U.S. patent application number 14/358339 was filed with the patent office on 2014-10-02 for node detection in a cellular communication network.
The applicant listed for this patent is Kyocera Corporation. Invention is credited to Henry Chang, David Comstock, Douglas Dunn, Amit Kalhan.
Application Number | 20140293858 14/358339 |
Document ID | / |
Family ID | 47226470 |
Filed Date | 2014-10-02 |
United States Patent
Application |
20140293858 |
Kind Code |
A1 |
Kalhan; Amit ; et
al. |
October 2, 2014 |
NODE DETECTION IN A CELLULAR COMMUNICATION NETWORK
Abstract
A technique for detecting a neighboring node in a cellular
communication network is disclosed. The neighboring node may employ
a different radio access technology (RAT) and/or operate at a
different frequency than adjacent nodes. The neighboring node
transmits cell-specific or user equipment (UE) specific information
using one or more Multicast Broadcast Single Frequency Network
(MBSFN) subframes. This information can include data and/or control
signaling for handover processing. A UE currently being served by
another node can monitor the MBSFN subframes and initiate a search
for the neighboring node, including inter-frequency measurements,
based on the information contained in the MBSFN subframes. This
allows UEs located at cell boundaries to become aware of the
presence of the neighboring node, and may reduce UE power
consumption used in searching for neighboring nodes, particularly
those operating at a different carrier frequency or having a
different RAT, for example, a wireless local area network
(WIAN).
Inventors: |
Kalhan; Amit; (San Diego,
CA) ; Chang; Henry; (San Diego, CA) ; Dunn;
Douglas; (San Diego, CA) ; Comstock; David;
(San Diego, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kyocera Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
47226470 |
Appl. No.: |
14/358339 |
Filed: |
November 12, 2012 |
PCT Filed: |
November 12, 2012 |
PCT NO: |
PCT/US2012/064704 |
371 Date: |
May 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61559860 |
Nov 15, 2011 |
|
|
|
Current U.S.
Class: |
370/311 |
Current CPC
Class: |
H04W 4/06 20130101; Y02D
70/1262 20180101; H04W 72/005 20130101; H04W 36/32 20130101; H04W
36/0072 20130101; Y02D 70/1242 20180101; H04W 52/0203 20130101;
Y02D 30/70 20200801; Y02D 70/142 20180101; H04W 36/0077
20130101 |
Class at
Publication: |
370/311 |
International
Class: |
H04W 52/02 20060101
H04W052/02; H04W 72/00 20060101 H04W072/00 |
Claims
1. An apparatus, comprising: an air interface configured to receive
one or more services from a first node in a cellular communication
network and to receive a Multicast Broadcast Single Frequency
Network (MBSFN) subframe from a second node in the cellular
communication network, the MBSFN subframe containing information
about the second node; and a controller configured to Initiate a
search for the second node based on the information contained in
the MBSFN subframe.
2. The apparatus of claim 1, wherein the information includes a
downlink (DL) transmit power level (P.sub.t) from the second
node.
3. The apparatus of claim 2, wherein the controller is further
configured to; measure a DL power (P.sub.r) at the apparatus,
compare the DL transmit power level and the DL receive power to
determine a path loss between the apparatus and the second node,
and initiate the search based on the path loss.
4. The apparatus of claim 3, further comprising: a radio frequency
(RF) transceiver configured to communicate with the second node,
wherein the RF transceiver is turned on only if the path loss is
less than a threshold.
5. The apparatus of claim 1, wherein the first node is operating at
a first carrier frequency and the second node is operating at a
second carrier frequency that is not the same as the first carrier
frequency.
6. The apparatus of claim 1, wherein the first node and the second
node each use a different radio access technology from one
another.
7. The apparatus of claim 6, wherein the second node is selected
from the group consisting of a home eNB and a wireless local area
network (WLAN) access point (AP).
8. The apparatus of claim 1, wherein the controller compares the
information to predetermined criteria, and initiates one or more
inter-frequency or inter-RAT measurements based on a result of
comparing the information to the predetermined criteria.
9. A method of defecting a neighboring node in a cellular
communication network, comprising: receiving, at a user equipment
(UE) currently being served by a first node, a Multicast Broadcast
Single Frequency Network (MBSFN) subframe from a second node, the
MBSFN subframe containing information about the second node; and
initiating a search for the second node based on the
information.
10. The method of claim 9, wherein the information includes a
downlink (DL) transmit power level (P.sub.t) from the second
node,
11. The method of claim 10, further comprising: measuring a DL
receive power (P.sub.r) at the UE; comparing the DL transmit power
level and the DL receive power to determine a path loss between the
UE and the second node; and initiating the search based on the path
loss,
12. The method of claim 11, further comprising: activating a radio
frequency (RF) transceiver included in the UE only if the path loss
is less than a threshold.
13. The method of claim 9, wherein the first node is operating at a
first carrier frequency and the second node is operating at a
second carrier frequency that is not the same as the first carrier
frequency.
14. The method of claim 9, wherein the first node and the second
node each use a different radio access technology from one
another.
15. The method of claim 14, wherein the second node is selected
from the group consisting of a home eNB and a wireless local area
network (WLAN) access point (AP).
16. The method of claim 9, further comprising: initiating one or
more inter-frequency measurements based on the information,
17. A cellular communication network, comprising: a user equipment
(UE) configured to: receive one or more wireless services from a
first node and a Multicast Broadcast Single Frequency Network
(MBSFN) subframe containing information about a second node, and
initiate a search for the second node based on the information in
the MBSFN subframe.
18. The cellular communication network of claim 17, further
comprising; the first node for providing the services to the UE;
and the second node for transmitting the MBSFN subframe to the
UE.
19. The cellular communication network of claim 17, wherein the
information includes a downlink (DL) transmit power level (P.sub.t)
from the second node.
20. The cellular communication network of claim 19, wherein the UE
is further configured to: measure a DL receive power (P.sub.r) at
the apparatus, compare the DL transmit power level and the DL
receive power to determine a path loss between the apparatus and
the second node, and initiate the search based on the path loss.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority to Provisional
Application No. 61/559,860 entitled "Different Frequency
Neighboring Cell MBSFN Subframe," filed Nov. 15, 2011, and assigned
to the assignee hereof and hereby expressly incorporated by
reference.
REFERENCE TO CO-PENDING APPLICATIONS FOR PATENT
[0002] The present application relates to PCI Application, entitled
"Inter-cell Messaging Using MBSFN Subframe," Reference Number TUTL
00209, filed concurrently with this application, and assigned to
the assignee hereof and expressly incorporated by reference herein;
to PCT Application, entitled "Handover Management Using a Broadcast
Channel in a Network Having Synchronized Base Stations," Reference
Number TUTL 00207, filed concurrently with this application; and to
PCT. Application No. entitled "Handover Signaling Using an MBSFN in
a Cellular Communication System," Reference Number TUTL 00210,
filed concurrently this application, and assigned to the assignee
hereof and expressly incorporated by reference herein.
TECHNICAL FIELD
[0003] The present disclosure generally relates to wireless
communications, and more particularly to cellular networks.
BACKGROUND
[0004] Generally, cellular communication networks include a number
of base stations, also referred to herein as nodes, located across
a geographic area. These base stations provide radio access to
wireless mobile devices, such as cellular smart phones, to a core
network of a cellular service provider. The base stations along
with various data routing and control mechanisms (e.g., base
station controllers, core and edge routers, and so on) facilitate
wireless communication and data services with the mobile
devices.
[0005] Each base station in the network provides wireless services
within a particular coverage area When a mobile device is turned
on, it typically uses a standard selection procedure to establish a
radio communications link with the nearest base station in order to
receive services. As the mobile device moves about within the
coverage area of the network, it will per test the signal quality
from its serving base station to determine whether it should
re-select another, neighboring base station with better signal
quality. If the signal quality from the serving base station has
decreased below a threshold, the mobile device can engage in a
standard reselection procedure to search for and subsequently
handover its radio connection to a neighboring base station having
a stronger signal.
[0006] Cellular network operational standards, such as Long-term
Evolution (LTE), specific certain cell reselection protocols. Some
of these reselection protocols require inter-frequency carrier
searches by mobile devices. In some situations, the mobile device
searches for a neighboring base station employing a different radio
access technology (RAT) than the serving base station, These
searches can have significant impact on a mobile devices power
consumption.
SUMMARY
[0007] Techniques for detecting a neighboring node (e.g., base
station) in a cellular communication network are disclosed, The
neighboring node may employ a different radio access technology
(RAT) and/or operate at a different frequency than adjacent nodes.
The neighboring node transmits cell-specific or user equipment (UE)
specific, information using one or more Multicast Broadcast Single
Frequency Network (MBSFN) subframes. This information may include
data and/or control signaling for handover processing. A UE, such
as a wireless mobile device, currently being served by another node
can monitor the MBSFN subframes and initiate a search, for the
second node, which may include one or more inter-frequency or
inter-RAT measurements, based on the information contained in the
MBSFN subframes. This allows UEs located at cell boundaries to
become aware of the presence of the neighboring node, and may
reduce UE power consumption in detecting neighboring nodes,
particularly those nodes operating at a different carrier frequency
or having a different RAT, such as a wireless local area network
(WLAN) type node, e.g., a Wi-Fi 802.11 access point (AP). Without
such assistance, the UE would likely need to search frequently for
a WLAN AP, even though no WLAN AP may be available, and with each
search, potentially searching more frequencies, thus increasing the
time of each search. This type of search is undesirable since it
typically wastes the UE's limited battery power.
[0008] According to an aspect of the techniques, an apparatus
includes an air interface configured to receive, one or more
services from a first node in a cellular communication network. The
air interface is also configured to receive a MBSFN subframe from a
second node in the cellular communication network. The MBSFN
subframe contains information about the second node. A controller
included in the apparatus initiates a search for the second node
based on the information contained in the MBSFN subframe.
[0009] According to another aspect of the techniques a method of
detecting a neighboring node in a cellular communication network
includes receiving, at a user equipment (UE) currently being served
by a first node, a MBSFN subframe from second node; and initiating
a search for the second node based on information about the second
node contained in the MBSFN subframe.
[0010] According, to a further aspect of the techniques, a cellular
communication network includes a UE configured to receive one or
more wireless services from a first node and to receive a MBSFN
subframe containing information about a second node. The UE
initiates a search for the second node based on the information in
the MBSFN subframe.
[0011] Other aspects, features, advantages of the foregoing
techniques w or will become apparent to one with skill in the art
upon examination of the following figures and detailed description.
It is intended that all such additional aspects features, and
advantages be it within this description and be protected by the
accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] It is to be understood that the drawings are solely for
purpose of illustration and do not define the limits of the
invention. Furthermore, the components in the figures are not
necessarily to scale. In the figures, like reference numerals
designate corresponding parts throughout the different views.
[0013] FIG. 1 illustrates an exemplary cellular communication
network including a macro node and home node.
[0014] FIG. 2 shows an exemplary transmission frame structure at
may be used on the downlinks in the networks of FIGS. 1 and 4.
[0015] FIG. 3 shows an exemplary resource-block structure for MBSFN
subframes.
[0016] FIG. 4 illustrates a second exemplary cellular communication
network including plural macro nodes.
[0017] FIG. 5 is to flowchart illustrating an exemplary method of
detecting a neighboring node in a cellular communication
network.
[0018] FIG. 6 is a block diagram illustrating certain components of
exemplary UE usable in the networks of FIGS. 1 or 4.
[0019] FIG. 7 is a block diagram illustrating certain components
exemplary cell node usable in the networks of FIG. 1 or 4.
[0020] FIG. 8 is a signal flow diagram illustrating a procedure for
transmitting inter-cell information using one or more MBSFN
subframes.
[0021] FIG. 9 is a conceptual diagram illustrating first method of
unicasting/multicasting node-specific information in MBSFN
subframes so as to reduce or avoid it with other nodes transmitting
MBSFN subframes.
[0022] FIG. 10 is conceptual diagram illustrating a second method
of unicasting/multicasting node-specific information in MBSFN
subframes so as to reduce or avoid interference with other nodes
transmitting MBSFN subframes.
DETAILED DESCRIPTION
[0023] The following detailed description, which references to and
incorporates the drawings, describes and illustrates one or more
specific embodiments. These embodiments, offered not to limit but
only to exemplify and teach, are shown and described in sufficient
detail to enable those skilled in the art to practice what is
claimed. Thus, where appropriate to avoid obscuring the invention,
the description may omit certain information known to those of
skill in the art.
[0024] The word "exemplary" is used throughout this disclosure to
mean "serving as an example, instance, or illustration." Anything
described herein as "exemplary" is not necessarily to be construed
as preferred or advantageous over other approaches or features.
[0025] FIG. 1 illustrates an exemplary cellular communication
network 10 including at least one macro node 12 and at least one
home node 16. The macro node 12 provides wireless services over a
larger coverage area 14, and the home node 16 provides wireless
services over a smaller coverage area 18. The home node 16 and
macro node 12 may communicate with each other over a backhaul
network 22. User equipment (UE) 20, which may operate as a terminal
device in the network 10, can receive wireless services from both
the macro nods 12 and home node 16. Although only one UE 20 and two
nodes 12, 16 are shown, the network 10 may include more UEs and
nodes (not shown for simplification).
[0026] The network 10 is an LTE network and nodes 12, 16 may be
evolved Node Bs (eNBs). The network 10 can include other network
entities as well, such as a network control entity. The
Third-Generation Partnership Project Long-Term Evolution (3GPP LTE)
communication specification is a specification for systems where
base stations (eNBs) provide service to mobile wireless
communication devices (UEs) using orthogonal frequency-division
multiplexing (OFDM) on the downlink and single-carrier
frequency-division multiple access (SC-FDMA) on the uplink.
Although the techniques described herein may be applied in other
types of communication systems, the exemplary networks discussed
herein operate in accordance with a 3GPP LTE communication
specification.
[0027] An eNB communicates with the UEs in the network and may also
be referred to as a base station, a Node B, an access point or the
like. Each eNB 12, 16 may provide communication coverage for a
particular geographic area. To improve network capacity, the
overall coverage area of an eNB may be partitioned into multiple
smaller areas. In 3GPP, the tents "cell" can refer to the coverage
area of an eNB and/or an eNB subsystem serving a smaller
partition.
[0028] An eNB may provide communication coverage for a macro cell,
a pico cell, a femto cell, and/or other types of cells. As depicted
in FIG. 1 the macro node 12 covers a macro cell that may span a
relatively large geographic area (e.g., several kilometers in
radius) and may allow network access to UEs with service
subscriptions. A pico cell may cover a smaller geographic area than
a macro cell. The home node 16, also referred to as a femto node,
may cover a femto cell, which is a relatively small geographic area
(e.g., about the size of a residence) and may allow access by UEs
having association with the femto cell, e.g., user UEs in a home,
user UEs subscribing to a special service plan, or the like.
[0029] A home eNB facilitates wireless communication over a
licensed cellular radio band, as opposed to an unlicensed band
utilized by wireless local area network (WLAN) routers. A home eNB
may be installed in a user's home and provide indoor wireless
coverage to UE. Such personal miniature base stations are also
known as access point (AP) base stations. Typically, such miniature
base stations are connected to the mobile operator's network via
the user's internet connection using Internet protocol (IP)
communication over a DSL router or cable modem.
[0030] In the alternative, the home node 16 may have different
radio access technology (RAT); for example, if may be a WLAN AP or
router, using an IEEE 802.11 Wi-Fi standard protocol Such WLAN APs
may be integrated with the LTE network.
[0031] The UE 20 may also be referred to as a terminal, mobile
station, subscriber unit, station, wireless communication device,
mobile device, or the like. The UE 20 may be a cellular phone,
smart phone, a personal digital assistant (PDA), a wireless modem,
a laptop computer, a cordless phone, or the like. The UE 20
communicates with either node 12, 16 via a downlink (DL) and an
uplink (UL). The downlink (or forward link) refers to the
communication link from the node 12, 14 to the UE 20, and the
uplink (or reverse link) refers to the communication link from the
UE 20 to the node 12, 16. In FIG. 1, the solid line 24 indicates
transmissions between the UE 20 and the serving macro node 12. A
serving node is a node designated to serve a UE on the downlink
and/or uplink. The dashed line 26 indicates transmissions between
the UE 20 and a non-serving node, in this example, the home node
16.
[0032] In the example shown, the UE 20 is operating near the
boundary of the macro node coverage area 14 and the home node
coverage area 18, and receiving services from the macro node 12.
The UE 20 can receive MBSFN subframe downlink (DL) transmissions 24
from the macro node 12 and the home node 16.
[0033] The home node 16 is synchronized to the cellular network to
transmit MBSFN subframes on the same frequency as the macro node
12. Based on the techniques described herein, including those
described in reference to FIGS. 8-10, a neighboring cell, such as
the home node 10, can unicast cell-specific and/or UE-specific
information in MBSFN subframe data slots to a UE located in another
cell, e.g., the UE 20. The other cell may be, for example, an
E-UTRAN cell.
[0034] Multimedia Broadcast Multicast Service (MBMS) is a
Point-to-Multipoint (PTM) interface specification designed to
provide efficient delivery of broadcast and multicast services
within 3GPP cellular networks. Examples of MBMS interface
specifications include those described in Universal Mobile
Telecommunications System (UMTS) and LTE communication
specifications. For broadcast transmission across multiple cells,
the specifications define transmission over single-frequency
network configurations. Intended applications include mobile TV,
news, radio broadcasting, file delivery, emergency alerts, and
others. When services are broadcasted by MBMS, all cells inside an
MBSFN area normally transmit the same MBMS service.
[0035] As depicted in FIG. 1, the home node 16 (e.g., a femto eNB
or WLAN AP) is synchronized to the network 10 to transmit one or
more MBSFN subframes 26 to notify the nearby UE 20 of its proximity
to the home node 16. If it is a WLAN AP, the home node 16 does not
necessarily need to be fully synchronized with network 10. Only the
WLAN AP's MBSFN transmissions to the UE 20 need to be synchronized
to the network 10. The WLAN AP can be configured to detect the
MBSFN transmissions from the macro node 12 in order to synchronize
its MBSFN transmissions to the UE. Alternatively, the WLAN AP may
monitor the primary and secondary synchronization channels (PSS and
SSS) to obtain subframe level synchronization with the macro node
12. Subsequently, the WLAN AP may be informed through macro network
of the subframes used for MBSFN.
[0036] To accomplish the notification, the home node 16 can
transmit MBSFN subframes containing cell-specific information about
itself, such as its carrier-frequency, cell-ID, SSID, transmit
power, physical cell ID (PCI), frame offset, and/or the like. The
cell-specific data can be included in the data region of the MBSFN
subframe(s) so as not to interfere with MBSFN transmissions from
other nodes by using the techniques described below, including
those described in reference to FIGS. 9 and 10.
[0037] If the home node 18 is a WLAN AP, there are several ways
that the WLAN AP can determine whether the UE 20 is within
proximity. A first way is to configure the WLAN AP to receive
measurement reports generated by the UE 20 via the UE's serving
node, as described herein in connection with FIG. 8. In this case,
the measurement reports may include the UE's periodic or
event-triggered, inter-frequency measurement reports for other
RATs. An alternative way is for the serving macro node 12 to inform
the WLAN AP (e.g., those within coverage area of the macro node 12)
of all the UE's that it currently serves. For example, the macro
node 12 could send all the UEs' C-RNTIs to the WLAN AP through the
backhaul network 22. In this scenario, the WLAN AP monitors the
candidate UEs and only sends MBSFN transmissions to those UEs that
meet certain threshold (e.g., proximity) criterion.
[0038] For its part, the UE 20 includes an air interface (see FIG.
6) configured to receive one or more services from the macro node
12 over radio links to the macro node 12. The air interface also
receives one or more MBSFN subframes from the home node 16
containing information about the home node 16. The UE 20 includes a
controller configured to initiate a search for the home node 16
based on the information contained in the MBSFN subframe. The
search can also be based on information contained in the MBSFN
subframe used in combination with other information. For example,
the UE 20 may compare the information in the MBSFN subframe with
information already stored in the UE 20 (e.g., provided or
pre-loaded into the UE 20 by the network operator) to determine
that the second node is valid.
[0039] The information carried In the MBSFN subframe may include,
for example, a downlink (DL) transmit power level from the home
node 18, The controller can cause the UE 20 to measure the DL
receive power at the UE 20 and compare it to the DL transmit power
level given in the MBSFN subframe(s) to estimate a path loss
between the UE 20 and the home node 16. The UE 20 can initiate the
search based on the estimated path loss. For example, the
controller can compute the ratio of the DL receiver power (P.sub.r)
to the DL transmit power level (P.sub.t). From this, the controller
can compute the path loss value, which is 1-P.sub.r/P.sub.t, The
calculated path loss is in general proportional to the distance
between the UE 20 and home node 16. The calculated path loss can be
compared to a predefined threshold. The predefined threshold may a
preset stored value or alternatively, it may be dynamically
configured by, for example, either the serving node or the target
node.
[0040] If the path loss is below the threshold (meaning that the UE
20 is close to the home node), the UE 20 initiates the
inter-frequency search, in performing the search, the UE 20 may
perform one or more inter-frequency measurements. The type and
number of measurements may be based on the estimated path loss and
the available measurement gaps. The search/measurement can be an
intra-frequency, inter-RAT and/or inter-frequency search, an
intra-RAT and/or inter-RAT search or any other suitable type or
combination of searches. For a UE in connected mode, the
measurements are reported to the source cell or the macro node 12.
If interworking between the macro node 12 and the home node 18 is
supported, the macro node 12 may handover the UE 20 to the home
node 16 based on the measurement reports. If interworking is not
supported, the macro node 12 may release the UE 20 from Connected
and redirect the UE 20 to the home node 16 where the UE 20 may
establish a new connection with the home node 16.
[0041] Alternatively; the ratio P.sub.r/P.sub.t which is known as
the transmission factor, can be used instead of the path loss for
determining whether to search for neighboring nodes. If the
transmission factor is low, that is small, the UE is far from the
node. If the ratio is close to one, the UE is close to the node.
Thus, to initiate the search using the transmission factor as the
determination criteria, the test is whether the transmission factor
is above the threshold.
[0042] The UE 20 can include one or more additional RF transceivers
so that it can communicate with non-serving nodes that use
different RATs than the serving macro node 12. For example, in
addition to the cellular WWAN interface, the UE can include a WLAN
interface, such as a Wi-Fi air interface. In this configuration,
the UE 20 can be set to turn on the additional RF transceiver(s)
only If the estimated distance (or path loss) Is less than the
threshold. This conserves UE power.
[0043] This scheme is very helpful since it may reduce or avoid
excessive inter-frequency measurements by the UE 20, and when the
neighboring home node 18 belongs to a different RAT (e.g., 802.11
WLAN), it avoids the need for the UE 20 to frequently
monitor/detect the presence of cells or APs using a different RAT
operating on another frequency or a different band. When the UE 20
is located at the cell-edge (as shown) and it receives one or more
MBSFN subframes transmitted by the neighboring home node 16, it can
initiate inter-frequency searches and/or inform serving macro node
12 about the other node's presence based on the cell-specific
information unicast/multicast in the MBSFN subframes by the
neighboring node (e.g., home node 16). In case the neighboring home
node 16 is a WLAN AP, the UE 20 may have the option to only turn on
its internal WLAN radio only after it receives a MBSFN subframe
which indicates to the UE 20 that a WLAN AP home node 16 is within
close proximity. Reducing inter-frequency or Inter-RAT searching
may conserve the UE's battery power.
[0044] FIG. 2 shows a transmission frame structure 40 that may be
used on the downlinks in the networks 10, 50 disclosed herein. The
transmission timeline is partitioned into units of radio frames.
Each radio frame has a predefined duration (e.g., 10 milliseconds)
and may be partitioned into 10 subframes, with indices of 0-9, as
shown. Each subframe may include two slots, and each slot may
include L symbol periods. In LTE, L may be equal to six for an
extended cyclic prefix or seven for a normal cyclic prefix.
[0045] As mentioned earlier, LTE utilizes OFDM on the downlink and
single-carrier SC-FDM on the uplink, OFDM and SC-FDM partition the
system bandwidth into multiple (K) orthogonal subcarriers, which
are also commonly referred to as tones or bins. Each subcarrier may
be modulated with data. In general, modulation symbols are sent in
the frequency domain with OFDM and In the time domain with SC-FDM.
The spacing between adjacent subcarriers may be fixed, and the
total number of subcarriers (K) may be dependent on the system
bandwidth. For example, K may be equal to 128, 256, 512, 1024 or
2048 for system bandwidth of 1.25, 2.5, 5, 10 or 20 MHz,
respectively. On the downlink, each subframe may include 2L OFDM
symbols in symbol periods 0 through 2L-1, as shown in FIG. 2.
[0046] LTE supports transmission of unicast information to specific
UEs, LTE also supports transmission of broadcast information to all
UEs and multicast information to a group of UEs using MBSFN
transmission. A subframe used for sending unicast information is
typically referred to as a regular subframe. A subframe used for
sending multicast and/or broadcast information is typically
referred to as an MBSFN subframe.
[0047] FIG. 3 depicts an exemplary resource-block structure 45 for
MBSFN subframes. Each DL subframe is normally divided into a
control region 46 consisting of the first few OFDM symbol periods,
and a data region 47, consisting of the remaining part of the
subframe. The control region is usually of length of one or two
OFDM symbols, followed by the data region 47, as shown in FIG. 3.
information about the set of subframes that are configured and
transmitted as MBSFN subframes is provided to eNBs as part of the
network system information, which may be maintained and distributed
by a network control entity included in the network (not
shown).
[0048] The exemplary MBSFN subframe format 45 may be used by an
eNB, such as the nodes 12, 16, 52, 54, 56 described herein.
Cell-specific reference signals 48 may be sent in symbol period 0
and other symbol periods (not shown) on a predefined set of
subcarriers. In the example shown, the PDCCH and other control
signals may be sent in symbol periods 0 to 1 in the control region
46. Data transmission may be sent in the resource elements of the
remaining symbol periods 2 to 13 of the data region 47.
[0049] FIG. 4 illustrates a second exemplary cellular communication
network 50 including plural macro nodes 52, 54, 56 and UEs 64, 66,
68. The macro nodes 52, 54, 56 may be eNBs as described in
connection with FIG. 1, and the UEs 64, 66, 68 may be the same
types described in connection with FIG. 1. Node one 52 provides
services in a first coverage area 58. As shown, a first UE 64
receives services from node one 52, including MBSFN subframe DL
transmissions 55. The first UE 64 may also receive MBSFN subframe
transmissions 72 from node two 54. Node two 54 provides services in
a second coverage area 60. As shown, a second UE 66 receives
services from node two 54, including MBSFN subframe DL
transmissions 70. The second UE 66 may also receive MBSFN subframe
transmissions 76 from node three 56. Node three 56 provides
services in a third coverage area 62. As shown, a third UE 68
receives services from node three 56, including MBSFN subframe DL
transmissions 76. The third UE 68 may also receive MBSFN subframe
transmissions 74, 75 from node one 52 and node two 54.
[0050] Nodes one, two and three 52, 54, 56 can be synchronized to
the cellular network 50 to transmit MBSFN subframes on the same
frequency and at the same time.
[0051] When a UE is close to the edge of its serving node's
coverage area, it can receive cell-specific information from an
adjacent neighboring node transmitted in one or more MBSFN
subframes to notify the nearby UE of its proximity to the
neighboring node. As discussed above in connection with FIG. 1, to
accomplish this notification, the neighboring node can transmit
cell-specific information about itself, such as its
carrier-frequency, cell-ID, SSID, transmit power, PCI, frame offset
and the like, in the data regions of the MBSFN subframes. The
cell-specific data can be included in the MBSFN subframe(s) so as
not to interfere with MBSFN transmissions from other nodes by using
the techniques described below, including those described in
reference to FIGS. 9 and 10.
[0052] Illustrating this operation in FIG. 4, node two 54 is shown
transmitting one or more MBSFN subframes 72 to the first UE 64 in
the first coverage area 58. Node two 54 also transmits one or more
MBSFN subframes 74 to the third UE 68 in the third coverage area
62. Node three 58 transmits one or more MBSFN subframes 76 to the
second UE 66 in the second coverage area 60.
[0053] Although FIGS. 1 and 4 describe two examples of network
configurations, the techniques disclosed herein are not limited to
these specific examples and can readily be applied to other
networks. For example, the networks 10, 50 may take other forms,
such as a homogeneous network that includes only macro eNBs; or
alternatively, a heterogeneous network that includes nodes of
different types, e.g., macro eNBs, pico eNBs, femto eNBs, WLAN APs,
and/or the like. These different types of nodes may have different
transmit power levels, different coverage areas. The networks 10,
50 may also include different numbers of elements, e.g., more or
fewer nodes and/or UEs, than those shown in the figures, and may
use different radio access technologies than those described.
[0054] FIG. 5 is a flowchart 100 illustrating an exemplary method
of detecting a neighboring node in a cellular communication
network, such as the networks 10, 50 depicted in FIGS. 1 and 4,
using cell-specific information and/or UE-specific information
contained in MBSFN subframes. FIG. 5 shows how a UE can use this
information received from the neighboring cell as a trigger for
searches, such as inter-frequency or inter-RAT
measurements/searches.
[0055] In box 102, the UE receives and decodes one or more MBSFN
subframes transmitted from a neighboring node. The MBSFN subframes
include cell-specific information, such as the transmit (Tx) power
level of the neighboring node. From the decoding process, the UE
obtains the Tx power level of the neighboring node. The Tx power
level Indicates the power level of the subframes when the left the
neighboring node,
[0056] The cell-specific data, e.g., Tx power level, can be
included in the data region of the MBSFN subframe(s) so as not to
interfere with MBSFN transmissions from other nodes by using the
techniques described below, including those described in reference
to FIGS. 9 and 10. The UE can be configured to decode the specific
regions of the MBSFN data portion assigned to the transmitting node
based on network system information provided to the UE indicating
which portion of the MBSFN data region corresponds to the node. The
network system information can be provided to the UE by the serving
node over control channels.
[0057] In box 104, the UE determines its path loss from the
neighboring node by comparing the measured DL receive (Rx) power
level (measured at the UE) to the Tx power level given in the MBSFN
subframe. For example, the UE can compute the ratio of the DL
receiver power to the DL transmit power level. The calculated path
loss can be compared to a predefined threshold (box 106). The
predefined threshold may a preset stored value or alternatively, it
may be be dynamically configured by, for example, either the
serving node or the target node.
[0058] If the path loss is greater than a predefined threshold,
then the UE does not initiate handover procedures to switch to the
neighboring node and instead waifs to receive another MBSFN frame
from a neighboring node (box 112). However, if the path loss is
less than the threshold, the UE Initiates inter-frequency and/or
inter-RAT measurements/searches (box 108) and a handover procedure
to switch its services to the neighboring node (box 110). The
handover procedure can include any of the handover procedures
specified by the LTE standard or any other applicable cellular
network handover procedure.
[0059] FIG. 6 is a simplified block diagram illustrating certain
components of an exemplary UE 200 usable in the networks 10, 50 of
FIGS. 1 or 4. The UE 200 includes, among other things, one or more
antennas 212 for permitting radio communications with the network
nodes, a wireless wide-area network (WWAN) interface 202 having a
transceiver (xcvr) 208. The WWAN interface 202 provides an air
interface for communicating with network nodes (e.g., base
stations), such as eMBs, The UE 200 also includes an air interface
for communicating with nodes that use a different RAT, such as a
Wi-Fi WLAN interface 204 having a transceiver (xcvr) 210.
[0060] A controller 208 is also included in the UE 200. The
controller 206 may include any suitable processor, processor
arrangement, memory, logic circuitry, circuit, arrangement of
electronics, programming code, data or combination thereof that
performs the functions described herein as well as facilitating the
overall operability of the UE 200. The controller 208 controls
components of the UE to manage the functions of the UE 200. The
controller 208 is connected to and/or Includes a memory (not shown)
which can be any suitable memory storage device capable of storing
computer programming code and data. Machine-readable data and
executable instructions (also referred to as applications,
software, firmware, code or program) are stored in the memory and
executed (or run) on the controller. All memory devices described
herein may comprise any suitable combination of volatile (e.g.,
random access memory) or non-volatile (e.g., read-only memory)
storage known In the art. The controller 206 may comprise one or
more microprocessors, microcontrollers, DSPs, IP-cores,
co-processors, similar devices or combinations thereof. Using known
programming techniques, software stored in the memory may cause the
controller 206 to operate the UE 200 to achieve the functionality
described herein. Indeed, the controller 206 may be configured to
perform the UE methods and functions disclosed herein, for example,
at least some of the process steps described in connection with
FIG. 5.
[0061] FIG. 7 is a simplified block diagram illustrating certain
components of an exemplary node 300 usable in the networks 10, 50
of FIGS. 1 or 4. The cell node 300 may be an eBM, and includes,
among other things, one or more antennas 308 configured to
communicate with at least the UEs operating in the network, an air
interface 302 for radio communication with the UEs and a backhaul
network interface 306 for communicating with other devices and
nodes in the network over a backhaul network.
[0062] A controller 304 is also included in the node 300. The
controller 304 may include any suitable processor, processor
arrangement, memory, logic circuitry, circuit, arrangement of
electronics, programming code, data or combination thereof that
performs the node functions described herein as well as
facilitating the overall operability of the node 300. The
controller 304 controls components of the node 300 to manage the
functions of the node 300. The controller 304 is connected to
and/or includes a memory (not shown) which can be any suitable
memory storage device capable of storing computer programming code
and data. Machine-readable data and executable instructions (also
referred to as applications, software, firmware, code or program)
are stored in the memory and executed (or run) on the controller.
All memory devices described herein may comprise any suitable
combination of volatile (e.g., random access memory) or
non-volatile (e.g., read-only memory) storage known in the art. The
controller 304 may comprise one or more microprocessors,
microcontrollers, DSPs, IP-cores, co-processors, similar devices or
combinations thereof. Using known programming techniques, software
stored in the memory may cause the controller 304 to operate the
node 300 to achieve the functionality described herein. The
controller 304 may be configured to perform the node methods and
functions disclosed herein.
[0063] The node 300 may be a home node, such as the home node 16 of
FIG. 1, or a macro node, such as macro node 12 of FIG. 1.
[0064] FIG. 8 is a signal flow diagram 400 illustrating a procedure
for transmitting inter-cell unicast messages in one or more MBSFN
subframes between a non-serving node 406 and a UE 402. The
procedure can be deployed in the networks 10, 50.
[0065] The diagram 400 shows LTE signal flows between the UE 402, a
serving node 404 and the non-serving node 60. The UE 402 can be any
of the UEs disclosed in this document. The serving node 404 is a
node that is presently providing services to the UE 402, and may be
an eNB. The non-serving node 406 is a node that is not presently
providing services to the UE 402, and may be, for example, an
adjacent node or home node in the cellular network, including a
WLAN AP. The non-serving node 406 may be an eNB.
[0066] FIG. 8 shows the signaling flow for unicast MBSFN Subframe
transmission by the non-serving node 406, which can be a
neighboring home node (home eNB) or macro node. The non-serving
node 406 may obtain the sounding reference signal (SRS), Cell Radio
Network Temporary Identifier (C-RNTI) and/or related Information of
the UE 402 by polling the serving node 404, or the serving node 404
can share this information autonomously with its neighboring nodes.
The neighboring, non-serving node 406 can then detect the UE 402 by
detecting SRS or any other uplink (UL) physical level (PHY) signal
transmitted by the UEs to its serving node 404 using the
information received from the serving node.
[0067] The process starts by the UE 402 sending one or more
measurement reports 408 to the serving node 404. The measurement
reports may include the reference symbol received power (RSRP) and
the carrier received signal strength indicator (RSSI), i.e., the
measured power levels of transmissions between the serving node 404
and the UE 402. The measurement reports may
additionally/alternatively include RSRP and RSSI measured between
the non-serving node 406 and the UE 24.
[0068] In response to the measurement reports 408, the serving node
404 identifies the strongest neighboring nodes corresponding to the
UE when, for example, the node 404 determines that the UE 402 is
nearing an edge of the serving node's coverage area (cell). The
information identifying the strongest neighbor may be programmed
into the serving node 404 so that it is known to the node 404 a
priori, it may be received by the node 404 over the backhaul
network from the network control entity, for example, or if may be
determined from neighboring node RF signals measured by the node
404.
[0069] If the serving node 404 determines that the UE 402 should
receive unicast information in MBSFN subframes from the neighboring
node 406, the serving node 404 transfers C-RNTI and SRS information
412 about the UE 402 to the non-serving node 406. The information
412 is sufficient to permit the non-serving node 408 to monitor the
PHY signals from the UE 402.
[0070] After receiving the information 412, the non-serving node
406 begins monitoring SRS PHY signals emitted from the UE 402,
based on the information 412 it received. Based on the monitored
signals, the non-serving node 406 detects the uplink (UL) channel
being used by the UE 402 and the UL timing (step 414). After
successfully identifying the UE 402, the non-serving node 406 sends
a UE-identified acknowledgement (ACK) 416 to the serving node 404.
Subsequent to the UE-ID ACK 416, the non-serving node 406 commences
transmission of unicast messages to the UE 402, which can be sent,
for example, over an MBSFN subframe of the k.sup.th frame. The
unicast messages are included in the data region of the MBSFN
subframe. Interference with other nodes transmitting in the MBSFN
subframes may avoided by using the techniques described below,
including those referencing FIGS. 9 and 10.
[0071] In step 420, the UE 402 receives the MBSFN subframe
transmission. The MBSFN subframe may include cell-specific
information about the non-serving node 408 that permits the UE 402
to more efficiently execute a handover from the serving node 404 to
the non-serving node 406, or perform a search, such as an
intra-frequency search, inter-frequency search, inter-RAT search or
the like.
[0072] Referring to FIG. 8, when the non-serving node 408 is a WLAN
AP there are two operational cases; 1) interworking (seamless
handover) between LTE and WLAN is available and 2) interworking
between LTE and WLAN is not available. For both cases, the WLAN AP
does not necessarily need to track the UL timing as shown in step
414 (i.e., for Timing Advance) of the UE. The WLAN may instead
detect the presence of the UE based on the C-RNTI provided by the
serving node 404. For case 1), after the WLAN AP detects the
presence of the UE (i.e., UL detection), the WLAN AP transmits the
UE-specific, unicast message over MBSFN and informs the UE with
handover related parameters necessary to complete the handover. For
case 2), the WLAN AP also transmits the UE-specific, unicast
message over MBSFN to the UE; however, in this case the
UE-specific, unicast message may contain only information necessary
for the UE to acquire the WLAN AP, since interworking is not
available. For example, the information may contain the WLAN AP's
SSID, frequency, the type of WLAN AP, such as IEEE 802.11n, or the
like.
[0073] FIG. 9 is a conceptual diagram 500 illustrating a first
method of unicasting/multicasting node-specific MBSFN subframes so
as to reduce or avoid interference with other nodes transmitting
MBSFN subframes. This method may be used in connection with the
procedures depicted in FIGS. 5 and 8 and/or the operation of the
networks 10, 50 of FIGS. 1 and 4.
[0074] If neighboring cell nodes use the same set of resources to
unicast/multicast their own data in MBSFN subframes at the same
time, then they may cause Interference to each other. In order to
avoid interference, orthogonal sets of resources can be assigned to
each cell (node). The resources may be the data region resource
elements of the MBSFN subframes, as depicted in FIG. 3,
[0075] FIG. 9 shows a frequency vs. time chart that depicts an
example DL frame transmission period of two neighboring nodes, Node
One and Node Two, which generally transmit on the different
frequency bands, with the exception of the MBSFN subframes, which
are transmitted on the same frequency band. Node One transmits a
first frame 502 during the period. The first frame 502 includes
PDCCH headers 506, PDSCH subframe data region 508, MBSFN subframe
data region 510, and a blank subframe data region 512. A PDCCH 508
is included in each subframe. Node Two transmits a second frame 504
during the period. The second frame 504 Includes PDCCH headers 514,
PDSCH subframe data region 516, MBSFN subframe data region 518, and
a blank subframe data region 520. A PDCCH 614 is included in each
subframe. Although only two nodes are depicted in FIG. 3, this
technique can be applied to any suitable number of nodes.
[0076] The method depicted in FIG. 9 provides that the two MBSFN
subframes 510, 518 within one frame duration can be assigned as
MBSFN subframes, without any overlap. The assignment of these
subframes can be made by the network control entity and the nodes
have a priori knowledge of the subframe assignments. To avoid
interference, Node One transmits data during the first MBSFN
subframe 510, white the Node Two "blanks" during the first MBSFN
subframe data region. Blanking means that the node does not
transmit during the period defined for the MBSFN subframe data
region 510 of the first frame 502. Thus, FIG. 9 shows that Node One
transmits unicast/multicast data in the first MBSFN subframe data
region 510 and during the same MBSFN subframe period 510, Node Two
does not transmit 520.
[0077] For the second MBSFN subframe 518, the roles of the nodes
are reversed, whereby Node Two unicasts/multicasts data during the
MBSFN subframe data region 518 and Node One blanks 512 during the
second MBSFN subframe data region 518.
[0078] During MBSFN subframe transmissions, each node is also
allowed to increase transmit power (if needed) so that their
downlink (DL) can reach further into the other node's coverage
area. This allows neighbor nodes to serve UEs which are at the cell
boundary, but still within coverage of the serving node. None of
the MBSFN transmissions from different cells interfere with one
another only since only one cell is transmitting data during any
MBSFN subframe data region. This allows a node to unicast/multicast
dedicated UE signaling or cell-specific messages using the MBSFN
subframe.
[0079] FIG. 10 is a conceptual diagram 600 illustrating a second
method of unicasting/multicasting node-specific MBSFN subframes so
as to reduce or avoid interference with other nodes transmitting
MBSFN subframes. In contrast to the method of FIG. 9, the second
method of FIG. 10 involves splitting each MBSFN subframe into three
sets of carrier sub-bands, with each carrier sub-hand to being
assigned to one of the three nodes. This method may be used in
connection with the procedures depicted in FIGS. 5 and 8 and/or the
operation of the networks 10, 50 of FIGS. 1 and 4. Although only
three nodes are depicted in FIG. 10, this technique can be applied
to any suitable number of nodes.
[0080] FIG. 10 shows a frequency vs. time chart that depicts an
exemplary DL frame transmission period of three neighboring nodes,
Nodes One, Two and Three, that transmit on the different frequency
channels, with the exception of MBSFN subframes. Node One transmits
a first frame 602 during the period. The first frame 602 includes
PDCCH headers 608, FDSCH subframe data regions 610, and an MBSFN
subframe data region 612. Node Two transmits a second frame 604
during the period. The second frame 802 includes PDCCH headers 620,
PDSCH subframe data regions 622, and an MBSFN subframe data region
624. Node Three transmits a third frame 606 during the period. The
third frame 606 includes PDCCH headers 630, PDSCH subframe data
regions 632, and an MBSFN subframe data region 634. The PDSCH and
MBSFN subframes in each frame 602, 604, 606 each include a PDCCH
header.
[0081] The MBSFN subframe data period is frequency divided into
three carrier sub-bands 614, 626, 636. In the example shown, the
first carrier sub-band 812 is assigned to Node One, the second
carrier sub-band 626 is assigned to the Node Two and the third
carrier sub-band 636 is assigned to the Node Three. If a carrier
sub-band is not assigned to a node, then that node blanks the
carrier sub-band in order to prevent Interference with other nodes.
For example, Node One transmits its MBSFN subframe data on the
first carrier sub-band 614 and simultaneously blanks 616 the other
two carrier sub-bands. Likewise, Node Two transmits its MBSFN
subframe data on the second earner sub-band 626 and simultaneously
blanks 628 the other two carrier sub-hands, while Node Three
transmits its MBSFN subframe data on the third carrier sub-band 636
and simultaneously blanks 638 the other two carrier sub-bands.
[0082] The frequency division of MBSFN subframes can be
accomplished by assigning predefined sets of one or more OFDM
subcarriers to each node in the MBSFN subframe data region to form
the carrier sub-bands. The OFDM subcarriers in each set may be
adjacent sub-carrier bands. The OFDM subcarrier node assignment can
be predefined by a network control entity or any other suitable
means, and knowledge of the assignments can be distributed to the
nodes over the network. The carrier sub-band assignments may be
static or dynamic.
[0083] The following are other methods that can be deployed in the
networks 10, 50 to avoid interference between neighboring nodes
during MBSFN subframe unicast/multicast transmissions.
[0084] Time-domain solution: a single MBSFN subframe data region is
split into time slots. For example, the MBSFN subframe data period
may be split info three adjacent time slots: the first time slot is
assigned to a first node, and the other two nodes blank the first
time slot. The second and third time slots are similarly assigned
to the second node and the third node, respectively. A node blanks
the MBSFN data region during the time slots in which it is not
unicasting/multicasting data. This method has the advantage that
the number of blanked subframes is reduced since only one-third of
an MBSFN subframe data period is allocated to each node.
[0085] The time division of MBSFN subframes can be accomplished by
assigning predefined sets of one or more OFDM symbol periods in the
MBSFN subframe to each node to form the carrier sub-bands. The OFDM
symbol period assignments can be predefined by a network control
entity or any other suitable means, and knowledge of the
assignments can be distributed to the nodes over the network. The
OFDM symbol period assignments may be static or dynamic.
[0086] Code-domain solution: Each node spreads its data
transmission during the MBSFN subframe data region with a unique
code. This requires the data to be multiplied by a spreading code
(i.e., a higher chip rate). This may require more bandwidth
depending on the spreading rate. This method has the advantage that
no subframes need to be blanked and all neighbor nodes can
unicast/multicast MBSFN subframe data simultaneously with little
node-to-node interference, With this solution, the UEs de-spread
the data by using an assigned spreading code in order to recover
the data. The spreading codes can be determined, assigned and
managed by the network elements, such as a network control entity
and/or the nodes, using known techniques.
[0087] The above time-domain and code-domain schemes can be set up
statically or dynamically. In addition, the foregoing methods of
unicasting/multicasting node-specific content in MBSFN subframes
can be combined together where appropriate to, for example,
increase the number of nodes that can simultaneously transmit
unique data in the MBSFN subframes.
[0088] Other embodiments and modifications of this invention will
occur readily to those of ordinary skill in the art in view of
these teachings. Thus, the above description is illustrative and
not restrictive. This invention is to be limited only by the
following claims, which include all such embodiments and
modifications when viewed in conjunction with the above
specification and accompanying drawings. The scope of the invention
should, therefore, be determined with reference to the appended
claims along with their full scope of equivalents.
* * * * *