Patent ID: 9736874
Date: 2017-08-15
CPC Classifications: H04W

Claim:
1. A method by a user equipment (UE) for selecting a synchronization master for device-to-device (D2D) communication, the method comprising: receiving, by a first UE, a discovery signal from a second UE, the discovery signal comprising a timing reference and a synchronization signal that indicates a synchronization state of the second UE, the synchronization signal being an in-coverage signal when the second UE is inside a coverage area of a cellular network and an out-of-coverage signal when the second UE is outside of the coverage area of the cellular network, the discovery signal having been received on a predefined uplink carrier; determining whether the first UE is to act as a timing slave entity or a timing master entity during a D2D communications session between the first UE and the second UE based on whether the synchronization signal received from the second UE is the in-coverage signal or the out-of-coverage signal; participating, by the first UE, in the D2D communication session with the second UE over the predefined uplink carrier as the timing slave entity or the timing master entity, wherein the first UE synchronizes the D2D communication session according to the timing reference received from the second UE when the first UE is the timing slave entity, and wherein the first UE synchronizes the D2D communication session according to its own timing reference when the first UE is the timing master entity; receiving, by the first UE, authorization from the cellular network, the authorization indicating the first UE is permitted to act as the timing master entity; and switching, by the first UE, to a timing master mode in response to receiving the authorization from the cellular network.