Systems and Methods for a User Equipment to Become a Synchronization Source

Abstract

Systems and methods for User Equipment (UE) synchronization for Device-to-Device (D2D) out-of-coverage communication are provided. In an embodiment, a method in an in-coverage (IC) UE for the IC UE to become a synchronization source for out-of-coverage UEs for D2D communication includes obtaining, by the IC UE scanning parameters; scanning, by the IC UE, for out-of-coverage synchronization signals; transmitting, by the IC UE, a measurement report to a Transmission Point (TP) in response to a report trigger, the measurement report comprising information of one or more received out-of-coverage synchronization signals; receiving, by the IC UE, a configuration command from the TP instructing the IC UE to become a synchronization source in response to a configuration command from the TP; and transmitting, by the IC UE, a D2D synchronization signal (SS) for a duration of time or until instructed not to do so by the TP.

What is claimed is: 
     
         1 . A method comprising:
 receiving, by a transmission point (TP), a measurement report from a first in-network-coverage user equipment (UE) of a plurality of in-network-coverage UEs, the measurement report corresponding to an out-of-network coverage UE;   selecting, by the TP, a second in-network-coverage UE of the plurality of in-network-coverage UEs to be a synchronization source for an out-of-network-coverage UE for device-to-device (D2D) communications; and   transmitting, by the TP, a configuration message to the second in-network-coverage UE, the configuration message identifying the second in-network-coverage UE as the synchronization source, the second in-network-coverage UE being the only one of the plurality of in-network-coverage UEs permitted to transmit a D2D synchronization signal (D2DSS) during a specified time frame.   
     
     
         2 . The method of  claim 1 , further comprising:
 transmitting, by the TP, a scanning message to at least some of the in-network-coverage UEs, the scanning message instructing the in-network-coverage UEs when to scan for out-of-network UE signals.   
     
     
         3 . The method of  claim 2 , wherein the scanning message comprises a first time duration indicating a duration of time for one of the in-network-coverage UEs to scan for D2DSSs from out-of-network UEs, a second time duration indicating a length of time between successive scans, and a third time duration indicating a time after which the one of the in-network-coverage UEs is to stop scanning. 
     
     
         4 . The method of  claim 2 , wherein the scanning message comprises a threshold, wherein in-network-coverage UEs that measure a received power from the TP above the threshold are prohibited from scanning. 
     
     
         5 . The method of  claim 2 , further comprising transmitting the scanning message as a broadcast message. 
     
     
         6 . The method of  claim 2 , wherein the scanning message instructs the in-network-coverage UEs to use preconfigured scanning parameters for the scan. 
     
     
         7 . The method of  claim 1 , further comprising:
 determining a number of scanning groups of in-network-coverage UEs; and   sending scanning parameters to each of the scanning groups.   
     
     
         8 . The method of  claim 7 , wherein the scanning parameters for a first group are different from the scanning parameters for a second group. 
     
     
         9 . The method of  claim 7 , wherein the scanning parameters comprise T 1 , T 2 , and T 3 , wherein T 1  is a time gap between scanning windows, T 2  is a length of time of each scanning window of the scanning windows, and T 3  is a total length of time for scanning. 
     
     
         10 . The method of claim i, wherein the first in-network-coverage UE is the second in-network-coverage UE. 
     
     
         11 . A transmission point (TP) comprising:
 a non-transitory memory storage comprising instructions; and   one or more processors in communication with the non-transitory memory storage, wherein the one or more processors execute the instructions to:
 receive a measurement report from a first in-network-coverage user equipment (UE) of a plurality of in-network-coverage UEs, the measurement report corresponding to an out-of-network-coverage UE; 
 select a second in-network-coverage UE of the plurality of in-network-coverage UEs to be a synchronization source for the out-of-network-coverage UE for device-to-device (D2D) communications; and 
 transmit a configuration message to the second in-network-coverage UE, the configuration message identifying the second in-network-coverage UE as the synchronization source, wherein the second in-network-coverage UE is the only one of the plurality of in-network-coverage UEs permitted to transmit a D2D synchronization signal (D2DSS) during a specified time frame. 
   
     
     
         12 . The TP of  claim 11 , wherein the one or more processors execute the instructions to:
 transmit a scanning message to at least some of the in-network-coverage UEs, the scanning message instructing the in-network-coverage UEs when to scan for out-of-network UE signals.   
     
     
         13 . The TP of  claim 12 , wherein the scanning message comprises a first time duration indicating a duration of time for one of the in-network-coverage UEs to scan for D2DSSs from out-of-network UEs, a second time duration indicating a length of time between successive scans, and a third time duration indicating a time after which the one of the in-network-coverage UEs is to stop scanning. 
     
     
         14 . The TP of  claim 12 , wherein the scanning message comprises a threshold, and wherein in-network-coverage UEs that measure a received power from the TP above the threshold are prohibited from scanning. 
     
     
         15 . The TP of  claim 12 , wherein the one or more processors execute the instructions to transmit the scanning message as a broadcast message. 
     
     
         16 . The TP of  claim 12 , wherein the scanning message instructs the in-network-coverage UEs to use preconfigured scanning parameters for the scan. 
     
     
         17 . The TP of  claim 11 , wherein the one or more processors execute the instructions to:
 determine a number of scanning groups of in-network-coverage UEs; and   send scanning parameters to each of the scanning groups.   
     
     
         18 . The TP of  claim 17 , wherein the scanning parameters for a first group are different from the scanning parameters for a second group. 
     
     
         19 . The TP of  claim 17 , wherein the scanning parameters comprise T 1 , T 2 , and T 3 , wherein T 1  is a time gap between scanning windows, T 2  is a length of time of each scanning window of the scanning windows, and T 3  is a total length of time for scanning. 
     
     
         20 . The TP of  claim 11 , wherein the first in-network-coverage UE is the second in-network-coverage UE.