U.S. patent application number 15/470404 was filed with the patent office on 2017-07-13 for method and apparatus for small cell discovery in heterogeneous networks.
The applicant listed for this patent is IDAC Holdings, Inc.. Invention is credited to Christopher R. CAVE, Samian J. KAUR, Paul MARINIER, Diana PANI.
Application Number | 20170201972 15/470404 |
Document ID | / |
Family ID | 46018104 |
Filed Date | 2017-07-13 |
United States Patent
Application |
20170201972 |
Kind Code |
A1 |
MARINIER; Paul ; et
al. |
July 13, 2017 |
METHOD AND APPARATUS FOR SMALL CELL DISCOVERY IN HETEROGENEOUS
NETWORKS
Abstract
A method for acquiring and applying offload area information for
offloading a wireless transmit/receive unit (WTRU) to a small cell
in a different frequency layer is disclosed. The WTRU may enter a
region or a macro cell and receive offload area information of the
region in which a small cell in the vicinity of the macro cell is
located. The offload area information may include at least one of a
global positioning system (GPS) coordinate, a radius over which the
area extends with respect to the GPS coordinate, a list of position
reference signals (PRS), a cell identity or a list of cell
identities, a frequency on which the small cell is located, and a
radio access technology (RAT) of the corresponding cell. The
offload information may be received in a system information block
(SIB), dedicated signaling, or any other radio signal. The WTRU may
perform measurements to determine the location of the WTRU and to
determine whether it has entered any offload areas. Upon a
determination that the offload area information is no longer valid,
the WTRU may delete the offload area information.
Inventors: |
MARINIER; Paul; (Brossard,
CA) ; KAUR; Samian J.; (Plymouth Meeting, PA)
; PANI; Diana; (Montreal, CA) ; CAVE; Christopher
R.; (Dollard-des-Ormeaux, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IDAC Holdings, Inc. |
Wilmington |
DE |
US |
|
|
Family ID: |
46018104 |
Appl. No.: |
15/470404 |
Filed: |
March 27, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14708479 |
May 11, 2015 |
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15470404 |
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13446671 |
Apr 13, 2012 |
9060328 |
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14708479 |
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61475063 |
Apr 13, 2011 |
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61480768 |
Apr 29, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 36/22 20130101;
H04W 72/042 20130101; H04W 36/04 20130101; H04W 48/08 20130101;
H04W 36/14 20130101; H04W 64/003 20130101; H04W 4/023 20130101;
H04W 84/045 20130101 |
International
Class: |
H04W 72/04 20060101
H04W072/04; H04W 4/02 20060101 H04W004/02; H04W 64/00 20060101
H04W064/00; H04W 36/14 20060101 H04W036/14; H04W 36/22 20060101
H04W036/22; H04W 36/04 20060101 H04W036/04 |
Claims
1. A method implemented in a wireless transmit/receive unit (WTRU)
for discovering cells in a wireless network, the method comprising:
storing at the WTRU offload area information disclosing a
geographical location of a cell; making a coverage area
determination, based on the offload area information, of whether
the WTRU may be within a coverage area of the cell, wherein the
coverage area determination is made by comparing a WTRU location
with the location of the cell as disclosed in the offload area
information; responsive to the coverage area determination meeting
a condition, transmitting an offload indication to the network
indicating that the WTRU is a candidate for offload to the cell;
and receiving, in response to the offload indication, configuration
information to enable offloading of the WTRU to the cell.
2. The method of claim 1 wherein the offload area information
further comprises any one or more of the following: (i) a frequency
of the cell, or, (ix) a radio access technology of the cell.
3. The method of claim 1 further comprising: receiving the offload
area information via a Radio Resource Control (RRC) message.
4. The method of claim 1 further comprising: receiving the offload
area information via a system information block.
5. The method of claim 1 further comprising: receiving the offload
area information based on expiry of a timer associated with cell
reselection/handover to a cell.
6. The method of claim 1 wherein the coverage area determination is
made by comparing a WTRU location with a reference location and a
radius, or by comparing a WTRU location with a plurality of
location reference points.
7. The method of claim 1 wherein the offload indication includes
one of: a WTRU location, the cell ID, the cell frequency, or an
index value of a stored location.
8. The method of claim 1 wherein the configuration information is
an inter-frequency, inter-RAT or intra-frequency measurement
configuration.
9. The method of claim 1 wherein transmitting the offload
indication to the network is conditioned on a mobility state of the
WTRU being lower than a threshold.
10. The method of claim 1 wherein transmitting the offload
indication to the network is conditioned on a traffic level of the
WTRU.
11. An apparatus comprising a Wireless Transmit Receive Unit (WTRU)
configured to store offload area information disclosing a
geographical location of a cell; make a coverage area
determination, based on the offload area information, of whether
the WTRU may be within a coverage area of the cell, wherein the
coverage area determination is made by comparing a location of the
WTRU with the location of the smaller cell as disclosed in the
offload area information; responsive to the coverage area
determination meeting a condition, transmit an offload indication
to a network; and receive, in response to the offload indication,
configuration information to enable handover of the WTRU to the
cell.
12. The apparatus of claim 11 wherein the WTRU is configured to
make the coverage area determination by comparing a WTRU location
with a reference location and a radius, or by comparing a WTRU
location with a plurality of location reference points.
13. The apparatus of claim 1 wherein the WTRU is further configured
to transmit the offload indication based on a mobility state of the
WTRU being lower than a threshold.
14. The apparatus of claim 11 wherein the WTRU is further
configured to transmit the offload indication based on a traffic
level of the WTRU.
15. The apparatus of claim 11 wherein the WTRU is further
configured to verify valid offload area information when at least
one of the following events occurs: expiry of a timer associated
with cell reselection/handover to a cell; expiry of a periodic
timer; and expiry of a timer started the last time the WTRU
verified whether it is lacking valid offload area information.
16. The apparatus of claim 11 wherein the WTRU is further
configured to delete stored offload area information based on any
one the following triggers: a validity timer expires for a given
offload area information; the WTRU moves out of a cell (e.g. either
due to cell reselection or due to a handover); the WTRU moves to
idle mode; the WTRU performs an inter-frequency or inter-RAT
handover; the WTRU moves out of a home network; the WTRU changes
public networks; the WTRU is explicitly told by a network to delete
the offload area information; the WTRU changes RRC states; or, the
WTRU gets new offload area information.
17. The apparatus of claim 11 wherein the offload indication
indicates that the WTRU has entered the cell coverage area, or that
the WTRU has left the cell coverage area.
18. A method implemented in a wireless transmit/receive unit (WTRU)
for discovering cells in a wireless network, the method comprising:
storing offload area information disclosing a geographical area
covered by a cell; making a determination based on the offload area
information that the WTRU is in a coverage area of the cell;
responsive to a determination that the WTRU is in a coverage area
of the cell: transmitting an offload indication to a network entity
indicating that the WTRU is a candidate for offload to the cell;
receiving an inter-frequency or inter-RAT measurement
configuration; and initiating inter-frequency and/or inter-RAT
measurements according to the configuration.
19. The method of claim 18 wherein the offload area information
further comprises any one or more of the following: (i) a frequency
of the cell, or, (ix) a radio access technology of the cell.
20. The method of claim 18 further comprising: receiving the
offload area information via a Radio Resource Control (RRC)
message.
21. The method of claim 18 further comprising: receiving the
offload area information via a system information block.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/708,479 filed May 11, 2015, entitled
"Method and Apparatus for Small Cell Discovery In Heterogeneous
Networks" which is a continuation of U.S. patent application Ser.
No. 13/446,671 filed Apr. 13, 2012, now U.S. Pat. No. 9,060,328,
issued on Jun. 16, 2015 entitled "Method and Apparatus for Small
Cell Discovery In Heterogeneous Networks" which claims priority to
U.S. Provisional Patent Application Ser. No. 61/475,063 filed Apr.
13, 2011, entitled "Method for Small Cell Discovery In
Heterogeneous Networks" and to U.S. Provisional Patent Application
Ser. No. 61/480,768 filed Apr. 29, 2011, entitled "Method and
Apparatus for Small Cell Discovery In Heterogeneous Networks", all
of which are incorporated herein by reference.
BACKGROUND
[0002] The autonomous search and proximity indication functions
facilitate inbound mobility of a Wireless Transmit-Receive Unit
(WTRU) to a Closed Subscriber Group (CSG) or hybrid cell of which
it is a member, in idle mode and connected mode.
[0003] Both functions may implicitly rely on the existence of a
"fingerprint" that allows the WTRU to infer the potential presence
of a CSG or hybrid cell of which it is a member, even if such cell
is operating in a frequency on which the WTRU is not measuring.
Fingerprint information may include information and/or measurements
used by the WTRU to determine whether it is in the vicinity of
certain cells or group of cells. Positioning functionality,
supported in wireless communication standards such as long term
evolution (LTE), provides a means to determine the geographical
position and/or velocity of the WTRU based on measuring radio
signals.
SUMMARY
[0004] A method for acquiring and applying offload area information
for offloading a wireless transmit/receive unit (WTRU) to a small
cell in a different frequency layer is disclosed. The WTRU may
enter a region or a macro cell and receive offload area information
of the region in which a small cell in the vicinity of the macro
cell is located. The offload area information may include at least
one of a global positioning system (GPS) coordinate, a radius over
which the area extends with respect to the GPS coordinate, a list
of position reference signals (PRS), a cell identity or a list of
cell identities, a frequency on which the small cell is located,
and a radio access technology (RAT) of the corresponding cell. The
offload information may be received in a system information block
(SIB), dedicated signaling, or any other radio signal. The WTRU may
perform measurements to determine the location of the WTRU and to
determine whether it has entered any offload areas. Upon a
determination that the offload area information is no longer valid,
the WTRU may delete the offload area information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] A more detailed understanding may be had from the following
description, given by way of example in conjunction with the
accompanying drawings wherein:
[0006] FIG. 1A is a system diagram of an example communications
system in which one or more disclosed embodiments may be
implemented;
[0007] FIG. 1B is a system diagram of an example wireless
transmit/receive unit (WTRU) that may be used within the
communications system illustrated in FIG. 1A;
[0008] FIG. 1C is a system diagram of an example radio access
network and an example core network that may be used within the
communications system illustrated in FIG. 1A; and
[0009] FIGS. 2A-2C are flow diagrams of example methods for small
cell discovery in heterogeneous networks.
DETAILED DESCRIPTION
[0010] FIG. 1A is a diagram of an example communications system 100
in which one or more disclosed embodiments may be implemented. The
communications system 100 may be a multiple access system that
provides content, such as voice, data, video, messaging, broadcast,
etc., to multiple wireless users. The communications system 100 may
enable multiple wireless users to access such content through the
sharing of system resources, including wireless bandwidth. For
example, the communications systems 100 may employ one or more
channel access methods, such as code division multiple access
(CDMA), time division multiple access (TDMA), frequency division
multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier
FDMA (SC-FDMA), and the like.
[0011] As shown in FIG. 1A, the communications system 100 may
include wireless transmit/receive units (WTRUs) 102a, 102b, 102c,
102d, a radio access network (RAN) 104, a core network 106, a
public switched telephone network (PSTN) 108, the Internet 110, and
other networks 112, though it will be appreciated that the
disclosed embodiments contemplate any number of WTRUs, base
stations, networks, and/or network elements. Each of the WTRUs
102a, 102b, 102c, 102d may be any type of device configured to
operate and/or communicate in a wireless environment. By way of
example, the WTRUs 102a, 102b, 102c, 102d may be configured to
transmit and/or receive wireless signals and may include user
equipment (WTRU), a mobile station, a fixed or mobile subscriber
unit, a pager, a cellular telephone, a personal digital assistant
(PDA), a smartphone, a laptop, a netbook, a personal computer, a
wireless sensor, consumer electronics, and the like.
[0012] The communications systems 100 may also include a base
station 114a and a base station 114b. Each of the base stations
114a, 114b may be any type of device configured to wirelessly
interface with at least one of the WTRUs 102a, 102b, 102c, 102d to
facilitate access to one or more communication networks, such as
the core network 106, the Internet 110, and/or the networks 112. By
way of example, the base stations 114a, 114b may be a base
transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a
Home eNode B, a site controller, an access point (AP), a wireless
router, and the like. While the base stations 114a, 114b are each
depicted as a single element, it will be appreciated that the base
stations 114a, 114b may include any number of interconnected base
stations and/or network elements.
[0013] The base station 114a may be part of the RAN 104, which may
also include other base stations and/or network elements (not
shown), such as a base station controller (BSC), a radio network
controller (RNC), relay nodes, etc. The base station 114a and/or
the base station 114b may be configured to transmit and/or receive
wireless signals within a particular geographic region, which may
be referred to as a cell (not shown). The cell may further be
divided into cell sectors. For example, the cell associated with
the base station 114a may be divided into three sectors. Thus, in
one embodiment, the base station 114a may include three
transceivers, i.e., one for each sector of the cell. In another
embodiment, the base station 114a may employ multiple-input
multiple output (MIMO) technology and, therefore, may utilize
multiple transceivers for each sector of the cell.
[0014] The base stations 114a, 114b may communicate with one or
more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116,
which may be any suitable wireless communication link (e.g., radio
frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible
light, etc.). The air interface 116 may be established using any
suitable radio access technology (RAT).
[0015] More specifically, as noted above, the communications system
100 may be a multiple access system and may employ one or more
channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA,
and the like. For example, the base station 114a in the RAN 104 and
the WTRUs 102a, 102b, 102c may implement a radio technology such as
Universal Mobile Telecommunications System (UMTS) Terrestrial Radio
Access (UTRA), which may establish the air interface 116 using
wideband CDMA (WCDMA). WCDMA may include communication protocols
such as High-Speed Packet Access (HSPA) and/or Evolved HSPA
(HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA)
and/or High-Speed Uplink Packet Access (HSUPA).
[0016] In another embodiment, the base station 114a and the WTRUs
102a, 102b, 102c may implement a radio technology such as Evolved
UMTS Terrestrial Radio Access (E-UTRA), which may establish the air
interface 116 using Long Term Evolution (LTE) and/or LTE-Advanced
(LTE-A).
[0017] In other embodiments, the base station 114a and the WTRUs
102a, 102b, 102c may implement radio technologies such as IEEE
802.16 (i.e., Worldwide Interoperability for Microwave Access
(WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard
2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856
(IS-856), Global System for Mobile communications (GSM), Enhanced
Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the
like.
[0018] The base station 114b in FIG. 1A may be a wireless router,
Home Node B, Home eNode B, or access point, for example, and may
utilize any suitable RAT for facilitating wireless connectivity in
a localized area, such as a place of business, a home, a vehicle, a
campus, and the like. In one embodiment, the base station 114b and
the WTRUs 102c, 102d may implement a radio technology such as IEEE
802.11 to establish a wireless local area network (WLAN). In
another embodiment, the base station 114b and the WTRUs 102c, 102d
may implement a radio technology such as IEEE 802.15 to establish a
wireless personal area network (WPAN). In yet another embodiment,
the base station 114b and the WTRUs 102c, 102d may utilize a
cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.)
to establish a picocell or femtocell. As shown in FIG. 1A, the base
station 114b may have a direct connection to the Internet 110.
Thus, the base station 114b may not be required to access the
Internet 110 via the core network 106.
[0019] The RAN 104 may be in communication with the core network
106, which may be any type of network configured to provide voice,
data, applications, and/or voice over internet protocol (VoIP)
services to one or more of the WTRUs 102a, 102b, 102c, 102d. For
example, the core network 106 may provide call control, billing
services, mobile location-based services, pre-paid calling,
Internet connectivity, video distribution, etc., and/or perform
high-level security functions, such as user authentication.
Although not shown in FIG. 1A, it will be appreciated that the RAN
104 and/or the core network 106 may be in direct or indirect
communication with other RANs that employ the same RAT as the RAN
104 or a different RAT. For example, in addition to being connected
to the RAN 104, which may be utilizing an E-UTRA radio technology,
the core network 106 may also be in communication with another RAN
(not shown) employing a GSM radio technology.
[0020] The core network 106 may also serve as a gateway for the
WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet
110, and/or other networks 112. The PSTN 108 may include
circuit-switched telephone networks that provide plain old
telephone service (POTS). The Internet 110 may include a global
system of interconnected computer networks and devices that use
common communication protocols, such as the transmission control
protocol (TCP), user datagram protocol (UDP) and the internet
protocol (IP) in the TCP/IP internet protocol suite. The networks
112 may include wired or wireless communications networks owned
and/or operated by other service providers. For example, the
networks 112 may include another core network connected to one or
more RANs, which may employ the same RAT as the RAN 104 or a
different RAT.
[0021] Some or all of the WTRUs 102a, 102b, 102c, 102d in the
communications system 100 may include multi-mode capabilities,
i.e., the WTRUs 102a, 102b, 102c, 102d may include multiple
transceivers for communicating with different wireless networks
over different wireless links. For example, the WTRU 102c shown in
FIG. 1A may be configured to communicate with the base station
114a, which may employ a cellular-based radio technology, and with
the base station 114b, which may employ an IEEE 802 radio
technology.
[0022] FIG. 1B is a system diagram of an example WTRU 102. As shown
in FIG. 1B, the WTRU 102 may include a processor 118, a transceiver
120, a transmit/receive element 122, a speaker/microphone 124, a
keypad 126, a display/touchpad 128, non-removable memory 106,
removable memory 132, a power source 134, a global positioning
system (GPS) chipset 136, and other peripherals 138. It will be
appreciated that the WTRU 102 may include any sub-combination of
the foregoing elements while remaining consistent with an
embodiment.
[0023] The processor 118 may be a general purpose processor, a
special purpose processor, a conventional processor, a digital
signal processor (DSP), a plurality of microprocessors, one or more
microprocessors in association with a DSP core, a controller, a
microcontroller, Application Specific Integrated Circuits (ASICs),
Field Programmable Gate Array (FPGAs) circuits, any other type of
integrated circuit (IC), a state machine, and the like. The
processor 118 may perform signal coding, data processing, power
control, input/output processing, and/or any other functionality
that enables the WTRU 102 to operate in a wireless environment. The
processor 118 may be coupled to the transceiver 120, which may be
coupled to the transmit/receive element 122. While FIG. 1B depicts
the processor 118 and the transceiver 120 as separate components,
it will be appreciated that the processor 118 and the transceiver
120 may be integrated together in an electronic package or
chip.
[0024] The transmit/receive element 122 may be configured to
transmit signals to, or receive signals from, a base station (e.g.,
the base station 114a) over the air interface 116. For example, in
one embodiment, the transmit/receive element 122 may be an antenna
configured to transmit and/or receive RF signals. In another
embodiment, the transmit/receive element 122 may be an
emitter/detector configured to transmit and/or receive IR, UV, or
visible light signals, for example. In yet another embodiment, the
transmit/receive element 122 may be configured to transmit and
receive both RF and light signals. It will be appreciated that the
transmit/receive element 122 may be configured to transmit and/or
receive any combination of wireless signals.
[0025] In addition, although the transmit/receive element 122 is
depicted in FIG. 1B as a single element, the WTRU 102 may include
any number of transmit/receive elements 122. More specifically, the
WTRU 102 may employ MIMO technology. Thus, in one embodiment, the
WTRU 102 may include two or more transmit/receive elements 122
(e.g., multiple antennas) for transmitting and receiving wireless
signals over the air interface 116.
[0026] The transceiver 120 may be configured to modulate the
signals that are to be transmitted by the transmit/receive element
122 and to demodulate the signals that are received by the
transmit/receive element 122. As noted above, the WTRU 102 may have
multi-mode capabilities. Thus, the transceiver 120 may include
multiple transceivers for enabling the WTRU 102 to communicate via
multiple RATs, such as UTRA and IEEE 802.11, for example.
[0027] The processor 118 of the WTRU 102 may be coupled to, and may
receive user input data from, the speaker/microphone 124, the
keypad 126, and/or the display/touchpad 128 (e.g., a liquid crystal
display (LCD) display unit or organic light-emitting diode (OLED)
display unit). The processor 118 may also output user data to the
speaker/microphone 124, the keypad 126, and/or the display/touchpad
128. In addition, the processor 118 may access information from,
and store data in, any type of suitable memory, such as the
non-removable memory 106 and/or the removable memory 132. The
non-removable memory 106 may include random-access memory (RAM),
read-only memory (ROM), a hard disk, or any other type of memory
storage device. The removable memory 132 may include a subscriber
identity module (SIM) card, a memory stick, a secure digital (SD)
memory card, and the like. In other embodiments, the processor 118
may access information from, and store data in, memory that is not
physically located on the WTRU 102, such as on a server or a home
computer (not shown).
[0028] The processor 118 may receive power from the power source
134, and may be configured to distribute and/or control the power
to the other components in the WTRU 102. The power source 134 may
be any suitable device for powering the WTRU 102. For example, the
power source 134 may include one or more dry cell batteries (e.g.,
nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride
(NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and
the like.
[0029] The processor 118 may also be coupled to the GPS chipset
136, which may be configured to provide location information (e.g.,
longitude and latitude) regarding the current location of the WTRU
102. In addition to, or in lieu of, the information from the GPS
chipset 136, the WTRU 102 may receive location information over the
air interface 116 from a base station (e.g., base stations 114a,
114b) and/or determine its location based on the timing of the
signals being received from two or more nearby base stations. It
will be appreciated that the WTRU 102 may acquire location
information by way of any suitable location-determination method
while remaining consistent with an embodiment.
[0030] The processor 118 may further be coupled to other
peripherals 138, which may include one or more software and/or
hardware modules that provide additional features, functionality
and/or wired or wireless connectivity. For example, the peripherals
138 may include an accelerometer, an e-compass, a satellite
transceiver, a digital camera (for photographs or video), a
universal serial bus (USB) port, a vibration device, a television
transceiver, a hands free headset, a Bluetooth.RTM. module, a
frequency modulated (FM) radio unit, a digital music player, a
media player, a video game player module, an Internet browser, and
the like.
[0031] FIG. 1C is a system diagram of the RAN 104 and the core
network 106 according to an embodiment. As noted above, the RAN 104
may employ an E-UTRA radio technology to communicate with the WTRUs
102a, 102b, 102c over the air interface 116. The RAN 104 may also
be in communication with the core network 106.
[0032] The RAN 104 may include eNode-Bs 160a, 160b, 160c, though it
will be appreciated that the RAN 104 may include any number of
eNode-Bs while remaining consistent with an embodiment. The
eNode-Bs 160a, 160b, 160c may each include one or more transceivers
for communicating with the WTRUs 102a, 102b, 102c over the air
interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may
implement MIMO technology. Thus, the eNode-B 160a, for example, may
use multiple antennas to transmit wireless signals to, and receive
wireless signals from, the WTRU 102a.
[0033] Each of the eNode-Bs may be associated with a particular
cell (not shown) and may be configured to handle radio resource
management decisions, handover decisions, scheduling of users in
the uplink and/or downlink, and the like. As shown in FIG. 1C, the
eNode-Bs may communicate with one another over an X2 interface.
[0034] The core network 106 shown in FIG. 1C may include a mobility
management gateway (MME) 162, a serving gateway 164, and a packet
data network (PDN) gateway 166. While each of the foregoing
elements are depicted as part of the core network 106, it will be
appreciated that any one of these elements may be owned and/or
operated by an entity other than the core network operator.
[0035] The MME 142 may be connected to each of the eNode-Bs 162a,
162b, 162c in the RAN 104 via an S1 interface and may serve as a
control node. For example, the MME 162 may be responsible for
authenticating users of the WTRUs 102a, 102b, 102c, bearer
activation/deactivation, selecting a particular serving gateway
during an initial attach of the WTRUs 102a, 102b, 102c, and the
like. The MME 162 may also provide a control plane function for
switching between the RAN 104 and other RANs (not shown) that
employ other radio technologies, such as GSM or WCDMA.
[0036] The serving gateway 164 may be connected to each of the
eNode Bs in the RAN 104 via the S1 interface. The serving gateway
164 may generally route and forward user data packets to/from the
WTRUs 102a, 102b, 102c. The serving gateway 144 may also perform
other functions, such as anchoring user planes during inter-eNode B
handovers, triggering paging when downlink data is available for
the WTRUs 102a, 102b, 102c, managing and storing contexts of the
WTRUs 102a, 102b, 102c, and the like.
[0037] The serving gateway 164 may also be connected to the PDN
gateway 166, which may provide the WTRUs 102a, 102b, 102c with
access to packet-switched networks, such as the Internet 110, to
facilitate communications between the WTRUs 102a, 102b, 102c and
IP-enabled devices.
[0038] The core network 106 may facilitate communications with
other networks. For example, the core network 106 may provide the
WTRUs 102a, 102b, 102c with access to circuit-switched networks,
such as the PSTN 108, to facilitate communications between the
WTRUs 102a, 102b, 102c and traditional land-line communications
devices. For example, the core network 106 may include, or may
communicate with, an IP gateway (e.g., an IP multimedia subsystem
(IMS) server) that serves as an interface between the core network
106 and the PSTN 108. In addition, the core network 106 may provide
the WTRUs 102a, 102b, 102c with access to the networks 112, which
may include other wired or wireless networks that are owned and/or
operated by other service providers.
[0039] LTE positioning protocol (LPP) is used point-to-point
between a location server, such as an evolved serving mobility
location server (E-SMLC) or secure user plane for location (SUPL)
location platform (SLP) and a target device, such as SUPL enabled
terminal (SET), or WTRU, to position the target device using
position-related measurements obtained by one or more reference
sources. An LPP session is used between a location server and the
target device to obtain location related measurements or a location
estimate or to transfer assistance data. The LPP session may be
initiated by either the WTRU, eNB or the E-SMLC. In case of eNB
initiated positioning, the eNB sends a Location Service Request to
the MME, who then forwards it to the E-SMLC. The E-SMLC processes
the location services request which may include transferring
assistance data to the target WTRU to assist with WTRU-based and/or
WTRU-assisted positioning and/or may include positioning of the
target WTRU. The E-SMLC then returns the result of the location
service back to the MME (e.g., a position estimate for the WTRU
and/or an indication of any assistance data transferred to the
WTRU). In the case of a location service requested by an entity
other than the MME (such as, the eNB); the MME returns the location
service result to the eNB.
[0040] Positioning reference signals (PRS) have been added in the
downlink physical transmission to assist in WTRU-based observed
time difference of arrival (OTDOA) position estimations. PRSs are
transmitted in resource blocks in configured downlink subframes,
with the resource mapping offset by the Physical cell identity
(PCI) of the cell.
[0041] System capacity may be maximized by offloading traffic from
the macro cells to the small cells. A "small cell" may refer to a
cell whose coverage area is usually of limited size, and to which
the WTRU has access, such as (but not limited to) an open cell or a
hybrid cell.
[0042] When a macro layer is deployed on another frequency than a
small-cell layer, a WTRU operating on the macro layer in a
battery-efficient way (in idle or connected mode) may take
inter-frequency measurements when the quality or signal strength of
its serving cell becomes low. Therefore, offloading to small cells
deployed in areas where the serving cell is sufficiently strong may
not occur. One exception may be when the small cell is a CSG or
hybrid cell of which the WTRU is a member, in which case the WTRU
may detect the need for inter-frequency measurements using
autonomous search and send a proximity indication to the network if
in connected mode.
[0043] Methods allowing offloading to small cells in a different
frequency layer, while not compromising the battery consumption of
the WTRU, are described in greater detail hereafter. The methods
described herein may also be applicable to small cells in same
frequency or to small cells in a different radio access technology
(RAT). The small cells may be for example, LTE, UMTS, GERAN, or
802.11 cells.
[0044] Methods to enable the acquisition and storing of information
for the detection of small cells are disclosed herein.
[0045] Methods are described to enable the WTRU to acquire and
store information on at least one location of at least one small
cell where the WTRU may be offloaded. Such information for a
specific location may be referred to as "offload area information"
in the following examples.
[0046] The Offload Area Information may comprise but is not limited
to one or a combination of the following: at least one Offload Area
that may include at least one small cell, which may be at least one
of: an area provided by center point (defined e.g. by GPS
coordinates) and a radius; set of GPS coordinates; an area defined
by a number of GPS coordinates (e.g. X coordinates define the
limits of the region in which small cells are available); the
coverage area of at least one macro cell, along with the identity
of this at least one macro cell (PCI, CGI); the intersection of at
least two of the above. Other examples of Offload Area information
may include: a list of Reference any reference signal (e.g.
Position Reference Symbols(PRS), CSI-RS, CRS; a PCI or a list of
PCIs; Cell Identity or a list of Cell Identities; a frequency in
which the cells are located; the RAT of the corresponding cells; or
an area under a certain macro cell, defined by any of the location
information described above; the speed of the WTRU as determined by
any of the well-known positioning methods described above
[0047] The WTRU may subsequently use the stored offload area
information for the at least one location to perform at least one
of the following, as described in more detail herein below: in idle
mode, initiate inter-frequency or inter-RAT measurements, enabling
potential cell reselection to a small cell included in the offload
area; or in connected mode, transmit an offload indication to
enable the network to provide appropriate updated configuration at
a proper time, as appropriate to enable potential handover to a
small cell included in the offload area; for example an
inter-frequency or inter-RAT or intra-frequency measurement
configuration, DRX configuration, or mobility state estimation
configuration.
[0048] Methods of transmission of Offload Indication to the RAN are
herein disclosed. In this embodiment, the WTRU may send an "offload
indication" to the RAN to indicate that it is entering or leaving
the vicinity of one or multiple neighboring cells (e.g. pico cell
operating on another frequency or RAT) and that it may be
configured with inter-frequency or inter-RAT measurements for
potential handover to one of these cells (for offload purposes), or
in case of leaving indication the measurement configuration on a
different frequency or a RAT may be removed.
[0049] A WTRU moving above a certain speed through the macro layer
may not be a good candidate for offloading to the small cell layer.
In this case the network may use the WTRU speed information to
assist in determining if offload is required or not.
[0050] The "offload indication" message may include any of the
following information elements. The IE's include but are not
limited to: a new RRC message, "Offload Indication", to indicate
that the WTRU is a candidate for traffic offload. The existing
"Proximity Indication" RRC message that may be used for indicating
to the RAN that a WTRU is in the vicinity of a CSG cell to which it
potentially has access. The existing "Proximity Indication" RRC
message may be modified to include additional information elements
that may be used for offload purposes and to indicate that the
reason for transmitting the indication is for offload purposes. Or
an existing RRC Measurement Report message may be modified to
include additional information elements that may be used for
offload purposes. In a further embodiment, a new measurement type
"Offload indication" maybe introduced and reported in a RRC
measurement report. Further still, the "proximity indication"
measurement type may be extended to provide offload information and
to explicitly indicate to the network that the proximity is due to
offloading rather than a CSG or both.
[0051] The offload indication message may also include at least one
of the following information elements: an indication whether the
WTRU is entering the offload area or leaving the offload area; the
offload area to which the WTRU may be offloaded, which may be
indicated by an identifier or an index, or an offload area tag; the
frequency on which the WTRU may be offloaded; the cell ID of the
potential target cell(s) to which the WTRU may be offloaded; the
PCI of the potential target cell(s) to which the WTRU may be
offloaded; the radio access technology to which the WTRU may be
offloaded; the area in which the WTRU is located (e.g. a GPS
coordinate(s) or other location based information may be provided);
the WTRU mobility state information. Additionally, the radio access
technology of the cell may be indicated (e.g LTE, UMTS, 802.11,
etc). For a 802.11 cell the WTRU may further provide additional
information, such as channel, SSID, MAC address, etc.
[0052] The transmission of the offload indication may be triggered
when the WTRU determines that it has entered an offload area. The
determination that the WTRU has entered an offload area may be made
by comparing its position to the stored offload area information or
the offload area information that is provided by the RAN.
[0053] The transmission of the offload indication may be triggered
when the WTRU determines that it has left an offload area. The
determination that the WTRU has left an offload area may be made by
comparing its position to the stored offload area information or
the offload area information that is provided by the RAN.
[0054] For the conditions described above, the WTRU may determine
its current position using any well-known positioning technique,
such as but not limited to: GPS coordinate estimation; LTE
positioning method (e.g. use of PRS transmitted from multiple
transmission points to estimate its position); or any other
positioning method.
[0055] Furthermore, it is understood that the UE may determine its
current positions based on detected neighboring cells or
neighboring cells that have a channel measurement above a
threshold.
[0056] The conditions described above for triggering the
transmission of the offload indication may be further refined based
on any of the conditions described herein.
[0057] For example, the triggering may further take into
consideration the mobility state of the UE. For example, the WTRU
transmits the offload indication if it determines that it is in a
"low mobility state" and/or in a "medium mobility state". More
specifically, if the UE determines an entering condition and if the
UE is considered to be in a "low mobility" state, then an offload
indication is triggered. Else if the UE is not in a low mobility
state it doesn't transmit an offload indication. The determination
of UE mobility state may be made based on using any well-known
positioning technique, such as but not limited to GPS information,
LTE positioning method, or any other positioning method. For
example, the WTRU may determine its mobility state based on the
velocity calculated through GPS measurements or via rate of change
of GPS coordinates. The WTRU velocity may be compared with a
predetermined threshold to determine whether the WTRU is in a low
mobility state or high mobility state. The "low mobility state" may
also be determined based on the rate of change of DL reference
signals transmitted by one or multiple transmission points. The
"low mobility state" may also be determined based on the rate of
change of best cell event or handover rate. The "low mobility
state" may also be determined based on the rate of change of a WTRU
position calculated using the LTE positioning method (e.g. use of
position reference symbols to determine WTRU position). The rate of
change of WTRU position may be compared with a predetermined
threshold to determine whether the WTRU is in a low mobility state
or high mobility state.
[0058] The mobility state of the UE may be dependent on existing
mobility state estimation procedures. The UE may then use the
mobility state in combination with the determination of entering or
leaving the offload area to trigger an offload indication. In one
example, if the WTRU is in an offload area and has already
triggered an indication and the mobility state changes to "high
mobility state" the WTRU may trigger an offload indication,
providing information that it is leaving the area or that it has
changed mobility state.
[0059] The triggering may also take into account the traffic
activity, such that the WTRU transmits the offload indication based
on traffic activity, i.e. traffic heavy WTRUs may be candidates for
offload to another cell. For example, the determination that a WTRU
is a high traffic activity WTRU may be based on the DL and/or UL
data rate transfers averaged over a certain period of time. The
triggering may also take into account network indication and
configuration, such that the WTRU transmits the offload indication
if it is allowed to do so by the network, as indicated (or
configured) by RRC configuration or in system information. The
triggering may also be restricted by a a restriction timer, which
restricts the WTRU from triggering a new offload indication message
unless a restriction time from the last "offload indication" has
elapsed (e.g. the WTRU is restricted from transmitting a new
offload indication for a configured period of time). An offload
indication may be further triggered, if it has been triggered once
(e.g. the UE is in an offload area) and handover to a new cell
occurs (e.g. upon handover to a new cell a new offload indication
is triggered to inform the new macro cell of the offload).
Alternatively, the WTRU may not need to resend the indication, but
the source eNB forwards the information to the target eNB in the
handover preparation (request) phase.
[0060] Control of inter-frequency measurements in idle mode is
disclosed herein. The WTRU may initiate or stop inter-frequency or
inter-RAT measurements in idle mode based on stored offline area
information, according to at least one of the following methods.
The WTRU may initiate inter-frequency or inter-RAT measurements on
at least one frequency or RAT if at least the WTRU determines that
it has entered an offload area where cells are deployed on this
frequency or RAT. The determination that the WTRU has entered an
offload area may be made by comparing its position to the stored
offload area information or the offload area information that is
provided by the RAN. The WTRU may stop inter-frequency or inter-RAT
measurements on at least one frequency or RAT if the WTRU
determines that it has left an offload area where cells are
deployed on this frequency or RAT (and is not in any other offload
area where cells are deployed on this frequency or RAT). The
determination that the WTRU has left an offload area may be made by
comparing its position to the stored offload area information or
the offload area information that is provided by the RAN. In one
example, when the WTRU determines it is in the vicinity of at least
a small or offload cell, the WTRU may consider the frequency of the
small cell as the highest priority frequency for cell reselection
purposes.
[0061] The conditions described above for initiating or stopping
inter-frequency or inter-RAT measurements may be further refined
based on any of the examples provided herein. The WTRU may initiate
inter-frequency or inter-RAT measurements if it determines that it
is in a certain mobility state, for example "low mobility state" or
in "medium mobility state". The determination of "low mobility
state" may be based GPS information. For instance, the WTRU may
determine its mobility state based on the velocity calculated
through GPS measurements or via rate of change of GPS coordinates.
The WTRU velocity may be compared with a predetermined threshold to
determine whether the WTRU is in a low mobility state or high
mobility state. Alternatively, the determination of "low mobility
state" may be based on the rate of change of DL reference signals
transmitted by one or multiple transmission points. Alternatively,
the determination of "low mobility state" may be based on the rate
of change of best cell event or handover rate. Alternatively, the
determination of "low mobility state" may be based on the rate of
change of WTRU position calculated using the LTE positioning method
(e.g. used of PRS reference symbols to determine WTRU position).
The rate of change of WTRU position may be compared with a
predetermined threshold to determine whether the WTRU is in a low
mobility state or high mobility state.
[0062] The mobility state of the UE may be dependent on existing
mobility state estimation procedures. The UE may then use the
mobility state in combination with the determination of entering or
leaving the offload area to determine to start inter-frequency or
inter-RAT measurements. In one example, if the WTRU is in an
offload area and has already triggered an indication and the
mobility state changes to "high mobility state" the WTRU may
trigger an offload indication, providing information that it is
leaving the area or that it has changed mobility state.
[0063] The WTRU may stop inter-frequency or inter-RAT measurements
even if it has not left the offload area if it determines that it
is no longer in a certain mobility state, for example "low mobility
state" or "medium mobility state".
[0064] The WTRU may stop performing measurements if the WTRU has
performed inter-frequency or inter-RAT measurements for a
configured period of time and has not detected any valid candidate
cells in the vicinity. This may also indicate that the offload area
information stored in the WTRU may no longer be valid. Possibly,
upon this determination the WTRU may remove the stored
information.
[0065] Management of offload area information is described herein.
The methods may be used to determine if the WTRU has the necessary
offload area information stored for potential transmission of an
offload indication message (in connected mode) or for initiation of
inter-frequency measurements (in idle mode).
[0066] The WTRU may autonomously store the offload area information
based on previously detected small cells, e.g. build a data base or
fingerprint of small cells, their frequencies, location, etc.
[0067] Alternatively, the network may explicitly provide to the
WTRU offload area information to assist the UE in finding and
reporting the vicinity of small cells. Alternatively, the WTRU may
use a combination of autonomous storing of information and based on
information explicitly provided by the network to build the offload
area information.
[0068] In one method, the WTRU may determine that it is lacking
valid offload area information for at least one small cell or that
it would like to request offload area information or that it would
like to initiate acquisition of offload area information. Such a
determination may be enabled using received information about the
small cells (such as PCI, CGI, CSG ID, operating frequency) for
which valid offload area information needs to be available, and
detecting that such information is not available for at least one
small cell. The WTRU may also determine that it is lacking valid
offload area information for at least one small cell by receiving
information about the macro cell (such as PCI, operating frequency)
or or by connecting to a macro cell for which a WTRU connected or
camped to this macro cell needs to have valid offload area
information. The WTRU may also determine that it is lacking valid
offload area information for at least one small cell by receiving a
value ("offload area tag") that identifies an offload area
information at the network level and determining if it has stored
offload area information associated with this identifier. The WTRU
may also determine that it is lacking valid offload area
information for at least one small cell by receiving a value
("offload area tag") that identifies an offload area information
associated to a macro cell and comparing this value to a identifier
that was stored by the WTRU when the offload area information was
acquired for this macro cell.
[0069] The WTRU may determine it is lacking a valid offload area
information if it is visiting the area for a first time and doesn't
have anything stored for this area or for the connected cell (e.g.
based on PCI, cell ID).
[0070] For example, an offload area tag may be associated to a
certain macro cell and the set of small cells in its vicinity.
Whenever the set of small cells is modified, or the offload area
information associated to these cells is modified (due to a change
in deployment), the network may change the offload area tag to a
different value. This allows the WTRU to detect that its stored
offload area information for the small cells in the vicinity of
this macro cell is invalid if the stored offload area tag is
different from the offload area tag provided by the network.
[0071] The WTRU may also determine that it is lacking valid offload
area information or that it would like to request or acquire an
offload area information for at least one small cell by determining
that the speed of the WTRU is lower than a threshold which may be
pre-defined or provided by higher layers. The WTRU may also
determine that it is lacking valid offload area information or that
it would like to request or acquire offload area information for at
least one small cell by determining that a certain minimum time has
elapsed since the last handover or cell reselection, where the
minimum time may be pre-defined or provided by higher layers. The
WTRU may also determine that it is lacking valid offload area
information or that it would like to request or acquire offload
area information for at least one small cell by determining that
the WTRU is in a "low-mobility" state.
[0072] A WTRU moving above a certain speed through the macro layer
may not be a good candidate for offloading to the small cell layer.
In this case the WTRU may determine that no offload area
information is required.
[0073] The WTRU may also determine that it is lacking valid offload
area information for at least one small cell by determining that a
certain minimum time has elapsed since the last handover or cell
reselection, where the minimum time may be pre-defined or provided
by higher layers. This is to prevent premature offloading to the
small cell layer if the WTRU is moving rapidly. Alternatively, the
WTRU may also determine that it is lacking valid offload area
information or that it would like to request or acquire an offload
area information or to update (e.g. modify, remove, add) the
offload area information for at least one small cell by comparing
the time at which the offload area information for at least one
small cell was updated, and determining that this time is before a
time limit determined by a maximum threshold. The maximum threshold
(or time or duration limit) may be pre-defined or provided by the
network. The WTRU may also determine that the offload area
information is invalid if the time since the offload area was
acquired exceeds the time limit.
[0074] The WTRU may determine that the existing offload area
information is invalid upon a handover to a new macro cell. For
example, if a handover to a macro cell takes place the WTRU may
determine that the offload area information stored is no longer
valid and may be removed. If a new offload area information is
provided in the handover message or in the SIBs of the new cell the
WTRU may store the new information. Alternatively, upon a handover
the WTRU may keep the previous offload area information (until
determined to be invalid based on other criteria above). If a new
offload area information is received from the new macro cell or
from a RRC reconfiguration message the WTRU may replace the store
offload area information or alternatively store the new offload
area information in addition to the already stored one.
[0075] In determining that the offload area information is invalid,
not present or acquired, the information may be obtained by
receiving information elements (IE's) in a reconfiguration message
(such as a handover procedure to the macro cell) or from the SIB of
the new macro cell the WTRU reselects to. For example, there may be
a Boolean IE indicating whether there are small cells in the
vicinity of the target macro cell for which offload area
information needs to be stored. In another example, there may be
IE's containing a list of small cells in the vicinity of the target
macro cell for which offload area information needs to be stored or
an IE containing the offload area information for the current UE
location (e.g. current connected macro cell).
[0076] In determining that the offload area information is invalid,
the information may be obtained by receiving information elements
from system information broadcast from the macro cell. For
instance, there may be a Boolean IE in a system information block
indicating whether there are small cells in the vicinity of the
macro cell for which offload area information needs to be
stored.
[0077] The WTRU may verify whether it is lacking valid offload area
information when at least one of the following events occurs: after
cell reselection or handover to a cell (or macro cell); upon expiry
of a timer started upon cell reselection or handover to a cell,
where the value of the timer may be pre-defined or provided by
higher layers; upon an explicit indication or request or
configuration by the network; periodically, where the period may be
pre-defined or provided by higher layers; or upon expiry of a timer
started the last time the WTRU verified whether it is lacking valid
offload area information.
[0078] The WTRU may always search and take measurements to
determine proximity to small cell based on offload area information
or fingerprint information on the small cells. The WTRU may
autonomously determine when to start taking measurements according
to the cell in which it is connected. For example the offload area
information may be associated with a cell in the used frequency.
The cell may be a cell on which the UE is connected to (serving
cell or camped cell) and may be associated to a PCI, a list of
neighboring PCIs, or CGI (cell identity) of the serving cell. When
the UE determines that the PCI or CGI corresponds to a cell stored
in its offload area then it may initiate measurement procedures to
detect vicinity of the small cell area (e.g. GPS, PRS, other
positioning method, or measurements on other frequencies).
[0079] Upon determining that it is lacking valid offload area
information, the WTRU may initiate a procedure to acquire offload
area information.
[0080] Methods for acquiring offload area information are described
in herein. In idle mode, the WTRU may initiate inter-frequency
measurements even if the signal strength and/or quality of the
serving cell are above the thresholds (SintrasearchP,
SintrasearchQ). Alternatively, the WTRU may perform inter-frequency
measurements if the signal strength and/or quality of the serving
cell are below new threshold values applicable to the case of
lacking valid fingerprint information.
[0081] The WTRU may indicate to the network the capability and
support of offload area and small cell detection.
[0082] WTRU may initiate a procedure to acquire offload area
information by sending an indication to the network to notify that
offload area information is missing. Upon reception of this
indication, the network may configure the WTRU to perform
inter-frequency measurements (in connected mode) or initiate a
procedure to provide offload area information to the WTRU. The
indication may be provided as part of a new or existing RRC
procedure, or by MAC signaling (MAC control element). The
indication may comprise a proximity indication or an offload
indication. The indication may contain at least one of: information
about cells for which associated offload area information is
lacking, such as PCI, range of PCI's, CSG, CSG ID, cell identity
(CGI), frequency, RAT, etc.; Offload area tag; or a cause
indication to indicate that the reason for sending the indication
is that the WTRU lacks valid offload area information.
[0083] The WTRU may also send an indication to the network to
notify that it has stored offload area information, when at least
one of the following events occur: after cell reselection or
handover to a cell (or macro cell); upon expiry of a timer started
upon cell reselection or handover to a cell, where the value of the
timer may be pre-defined or provided by higher layers; upon an
explicit indication or request by the network; periodically, where
the period may be pre-defined or provided by higher layers; upon
expiry of a timer started the last time the WTRU transmitted the
indication to the network; or after acquisition of offload area
information (e.g. using its own measurements).
[0084] The indication sent to the network may be provided as part
of a new or existing RRC procedure, or by MAC signaling (MAC
control element). The indication may comprise a proximity
indication or an offload indication. The indication may contain at
least one of: any information included as part of the offload area
information as described in previous paragraphs; or a cause
indication to indicate that the indication is providing offload
area information.
[0085] To avoid storing offload area information indefinitely and
to avoid having out-dated offload area information, the WTRU may
clear and delete its stored information according to at least one
of the following triggers: an validity timer expires for a given
offload area information; the WTRU moves out of a cell (e.g. either
due to cell reselection or due to a handover); the WTRU moves to
idle mode; the WTRU performs an inter-frequency or inter-RAT
handover; the WTRU moves out of a home PLMN; the WTRU changes
PLMNs; the WTRU enters a roaming PLMN or a visiting PLMN
(alternatively, the WTRU does not delete the offload area
information of the home PLMN, but doesn't store any information for
the roaming PLMN); the WTRU is explicitly told by the network to
delete the offload area information; the WTRU changes RRC states;
or the WTRU gets new offload area information (e.g. it deletes the
previously stored information and stores the new one).
[0086] Acquisition of offload area information is described herein.
The WTRU may apply the methods or procedures, for example, if it
determines that the offload area information is not available or
not valid according for instance to one of the methods described
herein.
[0087] In one embodiment, the WTRU may acquire and store offload
area information based on its own measurements. The measurements
may include of any possible information contained or part of the
offline area information. The acquisition and storage of offload
area information may be performed if at least one or a combination
of the following conditions is satisfied: the WTRU is camping or is
connected to a cell which is associated to this offload area
information; the cell is an open cell; the cell is a hybrid cell;
the WTRU determines that it does not have valid offload area
information associated to the cell, or the time elapsed since the
last time the WTRU acquired offload information is higher than a
threshold; the WTRU detects the presence of a cell which is
associated to this offload area information, through e.g.
synchronization signals (PSS/SSS); inter-frequency or inter-RAT
measurements are configured in connected mode; the WTRU determines
that it does not have valid offload area information associated to
the cell; the WTRU is configured to perform positioning
measurements based on e.g. GPS or positioning reference signals; or
the WTRU received an indication from the network to perform the
acquisition and storage of offload area information associated to
this cell. In the last case, the indication may be provided in any
RRC message such as the handover command for which the target cell
is the small cell, or a re-establishment command, or in system
information of the small cell. The indication may include
information about cells for which associated offload area
information may be acquired, such as PCI, range of PCI's, CSG, CSG
ID, cell identity (CGI), frequency, RAT, etc.
[0088] In another embodiment, the WTRU may be provided with
explicit offload area information by the network. The information
provided by the network may include any information that may be
part of offload area information as described in previous
paragraphs (e.g. GPS coordinates, radius, cell identities, etc.).
The network may provide this information in one or a combination of
the following events: the WTRU enters the coverage of a macro cell
(e.g. a handover takes place); the WTRU performs cell reselection
to a macro cell (e.g. the macro cell may broadcast the system
information); the network determines that no valid offload area
information is available in the WTRU; upon explicit request by the
WTRU to provide such information; at any point during operation.
More specifically, such offload area information may be provided in
at least one of the following ways: as part of a new information
element inserted into an existing RRC message, such as at least one
of: RRC connection reconfiguration (with or without
mobilityControlInfo), received upon handover to a macro cell whose
coverage area includes offload area(s); RRC connection
re-establishment; RRC connection setup; RRC connection release (to
provide fingerprint info in idle mode); system information (e.g.
for idle mode); a new RRC message, or as part of a new RRC
procedure.
[0089] The new RRC procedure may be initiated by the WTRU, upon
determination that it lacks valid offload area information for at
least one cell, as described in a previous section. This may avoid
unnecessary signaling if the WTRU already has valid information. To
enable initiation of such procedure by a WTRU in idle mode, the
WTRU may initiate an RRC connection request with a new cause
value.
[0090] The cell involved in the RRC signaling may be any cell, such
as the macro cell whose coverage area includes at least one offload
area, or a cell associated to an offload area.
[0091] An example realization of the methods described herein is
illustrated below. More specifically, this example illustrates a
method wherein the WTRU is explicitly provided an offload area
information.
[0092] In this example, the WTRU enters a region or a macro cell.
Upon handover, the macro cell provides the WTRU with offload area
information of the region in which the small cells in the vicinity
of the macro cell are located. For example, the offload area
information may include a GPS coordinate and a radius over which
the area extends with respect to the GPS coordinate. Alternatively,
a number of GPS locations (e.g. 4) are provided to the WTRU and the
offloading area may correspond to all the points located within
these coordinates. Another example of location information that may
be provided to the WTRU may be the PRS of a number of cells. If
more than one offloading area information is available under the
coverage of a macro cell, the WTRU may be provided more than one
offloading area location information. The WTRU may also be provided
with the frequency or RAT of the cell(s) within the signaled areas.
The WTRU may acquire this information from the SIBs or the macro
cell may provide to the WTRU via dedicated signaling.
[0093] Upon acquisition and/or storing of this information the WTRU
may perform measurements to determine its location and to determine
whether it has entered any of the stored offload areas. The WTRU
may use the reception of this offloading area information to
trigger and activate measurement procedures. For example, this may
include activating GPS if not already active, or initiate PRS
measurements. Alternatively, a message indicating that the UE
should start measurement procedures to detect proximity/vicinity to
an offload area (if already present in the WTRU) may be sent. This
message may not include the offload are information. These
measurements may be performed in the current operating frequency.
When the WTRU determines that it has entered the configured
offloading area according to any of the coordinates or location
information it may trigger the offload indication. The indication
may notify the network that the WTRU has entered the area. As an
example, the WTRU may provide to the network its location such that
the network may determine which offload area the WTRU is in the
vicinity of. In another example, the WTRU just reports the
frequency in which the offloading cells may be located. If more
than one offload area information is provided to the WTRU, the WTRU
may also report an index that indicates which area it has entered
within the configured or stored location areas.
[0094] The WTRU may then be configured to start taking
inter-frequency measurements or inter-RAT measurements. The
decision for inter-frequency measurements may be based on the
network or alternatively, for idle mode WTRUs the WTRU may
autonomously decide to start taking measurements when it determines
that it has entered the vicinity of such area.
[0095] In one example, when leaving the macro cell the WTRU may
delete this location information and may start the same procedure
if new coordinates are provided to the WTRU.
[0096] Methods of reporting positioning information to the network
are described herein. Another method of allowing WTRU mobility from
a macro cell to a small cell is to use positioning information from
the WTRU to determine if it might be in the vicinity of small
cells. This method may assist in self-organizing small cell
deployments, and in cases when small cells are turned on and off
dynamically to conserve energy. In this method, the WTRU may report
its position to the network. The position and measurements may be
taken on the used frequency. Using this information the network may
determine when and whether to configure inter-frequency
measurements for the WTRU. Once the positioning information is
available, the serving eNB may use this to calculate the absolute
distance between the WTRU and nearby small cell eNBs, and if the
WTRU is determined to be within the vicinity, appropriate
measurements may be initiated. The calculation of absolute distance
is possible when the serving eNB has the location information of
the small cell eNB also available. It may be assumed this
information is available to the network, either as the small cells
are network deployed, or in case of autonomous HeNB deployment,
HeNBs transmit their positioning information to the network to
ensure emergency call requirements are maintained.
[0097] WTRU based positioning methods are described herein. In case
of WTRU-based positioning, the results of the measurements may be
reported using at least one of the following means: by inserting
the information into a measurement report triggered by any event as
part of a LPP (LTE positioning protocol) message or alternatively
it may be reported by including the positioning information in the
offload indication or in the extended proximity report. In the case
of WTRU-based positioning determination, an LPP session may need to
be initiated to report the information to the eNB and the E-SMLC.
Similar methods may also be applicable for GPS measurements.
[0098] In one embodiment, the LPP session is initiated by the eNB
for candidate WTRUs for which it may like to receive positioning
information. The determination of the candidate WTRUs, made by the
eNB may be based on various factors including measurements,
detected serving and neighbor cell-ids, OA&M (Operations
Administration Maintenance) information, deployment vector map,
etc.
[0099] In another embodiment, the WTRU may be configured to
start/stop adding positioning information to the measurement report
when it reaches configured thresholds added to the measConfig
message. The request may be in the form of a one time request or in
a form of a period measurement request for offloading information
purposes.
[0100] In another embodiment, the WTRU may be configured to report
positioning information when the WTRU detects it's moved within the
proximity of pre-configured locations. For example, a new event may
be created to initiate sending positioning reports to the network
when the WTRU detects that it is within a radius of X meters within
a location specified by co-ordinates x.sub.i, y.sub.i, .apprxeq.i,
t.sub.i (x, y, and z components of position, and the time sent).
This event may be a new measurement event or a LPP event to trigger
a measurement/LPP message report.
[0101] In another alternative, the small cell eNB (i.e. pico cell
eNB or HeNB) operating on another frequency may send a reference
signal or message on the same frequency as the serving eNB, so the
WTRU operating in the serving eNB, and within the listening radius
of the small cell, may use autonomous procedures to detect it. This
may be reported to the network using an extension of an existing
measurement event, the extended proximity indication or new offload
indication report or a new LPP or measurement configuration event
may be defined to initiate a report sent to the network. For
example, in one alternative, the small cell eNB may send reference
signals (e.g. the PRSs, CRS, of CSI-RS) or on neighboring
frequencies (configured or detected), with a certain planned
periodicity so there is no collisions between neighboring eNBs. The
WTRU may be configured to detect all PRS symbols it hears from
subframe 0 to subframe T, where T is the superset of PRS
periodicity of all neighbors within a certain area. In one example,
the network may configure the WTRU with the information and
resources where the reference signals are transmitted). The WTRU
then monitors the same frequency as the used frequency for this
reference signals or PRS and when it detects them or when the
quality of one or a subset of these reference signals is above a
threshold then WTRU triggers an indication to the network.
[0102] To avoid reference symbol collision due to PCI confusion,
the schedule and periodicity of transmitting the reference symbols
may be managed centrally at the macro/network level or negotiated
between the neighbors. The WTRU may be configured to send a report
to the network if it detects any the reference signal within a
configured window set.
[0103] Network based positioning methods are described herein.
Separately from the location service support for particular WTRUs,
an E-SMLC may interact with elements in the E-UTRAN to obtain
measurement information to help assist one or more positioning
methods for all WTRUs. In one alternative, the WTRU may be
configured to autonomously initiate transmission of necessary
positioning reference signals for uplink-based WTRU positioning
measurements, so the eNB may estimate its position. This may be
initiated by the WTRU based on finger-printing information.
[0104] The measurement configuration may include additional
configuration thresholds that set rules on when the WTRU may
initiate transmission of the positioning reference signals.
[0105] FIG. 2A shows an example method. At 200, the WTRU receives
area offload information. At 202, the WTRU makes a coverage area
determination that the WTRU may be within the coverage area of a
small cell. At 204, the WTRU transmits an offload indication the
network. In connected mode, the WTRU may transmit the offload
indication over an established connection, while in the idle mode,
the WTRU may first initiate an RRC connection prior to transmitting
the offload indication. FIG. 2B shows an alternative example
method. At 206, the WTRU receives area offload information from the
network. At 208, the WTRU makes a coverage area determination that
the WTRU may be within the coverage area of a small cell. At 210,
the WTRU initiates inter-frequency and/or inter-RAT measurements.
FIG. 2C shows a further alternative example method. At 212, the
WTRU receives area offload information. At 214, the WTRU makes a
coverage area determination that the WTRU may be within the
coverage area of a small cell. At 216, the WTRU transmits an
offload indication the network. At 218, the WTRU receives an
inter-frequency or inter-RAT configuration message. At 220, the
WTRU initiates the measurements according to the received
configuration.
[0106] In one embodiment, the method comprises receiving offload
area information at a Wireless Transmit-Receive Unit (WTRU) from a
network; making a coverage area determination, based on the offload
area information, of the WTRU with respect to a coverage area of a
small cell; and, transmitting an offload indication to the
network.
[0107] In an embodiment, the method includes offload area
information that comprises any one or more of the following: (i) an
area defined by a center point and a radius, (ii) a set of GPS
coordinates, (iii) an area defined by a number of GPS coordinates,
(iv) a coverage area of at least one macro cell and an identity of
the at least one macro cell, (v) a list of Position Reference
Symbols, (vi) one or more PCIs, (vii) one or more Cell Identities,
(viii) a frequency at which a small cell operates, or, (ix) a radio
access technology of a small cell.
[0108] In an embodiment, the method may include the offload area
information being received via a Radio Resource Control (RRC)
message, via a system information block, or via dedicated
signaling.
[0109] In an embodiment, the method may include receiving the
offload area information by the WTRU based on the occurrence of at
least one of the following events: cell reselection; handover to a
cell; expiry of a timer associated with cell reselection/handover
to a cell; an explicit request by a network; expiry of a periodic
timer.
[0110] In an embodiment, the method may include the coverage area
determination being made by comparing a WTRU location with a
reference location and a radius, or by comparing a WTRU location
with a plurality of location reference points.
[0111] In an embodiment, the method may use an offload indication
that includes one of: a WTRU location, a small cell ID, a small
cell frequency, or an index value of a stored location.
[0112] In an embodiment, the method may further comprise receiving
a small cell configuration from the base station in response to the
offload indication.
[0113] In an embodiment, the method may include wherein the small
cell configuration is an inter-frequency, inter-RAT or
intra-frequency measurement configuration.
[0114] In an embodiment, the method may include wherein the offload
indication indicates that the WTRU has entered a small cell
coverage area, or that the WTRU has left a small cell coverage
area.
[0115] In an embodiment, the method may include wherein
transmitting the offload indication to the network is conditioned
on a low mobility state of the WTRU.
[0116] In an embodiment, the method may include wherein the low
mobility state is determined with respect to global positioning
system (GPS) information.
[0117] In an embodiment, the method may include wherein
transmitting the offload indication to the macro cell is
conditioned on a traffic level of the WTRU.
[0118] In an embodiment, the method may include wherein the offload
indication message comprises an RRC message.
[0119] In an embodiment, the method may include wherein the RRC
message is a modified proximity indication message that includes
information elements pertaining to offload.
[0120] In an embodiment, the method may include wherein the RRC
message is an RRC Measurement Report message modified to include
information elements indicating offloading.
[0121] In an embodiment, the method may include wherein the offload
indication message includes at least one of the following
information elements: an indication that the WTRU is entering the
offload area; an indication that the WTRU is leaving the offload
area; an identifier of the offload area to which the WTRU may be
offloaded; a frequency on which the WTRU may be offloaded; a cell
ID of a potential target cell to which the WTRU may be offloaded; a
PCI of a potential target cell to which the WTRU may be offloaded;
a radio access technology to which the WTRU may be offloaded; an
area in which the WTRU is located.
[0122] In an embodiment, the method may further comprise verifying
valid offload area information at the WTRU when at least one of the
following events occurs: cell reselection; handover to a cell;
expiry of a timer associated with cell reselection/handover to a
cell; an explicit request by a network; expiry of a periodic timer;
expiry of a timer started the last time the WTRU verified whether
it is lacking valid offload area information.
[0123] In an embodiment, the method may include wherein the WTRU
deletes stored offload area information based on any one the
following triggers: an validity timer expires for a given offload
area information; the WTRU moves out of a cell (e.g. either due to
cell reselection or due to a handover); the WTRU moves to idle
mode; the WTRU performs an inter-frequency or inter-RAT handover;
the WTRU moves out of a home network; the WTRU changes public
networks; the WTRU is explicitly told by a network to delete the
offload area information; the WTRU changes RRC states; or, the WTRU
gets new offload area information.
[0124] In an embodiment, one method may comprise: receiving offload
area information at a wireless Transmit-Receive Unit (WTRU) from a
macro cell base station; making a determination based on the
offload area information that the WTRU is in a coverage area of a
small cell; and, initiating inter-frequency and/or inter-RAT
measurements to detect the small cell.
[0125] In an embodiment, the method may include wherein the offload
area information comprises any one or more of the following: (i) an
area defined by a center point and a radius, (ii) a set of GPS
coordinates, (iii) an area defined by a number of GPS coordinates,
(iv) a coverage area of at least one macro cell and an identity of
the at least one macro cell, (v) a list of Position Reference
Symbols, (vi) one or more PCIs, (vii) one or more Cell Identities,
(viii) a frequency at which a small cell operates, or, (ix) a radio
access technology of a small cell.
[0126] In an embodiment, the method may include the offload area
information is received via a system information block.
[0127] In an embodiment, the method may include wherein the
coverage area determination is made by comparing a WTRU location
with a reference location and a radius, or by comparing a WTRU
location with a plurality of location reference points.
[0128] In an embodiment, the method may include wherein initiating
inter-frequency and/or inter-RAT measurements is conditioned on a
low mobility state of the WTRU.
[0129] In an embodiment, the method may include wherein initiating
inter-frequency and/or inter-RAT measurements is conditioned on a
traffic level of the WTRU.
[0130] In an embodiment, the method may further comprise verifying
valid offload area information at the WTRU when at least one of the
following events occurs: cell reselection; handover to a cell;
expiry of a timer associated with cell reselection/handover to a
cell; an explicit request by a network; expiry of a periodic timer;
expiry of a timer started the last time the WTRU verified whether
it is lacking valid offload area information.
[0131] In an embodiment the method may comprise: receiving offload
area information at a wireless Transmit-Receive Unit (WTRU) from a
base station; making a determination based on the offload area
information that the WTRU is in a coverage area of a small cell;
transmitting an offload indication to a network entity; receiving
an inter-frequency or inter-RAT measurement configuration; and,
initiating inter-frequency and/or inter-RAT measurements according
to the configuration.
[0132] In an embodiment, the method may include wherein the offload
area information comprises any one or more of the following: (i) an
area defined by a center point and a radius, (ii) a set of GPS
coordinates, (iii) an area defined by a number of GPS coordinates,
(iv) a coverage area of at least one macro cell and an identity of
the at least one macro cell, (v) a list of Position Reference
Symbols, (vi) one or more PCIs, (vii) one or more Cell Identities,
(viii) a frequency at which a small cell operates, or, (ix) a radio
access technology of a small cell.
[0133] In an embodiment, the method may include wherein the offload
area information is received via a system information block.
[0134] In an embodiment, the method may include wherein the
coverage area determination is made by comparing a WTRU location
with a reference location and a radius, or by comparing a WTRU
location with a plurality of location reference points.
[0135] In an embodiment, an embodiment may include an apparatus
comprising a Wireless Transmit Receive Unit (WTRU) configured to
receive offload area information from a macro cell base station;
make a coverage area determination, based on the offload area
information, of the WTRU with respect to a coverage area of a small
cell; and, transmit an offload indication to the macro cell.
[0136] In an embodiment, the apparatus may include the WTRU
configured to make the coverage area determination by comparing a
WTRU location with a reference location and a radius, or by
comparing a WTRU location with a plurality of location reference
points.
[0137] In an embodiment, the apparatus may be further configured to
receive a small cell configuration from the base station in
response to the offload indication.
[0138] In an embodiment, the apparatus is further configured to
transmit the offload indication to the macro cell based on a low
mobility state of the WTRU.
[0139] In an embodiment, the apparatus is further configured to
transmit the offload indication to the macro cell based on a
traffic level of the WTRU.
[0140] In an embodiment, the apparatus further configured to verify
valid offload area information when at least one of the following
events occurs: cell reselection; handover to a cell; expiry of a
timer associated with cell reselection/handover to a cell; an
explicit request by a network; expiry of a periodic timer; expiry
of a timer started the last time the WTRU verified whether it is
lacking valid offload area information.
[0141] In an embodiment, the apparatus is further configured to
delete stored offload area information based on any one the
following triggers: a validity timer expires for a given offload
area information; the WTRU moves out of a cell (e.g. either due to
cell reselection or due to a handover); the WTRU moves to idle
mode; the WTRU performs an inter-frequency or inter-RAT handover;
the WTRU moves out of a home network; the WTRU changes public
networks; the WTRU is explicitly told by a network to delete the
offload area information; the WTRU changes RRC states; or, the WTRU
gets new offload area information.
[0142] In an embodiment, an apparatus or system may be configured
to perform any of the methods described herein.
[0143] In an embodiment, a base station or evolved NodeB may be
configured to perform any of the methods described herein.
[0144] In an embodiment, a tangible computer readable storage
medium having stored thereon computer executable instructions for
performing any of the above methods.
[0145] Variations of the method, apparatus and system described
above are possible without departing from the scope of the
invention. In view of the wide variety of embodiments that can be
applied, it should be understood that the illustrated embodiments
are exemplary only, and should not be taken as limiting the scope
of the following claims. For instance, in the exemplary embodiments
described herein include handheld devices, which may include or be
utilized with any appropriate voltage source, such as a battery and
the like, providing any appropriate voltage.
[0146] Although features and elements are described above in
particular combinations, one of ordinary skill in the art will
appreciate that each feature or element can be used alone or in any
combination with the other features and elements. In addition, the
methods described herein may be implemented in a computer program,
software, or firmware incorporated in a computer-readable medium
for execution by a computer or processor. Examples of
computer-readable media include electronic signals (transmitted
over wired or wireless connections) and computer-readable storage
media. Examples of computer-readable storage media include, but are
not limited to, a read only memory (ROM), a random access memory
(RAM), a register, cache memory, semiconductor memory devices,
magnetic media such as internal hard disks and removable disks,
magneto-optical media, and optical media such as CD-ROM disks, and
digital versatile disks (DVDs). A processor in association with
software may be used to implement a radio frequency transceiver for
use in a WTRU, UE, terminal, base station, RNC, or any host
computer.
[0147] Moreover, in the embodiments described above, processing
platforms, computing systems, controllers, and other devices
containing processors are noted. These devices may contain at least
one Central Processing Unit ("CPU") and memory. In accordance with
the practices of persons skilled in the art of computer
programming, reference to acts and symbolic representations of
operations or instructions may be performed by the various CPUs and
memories. Such acts and operations or instructions may be referred
to as being "executed," "computer executed" or "CPU executed."
[0148] One of ordinary skill in the art will appreciate that the
acts and symbolically represented operations or instructions
include the manipulation of electrical signals by the CPU. An
electrical system represents data bits that can cause a resulting
transformation or reduction of the electrical signals and the
maintenance of data bits at memory locations in a memory system to
thereby reconfigure or otherwise alter the CPU's operation, as well
as other processing of signals. The memory locations where data
bits are maintained are physical locations that have particular
electrical, magnetic, optical, or organic properties corresponding
to or representative of the data bits. It should be understood that
the exemplary embodiments are not limited to the above-mentioned
platforms or CPUs and that other platforms and CPUs may support the
described methods.
[0149] The data bits may also be maintained on a computer readable
medium including magnetic disks, optical disks, and any other
volatile (e.g., Random Access Memory ("RAM")) or non-volatile
(e.g., Read-Only Memory ("ROM")) mass storage system readable by
the CPU. The computer readable medium may include cooperating or
interconnected computer readable medium, which exist exclusively on
the processing system or are distributed among multiple
interconnected processing systems that may be local or remote to
the processing system. It should be understood that the exemplary
embodiments are not limited to the above-mentioned memories and
that other platforms and memories may support the described
methods.
[0150] No element, act, or instruction used in the description of
the present application should be construed as critical or
essential to the invention unless explicitly described as such.
Also, as used herein, each of the articles "a" and "an" are
intended to include one or more items. Where only one item is
intended, the terms "a single" or similar language is used.
Further, the terms "any of" followed by a listing of a plurality of
items and/or a plurality of categories of items, as used herein,
are intended to include "any of," "any combination of," "any
multiple of," and/or "any combination of multiples of" the items
and/or the categories of items, individually or in conjunction with
other items and/or other categories of items. Further, as used
herein, the term "set" is intended to include any number of items,
including zero. Further, as used herein, the term "number" is
intended to include any number, including zero.
[0151] Moreover, the claims should not be read as limited to the
described order or elements unless stated to that effect. In
addition, use of the term "means" in any claim is intended to
invoke 35 U.S.C. .sctn.112, 6, and any claim without the word
"means" is not so intended.
* * * * *