Demodulation reference signal (dmrs) sequence design for device-to-device (d2d) discovery

Abstract

Technology for performing device-to-device (D2D) discovery is disclosed. A user equipment (UE) can identify a D2D discovery resource that is M subframes in a time domain, wherein M is a positive integer greater than one. The UE can generate K demodulation reference signal (DMRS) sequences to be transmitted from the UE for each subframe in the D2D discovery resource, wherein K is a positive integer greater than two. The UE can apply a predetermined orthogonal cover code (OCC) to each DMRS sequence. The predetermined OCC can be selected based on a value of M and a value of K. The UE can transmit the K DMRS sequences for each of the M subframes of the D2D discovery resource.

What is claimed is: 
     
         1 . A user equipment (UE) operable to perform device-to-device (D2D) discovery, the UE comprising one or more processors configured to:
 identify a D2D discovery resource of a single subframe;   generate K demodulation reference signal (DMRS) sequences to be transmitted from the UE using the D2D discovery resource, wherein K is a positive integer greater than two;   apply an orthogonal cover code (OCC) to each DMRS sequence, wherein the OCC is randomly selected from a pool of OCCs, wherein the OCCs in the pool are predefined based on a value of K; and   transmit the K DMRS sequences using the D2D discovery resource of the single subframe.   
     
     
         2 . The UE of  claim 1 , wherein the one or more processors are further configured to transmit the K DMRS sequences in a D2D discovery message using a physical uplink shared channel (PUSCH). 
     
     
         3 . The UE of  claim 1 , wherein the one or more processors are further configured to randomly select the D2D discovery resource from a D2D discovery resource pool, wherein the D2D discovery resource pool is allocated by an evolved node B (eNB) and indicated to the UE via a system information block (SIB). 
     
     
         4 . The UE of  claim 1 , wherein the one or more processors are further configured to receive an indication of the D2D discovery resource from an evolved node B (eNB) via radio resource control (RRC) signaling. 
     
     
         5 . The UE of  claim 1 , wherein the one or more processors are further configured to transmit the K DMRS sequences using the single subframe of the D2D discovery resource. 
     
     
         6 . The UE of  claim 1 , wherein the UE is configured to perform Type 1 D2D discovery or Type 2 D2D discovery. 
     
     
         7 . The UE 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. 
     
     
         8 . A user equipment (UE) operable to perform device-to-device (D2D) discovery, the UE comprising one or more processors configured to:
 identify a D2D discovery resource that is M subframes in a time domain, wherein M is a positive integer greater than one;   generate two demodulation reference signal (DMRS) sequences to be transmitted from the UE for each subframe in the D2D discovery resource;   apply an orthogonal cover code (OCC) to each DMRS sequence, wherein the OCC is randomly selected from a pool of OCCs, wherein the OCCs in the pool are predefined based on a value of M; and   transmit the two DMRS sequences for each of the M subframes of the D2D discovery resource.   
     
     
         9 . The UE of  claim 8 , wherein the one or more processors are further configured to transmit the two DMRS sequences in a D2D discovery message using a physical uplink shared channel (PUSCH). 
     
     
         10 . The UE of  claim 8 , wherein the one or more processors are further configured to randomly select the D2D discovery resource from a D2D discovery resource pool allocated by an evolved node B (eNB). 
     
     
         11 . The UE of  claim 8 , wherein the one or more processors are further configured to transmit the two DMRS sequences for each of the M subframes. 
     
     
         12 . A method for performing device-to-device (D2D) discovery, the method comprising:
 identifying, at a user equipment (UE), a D2D discovery resource that is M subframes in a time domain, wherein M is a positive integer greater than one;   generating K demodulation reference signal (DMRS) sequences to be transmitted from the UE for each subframe in the D2D discovery resource, wherein K is a positive integer greater than two;   applying an orthogonal cover code (OCC) to each DMRS sequence, wherein the OCC is randomly selected from a pool of OCCs, wherein the OCCs in the pool are predefined based on a value of M and a value of K; and   transmitting the K DMRS sequences for each of the M subframes of the D2D discovery resource from the UE.   
     
     
         13 . The method of  claim 12 , wherein the K DMRS sequences for each of the M subframes is transmitted using a physical uplink shared channel (PUSCH). 
     
     
         14 . The method of  claim 12 , wherein Type 1 D2D discovery or Type 2 D2D discovery is performed at the UE. 
     
     
         15 . A user equipment (UE) operable to perform device-to-device (D2D) discovery, the UE comprising:
 a selection module configured to:
 select a first demodulation reference signal (DMRS) sequence from a pool of DMRS sequences for D2D discovery; and 
 select a first D2D discovery resource from a first D2D discovery resource pool allocated by an evolved node B, wherein the selection module is stored in a digital memory device or is implemented in a hardware circuit; and 
   a communication module configured to transmit the first DMRS sequence from the UE using the first D2D discovery resource selected from the D2D discovery resource pool, wherein a second DMRS sequence is subsequently transmitted from the UE using a second D2D discovery resource that is selected from a second D2D discovery resource pool allocated by the eNB, wherein the communication module is stored in a digital memory device or is implemented in a hardware circuit.   
     
     
         16 . The UE of  claim 15 , wherein the selection module is further configured to:
 randomly select the first DMRS sequence from the pool of DMRS sequences; and   select the second D2D discovery resource based on the first D2D discovery resource.   
     
     
         17 . The UE of  claim 15 , wherein the communication module is further configured to transmit a DMRS sequence in each discovery subzone within a configured discovery period. 
     
     
         18 . The UE of  claim 15 , wherein the second DMRS sequence is identical to the first DMRS sequence 
     
     
         19 . The UE of  claim 15 , further comprising a generation module configured to generate the second DMRS sequence by performing DMRS sequence hopping on the first DMRS sequence, wherein the DMRS sequence hopping utilizes at least one of: base sequence hopping, cyclic shift hopping, or orthogonal code cover hopping, wherein the generation module is stored in a digital memory device or is implemented in a hardware circuit. 
     
     
         20 . The UE of  claim 15 , wherein the selection module is further configured to randomly select the first D2D discovery resource from the D2D discovery resource pool, wherein the second D2D discovery resource is deterministically associated with the first D2D discovery resource. 
     
     
         21 . The UE of  claim 15 , wherein the selection module is further configured to randomly select the first DMRS sequence and the second DMRS sequence at substantially a same time, wherein the second DMRS sequence is distinguishable from the first DMRS sequence. 
     
     
         22 . The UE of  claim 15 , wherein the selection module is further configured to randomly select the first D2D discovery resource and the second D2D discovery resource at substantially a same time, wherein the second D2D discovery resource is not associated with the first D2D discovery resource. 
     
     
         23 . The UE of  claim 15 , wherein the UE is configured to perform Type 1 D2D discovery or Type 2 D2D discovery. 
     
     
         24 . The UE of  claim 15 , further comprising a discovery module configured to perform the D2D discovery using a subset of the pool of DMRS sequences, wherein each DMRS sequence in the subset is associated with a configured number of cyclic shift (CS) and a configured number of orthogonal cover codes (OCCs), wherein the discovery module is stored in a digital memory device or is implemented in a hardware circuit.