PATENT DOCUMENT

Publication Number: US-11076401-B2
Application Number: US-201816110729-A
Country: US
Kind Code: B2

Title: User equipment discovery resource pool signalling for user equipments configured for Pro-Se direct discovery

Abstract:
Embodiments of a user equipment (UE) and method for resource allocation and device-to-device (D2D) discovery hopping are generally described herein. In some embodiments, the UE may receive signaling from an enhanced node B (eNB) indicating discovery resources to transmit discovery signals on within an LTE operation zone. The discovery resources may include a discovery zone which may comprise a plurality of physical resource blocks (PRBs) and a plurality of subframes. The UE may transmit a discovery signal for receipt by one or more other UEs for D2D discovery within some of the PRBs of the discovery zone. The PRBs for the transmission of the discovery signal may be determined in accordance with a hopping mode to provide increased frequency diversity within a bandwidth of the discovery zone. The hopping mode may comprise intra-subframe hopping, inter-subframe hopping or joint intra/inter-subframe hopping.

Claims:
What is claimed is: 
     
       1. An apparatus of a user equipment (UE) configured for proximity services (ProSe) direct discovery, the apparatus comprising:
 one or more processors configured to:
 configure the UE for a device-to-device (D2D) discovery operation, wherein as part of the D2D discovery operation, the one or more processors are configured to:
 decode, from radio resource control (RRC) signaling, a D2D discovery resource configuration for configuring a discovery resource zone within a discovery region; 
 determine, according to the D2D discovery resource configuration, resources of the discovery resource zone from a starting resource block index, a number of resource blocks and a plurality of subframes; and 
 encode, according to the D2D discovery resource configuration, a discovery signal for transmission in the resources of the discovery resource zone; 
 
 select a subframe and resource block within the discovery resource zone for transmission of the discovery signal, wherein the selection of the subframe and resource block within the discovery resource zone is random. 
 
 
     
     
       2. The apparatus of  claim 1 , wherein resource blocks of the discovery resource zone are arranged in an increasing order of resource block indices. 
     
     
       3. The apparatus of  claim 1 , wherein the one or more processors are configured to:
 detect signaling from another UE, the signaling including a discovery transport block; and 
 decode discovery signaling from the discovery transport block according to the D2D discovery resource configuration. 
 
     
     
       4. The apparatus of  claim 1 , wherein the one or more processors are configured to encode the discovery signal for transmission in two physical resource blocks per slot of a single subframe within a discovery period. 
     
     
       5. The apparatus of  claim 4 , wherein the two physical resource blocks are contiguous physical resource blocks. 
     
     
       6. The apparatus of  claim 1 , wherein the D2D discovery resource configuration is for one of a Type 1 discovery operation or a Type 2 discovery operation. 
     
     
       7. The apparatus of  claim 1 , wherein the one or more processors are configured to decode, from the RRC signaling, a system information block (SIB), the SIB including the D2D discovery resource configuration. 
     
     
       8. The apparatus of  claim 1 , wherein the apparatus further comprises two or more antennas and a transceiver, the two or more antennas and the transceiver configured to transmit the discovery signal, in the discovery resource zone during a discovery period, according to the D2D discovery resource configuration. 
     
     
       9. A computer-readable hardware storage device that stores instructions for execution by one or more processors of a user equipment (UE) configured for proximity services (ProSe) direct discovery, the instructions to configure the one or more processors to:
 configure the UE for a device-to-device (D2D) discovery operation, wherein as part of the D2D discovery operation, the instructions are to configure the one or more processors to:
 decode, from radio resource control (RRC) signaling, a D2D discovery resource configuration for configuring a discovery resource zone within a discovery region; 
 determine, according to the D2D discovery resource configuration, resources of the discovery resource zone from a starting resource block index, a number of resource blocks and a plurality of subframes; and 
 encode, according to the D2D discovery resource configuration, a discovery signal for transmission in the resources of the discovery resource zone; 
 
 select a subframe and resource block within the discovery resource zone for transmission of the discovery signal, wherein the selection of the subframe and resource block within the discovery resource zone is random. 
 
     
     
       10. The computer-readable hardware storage device of  claim 9 , wherein resource blocks of the discovery resource zone are arranged in an increasing order of resource block indices. 
     
     
       11. The computer-readable hardware storage device of  claim 9 , wherein the instructions are to configure the one or more processors to:
 detect signaling from another UE, the signaling including a discovery transport block; and 
 decode discovery signaling from the discovery transport block according to the D2D discovery resource configuration. 
 
     
     
       12. The computer-readable hardware storage device of  claim 9 , wherein the instructions are to configure the one or more processors to encode the discovery signal for transmission in two physical resource blocks per slot of a single subframe within a discovery period. 
     
     
       13. The computer-readable hardware storage device of  claim 12 , wherein the two physical resource blocks are contiguous physical resource blocks. 
     
     
       14. The computer-readable hardware storage device of  claim 9 , wherein the D2D discovery resource configuration is for one of a Type 1 discovery operation or a Type 2 discovery operation. 
     
     
       15. The computer-readable hardware storage device of  claim 9 , wherein the one or more processors are configured to decode, from the RRC signaling, a system information block (SIB), the SIB including the D2D discovery resource configuration. 
     
     
       16. An apparatus of a base station (BS), the apparatus comprising: one or more processors, configured to:
 configure a user equipment (UE) for a proximity services (ProSe) direct discovery operation, wherein to configure the UE for the ProSe direct discovery operation, the one or more processors are configured to:
 encode radio resource control (RRC) signaling, for transmission to the UE, the RRC signaling including a D2D discovery resource configuration for configuring a discovery resource zone within a discovery region 
 define resources of the discovery resource zone according to a starting resource block index, a number of resource blocks in the resource block pool and a plurality of subframes; and 
 transmit the RRC signaling to the UE for determining, according to the D2D discovery resource configuration, the discovery resource zone; 
 
 wherein, based on the RRC signaling, the UE is configured to select a subframe and resource block within the discovery resource zone for transmission of the discovery signal, wherein the selection of the subframe and resource block within the discovery resource zone is random. 
 
     
     
       17. The apparatus of  claim 16 , wherein the one or more processors are configured to configure the discovery resource zone to include resource blocks arranged in an increasing order of resource block indices. 
     
     
       18. The apparatus of  claim 16 , wherein the D2D discovery resource configuration is for one of a Type 1 discovery operation or a Type 2 discovery operation. 
     
     
       19. A computer-readable hardware storage device that stores instructions for execution by one or more processors of a base station (BS), the instructions to configure the one or more processors to:
 configure a user equipment (UE) for a proximity services (ProSe) direct discovery operation, wherein to configure the UE for the ProSe direct discovery operation, the instructions are to configure the one or more processors to:
 encode radio resource control (RRC) signaling, for transmission to the UE, the RRC signaling including a D2D discovery resource configuration for configuring a discovery resource zone within a discovery region 
 define resources of the discovery resource zone according to a starting resource block index, a number of resource blocks in the resource block pool and a plurality of subframes; and 
 transmit the RRC signaling to the UE for determining, according to the D2D discovery resource configuration, the discovery resource zone; 
 
 wherein, based on the RRC signaling, the UE is configured to select a subframe and resource block within the discovery resource zone for transmission of the discovery signal, wherein the selection of the subframe and resource block within the discovery resource zone is random. 
 
     
     
       20. The computer-readable hardware storage device of  claim 19 , wherein the instructions are to configure the one or more processors to:
 configure the discovery resource zone to include resource blocks arranged in an increasing order of resource block indices.

Description:
PRIORITY CLAIM 
     This application is a continuation of U.S. patent application Ser. No. 14/778,528, filed Sep. 18, 2015, which is a U.S. National Stage Filing under 35 U.S.C. 371 from international Application No. PCT/US2014/031996, filed Mar. 27, 2014 and published in English as WO 2014/209451 on Dec. 31, 2014, which, claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 61/841,230, filed Jun. 28, 2013, each of which are incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     Embodiments pertain to wireless communications. Some embodiments relate to 3GPP LTE (Long Term Evolution) networks. Some embodiments relate to direct device-to-device (D2D) communication. Some embodiments relate to direct device-to-device (D2D) communication in LTE networks. 
     BACKGROUND 
     Support for direct D2D communication as an integrated part of a wireless communication system is currently being considered for the further evolution of LTE networks. With direct D2D communication, user equipment (UE) may communicate directly with each other without involvement of a base station or an enhanced node B (eNB). One issue with D2D communication is device discovery to enable D2D service. Device discovery involves discovering one or more other discoverable UEs within communication range for D2D communication. Device discovery also involves being discovered by one or more other discovering UEs within communication range for D2D communication. There are many unresolved issues with respect to device discovery for D2D communication including resource allocation for device discovery. 
     Thus there are general needs for UEs and methods for device discovery for D2D communication in LTE networks. There are also general needs for UEs and methods for resource allocation for device discovery for D2D communication in LTE networks 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a portion of an end-to-end network architecture of an LTE network with various components of the network in accordance with some embodiments; 
         FIG. 2  shows a structure for a resource grid for communications in a network, such as the LTE network of  FIG. 1 , in accordance with some embodiments; 
         FIG. 3  illustrates Type 1 intra-subframe D2D discovery hopping in accordance with some embodiments; 
         FIG. 4  illustrates Type 1 inter-subframe D2D discovery hopping in accordance with some embodiments; 
         FIG. 5  illustrates Type 1 joint intra/inter-subframe D2D discovery hopping in accordance with some embodiments; 
         FIG. 6  illustrates Type 2 intra-subframe D2D discovery hopping in accordance with some embodiments; 
         FIG. 7  illustrates Type 2 inter-subframe D2D discovery hopping in accordance with some embodiments; 
         FIG. 8  illustrates Type 2 joint intra/inter-subframe D2D discovery hopping in accordance with some embodiments; 
         FIG. 9  illustrates a functional block diagram of a UE in accordance with some embodiments; and 
         FIG. 10  is a procedure for D2D discovery hopping discovery in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims. 
       FIG. 1  shows a portion of an end-to-end network architecture of an LTE network with various components of the network in accordance with some embodiments. The network  100  comprises a radio access network (RAN) (e.g., as depicted, the E-UTRAN or evolved universal terrestrial radio access network)  100  and the core network  120  (e.g., shown as an evolved packet core (EPC)) coupled together through an S1 interface  115 . For convenience and brevity sake, only a portion of the core network  120 , as well as the RAN  100 , is shown. 
     The core network  120  includes mobility management entity (MME)  122 , serving gateway (serving GW)  124 , and packet data network gateway (PDN GW)  126 . The RAN includes enhanced node B&#39;s (eNBs)  104  (which may operate as base stations) for communicating with user equipment (LIE)  102 . The eNBs  104  may include macro eNBs and low power (LP) eNBs. 
     In accordance with some embodiments, the UEs  102  may be arranged for device-to-device (D2D) communications including D2D discovery of other UEs  102  for direct D2D communication. These embodiments are discussed in more detail below. 
     The MME is similar in function to the control plane of legacy Serving GPRS Support Nodes (SGSN). The MME manages mobility aspects in 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, it may be a local mobility anchor point for inter-eNB handovers and also may provide an anchor for inter-3GPP mobility. Other responsibilities may include lawful intercept, charging, and some policy enforcement. The serving GW  124  and the MME  122  may be implemented in one physical node or separate physical nodes. The PDN GW  126  terminates an SGi interface toward the packet data network (PDN). The PDN GW  126  routes data packets between the EPC  120  and the external PDN, 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 accesses. The external PDN can be any kind 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 separated physical nodes. 
     The eNBs  104  (macro and micro) terminate the air interface protocol and may be the first point of contact for a UE  102 . In some embodiments, an eNB  104  may fulfill 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  is the interface that separates the RAN  100  and the EPC  120 . It is split into two parts: the S1-U, which carries traffic data between the eNBs  104  and the serving GW  124 , and the S1-MME, which is a signaling interface between the eNBs  104  and the MME  122 . The X2 interface is the interface between eNBs  104 . The X2 interface comprises two parts, the X2-C and X2-U. The X2-C is the control plane interface between the eNBs  104 , while the X2-U is the user plane interface between the eNBs  104 . 
     With cellular networks, LP cells are typically used to extend coverage to indoor areas where outdoor signals do not reach well, or to add 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 for implementing a narrower cell (narrower than a macro cell) such as a femtocell, a picocell, or a micro cell. Femtocell eNBs are typically provided by a mobile network operator to its residential or enterprise customers. A femtocell is typically the size of a residential gateway or smaller and generally connects to the user&#39;s broadband line. Once plugged in, the femtocell connects to the mobile operator&#39;s mobile network and provides extra coverage in a range of typically 30 to 50 meters for residential femtocells. Thus, a LP eNB might be a femtocell eNB since it is coupled through the PDN GW  126 . Similarly, a picocell is a wireless communication system typically covering a small area, such as in-building (offices, shopping malls, train stations, etc.), or more recently in-aircraft. A picocell eNB can generally connect through the X2 link to another eNB such as a macro eNB through its base station controller (BSC) functionality. Thus, LP eNB may be implemented with a picocell eNB since it is coupled to a macro eNB via an X2 interface. Picocell eNBs or other LP eNBs may incorporate some or all functionality of a macro eNB. In some cases, this may be referred to as an access point base station or enterprise femtocell. 
     In accordance with some embodiments, a UE  102  that is configured for D2D discovery operations may receive signaling from an eNB  104 . The signaling may indicate a discovery zone within an LTE operation zone. The LTE operation zone may comprise a plurality of physical resource blocks (PRBs) and the discovery zone may comprise PRBs within the LTE operation zone. A UE  102  may transmit a discovery signal  101  for receipt by one or more other UEs  102  (i.e., for D2D discovery) within a plurality of physical resource blocks (PRBs) of the discovery zone. The PRBs for transmission of the discovery signal  101  may be determined in accordance with a hopping mode to provide increased frequency diversity within the bandwidth of the discovery zone. In these embodiments, the hopping mode may comprise intra-subframe hopping, inter-subframe hopping or joint intra/inter-subframe hopping. These embodiments are described in more detail below. 
     The increased frequency diversity provided by discovery hopping may help the discovery signal  101  to be received by other UEs  102 . In some embodiments, the discovery signal  101  may comprise a discovery packet. In other embodiments, the discovery signal may comprise a discovery sequence. In some embodiments, the discovery signal  101  may comprise one or more discovery packets which may include a payload with discovery information. The discovery information may be used to identify the transmitting UE  102 . The discover information may indicate that the transmitting UE  102  wishes to be discovered or may indicate that the transmitting UE  102  wishes to discover other UEs. In some embodiments, device discovery may include proximity detection. 
     In some LTE embodiments, a physical downlink shared channel (PDSCH) carries user data and higher-layer signaling to a UE  102 . The physical downlink control channel (PDCCH) carries information about the transport format and resource allocations related to the PDSCH channel, among other things. It also informs the UE  102  about the transport format, resource allocation, and H-ARQ information related to the uplink shared channel. Typically, downlink scheduling (assigning 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 UEs  102  to the eNB  104 , and then the downlink resource assignment information is sent to a UE on a physical downlink control channel (PDCCH) used for (and possibly assigned to) the UE  102 . 
     The PDCCH uses CCEs (control channel elements) to convey the control information. Before being mapped to resource elements, the PDCCH complex-valued symbols may be first organized into quadruplets, which are then permuted using a sub-block inter-leaver for rate matching. Each PDCCH is transmitted using one or more of these control channel elements (CCEs), where each CCE corresponds to nine sets of four physical resource elements known as resource element groups (REGs). Four QPSK symbols are mapped to each REG. The PDCCH can be transmitted using one or more CCEs, depending on the size of DCI and the channel condition. There may be four or more different PDCCH formats defined in LTE with different numbers of CCEs (e.g., aggregation level, L,=1, 2, 4, or 8). 
       FIG. 2  shows a structure for a resource grid for communications in a network, such as the LTE network of  FIG. 1 , in accordance with some embodiments. The depicted grid is a time-frequency grid, called a resource grid, which is the physical resource in the downlink or uplink in each slot. The smallest time-frequency unit in a resource grid is denoted as a resource element (RE). The resource grid comprises a number of resource blocks (RBs), which describe the mapping of certain physical channels to resource elements. Each resource block comprises a collection of resource elements and in the frequency domain, represents the smallest quanta of resources that currently can be allocated. There are several different physical channels that are conveyed using such resource blocks. The resource grid illustrated in  FIG. 2  may comprise an LTE operation zone  202  which may comprise a plurality of PRBs for use by the RAN  100 . 
     In accordance with some embodiments, a UE  102  ( FIG. 1 ) may receive signaling from an eNB  104  indicating a discovery zone  204  within the LTE operation zone  202 . The discovery zone  204  may comprises a plurality of PRBs. The UE  102  may transmit a discovery signal  101  ( FIG. 1 ) for receipt by one or more other UEs  102  ( FIG. 1 ) for D2D discovery within some PRBs  206  of the discovery zone  204 . As discussed above, the PRBs  206  for transmission of the discovery signal  101  may be determined in accordance with a hopping mode which may provide increased frequency diversity within the bandwidth  208  of the discovery zone  204 . This may improve the chances of discovering other UEs and well as being discovered by other UEs. In some embodiments, device discovery may include proximity detection. 
     In accordance with embodiments, a PRB may be associated with a particular slot of a subframe in the time dimension and a particular group of frequency subcarriers in the frequency dimension. Each PRB, for example, may be identified by a RB index and a subframe index. In some embodiments, a discovery signal  101  may be transmitted within M subframes of N resources blocks where M and N are at least one and can be greater than one. These embodiments are described in more detail below. 
     In some embodiments, a PRB may comprise 12 sub-carriers in the frequency domain by 0.5 ms (one slot) in the time domain. The PRBs may be allocated in pairs (in the time domain), although this is not a requirement. In some embodiments, the PRB may comprise a plurality of resource elements (REs). A RE may comprise one sub-carrier by one symbol. When a normal CP is used, the resource block contains seven symbols. When an extended CP is used, the resource block contains six symbols. A delay spread that exceeds the normal CP length indicates the use of extended CP. Each subframe may be 1 ms and one frame may comprise ten such subframes. 
     There are two different approaches in D2D discovery: restricted/closed D2D discovery and open D2D discovery. Restricted/closed D2D discovery applies to use cases wherein a discoverable device may be discovered only by a select set of ProSe enabled discovering devices. A further implication of closed device discovery is consideration of scenarios wherein a discovering device tries to discover particular ProSe enabled device(s) (one or many from a set of ProSe enabled devices). Thus, for this use case, a discovering device would be assumed to know the ProSe enabled device it wishes to discover in its proximity. 
     Contrary to closed D2D discovery, open device discovery considers use cases wherein a discoverable device may want itself to be discovered by all ProSe enabled devices in its proximity. From the perspective of the discovering device, open device discovery implies that a discovering device may not be assumed to be aware of the identity of other ProSe enabled devices prior to discovery. Consequently, the device discovery mechanism for open discovery should aim towards discovering as many ProSe enabled devices in its proximity as possible. 
     Embodiments disclosed herein provide resource allocation mechanisms and hopping designs are may be applied for both restricted/close and open D2D discovery. Open D2D discovery is used in the various examples discussed below. For open D2D discovery, an eNB  104  may have a limited control on the discovery process among the UEs  102 . In particular, an eNB  104  may periodically allocate certain discovery resources in the form of D2D discovery zones  204  for a UE  102  to transmit discovery information. As mentioned above, the discovery information may be in the form of a discovery signal (e.g., a discovery sequence or discovery packet with payload information). The examples described below are described with respect to a discovery packet with payload information. The discovery related information that UEs  102  may intend to share with each other may include a unique ID for device identification, a service identity, etc. (e.g., 48 bits or more) as the data payload, which may be protected by a cyclic-redundancy check (CRC). The number of resource blocks for discovery packet transmission in open D2D discovery design, which is denoted as L RB   D2D , can be one or more, depending on the payload size and the overall discovery performance requirements. 
     In the examples illustrated below, the discovery zones  204  may be periodic discovery zones with each discovery zone comprising some RBs in the frequency domain and several subframes in time domain. In  FIG. 2  N RB   D2D , n RB   start , N SF   D2D  and n SF   start  are denoted as the number of allocated RBs, the starting RB index and the number of subframes, the starting subframe index of each discovery zone, respectively. The information regarding the partitioning of the D2D discovery zones (such as discover region  204 ) may be semi-statically signaled by the eNB  104  using radio-resource control (RRC) signaling or by system information blocks (SIBs) for within network coverage scenarios. For a partial network coverage scenario, such information can be forwarded by an in-network coordinator UE to a UE that may be outside network coverage. 
     For open D2D discovery, a UE  102  configured for D2D communication may randomly choose the subframe index and starting RB index within the discovery zone  204  to transmit a discovery packet. To increase the frequency diversity benefits, embodiments disclosed herein provide several options of hopping patterns for D2D discovery. One option is Type 1 D2D discovery hopping which utilizes an explicit hopping pattern. Another option is Type 2 D2D discovery hopping which uses a subband hopping and mirroring technique. These embodiments are described in more detail below. 
     In addition, a hopping mode may be based on intra-subframe hopping or inter-subframe hopping. Selection between intra-subframe and inter-subframe hopping may be provided by higher layer in a cell-specific manner as for the discovery zone information. Type 1 and Type 2 D2D discovery hopping for the various hopping modes are described in more detail below. 
     In accordance with some embodiments, a UE  102  may be configured for either Type 1 hopping or Type 2 hopping in accordance with one of the hopping modes. When configured for Type 1 hopping, the UE  102  may be configured to use an explicit hopping pattern to determine the PRBs for the transmission of the discovery signal  101 . When configured for Type 2 hopping, the UE  102  may be configured to use a subband hopping and mirroring technique to determine the PRBs for the transmission of the discovery signal  101 . 
     In some embodiments, the use of an explicit hopping pattern may be referred to as Type 1 hopping. Type 1 hopping may include Type 1 intra-subframe hopping, Type 1 inter-subframe hopping and Type 1 joint intra/inter-subframe hopping. Some examples of Type 1 hopping are illustrated in  FIGS. 3 through 5  described in more detail below. 
     In some embodiments, the use of a subband hopping and mirroring technique may be referred to as Type 2 hopping. Type 2 hopping may include Type 2 intra-subframe hopping, Type 2 inter-subframe hopping and Type 2 joint intra/inter-subframe hopping. Some examples of Type 2 hopping are illustrated in  FIGS. 6 through 8  described in more detail below. 
     In some embodiments, the UE  102  may be configured for either open D2D discovery or closed D2D discovery. When configured for closed D2D discovery, an initial subframe within the discovery zone  204  may be assigned by the eNB  102  for transmission of the discovery signal  101 . When configured for open D2D discovery, an initial subframe with the discovery zone  204  may be selected (e.g., randomly) by the UE  102  for transmission of the discovery signal  101 . In some embodiments when configured for open D2D discovery the initial subframe with the discovery zone  204  may be randomly selected by the UE  102  for transmission of the discovery signal  101 , although the scope of the embodiments is not limited in this respect. 
     In some embodiments, when hopping for D2D discovery is enabled, the discovery signal  101  may be transmitted within the determined PRBs  206  in accordance with the hopping mode. When hopping for D2D discovery is not enabled, the UE  102  may be arranged to transmit the discovery signal  101  over consecutive RB pairs within one subframe and/or spread over a set of consecutive subframes with a same RB index (i.e., without hopping) depending on the configuration of the discovery zone  204  (e.g., number of PRBs and number of subframes). In some embodiments, the signaling received from the eNB  104  indicating the discovery zone  204  may be either semi-statically signaled using RRC signaling or may be provided in one or more system-information blocks (SIBs). In some embodiments, the discovery zone  204  may comprise one of a plurality of periodic discovery zones (i.e., discovery zones that occur periodically). In some embodiments, the same discovery zone  204  may be provided to UEs in multiple cells for inter-cell D2D discovery. 
     In some embodiments, a UE  102  may be configurable by the eNB  104  for either Type 1 D2D discovery or Type 2 D2D discovery. When configured for Type 1 D2D discovery, resources (e.g., of the PUSCH) for transmission of the discovery signal  101  may be allocated by the eNB  104  on a non-UE specific basis. When configured for Type 2 D2D discovery, specific resources for transmission of the discovery signal  101  may be allocated by the eNB  104  to the UE  102  for transmission of the discovery signal. In these embodiments, for Type 1 D2D discovery, resources (i.e., PRBs) for transmission of the discovery signal  101  may be allocated on a non-UE specific basis. These allocated resources may be used by all UEs or a particular group of UEs for discovery. For Type 2 D2D discovery, the resources for transmission of the discovery signal  101  may be allocated on a per UE specific basis. Type 2 D2D discovery may include either Type 2A D2D discovery or Type 2B D2D discovery. For Type 2A D2D discovery, resources (i.e., PRBs) for transmission of a discovery signal  101  may be allocated to a UE for each specific transmission instance of the discovery signal  101 . For Type 2B D2D discovery, resources for transmission of a discovery signal  101  may be semi-persistently allocated for transmission of a discovery signal  101 . In these embodiments of Type 2 D2D discovery, the specific channel resources (i.e., PRBs) may be assigned by the eNB  104  or signaled in some manner (e.g., for an outside network scenario). 
     In accordance with these embodiments, a UE  102  that is configured for Type 1 D2D discovery may be configured for either Type 1 hopping or Type 2 hopping. A UE  102  that is configured for Type 2 D2D discovery may also be configured for either Type 1 hopping or Type 2 hopping. 
     In some embodiments, the UE  102  is arranged to receive signaling from an eNB  104  indicating discovery resources within an LTE operation zone. The discovery resources may comprise a plurality of PRBs. The UE  102  may transmit a discovery signal for receipt by one or more other UEs for D2D discovery within at least some PRBs of the discovery resources. The PRBs for transmission of the discovery signal may be in accordance with a hopping mode and may provide increased frequency diversity within a bandwidth of the discovery zone. In some embodiments, when the signaling from the eNB indicates that the discovery resources comprise a discovery zone  204 , the UE may be arranged to determine the PRBs for transmission of the discovery signal within the discovery zone  104  in accordance with the hopping mode. In some embodiments, the signaling from the eNB  104  may indicate a discovery period. In some embodiments, the signaling from the eNB  104  may indicate the exact resources to transmit discovery signals on. 
     For the outside and partial network coverage scenarios, such information can be forwarded by the coordinator UE to the UEs that are outside network coverage. In these embodiments, for UEs that are outside the network coverage region, the configuration details for the D2D discovery zone may be either pre-configured, or relayed by a UE within network coverage, or the configuration details be configured by another UE outside network coverage. In some embodiments, a pool of resources constituting the discovery zone may be associated with or configured by the synchronization source or any other coordinator UE. In these embodiments, a UE may either be in a partial network coverage scenario if, for example, there is a presence of a network close by and it can communicate with and/or discover other UEs that are within network coverage, or fully outside network coverage. 
     For partial network coverage scenarios, discovery resources may be configured by an eNB and being relayed by another UE (e.g., a coordinator UE) that is within network coverage (and so, within operation zone of the network). For outside network coverage case, a specific spectrum may be allocated, although the scope of the embodiments is not limited in this respect. Once a UE determines that it is not under any network coverage or cannot detect synchronization signals that have originated from the network, the UE may search for synchronization signals on certain pre-configured spectrum band(s) for synchronization signals that may be transmitted by other UEs (i.e., not originating from an eNB  104 ), and for the latter case, the resources may be associated with the originating source of the synchronization signal or may be pre-configured. In some of these embodiments, the configuration details of the hopping (hopping type, etc.) may be indicated as part of the D2D discovery zone/discovery period configuration or pre-configured for UEs that perform D2D discovery outside network coverage. 
       FIG. 3  illustrates Type 1 intra-subframe D2D discovery hopping in accordance with some embodiments. For Type 1 intra-subframe hopping  300 , the hopping pattern may comprise one of a plurality of intra-subframe hopping patterns and may be based at least in part on the bandwidth  208  of the discovery zone  204 . The hopping pattern may be selected or determined by the UE  102  or the eNB  104 . The hopping pattern may also be assigned by the eNB  104 . The hopping pattern may be one of a plurality of predetermined hopping patterns, such as one of the hopping patterns illustrated in Table 1 (below). 
     For Type 1 intra-subframe D2D discovery hopping, the discovery signal  101  may be transmitted in first and second slots  304 A and  304 B of an initially selected subframe  302 . The PRBs  306 A and  306 B of the first and second slots have different frequencies. The PRBs  306 A and  306 B may also be selected based on the intra-subframe hopping pattern and may be selected for frequency diversity within the discovery zone bandwidth  208 . 
     In these embodiments that use Type 1 intra-subframe hopping, the discovery signal  101  may be transmitted in two or more adjacent PRBs of the same slot. In the example illustrated in  FIG. 3 , the discovery signal  101  is transmitted in two adjacent PRBs  306 A in the first slot  304 A and in two adjacent PRBs  306 B in the second slot  304 B. As shown in Table 1, intra-subframe hopping pattern 1 may be selected for a discovery zone bandwidth  208  of less than 50 PRBs (in the frequency dimension) and intra-subframe hopping pattern 1, 2 or 3 may be selected for a discovery zone bandwidth  208  of at least 50 PRBs. 
     In these embodiments, the UE  102  may initially be assigned by eNB (for closed D2D discovery) or may randomly choose (for open D2D discovery) a subframe with index n SF  and starting RB index n RB  within the discovery zone  204 . With intra-subframe based type 1 D2D discovery hopping, n SF   start ≤n SF ≤n SF   start +N SF   D2D −1 and n RB   start ≤n RB ≤n RB   start +N RB   D2D −1. In the first slot (e.g., slot  304 A) the UE  102  may transmit a discovery packet with starting RB index n RB   s1 =n RB  over a set of consecutive L RB   D2D  RBs. In the second slot (e.g., slot  304 B) of the same subframe  302 , the UE  102  may determine the starting RB index n RB   s2  according to allocated D2D discovery zone bandwidth  208  and one of the hopping patterns in Table 1. These explicit hopping patterns may help guarantee hopping of the ½, ¼, and −¼ of D2D discovery zone bandwidth  208 , respectively. 
     For a D2D discovery zone bandwidth  208  of less than fifty RBs, the first hopping pattern (Hopping Pattern 1) in Table 1 may be applied, while for a D2D discovery zone bandwidth  208  greater than 50 RBs, one of the hopping patterns (Hopping Pattern 1, 2 or 3) may be applied. The selection between these three hopping patterns may be provided by higher layer in a cell-specific manner. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Hopping pattern for Type 1 intra-subframe hopping 
               
            
           
           
               
               
            
               
                 Hopping Pattern 
                 n RB   s2   
               
               
                   
               
               
                 1 
                 (└N RB   D2D /2┘ +n RB   s1  − n RB   start )mod N RB   D2D  + n RB   start   
               
               
                 2 
                 (└N RB   D2D /4┘ + n RB   s1  − n RB   start )mod N RB   D2D  + n RB   start   
               
               
                 3 
                 (−└N RB   D2D /4┘ + n RB   s1  − n RB   start )mod N RB   D2D  + n RB   start   
               
               
                   
               
            
           
         
       
     
     In the example embodiment illustrated in  FIG. 3 , N RB   D2D =12, n RB   start =0, N SF   D2D =4 n SF   start =0 and L RB   D2D =2. Initially, the UE  102  may randomly choose a subframe in the discovery zone as n SF =2 and the starting RB index as n RB =2. In these Type 1 intra-subframe D2D discovery hopping embodiments, the UE  102  would transmit a discovery packet in RB index 2 and 3 in the first slot and RB index 8 and 9 in the second slot in subframe 2, as highlighted in  FIG. 3 . 
       FIG. 4  illustrates Type 1 inter-subframe D2D discovery hopping in accordance with some embodiments. For Type 1 inter-subframe hopping  400 , the discovery signal  101  may be transmitted in first and second slots (e.g., slots  404 A and  404 B) of an initially selected subframe  402 A. The PRBs  406 A and  406 B of the first and second slots of the initially selected subframe  402 A may have the same frequencies. A discovery signal  101  may also be transmitted in first and second slots (e.g., slots  404 C and  404 D) of a subsequent selected subframe  402 B. The PRBs  406 C and  406 D of the first and second slots of subsequent selected subframe  402 B may have the same frequencies. In these embodiments, the frequencies of the PRBs ( 406 A and  406 B) of the first and second slots of the initially selected subframe  402 A are different from the frequencies of the PRBs ( 406 C and  406 D) of the first and second slots of the subsequent selected subframe  402 B and are selected based on a hopping pattern for frequency diversity within the discovery zone bandwidth  208 . 
     In these embodiments that use Type 1 inter-subframe hopping  400 , the discovery signal  101  may be transmitted within a set of two consecutive subframes  402 A and  402 B. The PRBs  406 A and  406 B of the first subframe  402 A and the PRBs  406 C and  406 D of the second subframe  402 A may be separated by a number of PRBs in frequency to provide frequency diversity. Although  FIG. 4  illustrates the transmission of one discovery packet per PRB in the frequency domain within a particular slot, the scope of the embodiments is not limited in this respect as a discovery packet may be transmitted in multiple PRBs in the frequency domain for a particular slot. 
     In these embodiments that use Type 1 inter-subframe hopping  400 , the discovery signal is spread in the frequency domain over time in order to increase the frequency diversity. Similar to intra-subframe hopping for open D2D discovery, initially the UE  102  may randomly select a subframe n SF  (n SF   start ≤n SF ≤n SF   start +N SF   D2D −L SF ) and the starting RB index n RB  within the discovery zone  204 , where L SF  is the number of subframes allocated for each discovery packet. With inter-subframe hopping, the UE  102  may transmit the discovery packet in a set of consecutive subframes, with L RB  RB pairs allocated in each subframe, i.e., L RB   D2D =L RB ·L SF . For the subframe with index i (n SF ≤i≤n SF +L SF −1), the UE  102  may calculate the RB pair index n RB (i) based on the following equation:
 
 n   RB ( i )=(|└ N   RB   D2D   /L   SF ┘·( i−n   SF )+ n   RB   −n   RB   start )mod  N   RB   D2D   +n   RB   start  
 
     In the example illustrated in  FIG. 4 , N RB   D2D =12, n RB   start =0, N SF   D2D =4, n SF   start =0, L RB   D2D =2 and L SF =2. Initially, the UE  102  may randomly select a subframe in the discovery zone  204  as n SF =1 and the starting RB index as n RB =2. In this example, based on inter-subframe D2D discovery hopping, the UE  102  may transmit the discovery packet in a RB pair with index 2 in subframe 1 and the RB pair with index 8 in subframe 2. 
       FIG. 5  illustrates Type 1 joint intra/inter-subframe D2D discovery hopping in accordance with some embodiments. For Type 1 joint intra/inter-subframe hopping  500 , the discovery signal  101  may be transmitted in first and second slots (e.g., slots  504 A and  504 B) of an initially selected subframe  502 A. The PRBs  506 A and  506 B of the first and second slots of the initially selected subframe  502 A may have the different frequencies. The discovery signal  101  may be transmitted in first and second slots (e.g., slots  504 C and  504 D) of a subsequent selected subframe  502 B. The PRBs  506 C and  506 D of the first and second slots of subsequent selected subframe  502 B may have different frequencies. The frequencies of the PRBs  506 A and  506 B of the first and second slots of the initially selected subframe  502 A are different from the frequencies of the PRBs  506 C and  506 D of the first and second slots of the subsequent selected subframe  502 B and are selected based on a hopping pattern for frequency diversity within the discovery zone bandwidth  208 . 
     Although the example of Type 1 joint intra/inter-subframe hopping  500  of  FIG. 5  illustrates the transmission of one discovery packet per PRB in the frequency domain within a particular slot, the scope of the embodiments is not limited in this respect as a discovery packet may be transmitted in multiple PRBs in the frequency domain for a particular slot. 
     In some embodiments, Type 1 joint intra/inter-subframe D2D discovery hopping may comprise a combination of intra-subframe and inter-subframe hopping that can also be configured for D2D discovery. In these embodiments, the hopping pattern for each slot n s  may be determined by the following equation:
 
 n   RB ( n   s )=(└ N   RB   D2D /(2 L   SF )┘·( n   s −2 n   SF )+ n   RB   −n   RB   start )mod  N   RB   D2D   +n   RB   start   n   SF   ≤└n   s /2┘≤ n   SF   +L   SF −1
 
     In the example of  FIG. 5 , the configuration parameters are adopted from the example of  FIG. 4  and are based on the above equation. 
       FIG. 6  illustrates Type 2 intra-subframe D2D discovery hopping in accordance with some embodiments. For Type 2 intra-subframe hopping  600 , the discovery signal  101  may be transmitted in first and second slots (e.g., slots  604 A and  604 B) of an initially selected subframe  602 . The PRBs ( 606 A and  6069 ) of the first and second slots are selected to be with different subbands (e.g., subbands  603 A and  603 B) and may be mirrored with respect to either the different subbands or a center  601  of the discovery zone  204 . In these embodiments, the PRBs  606 A and  606 B are mirrored with respect to the subband  603 B. In the example illustrated in  FIG. 6 , discovery packets are transmitted in subbands  603 A and  604 B in accordance with the subband hopping and mirroring technique, and no discovery packets are transmitted in subbands  605 A and  605 B. 
       FIG. 7  illustrates Type 2 inter-subframe D2D discovery hopping in accordance with some embodiments. For Type 2 inter-subframe hopping  700 , the discovery signal  101  may be transmitted in first and second slots (e.g., slots  704 A and  704 B) of an initially selected subframe  702 A. The PRBs  706 A and  706 B of the first and second slots of the initially selected subframe  702 A have the same frequencies within a first subband  703 B. A discovery signal  101  may also be transmitted in first and second slots (e.g., slots  704 C and  704 D) of a subsequent selected subframe  702 B. The PRBs  706 C and  706 D of the first and second slots of subsequent selected subframe  702 B have the same frequencies within a second subband  703 A. In these embodiments, the first and second subbands are selected in accordance with subband hopping and the PRBs within the subbands are mirrored with respect to either the subbands or a center  701  of the discovery zone  204 . The subframes  702 A and  702 B may be selected based on a hopping function. 
     Although  FIG. 7  illustrates the transmission of one discovery packet per PRB in the frequency domain within a particular slot, the scope of the embodiments is not limited in this respect as a discovery packet may be transmitted in multiple PRBs in the frequency domain for a particular slot. 
       FIG. 8  illustrates Type 2 joint intra/inter-subframe D2D discovery hopping in accordance with some embodiments. For Type 2 joint intra/inter-subframe hopping  800 , the discovery signal  101  may be transmitted in first and second slots (e.g., slots  804 A and  804 B) of an initially selected subframe  802 A. The PRBs  806 A and  806 B may be selected to be with different subbands (e.g., subbands  803 A and  803 B) in accordance with a hopping function and mirrored in accordance with a mirroring function with respect to either the different subbands or a center  801  of the discovery zone  204 . A discovery signal  101  may also be transmitted in first and second slots (e.g., slots  804 C and  804 D) of a subsequent selected subframe  802 B. The PRBs  806 C and  806 D may be selected to be with different subbands (e.g., subbands  803 A and  805 A) based on a hopping function. 
     In the example illustrated in  FIG. 8 , the PRBs ( 806 A and  806 B) of an initially selected subframe  802 A may be selected to be with different subbands ( 803 A and  803 B) and may be mirrored. In this example, no discovery signal is transmitted in subband  805 B. Although  FIG. 8  illustrates the transmission of one discovery packet per PRB in the frequency domain within a particular slot, the scope of the embodiments is not limited in this respect as a discovery packet may be transmitted in multiple PRBs in the frequency domain for a particular slot. 
     In the examples and embodiments illustrated in  FIGS. 6, 7 and 8  for Type 2 hopping, the number of subbands in the D2D discovery zone  204  ( FIG. 2 ) may be defined as N sb   D2D , which may be provided by higher layer in a cell-specific manner. In some embodiments, the same subband information may be coordinated among multiple cells in order to enable inter-cell D2D discovery. For open D2D discovery, a UE  102  may first randomly choose the subframe n SF  and starting RB index n RB  within the discovery zone  204 . For the intra-subframe hopping mode and the joint intra/inter-subframe hopping mode, the starting RB index n RB  may be selected in a way such that consecutive L RB  RBs are in the same subband. 
     When Type 2 D2D discovery hopping is enabled, the set of RBs to be used for discovery packet transmission in slot n s  may be determined by the following equation: 
     
       
         
           
             
               
                 n 
                 RB 
               
               ⁡ 
               
                 ( 
                 
                   n 
                   s 
                 
                 ) 
               
             
             = 
             
               ( 
               
                 
                   
                     
                       f 
                       hop 
                     
                     ⁡ 
                     
                       ( 
                       i 
                       ) 
                     
                   
                   · 
                   
                     N 
                     RB 
                     
                       sb 
                       , 
                       
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         D 
                       
                     
                   
                 
                 + 
                 
                   
                     
                       f 
                       m 
                     
                     ⁡ 
                     
                       ( 
                       i 
                       ) 
                     
                   
                   · 
                   
                     n 
                     RB 
                     mirror 
                   
                 
                 + 
                 
                   n 
                   RB 
                 
                 - 
                 
                   n 
                   RB 
                   start 
                 
               
               ) 
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 mod 
                 ⁡ 
                 
                   ( 
                   
                     
                       N 
                       RB 
                       
                         sb 
                         , 
                         
                           D 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                           ⁢ 
                           D 
                         
                       
                     
                     · 
                     
                       N 
                       sb 
                       
                         D 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         2 
                         ⁢ 
                         D 
                       
                     
                   
                   ) 
                 
               
               + 
               
                 n 
                 RB 
                 start 
               
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 n 
                 RB 
                 mirror 
               
               = 
               
                 
                   ( 
                   
                     
                       N 
                       RB 
                       
                         sb 
                         , 
                         
                           D 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                           ⁢ 
                           D 
                         
                       
                     
                     - 
                     1 
                   
                   ) 
                 
                 - 
                 
                   2 
                   ⁢ 
                   
                     ( 
                     
                       
                         n 
                         RB 
                       
                       ⁢ 
                       mod 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         N 
                         RB 
                         
                           sb 
                           , 
                           
                             D 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                             ⁢ 
                             D 
                           
                         
                       
                     
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 N 
                 RB 
                 
                   sb 
                   , 
                   
                     D 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                     ⁢ 
                     D 
                   
                 
               
               = 
               
                 ⌊ 
                 
                   
                     N 
                     RB 
                     
                       D 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                       ⁢ 
                       D 
                     
                   
                   / 
                   
                     N 
                     sb 
                     
                       D 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       2 
                       ⁢ 
                       D 
                     
                   
                 
                 ⌋ 
               
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               i 
               = 
               
                 { 
                 
                   
                     
                       
                         ⌊ 
                         
                           
                             n 
                             s 
                           
                           / 
                           2 
                         
                         ⌋ 
                       
                     
                     
                       
                         inter 
                         ⁢ 
                         
                           - 
                         
                         ⁢ 
                         subframe 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         hopping 
                       
                     
                   
                   
                     
                       
                         n 
                         s 
                       
                     
                     
                       
                         intra 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         and 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         joint 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         intra 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         and 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         inter 
                         ⁢ 
                         
                           - 
                         
                         ⁢ 
                         subframe 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         hopping 
                       
                     
                   
                 
               
             
           
         
       
     
     In these embodiments, the range of slot n s  for open D2D discovery may be defined as: 
     for intra-subframe hopping, └n s /2┘=n SF ; 
     for inter and joint intra and inter-subframe hopping, n SF ≤└n s /2┘≤n SF +L SF −1. 
     In these embodiments, the hopping function ƒ hop (i) and the mirroring function ƒ m (i) may be given by the following: 
     
       
         
           
             
               
                 f 
                 hop 
               
               ⁡ 
               
                 ( 
                 i 
                 ) 
               
             
             = 
             
               { 
               
                 
                   
                     
                       
                         0 
                       
                       
                         
                           
                             N 
                             sb 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               D 
                             
                           
                           = 
                           1 
                         
                       
                     
                     
                       
                         
                           
                             ( 
                             
                               
                                 
                                   f 
                                   hop 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     i 
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                               + 
                               
                                 
                                   ∑ 
                                   
                                     k 
                                     = 
                                     
                                       
                                         i 
                                         · 
                                         10 
                                       
                                       + 
                                       1 
                                     
                                   
                                   
                                     
                                       i 
                                       · 
                                       10 
                                     
                                     + 
                                     9 
                                   
                                 
                                 ⁢ 
                                 
                                   
                                     c 
                                     ⁡ 
                                     
                                       ( 
                                       k 
                                       ) 
                                     
                                   
                                   × 
                                   
                                     2 
                                     
                                       k 
                                       - 
                                       
                                         ( 
                                         
                                           
                                             i 
                                             · 
                                             10 
                                           
                                           + 
                                           1 
                                         
                                         ) 
                                       
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           ⁢ 
                           mod 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             N 
                             sb 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               D 
                             
                           
                         
                       
                       
                         
                           
                             N 
                             sb 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               D 
                             
                           
                           = 
                           2 
                         
                       
                     
                     
                       
                         
                           
                             ( 
                             
                               
                                 
                                   f 
                                   hop 
                                 
                                 ⁡ 
                                 
                                   ( 
                                   
                                     i 
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                               + 
                               
                                 
                                   ( 
                                   
                                     
                                       ∑ 
                                       
                                         k 
                                         = 
                                         
                                           
                                             i 
                                             · 
                                             10 
                                           
                                           + 
                                           1 
                                         
                                       
                                       
                                         
                                           i 
                                           · 
                                           10 
                                         
                                         + 
                                         9 
                                       
                                     
                                     ⁢ 
                                     
                                       
                                         c 
                                         ⁡ 
                                         
                                           ( 
                                           k 
                                           ) 
                                         
                                       
                                       × 
                                       
                                         2 
                                         
                                           k 
                                           - 
                                           
                                             ( 
                                             
                                               
                                                 i 
                                                 · 
                                                 10 
                                               
                                               + 
                                               1 
                                             
                                             ) 
                                           
                                         
                                       
                                     
                                   
                                   ) 
                                 
                                 ⁢ 
                                 mod 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   ( 
                                   
                                     
                                       N 
                                       sb 
                                       
                                         D 
                                         ⁢ 
                                         
                                             
                                         
                                         ⁢ 
                                         2 
                                         ⁢ 
                                         D 
                                       
                                     
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                               + 
                               1 
                             
                             ) 
                           
                           ⁢ 
                           mod 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             N 
                             sb 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               D 
                             
                           
                         
                       
                       
                         
                           
                             N 
                             sb 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               D 
                             
                           
                           &gt; 
                           2 
                         
                       
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       f 
                       m 
                     
                     ⁡ 
                     
                       ( 
                       i 
                       ) 
                     
                   
                 
                 = 
                 
                   { 
                   
                     
                       
                         
                           i 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           mod 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           2 
                         
                       
                       
                         
                           
                             N 
                             sb 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               D 
                             
                           
                           = 
                           
                             1 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             and 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             intra 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             and 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             joint 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             intra 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             and 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             inter 
                             ⁢ 
                             
                               - 
                             
                             ⁢ 
                             subframe 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             hopping 
                           
                         
                       
                     
                     
                       
                         
                           c 
                           ⁡ 
                           
                             ( 
                             
                               i 
                               · 
                               10 
                             
                             ) 
                           
                         
                       
                       
                         
                           
                             N 
                             sb 
                             
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               2 
                               ⁢ 
                               D 
                             
                           
                           &gt; 
                           1 
                         
                       
                     
                   
                 
               
             
           
         
       
     
     Where ƒ hop (−1)=0 and a pseudo-random sequence c(i), such as the pseudo-random sequence c(i) of section 7.2 of 3GPP TS 36.212. The pseudo-random sequence generator may be initialized with c init =N ID   D2D  for frame structure type 1 and c init =2 9 ·(n f  mod 4)+N ID   D2D  for frame structure type 2 at the start of each frame, where N ID   D2D  can be cell ID N ID   cell  for intra-cell discovery or virtual cell ID N ID   VCID  for inter-cell D2D discovery. 
     In the examples illustrated in  FIGS. 6-8 , it is assumed that N RB   D2D =12, n RB   start =0, N SF   D2D =4, n SF   start =0, L RB   D2D =2, N sb   D2D =3 and N ID   D2D =2. Initially, the UE  102  may randomly choose a subframe in the discovery zone  204  as n SF =1 and the starting RB index as n RB =1. For intra-subframe hopping, L RB =2 and L SF =1; for inter and joint intra and inter-subframe hopping, L RB =1 and L SF =2. 
     * 
       FIG. 9  illustrates a functional block diagram of a UE in accordance with some embodiments. The UE  900  may be suitable for use as any one or more of the UEs  102  illustrated in  FIG. 1 . The UE  900  may include physical layer circuitry  902  for transmitting and receiving signals to and from eNBs  104  ( FIG. 1 ) using one or more antennas  901 . UE  900  may also include medium access control layer (MAC) circuitry  904  for controlling access to the wireless medium. UE  900  may also include processing circuitry  906  and memory  908  arranged to configure the various elements of the UE to perform the operations described herein. 
     In accordance with some embodiments, the UE  900 , while in either RRC idle or RRC connected mode, may be configured to transmit a discovery signal  101  ( FIG. 1 ) to discover another UE as described herein and receive responses to the discovery signal  101  from another UE. The UE  900  may also be configured to monitor and attempt to decode a discovery signal that is transmitted in the discovery zone  204  ( FIG. 2 ) by another UE for discovery by another UE. The UE  900  may also be arranged to establish a D2D connection with another UE after either discovering the another UE or after being discovered by the another UE. The channel resources for the D2D discovery and the D2D connection may be assigned by the eNB  104 . 
     In some embodiments, the decoding of the discovery signals may be based on blindly identifying the DM-RS cyclic shifts (i.e., blind detection of the discovery packets) or may be done by first blindly decoding a preamble (other than or in addition to) the DM-RS embedded in a discovery packet transmission and using the detected information to decode the discovery packet. In some embodiments, UEs  102  ( FIG. 1 ) may be explicitly or implicitly signaled (i.e., by the eNB  104  or another LTE) to monitor and attempt to receive discovery signals on certain discovery resources instead of all resources within the discovery zone  204  (e.g., a discovery resource pool). 
     In some embodiments, the UE  900  may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a smartphone, 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 may receive and/or transmit information wirelessly. In some embodiments, the UE  900  may include one or more of a keyboard, a display, a non-volatile memory port, multiple antennas, a graphics processor, an application processor, speakers, and other mobile device elements. The display may be an LCD screen including a touch screen. 
     The one or more antennas  901  utilized by the UE  900  may comprise 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 transmission of RF signals. In some embodiments, instead of two or more antennas, a single antenna with multiple apertures may be used. In these embodiments, each aperture may be considered a separate antenna. In some multiple-input multiple-output (MIMO) embodiments, the antennas may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result between each of antennas and the antennas of a transmitting station. In some MIMO embodiments, the antennas may be separated by up to 1/10 of a wavelength or more. 
     Although the UE  900  is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements 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 medium, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable storage medium 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 medium may include read-only memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. In these embodiments, one or more processors of the UE  900  may be configured with the instructions to perform the operations described herein. 
     In some embodiments, the UE  900  may be configured to receive orthogonal frequency division multiplexed (OFDM) communication signals over a multicarrier communication channel in accordance with an orthogonal frequency division multiple access (OFDMA) communication technique. The OFDM signals may comprise a plurality of orthogonal subcarriers. In some embodiments, the OFDMA technique may be either a frequency domain duplexing (FDD) technique that uses different uplink and downlink spectrum or a time-domain duplexing (TDD) technique that uses the same spectrum for uplink and downlink. 
     In some LTE embodiments, two types of reference signals may be transmitted by an eNB including demodulation reference signals (DM-RS), channel state information reference signals (CIS-RS) and/or a common reference signal (CRS). The DM-RS may be used by the UE for data demodulation. The reference signals may be transmitted in predetermined PRBs. 
     In some other embodiments, the UE  900  and the eNBs  104  may be configured to communicate signals that were transmitted using one or more other modulation techniques such as spread spectrum modulation (e.g., direct sequence code division multiple access (DS-CDMA) and/or frequency hopping code division multiple access (FH-CDMA)), time-division multiplexing (TDM) modulation, and/or frequency-division multiplexing (FDM) modulation, although the scope of the embodiments is not limited in this respect. 
     In some LTE embodiments, the UE  900  may calculate several different feedback values which may be used to perform channel adaption for closed-loop spatial multiplexing transmission mode. These feedback values may include a channel-quality indicator (CQI), a rank indicator (RI) and a precoding matrix indicator (PMI). By the CQI, the transmitter selects one of several modulation alphabets and code rate combinations. The RI informs the transmitter about the number of useful transmission layers for the current MIMO channel, and the PMI indicates the codebook index of the precoding matrix (depending on the number of transmit antennas) that is applied at the transmitter. The code rate used by the eNB may be based on the CQI. The PMI may be a vector that is calculated by the UE and reported to the eNB. In some embodiments, the UE may transmit a physical uplink control channel (PUCCH) of format 2, 2a or 2b containing the CQI/PMI or RI. 
     In these embodiments, the CQI may be an indication of the downlink mobile radio channel quality as experienced by the UE  900 . The CQI allows the UE  900  to propose to an eNB an optimum modulation scheme and coding rate to use for a given radio link quality so that the resulting transport block error rate would not exceed a certain value, such as 10%. In some embodiments, the UE may report a wideband CQI value which refers to the channel quality of the system bandwidth. The UE may also report a sub-band CQI value per sub-band of a certain number of resource blocks which may be configured by higher layers. The full set of sub-bands may cover the system bandwidth. In case of spatial multiplexing, a CQI per code word may be reported. 
     In some embodiments, the PMI may indicate an optimum precoding matrix to he used by the eNB for a given radio condition. The PMI value refers to the codebook table. The network configures the number of resource blocks that are represented by a PMI report. In some embodiments, to cover the system bandwidth, multiple PMI reports may be provided. PMI reports may also be provided for closed loop spatial multiplexing, multi-user MIMO and closed-loop rank 1 precoding MIMO modes. 
     In some cooperating multipoint (CoMP) embodiments, the network may be configured for joint transmissions to a UE in which two or more cooperating/coordinating points, such as remote-radio heads (RRHs) transmit jointly. In these embodiments, the joint transmissions may be MIMO transmissions and the cooperating points are configured to perform joint beamforming. 
       FIG. 10  is a procedure for D2D discovery hopping in accordance with some embodiments. Procedure  1000  may be performed by a UE, such as UE  102  ( FIG. 1 ), for discovering another UE and establishing a D2D connection with a discovered UE. 
     Operation  1002  may comprise receiving signaling from an eNB  104  ( FIG. 1 ) indicating a discovery zone  204  ( FIG. 2 ) within an LTE operation zone  202  ( FIG. 2 ). The discovery zone  204  may comprise a plurality of PRBs  206  ( FIG. 2 ). 
     Operation  1004  may comprise determining PRBs  206  within the discovery zone  204  for transmission of a discovery signal in accordance with a hopping mode. The hopping mode may comprise intra-subframe hopping, inter-subframe hopping or joint intra/inter-subframe hopping. As discussed above, the UE  102  may be configured for either Type 1 hopping or Type 2 hopping in accordance with one of the hopping modes. 
     Operation  1006  may comprise transmitting a discovery signal  101  ( FIG. 1 ) for receipt by one or more other UEs  102  for D2D discovery within the determined PRBs  206  of the discovery zone  204 . In these embodiments, the PRBs  206  for transmission of the discovery signal  101  are determined in accordance with the hopping mode. The transmission of a discovery signal on PRBs that are determined in accordance with a hopping mode may provide increased frequency diversity within the bandwidth  208  ( FIG. 2 ) of the discovery zone  204 . 
     *In an example, User Equipment (LTE) arranged for device-to-device (D2D) discovery operations in an LTE network. The UE configured to: receive signaling from an enhanced node B (eNB) indicating discovery resources within an LTE operation zone, the discovery resources comprising a plurality of physical resource blocks (PRBs); and transmit a discovery signal for receipt by one or more other UEs for D2D discovery within at least some PRBs of the discovery resources, wherein the PRBs for transmission of the discovery signal are in accordance with a hopping mode and provide increased frequency diversity within a bandwidth of the discovery zone. 
     In another example, when the signaling from the eNB indicates that the discovery resources comprises a discovery zone, the UE is arranged to determine the PRBs for transmission of the discovery signal within the discovery zone in accordance with the hopping mode. 
     In another example, the hopping mode comprises one of intra-subframe hopping, inter-subframe hopping or joint intra/inter-subframe hopping. 
     In another example, when hopping for D2D discovery is enabled, the discovery signal is transmitted within the determined PRBs in accordance with the hopping mode, and wherein when hopping for D2D discovery is not enabled, the UE is arranged to transmit the discovery signal: over consecutive RB pairs within one subframe and/or spread over a set of consecutive subframes with a same RB index. 
     In another example, the UE is configured for either Type 1 hopping or Type 2 hopping in accordance with one of the hopping modes, wherein when configured for Type 1 hopping, the UE is configured to use an explicit hopping pattern to determine the PRBs for the transmission of the discovery signal, and wherein when configured for Type 2 hopping, the UE is configured to use a subband hopping and mirroring technique to determine the PRBs for the transmission of the discovery signal. 
     In another example, wherein the signaling received from the eNB indicating the discovery zone is either semi-statically signaled using radio-resource control (RRC) signaling or is provided in one or more system-information blocks (SIBs), wherein the UE is configurable by the eNB for either Type 1 D2D discovery or Type 2 D2D discovery, wherein when configured for Type 1 D2D discovery, resources for transmission of the discovery signal are allocated by the eNB on a non-UE specific basis, and wherein when configured for Type 2 D2D discovery, specific resources for transmission of the discovery signal are allocated by the eNB to the UE for transmission of the discovery signal. 
     In another example, for Type 1 intra-subframe hopping: a hopping pattern comprises one of a plurality of intra-subframe hopping patterns and is based at least in part on the bandwidth of the discovery zone, and the discovery signal is transmitted in first and second slots of an initially selected subframe, wherein the PRBs of the first and second slots have different frequencies, the PRBs selected based on the intra-subframe hopping pattern and are selected for frequency diversity within the discovery zone bandwidth. 
     In another example, for Type 1 inter-subframe hopping, the discovery signal is: transmitted in first and second slots of an initially selected subframe, wherein the PRBs of the first and second slots of the initially selected subframe have the same frequencies; and transmitted in first and second slots of a subsequent selected subframe, wherein the PRBs of the first and second slots of subsequent selected subframe have the same frequencies, wherein the frequencies of the PRBs of the first and second slots of the initially selected subframe are different from the frequencies of the PRBs of the first and second slots of the subsequent selected subframe and are selected based on a hopping pattern for frequency diversity within the discovery zone bandwidth. 
     In another example, for Type 1 joint intra/inter-subframe hopping, the discovery signal is: transmitted in first and second slots of an initially selected subframe, wherein the PRBs of the first and second slots of the initially selected subframe have the different frequencies; and transmitted in first and second slots of a subsequent selected subframe, wherein the PRBs of the first and second slots of subsequent selected subframe have the different frequencies, wherein the frequencies of the PRBs of the first and second slots of the initially selected subframe are different from the frequencies of the PRBs of the first and second slots of the subsequent selected subframe and are selected based on a hopping pattern for frequency diversity within the discovery zone bandwidth. 
     In another example, for Type 2 intra-subframe hopping, the discovery signal is transmitted in first and second slots of an initially selected subframe, and wherein the PRBs of the first and second slots are selected to be with different subbands and mirrored with respect to either the different subbands or a center of the discovery zone. 
     In another example, for Type 2 inter-subframe hopping, the discovery signal is: transmitted in first and second slots of an initially selected subframe, wherein the PRBs of the first and second slots of the initially selected subframe have the same frequencies within a first subband; and transmitted in first and second slots of a subsequent selected subframe, wherein the PRBs of the first and second slots of subsequent selected subframe have the same frequencies within a second subband, wherein the first and second subbands are selected in accordance with subband hopping and the PRBs within the subbands are mirrored with respect to either the subbands or a center of the discovery zone, and wherein the subframes are selected based on a hopping function. 
     In another example, for Type 2 joint intra/inter-subframe hopping, the discovery signal is: transmitted in first and second slots of an initially selected subframe, wherein the PRBs are selected to be with different subbands in accordance with a hopping function and mirrored in accordance with a mirroring function with respect to either the different subbands or a center of the discovery zone; and transmitted in first and second slots of a subsequent selected subframe, wherein the PRBs are selected to be with different subbands. 
     In another example, while in either radio-resource control (RRC) idle or RRC connected mode, is further configured to: transmit the discovery signal to discover another UE and receive responses to the discovery signal from the another UE; monitor and attempt to decode a discovery signal transmitted in the discovery zone by another UE for discovery by the another UE; establish a D2D connection with the another UE after either discovering the another UE or after being discovered by the another UE, wherein channel resources for the D2D connection are assigned by the eNB. 
     In another example, a method is performed by User Equipment (LIE) for device-to-device (D2D) discovery operations in an LTE network. The method comprises: receiving signaling from an enhanced node B (eNB) indicating discovery resources within an LTE operation zone, the discovery resources comprising a plurality of physical resource blocks (PRBs); and transmitting a discovery signal for receipt by one or more other UEs for D2D discovery within at least some PRBs of the discovery resources, wherein the PRBs for transmission of the discovery signal are in accordance with a hopping mode and provide increased frequency diversity within a bandwidth of the discovery zone. 
     In another example, when the signaling from the eNB indicates that the discovery resources comprises a discovery zone, the method includes the UE determining the PRBs for transmission of the discovery signal within the discovery zone in accordance with the hopping mode. 
     In another example, the hopping mode comprises one of intra-subframe hopping, inter-subframe hopping or joint intra/inter-subframe hopping. 
     In another example, the UE is configured for either Type 1 hopping or Type 2 hopping in accordance with one of the hopping modes, wherein when configured for Type 1 hopping, the method includes using an explicit hopping pattern to determine the PRBs for the transmission of the discovery signal, and wherein when configured for Type 2 hopping, the method includes using a subband hopping and mirroring technique to determine the PRBs for the transmission of the discovery signal. 
     In another example, the signaling received from the eNB indicating the discovery zone is either semi-statically signaled using radio-resource control (RRC) signaling or is provided in one or more system-information blocks (SIBS), wherein the UE is configurable by the eNB for either Type 1 D2D discovery or Type 2 D2D discovery, wherein when configured for Type 1 D2D discovery, resources for transmission of the discovery signal are allocated by the eNB on a non-UE specific basis, and wherein when configured for Type 2 D2D discovery, specific resources for transmission of the discovery signal are allocated by the eNB to the UE for transmission of the discovery signal. 
     In another example, a non-transitory computer-readable storage medium that stores instructions for execution by one or more processors is arranged to perform operations for device-to-device (D2D) discovery. The operations may configure user equipment (UE) for: receiving signaling from an enhanced node B (eNB) indicating discovery resources within an LTE operation zone, the discovery resources comprising a plurality of physical resource blocks (PRBs); and transmitting a discovery signal for receipt by one or more other UEs for D2D discovery within at least some PRBs of the discovery resources, wherein the PRBs for transmission of the discovery signal are in accordance with a hopping mode and provide increased frequency diversity within a bandwidth of the discovery zone. 
     The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.

Metadata:
Filing Date: 20180823
Publication Date: 20210727
Grant Date: 20210727
Priority Date: 20130628
Inventors: XIONG, GANG
NIU, HUANING
CHATTERJEE, Debdeep
FWU, JONG-KAE
Assignee: APPLE INC
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Family ID: 52115514