What is claimed is:

1. An enhanced node B (eNB) comprising hardware processing circuitry configured to:

transmit signaling to indicate a device-to-device (D2D) discovery zone configuration to proximity service (ProSe) enabled user equipment (UE), the signaling to indicate time and frequency resources and a periodicity of a discovery zone and to indicate operational parameters for the discovery zone, wherein the resources of the D2D discovery zone are allocated for D2D discovery signal transmission by the ProSe-enabled UEs.

2. The eNB of claim 1 wherein the signaling for the D2D discovery zone configuration indicates one or more occurrences of the discovery zone, and wherein the signaling is sent by the eNB either using dedicated radio-resource control (RRC) signaling or sent using common radio-resource control (RRC) signaling via system information blocks (SIBs).

3. The eNB of claim 1 wherein when the signaling sent by the eNB uses common RRC signaling via SIBs, the signaling sent by the eNB includes at least one of a SIB transmission and a paging transmission.

4. The eNB of claim 2 wherein the signaling for the D2D discovery zone configuration indicates at least one of:

a non-contention-based D2D discovery zone (NCB-D2D DZ) for which periodic resources are allocated for non-contention based transmission of discovery signals by only ProSe-enabled UEs in RRC connected mode; and a contention-based D2D discovery zone (CB-D2D DZ) for which periodic resources are allocated for contention-based transmission of discovery signals by any ProSe-enabled UEs including ProSe-enabled UEs in RRC connected mode, RRC idle mode and out of coverage UEs.

5. The eNB of claim 2 further configured to:

receive discovery zone loading metrics, the discovery zone loading metrics based on monitoring of discovery signals within the discovery zone by one or more ProSe-enabled UEs; and

determine whether or not to make changes to a resource allocation configuration for D2D activities based on the discovery zone loading metrics.

6. The eNB of claim 2 wherein the eNB is configured to receive D2D discovery zone configuration information of one or more neighbor eNBs, and wherein the eNB is configured to signal the D2D discovery zone configuration information of the one or more neighbor eNBs to the ProSe enabled UEs via SIB signaling.

7. The eNB of claim 2 wherein the eNB is configured to receive D2D discovery zone configuration information of one or more neighbor eNBs, and wherein based on the D2D discovery zone configuration information of the one or more neighbor eNBs, the eNB is further configured to engage in an interference reduction technique to reduce intra-cell and inter-cell interference within the discovery zone and inter-cell interference between discovery signal transmissions and uplink cellular transmissions, the technique to include one or more of:

cooperative subframe power control for D2D discovery signal transmissions wherein uplink subframe sets are configured with separate power control parameters for interference reduction between the uplink cellular transmissions and the D2D discovery signal transmissions;

transmit power level control for the D2D discovery signal transmission; cooperative cell clustering to align discovery zones of the one or more neighbor eNBs; and

geometry-based intra-cell discovery zone partitioning.

8. The eNB of claim 7 wherein the discovery zone operational parameters include at least one of a silencing factor, a transmit power control configuration, hopping related parameters and a scrambling ID.

9. The eNB of claim 8 wherein the eNB is further configured to reduce interference within the discovery zone by employing a silencing and muting protocol for discovery signal transmissions and configured to include the silencing factor in the discovery zone parameters, and

wherein the silencing and muting protocol configures the ProSe-enabled UEs with the silencing factor for use in D2D discovery signal transmission on randomly selected resources of the D2D discovery zone based on probability indicated by the silencing factor.

10. The eNB of claim 8 wherein when the discovery zone parameters comprise include the transmit power control configuration, the ProSe-enabled UEs are configured with a maximum transmit power for D2D discovery signal transmission that is lower than a transmit power specified by a respective UE category,

wherein when the discovery zone parameters include the hopping related parameters, the hopping related parameters indicate:

the parameters needed for discovery resource hopping in a contention-free D2D discovery zone;

a hopping type comprising either type 1 or type 2 hopping;

a hopping mode comprising either intra-subframe or inter-subframe hopping;

a subband size for the type 2 hopping; and

a pseudorandom sequence initialization for the type 2 hopping, and wherein when the discovery zone parameters include the scrambling identity, the ProSe enabled UEs are configured to use the scrambling identity for scrambling of a cyclic -redundancy check (CRC) mask of the D2D discovery packets, and the eNB is configured to assign a common scrambling ID per discovery group.

11. The eNB of claim 1 wherein the signaling comprise one or more of radio-resource control (RRC) and Layer 1 signaling to indicate a semi-persistent allocation of discovery resources to the ProSe enabled UEs in RRC connected mode for contention-free transmission of D2D discovery signals, and

wherein the eNB is configured to release the allocation of discovery resources by transmission of a discovery resource release.

12. The eNB of claim 11 wherein the eNB allocates the discovery resources to the ProSe enabled UEs in RRC connected mode for contention-free transmission of D2D discovery signals in response to a RRC resource request from the ProSe enabled UE; and

wherein, the eNB is further configured to release the allocation of discovery resources in response to reception of a resource release request via RRC signaling from the ProSe enabled UEs.

13. An enhanced node B (eNB) comprising hardware processing circuitry and configured to:

transmit signaling to indicate a device-to-device (D2D) discovery zone configuration to proximity service (ProSe) enabled user equipment (UE), the signaling to indicate at least time and frequency resources and a periodicity of a discovery zone;

receive discovery zone loading metrics, the discovery zone loading metrics based on monitoring of discovery signals within the discovery zone by one or more ProSe-enabled UEs; and

determine whether or not to make changes to a resource allocation configuration for D2D activities based on the discovery zone loading metrics.

14. The eNB of claim 13 wherein the discovery zone metrics include at least one of:

a number of discovery signal transmissions in a number of occurrences of the discovery zone;

a number of successfully detected discovery signals in a number of occurrences of the discovery zone; and

an indication of the interference level in a number of occurrences of the discovery zone,

wherein the eNB is further configured to determine a number of the ProSe enabled UEs based on the discovery zone loading metrics.

15. The eNB of claim 13 wherein the eNB is further configured to determine the number of the ProSe enabled UEs based on radio-resource control (RRC) signaling received from the ProSe enabled UEs during a contention-based random access (CBRA) procedure as part of an initial access procedure,

wherein the RRC signaling includes a D2D capability indication.

16. The eNB of claim 13 further configured to:

transmit a D2D counting request message; and

receive a D2D counting response message from the ProSe enabled UEs that are in radio-resource control (RRC) connected mode.

17. The eNB of claim 13 wherein the eNB is further configured to determine the number of the ProSe enabled UEs based on reception of periodic tracking area (TA) messages having a D2D capability indication transmitted by the ProSe-enabled UEs that are in RRC idle mode.

18. User Equipment (UE) enabled for proximity services (ProSe), the ProSe-enabled UE comprising hardware processing circuitry and configured to: receive device-to-device (D2D) discovery zone configuration signaling from an enhanced node B (eNB) to indicate time and frequency resources and a periodicity of a discovery zone and to indicate one or more discovery zone operational parameters; and

transmit D2D discovery signals within the resources to discover one or more other ProSe-enabled UEs.

19. The UE of claim 18 wherein when the UE is in radio-resource control (RRC) idle mode (RRC_IDLE), the UE is configured to transition to RRC connected mode (RRC_CONNECTED) to send a discovery resource request to a serving eNB, and

wherein the UE is further configured to autonomously switch back to the RRC idle mode upon reception of a resource configuration message from the serving eNB, at least for transmission in a contention-based D2D discovery zone (CB-D2D DZ).

20. The UE of claim 18 wherein the signaling for the D2D discovery zone configuration indicates one or more occurrences of the discovery zone and is sent by the eNB either using dedicated radio-resource control (RRC) signaling or using common radio-resource control (RRC) signaling via system information blocks (SIBs),

wherein the UE is further configured to

monitor the discovery zone for D2D discovery signals transmitted by other UEs; and

report discovery zone loading metrics to the eNB based on the monitored discovery signals, and

wherein the discovery zone loading metrics comprise one or more of: a count of the number of D2D discovery signals transmitted by other UEs during a number of occurrences of the discovery zone;

a count of the number of D2D discovery signals transmitted by itself during a number of occurrences of the discovery zone; and

an indication of interference level in a number of occurrences of the discovery zone.

21. The UE of claim 20 wherein when the signaling for the discovery zone configuration indicates a periodic occurrence of the discovery zone for which periodic disco very- zone resources are allocated for D2D discovery, the UE is further configured to:

monitor a number of the occurrences of the discovery zone for D2D discovery signals transmitted by other UEs; and

report the discovery zone loading metrics to the eNB based on the D2D discovery signals monitored in the occurrences of the discovery zone.

22. The UE of claim 18 wherein the UE is configured to receive signaling from the eNB indicating D2D discovery zone configuration information of one or more neighbor eNBs, and

wherein the UE is further configured to :

transmit D2D discovery signals in an indicated D2D discovery zone of the one or neighbor eNBs, and

monitor the indicated D2D discovery zone of the one or neighbor eNBs for D2D discovery signals.

23. The UE of claim 18 wherein the UE wherein for geometry-based intra-cell D2D discovery zone partitioning the UE is configured to receive signaling from the eNB indicating D2D discovery zone configuration information of a serving eNB and of one or more neighbor eNBs including discovery resources of the D2D discovery zone used for at least one of cell-center D2D UEs and cell edge D2D UEs, and

wherein the UE is further configured to select resources indicated for cell-center D2D UEs or cell edge D2D UEs for transmission of D2D discovery signals based at least on a reference signal received power (RSRP) of the serving eNB.

24. The UE of claim 20 wherein the signaling for the D2D discovery zone configuration is configured to indicate at least one of:

a non-contention-based D2D discovery zone (NCB-D2D DZ) for which periodic resources are allocated for non-contention based transmission of discovery signals by ProSe-enabled UEs in RRC connected mode; and

a contention-based D2D discovery zone (CB-D2D DZ) for which periodic resources are allocated for contention-based transmission of discovery signals by the ProSe-enabled UEs including ProSe-enabled UEs in RRC connected mode, RRC idle mode and out of coverage ProSe-enabled UEs, wherein the UE is configured to monitor any signaled of the NCB-D2D DZs and CB-D2D DZs for discovery signals transmitted by other UEs.

25. The UE of claim 20 wherein the discovery signal transmissions include a demodulation reference signal (DMRS) sequence comprising a randomly selected choice of at least one of a base sequence, a cyclic shift value and an orthogonal cover code, and

wherein the discovery zone metrics further include a number of blindly detected unique DMRS sequences.

26. A method performed by an enhanced node B (eNB) for signaling for device-to-device (D2D) discovery operations, the method comprising:

transmitting signaling to indicate a D2D discovery zone configuration to proximity service (ProSe) enabled user equipment (UE), the signaling to indicate time and frequency resources and a periodicity of a discovery zone and to indicate operational parameters for the discovery zone,

wherein the resources of the D2D discovery zone are allocated for D2D discovery signal transmission by the ProSe-enabled UEs,

wherein the signaling for the D2D discovery zone configuration indicates one or more occurrences of the discovery zone, and

wherein the signaling is sent by the eNB either using dedicated radio-resource control (RRC) signaling or sent using common radio-resource control (RRC) signaling via system information blocks (SIBs).

27. The method of claim 26 wherein when the signaling sent by the eNB uses common RRC signaling via SIBs, the signaling sent by the eNB includes at least one of a SIB transmission and a paging transmission, and

wherein the discovery zone operational parameters include at least one of a silencing factor, a transmit power control configuration, hopping related parameters and a scrambling ID.

28. A non-transitory computer-readable storage medium that stores instructions for execution by one or more processors to configure an enhanced node B (eNB) for signaling for device-to-device (D2D) discovery operations, the operations to configure the eNB to:

transmit signaling to indicate a D2D discovery zone configuration to proximity service (ProSe) enabled user equipment (UE), the signaling to indicate time and frequency resources and a periodicity of a discovery zone and to indicate operational parameters for the discovery zone,

wherein the resources of the D2D discovery zone are allocated for D2D discovery signal transmission by the ProSe-enabled UEs,

wherein the signaling for the D2D discovery zone configuration indicates one or more occurrences of the discovery zone, and

wherein the signaling is sent by the eNB either using dedicated radio-resource control (RRC) signaling or sent using common radio-resource control (RRC) signaling via system information blocks (SIBs).

29. The non-transitory computer-readable storage medium of claim 28 wherein when the signaling sent by the eNB uses common RRC signaling via SIBs, the signaling sent by the eNB includes at least one of a SIB transmission and a paging transmission, and

wherein the discovery zone operational parameters include at least one of a silencing factor, a transmit power control configuration, hopping related parameters and a scrambling ID.