| CPC H04W 56/001 (2013.01) [H04W 56/002 (2013.01); H04W 8/005 (2013.01); H04W 76/14 (2018.02)] | 18 Claims |

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1. A method comprising:
receiving, by a user equipment (UE) from a base station serving the UE, a radio resource control (RRC) signaling, the RRC signaling identifying a synchronization resource for transmitting a device-to-device synchronization signal (D2DSS) by the UE; and
transmitting, by the UE, the D2DSS over the synchronization resource in accordance to one of:
determining that a reference signal received power (RSRP) measurement of reference signals received from the base station is lower than a threshold, wherein the RRC signaling further indicates the threshold, or
receiving another RRC signaling instructing the UE to transmit the D2DSS, wherein the RRC signaling is before the another RRC signaling.
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