Demodulation reference signal (DMRS) sequence design for device-to-device (D2D) discovery

1. An apparatus of a user equipment (UE) operable to perform device-to-device (D2D) communication, the apparatus comprising:

one or more processors configured to:

select, at the UE, a cyclic shift (ncs) that is randomly selected from a set of cyclic shifts, wherein the set of cyclic shifts consists of cyclic shift values of {0, 3, 6, 91 }

apply, at the UE, the selected cyclic shift to all demodulation reference signals (DM-RSs) in a subframe, the subframe including at least three DM-RS symbols, wherein each of the DM-RSs are associated with a D2D transmission from the UE;

encode, at the UE, the DM-RSs for transmission from the UE; and

perform D2D communication with a second UE via a physical channel between the UE and the second UE; and

memory configured to store the set of cyclic shifts.

2. The apparatus of claim 1 , further comprising a transceiver configured to transmit the DM-RSs to a second UE.

3. The apparatus of claim 1 , further comprising a transceiver configured to send the D2D transmission to a second UE.

4. The apparatus of claim 1 , wherein the UE includes an antenna, a touch sensitive display screen, a speaker, a microphone, a graphics processor, an application processor, an internal memory, or a non-volatile memory port.

5. An apparatus of a first user equipment (UE) operable to decode a device-to-device (D2D) transmission received from a second UE, the apparatus comprising:

one or more processors configured to:

detect, at the first UE, a demodulation reference signal (DM-RS) received from the second UE in a subframe, wherein the DM-RS is associated with a D2D transmission from the second UE;

determine, at the first UE, a cyclic shift (ncs) utilized to generate the DM-RS, wherein the cyclic shift has been applied to all DM-RSs in the subframe and is included in a set of cyclic shifts, the subframe including at least three DM-RS symbols, wherein the set of cyclic shifts consists of cyclic shift values of (0, 3, 6, 9}, wherein the cyclic shift used to generate the DM-RS is randomly selected from the set of cyclic shifts;

perform, at the first UE, a channel estimation based on the DM-RS and the cyclic shift to decode the D2D transmission received from the second UE; and

perform D2D communication with the second UE via a physical channel between the first UE and the second UE; and

memory configured to store the DM-RS and the set of cyclic shifts.

6. The apparatus of claim 5 , further comprising a transceiver configured to receive the DM-RS from the second UE.

7. The apparatus of claim 5 , further comprising a transceiver configured to receive the D2D transmission from the second UE.

8. The apparatus of claim 5 , wherein the one or more processors are configured to perform Type 1 D2D discovery or Type 2 D2D discovery between the first UE and the second UE.

9. The apparatus of claim 5 , wherein the first UE includes an antenna, a touch sensitive display screen, a speaker, a microphone, a graphics processor, an application processor, an internal memory, or a non-volatile memory port.

10. At least one non-transitory machine readable storage medium having instructions embodied thereon for performing device-to-device (D2D) communication at a user equipment (UE), the instructions when executed perform the following:

selecting, at the UE, a cyclic shift (ncs) that is randomly selected from a set of cyclic shifts consisting of cyclic shift values of (0, 3, 6, 9 };

applying, at the UE, the selected cyclic shift to all demodulation reference signals (DM-RSs) in a subframe, the subframe including at least three DM-RS symbols, wherein each of the DM-RSs are associated with a D2D transmission from the UE;

encoding, at the UE, the DM-RSs for transmission from the UE; and

performing D2D communication with a second UE via a physical channel between the UE and the second UE.

11. The at least one non-transitory machine readable storage medium of claim 10 , further comprising instructions when executed perform the following: encoding the DM-RSs for transmission to a second UE.

12. The at least one non-transitory machine readable storage medium of claim 10 , further comprising instructions when executed perform the following: encoding the D2D transmission for delivery to a second UE.

13. At least one non-transitory machine readable storage medium having instructions embodied thereon for decoding a device-to-device (D2D) transmission received from a second UE, the instructions when executed perform the following:

detecting, at a first UE, a demodulation reference signal (DM-RS) received from the second UE in a subframe, wherein the DM-RS is associated with a D2D transmission from the second UE;

determining, at the first UE, a cyclic shift (ncs) utilized to generate the DM-RS, wherein the cyclic shift has been applied to all DM-RSs in the subframe and is included in a set of cyclic shifts, the subframe including at least three DM-RS symbols, wherein the set of cyclic shifts consists of cyclic shift values of (0, 3, 6, 9 }, wherein the cyclic shift used to generate the DM-RS is randomly selected from the set of cyclic shifts;

performing, at the first UE, a channel estimation based on the DM-RS and the cyclic shift to decode the D2D transmission received from the second UE; and

performing D2D communication with the second UE via a physical channel between the first UE and the second UE.

14. The at least one non-transitory machine readable storage medium of claim 13 , further comprising instructions when executed perform the following: performing Type 1 D2D discovery or Type 2 D2D discovery between the first UE and the second UE.