Power control of device-to-device synchronization signal

1. A method of setting a power of a secondary device-to-device synchronization signal, SD2DSS, by a first wireless device to enable a second wireless device to synchronize timing of the second wireless device to a timing derived from the first wireless device, the method comprising:

determining power of a primary device to device synchronization signal, PD2DSS, transmitted by the first wireless device;

setting the power of the SD2DSS to be less than the power of the PD2DSS; and

transmitting the SD2DSS with a power less than the PD2DSS.

2. The method of claim 1 , wherein the PD2DSS includes a Zadoff-Chu, ZC, sequence and the SD2DSS includes an M sequence.

3. The method of claim 1 , wherein the power of the SD2DSS is the minimum of a nominal value of the power of the PD2DSS and a power threshold.

4. The method of claim 1 , wherein the set power of the SD2DSS is adjusted only when the power of the PD2DSS exceeds a predetermined amount.

5. The method of claim 1 , wherein a same circuitry generates the SD2DSS and a secondary synchronization signal, SSS.

6. The method of claim 1 , wherein the SD2DSS is transmitted with a power less than the PD2DSS as determined by a power offset compared to the PD2DSS.

7. The method of claim 6 , wherein the power offset is −4 dB.

8. The method of claim 6 wherein the power offset is determined autonomously by the first wireless device.

9. A wireless device configured to set a power of a secondary device-to-device synchronization signal, SD2DSS, to enable a second wireless device to synchronize timing of the second wireless device to a timing of the wireless device, the wireless device comprising:

a processor; and

a memory, the memory containing instructions executable by the processor, the instructions when executed configure the processor to:

determine power of a primary device to device synchronization signal, PD2DSS, transmitted by the wireless device;

set the power of the SD2DSS to be less than the power of the PD2DSS; and

transmit the SD2DSS with a power less than the PD2DSS.

10. The wireless device of claim 9 , wherein the PD2DSS includes a Zadoff-Chu, ZC, sequence and the SD2DSS includes an M sequence.

11. The wireless device of claim 9 , wherein the power of the SD2DSS is a minimum of a nominal value of the power of the PD2DSS and a power threshold.

12. The wireless device of claim 9 , wherein the SD2DSS is transmitted with a power less than the PD2DSS as determined by a power offset compared to the PD2DSS.

13. The wireless device of claim 12 , wherein the power offset is determined autonomously by the wireless device.

14. The wireless device of claim 12 , wherein the power offset is one of configurable and predetermined.

15. A method of determining and transmitting one of a power offset and a power threshold to a wireless device, the method comprising:

determining at least one of a power offset and a power threshold for setting a power of a secondary device to device synchronization signal, SD2DSS, by a wireless device, the SD2DSS being transmitted with a power less than a primary device to device synchronization signal, PD2DSS; and

transmitting at least one of the power offset and the power threshold to the wireless device.

16. A network node, comprising:

a processor;

a memory containing instructions that when executed by the processor configure the processor to determine at least one of a power offset and a power threshold for setting a power of secondary device to device synchronization signal, SD2DSS by a wireless device;

a communication interface configured to transmit at least one of the power offset and the power threshold to the wireless device, the power of the SD2DSS being transmitted with a power less than a primary device to device synchronization signal, PD2DSS; and

the memory configured to store the at least one of the power offset and the power threshold.