HK1233110B - Adaptive silencing mechanism for device-to-device (d2d) discovery - Google Patents

Description

Adaptive Silencing Mechanism for Device-to-Device (D2D) Discovery

Background Art

Proximity-based applications and services represent a rapidly growing social technology trend that may have a significant impact on the evolution of cellular wireless/mobile broadband technologies. These services are based on the awareness of two devices or two users that are close to each other, and these services may include applications such as public safety operations, social networking, mobile commerce, advertising, gaming, and the like. Device-to-device (D2D) discovery is the first step in enabling D2D services. With direct D2D communication, user equipments (UEs) can communicate directly with each other without involving a base station or enhanced node B (eNB). One problem with D2D communication is device discovery to enable D2D services. Device discovery involves discovering one or more other discoverable UEs within the communication range of the D2D communication. Device discovery also involves being discovered by one or more other discoverable UEs within the communication range of the D2D communication. There are many unresolved issues regarding device discovery for D2D communication, including resource allocation and signaling, especially for Proximity Services (ProSe) D2D discovery.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present disclosure will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which together illustrate features of the present disclosure by way of example; and wherein:

FIG1 illustrates a portion of an end-to-end network architecture of an LTE network according to some embodiments;

FIG2 illustrates a structure of a resource grid including a discovery zone for D2D communication according to some embodiments;

FIG3A illustrates reporting of discovery zone metrics according to some embodiments;

FIG3B illustrates counting ProSe-enabled UEs using a random access channel (RACH) according to some embodiments;

FIG4 illustrates a process of counting ProSe-enabled UEs for a UE in Radio Resource Control (RRC) Connected mode;

FIG5 illustrates cooperative uplink subframe power control for D2D discovery signaling according to some embodiments;

FIG6 illustrates an eNB triggering contention-free D2D discovery zone resources according to some embodiments;

FIG7 illustrates UE triggering of contention-free D2D discovery zone resources according to some embodiments;

FIG8 illustrates the functionality 800 of computer circuitry of a UE enabled for proximity services; and

FIG9 illustrates a functional block diagram of a wireless communication device in accordance with some embodiments.

Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will however be understood that no limitation of the scope of the invention is intended.

DETAILED DESCRIPTION

Before disclosing and describing some embodiments, it is to be understood that the claimed subject matter is not limited to the specific structures, processing operations, or materials disclosed herein, but is extended to equivalent forms thereof recognized by those skilled in the relevant art. It should also be understood that the terminology employed herein is used only for the purpose of describing specific examples and is not intended to be limiting. The same reference numerals in different figures represent the same elements. The sequence numbers provided in the flowcharts and processes are provided for the purpose of clearly illustrating the operations and do not necessarily indicate a specific order or sequence.

Example Embodiments

The following provides a preliminary overview of the technology embodiments, and specific technology embodiments are described in detail later. The preliminary summary is intended to help readers understand the technology more quickly, but is not intended to identify key features or essential features of the technology, nor is it intended to limit the scope of the claimed subject matter.

Embodiments disclosed herein provide a signaling design for supporting LTE Proximity Services (ProSe) D2D discovery. In these embodiments, the UE may be a ProSe-enabled UE configured for D2D discovery signaling and D2D communication. Some embodiments provide configuration of a D2D discovery zone (i.e., a discovery resource pool) by dividing the D2D discovery zone into contention-based and non-contention-based discovery zones, both for network-wide and cell-specific configuration of the discovery zone. Some embodiments provide a UE feedback mechanism for providing information about the load of the discovery zone to the eNB. Some embodiments provide options for supporting inter-cell/eNB discovery. Some embodiments provide for using and configuring a muting factor for random muting/adaptive random muting for transmitting D2D discovery packets. Some embodiments provide signaling content including: discovery zone configuration, muting factor, transmit power control configuration, hopping-related parameters, and a scrambling identifier for scrambling the cyclic redundancy check (CRC) mask of the discovery packet. Some embodiments provide a signaling mechanism for the above signaling content. Some embodiments provide for static provisioning and/or pre-configuration of D2D discovery resources. Some embodiments provide network and UE behaviors to support contention-free direct device discovery. These embodiments are discussed in detail below.

1 is a portion of an end-to-end network architecture of an LTE network with various network components according to some embodiments. The network 100 includes a radio access network (RAN) (e.g., E-UTRAN or Evolved Universal Terrestrial Radio Access Network as depicted) 100 and a core network 120 (e.g., shown as an Evolved Packet Core (EPC)) coupled together via an S1 interface 115. For convenience and brevity, only the core network 120 and a portion of the RAN 100 are shown.

The core network 120 includes a mobility management entity (MME) 122, a serving gateway (serving GW) 124, and a packet data network gateway (PDN GW) 126. The RAN includes an evolved Node B (eNB) 104 (which can operate as a base station) for communicating with a user equipment (UE) 102. The eNB 104 can include a macro eNB and a low power (LP) eNB. The UE 102 can be ProSe-enabled.

The MME is functionally similar to the control plane of a traditional Serving GPRS Support Node (SGSN). The MME manages mobility aspects of access, such as gateway selection and tracking area list management. The Serving GW 124 terminates the interface toward the RAN 100 and routes data packets between the RAN 100 and the core network 120. In addition, the Serving GW 124 can be the local mobility anchor point for inter-eNB handovers and can also provide an anchor point for inter-3GPP mobility. Other responsibilities may include lawful interception, charging, and some policy enforcement. The Serving GW 124 and the MME 122 can be implemented in one physical node or in separate physical nodes. The PDN GW 126 terminates the SGi interface toward the Packet Data Network (PDN). The PDN GW 126 routes data packets between the EPC 120 and external PDNs and can be a key node for policy enforcement and charging data collection. The PDN GW 126 can also provide an anchor point for mobility for non-LTE accesses. The external PDN may be any type of IP network, as well as an IP Multimedia Subsystem (IMS) domain. The PDN GW 126 and the Serving GW 124 may be implemented in one physical node or in separate physical nodes.

The (macro and micro) eNBs 104 terminate the air interface protocols and may be the first point of contact for the UE 102. In some embodiments, the eNBs 104 may fulfill various logical functions of the RAN 100 including, but not limited to, RNC (Radio Network Controller) functions, such as radio bearer management, uplink and downlink dynamic radio resource management and data packet scheduling, and mobility management.

The S1 interface 115 is an interface that separates the RAN 100 and the EPC 120. This interface is divided into two parts: S1-U and S1-MME. S1-U carries traffic data between the eNB 104 and the Serving GW 124, and S1-MME is a signaling interface between the eNB 104 and the MME 122. The X2 interface is an interface between eNBs 104. The X2 interface consists of two parts: X2-C and X2-U. X2-C is a control plane interface between eNBs 104, while X2-U is a user plane interface between eNBs 104.

With cellular networks, LP cells are typically used to extend coverage to indoor areas where outdoor signals don't reach well, or to increase network capacity in areas with high phone usage (e.g., train stations). As used herein, the term low-power (LP) eNB refers to any suitable lower-power eNB used to implement narrower cells (narrower than macrocells) (e.g., femtocells, picocells, or microcells). Femtocell eNBs are typically provided by mobile network operators to their residential or enterprise customers. Femtocells are typically the size of a residential gateway or smaller and are typically connected to a user's broadband line. Once powered on, femtocells connect to the mobile operator's mobile network and provide additional coverage for residential femtocells, typically with a range of 30 to 50 meters. Therefore, since the LP eNB is coupled via PDN GW 126, the LP eNB may be a femto eNB. Similarly, picocells are wireless communication systems that typically cover small areas, such as within buildings (offices, shopping malls, train stations, etc.) or, more recently, on airplanes. A picocell eNB can typically connect to another eNB via an X2 link, for example, to a macro eNB via its base station controller (BSC) functionality. Therefore, since an LP eNB is coupled to a macro eNB via the X2 interface, the LP eNB can be implemented as a picocell eNB. A picocell eNB or other LP eNB can include some or all of the functionality of a macro eNB. In some cases, this may be referred to as an access point base station or enterprise femtocell.

In some LTE embodiments, the physical downlink shared channel (PDSCH) carries user data and higher-layer signaling to UE 102. The physical downlink control channel (PDCCH) carries information about, among other things, the transport format and resource allocation associated with the PDSCH channel. The PDCCH also informs UE 102 of the transport format, resource allocation, and H-ARQ information associated with the uplink shared channel. Typically, downlink scheduling (allocation of control and shared channel resource blocks to UEs within a cell) is performed at eNB 104 based on channel quality information fed back to eNB 104 from UE 102. Downlink resource allocation information is then sent to UE 102 on the physical downlink control channel (PDCCH) intended for (and potentially allocated to) the UE.

PDCCH uses CCE (control channel elements) to convey control information. Before being mapped to resource elements, PDCCH complex symbols are first grouped into quadruplets, and then the quadruplets are arranged using a sub-block interleaver for rate matching. Each PDCCH is transmitted using one or more of these control channel elements (CCEs), where each CCE corresponds to 9 groups of physical resource elements (called resource element groups (REGs)), with 4 physical resource elements in each group. 4 QPSK symbols are mapped to each REG. Based on the size of the DCI and the channel conditions, one or more CCEs can be used to transmit the PDCCH. Four or more different PDCCH formats may be defined in LTE, with different numbers of CCEs (e.g., aggregation levels, L=1, 2, 4, or 8).

According to some embodiments, a ProSe-enabled UE 102 may be arranged for device-to-device (D2D) communication, including D2D discovery of other UEs 102 for direct D2D communication. In these embodiments, the ProSe-enabled UE 102 may transmit a discovery signal 101 within a discovery resource to discover one or more other ProSe-enabled UEs. These embodiments will be discussed in more detail below.

Figure 2 shows the structure of a resource grid including a discovery zone for D2D communications according to some embodiments. The grid depicted is a time-frequency grid (referred to as a resource grid), which is the physical resource for downlink or uplink in each time slot. The smallest time-frequency unit in the resource grid is represented as a resource element (RE). The resource grid includes multiple resource blocks (RBs), which describe the mapping of certain physical channels to resource elements. Each resource block includes a set of resource elements, and in the frequency domain, each resource block represents the minimum amount of resources that can be allocated, but the scope of the embodiments is not limited in this respect. There are several different physical channels that are communicated using such resource blocks. The resource grid shown in Figure 2 may include an LTE operating area 202, which may include multiple physical RBs (PRBs) used by the RAN 100.

According to some embodiments, UE 102 ( FIG. 1 ) may receive signaling from eNB 104 ( FIG. 1 ) indicating a discovery zone 204 within LTE operating area 202. Discovery zone 204 may include a plurality of PRBs 206 of discovery resources. UE 102 may transmit discovery signals or discovery packets 101 ( FIG. 1 ) within some of the PRBs 206 within discovery zone 204 for reception by one or more other UEs for D2D discovery. In some embodiments, the resources allocated for D2D discovery may be physical uplink shared channel (PUSCH) resources, although the scope of the embodiments is not limited in this respect.

A PRB may be associated with a specific time slot of a subframe in the time dimension and a specific set of frequency subcarriers in the frequency dimension. For example, each PRB may be identified by an RB index and a subframe index. In some embodiments, a discovery packet 101 may be sent within M subframes of N resource blocks, where M and N are at least one and may be greater than one. These embodiments are described in more detail below.

In some embodiments, a PRB may include twelve subcarriers in the frequency domain × 0.5 ms in the time domain (i.e., one time slot). PRBs may be allocated in pairs (in the time domain), but this is not required. In some embodiments, a PRB may include multiple REs. REs may include one subcarrier × one symbol. When a regular CP is used, an RB includes seven symbols. When an extended CP is used, an RB includes six symbols. A delay extension exceeding the length of the regular CP indicates that an extended CP is used. Each subframe may be one millisecond (ms), and a frame may include ten such subframes.

There are two different approaches to D2D discovery: restricted/closed D2D discovery and open D2D discovery. Restricted/closed D2D discovery is suitable for use cases where discoverable devices can only be discovered by a selected set of ProSe-enabled discovery devices. Another implication of closed device discovery is to consider the following scenario: the discovering device attempts to discover specific (one or more) ProSe-enabled devices (one or more ProSe-enabled devices from a set of ProSe-enabled devices). Therefore, for this use case, it will be assumed that the discovering device knows the ProSe-enabled devices it wants to discover within its proximity.

Compared to closed D2D discovery, open device discovery considers use cases where a discoverable device may want to be discovered by other ProSe-enabled devices in its vicinity. From the perspective of the discovering device, open device discovery implies that it can be assumed that the discovering device knows the identities of other ProSe-enabled devices before discovery. Therefore, the device discovery mechanism of open discovery should aim to discover as many ProSe-enabled devices in its vicinity as possible.

For open D2D discovery, the eNB 104 has limited control over the discovery process between UEs 102. Specifically, the eNB 104 can allocate a discovery resource in the form of a D2D discovery area to the UE 102 for sending discovery information. The discovery information can be in the form of a discovery packet or discovery sequence with payload information. The content of discovery-related information that users expect to share with each other may be high because the design will need to send a unique ID for device identification, service identification, etc. (e.g., 48 bits or more) as a data payload protected by a CRC. Depending on the payload size and the overall discovery performance requirements, the number of resource blocks (RBs) required for discovery packet transmission in the open D2D discovery design (denoted by ) can be 1 or greater.

In some embodiments, the discovery area may include multiple occurrences of periodic discovery areas, each discovery area including a number of RBs in the frequency domain and a number of subframes in the time domain. Figure 2 shows an example of a discovery area 204 within the LTE operating area 202, where and represent the number of allocated RBs, the starting RB index, the number of subframes, and the starting subframe index of each discovery area, respectively. Information about the division of these D2D discovery areas can be semi-statically signaled by the eNB using RRC signaling or through a system information block (SIB) for scenarios within network coverage. For partial network coverage scenarios, such information can be forwarded by the coordinator UE to UEs outside network coverage. For scenarios outside network coverage, the discovery area can be predefined or broadcast by a centralized D2D device.

In some embodiments, the sum parameter is not included in the D2D zone configuration message. Instead, from a system perspective, the entire system bandwidth except for the PUCCH region (at the edge of the frequency band) can be designed to be reserved specifically for D2D discovery, but the scope of the embodiments is not limited in this respect. In some embodiments, the parameter can be configured as the period of D2D discovery zone allocation.

Even for the case of UE-based open discovery, it would be beneficial to utilize possible network assistance in UE-specific discovery resource allocation for sending discovery signals for UEs in RRC_CONNECTED mode, thereby improving the efficiency of the discovery process. In this regard, each D2D discovery zone (D2D-DZ) or discovery resource pool can also be divided into two orthogonal time-frequency zones: (1) a non-contention-based D2D DZ (NCB-D2D DZ), for which the eNB sends periodic resources for sending discovery signals and which is accessible to D2D UEs in RRC_CONNECTED mode; and (2) a contention-based D2D DZ (CB-D2D DZ) (also referred to as a discovery resource pool for UE autonomous resource selection or a type I discovery resource pool). Generally, this zone is available to all D2D UEs (including out-of-coverage UEs), where D2D-enabled UEs follow a purely contention-based transmission of discovery signals. Furthermore, the D2D discovery resources used for the CB-D2D DZ can be further divided into two parts, referred to as part A and part B, to enable D2D discovery and to roughly indicate the size of the required D2D communication resources (e.g., the number of subframes used for D2D communication) based on the amount of D2D data buffered on the UE side (particularly due to the fact that D2D communication operations can follow the D2D discovery process). The usage of D2D discovery resources in a group indicates the tendency of a large amount of resources relative to a predetermined threshold.

According to some embodiments, D2D discovery zones may be configured in two different ways: network-wide D2D discovery zones and cell-specific D2D discovery zones, which are described in detail below. For network-wide discovery zones, a common set of time-frequency resources may be reserved for D2D discovery across the entire network. This configuration may be different between different Public Land Mobile Networks (PLMNs), thereby enabling a certain degree of flexibility in resource allocation for the respective operators. Discovery zones may be configured by each PLMN via Operation, Administration and Maintenance (OAM) tools. The network-wide configuration of the discovery zones may be signaled in a variety of ways. The exact resource allocation may be determined based on statistics of the number of ProSe-enabled UEs in the network, their respective capacities and locations (up to Tracking Area (TA) granularity). This information may be available at the D2D server, and the D2D server may inform the eNB of the exact resource configuration via the Mobility Management Entity (MME).

For cell-specific discovery zones, each eNB 104 can use information about the current number of active ProSe-enabled UEs 102 and the interference scenario to determine the exact resource configuration of the cell-specific discovery zone or discovery resource pool. Some of this information can be obtained via periodic/time-triggered/on-demand feedback from ProSe-enabled UEs 102 participating in the discovery process. To enable inter-eNB D2D discovery, a certain level of coordination exists between neighbor eNBs, and this level of coordination can be achieved by exchanging information about the configuration of the discovery zone between neighbor eNBs over the X2 interface.

According to an embodiment, the eNB 104 may send signaling indicating the D2D discovery zone configuration to the ProSe-enabled UE 102. The signaling may indicate the time and frequency resources and period of the discovery zone 204, and may indicate the operating parameters of the discovery zone 204. Resources of the D2D discovery zone 204 may be allocated for D2D discovery signal transmission by the ProSe-enabled UE 102.

In some embodiments, the D2D discovery zone configuration signaling may indicate one or more occurrences of the discovery zone 204, and the D2D discovery zone configuration signaling may be sent semi-statically using radio resource control (RRC) signaling or using SIBs by the eNB 104. In the example shown in FIG2 , the discovery zone 204 includes a plurality of PRBs 206 within the LTE operating area 202, and the discovery zone 204 may occur periodically or regularly.

In some embodiments, the signaling is sent by the eNB using dedicated RRC signaling or using public radio resource control (RRC) signaling (i.e., SIB signaling) via a SIB. When the signaling sent by the eNB uses public RRC signaling via a SIB, the signaling sent by the eNB may include at least one of SIB transmission and paging transmission. In some embodiments, the configuration information may be added to an existing SIB (e.g., in accordance with LTE Release 11) or signaled via a newly defined SIB (e.g., in accordance with a subsequent LTE release).

For both network-wide and cell-specific discovery area allocation signaling, the network should be able to signal this information to the UE in both RRC_CONNECTED and RRC_IDLE operating modes. For network-wide D2D discovery area allocation, different signaling mechanisms may be applicable. In some embodiments, existing system information blocks (SIBs) (e.g., SIB2) may be used to signal D2D discovery area configuration information, including the quieting factor and other relevant cell-wide or network-wide parameters discussed in detail below.

In some embodiments, the discovery zone 204 relates to or considers a discovery period. In some embodiments, contention-based D2D discovery is referred to or considered as type 1 discovery, while non-contention-based D2D discovery may be referred to or considered as type 2 discovery.

In some embodiments, the D2D discovery zone configuration signaling indicates at least one of a non-contention-based D2D discovery zone (NCB-D2D DZ) and a contention-based D2D discovery zone (CB-D2D DZ), wherein for the NCB-D2D DZ, periodic resources are allocated for only ProSe-enabled UEs in RRC connected mode to transmit the discovery signal 101 in a non-contention-based manner, and for the CB-D2D DZ, periodic resources are allocated for any ProSe-enabled UE (including UEs in RRC connected mode, RRC idle mode, and out-of-coverage) to transmit the discovery signal 101 in a contention-based manner. In these embodiments, the non-contention-based D2D discovery zone may be designated for ProSe-enabled UEs in RRC connected mode to transmit the discovery signal 101 according to the non-contention-based technique. In some embodiments, the ProSe-enabled UE in RRC connected mode may be allocated specific discovery resources based on the non-contention D2D discovery zone for transmitting the discovery signal 101. In some embodiments, the D2D discovery zone configuration signaling may indicate that the discovery zone 204 is divided into a non-contention-based D2D discovery zone and a contention-based D2D discovery zone.

In some of these embodiments, a contention-based D2D discovery zone may be designated for any ProSe-enabled UE to transmit a discovery signal 101 according to a purely contention-based technique. In these embodiments, the ProSe-enabled UE is not allocated specific discovery resources for contention-based transmission of the discovery signal 101. ProSe-enabled UEs utilizing the contention-based D2D discovery zone may include ProSe-enabled UEs in RRC connected mode, ProSe-enabled UEs in RRC idle mode, and ProSe-enabled UEs out of coverage.

In some of these embodiments, the eNB 104 may provide D2D discovery resource signaling, and both contention-based and contention-free D2D discovery resources may be divided and configured by the eNB. In some embodiments, this division may be logical. The actual division of resources is ultimately the responsibility of the network or the eNB (i.e., implementation-dependent). In some embodiments, some physical resources overlap between the two zones/resource pools, but the scope of the embodiments is not limited in this respect.

In some embodiments, application layer signaling may be used to signal the D2D discovery zone configuration. In these embodiments, the D2D server may signal the D2D discovery zone configuration during the D2D registration of the ProSe-enabled UE. Changes to the D2D discovery zone configuration may be sent from the D2D server to the ProSe-enabled UE via an application layer configuration message.

In some embodiments, non-access stratum (NAS) signaling may be used to signal the D2D transmission zone configuration. In these embodiments, the mobility management entity (MME) may signal the D2D discovery zone configuration during the D2D registration of a ProSe-enabled UE with a D2D server. In these embodiments, the UE or the D2D server may request the discovery zone information. For both signaling options (application layer or NAS signaling), supporting contention-free resource allocation to RRC_CONNECTED UEs may be less efficient because the discovery zone resources are managed by the MME rather than the eNB. Therefore, dynamic resource allocation is not preferred due to the signaling overhead in the core network.

FIG3A illustrates reporting of discovery zone metrics according to some embodiments. In these embodiments, the eNB 104 ( FIG1 ) may be configured to receive discovery zone load metrics based on monitoring of discovery signals 101 ( FIG1 ) within a discovery zone 204 ( FIG2 ) by one or more ProSe-enabled UEs 102 ( FIG1 ). The eNB 104 may determine whether to change resource allocation configurations for D2D activities based on the discovery zone load metrics. In these embodiments, the ProSe-enabled UE 102 may monitor the discovery zone 204 for D2D discovery signals 101 transmitted by other ProSe-enabled UEs 102 and report the discovery zone load metrics to the eNB 104. Based on the discovery zone load metrics, the eNB 104 may make changes to resource allocation configurations for D2D activities, including resources for D2D discovery and resources for D2D communication. In some embodiments, based on the discovery zone load metrics, the eNB 104 may make changes to optimize the resource allocation configurations for D2D activities. For example, the eNB 104 may change the size of the resource pool for D2D activity and may allocate subsequent discovery zone resources and resources for subsequent D2D communications based on the discovery zone load metric. Based on the discovery zone load metric, the eNB 104 may also apply or suppress one or more interference control techniques, for example, by changing interference suppression parameters (e.g., random muting or random probability transmission). As shown in FIG3A , the ProSe-enabled UE 102 may receive signaling 312 indicating a discovery zone configuration from the eNB 104. The UE 102 may monitor the discovery zone in operation 313 and may report the discovery zone metric in a message 314.

In some embodiments, the discovery zone metric includes a count (e.g., a count value) of discovery signal transmissions in multiple occurrences of the discovery zone. In some embodiments, the discovery zone metric also includes the number of unique discovery signal transmissions, and the eNB may determine the number of ProSe-enabled UEs 102 based on the discovery zone load metric. In some embodiments, the discovery zone metric may include at least one of the following: the number of discovery signal transmissions in multiple occurrences of the discovery zone; the number of discovery signals successfully detected in multiple occurrences of the discovery zone; and at least one of the interference levels in multiple occurrences of the discovery zone. In some of these embodiments, the ProSe-enabled UE may distinguish discovery signal transmissions of other UEs based on DMRS, and the discovery zone metric may include some blindly detected unique DMRS sequences or unique cyclic shift values.

In these embodiments, the UE may be configured to provide feedback on the configuration of the D2D discovery zone. For the case of cell-specific discovery zone configuration, the eNB may receive information about the load in the cell from ProSe-enabled UEs participating in the discovery process. However, the eNB may only know the number of such ProSe-enabled UEs in RRC_CONNECTED mode. The eNB may not know the number of RRC_IDLE mode UEs participating in D2D discovery within its service area. Some embodiments provide the eNB with information about the load of the discovery zone via feedback from enabled UEs.

In some embodiments, in the form of a paging response, a ProSe-enabled UE may report the number of transmissions in the past N discovery zones, where N may be a predetermined or configurable parameter. Since the paging cycle may be configured in a UE-specific manner for different groups of UEs that are allocated different subframes for monitoring paging, the number of UEs that initiate a random access (RA) procedure as a paging response to provide this feedback may be managed by the eNB. Note that given the configured low duty cycle of the discovery zones, it may not be necessary for the eNB to request this feedback from all RRC_IDLE mode UEs during the same paging subframe for estimating the load on the discovery zones. Since the quieting factor is configurable by the eNB, its impact may be taken into account by the eNB when deriving this estimate.

When the eNB requires a UE or a group of UEs to report feedback on the number of transmissions in the past N discovery zones, the request for this metric can be added by the eNB to the paging message and enabled by the eNB. In addition, the eNB can know the number of RRC_CONNECTED mode UEs participating in D2D discovery by using the above mechanism or through feedback requests indicated by dedicated RRC or MAC CE signaling.

In some other embodiments, the UE may report discovery-related metrics or measurements, which are similar to or part of a Minimization Driving Test (MDT) report. In idle mode, the UE stores and accumulates the measurements and reports the recorded measurements once the UE is connected. In connected mode, the UE may report discovery-related measurements in a periodic or event-triggered manner. Since the report is not immediate in idle mode, it may not be necessary to include a timestamp indicating the moment when the measurement result was recorded. In addition, detailed location-related information (e.g., cell index or GPS information) may also be included. For discovery-related metrics or measurements, as described above, the number of transmissions in the past N discovery zones may be reported. Alternatively, the interference level or the number of successfully detected D2D discovery packet transmissions may be reported. For example, (for PUSCH-based discovery packet transmission) assuming that the discovery packet transmission uses a randomly selected DM-RS library sequence and/or cyclic shift, the UE may report the number of blindly detected unique DM-RS sequences or cyclic shifts averaged or summed for the last N1 D2D discovery zones, where N1 may be predefined or configurable.

3B illustrates counting ProSe-enabled UEs using a random access channel (RACH) according to some embodiments. In these embodiments, as part of an initial access procedure, the eNB 104 may determine the number of ProSe-enabled UEs 102 based on radio resource control (RRC) signaling received from the ProSe-enabled UE 102 during a contention-based random access (CBRA) procedure 300 (operation 308). The RRC signaling may, for example, include transmitting a D2D capability indication of the ProSe-enabled UE 102. In these embodiments, the eNB 104 may determine whether to make changes to the resource allocation configuration for D2D activity based on a discovery area load metric and the number of ProSe-enabled UEs 102 determined based on the RRC signaling.

In these embodiments, RACH is used for D2D UE counting: Counting of ProSe-enabled (i.e., D2D-capable) UEs is performed during the UE's initial contention-based random access (CBRA) procedure (operations 302, 304, 306, 308, and 310). In these embodiments, the UE's ProSe capabilities may be included in the message sent in operation 308. These embodiments may be used to count RRC_CONNECTED mode UEs as well as RRC_IDLE mode UEs.

FIG4 illustrates a process for counting ProSe-enabled UEs in radio resource control (RRC) connected mode. In these embodiments, the eNB 104 may be configured to send a D2D counting request message (operation 402) and receive a D2D counting response message (operation 404) from the ProSe-enabled UE 102 in radio resource control (RRC) connected mode. In these embodiments, the D2D counting response message 404 may indicate that the responding UE is a ProSe-enabled UE that allows the eNB 104 to roughly estimate the number of ProSe-enabled UEs based on the number of received D2D counting response messages 404. In some of these embodiments, the D2D counting response message 404 may indicate that the UE in RRC connected mode is not ProSe-enabled.

In some embodiments, the D2D counting request message (operation 402) may include multiple dedicated RACH preambles allocated for D2D counting, and the D2D counting response message (operation 404) may include one of the RACH preambles selected by the ProSe-enabled UE 102 and sent within the allocated access slot (e.g., RACH time/frequency resource).

In these embodiments, a set of dedicated RACH preambles may be included in the D2D Counting Request message. Upon receiving a Counting Request for D2D UE counting purposes from the network, a D2D-capable UE responds by sending a RACH preamble selected from a pool of RACH preambles allocated for D2D UE counting purposes; the UE transmits the selected preamble on the allocated access slot (RACH channel time/frequency resource). Note that a relatively rough estimate of the number of D2D-capable UEs compared to the current configuration (which can be obtained by comparing to a certain threshold number for the current D2D resource configuration) may be sufficient to determine whether D2D discovery resources need to be added or reduced. A very accurate count of a large number of UEs is not required. Therefore, by allocating a number of preamble signature-slot combinations similar to or only slightly greater than the threshold number, the required information is straightforward to derive.

In these embodiments, counting D2D-capable UEs in RRC_CONNECTED mode may be sufficient in some cases of optimized discovery resource allocation due to the fact that discovery signal resources are typically allocated in a semi-static manner, and due to the lack of an RRC context in the radio access network, any D2D-capable UE in RRC_IDLE mode must use contention-based resources for D2D discovery. The network has the ability to gradually adjust resources based on detected D2D resource usage statistics and the likelihood of collisions. Therefore, as defined in the section on MBMS counting procedures, the E-UTRAN first initiates the procedure by sending a D2DCountingRequest message. Upon receiving the D2DCountingRequest message, the D2D discovery-capable UE in RRC_CONNECTED mode will send a D2DCountingResponse message.

In some embodiments, the eNB may determine the number of ProSe-enabled UEs 102 based on RRC messages indicating discovery resource release sent by ProSe-enabled UEs in RRC connected mode. In some of these embodiments, even if the ProSe-enabled UEs in RRC_CONNECTED mode have not been configured with dedicated discovery resources, these UEs may still send RRC messages indicating discovery resource release. This information may help the eNB estimate the number of ProSe-enabled UEs in RRC_CONNECTED mode for residual D2D discovery, thereby optimizing resource allocation for RRC_CONNECTED mode UEs.

In some embodiments, the eNB may determine the number of ProSe-enabled UEs 102 based on receiving a periodic Tracking Area (TA) message with a D2D capability indication sent by a ProSe-enabled UE in RRC idle mode. In these embodiments, the ProSe-enabled UE may be configured to add a D2D capability indication to the periodic Tracking Area (TA) message.

In some embodiments, a ProSe-enabled UE may be configured to receive device-to-device (D2D) discovery zone configuration signaling from an enhanced Node B (eNB), the D2D discovery zone configuration signaling indicating time and frequency resources and a periodicity of the discovery zone, and indicating one or more discovery zone operating parameters. In some embodiments, when the UE is in radio resource control (RRC) idle mode (RRC_IDLE), the UE may transition to RRC connected mode (RRC_CONNECTED) to send a discovery resource request to the eNB. Upon receiving the resource configuration message from the eNB, the UE may autonomously switch back to RRC idle mode, at least for transmission in a contention-based D2D discovery zone (CB-D2D DZ).

In some embodiments, the eNB 104 may be configured to exchange D2D discovery zone configuration information with one or more neighbor eNBs. The eNB 104 may be configured to signal (e.g., via signaling) the D2D discovery zone configuration information of one or more neighbors to a ProSe-enabled UE. In these embodiments, a certain level of coordination between neighbor eNBs may support inter-eNB discovery, particularly for the case of cell-specific configuration of D2D discovery zones. In some embodiments, the eNB 104 may exchange information regarding the configuration of D2D discovery zones in its respective cells. The D2D discovery configuration of the neighbor cells may be signaled to the UE 102 by the respective serving cell. In some alternative embodiments, the serving cell may inform the UE of the location of the relevant System Information Blocks (SIBs) transmitted by the neighboring cells, and the UE may obtain the corresponding SIBs to be aware of the D2D discovery zone configuration in the neighboring cells. For both scenarios, whether to transmit and/or listen on the D2D discovery zones of only a selected subset of all cells in its neighbor cell list (not overlapping with the D2D discovery zone of its serving cell) may be based on UE implementation, particularly for UE-based open discovery.

For a network-wide configuration of D2D discovery zones, the constituent cells can be configured to maintain strict time synchronization with respect to subframe boundaries, subframe numbers (SFNs), etc., thereby enabling a universal D2D discovery zone. This can be achieved, for example, using backhaul-based synchronization or using GPS. In some embodiments, the strict time synchronization requirement can be relaxed by using an extendable cyclic prefix (CP) for the D2D discovery zone and a regular-length cyclic prefix for the non-discovery zone.

For D2D discovery zones configured on a cell-by-cell basis, the coexistence of D2D discovery transmission/reception and cellular (WAN) traffic creates a challenge. Since the D2D discovery zone is configured in the currently defined UL subframes, inter-cell interference between D2D discovery signal transmission and UL PUSCH transmission can be managed, for example, by UL power control and UL scheduling for PUSCH transmission, incorporating some form of transmit power control for transmitting discovery signals (e.g., by configuring a maximum transmit power), employing a cell clustering approach, and/or selecting discovery resources by the UE based on UE geometry. These embodiments are discussed in more detail below.

In some embodiments, to signal the D2D discovery zone configuration information of one or more neighbor eNBs, eNB 104, when operating as a serving eNB, is configured to provide location information of system information blocks (SIBs) transmitted by one or more neighbor eNBs, thereby allowing a UE served by the serving eNB to obtain the SIBs indicating the D2D discovery zone configuration of the one or more neighbor eNBs. In these embodiments, whether to transmit and/or listen on the D2D discovery zones of only a selected subset of all cells in its neighbor cell list (not overlapping with the D2D discovery zone of its serving cell) may be based on UE implementation, particularly for UE-based open discovery. In these embodiments, the UE may receive signaling from the serving eNB when in RRC connected mode, and may receive signaling from the eNB on which the UE is camped when in RRC idle mode. According to an embodiment, when the UE is in RRC connected mode, it has a serving eNB, and when it is in RRC idle mode, it is camped on an eNB (because when it is in idle mode, it is not served by an eNB).

In some embodiments, the eNB 104 is configured to exchange D2D discovery zone configuration information of one or more neighboring eNBs. Based on the D2D discovery zone configuration information of one or more neighboring eNBs, the eNB 104 may be configured to employ inter-cell interference reduction techniques to reduce intra-cell and inter-cell interference within the discovery zone, as well as inter-cell interference between discovery signal transmissions and uplink cellular transmissions. The inter-cell interference reduction techniques may include one or more of the following:

Performing cooperative subframe power control for D2D discovery signal transmission, where uplink subframe settings are configured with independent power control parameters for interference reduction between uplink cellular transmission (e.g., Physical Uplink Shared Channel (PUSCH) transmission) and D2D discovery signal transmission;

Configuring the transmit power control level for discovery signal transmission;

Using cooperative cell clustering to align the discovery areas of one or more neighbor eNBs; and

Adopting geometry-based intra-cell discovery zone division.

FIG5 illustrates cooperative uplink subframe power control for D2D discovery signal transmission according to some embodiments. In some of these embodiments, UL scheduling and UL power control for PUSCH transmissions may be configured by the serving cell, as the serving cell is aware of the configuration of the D2D discovery zones in the neighboring cells. In some embodiments, the two UL subframe settings may be configured to have independent power control parameters (e.g., open-loop power control parameters P0 and alpha) for different UL subframe settings. This can be achieved by using one UL subframe setting to cover the D2D discovery resources of (one or more) neighboring cells, thereby avoiding strong inter-cell interference from cellular PUSCH transmissions on D2D discovery signal reception in neighboring cells, as shown in FIG5 .

Some embodiments may incorporate a form of transmit power control for transmitting discovery signals (e.g., by configuring a maximum transmit power). In some embodiments, multiple maximum power levels for D2D discovery signals may be predefined, and the selected maximum transmit power level may be signaled to the UE via D2D discovery configuration signaling.

Some embodiments may employ a cell clustering approach, whereby neighboring cells align their D2D discovery zone configurations through information exchange via X2115 ( FIG1 ). In these embodiments, time-frequency resources reserved only for the D2D discovery zone need to be aligned, and each cell may independently configure a quieting factor (discussed in more detail below) to adjust for changes in the load of the D2D discovery zone, thereby managing intra-cell/intra-cluster interference within the D2D discovery zone.

In some embodiments, the discovery zone operation parameters may include at least one of the following: a quieting factor, a transmit power control configuration, a hopping-related parameter, and a scrambling ID. In these embodiments, regardless of the type of D2D discovery operation (open discovery or restricted discovery), for an RRC_CONNECTED or RRC_IDLE ProSe-enabled UE, certain parameters related to configuring and transmitting a discovery zone and signal (e.g., a discovery packet) may be signaled to the corresponding UE.

In these embodiments, discovery zone configuration may include arbitrarily dividing all zones into contention-based discovery zones and contention-free discovery zones. Parameters may be included to indicate the extent of each discovery zone in the time and frequency domains, and to indicate the periodicity and time offset of the zone configuration. For cell-specific discovery zone allocation, this information will be cell-specific, and the serving cell may signal parameters corresponding to neighbor cells to support inter-eNB discovery.

In some embodiments, if fixed random muting is configured, a single value of the muting factor may be signaled. On the other hand, to support more advanced adaptive muting mechanisms, more than one parameter may need to be signaled. In one embodiment, each ProSe-enabled UE 102 may be configured with a nominal muting factor that applies to the first occurrence of a discovery zone for the corresponding UE. For subsequent discovery zone occurrences, the muting factor to be applied by the UE may be increased or decreased (some factor signaled by the network/eNB) within certain lower and upper bounds, depending on whether the UE has transmitted in the previous zone. These bounds may be static (pre-configured) or configured and updated at a very low rate by the network and/or eNB, but the scope of the embodiments is not limited in this respect.

In some embodiments, the eNB may be configured to reduce interference within the discovery zone by employing a silence and muting protocol for discovery signal transmission, and may be configured to include a silence factor in the discovery zone parameters. In these embodiments, the silence and muting protocol configures the ProSe-enabled UE with a silence factor for D2D discovery signal transmission on randomly selected resources in the D2D discovery zone based on a probability indicated by the silence factor. The effective arrival rate of discovery packets and the interference level within the D2D discovery zone may be controlled. In these embodiments, each ProSe-enabled UE that intends to transmit a discovery packet may randomly select a resource from within the D2D discovery zone and may transmit the packet with a certain probability (e.g., (1-p), where 0≤p≤1). In these embodiments, p may be defined as a silence factor, which may be configured by the network in a network-wide manner or by each serving cell in a cell-specific manner. Alternatively, the silence factor may be represented by 1 minus the transmission probability factor, as the transmission probability factor is defined as 1 minus the silence factor.

In some embodiments, signaling to the UE indicates whether the quieting factor is to be increased or decreased for a subsequent discovery period, depending on whether the UE has sent a D2D discovery signal in a previous discovery period of the discovery zone.

There are many methods for estimating the load condition of a D2D discovery zone. The load condition is in turn used to help determine how to adjust the applicable quieting factor for subsequent DZs. In one embodiment (Option 1), a ProSe-enabled UE may count the number of successful cyclic redundancy checks (CRCs) when decoding discovery packets from other UEs in the current D2D discovery zone; this successful CRC count may be represented by I _CRCsucc . A threshold number Thres _CRCsucc may be defined such that when I _CRCsucc is greater than Thres _CRCsucc , the UE may consider the current discovery zone to be heavily loaded and, therefore, increase the quieting factor by an amount q ₀ for the next discovery zone. On the other hand, if I _CRCsucc is less than or equal to Thres _CRCsucc in the current discovery zone, the UE may decrease the quieting factor by an amount q ₁ for the next discovery zone. The threshold number Thres _CRCsucc may be static or configured and updated by the network at a slower rate.

In an embodiment for contention-based discovery (option 2), when a ProSe-enabled UE transmits a discovery packet, the ProSe-enabled UE may randomly select a demodulation reference signal (DM-RS) sequence or a discovery preamble. At the receiving end, the UE receiving the discovery transmission may need to perform discovery preamble detection or packet detection to find out whether a discovery packet exists in a given discovery resource and perform DM-RS identification to ensure proper channel estimation and time/frequency offset compensation. When performing discovery preamble detection or packet detection including DM-RS blind detection, the ProSe-enabled UE may calculate the correlation energy of all candidate DM-RS sequences and select the DM-RS sequence with the highest correlation energy for further bandwidth processing.

In other embodiments for contention-based discovery, a ProSe-enabled UE may first determine the maximum correlation energy of all candidate DM-RS sequences within each monitored discovery resource. The average maximum correlation energy (referred to herein as MaxEn _DZ ) across all monitored discovery resources in a discovery zone (e.g., a discovery period) may be determined subject to half-duplex constraints. A threshold (referred to herein as Thres _MAXENDR ) is selected. If MaxEn _DZ is greater than or equal to Thres _MAXENDR for the current discovery zone, the UE may consider the current discovery zone to be heavily loaded with discovery packet transmissions and may increase the quieting factor by an amount q ₀ for the next discovery zone. Accordingly, if MaxEn _DZ is less than Thres _MAXENDR for the current discovery zone, the UE may decrease the quieting factor by an amount q ₁ for the next discovery zone. Thres _MAXENDR may be static or configured and updated by the network at a slower rate.

In another embodiment (option 3), the ProSe-enabled UE may calculate the maximum and second-largest (i.e., second-highest) correlation energies of the candidate DM-RS sequences within each monitored discovery resource. The UE may then calculate the average of the second-largest correlation energies across all monitored discovery resources in the discovery zone, subject to the half-duplex constraint (referred to herein as MaxSecMaxEn _Dz ). A threshold value (referred to herein as _{ThresMAXSECMAXENDR} ) is selected. If MaxSecMaxEn _DZ is greater than or equal to _{ThresMAXSECMAXENDR} for the current discovery zone, the UE may consider the current discovery zone to be heavily loaded with discovery packet transmissions and may increase the muting factor by an amount _q0 for the next discovery zone. Therefore, if MaxSecMaxEn _DZ is less than _{ThresMAXSECMAXENDR} for the current discovery zone, the UE may decrease the muting factor by an amount _q1 for the next discovery zone. _{ThresMAXSECMAXENDR} may be static or configured and updated by the network at a slower rate.

In another embodiment (Option 4), the maximum and second-largest (i.e., second-highest) correlation energies of the candidate DM-RS sequences within each monitored discovery resource are calculated. The UE may then calculate the ratio between the maximum and second-largest correlation energies within each monitored discovery resource and compare the calculated ratio with a threshold ratio (referred to herein as Thres _{ratio DR} ). The UE may then calculate a count of the number of discovery resources (in the current discovery zone) for which the calculated ratio is greater than or equal to Thres _{ratio DR} . The average count across all monitored discovery resources within the discovery period, subject to half-duplex constraints, may be determined, referred to herein as I _ratio . The I _ratio may then be compared with a threshold (referred to herein as Thres _{ratio DZ} ). If the I _ratio is less than Thres _{ratio DZ} for the current discovery zone, the UE may consider the current discovery zone to be heavily loaded with discovery packet transmissions and may increase the quieting factor by an amount q ₀ for the next discovery zone. Therefore, if the I _ratio is greater than or equal to Thres _{ratio DZ} for the current discovery zone, the UE may decrease the quieting factor by an amount q ₁ for the next discovery zone. Thres _ratioDZ may be static or configured and updated by the network at a slower rate.

In another embodiment (option 5), multiple options 1-4 can be used in combination to obtain a composite metric to estimate the load situation in the discovery area. Another option that takes into account whether the UE has transmitted in the previous discovery area can also be used in combination with any combination of options 1-4 to obtain such a composite metric. A threshold value for the composite metric (referred to herein as Thres _comb ) can be selected. If the value of the composite metric for the current discovery area is greater than or equal to Thres _comb , the UE can consider that the load of discovery packet transmission in the current discovery area is heavy, and for the next discovery area, the silence factor can be increased by q _0. Therefore, if the value of the composite metric for the current discovery area is less than Thres _comb , the UE can reduce the silence factor by q ₁ for the next discovery area. Thres _comb can be static or configured and updated by the network at a slower rate.

In another embodiment, one or more of the criteria listed above (e.g., options 1-5) may be used as parameters of a function defining the increase factor q ₀ and the decrease factor q _1. The predefined function f, for example, may accept the criteria as parameters and use these parameters to determine the value of the increase factor q ₀ used to adjust the silence factor of the subsequent discovery zone. In another example, the predefined function may accept the criteria as parameters and use these parameters to determine the value of the decrease factor q ₁ used to adjust the silence factor of the subsequent discovery zone.

In the embodiment of estimating the load of the D2D discovery area and adjusting the quieting factor, the quieting factor may be constrained to comply with a lower limit and/or an upper limit. Such lower limit and/or upper limit may be static or configured and updated by the network at a slower rate.

In some embodiments, a ProSe-enabled UE may be allowed to send multiple copies of a discovery packet within the same discovery zone. In embodiments where this is allowed, the discovery zone may be divided into sub-discovery zones (sub-DZs). Sub-discovery zones (sub-DZs) may be used instead of DZs to adjust the muting probability scheme (as described in options 1-5).

In some embodiments, a conditional silence probability, p _rcTx , may be defined for repeated transmissions within a DZ. This conditional silence probability is conditional on the event that the UE transmits an initial discovery signal in the DZ. If the initial discovery signal is actually transmitted during the DZ, one or more subsequent repetitions of the discovery signal are sent with probability p _rcTx . The conditional silence probability, p _{rcTx ,} may be static or configured and updated by the network at a slower rate.

In another embodiment, different types of D2D discovery messages may have different sizes. For example, discovery packets for public safety (PS) D2D discovery messages and non-PS D2D discovery messages typically have different sizes. A ProSe-enabled UE may be configured to transmit/retransmit discovery packets in a DZ (or sub-DZ) a different number of times, depending on the size of the discovery packets. A fixed or adaptive quieting factor may be used for initial discovery signal transmission, repeated transmissions, or both. The methods described (e.g., options 1-5) may be used to adjust the adaptive quieting factor based on load conditions.

In another embodiment, the above methods (e.g., options 1-5) can be used to estimate the load situation over a set of discovery cycles. For example, the comparison metrics described in options 1-5 can be averaged over n previous discovery cycles in the discovery zone to obtain a larger discovery cycle sample size for estimating the current load situation. The set of n previous discovery cycles can include a sliding window of discovery cycles, such that to estimate the load situation for discovery cycle t, metrics from discovery cycles t-n to t-1 are included in the set.

In some embodiments, when the discovery zone parameters include a transmit power control configuration, the UE may be configured with a maximum transmit power for transmitting D2D discovery signals that is lower than the transmit power specified for the corresponding UE class. In these embodiments, depending on the discovery traffic situation and use case, the ProSe-enabled UE may be configured with a maximum transmit power that may be lower than the transmit power specified for the corresponding UE class. The maximum transmit power may be used for discovery packet transmission. If supported, other parameters related to more advanced adaptive power control options will need to be signaled.

In some embodiments, when the discovery zone parameter includes a jump-related parameter, the jump-related parameter indicates:

Parameters for discovery resource hopping in contention-free D2D discovery zone configuration;

Jump type, including type 1 or type 2 jump;

Hopping modes, including intra-subframe or inter-subframe hopping;

• Subband size for type 2 hopping; and

• Pseudo-random sequence initialization for type 2 hopping.

In these embodiments, for contention-free discovery resource allocation, some randomized hopping-related signaling may be provided to the UE. Additionally, for payload-based transmissions (where each discovery packet transmission spans multiple PRB pairs), different types of intra-subframe or inter-subframe hopping may be configured.

In some embodiments, when the discovery zone parameters include a scrambling identifier, the scrambling identifier may be used to scramble the CRC mask of the D2D discovery packet. A universal scrambling ID may be allocated on a per-discovery group basis. In these embodiments, a scrambling identifier (ID) may be used to scramble the CRC mask of the discovery packet. The scrambling identifier may be universal on a per-discovery group basis. For open discovery, all ProSe-enabled UEs within the network (for network-wide discovery resource configuration) or within a cell cluster or cell (for cell-specific discovery resource configuration) may be configured with a universal scrambling ID.

For restricted discovery, the scrambling ID can be used by the discovering UE to filter the decoded candidates before sending the candidate list to the upper layer to verify the restricted discovery. For closed discovery, the scrambling is the same as for restricted discovery on a per-whitelist basis. Thus, those ProSe-enabled UEs not in the whitelist will not be able to decode the packet. The closed group scrambling seed should be generated by the D2D server and sent along with the whitelist group information during D2D registration (not through SIB/paging).

In some embodiments, for restricted discovery, a temporary identifier (Temp_ID) may be used to distinguish the same ProSe-enabled UE belonging to different discovery groups (different whitelists of other ProSe-enabled UEs). Each ProSe-enabled UE transmitting as part of restricted discovery is assigned one or more Temp_IDs, which replace the UE identity in the discovery packet. When a discovery UE decodes such a packet, it forwards the decoded Temp_ID(s) to the network for further identification and verification as part of the restricted discovery process. For example, consider three ProSe-enabled UEs participating in restricted discovery: UE_A, UE_B, and UE_C. UE_A and UE_B belong to different groups A and B, respectively, and do not have each other in their respective whitelists, while UE_C is in both whitelists. UE_C may then be assigned two different Temp_IDs (UE_Ca and UE_Cb) so that both UE_A and UE_B can discover UE_Ca and UE_Cb, respectively, and thus, with subsequent identification from the network, UE_C can be discovered. However, UE_A and UE_B can only discover each other via an open discovery operation.

FIG6 illustrates an eNB-triggered allocation of contention-free D2D discovery zone resources according to some embodiments. In these embodiments, the eNB may use RRC and/or Layer 1 (physical layer) signaling to indicate the semi-persistent allocation of discovery resources to a ProSe-enabled UE in RRC-connected mode for contention-free transmission of D2D discovery signals. The eNB may be configured to release the allocation of discovery resources by sending a discovery resource release. In these embodiments, the contention-free mode of D2D discovery may be supported in a variety of ways. In some embodiments, this mode of operation may be triggered by the eNB (operation 602), wherein, in operation 604, the eNB configures dedicated resources for transmitting discovery signals to one or more RRC_CONNECTED mode ProSe-enabled UEs. Resource allocation in this scenario may be implemented using a combination of RRC and Layer 1 signaling in the form of semi-persistent allocation of discovery resources (operation 606). Depending on the load and overall D2D discovery resource allocation status, the configured dedicated resources may also be released (operation 608) by the eNB.

FIG7 illustrates UE-triggered contention-free D2D discovery zone resources according to some embodiments. In these embodiments, the eNB may allocate discovery resources to a ProSe-enabled UE in RRC connected mode in response to an RRC resource request from the ProSe-enabled UE for contention-free transmission of D2D discovery signals. In addition to the eNB-determined release of discovery resources, the eNB may release the allocation of discovery resources in response to receiving a resource release request from the ProSe-enabled UE via RRC signaling. In these embodiments, an RRC_CONNNECTED UE (e.g., upon initialization from a higher layer) may request (operation 702) resources for D2D discovery signal transmission from a serving cell via the RRC layer. Subsequently, subject to the eNB's decision, the serving cell may configure the UE with resource allocation configuration via RRC signaling (operation 704) and ultimately configure with semi-persistent allocation via Layer 1 signaling. No layer 1 signaling/activation is used, as resources can be configured via RRC (operation 704), and then discovery transmission is automatically activated starting from the next occurrence of a discovery resource pool/zone (operation 706). In addition to the release of resources determined by the eNB (operation 710), the UE can also request discovery resource release via the RRC layer (operation 708).

In these embodiments, when D2D discovery resources are explicitly allocated via PDCCH, RRC resource configuration (operation 704) may not be required. A combination of eNB-triggered, UE-triggered contention-free resource allocation schemes and eNB-determined and UE-requested resource release mechanisms may also be implemented.

In addition, depending on the presence of active ProSe-enabled UEs, resources for D2D discovery may not be reserved at the cell level/cell cluster level or network level (i.e., no discovery zone is configured). In such a situation, a ProSe-enabled UE in RRC_CONNECTED mode may send a request for allocation of D2D discovery resources via the RRC or application layer. If the request is made via the application layer, the request will be sent to the D2D server, which in turn requests the eNB to enable a discovery zone or allocate additional resources for contention-free discovery as needed. In addition, a ProSe-enabled UE in RRC_IDLE mode may transition to connected mode to send a discovery resource request. However, this ProSe-enabled UE may not be involved in the RRC connection setup. For example, the UE may send an RRC connection request indicating only a discovery zone request. Alternatively, the UE autonomously transitions to idle mode when the eNB sends an acknowledgment (or discovery radio resource configuration) message for the discovery request message.

In some embodiments, D2D discovery resources may be statically configured. To support D2D discovery for National Security and Public Safety (NSPS) use cases in out of coverage or partial coverage scenarios, certain periodic time-frequency resources may be pre-configured as D2D discovery resources for Public Safety (PS) ProSe-enabled UEs. Such resources may be configured with a low duty cycle and, where appropriate, and depending on the exact D2D discovery protocol, additional resources may be allocated to supplement the pre-configured D2D discovery areas by coordinating UEs for partial or out of coverage scenarios. The configuration of additional resources may follow the principles described above while taking into account the static pre-configured default D2D discovery areas.

In some embodiments, for geometry-based intra-cell D2D discovery zone partitioning, the UE may receive signaling from the serving eNB indicating D2D discovery zone configuration information for one or more neighbor eNBs, the information including discovery resources for the D2D discovery zone for at least one of the cell-center D2D UE and the cell-edge D2D UE. The UE may select the resources indicated for the cell-center D2D UE or the cell-edge D2D UE for transmitting D2D discovery signals based at least on the RSRP of the serving eNB. In these embodiments, the UE may select discovery resources based on UE geometry. The discovery zone may be partitioned, and if some discovery resources are used for regular UL scheduling in neighbor cells, these discovery resources are primarily used for cell-center UEs. A ProSe-enabled UE with an RSRP _serving /RSRP _{strongest_neighbor} ratio greater than some predefined or configured threshold may transmit D2D discovery packets in the discovery zone reserved for the cell-center ProSe-enabled UE. In the above, RSRP _serving is the serving cell RSRP, and RSRP _{strongest_neighbor} corresponds to the RSRP of the link to the cell with the largest RSRP value in the neighbor cell list. Geometry-based intra-cell D2D discovery area partitioning combined with careful scheduling of PUSCH transmissions within the cell with WAN traffic can enable coexistence of LTE UL transmissions in neighbor cells with D2D discovery areas. The eNBs can exchange information about discovery resources for cell-center D2D UEs or cell-edge D2D UEs. In some of these embodiments, the UE can select discovery resources based on RSRP _serving instead of a ratio, and will operate similarly, especially in NWs where the eNBs have similar transmit power (e.g., for macro-only networks).

FIG8 illustrates functionality 800 of computer circuitry of a UE enabled for proximity services (ProSe). At 810, the ProSe-enabled UE may receive device-to-device (D2D) discovery zone configuration information from an enhanced Node B (eNB), the D2D discovery zone configuration information indicating periodicity and time and frequency resources of the discovery zone, and indicating one or more discovery zone operating parameters. At 820, the ProSe-enabled UE may monitor a first discovery period of the D2D discovery zone for D2D discovery signals transmitted by other UEs. At 830, the ProSe-enabled UE may receive discovery packets in the first discovery period from the other UEs. At 840, the ProSe-enabled UE may estimate a load condition in the first discovery period. At 850, the ProSe-enabled UE may adjust a quieting factor based on the estimated load condition in the first discovery period. The quieting factor may include a probability that the UE will not transmit a D2D discovery signal in a second discovery period following the first discovery period.

In one example, a ProSe-enabled UE may estimate the load situation in a first discovery period of a discovery zone (e.g., a contention-based D2D discovery zone) by: counting the number of successful cyclic redundancy checks (CRCs) when the ProSe-enabled UE decodes discovery packets received from other UEs, subject to half-duplex constraints; comparing the number of successful cyclic redundancy checks (CRCs) with a threshold number (the threshold number may be static or periodically updated by a signal from an eNB); increasing a quieting factor if the number of successful cyclic redundancy checks (CRCs) is equal to or greater than the threshold number; and decreasing the quieting factor if the number of successful cyclic redundancy checks (CRCs) is less than the threshold number.

In another example, a ProSe-enabled UE may estimate a load condition within a first discovery period of a discovery zone (e.g., a contention-based D2D discovery zone) by: performing discovery preamble detection or discovery packet detection (including demodulation and reference signal (DM-RS) blind detection); receiving multiple DM-RS sequences within each of a plurality of discovery resources within the first discovery period; calculating correlation energies of all DM-RS sequences, wherein the DM-RS sequences include multiple DM-RS sequences within the first discovery zone; and selecting a DM-RS sequence from the multiple DM-RS sequences within each of the plurality of discovery resources, wherein the selected DM-RS sequence has a calculated maximum correlation energy relative to the calculated correlation energies of all DM-RS sequences, wherein all DM-RS sequences include multiple DM-RS sequences that can be sent on the corresponding discovery resource.

The ProSe-enabled UE may also be configured to estimate the load situation by: calculating the average maximum correlation energy within the first discovery area across all monitored discovery resources within the discovery period subject to half-duplex constraints; comparing the average maximum correlation energy with a threshold correlation energy (which may be static or periodically updated by a signal from the eNB); increasing the quieting factor if the average maximum correlation energy is equal to or greater than the threshold correlation energy; and decreasing the quieting factor if the average maximum correlation energy is less than the threshold correlation energy.

The ProSe-enabled UE may also be configured to select a second DM-RS sequence from a plurality of DM-RS sequences within each discovery resource of a plurality of discovery resources within a first discovery period, wherein the second DM-RS sequence has a calculated second maximum correlation energy relative to the calculated correlation energies of all DM-RS sequences, wherein all DM-RS sequences include a plurality of DM-RS sequences that may be transmitted on the corresponding discovery resource; calculate an average second maximum correlation energy within a first discovery area across all monitored discovery resources within the discovery period subject to a half-duplex constraint; compare the second maximum correlation energy with a threshold correlation energy (which may be static or periodically updated by a signal from the eNB); increase a silencing factor if the second maximum correlation energy is equal to or greater than the threshold correlation energy; and decrease the silencing factor if the second maximum correlation energy is less than the threshold correlation energy.

In another example, a ProSe-enabled UE may be configured to estimate a load condition by: performing discovery preamble or packet detection (including demodulation and reference signal (DM-RS) blind detection); receiving a plurality of DM-RS sequences within each of a plurality of discovery resources within a first discovery period; calculating a correlation energy of each DM-RS sequence within each of a plurality of discovery resources within the first discovery period; determining a maximum correlation energy for each of the plurality of discovery resources within the first discovery period, wherein the maximum correlation energy for each of the plurality of discovery resources within the discovery period includes a maximum correlation energy of any DM-RS sequence that may be sent on the corresponding discovery resource; determining a second maximum correlation energy for each of the plurality of discovery resources within the first discovery period; calculating a correlation energy ratio for each of the plurality of discovery resources within the first discovery period, wherein The relevant energy ratio of the selected discovery resource includes the ratio between the maximum relevant energy of the selected discovery resource and the second largest relevant energy of the selected discovery resource; calculating the threshold satisfaction count of each discovery resource on each of the multiple discovery resources located in the first discovery cycle, wherein when the relevant energy ratio of the selected discovery resource is greater than or equal to the threshold ratio (the threshold ratio can be static or periodically updated by a signal from the eNB), the threshold satisfaction count of the selected discovery resource is increased; calculating the average threshold satisfaction count across all discovery resources monitored in the first discovery area; comparing the average threshold satisfaction count with a threshold number (the threshold number can be static or periodically updated by a signal from the eNB); if the average threshold satisfaction count is less than the threshold number, increasing the silencing factor; and if the average threshold satisfaction count is greater than or equal to the threshold number, reducing the silencing factor.

In another example, a ProSe-enabled UE may be configured to estimate a load condition by using a function that quantifies the load condition within a first discovery cycle, the function receiving inputs including one or more of the following: an indicator indicating whether the UE has transmitted in a previous discovery cycle; a number of successful cyclic redundancy checks (CRCs), wherein the hardware circuit is further configured to count the number of successful CRCs when decoding discovery packets received from other UEs within the first discovery cycle; a maximum correlation energy within a first discovery region, wherein the hardware circuit is further configured to calculate the correlation energy of multiple DM-RS sequences for each discovery resource in a plurality of discovery resources within the first discovery cycle received at the UE and setting the maximum correlation energy equal to the calculated correlation energy associated with the DM-RS sequence in the plurality of DM-RS sequences. The ProSe-enabled UE may further include a first discovery zone, a second discovery zone, and a second discovery zone, wherein the hardware circuit is further configured to determine the second maximum correlation energy by calculating the correlation energies of multiple DM-RS sequences for each discovery resource in a first discovery period received at the UE and setting the second maximum correlation energy equal to the calculated second highest correlation energy associated with the DM-RS sequence in the multiple DM-RS sequences; or an average threshold satisfaction count, wherein the hardware circuit is further configured to calculate the average threshold satisfaction count by counting the number of discovery resources in the first discovery period for which the ratio of the maximum correlation energy to the second maximum correlation energy is greater than or equal to a threshold ratio and averaging the number of discovery resources in the first discovery period relative to the number of discovery resources in the discovery zone. When the load condition quantified by the function is greater than or equal to the threshold, the ProSe-enabled UE may increase the silence factor, and when the load condition quantified by the function is less than the threshold, the ProSe-enabled UE may decrease the silence factor. These thresholds may be static or periodically updated by a signal from the UE. The silence factor may be bounded by an upper limit and a lower limit. When the load condition quantified by the function is greater than or equal to a threshold, the quieting factor may be increased to increment the factor Q ₀ , and when the load condition quantified by the function is less than the threshold, the quieting factor may be decreased to decrement the factor Q ₁ .

Figure 9 provides an example diagram of a wireless device (e.g., a user equipment (UE), a mobile station (MS), a mobile wireless device, a mobile communication device, a tablet, a mobile phone, or other types of wireless devices). The wireless device may include one or more antennas configured to communicate with a node, macro node, low power node (LPN), or transmission station (e.g., a base station (BS), an evolved Node B (eNB), a baseband unit (BBU), a remote radio head (RRH), a remote radio equipment (RRE), a relay station (RS), a radio equipment (RE), or other types of wireless wide area network (WWAN) access points). The wireless device may be configured to communicate using at least one wireless communication standard, including 3GPP LTE, WiMAX, High Speed Packet Access (HSPA), Bluetooth, and Wi-Fi. The wireless device may use a separate antenna for each wireless communication standard or a shared antenna for multiple wireless communication standards. The wireless device may communicate in a wireless local area network (WLAN), a wireless personal area network (WPAN), and/or a WWAN.

FIG8 also provides an illustration of a microphone and one or more speakers that can be used for audio input and output from the wireless device. The display screen can be a liquid crystal display (LCD) screen, or other types of display screens (e.g., organic light emitting diode (OLED) displays). The display screen can be configured as a touch screen. The touch screen can use capacitive touch screen technology, resistive touch screen technology, or another type of touch screen technology. An application processor and an image processor can be coupled to internal memory to provide processing and display capabilities. A non-volatile memory port can also be used to provide data input/output options to the user. The non-volatile memory port can also be used to expand the memory capacity of the wireless device. A keyboard can be integrated with the wireless device, or a keyboard can be wirelessly connected to the wireless device to provide additional user input. A touch screen can also be used to provide a virtual keyboard.

Various technologies or some aspects or portions thereof may take the form of program code (i.e., instructions) embedded in a tangible medium (e.g., a floppy disk, CD-ROM, hard drive, non-transitory computer-readable storage medium, or any other machine-readable storage medium), wherein when the program code is loaded into a machine (e.g., a computer) and run by the machine, the machine becomes a device for implementing various technologies. Circuits may include hardware, firmware, program code, executable code, computer instructions, and/or software. Non-volatile computer-readable storage media may include computer-readable storage media that do not include signals. In the case where the program code runs on a programmable computer, the computing device may include a processor, a storage medium readable by the processor (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. Volatile and non-volatile memory and/or storage elements may be RAM, EPROM, flash drive, optical drive, magnetic hard drive, or other media for storing electronic data. Nodes and wireless devices may also include a transceiver module, a counter module, a processing module, and/or a clock module or a timer module. One or more programs that can implement or utilize the various technologies described herein can use application programming interfaces (APIs), reusable controls, etc. Such programs can be implemented in high-level procedural or object-oriented programming languages to communicate with a computer system. However, the program(s) can be implemented in component or machine language as needed. In any case, the language can be a compiled language or an interpreted language and combined with a hardware implementation.

It should be understood that many of the functional units described in this specification are labeled as modules to emphasize the independence of their implementation. For example, a module can be implemented as a hardware circuit comprising conventional VLSI circuits or gate arrays, off-the-shelf semiconductors (e.g., logic chips, transistors, or other discrete components). A module can also be implemented in a programmable hardware device (e.g., a field programmable gate array, programmable array logic, a programmable logic device, etc.).

Module can also be implemented in the software that is run by various types of processors.The module of the executable code of being identified can for example comprise one or more physical blocks or logical blocks of computer instructions, and it can for example be organized as object, program, or function.Yet the executable property of being identified module does not need to be physically located together, but can comprise the different instructions that are stored in different locations, and when these different instructions that are stored in different locations are logically combined together, it comprises this module and realizes the purpose that this module is stated.

In fact, the module of executable code can be a single instruction or many instructions, and can even be distributed on several different code segments across several storage devices and between different programs.Similarly, operational data can be identified and illustrated in this article in module, and can be embedded in and organized into the data structure of any appropriate type in any suitable form.Operational data can be collected as a single data set, or can be distributed in different positions (comprising on different storage devices), and can only exist as the electronic signal on system or network at least in part.Module can be active or passive, comprises the agent that can be operated to perform desired function.

References throughout this specification to an "example" are intended to refer to a particular feature, structure, or characteristic described in connection with the example as included in at least one embodiment of the present invention. Thus, the appearances of the phrase "in an example" in various places throughout this specification are not necessarily all referring to the same embodiment.

As used herein, for convenience, multiple items, structural elements, constituent elements, and/or materials can be presented in a general list. However, these lists should be understood as if each member in the list is independently identified as a separate and unique member. Therefore, based on its presentation in a general group without the need for contrary instructions, the independent members in such a list should not be interpreted as the de facto equivalence of any other member of the same list. In addition, various embodiments and examples of the present invention can be referred to together with the replacement of its various components herein. It should be understood that such embodiments, examples and replacements are not interpreted as de facto equivalence to each other, but are considered to be independent and autonomous representations of the present invention.

Moreover, described features, structures, or characteristics can be combined in any appropriate manner in one or more embodiments. In the following description, a large amount of specific details (such as, the example of layout, distance, network example, etc.) are provided to provide a thorough understanding of embodiments of the present invention. However, those skilled in the relevant art will recognize that the present invention can be implemented without the need for one or more of these specific details, or other methods, components, layouts, etc. are utilized to implement the present invention. In other examples, in order to avoid blurring the various aspects of the claimed subject matter, well-known structure, material, or operation are not shown or described in detail.

Although the foregoing examples are illustrative of the principles of the present invention in one or more specific applications, it will be apparent to those skilled in the art that numerous modifications in form, use, and details of implementation may be made without departing from the concepts and principles of the present invention and without requiring practice of the inventor. Therefore, it is not intended that the present invention be limited except as set forth in the appended claims.

Claims (28)

1. A user equipment (UE) enabled for Proximity Service ProSe, the UE including hardware circuitry configured to: The enhanced node (B eNB) receives device-to-device D2D discovery zone configuration information, which indicates the periodicity and time and frequency resources of the discovery zone, and indicates one or more discovery zone operation parameters. The first discovery cycle of the discovery area is monitored in response to D2D discovery signals sent by other UEs; Receive discovery packets from the other UEs during the first discovery period; Estimate the load situation during the first detection period; The silence factor is adjusted based on the estimated load conditions during the first discovery period, wherein the silence factor includes the probability that the UE will not send a D2D discovery signal during a second discovery period following the first discovery period. 2. The UE of claim 1, wherein the hardware circuitry configured to estimate the load condition during the first discovery period of the discovery area is further configured to: When the discovery packet received from the other UE is decoded under half-duplex constraints, the number of successful cyclic redundancy check (CRC) packets is counted. The number of successful cyclic redundancy checks (CRC) is compared with the threshold number. If the number of successful cyclic redundancy checks (CRCs) is equal to or greater than the threshold number, then the silence factor is increased; and If the number of successful cyclic redundancy checks (CRCs) is less than the threshold number, then the quiescent factor is reduced. 3. The UE as claimed in claim 2, wherein the number of thresholds is static. 4. The UE as described in claim 2, wherein the hardware circuit is further configured to: Periodically receive updated thresholds from the eNB; and The threshold number is updated based on the updated threshold. 5. The UE as claimed in claim 1, wherein the first discovery period and the second discovery period of the discovery area are based on a contention-based D2D discovery area. 6. The UE of claim 1, wherein the hardware circuitry configured to estimate the load condition during the first discovery period is further configured to: Perform detection preamble detection or detection group detection, wherein the detection preamble detection or detection group detection includes demodulation and blind detection of reference signal DM-RS; Receive multiple DM-RS sequences within each of multiple discovery resources located within the first discovery period; Calculate the correlation energy of all DM-RS sequences, including the plurality of DM-RS sequences within the first discovery period; and A DM-RS sequence is selected from the plurality of DM-RS sequences within each of the plurality of discovery resources, wherein the selected DM-RS sequence has the calculated maximum correlation energy relative to the correlation energy of all calculated DM-RS sequences, the plurality of DM-RS sequences including multiple DM-RS sequences that can be transmitted on the respective discovery resource. 7. The UE of claim 6, wherein the hardware circuitry configured to estimate the load condition during the first discovery period is further configured to: Calculate the average maximum correlation energy within the first discovery period across all monitored discovery resources under half-duplex constraints; The average maximum correlation energy is compared with the threshold correlation energy; If the average maximum correlation energy is equal to or greater than the threshold correlation energy, then the silencing factor is increased; and If the average maximum correlation energy is less than the threshold correlation energy, then the silencing factor is reduced. 8. The UE of claim 7, wherein the threshold-related energy is static. 9. The UE of claim 7, wherein the hardware circuit is further configured to: Periodically receive signals from the eNB; and The threshold-related energy is updated based on information from the eNB. 10. The UE as described in claim 6, further configured to: A second DM-RS sequence is selected from a plurality of DM-RS sequences within each of a plurality of discovery resources located within the first discovery period, wherein the second DM-RS sequence has a calculated second largest correlation energy relative to the correlation energy of all calculated DM-RS sequences, the plurality of DM-RS sequences including a plurality of DM-RS sequences that can be transmitted on the discovery resource; Calculate the average second largest correlation energy within the first discovery period across all monitored discovery resources within the discovery period, constrained by half-duplex constraints; Compare the calculated second-largest correlation energy with the threshold correlation energy; If the calculated second largest correlation energy is greater than or equal to the threshold correlation energy, then the silencing factor is increased; and If the calculated second largest correlation energy is less than the threshold correlation energy, then the quiescence factor is reduced. 11. The UE of claim 10, wherein the threshold-related energy is static. 12. The UE of claim 10, wherein the hardware circuit is further configured to: Periodically receive signals from the eNB; and The UE updates the threshold-related energy based on the signal from the eNB. 13. The UE as described in claim 1, further configured to: Perform detection preamble or group detection, which includes demodulation and blind detection of reference signal DM-RS; Receive multiple DM-RS sequences within each of multiple discovery resources located within the first discovery period; Calculate the correlation energy of each DM-RS sequence for each of the multiple discovery resources located within the first discovery period; Determine the maximum correlation energy of each discovery resource in the first discovery period, wherein the maximum correlation energy of each discovery resource among the plurality of discovery resources in the discovery period includes the maximum correlation energy of any DM-RS sequence that can be transmitted on the corresponding discovery resource; Determine the second largest relevant energy for each of the multiple discovery resources located in the first discovery period; Calculate the relevant energy ratio of each of the plurality of discovery resources located in the first discovery cycle, wherein the relevant energy ratio of the selected discovery resource includes the ratio between the maximum relevant energy of the selected discovery resource and the second maximum relevant energy of the selected discovery resource. Calculate the threshold satisfaction count for each of the multiple discovery resources located in the first discovery cycle, wherein the threshold satisfaction count for the selected discovery resource is increased when the relevant energy ratio of the selected discovery resource is greater than or equal to the threshold ratio. Calculate the average threshold satisfaction count across all discovery resources monitored during the first discovery period; The average threshold satisfaction count is compared with the threshold number; If the average threshold satisfies the condition that the count is less than the threshold number, then the silence factor is increased; and If the average threshold satisfies a count greater than or equal to the threshold number, then the silencing factor is reduced. 14. The UE of claim 13, wherein the threshold ratio is static. 15. The UE of claim 13, wherein the number of thresholds is static. 16. The UE of claim 13, wherein the UE periodically receives signals from the eNB, and the UE updates the threshold ratio based on the signals from the eNB. 17. The UE of claim 13, wherein the UE periodically receives signals from the eNB, and the UE updates the threshold number based on the signals from the eNB. 18. A user equipment (UE) enabled for Proximity Service ProSe, the UE including hardware circuitry configured to: The enhanced node (B eNB) receives device-to-device D2D discovery zone configuration information, which indicates the periodicity and time and frequency resources of the discovery zone, and indicates one or more discovery zone operation parameters. Monitor the first discovery cycle of the D2D discovery area in response to D2D discovery signals sent by other UEs; Receive discovery packets from the other UEs during the first discovery period; A function is used to quantify the load condition during the first discovery period, wherein the load condition is associated with a metric; and The silence factor is adjusted based on the load situation during the quantified first discovery period, wherein the silence factor includes the probability that the UE will not send a D2D discovery signal during a second discovery period following the first discovery period. 19. The UE of claim 18, wherein the function receiving input used to quantify the load situation during the first discovery period includes one or more of the following: An indicator that indicates whether the UE has sent data in a previous discovery period; The number of successful cyclic redundancy check (CRC) records, wherein the hardware circuit is further configured to count the number of successful CRC records when decoding discovery packets received from the other UEs during the first discovery period; The maximum correlation energy within the first discovery period, wherein the hardware circuitry is further configured to determine the maximum correlation energy by calculating the correlation energy of a plurality of DM-RS sequences of each of a plurality of discovery resources received at the UE within the first discovery period, and setting the maximum correlation energy equal to the calculated highest correlation energy associated with the DM-RS sequence among the plurality of DM-RS sequences; The second largest correlation energy within the first discovery period, wherein the hardware circuitry is further configured to determine the second largest correlation energy by calculating the correlation energy of multiple DM-RS sequences of each of a plurality of discovery resources received at the UE within the first discovery period, and setting the second largest correlation energy equal to the calculated second high correlation energy associated with the DM-RS sequences among the plurality of DM-RS sequences; or The average threshold satisfaction count is further configured to calculate the average threshold satisfaction count by averaging the number of discovery resources located on each of the plurality of discovery resources within the first discovery period whose ratio of maximum correlation energy to second maximum correlation energy is greater than or equal to a threshold ratio, relative to the number of discovery resources in the first discovery period of the discovery area. 20. The UE of claim 18, wherein the hardware circuitry is further configured to: When the load condition quantified by the function is greater than or equal to a threshold, the silencing factor is increased; and When the load condition quantified by the function is less than the threshold, the quiescent factor is reduced. 21. The UE of claim 20, wherein the hardware circuit is further configured to: The quiescent factor will not be increased beyond its upper limit; and Do not reduce the quiescent factor to a value exceeding the lower limit. 22. The UE of claim 20, wherein the threshold is static. 23. The UE of claim 20, wherein the hardware circuit is further configured to: Periodically receive communications from the eNB; and The threshold is updated based on the signal from the eNB. 24. The UE of claim 18, wherein the hardware circuitry is further configured to: When the load condition quantified by the function is greater than or equal to the threshold, the silencing factor is increased by an increment factor _Q0 ; and when the load condition quantified by the function is less than the threshold, the silencing factor is decreased by a reduction factor _Q1 . 25. The UE of claim 24, wherein at least one of the increment factor or the decrement factor is static. 26. The UE of claim 24, wherein the hardware circuit is further configured to: change one or more of the increment factor or the decrement factor when the quiescent factor increases or decreases. 27. A user equipment (UE) enabled for Proximity Service ProSe, the UE including hardware circuitry configured to: The enhanced node (B eNB) receives device-to-device D2D discovery area configuration information, which indicates the location of the discovery area. The discovery area is monitored in response to D2D discovery signals sent by other UEs; Receive discovery packets from the discovery area from the other UEs; A detection signal is sent during the first detection cycle in the detection area; and The discovery signal is repeatedly transmitted in one or more subsequent discovery cycles, wherein the hardware circuitry is further configured to probabilistically select whether to repeatedly transmit the discovery signal in the one or more subsequent discovery cycles based on a conditional silence probability, the conditional silence probability being dynamically adjusted based on the number of times the discovery signal has previously been transmitted in the discovery area. 28. The UE of claim 27, wherein the conditional silence probability is subject to one or more of the following constraints: an upper limit or a lower limit.