HK1228158B - Method for proximity service and apparatus used in user equipment configured for proximity service - Google Patents

Description

Method for proximity service and apparatus for use in user equipment configured for proximity service

Divisional Application Instructions

This application is a divisional application of the Chinese invention patent application with application number 201480038488.5 and application date of August 7, 2014, entitled “Signaling for proximity services and D2D discovery in LTE networks”.

Priority claim

This application claims the benefit of priority to U.S. Utility Patent Application Serial No. 14/314,957, filed on June 25, 2014, which claims the benefit of priority to U.S. Provisional Patent Application Serial No. 61/863,902, filed on August 8, 2013, and U.S. Provisional Patent Application Serial No. 61/909,938, filed on November 27, 2013, each of which is incorporated herein by reference in its entirety.

Technical Field

Embodiments relate to wireless communications. Some embodiments relate to 3GPP LTE (Long Term Evolution) networks. Some embodiments relate to direct device-to-device (D2D) communications. Some embodiments relate to device discovery in LTE networks.

Background Art

Proximity-based applications and services represent a rapidly growing social and technological trend that has a major impact on the evolution of cellular wireless/mobile broadband technologies. These services are based on the perception that two devices or two users are in close proximity to each other and 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 the involvement of a base station or enhanced node B (eNB). One issue with D2D communication is device discovery to enable D2D services. Device discovery includes discovering one or more other discoverable UEs within communication range for D2D communication. Device discovery also includes being discovered by one or more other discovering UEs within communication range for D2D communication. There are many unresolved issues with device discovery for D2D communication, including resource allocation and signaling, particularly resource allocation and signaling for Proximity Services (ProSe) D2D discovery.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG2 illustrates the 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 the use of a random access channel (RACH) to count ProSe-enabled UEs according to some embodiments;

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

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

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

FIG7 illustrates UE-triggered contention-free D2D discovery zone resources according to some embodiments; and

FIG8 illustrates a functional block diagram of a wireless communication device in accordance with some embodiments.

DETAILED DESCRIPTION

The following description and accompanying drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural variations, logical variations, process variations, and other variations. Portions and features of some embodiments may be included in other embodiments, or portions and features of some embodiments may be substituted for portions and features of other embodiments. The embodiments set forth in the claims encompass all available equivalents of those claims.

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 signal transmission and D2D communication. Some embodiments provide configuration of a D2D discovery zone, wherein the D2D discovery zone is divided into a contention-based discovery zone and a non-contention-based discovery zone for both network-common configuration and cell-specific configuration of the discovery zone. Some embodiments provide a UE feedback mechanism to provide information about the load of the discovery zone to the eNB. Some embodiments provide options for supporting discovery between cells/eNBs. Some embodiments provide the use and configuration of a silence factor for random silence/adaptive random silence for the transmission of D2D discovery packets. Some embodiments provide signaling content including the following: discovery zone configuration, silence factor, transmit power control configuration, frequency 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-mentioned signaling content. Some embodiments provide for static configuration and/or pre-configuration of D2D discovery resources. Some embodiments provide for network and UE behavior that supports contention-free direct device discovery. These embodiments are discussed in detail below.

FIG1 illustrates a portion of an end-to-end network architecture of an LTE network and various components of the network, according to some embodiments. The network 100 includes a radio access network (RAN) (e.g., as described, E-UTRAN or Evolved Universal Terrestrial Radio Access Network) 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 enhanced Node B (eNB) 104 (which can be used 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. Additionally, it may be the local mobility anchor point for inter-eNB handovers and may also provide an anchor for inter-3GPP mobility. Other responsibilities may include lawful interception, charging, and some policy enforcement. The Serving GW 124 and MME 122 may be implemented on the same physical node or on 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 may be a key node for policy enforcement and charging data collection. It may also provide an anchor point for mobility with non-LTE access. External PDNs can be any type of IP network, as well as the IP Multimedia Subsystem (IMS) domain. The PDN GW 126 and the Serving GW 124 may be implemented on one physical node or separate physical nodes.

The eNBs 104 (macro and micro eNBs) terminate the air interface protocol and may be the first point of contact for the UE 102. In some embodiments, the eNBs 104 may implement various logical functions for 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 separates the RAN 100 from the EPC 120. It is divided into two parts: S1-U, which carries traffic data between the eNB 104 and the Serving GW 124; and S1-MME, which is the 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 the control plane interface between eNBs 104, while X2-U is the user plane interface between eNBs 104.

For 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 very dense phone usage, such as train stations. As used herein, the term low-power (LP) eNB refers to any suitable relatively low-power eNB used to implement narrower cells (narrower than macrocells), such as 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 the user's broadband line. Once installed, the femtocell connects to the mobile operator's mobile network and provides additional coverage to the residential femtocell, typically within a range of 30 to 50 meters. Therefore, an LP eNB may be a femtocell eNB because it is coupled through the PDN GW 126. Similarly, a picocell is a wireless communication system that typically covers a small area, such as within a building (office, shopping mall, train station, etc.) or, more recently, an airplane. A picocell eNB is typically connected to another eNB via an X2 link, such as a macro eNB through its base station controller (BSC) functionality. Thus, a low-end eNB can be implemented using a picocell eNB, as the picocell eNB is coupled to the macro eNB via the X2 interface. A picocell eNB or other low-end 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 the UE 102. The physical downlink control channel (PDCCH) carries, among other things, information about resource allocations and transport formats associated with the PDSCH channel. It also informs the UE 102 about H-ARQ information, transport formats, and resource allocations 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 the eNB 104 based on channel quality information fed back from the UE 102 to the eNB, and then downlink resource allocation information is sent to the UE 102 on the physical downlink control channel (PDCCH) intended for (and possibly allocated to) the UE 102.

PDCCH uses CCE (control channel elements) to transmit control information. Before being mapped to resource elements, PDCCH complex symbols are first organized into, which are then permuted (premuted) for rate matching using a sub-block interleaver. Each PDCCH is sent using one or more of these channel control elements (CCEs), where each CCE corresponds to nine groups of four physical resource elements called resource element groups (REGs). Four QPSK symbols are mapped to each REG. Depending on the size of the DCI and the channel conditions, the PDCCH can be sent using one or more CCEs. Four or more different PDCCH formats are defined in LTE, depending on the different number of CCEs (e.g., aggregation level, 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, which are discussed in more detail below, the ProSe-enabled UE 102 may transmit a discovery signal 101 within a discovery resource to discover one or more other ProSe-enabled UEs.

Figure 2 shows the structure of a resource grid including a discovery zone for D2D communication according to some embodiments. The resource grid shown is a time-frequency grid, referred to as a resource grid, which is the physical resource in the downlink or uplink in each time slot. The smallest time-frequency unit of the resource grid is represented as a resource element (RE). The resource grid includes multiple resource blocks that describe the mapping of certain physical channels to resource elements. Each resource block includes a set of resource elements and is in the frequency domain, which represents the minimum amount of resources that can be allocated, but does not limit the scope of the embodiment in this regard. There are several different physical channels that are transmitted 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) for use 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 multiple PRBs 206 of discovery resources. UE 102 may transmit discovery signals or discovery packets 101 ( FIG. 1 ) within some 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 resources of a physical uplink shared channel (PUSCH), 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 with a specific group 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, the discovery packet 101 may be sent within M subframes of N resource blocks, where M and N are at least 1 and may be greater than 1. These embodiments are described in more detail below.

In some embodiments, a PRB may include 12 subcarriers in the frequency domain and 0.5 milliseconds (i.e., one time slot) in the time domain. PRBs may be allocated in pairs (in the time domain), but this is not required. In some embodiments, a PRB may include multiple REs. An RE may include one subcarrier times one symbol. When a normal CP is used, an RB contains seven symbols. When an extended CP is used, an RB contains six symbols. A delay extension beyond the normal CP length indicates the use of an extended CP. Each subframe may be 1 millisecond (ms) and a frame may include 10 such subframes.

There are two different approaches to D2D discovery: restricted/closed D2D discovery and open D2D discovery. Restricted/closed D2D discovery can be applied to use cases where discoverable devices are only discoverable by a select group of ProSe-enabled discovery devices. Another implication of closed device discovery is to consider a scenario where the discovery device attempts to discover (one or more) specific ProSe-enabled devices (from one or more of a group of ProSe-enabled devices). Therefore, for this use case, the discovery device will be assumed to know the ProSe-enabled devices it wishes to discover in its vicinity.

Compared to closed D2D discovery, open device discovery considers that a discoverable device wishes to be discovered by all nearby ProSe-enabled devices. From the perspective of the discovering device, open device discovery implies that the discovering device is not assumed to know the identities of other ProSe-enabled devices before discovery. Therefore, the device discovery mechanism for open discovery should aim to discover as many ProSe-enabled devices as possible in its vicinity.

For open D2D discovery, the eNB 104 has limited control over the discovery process between UEs 102. In particular, the base station 104 may periodically allocate certain discovery resources in the form of a D2D discovery region to the UE 102 to transmit discovery information. The discovery information may be in the form of a discovery packet or discovery sequence with payload information. The content of the discovery-related information that the UEs intend to share with each other may be higher, as the design will require sending a unique ID for device identification, service identification, etc. (e.g., 48 bits or more) as the data payload, which may be protected by a CRC. Depending on the payload size and the overall discovery performance requirements, the number of resource blocks (denoted as ) used for discovery packet transmission in an open D2D discovery design may be one or more.

In some embodiments, the discovery area may include multiple occurrences of periodic discovery zones, where each discovery zone includes 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 zone 204 within an LTE operating area 202, where and represent the number of allocated RBs, the starting RB index, and the number of subframes, the starting subframe index, for each discovery zone, respectively. Information about the partitioning of these D2D discovery areas can be signaled semi-statically by the eNB using RRC signaling or by a system information block (SIB) within a network coverage scenario. For partial network coverage scenarios, this information can be forwarded by the coordinator UE to UEs outside of network coverage. For scenarios without network coverage, the discovery zones can be predefined or broadcast by the central 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 band edge)) may be designed to be reserved exclusively for D2D discovery, without limiting the scope of the embodiments in this respect. In some embodiments, the parameter may be configured as the period of D2D discovery zone allocation.

Even for the case of UE-based open discovery, it would be beneficial to explore potential network assistance in UE-specific discovery resource allocation for UEs in RRC_CONNECTED mode for the transmission of discovery signals, thereby improving the efficiency of the discovery process. In this regard, each D2D discovery zone (D2D=DZ) can be further divided into two orthogonal time-frequency zones: (1) non-contention-based D2D DZ (NCB-D2D DZ), where the eNB allocates periodic resources for the transmission of discovery signals and D2D UEs in RRC_CONNECTED mode can access this zone; (2) contention-based D2D DZ (CB-D2D DZ): this zone is generally available to all D2D UEs (including out-of-coverage UEs), where D2D-enabled UEs follow a purely contention-based transmission of discovery signals. Additionally, the D2D discovery resources used for the CB-D2D DZ can be divided into two parts (referred to as part A and part B) to enable D2D discovery and to roughly indicate the size of the D2D communication resource requirements based on the amount of D2D data buffered on the UE side (particularly due to the fact that the D2D discovery process can follow the D2D communication operation). The use of D2D discovery resources from a group indicates a preference for a larger amount of resources than a predetermined threshold.

According to some embodiments, D2D discovery zones may be configured in two different ways: network-common D2D discovery zones and cell-specific D2D discovery zones, details of both of which are described below. For network-common discovery zones, a common set of time-frequency resources may be reserved for D2D discovery across the entire network. The configuration may be different between different public land mobile networks (PLMNs) to allow the respective operators a degree of flexibility in resource configuration. Discovery zones may be configured by each PLMN via operations, administration and maintenance (OAM) tools. The network-common configuration of discovery zones may be signaled via a variety of means. The exact resource configuration may be determined based on statistics of the number of ProSe-enabled UEs in the network, their respective capabilities and locations (up to Tracking Area (TA) granularity). This information is available at the D2D server and the D2D server may inform the eNB of the precise resource configuration via the Mobility Management Entity (MME).

For a cell-specific discovery zone, each eNB 104 can use information about the current number of active ProSe-enabled UEs 102 and the interference situation to determine the exact resource configuration for the cell-specific discovery zone. Some of this information can be obtained via periodic/event-triggered/on-demand feedback from ProSe-enabled UEs 102 participating in the discovery process. To enable inter-eNB D2D discovery, a certain degree of cooperation between neighboring eNBs exists and can be achieved through the exchange of information about the configuration of the discovery zone between neighboring eNBs over the X2 interface.

According to an embodiment, the eNB 104 may send signaling to indicate the D2D discovery zone configuration to the ProSe-enabled UE 102. The signaling may indicate the time and frequency resources and periodicity of the discovery zone 204 and may indicate operating parameters for 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 may be semi-statically sent using radio resource control (RRC) signaling or sent using SIBs by the eNB 104. In the example shown in FIG2 , the discovery zone 204 includes multiple 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 a SIB transmission and a 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 all subsequent LTE releases).

For signaling in both network-common and cell-specific discovery zone allocation scenarios, the network should be able to signal this information to UEs in both RRC_CONNECTED and RRC_IDLE operating modes. For network-common D2D discovery zone allocation, a different signaling mechanism may be applied. In some embodiments, an existing system information block (SIB) (e.g., SIB2) may be used to signal D2D discovery zone configuration information including the quieting factor and other relevant cell- or network-common parameters, as described in more detail below.

In some embodiments, the discovery zone 204 may be referred to or considered a discovery period.In some embodiments, contention-based D2D discovery may be referred to or considered a type 1 discovery, while non-contention-based D2D discovery may be referred to or considered a 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-D2DDZ) and a contention-based D2D discovery zone (CB-D2D DZ). For the non-contention-based D2D discovery zone, periodic resources are allocated for non-contention-based transmission of discovery signals 101 by only ProSe-enabled UEs in RRC connected mode; and for the contention-based D2D discovery zone, periodic resources are allocated for contention-based transmission of discovery signals 101 by any ProSe-enabled UEs in RRC connected mode, RRC idle mode, and out-of-coverage UEs. In these embodiments, the non-contention-based D2D discovery zone may be designated for transmission of discovery signals 101 by ProSe-enabled UEs in RRC connected mode according to a non-contention-based technique. In some embodiments, ProSe-enabled UEs in RRC connected mode may be allocated specific discovery resources of the non-contention-based D2D discovery zone for transmission of their discovery signals 101. In some embodiments, the D2D discovery zone configuration signaling may indicate that the discovery zone 204 is partitioned 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 transmission of the discovery signal 101 by any ProSe-enabled UE according to pure contention-based transmission. In these embodiments, the ProSe-enabled UE is not allocated specific discovery resources for contention-based transmission of the discovery signal 101. The 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 other ProSe-enabled UEs such as out-of-coverage UEs (e.g., UEs connected to other eNBs).

In some of these embodiments, the eNB 104 may provide signaling for D2D discovery resources, and both contention-based and contention-free D2D discovery resources may be partitioned and configured by the eNB. In some embodiments, the partitioning may be logical. The actual partitioning 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 signaled from the D2D server to the ProSe-enabled UE via an application layer reconfiguration message.

In some embodiments, non-access stratum (NAS) signaling may be used to signal the D2D discovery 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 of the above 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, and therefore dynamic resource allocation is not preferred due to 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 a discovery zone load metric 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 make changes to a resource allocation configuration for D2D activities based on the discovery zone load metric. 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 metric to the eNB 104. Based on the discovery zone load metric, the eNB 104 may make changes to its resource allocation configuration for D2D activities (including resources used for D2D discovery and resources used for D2D communication). In some embodiments, based on the discovery zone load metric, the eNB 104 may make changes to optimize the resource allocation configuration for D2D activities. For example, based on the discovery zone load metric, the eNB 104 may change the size of the resource pool used for D2D activity and may allocate subsequent discovery zone resources and allocate resources for subsequent D2D communications. Based on the discovery zone load metric, the eNB 104 may also apply or suspend one or more interference control techniques (e.g., random muting or random probability transmission), for example, by changing parameters used for interference mitigation. 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 message 314.

In some embodiments, the discovery zone metric includes a count (e.g., a counted number) of discovery signal transmissions in the multiple occurrences of the discovery zone. In some embodiments, the discovery zone metric also includes a plurality of unique discovery signal transmissions, and the eNB may determine a plurality 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: a plurality of discovery signal transmissions in the multiple occurrences of the discovery zone; a plurality of discovery signals successfully detected in the multiple occurrences of the discovery zone; and an indication of the degree of interference in the multiple occurrences of the discovery zone. In some of these embodiments, the ProSe-enabled UE is capable of distinguishing discovery signal transmissions of other UEs based on DMRS, and the discovery zone metric may include a plurality of blindly detected unique DMRS sequences or unique cyclic shift values.

In these embodiments, the UE may be configured to provide feedback regarding the configuration of the D2D discovery area. For the case of cell-specific discovery area 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 is not aware of the number of UEs in RRC_IDLE mode participating in D2D discovery within its service area. Some embodiments provide information about the load of the service area to the eNB via enabling UE feedback.

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

A request for feedback on the number of transmissions in the past N discovery zones may be added to the paging message and enabled by the eNB when a UE or a group of UEs is required to report this metric. In addition, the number of UEs in RRC_CONNECTED mode participating in D2D discovery may be known by the eNB using the above mechanism or by a feedback request indicated via dedicated RRC or MAC CE signaling.

In some other embodiments, the UE may report discovery-related metrics or measurement reports similar to Minimization of Drive Tests (MDT) or as part of an MDT report. In idle mode, the UE stores and accumulates measurements and reports the recorded measurements once the UE is connected. In connected mode, the UE may report discovery-related measurements periodically or in an event-triggered manner. Since reporting is not immediate in idle mode, a timestamp indicating the moment the measurement result was recorded may need to be included. 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 number of successfully detected D2D discovery packet transmissions or the degree of interference may be reported. For example, assuming that the discovery packet transmission uses a randomly selected DM-RS base sequence and/or cyclic shift (for PUSCH-based discovery packet transmission), the UE may report the number of unique DM-RS sequences or cyclic shifts that were blindly detected, accumulated or averaged in the most recent N1 D2D discovery zones, where N1 may be predetermined or configurable.

FIG3B illustrates counting ProSe-enabled UEs using a random access channel (RACH) according to some embodiments. In these embodiments, 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 as part of an initial access procedure (operation 308). The RRC signaling may, for example, include an indication of the D2D capabilities of the transmitting ProSe-enabled UE 102. In these embodiments, the eNB 104 may determine whether to make changes to a resource allocation configuration for D2D activity based on the number of ProSe-enabled UEs 102 and a discovery area load metric 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 UEs in RRC_CONNECTED mode as well as UEs in RRC_IDLE mode.

FIG4 illustrates a process for counting ProSe-enabled UEs for a UE in radio resource control (RRC) connected mode. In these embodiments, the eNB 104 may be configured to send a D2D counting request message (message 402) and receive a D2D counting response message (operation 404) from a 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, which 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 a plurality of 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 transmitted within an 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 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 RACH preamble on the allocated access slot (e.g., RACH time/frequency resource). Note that a relatively rough estimate of the number of D2D-capable UEs is sufficient to determine whether D2D discovery resources need to be increased or decreased compared to the current configuration (this can be achieved by comparing to a certain threshold number related to the current D2D resource configuration). A very accurate count of a larger number of UEs is not necessary. Therefore, by allocating a number of preamble signature-slot combinations similar to or only slightly greater than this threshold number, the required information is straightforward to derive.

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

In some embodiments, the eNB may determine the number of ProSe-enabled UEs 102 based on an RRC message indicating discovery resource release sent by a ProSe-enabled UE in RRC connected mode. In some of these embodiments, ProSe-enabled UEs in RRC_CONNECTED mode may send an RRC message indicating discovery resource release even if they have not been configured with dedicated discovery resources. This information may help the eNB estimate the number of ProSe-enabled UEs in RRC_CONNECTED mode participating in D2D discovery and thus optimize resource allocation for UEs in RRC_CONNECTED mode.

In some embodiments, the eNB may determine the number of ProSe-enabled UEs 102 based on reception of 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 in RRC idle mode 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) to indicate time and frequency resources and the periodicity of the discovery zone and to indicate one or more discovery zone operating parameters. In some embodiments, while 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. The UE may automatically transition back to RRC idle mode upon receiving a resource configuration message from the eNB, the resource configuration message being used for at least transmissions 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 neighboring eNBs. The eNB 104 may be configured to signal the D2D discovery zone configuration information of one or more neighboring eNBs to a ProSe-enabled UE (e.g., via SIB signaling). In these embodiments, a certain degree of collaboration between neighboring eNBs may support inter-eNB discovery, particularly for scenarios involving cell-specific configuration of D2D discovery zones. In some embodiments, the eNBs 104 may exchange information regarding the configuration of D2D discovery zones in their respective cells. The D2D discovery configuration of the neighboring cells may be signaled to the UE 102 by the corresponding 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 and thereby be aware of the D2D discovery zone configuration in the neighboring cells. For both scenarios, it may depend on the UE implementation (particularly for UE-based open discovery) to determine whether to transmit and/or listen on the D2D discovery areas of all cells in its neighbor cell list (not overlapping with the D2D discovery area of its serving cell) or only on the D2D discovery areas of a selected subset of it.

For network-common configuration of D2D discovery zones, the constituent cells may be configured to maintain tight time synchronization with respect to subframe boundaries, subframe numbers (SFNs), etc., to enable a common D2D discovery zone. This may be achieved, for example, by using backhaul-based synchronization or using GPS. In some embodiments, the requirement for tight time synchronization may be relaxed by using an extended cyclic prefix (CP) for the D2D discovery zone and a normal-length cyclic prefix for the non-discovery zone.

For D2D discovery zones configured on a cell-specific basis, a challenge arises in the coexistence of D2D discovery transmission/reception and cellular (WLAN) traffic. 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 scheduling and UL power control of PUSCH transmission; incorporating some form of transmit power control for discovery signal transmission (e.g., by configuring a maximum transmit power); employing a cell clustering approach; and/or UE selection of discovery resources based on UE geometry. These embodiments are described in more detail below.

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

In some embodiments, the eNB 104 is configured to exchange D2D discovery zone configuration information with one or more neighboring eNBs. Based on the D2D discovery zone configuration information of the one or more neighboring eNBs, the eNB 104 can be configured to engage in inter-cell interference cancellation 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 cancellation techniques include one or more of the following:

● Implementation of cooperative subframe power control for D2D discovery signal transmissions, where uplink subframe sets are configured with separate power control parameters for interference cancellation between uplink cellular transmissions (e.g., Physical Uplink Shared Signal (PUSCH) transmissions) and D2D discovery signal transmissions;

● Configuration of transmit power control levels for transmission of discovery signals;

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

● Adoption of inter-cell discovery zone partitioning based on geometric layout.

FIG5 illustrates cooperative uplink subframe power control for D2D discovery signal transmissions, according to some embodiments. In some of these embodiments, because the configuration of the D2D discovery zone in the neighboring cell is known to the serving cell, UL scheduling and UL power control for PUSCH transmissions can be configured by the serving cell. In some embodiments, two UL subframe sets can be configured with separate power control parameters (e.g., open-loop power control parameters P0 and alpha) for different UL subframe sets. By using one UL subframe set to cover the D2D discovery resources of (one or more) neighboring cells, this can avoid strong inter-cell interference from cellular PUSCH transmissions to D2D discovery signal reception in the neighboring cell, as shown in FIG5 .

Some embodiments may incorporate a form of transmit power control (e.g., by configuring a maximum transmit power) for the transmission of discovery signals. 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 by exchanging information via X2 115 ( FIG. 1 ). In these embodiments, only the time-frequency resources reserved for the D2D discovery zone need to be aligned, and each cell may independently configure a quieting factor (as described in more detail below) to adjust for variations in the load of the D2D discovery zone to manage intra-cell/intra-cluster interference within the D2D discovery zone.

In some embodiments, the discovery zone operation parameters may include at least one of a quieting factor, a transmit power control configuration, frequency hopping-related parameters, and a scrambling ID. In these embodiments, regardless of the type of D2D discovery operation (open or restricted discovery), for a ProSe-enabled UE in RRC_CONNECTED or RRC_IDLE mode, certain parameters related to the configuration and transmission of the discovery zone and signals (e.g., discovery packets) may be signaled to the corresponding UE.

In these embodiments, the discovery zone configuration may include any partitioning of the entire zone 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 may indicate the time offset and periodicity of the configuration of these zones. For cell-specific discovery zone allocations, this information will be cell-specific, and the serving cell may signal parameters corresponding to neighboring 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 needs to be signaled. In one embodiment, each ProSe-enabled UE 102 may be configured with a named muting factor that is applied to the first occurrence of a discovery zone for the respective UE. For subsequent discovery zone occurrences, the muting factor applied by the UE may be increased or decreased within certain upper and lower bounds (based on certain factors signaled by the network/eNB) depending on whether the UE was transmitting in the previous zone. The bounds may be static (pre-configured) or configured and updated at a very slow 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 that is configured to include a muting factor in the discovery zone parameters. In these embodiments, the silence and muting protocol configures the ProSe-enabled UE with the muting factor for D2D discovery signal transmission on randomly selected resources in the D2D discovery zone based on a probability indicated by the muting factor. The effective arrival rate of the discovery packets and, thereby, the level of interference within the D2D discovery zone may be controlled. In these embodiments, each ProSe-enabled UE intending to send a discovery packet may randomly select a resource from within the D2D discovery zone and may send the packet with a certain probability (e.g., (1-p), where 0≤p≤1). In these embodiments, p may be defined as a muting factor or transmission probability factor configured by the network, which may be implemented by the individual serving cell in a network-common manner or in a cell-specific manner.

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

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 transmission of D2D discovery signals that is lower than the transmit power specified by the corresponding UE class. In these embodiments, depending on the discovery traffic conditions and use case, the ProSe-enabled UE may be configured with a maximum transmit power that is lower than the transmit power specified by the corresponding UE class. The maximum transmit power may be applied to discovery packet transmissions. If supported, additional parameters related to more advanced adaptive power control options will also need to be signaled.

In some embodiments, when the discovery zone parameter includes a frequency hopping related parameter, the frequency hopping related parameter indicates:

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

Frequency hopping type including Type 1 or Type 2 frequency hopping;

Frequency hopping modes including intra-subframe or inter-subframe hopping;

• Subband size for Type 2 frequency hopping; and

● Pseudo-random sequence initialization for Type 2 frequency hopping.

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

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

For restricted discovery, the scrambling ID can be used to filter decoded candidates by the discovering UE before sending the candidate list to higher layers for validation for restricted discovery. For restricted discovery, the scrambling is the same on a whitelist-by-whitelist basis for restricted discovery. Thus, those ProSe-enabled UEs that are no longer on the whitelist will not be able to decode the packet. The closed group scrambling seed should be generated by the D2D server and sent 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 for 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 the 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 are not in each other's respective whitelists, while UE_C is in both whitelists. UE_C may then be assigned two different Temp_IDs (UE_Ca and UE_Cb), such that both UE_A and UE_B can discover UE_Ca and UE_Cb, respectively, and thus, upon subsequent identification from the network, can discover UE_C. However, UE_A and UE_B can only discover each other via an open discovery operation.

FIG6 illustrates eNB-triggered 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 to a ProSe-enabled UE in RRC_connected mode a semi-persistent allocation of discovery resources 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), where the eNB configures dedicated resources for transmission of discovery signals to one or more ProSe-enabled UEs in RRC_CONNECTED mode in operation 604. Resource allocation in this scenario may be implemented using a combination of RRC and Layer 1 signaling in the form of a semi-persistent allocation of discovery resources (operation 606). The configured dedicated resources may also be released by the eNB based on load and overall D2D discovery resource allocation status (operation 608).

FIG7 illustrates eNB-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 for contention-free transmission of D2D discovery signals in response to an RRC resource request from the ProSe-enabled UE. In addition to eNB-determined discovery resource release, 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_CONNECTED UE, for example, upon initiation from higher layers, may request resources for D2D discovery signal transmission from a serving cell via the RRC layer (operation 702). Then, based on the eNB's decision, the serving cell may configure the UE with resource allocation via RRC signaling (operation 704) and ultimately, semi-persistent allocation via Layer 1 signaling. Layer 1 signaling/activation is not used, as resources may be configured via RRC (operation 704) and discovery transmission is then automatically activated starting with the next occurrence of a discovery resource pool/zone (operation 706). In addition to the release of resources decided by the eNB (operation 710), the UE may 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 can be well implemented.

Furthermore, resources for D2D discovery may be reserved at the cell/cell cluster level or the network level independently of the presence of an active ProSe-enabled UE (i.e., no discovery zone is configured). In such a case, a ProSe-enabled UE in RRC_CONNECTED mode may send an allocation of D2D discovery resources via the RRC or application layer. If it is requested via the application layer, the request will be sent to the D2D server, which in turn requests the eNB to open a discovery zone or allocate additional resources as needed for contention-free discovery. In addition, a ProSe-enabled UE in RRC_IDLE mode also transitions to connected mode to send a discovery resource request. However, this does not involve RRC connection establishment. For example, the UE may send an RRC connection request indicating only a discovery zone request. Alternatively, the UE automatically enters 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 National Security and Public Safety (NSPS) use cases for D2D discovery in outdoor and partial network coverage scenarios, certain periodic time-frequency resources may be pre-configured for use by Public Safety (PS) ProSe-enabled UEs as D2D discovery resources. Such resources may be configured with a low duty cycle, and under appropriate conditions, and in accordance with the specific D2D discovery protocol, additional resources may be allocated to supplement the pre-configured D2D discovery areas by coordinating UEs for partial network coverage or out of network coverage scenarios. The configuration of additional resources may follow the principles outlined above and take into account the existence of a statically pre-configured default D2D discovery area.

In some embodiments, for intra-cell D2D discovery zone partitioning based on geometric layout, a UE may receive signaling from a serving eNB indicating D2D discovery zone configuration information for one or more neighbor eNBs, including discovery resources for the D2D discovery zone for at least one of a cell-center D2D UE and a cell-edge D2D UE. The UE may select resources designated for the cell-center D2D UE or the cell-edge D2D UE for transmission of D2D discovery signals based at least on the RSRP of the serving eNB. In these embodiments, the UE may select discovery resources based on the UE geometric layout. The discovery zone may be partitioned, with some discovery resources primarily used for cell-center UEs (if these discovery resources are used for normal UL scheduling in neighboring cells). A ProSe-enabled UE with an RSRP _Service /RSRP _{Strongest Neighbor} ratio greater than a predetermined or configured threshold may transmit D2D transmission packets in the service area reserved for the cell-center ProSe-enabled UE. In the above, RSRP _Service refers to the RSRP of the serving cell, and RSRP _{Strongest Neighbor} corresponds to the RSRP of the cell with the largest RSRP value in the neighbor cell list. This geometrically based inter-cell D2D discovery zone partitioning, coupled with detailed scheduling of PUSCH transmissions and WAN traffic within a cell, enables the coexistence of D2D discovery zones and LTE UL transmissions in neighboring cells. The eNBs can exchange information about discovery resources for D2D UEs in the cell center or at the cell edge. In some of these embodiments, UEs can select discovery resources based on RSRP _service rather than this ratio and will function similarly, particularly in NWs with eNBs of similar transmit power (e.g., for macro-only networks).

FIG8 illustrates a functional block diagram of a wireless communication device, according to some embodiments. A wireless communication device (WDC) 800 may be suitable for use as a UE 102 ( FIG1 ) or an eNB 104 ( FIG1 ). WDC 800 may include physical layer (PHY) circuitry 802 for transmitting and receiving signals to and from other WDCs (eNBs and UEs) using one or more antennas 801, as well as for D2D communication with other UEs. WDC 800 may also include medium access control (MAC) circuitry 804 for controlling access to the wireless medium. WDC 800 may also include processing circuitry 806 and memory 808, which are arranged to configure various elements of WDC 800 to perform the various operations described herein.

In some embodiments, the mobile device can be part of a portable wireless communication device (such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capabilities, a web tablet, a wireless phone, a smart phone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.)), or other device that can wirelessly receive and/or send information. In some embodiments, the mobile device can include one or more of a keyboard, a display, a non-volatile memory port, multiple antennas, a graphics processor, an application processor, a speaker, and other mobile device components. The display can be an LCD screen including a touch screen.

Antenna 801 may include one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas, or other types of antennas suitable for transmitting RF signals. In some multiple-input multiple-output (MIMO) embodiments, the antennas may be effectively separated to exploit spatial diversity and potentially different channel characteristics.

Although the mobile device is shown as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by a combination of software-configured elements (such as a processing element including a digital signal processor (DSP)) and/or other hardware elements. For example, some elements may include one or more microprocessors, DSPs, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio frequency integrated circuits (RFICs), and various hardware and logic circuits for performing at least the functions described herein. In some embodiments, a functional element may refer to one or more processes operating on one or more processing elements.

Embodiments may be implemented in one or a combination of hardware, firmware, and software. Embodiments may also be implemented as instructions stored on a computer-readable storage device, which may be read and executed by at least one processor to implement the operations described herein. A computer-readable storage device may include any non-transitory mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a computer-readable storage device may include a read-only memory (ROM), a random access memory (RAM), a magnetic disk storage medium, an optical storage medium, a flash memory device, and other storage devices and media. Some embodiments may include one or more processors and may be configured with instructions stored on a computer-readable storage device.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b): The Abstract will allow the reader to ascertain the nature and gist of the technical disclosure. It should be understood that it will not be used to limit or interpret the scope or meaning of the claims. The appended claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.

Claims (13)

1. An apparatus for use in a user equipment (UE) configured for proximity service ProSe, the apparatus comprising: a memory; and processing circuitry configured to: Receive a System Information Block (SIB) from an Enhanced Node B (eNB), the SIB including discovery area configuration information for direct UE-to-UE communication, the SIB including indications for resources in the discovery area used for discovery signal transmission; For other UEs monitoring certain resources in the discovery area; and The eNB-based Reference Signal Received Power (RSRP) is selected to choose the resources in the discovery area used for transmitting discovery signals. 2. The apparatus of claim 1, wherein the processing circuitry configures the UE to send Radio Resource Control (RRC) signaling to the eNB to include UE-to-UE capabilities, the UE-to-UE capabilities indicating whether the UE supports UE-to-UE discovery. 3. The apparatus of claim 1, wherein the processing circuitry configures the UE to transmit the discovery signal at a power level based at least in part on a power factor associated with the discovery area configuration. 4. The apparatus of claim 1, wherein the SIB indicates the periodicity and time and frequency of resources in the discovery area. 5. The apparatus of claim 4, wherein when the UE is in Radio Resource Control (RRC) Idle mode (RRC_IDLE), the UE is configured to switch to RRC Connected mode (RRC_CONNECTED) to send a Discovery Resource Request to the eNB, and The UE is also configured to switch back to the RRC idle mode after receiving a resource configuration message from the serving eNB, the resource configuration message being used at least for transmissions in the resources of the discovery area that are indicated for contention-based transmissions. 6. The apparatus of claim 5, wherein the SIB indicates: The periodic resources of the discovery area are allocated for contention-free transmission of discovery signals by ProSe-enabled UEs in RRC connection mode; and The periodic resources of the discovery area are allocated for contention-based transmission of discovery signals by ProSe-enabled UEs in RRC connected mode and RRC idle mode. 7. The apparatus of claim 1 further includes a transceiver circuit configured to transmit and receive signals over the discovery area. 8. A non-transitory computer-readable storage medium storing instructions for execution by a processing circuit of a user equipment (UE) to configure the UE to perform operations for Proximity Service ProSe, the processing circuit being configured to: Receive a System Information Block (SIB) from an Enhanced Node B (eNB), the SIB including discovery area configuration information for direct UE-to-UE communication, the SIB including indications for resources in the discovery area used for discovery signal transmission; For other UEs monitoring certain resources in the discovery area; and The eNB-based Reference Signal Received Power (RSRP) is selected to choose the resources in the discovery area used for transmitting discovery signals. 9. The non-transitory computer-readable storage medium of claim 8, wherein the processing circuitry configures the UE to send Radio Resource Control (RRC) signaling to the eNB to include UE-to-UE capability, the UE-to-UE capability indicating whether the UE supports UE-to-UE discovery. 10. The non-transitory computer-readable storage medium of claim 8, wherein the processing circuitry configures the UE to transmit the discovery signal at a power level based at least in part on a power factor associated with the discovery area configuration. 11. A method for ProSe (Proximity Service), comprising the following operations performed by a user equipment (UE): Receive a System Information Block (SIB) from the Enhanced Node (BeNB), which includes discovery area configuration information for direct UE-to-UE communication. The SIB includes an indication of a resource in the discovery area that is used for discovering signal transmissions; For other UEs monitoring certain resources in the discovery area; and The eNB-based Reference Signal Received Power (RSRP) is selected to choose the resources in the discovery area used for transmitting discovery signals. 12. The method of claim 11, further comprising: The UE is configured to send Radio Resource Control (RRC) signaling to the eNB to include UE-to-UE capabilities, which indicate whether the UE supports UE-to-UE discovery. 13. The method of claim 11, further comprising: configuring the UE to transmit the discovery signal at a power level based at least in part on a power factor associated with the discovery area configuration.