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 Upon a determination that the offload area information is no longer valid, the WTRU may delete the offload area information.

1 - 18 . (canceled) 
     
     
         19 . A method performed at a wireless network node of a heterogeneous network, the method comprising:
 transmitting offload area information to a Wireless Transmit Receive Unit (WTRU) disclosing a location of a small cell; and   receiving from the WTRU responsive to the offload area information transmitted to the WTRU an offload indication indicating that the WTRU is a candidate for offload to the small cell.   
     
     
         20 . The method of claim  18  wherein the offload area information comprises any one or more of the following: (i) a frequency at which a small cell operates, or, (ii) a radio access technology of a small cell. 
     
     
         21 . The method of claim  18  wherein the offload area information is transmitted via a Radio Resource Control (RRC) message. 
     
     
         22 . The method of claim  18  wherein the offload area information is transmitted via a system information block. 
     
     
         23 . The method of claim  18  further comprising:
 receiving from the WTRU a notification that the WTRU is missing offload information; and 
 responsive to the indication that the WTRU is missing offload information, transmitting offload area information to the WTRU. 
 
     
     
         24 . The method of claim  18  wherein the offload indication includes at least one of: a WTRU location, a small cell ID, a small cell frequency, and an index corresponding to an offload area. 
     
     
         25 . The method of claim  18  further comprising:
 transmitting a small cell configuration in response to the offload indication. 
 
     
     
         26 . The method of  claim 25  wherein the small cell configuration is an inter-frequency, inter-RAT or intra-frequency measurement configuration. 
     
     
         27 . A base station comprising:
 a transmitter;   a receiver;   a processor configured to:
 transmit offload area information to a Wireless Transmit Receive Unit (WTRU) disclosing a location of a small cell; and 
 receive from the WTRU responsive to the offload area information transmitted to the WTRU an offload indication to the macro cell indicating that the WTRU is a candidate for offload to the small cell. 
   
     
     
         28 . The base station of  claim 27  wherein the processor is further configured to transmit a small cell configuration in response to the offload indication. 
     
     
         29 . The base station of  claim 27  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. 
     
     
         30 . The base station of  claim 27  wherein the offload area information comprises any one or more of: (i) a frequency at which a small cell operates, or, (ii) a radio access technology of a small cell. 
     
     
         31 . The base station of  claim 27  wherein the processor is configured to transmit the offload area information via a Radio Resource Control (RRC) message. 
     
     
         32 . The base station of  claim 27  wherein the processor is configured to transmit the offload area information via a system information block. 
     
     
         33 . The base station of  claim 27  wherein the processor is further configured to:
 receive from the WTRU a notification that the WTRU is missing offload information; and 
 responsive to the indication that the WTRU is missing offload information, transmit offload area information to the WTRU. 
 
     
     
         34 . The base station of  claim 27  wherein the offload indication includes at least one of: a WTRU location, a small cell ID, a small cell frequency, and an index corresponding to an offload area. 
     
     
         35 . The base station of  claim 27  further comprising:
 transmitting a small cell configuration in response to the offload indication. 
 
     
     
         36 . The base station of  claim 35  wherein the small cell configuration is an inter-frequency, inter-RAT or intra-frequency measurement configuration. 
     
     
         37 . A Wireless Transmit Receive Unit (WTRU) comprising:
 a transmitter;   a receiver;   a processor configured to;
 receive offload area information disclosing an area covered by a small cell from a macro cell base station; 
 make a determination based on the offload area information that the WTRU is in a coverage area of a small cell; and 
 responsive to a determination that the WTRU is in a coverage area of a small cell, initiate inter-frequency and/or inter-RAT measurements to detect the small cell. 
   
     
     
         38 . The WTRU of  claim 37  wherein the processor is further configured to initiate inter-frequency and/or inter-RAT measurements further conditioned on a mobility state of the WTRU. 
     
     
         39 . The WTRU of  claim 37  wherein the processor is further configured to initiate inter-frequency and/or inter-RAT measurements further conditioned on a traffic level of the WTRU. 
     
     
         40 . A Wireless Transmit Receive Unit (WTRU) comprising:
 a transmitter;   a receiver;   a processor configured to;
 receive offload area information disclosing an area covered by a small cell from a base station; 
 make a determination based on the offload area information that the WTRU is in a coverage area of a small cell; and 
 responsive to a determination that the WTRU is in a coverage area of a small cell:
 transmit an offload indication to a network entity; 
 receive an inter-frequency or inter-RAT measurement configuration; and 
 initiate inter-frequency and/or inter-RAT measurements according to the configuration.