, or RRC layer for
D2UE connection 710. The control signaling may include information
for the radio bearers.
[0112] In addition, the control signaling may include radio
resource control information for D2UE connection 710. As described
above, the radio resource control information for D2UE connection
710 may include radio resource information that can be utilized by
D2UE connection 710 or may include radio resource information that
cannot be utilized by the D2UE connection. The radio resource may
include at least one of a time domain resource, a frequency domain
resource, and a code domain resource. The radio resource control
information may also be transmitted to the D2UE connection.
[0113] Furthermore, the control signaling may include link
adaptation information for the D2UE connection. More specifically,
the link adaptation may be one of power control and adaptive
modulation and coding. The power control information may include
information on the maximum transmission output power in the D2UE
connection.
[0114] Finally, the control signaling may include measurement
results for D2UE connection 710. More specifically, BS2UE
communication section 102 may transmit measurement results, which
are obtained by D2UE communication section 104. The measurement
results include radio link quality in DL for the D2UE link such as
path loss between the small-node device and the user equipment,
received signal-to-interference ratio (SIR) in DL for the D2UE
link, DL interference power, and so on. The measurements for
small-node device may concern the currently-connected small-node
device or may concern neighbor small-node devices. The
currently-connected small-node device may be denoted as a serving
small-node device. Details of the radio link quality in DL will be
described further below.
[0115] D2UE communication section 104 communicates with small-node
device 500 over D2UE connection 710. More specifically, D2UE
communication section 104
establishes/configures/re-configures/re-establishes/releases D2UE
connection 710 between small-node device 500 and user equipment
100. The management of D2UE connection 710 may be based on the
control signaling transmitted by base station 200. D2UE
communication section 104 may conduct a link adaptation for D2UE
connection 710, such as power control and adaptive modulation and
coding. Furthermore, D2UE communication section 104 transmits data
to small-node device 500 in UL and receives data from the
small-node device in DL utilizing D2UE connection 710. As described
above, data for some of the radio bearers may be transmitted in
D2UE connection 710.
[0116] D2UE communication section 104 also conducts measurements
for D2UE connection 710. More specifically, D2UE communication
section 104 makes measurements of the DL radio link quality for the
D2UE connection between user equipment 100 and the
currently-connected small-node device or a neighbor small-node
device. The DL radio link quality may be at least one of pilot
signal received power, path loss, signal-to-interference ratio,
channel state information, channel quality indicator, and received
signal strength indicator. The radio link quality may be calculated
by the pilot signal transmitted by the serving small-node device or
a neighbor small node device. The path loss is the one between user
equipment 100 and the serving small-node device or a neighbor small
node device. D2UE communication section 104 reports the measurement
results to base station 200 via BS2UE communication section 102 and
BS2UE connection 720.
[0117] A block diagram for an example base station 200 is shown in
FIG. 13. Base station 200 includes a BS2UE communication section
201, a BS2D communication section 202, a D2UE communication control
section 204, and a backhaul communication section 206, which are
all connected to each other.
[0118] BS2UE communication section 201 communicates with the user
equipment utilizing BS2UE connection 720. As described above, data
for some of radio bearers are transmitted in BS2UE connection 720.
For example, control signaling such as RRC signaling and NAS
signaling and MAC layer signaling may be transmitted in BS2UE
connection 720. Furthermore, packets for Voice over IP (VoIP) may
also be transmitted in BS2UE connection 720. Data for some other
data bearers may also be transmitted in the BS2UE connection
720.
[0119] As also described above, BS2UE communication section 201 may
transmit/receive data for all radio bearers to and from user
equipment 100, when D2UE connection 710 is dropped or not
available. Some parts of data, such as U-plane data, transmitted
from user equipment 100 are transferred to core network 400 via
BS2UE communication section 201 and backhaul communication section
206. Some parts of data, such as U-plane data, transmitted from
server 400 are transferred to user equipment 100 via backhaul
communication section 206 and the BS2UE communication section
201.
[0120] Furthermore, BS2UE communication section 201 receives
control signaling for D2UE connection 710 from user equipment 100
and transmits control signaling for D2UE connection 710 to user
equipment 100. This control signaling is the same as that for user
equipment 100 and thus its description will not be repeated.
[0121] BS2D communication section 202 communicates with small-node
device 500 utilizing BS2D connection 730. BS2D communication
section 202 receives control signaling for D2UE connection 710 from
small-node device 500 and transmits control signaling for D2UE
connection 710 to small-node device 500. This control signaling is
the same as that for small-node device 500 and thus its description
will not be repeated.
[0122] The control signaling for D2UE connection 710 is produced by
the D2UE communication control section 204 as described below and
is transferred to the user equipment 100 via the BS2UE
communication section 201. The control signaling is also
transmitted to the small-node device via the BS2D communication
section 202.
[0123] D2UE communication control section 204 conducts radio link
connection control for D2UE connection 710. The radio link
connection control includes at least one of
establishing/configuring/re-configuring/re-configuring/re-establishing/re-
leasing D2UE connection 710. The parameters for the radio link
connection control are transmitted to user equipment 100 via BS2UE
communication section 201 and to small-node device 500 via BS2D
communication section 202. These parameters may include at least
one of physical layer, MAC layer, RLC layer, PDCP layer, and RRC
layer parameters. The parameters may include the information for
the radio bearers. The radio link connection control may be denoted
herein as radio resource control.
[0124] More specifically, D2UE communication control section 204
may determine that D2UE connection 710 should be released when the
path loss between user equipment 100 and small-node device 500 is
larger than a threshold. For example, D2UE communication control
section 204 may send control signaling to release D2UE connection
710. The D2UE communication control section may conduct such
determination based on the measurement reports which are
transmitted by at least one of user equipment 100 and small-node
device 500. More specifically, at least one of user equipment 100
and small-node device 500 may detect whether or not the path loss
is larger than the threshold and send the measurement reports in
case that the path loss is larger than the threshold. D2UE
communication control section 204 may send the control signaling to
at least one of the user equipment 100 and the small-node device
500 after it receives the measurement reports. In the above
examples, DL transmission power or UL transmission power in D2UE
connection 710 may be utilized instead of the path loss.
[0125] D2UE communication control section 204 also controls
handover of the D2UE connection between the user equipment 100 and
small-node device 500. More specifically, D2UE communication
control section 204 receives the measurement reports from user
equipment 100 and determines whether or not user equipment 100
should hand over to a closer neighboring small-node device. Here,
the designation of a "serving small-node device" refers to the
small-node device that currently has the D2UE connection with the
user equipment.
[0126] In addition, D2UE communication control section 204 may
control the radio resource for the D2UE connections. More
specifically, D2UE communication control section 204 may assign the
radio resource for a D2UE connection so that it will not interfere
with other D2UE connection and vice versa. In this fashion the
radio resource of one D2UE connection will not overlap with
remaining D2UE connections. The radio resource may be indicated to
the user equipment and the small-node device by radio resource
control parameters. The parameters may include at least one of ID
of the frequency domain resource, ID of the time domain resource,
and ID of the code domain resource. The radio resource, which is
assigned to the D2UE connection, may be determined based on the
number of user equipment in the cell having the serving small-node
device or based on an interference level in the frequency band in
which the D2UE communication operates.
[0127] Furthermore, D2UE communication control section 204 may
control the link adaptation for D2UE connection 710. More
specifically, the link adaptation may be one of power control and
adaptive modulation and coding. The power control information may
include information on the maximum transmission output power for DL
or UL in the D2UE connection 710.
[0128] The control signaling, which is determined based on the
above-described control in D2UE communication control section 204,
is transmitted to the user equipment via BS2UE communication
section 201. The control signaling is transmitted to the small-node
device via BS2D communication section 202.
[0129] Backhaul communication section 206 provides the downlink
data received from core network 400 to BS2UE communication section
201. Similarly, BS2UE communication section 201 provides uplink
data to backhaul communication section 206, which then transmits
the uplink data to core network 400.
[0130] One of ordinary skill will readily appreciate that the
functional blocks shown in FIGS. 12 and 13 for user equipment 100
and base station 200, respectively, would map to analogous
components as discussed with regard to user equipment 500. For
example, the user equipment would require two analogous RF
interfaces for Macro2D communication section 102 and D2D
communication section 104. These RF interfaces would cooperate with
appropriate processor such as a baseband processor and a host
microprocessor.
[0131] Operation of the mobile communication system described
herein may be better understood with reference to the flowchart
shown in FIGS. 14 and 14A, which address the establishment of
connections in response to the occurrence of traffic data to be
transmitted. The flowchart begins with a step S801 with the
occurrence of traffic data, either uplink and/or downlink data. For
example, the traffic data may correspond to sending/receiving
e-mails, browsing web sites, downloading files, or uploading
files.
[0132] In a step S802, an LTE connection (BS2UE connection 720)
between base station 200 and user equipment 100 is established. If
the connection is triggered by the user equipment, the user
equipment may initiate the connection by random access procedures.
If the connection is triggered by server 600, the base station may
send a paging message to initiate the connection. Step S802
corresponds to Step A802 in FIG. 14A.
[0133] In the embodiments of FIGS. 14 and 14A, it is assumed that
BS2D connection 730 is always configured between base station 200
and small-node device 500. In some other embodiments, however, a
connection between base station 200 and small-node device 500 (the
BS2D connection 730) is established in step S802 or just after step
S802. The establishment may be triggered by base station 200 using
control signaling. Furthermore, small-node device 500 may start
transmitting pilot signals for D2UE connection 710 after it is
requested by base station 200 in the above establishment
procedures. As a result, it may not cause significant interference
with other communications in the frequency band when it does not
transmit the pilot signals.
[0134] In a step S803, user equipment 100 makes measurements for
the D2UE connection. In particular, user equipment 100 makes
measurements for the DL radio link quality in the D2UE connection.
More specifically, user equipment 100 transmits to the base station
a measurement report, which notifies the base station of an
identification number for the small-node device having the best DL
radio link quality.
[0135] In one embodiment, the measurements for the D2UE connection
may be conducted as illustrated in the steps A803a, A803b and A803c
in FIG. 14A. In a step A803a, the base station transmits control
signaling to the user equipment in BS2UE connection 720 and orders
for the user equipment to make measurements for the D2UE connection
so that the user equipment detects the small-node device with the
best radio link quality.
[0136] The control signaling may include information for the
measurements. For example, the control signaling may include at
least one of carrier frequency for the D2UE connection, bandwidth
of the D2UE connection, an identification number for the small-node
device, information on measurement quantity, information on the
pilot signals transmitted by the small-node device and so on. The
information on the measurement quantity may be an indicator of RSRP
or RSRQ. The information on the pilot signals may concern the radio
resource of the pilot signals. More specifically, the pilot signal
information may be at least one of the transmission periodicity of
the pilot signals, the frequency-domain resource information of the
pilot signals, the time-domain resource information of the pilot
signals, and the like. As discussed further, a time offset between
the D2UE connection and the BS2UE connection may also be included
in the information on the pilot signals. Furthermore, transmission
power of the pilot signals may be include in the information on the
pilot signals.
[0137] Furthermore, rules for sending measurement reports to the
base station 200 may also be included in the information for the
measurements. The rules may include criteria, which are similar to
the ones for LTE, such as Event A1, A2, A3, A4, A5 and the like,
which is specified in TS 36.331. Threshold value or Layer-3
filtering coefficient, Time-to-trigger may also be included in the
information for the measurements. In addition, control signaling
for cell selection/reselection may also be included in the
information for the measurements. For example, control signaling
for idle-mode measurements may also be included in the information
for the measurements.
[0138] The control signaling may be transmitted in the dedicated
control signaling or in the broadcast information.
[0139] The control signaling in the step S803 may include an
indicator whether or not the D2UE connection is available in the
cell wherein base station 200 provides the radio communication
system for user equipment 100. The control signaling may be
transmitted in the step A802, instead of the step A803a.
[0140] In a step A803b, user equipment 100 makes measurements for
the DL radio link quality in the D2UE connection.
[0141] In a step A803c, user equipment 100 transmits to base
station 200 a measurement report in BS2UE connection 720, which
notifies base station 200 of an identification number of the
small-node device having the best DL radio link quality.
[0142] In a step S804, the D2UE connection between the user
equipment and the small-node device (D2UE connection 710) is
established. The base station orders for the user equipment and the
small-node device to configure D2UE connection 710. The parameters
for D2UE connection 710 are transmitted from base station 200 to
user equipment 100 and small-node device 500 in BS2UE connection
720 and in BS2D connection 730, respectively. Furthermore, the
establishment of D2UE connection 710 may be reported to base
station 200 by user equipment 100 and/or the small-node device.
Step S804 corresponds to steps A804a to A804f in FIG. 14A. In other
words, the establishment of D2UE connection 710 may be conducted as
illustrated in steps A804a, A804b, A804c, A804d, A804e, and A804f
in FIG. 14A.
[0143] In a step A804a, base station 200 transmits control
signaling to small-node device 500 in BS2D connection 730 and
orders small-node device 500 to establish D2UE connection 710 with
user equipment 100. In general, this small-node device is the one
which has the best DL radio link quality based on the measurement
report. In a step A804b, small-node device 500 may transmit
acknowledgement of the received control signaling from step A804a.
The control signaling may include at least one of an identification
number of user equipment 100, capability information of user
equipment 100, and the like.
[0144] In a step A804c, base station 200 transmits control
signaling to user equipment 100 in BS2UE connection 720 and orders
user equipment 100 to establish D2UE connection 710 with small-node
device 500. For example, the control signaling of step A804c may
include at least one of the following parameters: [0145] Radio
bearer information for D2UE connection 710 [0146] Carrier frequency
information of D2UE connection 710 [0147] Frequency band indicator
of D2UE connection 710 [0148] System bandwidth (Channel bandwidth)
of D2UE connection 710 [0149] Cell barred information on D2UE
connection 710 [0150] Identification number of small-node device
500 [0151] UL Maximum transmission power in D2UE connection 710
[0152] Information of DL and UL slots in D2UE connection 710 (in
case of TDD) [0153] Information of random access channel for D2UE
connection 710 [0154] Information of uplink physical control
channels, such as PUCCH for D2UE connection 710 [0155] Information
of downlink physical control channels, such as PDCCH, PHICH for
D2UE connection 710 [0156] Information of uplink physical shared
channel for D2UE connection 710 [0157] Information of downlink
physical shared channel for D2UE connection 710 [0158] Information
of uplink sounding reference signal for D2UE connection 710 [0159]
Information of uplink power control information for D2UE connection
710 [0160] Information of downlink or uplink cyclic prefix
information for D2UE connection 710 [0161] Information of time
alignment control in uplink for D2UE connection 710 [0162]
Information of RLC or PDCP configuration for each radio bearer for
D2UE connection 710 [0163] Information of MAC configuration for
D2UE connection 710 [0164] Information of security for D2UE
connection 710
[0165] Part or all of the information in step A804c may be
transmitted to the small-node device 500 in step A804a.
[0166] The radio bearer information may indicate what kind of radio
bearers should be configured for D2UE connection 710 or what kind
of priority should be specified for each radio bearer. Since the
parameters for D2UE connection 710 can be transmitted in step
A804c, small-node device 500 may not have to transmit broadcast
channels, which reduces small-node device complexity.
[0167] In a step A804d, user equipment 100 transmits control
signaling to establish a connection between user equipment 100 and
small-node device 500 (the D2UE connection 710). The control
signaling may be a random access signaling. Alternatively, the
control signaling may be a pre-assigned access signaling. Radio
resource information of the pre-assigned access signaling may be
transmitted to user equipment 100 by base station 200 in step
A804c.
[0168] The radio resource information of the pre-assigned access
signaling may be configured by base station 200. In this case, base
station 200 may notify small-node device 500 of the radio resource
information in step A804a. Alternatively, the radio resource
information of the pre-assigned access signaling may be configured
by small-node device 500. In such an embodiment, small-node device
500 may notify the base station 200 of the radio resource
information in step A804b.
[0169] In a step A804e, small-node device 500 transmits
acknowledgement of the control signaling transmitted in step A804d.
As a result, D2UE connection 710 can be established.
[0170] In a step A804f, user equipment 100 transmits control
signaling to base station 200 and notifies base station 200 that
D2UE connection 710 has been successfully established.
[0171] In a step S805, some parts (for example, Data #2 in FIG. 3)
of the traffic data are transferred between user equipment 100 and
server 600 via D2UE connection 710 and small-node device 500 as
discussed above with regard to FIG. 3. The data transmitted in D2UE
connection 710 may be data for some parts of radio bearers, which
are configured for the communication between user equipment 100 and
server 600. More specifically, the data transferred via D2UE
connection 710 may be at least one of best effort packets, non-real
time service packets, and real time service packets. The data
transferred via D2UE connection 710 may be U-plane data. Step S805
corresponds to Step A805 in FIG. 14A.
[0172] In a step S806, some parts (e.g., Data #1 in FIG. 3) of the
traffic data are transferred between user equipment 100 and server
600 via BS2UE connection 720 and base station 200 as also discussed
above with regard to FIG. 3. C-plane data may also be transmitted
in BS2UE connection 720 instead of D2UE connection 710. Step S806
corresponds to step A806 in FIG. 14A.
[0173] The operations shown in FIG. 14 may be described in terms of
the operations in the small-node device 500 as follows. The
operations of small-node device 500 comprise establishing D2UE
connection 710 with user equipment 100 (step S804) and transferring
some parts of data, which are transferred between user equipment
100 and server 600 using D2UE connection 710 (step S805).
[0174] The operations shown in FIG. 14 may be described in terms of
the operations in user equipment 100 as follows. The operations of
user equipment 100 comprise establishing the LTE connection (BS2UE
connection 720) with base station 200 (step S802), making
measurements for small-node device (step S803), establishing D2UE
connection 710 with small-node device 500 (step S804), transferring
some parts of data (which are transferred between user equipment
100 and server 600) via D2UE connection 710 and small-node device
500 (step S805), and transferring some parts of data (which are
transferred between user equipment 100 and server 600) via BS2UE
connection 720 and base station 200 (step S806).
[0175] The process shown in FIG. 14 may be described in terms of
the operations in the base station 200 as follows. The operations
of the base station 200 comprise establishing the LTE connection
(BS2UE connection 720) with user equipment 100 (step S802),
transmitting control signaling for establishing D2UE connection 710
(step S804), and transferring some parts of data (which are
transferred between user equipment 100 and server 600) using BS2UE
connection 720 (step S806). In D2UE connection 710, some parts of
data (which are transferred between user equipment 100 and the
server 600) are transferred via D2UE connection 710 and the
small-node device 500.
[0176] Referring to FIG. 15, an operation of the mobile
communication system according to an embodiment is described. In a
step S901, some parts of the traffic data are transferred between
user equipment 100 and server 600 via D2UE connection 710 and
small-node device 500. In a step S902, some parts of the traffic
data are transferred between user equipment 100 and server 600 via
BS2UE connection 720 and base station 200. Steps S901 and S902 may
be the same as steps S805 and S806, respectively, i.e. steps S901
and S902 may be a continuation of steps S805 and S806.
[0177] In a step S903, there is no more traffic data to be
transferred between the user equipment 100 and the server 600. More
specifically, step S903 may correspond to the end of
sending/receiving e-mails, browsing web sites, downloading files,
uploading files and the like.
[0178] In a step S904, base station 200 transmits control signaling
to small-node device 500 and notifies small-node device 500 that
D2UE connection 710 should be released. In a step S905, small-node
device 500 transmits acknowledgement of the notification of step
S904.
[0179] In a step S906, base station 200 transmits control signaling
to user equipment 100 and notifies user equipment 100 that D2UE
connection 710 should be released. In a step S907, user equipment
100 transmits acknowledgement of the notification of step S906.
Steps S906 and S907 may be conducted before steps S904 and S905.
Alternatively, steps S906 and S907 may be conducted simultaneously
with steps S904 and S905.
[0180] Responsive to the control signaling in steps S904 and S906,
D2UE connection 710 is released in a step S908. Steps S905 and S907
may be conducted after step S908 so that user equipment 100 or
small-node device 500 can report that D2UE connection 710 is
released.
[0181] In a step S909, base station 200 transmits control signaling
to user equipment 100 and notifies user equipment 100 that BS2UE
connection 720 is released. In a step S910, user equipment 100
transmits acknowledgement of the control signaling of step S909 to
base station 200. Steps S909 and S910 correspond to normal
procedures to release a LTE connection.
[0182] In the embodiment described in FIG. 15, base station 200
transmits control signaling to command a release of D2UE connection
710. However, in alternative embodiments, user equipment 100 or
small-node device 500 may transmit the control signaling.
[0183] The process shown in FIG. 15 may be described in terms of
the operations performed by small-node device 500 as follows. The
operations of small-node device 500 comprise transferring some
parts of data (which are transferred between user equipment 100 and
server 600) using D2UE connection 710 (step S901), receiving the
control signaling transmitted by base station 200 (step S904),
transmitting the acknowledgement of the control signaling to base
station 200 (step S905) and releasing D2UE connection 710 with user
equipment 100 (step S908).
[0184] The process shown in FIG. 15 may be described in terms of
the operations performed by user equipment 100 as follows. The
operations of user equipment 100 comprise transferring some parts
of data (which are transferred between user equipment 100 and
server 600) via D2UE connection 710 and small-node device 500 (step
S901), transferring some parts of data (which are transferred
between user equipment 100 and server 600) via BS2UE connection 720
and base station 200 (step S902), receiving the control signaling
transmitted by base station 200 (step S906), transmitting the
acknowledgement of the control signaling to base station 200 (step
S907), releasing the D2UE connection 710 with user equipment 100
(step S908), and releasing the LTE connection (BS2UE connection
720) in steps S909 and S910.
[0185] The process shown in FIG. 15 may be described in terms of
the operations performed by base station 200 as follows. The
operations of base station 200 comprise transmitting to small-node
device 500 control signaling for releasing D2UE connection 710
(step S904), transmitting to user equipment 100 control signaling
for releasing D2UE connection 710 (step S906), and releasing BS2UE
connection 720 (steps S909 and S910).
[0186] Referring to FIG. 16, an operation of the mobile
communication system according to another embodiment is
illustrated. In a step S1001, some parts of the traffic data are
transferred between user equipment 100 and server 600 via D2UE
connection 710 and small-node device 500. In a step S1002, some
parts of the traffic data are transferred between user equipment
100 and server 600 via BS2UE connection 720 and base station 200.
Steps S1001 and S1002 may be the same as steps S805 and S806,
respectively, i.e. steps S1001 and S1002 may be a continuation of
steps S805 and S806.
[0187] In a step S1004, base station 200 transmits control
signaling to small-node device 500 and notifies small-node device
500 that D2UE connection 710 should be reconfigured. In a step
S1005, base station 200 transmits control signaling to user
equipment 100 and notifies user equipment 100 that D2UE connection
710 should be reconfigured. More specifically, the parameters
described for the A804c may be included in the control signaling
for step 1004 or step S1005.
[0188] In a step S1006, D2UE connection 710 is re-configured. More
specifically, some of the parameters for D2UE connection 710 are
changed. The parameters may include at least one of parameters for
a frequency domain resource, parameters for a time domain resource,
parameters for a code domain resource, parameters for pilot signals
for D2UE connection 710, parameters for initial access for D2UE
connection 710, parameters for the radio bearers, and parameters
for the power control for D2UE connection 710. The parameters for
the power control include the information on the maximum
transmission output power for DL or UL in D2UE connection 710.
[0189] In a step S1007, small-node device 500 transmits control
signaling to base station 200 and notifies base station 200 that
D2UE connection 710 has successfully been reconfigured. In a step
S1008, user equipment 100 transmits control signaling to base
station 200 and notifies base station 200 that D2UE connection 710
has successfully been reconfigured.
[0190] The process shown in FIG. 16 may be described in terms of
the operations in small-node device 500 as follows. The operations
of small-node device 500 comprise transferring some parts of data,
which are transferred between user equipment 100 and server 600,
using D2UE connection 710 (step S1001), receiving control signaling
to reconfigure D2UE connection 710 (step S1004), reconfiguring D2UE
connection 710 (step S1006), and transmitting control signaling to
report that D2UE connection 710 has been reconfigured (step
S1008).
[0191] The process shown in FIG. 16 may be described in terms of
the operations in user equipment 100 as follows. The operations of
user equipment 100 comprise transferring some parts of data, which
are transferred between user equipment 100 and server 600, using
D2UE connection 710 (step S1001), transferring some parts of data,
which are transferred between user equipment 100 and server 600,
using BS2UE connection 720 (step S1002), receiving control
signaling to reconfigure D2UE connection 710 (step S1005),
reconfiguring D2UE connection 710 (step S1006), and transmitting
control signaling to report that D2UE connection 710 has been
reconfigured (step S1008).
[0192] The process shown in FIG. 16 may be described in terms of
the operations in base station 200 as follows. The operations of
base station 200 comprise transferring some parts of data, which
are transferred between user equipment 100 and server 600, using
BS2UE connection 720 (step S1002), transmitting to small-node
device 500 control signaling to reconfigure D2UE connection 710
(step S1003), transmitting to user equipment 100 control signaling
to reconfigure D2UE connection 710 (step S1004), receiving control
signaling to report that D2UE connection 710 has been reconfigured
(step S1007), and receiving control signaling to report that D2UE
connection 710 has been reconfigured (step S1008).
[0193] Referring to FIG. 17, an operation of the mobile
communication system according to another embodiment is
illustrated. In a step S1101, some parts of the traffic data are
transferred between user equipment 100 and server 600 via D2UE
connection 710 and source small-node device 500. In a step S1102,
some parts of the traffic data are transferred between user
equipment 100 and server 600 via BS2UE connection 720 and base
station 200. Steps S1101 and S1102 may be the same as steps S805
and S806, respectively, i.e. steps S1101 and S1102 may be a
continuation of steps S805 and S806.
[0194] In a step S1103, user equipment 100 makes measurements for
the D2UE connection, as described below. That is, user equipment
100 makes measurements for the DL radio link quality of the serving
small-node device and the neighbor small-node device. The DL radio
link quality may be at least one of pilot signal received power,
path loss, signal-to-interference ratio (SIR), channel state
information, channel quality indicator, received signal strength
indicator, and the like.
[0195] More specifically, user equipment 100 determines whether or
not a neighbor small-node device, which is closer to the user
equipment 100 than the serving small-node device, is detected and
transmits to the base station a measurement report if the neighbor
small-node device is detected as illustrated in FIG. 17A. User
equipment 100 makes measurements for the D2UE connection in a step
A1103a.
[0196] In a step A1103b, user equipment 100 determines whether or
not a neighbor small-node device, which is closer to the user
equipment than the serving small-node device, is detected. The
serving small-node device means the small-node device (a source
small-node device), which is currently communicating with the user
equipment. More specifically, if the radio link quality of the
neighbor small-node device is higher than that of the serving
small-node device, it may be determined that the neighbor
small-node device is closer to the user equipment than the serving
small-node device.
[0197] If the neighbor small-node device is closer to the user
equipment than the serving small-node device (step A1103b: YES),
the user equipment transmits a measurement report to the base
station so as to notify the base station that the neighbor
small-node device is detected. Step A1103b corresponds to step
S1104 in FIG. 17.
[0198] If the neighbor small-node device is not closer to the user
equipment than the serving small-node device (step A1103b: NO), the
user equipment does not transmits the measurement report to the
base station. Steps A1103a and A1103b of FIG. 17A correspond to
step S1103 in FIG. 17.
[0199] In a step S1104, the user equipment transmits a measurement
report to the base station so as to notify it that a closer
neighbor small-node device is detected. Hereinafter, the serving
small-node device is denoted as a "Source small-node device" and
the neighbor small-node device is denoted as a "Target small-node
device."
[0200] The base station makes a decision that the user equipment
should handover to the neighbor small-node device (the target
small-node device) in a step S1105.
[0201] In a step S1106, the base station transmits control
signaling to the target small-node device for handover preparation.
The control signaling may be called "handover request for D2UE
connection." More specifically, the base station notifies the
target small-node device of parameters for it to establish the D2UE
connection with the user equipment. The parameters described in
step A804a may be included in the control signaling of step
S1106.
[0202] In a step S1107, the target small-node device transmits
acknowledgement of the control signaling of step S1106.
[0203] In step S1108, the base station 200 transmits control
signaling to the user equipment and orders for the user equipment
to make handover to the target small-node device. The control
signaling may include connection information for D2UE connection
710. More specifically, the connection information may include at
least one of information on measurement configuration for D2UE
connection 710, information on mobility control for D2UE connection
710, radio resource control information for D2UE connection 710,
and the like.
[0204] Furthermore, the radio resource control information for D2UE
connection 710 may include at least one of radio bearer information
for D2UE connection 710, information for PDCP layer configuration
in D2UE connection 710, information for RLC layer configuration in
D2UE connection 710, information for MAC layer configuration in
D2UE connection 710, information for physical layer configuration
in D2UE connection 710, and the like. More specifically, the
parameters described for step A804c may be included in the radio
resource control information for D2UE connection 710.
[0205] In a step S1109, base station 200 transmits control
signaling to the source small-node device 500 and notifies it that
user equipment 100 should make handover to the target small-node
device. Source small-node device 500 ends the communications with
user equipment 100 based on the control signaling, i.e. the source
small-node device releases D2UE connection 710.
[0206] In a step S1110, the user equipment transmits control
signaling to establish a connection between the user equipment and
the target small-node device. The control signaling may be a random
access signaling and may be the same as the one in step A804c.
[0207] In a step S1111, the target small-node device 500 transmits
acknowledgement of the control signaling transmitted in step S1110.
As a result, the D2UE connection can be established between user
equipment 100 and the target small-node device.
[0208] In a step S1112, the user equipment transmits control
signaling to the base station and notifies the base station that
the handover to the target small-node device has been successfully
conducted.
[0209] In the steps S1113, some parts of the traffic data are
transferred between user equipment 100 and server 600 via D2UE
connection 710 and target small-node device 500.
[0210] In a step S1114, some parts of the traffic data are
transferred between user equipment 100 and server 600 via BS2UE
connection 720 and base station 200. Step S1114 is the same as step
S1102. That is, step (S1102 and S1114) may be continuously
conducted during the procedures described in FIG. 17.
[0211] The process shown in FIG. 17 may be described in terms of
the operations in source small-node device 500 as follows. The
operations of source small-node device 500 comprise transferring
some parts of data, which are transferred between user equipment
100 and server 600, using D2UE connection 710 (step S1101),
receiving control signaling to notify source small-node device 500
that the user equipment should make handover to the target
small-node device, and ending D2UE connection 710 with user
equipment 100 (step S1109).
[0212] The process shown in FIG. 17 may be described in terms of
the operations in target source small-node device 500 as follows.
The operations of target small-node device 500 comprise receiving
control signaling for handover preparation, which is transmitted by
the base station (step S1106), transmitting acknowledgement of the
control signaling (step S1107), receiving control signaling to
establish a connection between the user equipment and the target
small-node device (step S1110), transmitting acknowledgement of the
control signaling (step S1111), and transferring some parts of
data, which are transferred between the user equipment and the
server, using D2UE connection 710 (step S1113).
[0213] The process shown in FIG. 17 may be described in terms of
the operations in user equipment 100 as follows. The operations of
the user equipment comprise transferring some parts of data, which
are transferred between the user equipment and server 600, using
D2UE connection 710 with the source small-node device (step S1101),
transferring some parts of data, which are transferred between the
user equipment and server 600, using BS2UE connection 720 (step
S1102), making measurements for the D2UE connection (step S1103),
transmitting a measurement report to the base station (step S1104),
receiving control signaling which orders the user equipment to make
handover to the target small-node device (step S1108), transmitting
control signaling to establish a connection between the user
equipment and the target small-node device (step S1110), receiving
acknowledgement of the control signaling (step S1111), transmitting
control signaling to the base station to notify the base station
that the handover to the target small-node device has been
successfully conducted (step S1112), transferring some parts of
data, which are transferred between the user equipment and server
600, using D2UE connection 710 with the target small-node device
(step S1113), and transferring some parts of data, which are
transferred between the user equipment and server 600, using BS2UE
connection 720 (step S1114). It is noted that step S1102 is the
same as step S1114, and this procedure may be continuously
conducted during all the steps.
[0214] The process shown in FIG. 17 may be described in terms of
the operations in base station 200 as follows. The operations of
the base station comprise transferring some parts of data, which
are transferred between the user equipment and server 600, using
BS2UE connection 720 (step S1002), receiving a measurement report
transmitted by the user equipment 100 (step S1104), making a
decision that the user equipment should handover to the target
small-node device (step S1105), transmitting control signaling to
the target small-node device for handover preparation (step S1106),
receiving acknowledgement of the control signaling (step S1107),
transmitting control signaling to the user equipment to order for
the user equipment to make handover to the target small-node device
(step S1108), transmitting control signaling to the source
small-node device to notify it that the user equipment should make
handover to the target small-node device (step S1109), receiving
control signaling to notify the base station that the handover to
the target small-node device has been successfully conducted (step
S1112), and transferring some parts of data, which are transferred
between the user equipment and server 600, using BS2UE connection
720 (step S1114).
[0215] Referring to FIG. 18, an operation of base station 200
according to an embodiment is illustrated. The control method shown
in FIG. 18 is one example of the radio resource control or call
admission control for D2UE connection 710. In a step S1201, the
base station determines whether or not the number of the user
equipment using D2UE connection 710 is larger than a predetermined
threshold. Alternatively, the base station may define a congestion
level, which may be determined based on at least one of the number
of active user equipment, the number of the D2UE connections,
amount of traffic data, interference level in the frequency band
where the D2UE communications operate, and the like, and may
determine whether or not the congestion level is higher than a
predetermined threshold. In other words, the base station may
determine whether or not the congestion level is high in the cell
in step S1201.
[0216] If the number of the user equipment is not larger than the
predetermined threshold (step S1201; NO), the base station allows a
newly configuring D2UE connection between the small-node device and
the user equipment in a step S1203. More specifically, when a
traffic data occurs similarly to step S801 and the user equipment
tries to configure a new BS2UE connection with the base station and
a new D2UE connection with the small-node device, the base station
allows a configuring of the new D2UE connection with the small-node
device in addition to a configuring of the new BS2UE connection
with the base station. Alternatively, when the user equipment tries
to configure a new D2UE connection with the small-node device in a
state wherein the user equipment has a BS2UE connection with the
base station, the base station may allow the new D2UE connection
with the small-node device.
[0217] If the number of the user equipment is larger than the
predetermined threshold (step S1201: YES), the base station does
not allow newly configuring D2UE connection between the small-node
device and the user equipment in a step S1203. More specifically,
when a traffic data occurs similarly to step S801 and the user
equipment tries to configure a new BS2UE connection with the base
station and a new D2UE connection with the small-node device, the
base station does not allow configuring the new D2UE connection
with the small-node device. Here, the base station may allow
configuring the new BS2UE connection with the base station, but may
not allow only the new D2UE connection with the small-node device.
Alternatively, when the user equipment tries to configure a new
D2UE connection with the small-node device in a state wherein the
user equipment has a BS2UE connection with the base station, the
base station may not allow the new D2UE connection with the
small-node device.
[0218] In the above examples, the small-node device has one D2UE
connection with one user equipment, but it may have more than one
D2UE connections with more than one user equipment, similarly to a
conventional base station. The radio resource for each D2UE
connection may be shared by the multiple user equipment and may be
controlled by the base station or the small-node device.
[0219] In the above examples, D2UE connection 710 and BS2UE
connection 720 transmissions can operate in different frequency
bands, but in other embodiments the D2UE connection may operate
concurrently in the same frequency band as the BS2UE connection. In
this scenario, some interference mitigation technique may be
utilized in order to achieve co-existence between the D2UE and
BS2UE transmission in the same frequency band.
[0220] For example, since the base station configures D2UE
connection 710, the base station is aware that the user equipment
will not respond to signaling by the base station in various
frequency/time slots. In some such embodiments, D2UE connection 710
is configured so as to allow transmission slots where BS2UE
communications (the base station to the user equipment) can be made
in order to support continued connection and management by the base
station. In other words, the user equipment can communicate with
the base station in predetermined on-durations, and the user
equipment can communicate with the small-node device in the other
durations (off-durations).
[0221] Alternatively, in other embodiments where D2UE connection
710 transmissions occur concurrently in the same band as with
transmissions of the base station, OFDM Resource Elements (RE) in
various resource blocks (RBs) are reserved for each link. In one
embodiment REs used for control signaling are not used by the D2UE
link and thus are left blank in any D2UE link transmission. D2UE
link transmissions, including its own control signaling to the user
equipment, are sent in other REs. In such an embodiment the user
equipment is in fact able to receive REs, e.g. control REs, from
the base station concurrently with communication from the
small-node device. The base station may turn off transmissions or
reduce transmission power in the BS2UE link in the radio resource
in which transmissions in the D2UE link may occur. The radio
resource may be a time domain resource or a frequency domain
resource.
[0222] In the above embodiments, the D2UE link may be similar to
normal BS2UE link, i.e. the small-node device may transmit common
pilot signals, broadcast signals, synchronization signals, physical
layer control signaling and the like. Alternatively, some parts of
the signals and channels may be transmitted and others may not be
transmitted in the D2UE link. For example, common pilot signals and
physical layer control signaling may be transmitted in the D2UE
link, and other channels and signals, such as broadcast
channels/signals, synchronization signals and the like, may not be
transmitted in the D2UE link. Alternatively, common pilot signals
may be transmitted in the D2UE link, and other channels and
signals, such as physical layer control signaling, broadcast
channels/signals, synchronization signals and the like, may not be
transmitted in the D2UE link. Alternatively, only
infrequently-transmitted pilot or synchronization signals may be
transmitted in the D2UE link, and other channels and signals, such
as common pilot signals, physical layer control signaling,
broadcast channels/signals, conventional synchronization signals
and the like, may not be transmitted in the D2UE link.
[0223] Alternatively, the D2UE link may be a device-to-device (D2D)
link. In such a scenario, most of the common signals/channels, such
as common pilot signals, broadcast signals, synchronization
signals, physical layer control signaling and the like, can be
omitted in the D2UE link, and only channels transferring data may
be transmitted in the D2UE link. Alternatively, some of
channels/signals, such as infrequently-transmitted pilot or
synchronization signals and physical layer control signaling and
the like, may be transmitted in the D2UE link even in this
scenario.
[0224] Irrespective of whether the D2UE link is similar to a normal
BS2UE link or to a D2D link, the D2UE link may be based on an
LTE-based radio interface, or may be based on other radio
system-based interface. For example, the D2UE link may be based on
WCDMA or CDMA2000 or WiFi or WiMAX or LTE advanced or TD-SCDMA or
TD-LTE.
[0225] For example, D2UE connection 710 may be specified based on a
WiFi-based radio interface. In this use case, a WiFi access point
may be regarded as small-node device 500. In particular, D2UE
communication section 504 in small-node device 500 communicates
with user equipment 100 utilizing the WiFi radio interface whereas
the radio resource control of the WiFi radio interface may be
controlled by base station 200. The control signaling for the radio
resource control may be transmitted in BS2UE connection 720 and
BS2D connection 730.
[0226] In mobile communication systems, mobility procedures, such
as cell identification, measurements, handover, cell
selection/reselection and the like, are quite important, because
mobile communication connectivity should be maintained even when a
mobile station (user equipment) moves from one cell to other cells.
Here it should be noted that if the mobile station tries to detect
neighbor cells and make measurements for the detected neighbor
cells very frequently, the connectivity is improved, but battery
consumption of the mobile station increases, which degrades service
quality in the mobile communication system. In such a case, the
mobile station has to minimize the battery consumptions due to the
mobility procedures, simultaneously with achieving good quality
mobility performance.
[0227] Furthermore, the mobility procedures are quite important
also in terms of interference in the mobile communication systems.
That is, it is also quite important that the mobile station
communicate with a base station with the highest radio link
quality. The radio link quality is equivalent to at least one of
path loss, pilot signal received power, signal-to-interference
ration and the like. If the mobile station does not communicate
with the base station with the highest link quality, i.e. it
communicates with the second highest quality base station, it may
interfere with other communications because its transmit power may
be too high for other radio links, as illustrated in FIGS. 19 (a)
and 19 (b).
[0228] In FIG. 19 (a), the mobile station #A1 communicates with the
base station with the second highest radio link quality, instead of
the base station with the highest radio link quality. As a result,
signals transmitted by the mobile station #A1 may interfere with
the communication between the base station with the highest radio
link quality and other mobile stations. In FIG. 19 (b), however,
the mobile station #A1 communicates with the base station with the
highest radio link quality, and therefore the signals transmitted
by the mobile station #A1 may not interfere with other
communications.
[0229] The interference may be intra-frequency interference, or may
be inter-frequency interference. In the inter-frequency
interference case, adjacent channel interference in the transmitter
side or receiver blocking characteristics in the receiver side may
degrade the quality in other communications. The interference
issues may be handled by not only the mobility procedures, but also
other radio resource management procedures. In sum, the mobility
procedures and other radio resource management procedures should be
appropriately conducted in the mobile communication systems in
order to achieve good quality connectivity, long battery life in
the mobile stations, less interference in the systems and the
like.
[0230] Furthermore, pilot pollution problems may take place in
addition to the abovementioned interference problems. If a pilot
signal transmitted by one cell collides with the pilot signal
transmitted by another cell, the colliding pilot signals interfere
with each other if they are not orthogonal with each other. If the
user equipment needs to make measurements for multiple cells for
which received signal power is strong in the user equipment
receiver, signal-to-interference ratio (SIR) for each cell is
degraded due to the interference and cell search/measurement
performance is deteriorated. It is noted that the cell search and
measurements for low SIR cells need more power consumption than
those for high SIR cells, because it needs more time for cell
search and measurements.
[0231] In the above mentioned hybrid D2UE and BS2UE system, such
mobility procedures and radio resource management procedures are
conducted in the D2UE link, in addition to the BS2UE link. It is
noted that since the cell size in the D2UE link is small, mobility
performance can be more easily degraded and interference issues can
happen more frequently. Therefore, the above mobility procedures
and other radio resource management procedures are quite important
for the D2UE link. More details of the mobility procedures and
other radio resource management procedures in the D2UE link are
explained below:
[0232] In the following examples, it is assumed that the carrier
frequency in D2UE connection 710 is 3.5 GHz, and the carrier
frequency in the BS2UE connection between the base station and the
user equipment is 2 GHz, similarly to the above examples. It is
noted that the frequency bands are just examples, and other
frequency bands can be applicable in other embodiments.
[0233] FIG. 20 illustrates the radio communication system in one
embodiment. It is basically the same as FIG. 1, but is slightly
modified compared to FIG. 1 so that the mobility procedures and
radio resource managements for the radio communication system can
be illustrated. In FIG. 20, three small-node devices (500A, 500B,
500C) are shown for illustrative purpose.
[0234] Referring to FIG. 21, an operation of the mobile
communication system according to the embodiment of the present
invention is described. The operation is related to connection
establishment in D2UE connection 710. The operation may correspond
to details of steps S803 and S804 in FIG. 14 or steps A803a, A803b,
A803c, A804a, A804b, A804c, A804d, A804e, and A804f in FIG.
14A.
[0235] In a step S1301, base station 200 transmits control
signaling for D2UE connection 710 to user equipment 100. The
control signaling may be transmitted in step A803a in FIG. 14A,
instead of step S1301. Alternatively, the control signaling may be
transmitted as parts of broadcast information to user equipment
100. The control signaling may include at least one of information
on a frequency resource for D2UE pilot signals, information on a
time resource for the D2UE pilot signals, and information on a code
resource for the D2UE pilot signals. Some examples for the D2UE
pilot signals are explained further below.
[0236] The control signaling may include information on
transmission power for the D2UE pilot signals. That is, the
transmission power for the D2UE pilot signals may be transmitted as
one information element of the control signaling. Furthermore, the
control signaling may include information on measurement behaviors
in user equipment 100.
[0237] In a step S1302, the small-node device transmits the D2UE
pilot signals in predetermined radio resources. More specifically,
small-node device 500A, 500B, 500C transmits the D2UE pilot signals
in the predetermined radio resources. The radio resources may
consist of at least one of a time resource, a code resource and a
frequency resource. The information on the predetermined radio
resources may be signaled by the control signaling described for
step S1301. In this sense, "predetermined radio resources"
correspond to the radio resource indicated by the base station.
The D2UE Pilot Signals
[0238] FIG. 22 illustrates one example of the radio resources for
the D2UE pilot signals. In FIG. 22, the frequency resource #3 is
assigned as the frequency radio resource, and the time resource #6
is assigned as the time radio resource. Furthermore, each
small-node device receives its own code resource. For example, code
resources #0, #1, and #2 may be assigned to small-node device 500A,
500B, and 500C, respectively. The code resource may be combination
of the CAZAC sequence (or Zadoff-Chu sequence) and cyclic shift, as
shown below.
[0239] It is assumed that time synchronization is achieved for all
the D2UE connections, i.e. time slots for all the D2UE connections
are aligned with each other. For each small-node device 500, the
time synchronization may be achieved by using GPS. Alternatively,
the time synchronization may be achieved by the BS2D connections,
that is, the timeframe synchronization of the D2UE connections is
based on the signals transmitted by the base station such that the
D2UE connections are synchronized with each other. Other time
synchronization techniques may be utilized in order to synchronize
the D2UE connections. In any case, the timeframe timing of the D2UE
connections is specified so that the D2UE connections are
time-synchronized with each other.
[0240] For user equipment 100, the time synchronization may be
achieved by BS2UE connection 720 using signals transmitted by the
base station 200 such that the timeframe timing of each D2UE
connection is aligned with the remaining D2UE connections. Other
time synchronization techniques may be utilized in order to achieve
the time synchronization for the D2UE connections. As a result, the
timeframe timing of each D2UE connection is time-synchronized with
the remaining D2UE connections for both small-node device 500 and
user equipment 100.
[0241] Time synchronization will be explained further below. For
example, as illustrated in FIG. 22A, the time slots for the D2UE
connections may be completely aligned with those for the BS2UE
connections. Alternatively, as illustrated in FIG. 22B, there may
be a time offset between the time slots for the D2UE connections
and the time slots for the BS2UE connections.
[0242] More specifically, as illustrated in FIGS. 22C and 22D, each
time offset between the time slots for the D2UE connections and the
ones for the BS2UE connections may be respectively specified for
each macro (base station) coverage area, which corresponds to the
area supported by each base station 200. FIG. 22C illustrates two
macro (base station) coverage areas #A and #B in which some
small-node devices are deployed. FIG. 22D illustrates a time
relationship for the BSUE connections and D2UE connections of FIG.
22C. In FIG. 22D, time offset #A is specified for the macro (base
station) #A coverage area whereas time offset #B is specified for
the macro (base station) #B coverage area. Each time offset can be
specified so that all D2UE connections can be synchronized. The
base station 200 may inform user equipment 100 of the time offset
value (time offset #A or time offset #B in FIG. 22D) as part of the
control signaling. Furthermore, base station 200 may inform
small-node device 500 of the time offset value (time offset #A or
time offset #B in FIG. 22D) as part of the control signaling. The
time offset value may be included in the control signaling in step
S1301 of FIG. 21. As a result, even if there is no time
synchronization for the macro (base station) network, i.e. Macro #A
is not aligned with Macro #B in terms of time, D2UE connections in
the macro #A coverage area can be aligned with those in the macro
#B coverage area as illustrated in FIG. 22D.
[0243] With regard to user equipment 100, the user equipment may
decode the D2UE pilot signals transmitted by multiple small-node
devices only in the predetermined radio resource (the frequency
resource #3 and the time resource #6) so as to minimize power
consumption. More detailed examples are shown below. User equipment
100 does not have to achieve battery-consumed time synchronization
with multiple small-node devices (as analogously performed for
conventional time synchronization in LTE using PSS/SSS), because it
has already been achieved by the time synchronization with the
BS2UE connections as mentioned above. In this fashion, complexity
for the cell identification is reduced, which reduces the power
consumption for the cell identification.
UE Behavior for Receiving the D2UE Pilot Signals
[0244] As illustrated in FIG. 22E, small-node devices 500A, 500B,
500C and 500D transmit the D2UE pilot signals to user equipment
100. As mentioned above, the D2UE pilot signals may have common
time-domain and frequency-domain resources but each D2UE pilot
signal has a unique code-domain resource. For example, code
resources #0, #1, #2, and #3 may be assigned to small-node devices
500A, 500B, 500C and 500D, respectively. In one embodiment, CAZAC
(Constant Amplitude Zero AutoCorrelation) sequence may be used for
the code. More specifically, a Zadoff-Chu sequence may be used for
the code. Alternatively, a Walsh sequence may be used for the code.
In an orthogonal code embodiment, the code sequences from a given
small-node device are orthogonal to the sequences used by
neighboring small-node device. In addition, partially orthogonal
code sequences may be used for the small-node device. In such an
embodiment, some code sequence pairs may be orthogonal with each
other, but others may not be orthogonal with each other.
[0245] Orthogonal code sequences do not interfere with each other.
As a result, so-called pilot pollution problems can be avoided,
even when the D2UE pilot signals transmitted by multiple small-node
device collide with each other. Moreover, power consumptions for
cell search and measurements can be reduced, because SIR for the
D2UE pilot signals can be improved by avoiding the pilot pollution
problems.
[0246] Each pilot signal may have a physical layer format as
illustrated in FIG. 22F. This physical layer format may comprise a
cyclic prefix, a sequence part, and a guard period. The guard
period may be the same as a blank part. A CAZAC sequence may apply
to the sequence part. In such an embodiment, user equipment 100 may
have a receiving window as illustrated in FIG. 22G, and has only to
decode each D2UE pilot signal transmitted by each small-node device
in one or a few attempts. User equipment 100 may obtain delay
profiles for each D2UE pilot signal as illustrated in FIG. 22H,
which shows the delay profiles for each D2UE pilot signal being
shifted due to the cyclic shift of the Zadoff-Chu sequence. It is
noted that the cyclic shift for small-node device 500A is assumed
to be zero in FIG. 22H. As a result, user equipment 100 can easily
make measurements for delay and received power level of the D2UE
pilot signal for each small-node device. In this fashion, UE
complexity for cell search and measurements can be reduced.
[0247] The cyclic shift may be adjusted based on the cell range for
each small-node device 500. Alternatively, the cyclic shift may be
adjusted based on the cell range of base station 200. If the cell
range is large, time difference among the D2UE pilot signals is
also large such that a large cyclic shift is necessary. On the
other hand, if the cell range is small the cyclic shift may also be
small. Base station 200 may notify user equipment 100 of the cyclic
shift setting for each small-node device using control signaling.
More specifically, the information of the cyclic shift may be
included in the control signaling in step S1301 of FIG. 21.
Similarly, base station 200 may also notify the small-node device
500 of its cyclic shift setting using control signaling.
[0248] The physical random access channel (PRACH) or a physical
channel similar to PRACH may be used for the D2UE pilot signals.
PRACH is defined as an LTE physical channel in TS 36.211. In this
fashion, each small-node device 500 transmits signals similar to a
random-access-preamble in the predetermined radio resource. Base
station 200 may assign each small-node device its own unique
random-access preamble. The radio resource for the signals may be
assigned by the base station 200.
[0249] The D2UE pilot signals may be transmitted infrequently as
described above. For example, the D2UE pilot signals may be
transmitted once per second. Since time synchronization is achieved
by utilizing the BS2UE connections, the D2UE pilot signals do not
have to be transmitted frequently. As a result, the user equipment
has only to decode the D2UE pilot signals once per second, which
minimizes power consumptions for the resulting pilot signal
measurements. Furthermore, the D2UE pilot signals are transmitted
much less frequently than the common reference signals or the
synchronization signals in LTE such that interference from the D2UE
pilot signals is not a problem as it would be if conventional LTE
femto/pico base stations were used in place of the small-node
devices. The periodicity of the D2UE pilot signals may be very
large, e.g. 1 second or 2 seconds, or may be reasonably large, e.g.
100 milliseconds or 200 milliseconds. If the periodicity is very
large, the power consumption for measurements and the interference
issues can be reduced significantly but user equipment 100 may need
more time to detect neighbor small-node devices and make
measurements for them because it needs some measurement samples to
achieve good accuracy. As a result, latency of mobility procedures
may be increased. Conversely, if the periodicity is reasonably
large, the power consumption for measurements and interference
issues may be reduced to some extent, but the latency will be
decreased. So, the periodicity of the D2UE pilot signals can be
optimized based on the above aspects, such as power consumption for
measurements, interference issues, latency of mobility procedures,
and the like. The periodicity of the D2UE pilot signals may be
network configurable such that base station 200 may inform user
equipment 100 of the periodicity by utilizing a control signal. For
example, the control signaling in step S1301 of FIG. 21 may be
utilized in this fashion. Similarly, base station 200 may inform
small-node device 500 of the periodicity by utilizing a control
signal.
[0250] If the user equipment does not support multiple radio
frequency components such that a first frequency carrier may be
used for BS2UE connection 720 and a second frequency carrier may be
used for D2UE connection 710 simultaneously, the user equipment may
stop transmitting/receiving signals in BS2UE connection 720 during
the time when the D2UE pilot signals are transmitted so that the
user equipment can make measurements for D2UE connection 710. In
this case, the base station may consider such behaviors of the user
equipment in its scheduling for BS2UE connection 720, i.e. the base
station may avoid assigning radio resource to the user equipment
during times when the D2UE pilot signals are transmitted.
[0251] The D2UE pilot signal may be denoted as a D2UE sounding
reference signal or a D2UE synchronization signal. The D2UE pilot
signal may be distributed in the frequency domain to suppress
signal strength fluctuation due to Rayleigh fading and achieve more
accurate measurements for the radio link quality. The base station
may notify the user equipment of D2UE pilot signal information for
each small-node device. This information may be included in the
control signaling in step S1301 of FIG. 21. Some examples of the
pilot signal information include: [0252] Code domain resource for
the D2UE pilot signal [0253] For example, index of the Zadoff-Chu
sequence [0254] Frequency domain resource for the D2UE pilot signal
[0255] Time domain resource for the D2UE pilot signal [0256] Time
offset between the D2UE connection and the BS2UE connection [0257]
Transmission power of the D2UE pilot signal [0258] Cyclic shift
information of the D2UE pilot signal
[0259] The above information may be specified for each small-node
device, and therefore may be included in a neighbor small-node
device list for each small-node device. The above information may
be signaled by broadcast information in the BS2UE connection or by
dedicated signaling in the BS2UE connection. In the above examples,
a single time domain resource and a single frequency domain
resource are specified as shown in FIG. 22. But more than one time
domain resource or frequency domain resource may be configured for
the small-node devices. For example, if a cell includes a
relatively large number of small-node device, the code-domain
resource may not be sufficient and more than one time domain
resource or frequency domain resource may be necessary.
[0260] Referring again to FIG. 21, in a step S1303, user equipment
100 receives the D2UE pilot signals and makes measurements for the
D2UE pilot signals in the predetermined radio resources. The user
equipment decodes the D2UE pilot signals transmitted by multiple
small-node devices 500 and make measurements for the multiple
small-node devices. More specifically, the user equipment obtains
the radio link quality of the D2UE connections between itself and
the multiple small-node devices. The radio link quality may be at
least one of path loss, received power of the D2UE pilot signal,
SIR of the D2UE pilot signal, received quality of the D2UE pilot
signal, and the like. The user equipment may detect the small-node
device which has the highest radio link quality based on the
measurements. The path loss may be derived from the received power
of the D2UE pilot signals and the transmission power of the D2UE
pilot signals, which are included in the control signaling in step
S1301. The received quality of the D2UE pilot signal may be the
ratio of the receive power of the D2UE pilot signal to total
received signal strength.
[0261] In a step S1304, the user equipment transmits measurement
reports to the base station. The measurement reports include the
measurement results obtained in step S1303. More specifically, the
measurement reports may include the identity of the small-node
device with the highest radio link quality. In other words, the
user equipment 100 may identify the best small-node device in terms
of the radio link quality of D2UE connections in step S1304. The
small-node device information may thus include an identification
number of the small-node device and the radio link quality of the
small-node device.
[0262] Furthermore, the measurement report may include information
on neighbor small-node devices that do not have the highest radio
link quality, i.e. the measurement report may include information
on the neighbor small-node device with the second or third highest
radio link quality. In alternative embodiments, even lower radio
link qualities may be in included in the small-node device
information such as information on the neighbor small-node device
with the fourth or more radio link quality may be included. The
base station in step S1301 may indicate how many small-node devices
should have information included in the measurement report.
Alternatively the measurement reports may include all small-node
devices for which the radio link quality is higher than a
threshold. The base station may indicate the desired threshold in
step S1301. In yet another alternative embodiment, the measurement
reports may include information on all small-node devices for which
the radio link quality is lower than a threshold (which can also be
indicated by base station 200 in step S1301).
[0263] In a step S1305, the base station establishes D2UE
connection 710. More specifically, the base station establishes the
radio link between the user equipment and the small-node device
with the highest radio link quality as reported in step S1304. In
addition, the base station may assign the radio resource to D2UE
connection 710 in step S1305. The radio resource may be at least
one of the frequency domain resource, the time domain resource, the
code domain resource, and the like. More specifically, the radio
resource may be a carrier frequency for D2UE connection 710. For
example, base station 200 may select the radio resource which is
not used by the small-node device with the second or third highest
radio link quality as reported in step S1304. As a result,
interference with other D2UE connections in the neighbor small-node
devices may be avoided. Alternatively, the base station may assign
the radio resource, which is not used by other small-node device
500, which is located near the small-node device with the highest
radio link quality. The base station may have location information
for small-node device 500. According to the embodiment illustrated
in FIG. 21, lower power consumption for the measurements can be
achieved. Furthermore, interference mitigation can also be
realized.
[0264] Referring to FIG. 23, an operation of the mobile
communication system according to an embodiment is illustrated. The
operation is related to connection establishment in D2UE connection
710. The operation may correspond to step S804 in FIG. 14 or steps
A803a, A803b, A803c, A804a, A804b, A804c, A804d, A804e, and A804f
in FIG. 14A. Since steps S1401 to S1404 of FIG. 23 are the same as
steps S1301 to S1304 in FIG. 21, further explanation of the steps
S1401 to S1404 is omitted.
[0265] In a step S1405, the base station 200 determines whether or
not the path loss is lower than a threshold. More specifically,
base station 200 determines whether or not the path loss for the
small-node device with the highest radio link quality is lower than
the threshold. If the path loss for the small-node device with the
highest radio link quality is lower than the threshold (Step S1405:
YES), base station 200 establishes the D2UE connection 710 in a
step S1406. In step S1406, the base station may assign the radio
resource to D2UE connection 710, in addition to establishing the
radio resource, similarly as discussed with regard to step
S1305.
[0266] If the path loss for the base station with the highest radio
link quality is not lower than the threshold (Step S1405: NO), base
station 200 does not establish the D2UE connection 710 in a step
S1407. In particular, base station 200 does not command the user
equipment and the small-node device to establish D2UE connection
710 such that the user equipment communicates with server 600 only
in the BS2UE connection. Since the path loss is high and required
transmission power is high, the resulting D2UE connection may
interfere with other D2UE connections or communications. Such
interference issues can be mitigated by utilizing the control
illustrated in FIG. 23.
[0267] In step S1405, the path loss is used for the determination
but other indicia of radio link quality such as the received power
of the D2UE pilot signal, the received quality of the D2UE pilot
signal, the SIR of the D2UE pilot signal, and the like may be used.
In this case, if the radio link quality is better than a threshold,
the decision should be YES in step S1405. Otherwise the decision
should be NO in step S1405.
[0268] In addition to relying on the path loss for the small-node
device with the highest radio link quality, the determination in
step S1405 may also rely on the path loss for the neighbor
small-node device with the second or third highest radio link
quality. More specifically, a difference between the highest radio
link quality and the second highest radio link quality may be
utilized in the determination in step S1405. If such a difference
is higher than a threshold, base station 200 may establish D2UE
connection 710 (step S1406). Conversely, if the difference is not
higher than the threshold, base station 200 may not establish D2UE
connection 710 (step S1407). If the difference is small, the D2UE
connection may cause interference with other connections.
Therefore, such interference issues may be mitigated by utilizing
the above control. This control may apply to an embodiment in which
the small-node device with the second or third highest radio link
quality has D2UE connections with other user equipment in the radio
resources.
[0269] Referring to FIG. 24, an operation of the mobile
communication system according to an embodiment is illustrated. The
operation is related to mobility control in D2UE connection 710.
The operation may correspond to steps S1103 to S1112 in FIG.
17.
[0270] Steps S1501 to S1503 are analogous to steps S1301 to S1303
of FIG. 21. The only difference is that steps S1301 to S1303 are
conducted before the D2UE connection has been established whereas
steps S1501 to S1503 are conducted after the D2UE connection is
established. Even if the D2UE connection is established, the user
equipment has to make measurements for known or unknown neighbor
small-node devices. In this sense, the measurements in steps S1301
to S1303 are equivalent to steps S1501 to S1503. Therefore, further
explanation for steps S1501 to S1503 is omitted.
[0271] In a step S1504, user equipment 100 determines whether there
are neighbor small-node devices that are closer to the user
equipment 100 than the serving small-node device. As indicated
above, the serving small-node device denotes the small-node device
that is currently communicating with user equipment 100. More
specifically, if the radio link quality of the neighbor small-node
device is higher than that of the serving small-node device, the
determination in step S1504 may be deemed to be positive.
[0272] In the determination of step S1505, hysteresis may be taken
into account. More specifically, if the following expression is
true
(Radio link quality of Neighbor cell)>(Radio link quality of
Serving cell)+Hyst
where Hyst corresponds to the hysteresis, then the determination of
step S1404 is deemed to be positive. For example, Hyst may be 3 dB.
In addition, a time domain hysteresis may also be used. The time
domain hysteresis may be called time-to-trigger.
[0273] If a closer neighbor small-node device is detected (step
S1504: YES), the user equipment transmits measurement reports to
the base station in a step S1505. These measurement reports include
the determination of the closer neighbor small-node device.
[0274] In a step S1506, the base station transmits a handover
command to the user equipment. The base station transmits control
signaling to the neighbor small-node device for handover
preparation. Furthermore, the base station may inform the serving
small-node device that the user equipment is handed over to the
neighbor small-node device.
[0275] In a step S1507, the user equipment conducts the handover to
the neighbor small-node device.
[0276] Conversely, if no closer neighbor small-node device is
detected (step S1504: NO), the user equipment maintains the D2UE
connection with the small-node device in a step S1508.
[0277] Referring to FIG. 25, an operation of the mobile
communication system according to an embodiment is illustrated. The
operation is related to mobility control in D2UE connection 710.
The operation is conducted while the D2UE connection is established
already. Steps S1601 to S1603 are analogous to steps S1301 to S1303
of FIG. 21. The only difference is that the steps S1301 to S1303
are conducted before the D2UE connection is established whereas
steps S1601 to S1603 are conducted after the D2UE connection is
established. Therefore, further explanation for steps S1601 to
S1603 is omitted herein.
[0278] In a step S1604, the user equipment determines whether the
path loss is higher than a threshold. More specifically, the user
equipment determines whether the path loss for the serving
small-node device is higher than the threshold. The base station
may inform the user equipment of the threshold by using the control
signaling in step S1601.
[0279] In steps S1602 and 1603, the user equipment measures the
path loss by using the D2UE pilot signals but other signals or
channels may be used for the path loss measurements. For example,
pilot signals for the channel estimation or demodulation in D2UE
connection 710 may be used for the path loss measurements. The
pilot signals for the channel estimation or demodulation may
provide better accuracy for path loss measurements than the D2UE
pilot signals, which are used for mobility measurements. If the
path loss is calculated by using other signals or channels,
transmission power information of the other signals or channels may
be included in the other signals or channels. The user equipment
may calculate the path loss based on the received power of the
other signals or channels and the transmission power of the other
signals or channels.
[0280] If the path loss for the serving small-node device is higher
than the threshold (step S1604: YES), the user equipment transmits
measurement reports to the base station in a step S1605. The
measurement reports indicate that the path loss for the serving
small-node device is higher than the threshold.
[0281] In a step S1606, the base station releases the radio
resource for D2UE connection 710. More specifically, base station
200 sends control messages to release D2UE connection 710. As a
result, D2UE connection 710 is released.
[0282] If the path loss for the serving small-node device is not
higher than the threshold (step S1604: NO), user equipment 100
maintains the D2UE connection with the small-node device 500 in a
step S1607.
[0283] In the above examples, other values which represent the
radio link quality besides the path loss may be used. For example,
at least one of the received power of the pilot signal, the SIR of
the pilot signal, the received quality of the pilot signal, and the
like may be used. In this case, if the radio link quality is lower
than a threshold, the decision should be YES is step S1604,
otherwise the decision should be NO in step S1604. Based on the
radio resource management described in FIG. 25, interfering D2UE
links can be removed such that good system quality can be
maintained.
[0284] In other embodiments, some of conventional BS2UE operations
may be omitted in D2UE connection 710. More specifically, at least
one of the following operations may be omitted: [0285] Transmitting
broadcast channels in DL [0286] Transmitting common reference
signals in DL [0287] Transmitting primary synchronization
signals/secondary synchronization signals in DL [0288] Transmitting
paging signals in DL [0289] Transmitting dedicated RRC signaling
related to RRC procedures, such as connection establishment,
connection re-establishment, connection setup, connection
reconfiguration, connection release, and the like [0290]
Transmitting control signaling for handover, such as control
information of measurement configuration, measurement control,
handover command, handover complete and the like [0291]
Furthermore, some others of conventional BS2UE operations may be
supported in D2UE connection 710 in some embodiments. More
specifically, at least one of the following operations may be
supported: [0292] Transmitting PDCCH in DL [0293] Transmitting
PHICH in DL [0294] Transmitting PCFICH in DL [0295] Transmitting
PUCCH in UL [0296] Transmitting PUSCH in UL [0297] Transmitting
PRACH in UL [0298] Uplink power control [0299] DL power control
[0300] Adaptive modulation and coding for DL and UL [0301] DRX
[0302] HARQ
Traffic Measurements
[0303] In mobile communication systems, it is quite important to
collect measurement results in the radio interface. The measurement
results can be utilized for parameter optimization, determining
whether additional base stations should be installed, handing off
to additional base stations or additional carriers, etc. This
parameter optimization may be denoted as network optimization in
general. In addition, the measurement results can be utilized for
self-organized network (SON) purposes. The measurement results can
be given to the SON entity and the SON entity modifies some of
parameters based on the measurement results. Generally speaking, as
the number of nodes increases, complexity and cost for such
measurements increases. Therefore, if network operators utilize a
lot of small nodes, such as Pico base stations or Femto base
stations, how to collect such measurement results efficiently is a
challenging problem.
[0304] In the present disclosure, the addition of the small-node
device presents such a measurement problem. Since the number of the
small-node devices is larger than the existing deployed base
stations, more efficient measurement procedures and network
optimization are required. These measurement procedures may be
explained as follows:
[0305] FIG. 26 illustrates an example communication system. As
compared to the system discussed with regard to FIG. 2, the system
of FIG. 26 is analogous except that a D2UE measurement data
collection section 208 for base station 200 is added. D2UE
measurement data collection section 208 is configured to collect
measurement data for the D2UE link.
[0306] D2UE measurement data collection section 208 is shown in
FIG. 26 as being external to base station 200, but it may be
located inside the base station 200 and may be integrated into base
station 200. Alternatively, D2UE measurement data collection
section 208 may be located in other nodes, such as access gateway
300 or a node in core network 400. There are two kinds of
measurement data in the system of FIG. 26. One is the measurement
data which are measured in base station 200, and the other is the
measurement data which are measured in small-node device 500. In
the following, these two kinds of measurement data will be
explained separately.
Measurement data measured in the base station 200:
[0307] FIG. 27 shows examples of measurements conducted by base
station 200. In this embodiment, D2UE communication control section
204 performs the measurements listed in FIG. 27 because section 204
conducts radio link connection control for D2UE connection 710 as
described above and can thus readily make the measurements. The
radio link connection control includes at least one of
establishing/configuring/re-configuring/re-establishing/releasing
D2UE connection 710. Furthermore, the radio link connection control
may include handover or radio link failure handling for D2UE
connection 710.
[0308] D2UE communication control section 204 makes the
measurements and sends the measurement results to D2UE measurement
data collection section 208. A measurement index #0 in FIG. 27
corresponds to the number of D2UE connections. The number of D2UE
connections may be the total number of D2UE connections in the
macro cell coverage area in which base station 200 provides radio
communication service for user equipment 100. Alternatively, the
number of D2UE connections may equal the D2UE connections for the
small-node device. According to this measurement item, network
operators can detect how many D2UE connections are utilized in the
macro coverage area or in each small-node device. Such information
can be utilized when network operators determine whether or not new
small-node device should be installed. If the number of the D2UE
connections in small-node device 500 is larger than a threshold
value, network operators may determine that a new small-node device
should be installed.
[0309] Alternatively, network operators may determine that radio
resources for the small-node device should be increased if the
number of the D2UE connections for small-node device 500 is larger
than a threshold value. The radio resource may be the frequency
resource. For example, network operators may determine that
frequency carriers for the D2UE connections handled by the
small-node device should be increased if the number of the D2UE
connections in small-node device 500 is larger than the threshold
value.
[0310] In addition to the number of D2UE connections, the number of
logical channels in the D2UE connections may be measured as part of
measurement item #0. Alternatively, the number of D2UE connections
may be measured for each logical channel. More specifically, the
number of D2UE connections in which logical channel supporting best
effort packets is transferred may be measured.
[0311] A measurement index #1 corresponds to the radio resources
used by the D2UE connections. The radio resources for the D2UE
connections may correspond to the radio resources for all D2UE
connections in the macro cell coverage area. Alternatively, the
radio resources may correspond to those used by each small-node
device. Responsive to this measurement item, network operators can
detect how much radio resource is utilized for the D2UE connections
in the macro coverage area or in each small-node device. Such
information can be utilized when network operators determine
whether a new small-node device should be installed. For example,
if the amount of the radio resources in the D2UE connections used
by the small-node device is larger than a threshold value, network
operators may determine that a new small-node device should be
installed. Alternatively, network operators may determine that
radio resources for the small-node device should be increased if
the amount of the radio resources in the D2UE connections for the
small-node device is larger than the threshold value.
[0312] The radio resource may be the frequency domain resource. For
example, network operators may determine that frequency carriers
for the D2UE connections handled by the small-node device should be
increased if the amount of the radio resource for the small-node
device is larger than the threshold value. Alternatively, the radio
resource may be the time-frequency resource.
[0313] The measurements of the radio resource may be done
separately for DL (from the small-node device to the user
equipment) and UL (from the user equipment to the small-node
device). Instead of the actual radio resource, the usage of the
radio resource may be measured. The usage of the radio resource may
be calculated as follows:
usage #1 = r ( T ) total_r ( T ) ##EQU00001##
[0314] where r(T) is the amount of assigned radio resource during
time period T, total.sub.-- r(T) is the amount of available radio
resource during time period T, and T is the time period during
which the measurement is performed.
[0315] Measurement index #2 corresponds to a data rate in the D2UE
connections. The data rate in the D2UE connections may be the total
data rate in the D2UE connections in the macro cell coverage area.
Alternatively, the data rate in the D2UE connections may be the
data rate in each small-node device. According to this measurement
item, network operators can detect how much data rate is achieved
for the D2UE connections in the macro coverage area or for each
small-node device.
[0316] The data rate may be calculated in the Physical layer, the
MAC layer, the RLC layer, or the PDCP layer. Moreover, the data
rate may be calculated for each logical channel in the D2UE
connections. The data rate may be calculated separately for
downlink (from small-node device to user equipment) and uplink
(from user equipment to small-node device). A status report may be
utilized for the calculation. For example, the actual data
transmission is conducted in D2UE connection 710 but the status
report for D2UE connection 710 may be transmitted to base station
200 utilizing BS2UE connection 720 through BS2UE communication
section 102 in user equipment 100. The status report transmission
from user equipment 100 to base station 200 is illustrated in FIG.
27A. The status report (which may include status for each logical
channel) may be thus transmitted both in D2UE connection 710 and in
BS2UE connection 720. The status report may include status for each
logical channel. As a result, D2UE communication control section
204 in base station 200 can easily utilize the status report to see
how many bits are transmitted in the D2UE connection per second.
The number of bits per second corresponds to the data rate in D2UE
connection 710. Alternatively, D2UE communication control section
204 may calculate the amount of transferred data in D2UE connection
710 utilizing a sequence number in the status report. The change of
the sequence number during one time duration corresponds to the
amount of transferred data during the time duration.
[0317] In the above example, user equipment 100 transmits the
status report to base station 200. However, BS2D communication
section 502 in small-node device 500 may alternatively transmit a
status report to base station 200 through BS2D connection 730. The
data rate may correspond to one D2UE connection in one small-node
device. Alternatively, the data rate may be the sum of the data
rate for multiple D2UE connections in a single small-node device.
In yet another embodiment, the data rate may be the sum of the data
rate for all the D2UE connections in the macro coverage area. For
example, a total data rate (Total_data_rate) for all the D2UE
connections may be calculated using the following equation:
Total_data _rate = n = 1 N data_rate ( n ) ##EQU00002##
where data_rate is the data rate for one D2UE connection, n is the
index of the D2UE connections, and N is the total number of the
D2UE connections. Such information can be utilized by network
operators to determine whether a new small-node device should be
installed as discussed above with regard to the analogous
user-equipment-reported data rate measurement.
[0318] Measurement index #3 of FIG. 27 corresponds to a success
rate of the D2UE connection establishment. The success rate of the
D2UE connection establishment (Rate.sub.#3) may be defined as
follows:
Rate #3 = N 1 N 1 + N 2 ##EQU00003##
where N.sub.1 is the number of successful D2UE connection
establishments and N.sub.2 is the number of unsuccessful D2UE
connection establishments. The success rate of the D2UE connection
establishment may be that for all the D2UE connections in the macro
cell coverage area. Alternatively, the success rate of the D2UE
connection establishment may be determined for each small-node
device. A failure rate of the D2UE connection establishment may be
measured instead of the success rate of the D2UE connection
establishment. The failure rate of the D2UE connection
establishment may be defined as follows:
(Failure rate of D2UE connection establishment)=1-(Success rate of
D2UE connection establishment)
[0319] According to the success (or failure) of the D2UE connection
establishment, network operators can determine whether some radio
interface parameters should be modified. For example, if the
success rate is lower than a threshold value, network operators
require a change in the radio interface parameters.
[0320] A measurement index #4 corresponds to a handover success
rate in the D2UE connections. The handover success rate
(Rate.sub.#4) may be defined as follows:
Rate #4 = N 3 N 3 + N 4 ##EQU00004##
where N.sub.3 is the number of successful handovers in the D2UE
connections and N.sub.4 is the number of unsuccessful handover in
the D2UE connections. The handover success rate may be that for all
the D2UE connections in the macro cell coverage area.
Alternatively, the success rate of the D2UE handover for individual
small-node devices may be measured. In yet another alternative
embodiment, the handover failure rate in the D2UE connections may
be measured instead of the success rate. The handover failure rate
in the D2UE connections may be defined as follows:
(Failure rate of the handover in the D2UE connections)=1-(Success
rate of the handover in the D2UE connections)
According to this handover success (or failure) measurement item,
network operators can determine whether the handover parameters
should be modified. For example, if the handover success rate is
lower than a threshold value, network operators may require a
modification of the handover parameters.
[0321] Measurement index #5 corresponds to a success rate of D2UE
connection re-establishments. The success rate of the connection
re-establishments in the D2UE connections (Rate.sub.#5) may be
defined as follows:
Rate #5 = N 5 N 5 + N 6 ##EQU00005##
[0322] where N.sub.5 is the number of successful connection
re-establishments in the D2UE connections, and N.sub.6 is the
number of unsuccessful connection re-establishments in the D2UE
connections. The success rate of the D2UE connection
re-establishments may be that for all the D2UE connections in the
macro cell coverage area. Alternatively, the success rate may
correspond to individual D2UE connections. Alternatively, a failure
rate of the D2UE connection re-establishments may be measured
instead of the success rate of the connection re-establishments in
the D2UE connections. The failure rate of the connection
re-establishments in the D2UE connections may be defined as
follows:
(Failure rate of the connection re-establishments in the D2UE
connections)=1-(Success rate of the connection re-establishments in
the D2UE connections).
[0323] Responsive to this measurement item, network operators can
determine whether some D2UE connection re-establishments parameters
should be modified. For example, if the success rate of the D2UE
connection re-establishments is lower than a threshold value,
network operators may determine that some D2UE connection
re-establishments parameters should be modified.
[0324] Measurement index #6 corresponds to the number of D2UE
connection handovers in the D2UE connections. This number may be
that for all the D2UE connections in the macro cell coverage area.
Alternatively, the number may be that for the D2UE connection
handovers for the small-node device. Responsive to this measurement
item, network operators can determine whether D2UE connection
handover parameters should be modified. For example, if the number
of handovers in the D2UE connections is higher than a threshold
value (which may imply that some ping-pong problems exist in the
handovers), network operators may require some modifications for
the handover parameters.
[0325] Measurement index #7 corresponds to the number of radio link
failures in the D2UE connections. This number may be that for all
the radio link failures in the macro cell coverage area.
Alternatively, the number may that for small-node device radio link
failures. The number of radio link failures may be reported by the
user equipment 100 over BS2UE connection 720. Alternatively, it may
be reported by small-node device 500 over BS2D connection 730. The
report on the radio link failures may be included in the control
signaling in step S1301. Through this measurement item, network
operators can determine whether some of the radio interface
parameters should be modified. For example, if the number of radio
link failures in the D2UE connections is higher than a threshold
value (which may imply that some of the radio interface parameters
are not optimized), network operators may determine that some of
the radio interface parameters should be modified.
[0326] Finally, a measurement index #8 of FIG. 27 corresponds to
the number of D2UE connection re-establishments. This number may be
that for all the D2UE connections in the macro cell coverage area.
Alternatively, the number may be that the D2UE connection
re-establishments in each of the small-node device. Using this
measurement item, network operators can determine whether some of
the radio interface parameters should be modified. For example, if
the number of connection re-establishments in the D2UE connections
is higher than a threshold value (which may imply that some of the
radio interface parameters are not optimized), network operators
may determine that some of the radio interface parameters should be
modified.
Measurement data in the small-node device 500:
[0327] FIG. 28 shows examples of measurement items which are
measured in the small-node device 500. D2UE communication section
504 (FIG. 11) makes the measurements listed in FIG. 28 whereas BS2D
communication section 502 sends the measurement results to the base
station via BS2D connection 730. The measurement results may be
sent to base station 200 as part of the control signaling. The
measurement results are transferred to the D2UE measurement data
collection section 208. The D2UE measurement data collection
section 208 can thus readily obtain the measurement results for the
D2UE connections by utilizing BS2D connection 730, which makes the
collection of the measurements very efficient.
[0328] A measurement index #A0 of FIG. 28 corresponds to a central
processing unit (CPU) usage rate in small-node device 500. The CPU
usage rate may be used to determine whether or not a congestion
level in the small-node device is relatively high. For example, if
the CPU usage rate is higher than a threshold value, the network
operators may determine that a new small-node device should be
installed.
[0329] A measurement index #A1 corresponds to a memory usage rate
in small-node device 500. The memory usage rate may also be
utilized to determine whether the congestion level in the
small-node device is relatively high. For example, if the memory
usage rate is higher than a threshold value, the network operators
may deter that a new small-node device or additional memory should
be installed.
[0330] A measurement index #A2 corresponds to a buffer usage rate
of buffer in the small-node device 500 and is thus analogous to
measurement index #A1. The buffer usage rate may also be utilized
to determine whether the congestion level in the small-node device
is relatively high. For example, if the buffer usage rate is higher
than a threshold value, the network operators may determine that
new small-node device or additional buffer should be installed.
[0331] A measurement index #A3 is a baseband processing usage rate
in the small-node device. The baseband usage rate may also be
utilized to determine whether the congestion level in the
small-node device is relatively high. The indices A0 through A3
thus correspond to a processing load in the small-node device.
[0332] A measurement index #A4 corresponds to an amount of radio
resources in the D2UE connections. The radio resources may
correspond to that which is actually utilized for data transmission
as opposed to that which is assigned by base station 200 for the
D2UE connections. In such a case, the utilized radio resource may
correspond to the congestion level in the D2UE connections. The
amount of the utilized radio resource in the D2UE connections may
thus be used to determine whether the congestion level in
small-node device 500 is relatively high as compared to a threshold
value. If the threshold value is exceeded, network operators may
require that new small-node device be installed. The measurements
of the utilized radio resource may be done separately for DL (from
the small-node device to the user equipment) and UL (from the user
equipment to the small-node device).
[0333] A measurement index #A5 corresponds to a backhaul usage rate
in the small-node device to determine whether the congestion level
in the backhaul link is relatively high as compared to, for
example, a threshold value. If the threshold value is exceeded, the
network operators may determine that additional bandwidth for the
backhaul link should be installed.
[0334] A measurement index #A6 corresponds to the D2UE connection
data rate. The data rate may be calculated in the Physical layer,
the MAC layer, the RLC layer, or the PDCP layer. The data rate may
be calculated by setting an average period as a time when data to
be transmitted are present in the transmission buffer. For example,
if there is data only in a period of 300 ms in a measurement period
of 500 ins, the data rate is calculated by averaging over the
period of 300 ms and not over the remaining periods as shown in
FIG. 29. Alternatively, the data rate may be calculated over all
the measurement period regardless of the presence/absence of the
data to be transmitted in the transmission buffer. The measurements
of the data rate may be done separately for DL (from the small-node
device to the user equipment) and UL (from the user equipment to
the small-node device). The data rate may be calculated for each
logical channel in the D2UE connections.
[0335] The data rate in the D2UE connections may be utilized to
determine whether the congestion level in small-node device 500 is
relatively high. For example, the amount of the data rate may be
compared to a threshold value. If the threshold value is not
exceeded, network operators may determine that the congestion level
is relatively high such that a new small-node device should be
installed.
[0336] A measurement index #A7 corresponds to a time duration for
communications in the D2UE connections. In some embodiments, the
radio resource for the D2UE connections is assigned by base station
200, but the radio resource is used only when there is data to be
transmitted in the D2UE connections. The time duration for D2UE
communications thus corresponds to a time duration when data is
actually transmitted. The time duration may be utilized to
investigate data traffic patterns, i.e. to investigate whether data
is bursty or not.
[0337] In contrast to index #A7, a measurement index #A8
corresponds to a time duration for which there is no data
communications in the D2UE connections. This time duration can also
be used to investigate data traffic patterns.
[0338] A measurement index #A9 corresponds to the path loss in the
D2UE connection. The path loss may be utilized to estimate actual
coverage area in which the small-node device provides radio
communication services. The network operators may utilize such
information as compared to a threshold to determine whether new
small-node devices should be installed in the area. The path loss
measurement may be an average value of the path loss for the D2UE
connections that are handled by small-node device 500.
[0339] A measurement index #A10 corresponds to a radio link quality
in the D2UE connection. The radio link quality may be utilized to
estimate the communication quality in the coverage area for which
the small-node device provides radio communication services. The
network operators may utilize such information to determine whether
some of the radio interface parameters should be modified. The
radio link quality may be an average value of the radio link
quality for the D2UE connections which are handled by the
small-node device 500. The radio link quality may be at least one
of a signal-to-interference ratio in the D2UE connections and a
channel quality indicator (CQI) in the D2UE connections. More
specifically, if the radio link quality for the D2UE connections is
lower than a threshold, the network operators may determine that
some of the radio interface parameters should be modified. The
measurements of the radio link quality may be done separately for
DL (from the small-node device to the user equipment) and UL (from
the user equipment to the small-node device).
[0340] A measurement index #A11 corresponds to a block error rate
(BLER) for the D2UE connection. The BLER may be utilized to
estimate communication quality in the small-node device 500
coverage area. The network operators may utilize such information
to determine whether or not some of the radio interface parameters
should be modified. The BLER may be average value of the BLER for
the D2UE connections that are handled by small-node device 500. A
bit error rate may be utilized instead of the BLER. If the BLER for
the D2UE connections is higher than a threshold, the network
operators may determine that some of the radio interface parameters
should be modified. The measurements of the BLER may be done
separately for DL (from the small-node device to the user
equipment) and UL (from the user equipment to the small-node
device).
[0341] A measurement index #A12 corresponds to a received signal
power for the D2UE connections. The received signal power is
utilized to estimate communication quality in the small-node device
coverage area. The network operators may utilize such information
when they determine whether or not some of the radio interface
parameters should be modified. The received signal power may be an
average value of the received signal power for the D2UE connections
that are handled by small-node device 500. If the received signal
power for the D2UE connections is higher than a threshold, the
network operators may determine that some of the radio interface
parameters should be modified. The measurements of the received
signal power may be done separately for DL (from the small-node
device to the user equipment) and UL (from the user equipment to
the small-node device). For DL, the user equipment may report the
received signal power to the small-node device.
[0342] A measurement index #A13 corresponds to a transmitted signal
power for the D2UE connections. The transmitted signal power is
utilized to estimate communication quality in the small-node device
coverage area in which small-node device 500 provides radio
communication services. The network operators may utilize such
information when they determine whether or not some of the radio
interface parameters should be modified. The transmitted signal
power may be an average value of the transmitted signal power for
the D2UE connections which are handled by small-node device 500.
The measurements of the transmitted signal power may be done
separately for DL (from the small-node device to the user
equipment) and UL (from the user equipment to the small-node
device). For UL, the user equipment may report the transmitted
signal power to the small-node device. If the transmitted signal
power for the D2UE connections is higher than a threshold, the
network operators may determine that some of the radio interface
parameters should be modified.
[0343] A measurement index #A14 corresponds to an interference
power for the D2UE connections. The interference power is utilized
to estimate communication quality in the coverage area which
small-node device 500 provides radio communication services. The
network operators may utilize such information when they determine
whether some of the radio interface parameters should be modified.
The interference power may be an average value of the interference
power for the D2UE connections which are handled by the small-node
device 500. If the interference power for the D2UE connections is
higher than a threshold, the network operators may determine that
some of the radio interface parameters should be modified. The
measurements of the interference power may be done separately for
DL (from the small-node device to the user equipment) and UL (from
the user equipment to the small-node device). For DL, the user
equipment may report the interference power to the small-node
device.
[0344] A measurement index #A15 corresponds to location information
of the small-node device 500. The location information may be
utilized for SON operation.
[0345] A measurement index #A16 corresponds to the number of user
equipment for which data to be transmitted is present in the
transmission buffer. This number may be utilized to determine
whether the congestion level in small-node device 500 is relatively
high. If the number of user equipment for which data to be
transmitted is present is higher than a threshold value, network
operators may determine that the congestion level is relatively
high such that a new small-node device should be installed. The
measurements of the number of user equipment for which data to be
transmitted is present may be done separately for DL (from the
small-node device to the user equipment) and UL (from the user
equipment to the small-node device). For UL, user equipment 100 may
report to small-node device 500 whether there is data to be
transmitted in its transmission buffer. The number of user
equipment having data to be transmitted may be calculated for each
logical channel in the D2UE connections, i.e. the number of logical
channels having data to be transmitted may be calculated. User
equipment for which data to be transmitted is present may be
denoted as an active user.
[0346] A measurement index #A17 corresponds to the number of user
equipment whose data rate is lower than a threshold. This number
may be utilized to determine whether the congestion level in the
small-node device is relatively high. If the number of user
equipment whose data rate is lower than a threshold is higher than
another threshold value, network operators may determine that the
congestion level is relatively high such that new small-node
devices should be installed. The measurements of the number of user
equipment for whose data rate is lower than a threshold may be done
separately for DL (from the small-node device to the user
equipment) and UL (from the user equipment to the small-node
device). The number of user equipment whose data rate is lower than
a threshold may be calculated for each logical channel in the D2UE
connections.
[0347] A measurement index #A18 corresponds to a number of inactive
user equipment in the D2UE connections. In some embodiments, the
radio resource for the D2UE connections is assigned by the base
station, but the radio resource is used only when there is data to
be transmitted. Thus there is a time duration when there is no data
to be transmitted. The inactive user equipment corresponds to the
ones that have no data to be transmitted in the D2UE
connection.
[0348] Regardless of whether the user equipment and/or the
small-node device make the traffic measurements, D2UE measurement
data collection section 208 may utilize some parts of the
measurement data described above for call admission control of the
D2UE connections. For example, D2UE measurement section 208 may
determine that new D2UE connections should be prohibited if the
number of D2UE connections in the small-node device is higher than
a threshold. Other measurement items, such as the amount of the
utilized radio resources may be used for the call admission control
instead of the number of D2UE connections. The call admission
control may be performed by D2UE communication control section 204
instead of D2UE measurement data collection section 208.
[0349] The operation of the above-described base station, the user
equipment, and the small-node device may be implemented by a
hardware, may also be implemented by a software module executed by
a processor, and may further be implemented by the combination of
the both.
[0350] The software module may be arranged in a storing medium of
an arbitrary format such as RAM (Random Access Memory), a flash
memory, ROM (Read Only Memory), EPROM (Erasable Programmable ROM),
EEPROM (Electronically Erasable and Programmable ROM), a register,
a hard disk, a removable disk, and CD-ROM.
[0351] Such a storing medium is connected to the processor so that
the processor can write and read information into and from the
storing medium. Such a storing medium may also be accumulated in
the processor. Such a storing medium and processor may be arranged
in an ASIC. Such an ASIC may be arranged in the base station, the
user equipment, and the small-node device. As a discrete component,
such a storing medium and processor may be arranged in the base
station, the user equipment, and the small-node device.
[0352] Thus, the present invention has been explained in detail by
using the above-described embodiments; however, it is obvious that
for persons skilled in the art, the present invention is not
limited to the embodiments explained herein. The present invention
can be implemented as a corrected, modified mode without departing
from the gist and the scope of the present invention defined by the
claims. Therefore, the description of the specification is intended
for explaining the example only and does not impose any limited
meaning to the present invention.
* * * * *