METHOD AND APPARATUS FOR SMALL CELL DISCOVERY IN HETEROGENEOUS NETWORKS
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 Upon a determination that the offload area information is no longer valid, the WTRU may delete the offload area information.
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.