HK1248963A1 - Signaling for inter-cell d2d discovery in an lte network - Google Patents

Description

Signaling for inter-cell D2D discovery in LTE networks

The application is a divisional application with the national application number of 201480053377.1, the application date of 2014 of 10 and 21 and the invention name of' signaling for discovery between cells D2D in LTE network

Priority requirement

This application claims U.S. provisional patent application serial No. 61/898, 425, filed on 31/10/2013, the entire contents of which are incorporated herein by reference.

Technical Field

The embodiments are applicable 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 device discovery in LTE networks.

Background

Proximity-based applications and services represent a rapidly evolving social and technical trend that mainly affects the evolution of cellular wireless/mobile broadband technologies. These services are known to each other based on two devices or two users in close proximity to each other and may include applications such as public safety operations, social networks, mobile commerce, advertising, gaming, etc. Device-to-device (D2D) discovery is the first step in implementing D2D services. Device discovery for D2D communication, and in particular for inter-cell Proximity based Service (ProSe) D2D discovery, still presents a number of unresolved issues.

Drawings

FIG. 1 illustrates an example operating environment in which some embodiments may be implemented.

Fig. 2 illustrates a portion of a wireless channel in accordance with some embodiments.

Fig. 3 is a flow diagram of a method of supporting inter-cell D2D discovery in accordance with some embodiments.

Fig. 4 is a block diagram of basic components of a communication device in accordance with some embodiments.

FIG. 5 is a block diagram of a machine that performs various embodiments.

Detailed Description

The following description and the annexed drawings set forth in detail certain illustrative embodiments that enable those skilled in the art to practice the invention. Other embodiments may incorporate structural, logical, circuit, procedural, and other changes. Portions and features of some embodiments are included in or substituted for those of others. The foregoing embodiments in the claims encompass all available equivalent arrangements of such claims.

FIG. 1 illustrates an example operating environment 100 in which some embodiments may be implemented. In operating environment 100, an evolved node b (enb)102 spreads a synchronization signal 103 within a serving cell 106. In some embodiments, mobile devices such as UEs that operate as synchronization sources or Peer Radio Heads (PRH) (not shown in FIG. 1) can disseminate these synchronization signals 103. The PRH can also serve as a synchronization reference point. In some embodiments, the synchronization signal 103 may include information defining a common timing reference.

In various embodiments, one or more UEs 108 located within the serving cell 106 may receive the synchronization signals 103 from the eNB102 and utilize these synchronization signals 103 to enter a synchronization mode of operation according to a common timing reference defined by the synchronization signals 103. One or more UEs 108 may support LTE proximity-based services (ProSe). In some embodiments, a UE110 located outside the serving cell 106 may not be able to receive the synchronization signal 103 from the eNB102 and operate in an asynchronous mode. With respect to the serving cell 106, these UEs 110 operate within one or more neighboring cells 112.

UEs 108 in the synchronous mode utilize a synchronous discovery protocol to discover each other using the discovery signal 104. In accordance with the synchronization discovery protocol, a UE108 in a synchronization mode may only need to monitor the air interface and/or transmit a discovery signal 104 over the air interface during a predetermined periodic time interval. The sync discovery protocol may include a low duty cycle to allow the UE108 in the synchronization mode to enter a sleep state in between periodic time intervals, thereby saving energy for the portion of the UE108 in the synchronization mode. However, the UE110 in the asynchronous mode may not be able to use the synchronous discovery protocol, but needs to use the asynchronous discovery protocol. The asynchronous discovery protocol may require the UE110 in asynchronous mode to continuously transmit the discovery signal 104 and/or to continuously monitor the air interface for discovery signals 104 transmitted by other UEs 108, resulting in a significant increase in power consumption levels. Thus, inter-cell device-to-device (D2D) discovery may become difficult or impractical in other operations.

Fig. 2 illustrates a portion of a wireless channel 200 in accordance with some embodiments. As shown in fig. 2, a portion of the time resources of the wireless channel 200 are allocated to implement a discovery resource pool (discovery resource pool)202, while other time resources of the wireless channel 200 are included in a non-discovery time interval 204. The wireless channel 200 also includes a wireless notification field (discovery notification region) 206.

To conserve power associated with discovery operations, a UE in a synchronized mode, such as UE108 (fig. 1), may utilize and/or monitor the wireless channel 200 only during the discovery resource pool 202 and not during the non-discovery time interval 204. However, a UE in asynchronous mode, such as UE110 (fig. 1), may not be aware of a common timing reference, depending on which discovery resource pool 202 is delimited from the non-discovery time interval 204. Thus, in order to ensure that they transmit discovery signals during the time that the UE108 in synchronous mode is monitoring the wireless channel 200, the UE110 in asynchronous mode in existing systems may be forced to transmit such discovery signals continuously. This will cause interference with non-discovery communications over the wireless channel 200 during the non-discovery time interval 204 and increase power consumption of the portion of the UE110 in the asynchronous mode, thereby further complicating the inter-cell D2D discovery operation.

To guide these and other relationships, embodiments provide an apparatus and method to support inter-cell D2D discovery that may be applied to asynchronous network arrangements. Depending on the synchronization characteristics of the arrangement, such as the synchronization arrangement in a time-division duplexing (TDD) system or the synchronization arrangement in a typical frequency-division duplexing (FDD) system, inter-cell D2D discovery may be supported in a number of different ways. Inter-cell D2D discovery may also be supported differently based on a level of coordination between neighboring cells, a level of network assistance (network assistance) available at the UE terminal for inter-cell D2D discovery, and so on.

For a synchronous arrangement, a network-generic configuration of the D2D discovery resource pool may be achieved, thus considerably simplifying the inter-cell D2D discovery process. For asynchronous arrangements, the D2D discovery resource pool may generally be configured in a cell-specific manner, and embodiments may provide a way to avoid overlap of D2D discovery resources of neighboring cells, thereby avoiding asynchronous interference, which may be more difficult than controlling synchronous interference. At least some inter-eNB coordination may help minimize the overlapping D2D discovery resource pools between asynchronous cells. Thus, some embodiments provide coarse inter-eNB time resolution up to multiple radio frames.

In addition to configuration information of the D2D discovery resource pool of the neighboring cell, the participating UEs supporting inter-cell D2D discovery also use synchronization reference time and frequency synchronization source information for the cell to discover other UEs. Embodiments provide a method for making configuration information of a D2D discovery resource pool of a neighboring cell available to UEs desiring to participate in inter-cell D2D discovery.

With respect to reference time and frequency synchronization source information, in some current systems, based on a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS), or a Positioning Reference Signal (PRS) of a neighboring cell, a UE can obtain such information directly from the neighboring cell. However, not all UEs are able to obtain the PSS/SSS/CRS of the neighboring cells. In accordance with current Long Term Evolution (LTE) specifications, UEs require wideband signals to have a signal-to-noise ratio (SINR) of at least-6 dB to detect PSS/SSS, but the near-far effect may prevent some UEs from detecting PSS/SSS of neighboring cells. Thus, D2D finds performance degradation at least for these UEs. Instead of using PSS/SSS/CRS to obtain such information, embodiments provide a method for a UE to relay D2D discovery resource pool configuration information, reference time information, and frequency synchronization information of the serving cell to other UEs that may be served by neighboring cells.

In some embodiments, the eNB102 or the PRH can select the UE108 or a group of UEs to relay the transmission timing of the respective serving cell, so that UEs belonging to other cells and in the vicinity can use this "two-hop" (two-hop) synchronization reference to obtain time and frequency synchronization of neighboring cells for inter-cell discovery. Thus, in accordance with an embodiment, the eNB102 includes hardware processing circuitry to send configuration information of the D2D discovery resource pool that has been configured by the neighboring cell 112 to the selected UE108 or group of UEs. The configuration information will include a time offset (timing offset) between the serving cell 106 and the neighboring cell 112 of the UE 108. Although only one neighboring cell 112 is described, the embodiment is not limited thereto, and the configuration information may include configuration information of a plurality of D2D discovery resource pools configured by a plurality of neighboring cells 112. The selected UE108 may then relay some or all of this information to other UEs outside the serving cell 106.

In order for the UE108 to perform the relay, the eNB102 will allocate resources to the UE108, which the UE108 uses to periodically transmit synchronization information of the serving cell 106. At the beginning of each occurrence of D2D discovery resource pool 202 (fig. 2), these resources can also include time resources for a discovery notification signal that includes data for the corresponding discovery notification field 206 (fig. 2).

In some embodiments, the discovery notification signal may be the same signal as the synchronization signal. However, in some embodiments, the relay UE108 may need to send the synchronization signal more frequently than the discovery notification signal (i.e., more frequently than the D2D discovery resource pool 202 occurs). Although the discovery notification signal can carry D2D discovery resource pool configuration information in addition to the synchronization information for the serving cell 106, the UE108 may need to relay the synchronization information for the serving cell more frequently than the resource pool configuration information indicated by the discovery notification signal. This is because, according to the level of synchronous/asynchronous characteristics (nature) between neighboring cells, if these relayed synchronization signals are transmitted just before D2D of the corresponding cell discovers a resource pool as only a part of a discovery notification signal, a UE receiving synchronization and configuration information cannot obtain time/frequency synchronization of the cells. This will present at least two problems. First, since a synchronization signal having a shorter period than a conventional discovery period is additionally periodically transmitted in addition to transmission of a discovery notification signal each time the start of a discovery resource pool periodically occurs, the UE will exhibit increased power consumption. Second, resource allocation is required for the transmission of the "relay" synchronization signal.

To address the second issue, eNB102 may allocate the above resources such that UE108 transmits synchronization information to other UEs in neighboring cell 112, such as UE110, more frequently than UE108 transmits discovery notification signals (i.e., more frequently than the D2D pool of discovery resources occurs).

With respect to the first problem, for example, if information of a coarse time offset between a serving and a neighboring cell is transmitted (signaled) by each corresponding serving cell to an associated UE, an increase in power consumption can be minimized. If this coarse time offset information is transmitted, the discovery notification signal itself is sufficient for the UE to obtain synchronization of inter-cell discovery operations, thus avoiding the need to relay synchronization information of the serving cells separately.

However, in some circumstances, the discovery notification signal itself may not be sufficient to provide this synchronization information. In at least these cases, the eNB102 will allocate resources to the selected UEs to relay the synchronization information. The eNB102 may allocate these resources so that the UE108 can send synchronization information more frequently than the occurrence of the D2D discovery resource pool.

The eNB102 may also allocate resources to avoid overlapping of transmissions of synchronization information relayed from UEs served by different cells. In one embodiment, the eNB102 can reserve subframes for synchronization information of the relay serving cell 106 to reduce or eliminate overlap of the subframes for synchronization information of the relay serving cell 106 with the subframes for synchronization information of one or more serving cells of the relay neighbor cells 112. This is particularly important in the case where the respective D2D find the resource pools 202 to be non-overlapping. In particular, in some embodiments, to this end, eNB102 can reserve time-frequency resources on every kth subframe (e.g., "synchronization relay subframe") within D2D discovery resource pool 202, where K is greater than 1. In other embodiments, the eNB102 reserves time-frequency resources for this purpose on every kth subframe within a set of available D2D subframes of the serving cell 106.

In embodiments where the synchronization signal is a narrowband signal, the UE108 may use unused Physical Resource Block (PRB) pairs of these synchronized relay subframes to transmit the discovery signal 104. However, the UE108 should ensure adequate protection of the synchronization signal transmission from in-band emission (in-band emission). For example, listening UEs 110 in cell 112 (fig. 1) may not be able to receive synchronization signals relayed by UEs 108 in cell 106 due to high interference of in-band transmissions resulting from other discovery signals 104 transmitted in cell 106 at maximum transmission power in adjacent PRB pairs of the synchronization relay subframe. Thus, in embodiments, the eNB102 may define the transmission power of the D2D transmission on the PRB in addition to those carrying the relayed synchronization signal on subframes allocated for transmitting the discovery notification signal or the relayed synchronization signal, such that the transmission power is less than the maximum transmission power. The maximum transmission power value on the synchronous relay subframe may be predefined or configured by the network 100 by higher layers.

It should be noted that the impact of the actual measured in-band transmissions may depend on the number of UEs selected to relay the serving cell synchronization signal. Generally, having only some selected UEs relay this information is beneficial to minimize the impact on UE power consumption.

In addition to interspersed synchronization relay subframes within the D2D discovery resource pool, the eNB102 may also configure additional subframes as synchronization relay subframes between the D2D discovery resource pool to increase the speed and reliability of acquiring synchronization information of the neighboring cells 112. For both types of synchronous relay subframes, the actual synchronization signal transmitted by the UE may be confined to a central PRB pair in the frequency dimension (frequency dimension), such that the set of PRB pairs is centered in the system Uplink (UL) bandwidth. Alternatively, the eNB102 can allocate a set of PRB pairs according to a cell-specific offset relative to the center of the system UL bandwidth. Such cell-specific mapping in the frequency dimension is more beneficial for two D2D to find out the synchronized relay subframes occurring between the resource pools to avoid overlapping of the synchronization signals transmitted by UEs belonging to different neighboring cells.

The eNB102 may also allocate resources to meet other additional criteria (additional criteria). For example, UEs selected to relay synchronization information of a particular cell may transmit their relayed synchronization signals on the same physical resources to benefit from Single Frequency Network (SFN) gain while being able to trade-off the increase in effective delay spread (effective delay spread). However, some embodiments may reduce the available delay spread by configuring the extended Cyclic Prefix (CP) for the D2D discovery resource pool.

Fig. 3 is a flow diagram of a method 300 of supporting inter-cell D2D discovery in accordance with some embodiments. Example method 300 is described with reference to elements of fig. 1-2. The eNB102 (fig. 1) may be capable of performing at least some operations of the method 300 such that the UEs 108 and 110 may obtain information needed for inter-cell D2D discovery. By way of non-limiting example, and as previously described herein, such information can include reference time and frequency synchronization source information for the neighboring cell and configuration information for the D2D discovery resource pool of the neighboring cell.

In operation 302, the eNB102 sends signaling to the UE108 to indicate configuration information for at least a device-to-device (D2D) discovery resource pool 202. The configuration information includes a time offset between the serving cell 106 and one or more neighboring cells 112 of the UE 108. Each D2D discovery resource pool 202 includes D2D resources that have been configured by a respective neighboring cell 112. With respect to various embodiments, while one neighboring cell 112 has been described, it is to be understood that information may be provided to inter-cell D2D discovery between multiple neighboring cells.

In operation 304, the eNB102 allocates resources to the UE108 for periodic transmission of synchronization information of the serving cell 106 by the UE 108. As previously described herein, the eNB102 can allocate resources according to different criteria to achieve different effects. For example, the eNB102 can allocate resources such that the UE108 can send synchronization information to the UE108 of a neighboring cell more frequently than the UE108 sends a discovery notification signal.

The eNB102 can perform other operations as part of the example method 300 to support inter-cell D2D discovery. For example, the eNB102 may define a transmission power for the D2D transmission, and the eNB102 may allocate resources to the PRB pairs to avoid overlap between subframes relaying synchronization information of the serving cell and subframes relaying synchronization information of one or more of the neighboring cells.

Fig. 4 is a block diagram of the basic components of a communication device 400 according to some embodiments. The communication device 400 may be suitable for use as a UE108 or 110 (fig. 1) or an eNB102 (fig. 1). According to the above embodiments described with reference to fig. 1-3, the communication device 400 may support a method of inter-cell D2D discovery. It should be noted that when the communication device 400 acts as an eNB102, the communication device 400 may be stationary and non-mobile.

In some embodiments, the communication device 400 may include one or more processors and may be configured with instructions stored on a computer-readable storage device. When the communication device 400 is acting as the UE108, the instructions may cause the communication device 400 to receive signaling to indicate configuration information of a D2D discovery resource pool of at least one neighboring cell 112 (fig. 1). As previously described herein, the signaling may also include a time offset between the serving cell 106 (fig. 1) and at least one neighboring cell 112, such that the communication device 400 can receive and interpret the discovery signal 104 from UEs outside the serving cell 106. The communication device 400 can then transmit a transmission notification signal including the time offset and synchronization information of the serving cell 106 to a second communication device outside the serving cell 106.

When the communication device 400 is acting as the eNB102 (fig. 1), the instructions will cause the communication device 400 to send signaling to the UE108 (fig. 1) to indicate the D2D to discover the configuration information of the resource pool. As previously described herein, the configuration information will include a time offset between the serving cell 106 (fig. 1) and the neighboring cell 112 for that UE 108. Although one neighbor cell 112 is described, it is to be appreciated that embodiments are not so limited and the time offset can be provided to any number of neighbor cells associated with the serving cell.

The communication device 400 may include physical layer circuitry 402 to transmit and receive signals to and from other communication devices using one or more antennas 401. The physical layer circuitry 402 may also include Media Access Control (MAC) circuitry 404 for controlling access to the wireless medium. The communication device 400 may also include processing circuitry 406 and memory 408 configured to perform the operations described herein. In some embodiments, the physical layer circuitry 402 and the processing circuitry 406 may be configured to perform the operations described in fig. 1-3.

According to some embodiments, MAC circuitry 404 may be configured to contend for the wireless medium and to configure subframes or packets for communication over the wireless medium, and physical layer circuitry 402 may be configured to transmit and receive signals. The physical layer circuit 402 may include a modulation/demodulation circuit, an up-conversion/down-conversion circuit, a filter circuit, an amplification circuit, and the like.

In some embodiments, the processing circuitry 406 of the communication device 400 may include one or more processors. In some embodiments, two or more antennas 401 may be coupled to physical layer circuitry 402 configured to transmit and receive signals. The memory 408 may store information for configuring the processing circuitry 406 to perform operations for configuring and transmitting message frames and to perform various operations described herein. Memory 408 can comprise any type of memory, including non-transitory memory, for storing information in a form readable by a machine (e.g., a computer). For example, memory 408 may include a computer-readable storage device, a Read Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk storage media, an optical storage media, a flash memory device, and other storage devices and media.

Antenna 401 may include one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other antennas suitable for transmission of RF signals. In some embodiments, a single antenna with multiple apertures may be used instead of two or more antennas. 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 by spatial diversity and different channel characteristics that may arise between each of the antennas and the antennas of the transmitting station.

In some embodiments, the communication device 400 may include one or more of a keypad, a display, a non-volatile memory port, a multiple antenna (multiple antennas), a graphics processor, an application processor, a speaker, and other mobile device components. The display may be an LCD screen including a touch screen.

In some embodiments, the communication device 400 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 netbook, a wireless telephone, a smart phone, a wireless headset, a pager, an instant messaging device (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.

Although communication device 400 is illustrated as having a number of separate functional elements, two or more of the functional elements may be combined or implemented as a combination 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 one of the functions described herein. In some embodiments, the functional elements of communication device 400 may refer to one or more processors operating on one or more processing elements.

Embodiments may be implemented in hardware, firmware, and software, alone or in combination. Embodiments may also be implemented as instructions stored on a computer-readable device, which may be read and executed by at least one processor to perform the operations described herein. Computer storage devices may include any non-volatile storage mechanism for storing information in a form readable by a machine (computer). For example, a computer-readable storage device 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.

Fig. 5 is a block diagram of a machine 500 for performing various embodiments. In alternative embodiments, machine 500 may operate as a standalone (standby) device or may be connected (e.g., networked) to other machines.

The machine (e.g., computer system) 500 may include a hardware processor 502 (e.g., a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), a hardware processor core, or any combination thereof), a main memory 504 and a static memory 506, some or all of which may be capable of communicating with each other via an inter-link 508 (e.g., a bus). The machine 500 may also include a power management device 532, a graphical display device 510, an alphanumeric input device 512 (e.g., a keyboard), and a User Interface (UI) navigation device 514 (e.g., a mouse). In some embodiments, the graphical display device 510, alphanumeric input device 512, and UI navigation device 514 may be touch screen displays. The machine 500 may additionally include a storage device 516 (i.e., a drive unit), a signal generation device 518 (e.g., a speaker), a network interface device/transceiver 520 coupled to an antenna 530, and one or more sensors 528, such as a Global Positioning System (GPS) sensor, compass, accelerator, and other sensors. The machine 500 may include an output controller 534, such as a serial (e.g., Universal Serial Bus (USB), parallel, or other wired or wireless connection (e.g., Infrared (IR), Near Field Communication (NFC), etc.) to communicate with or control one or more peripheral devices (e.g., a printer, card reader, etc.).

The storage device 516 may include a machine-readable medium 522 on which is stored one or more sets of data structures or instructions 524 (e.g., software) implemented or utilized with any one or more of the techniques or functions described herein. The instructions 524 may also reside, completely or at least partially, within the main memory 504, within static memory 506, or within the hardware processor 502 during execution thereof by the machine 500. In one example, one or any combination of the hardware processor 502, the main memory 504, the static memory 506, and the storage device 516 may constitute machine-readable media.

While the machine-readable medium 522 is shown to be a single medium, the term "machine-readable medium" can include a single medium or multiple media (e.g., a centralized or distributed database, and/or a combination of caches and servers) configured to store the one or more instructions 524.

The term "machine-readable medium" may include any medium that is capable of storing, encoding or carrying instructions 524 for execution by the machine 500 and that cause the machine 500 to perform any one or more of the techniques of the present invention or that is capable of storing, encoding or carrying data structures used by the instructions 524 or associated with the instructions 524. Non-limiting examples of machine-readable media may include solid-state memory and magneto-optical media. In one example, a large-scale machine-readable medium may include a machine-readable medium with a particle having a plurality of stationary masses. Specific examples of large-scale machine-readable machines may include: non-volatile memory, such as semiconductor memory devices (e.g., electrically programmable read-only memory (EPROM), or electrically erasable programmable read-only memory (EEPROM)) and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

The instructions 524 may also be transmitted or received using a transmission medium via the network interface device/transceiver 520 using any of a number of transmission protocols, such as frame relay (frame relay), Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP), hypertext transfer protocol (HTTP), etc.

Although the present subject matter has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. One skilled in the art will recognize in light of this disclosure that various features of the described embodiments may be combined. Moreover, it should be appreciated that various modifications and substitutions may be made by those skilled in the art without departing from the scope of the present invention.

The abstract is provided to comply with 37c.f.r section1.72(b), which is required to ascertain the characteristics 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. Thus the following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.

Claims (25)

1. An apparatus of a User Equipment (UE), comprising:

a processing circuit configured to:

decoding signaling with discovery configuration information for sidelink communications, the discovery configuration information indicating a discovery resource pool with a set of subframes and sidelink synchronization signals of a serving cell;

decoding signaling indicating a synchronization time offset between the secondary link synchronization signal and a secondary link synchronization signal associated with a cell of another UE; and

supporting inter-cell device-to-device (D2D) discovery by encoding the discovery configuration information for transmission to the other UE based on a sidelink synchronization signal of the cell of the other UE obtained with the indicated synchronization time offset; and

a memory coupled with the processing circuit and configured to store the synchronous time offset.

2. The apparatus of claim 1, wherein the synchronization time offset is indicated by a synchronization window with respect to synchronization resources of the cell of the other UE indicated by a higher layer.

3. The apparatus of claim 1, wherein the processing circuit is configured to:

encoding the discovery configuration information for transmission to the cell of the other UE based on Physical Sidelink Discovery Channel (PSDCH) resources indicated by a higher layer.

4. The apparatus of claim 1, wherein the signaling indicating the synchronization time offset further indicates a cell identity of the cell of the other UE.

5. The apparatus of claim 1, wherein the processing circuit is configured to:

encoding a discovery notification signal for transmission to the cell of the other UE at a start of the discovery configuration information.

6. The apparatus of claim 5, wherein the processing circuit is configured to:

encoding the sidelink synchronization signal and the discovery notification signal for transmission, wherein the sidelink synchronization signal is transmitted more frequently than the discovery notification signal.

7. The apparatus of claim 1, further comprising:

one or more antennas; and

transceiver circuitry coupled with the processing circuitry and the one or more antennas and configured to transmit the discovery configuration information.

8. The apparatus of claim 1, wherein the processing circuit is configured to:

encoding a discovery announcement signal for transmission to the other UE, the discovery announcement signal comprising the sidelink synchronization signal and the discovery resource pool.

9. The apparatus of claim 8, wherein the processing circuit is configured to:

encoding the secondary link synchronization signal for transmission to the other UE.

10. The apparatus of claim 9, wherein the processing circuit is configured to:

encoding the synchronization signal for periodic transmission to the other UE, wherein the periodic transmission is more frequent than the transmission of the discovery notification signal.

11. The apparatus of claim 10, wherein the secondary link synchronization signal is transmitted periodically with a periodicity defined by the serving cell.

12. A non-transitory computer-readable storage device comprising instructions stored thereon, which, when executed by one or more processors of a User Equipment (UE), cause the UE to:

decoding signaling with discovery configuration information of a first cell, the discovery configuration information including a sidelink synchronization signal;

decoding signaling indicating a synchronization time offset between the secondary link synchronization signal of the first cell and a secondary link synchronization signal of a second cell; and

inter-cell device-to-device (D2D) discovery is supported by encoding discovery configuration information for the first cell for transmission to the second cell based on a sidelink synchronization signal for the second cell obtained with the indicated synchronization time offset.

13. The non-transitory computer-readable storage device of claim 12, wherein the signaling with the D2D service configuration information for the first cell is higher layer signaling.

14. The non-transitory computer-readable storage device of claim 12, the synchronization time offset is indicated by a synchronization window for synchronization resources of the second cell.

15. The non-transitory computer-readable storage device of claim 12, wherein the instructions further cause the UE to:

encoding the discovery configuration information for transmission to the second cell based on Physical Sidelink Discovery Channel (PSDCH) resources indicated by a higher layer.

16. The non-transitory computer-readable storage device of claim 12, wherein the signaling indicating the synchronization time offset further indicates a cell identity of the second cell.

17. The non-transitory computer-readable storage device of claim 12, wherein the instructions further cause the UE to:

encoding a discovery notification signal for periodic transmission to the second cell at a start of the discovery configuration information.

18. The non-transitory computer-readable storage device of claim 12, wherein the instructions further cause the UE to:

encoding the secondary link synchronization signal and the discovery notification signal for transmission to the second cell, wherein the secondary link synchronization signal is transmitted more frequently than the discovery notification signal.

19. An evolved node b (enb), comprising:

hardware processing circuitry configured to:

supporting sidelink discovery by encoding signaling for transmission to a first User Equipment (UE) within a first cell associated with the eNB to indicate configuration information for discovering a resource pool that has been configured by a second cell, wherein the configuration information includes a time offset between the first cell and the second cell of the first UE, the time offset indicating a difference in timing synchronization of the first cell and the second cell; and

a memory coupled with the hardware processing circuit, the memory configured to store the time offset.

20. The eNB of claim 19, wherein the hardware processing circuitry is further configured to:

allocating resources to the first UE for sending synchronization information of the first cell to at least a second UE in the second cell by the first UE based on the time offset.

21. The eNB of claim 20, wherein the resources include time resources for a discovery announcement signal at the beginning of each occurrence of the D2D discovery resource pool.

22. The eNB of claim 21, wherein the resources are allocated such that the first UE transmits the synchronization information more frequently than the first UE transmits the discovery notification signal.

23. The eNB of claim 20, wherein the resources are defined in a frequency dimension to a set of Physical Resource Block (PRB) pairs, wherein the set of PRB pairs are located at a center of a system uplink bandwidth.

24. The eNB of claim 20, wherein the resources are defined in a frequency dimension to a set of Physical Resource Block (PRB) pairs, wherein the set of PRB pairs are allocated according to a cell-specific offset from a center of the system uplink bandwidth.

25. The eNB of claim 20, wherein the hardware processing circuitry is further configured to:

the transmission power of the D2D transmission on the PRB is defined except for the transmission power carrying the synchronization information on the subframe allocated for transmission of the discovery notification signal or the relayed synchronization signal, such that the transmission power is less than the maximum transmission power.