CLAIM OF PRIORITY

[0001] The present application claims priority to Provisional Application No.

62/056,131 entitled "ENB Related D2D Synchronization Procedure," docket number TPRO 00259 US, filed September 26, 2014, assigned to the assignee hereof and hereby expressly incorporated by reference in its entirety.

FIELD

[0002] This invention generally relates to wireless communications and more particularly to management of device-to-device (D2D) synchronization signals.

BACKGROUND

[0003] Many wireless communication systems use eNBs (base stations, eNodeBs, eNBs) to provide geographical service areas where wireless communication user equipment devices (UE devices) communicate with the eNB providing the particular geographical service area in which the UE devices are located. The eNBs are connected within a network allowing communication links to be made between the wireless communication devices and other devices. In some circumstances, the communication links are between wireless communication UE devices that are close to each other. In these situations, it may be preferred to have a direct communication link between the two wireless UE devices rather than communicating through a base station. Such direct communication between devices is often referred to as device-to- device (D2D) communication or peer-to-peer (P2P) communication. The

communication resources (e.g., time frequency blocks) used for D2D communication are typically a subset of the communication resources used by the communication system for communication between UE devices and the eNBs.

[0004] An in-coverage UE device (InC UE device) is a UE device that is within the service area of an eNB and is capable of communication with the eNB. An out-of- coverage UE device (OoC UE device) is a UE device that is not within a service area of any eNB. D2D UE devices that are engaged in D2D communication with each other form a D2D group. A D2D group, therefore, includes two or more D2D UE devices. There are several coverage scenarios that may occur with D2D groups. In an InC coverage scenario, all the UE devices of the D2D group are located in a service area of a single eNB. For the InC scenario, therefore, all of the D2D UE devices of the D2D group are InC UE devices in a single service area. In an OoC coverage scenario, none of the UE devices of the D2D group are located inside any service area of any eNB. For such a scenario, therefore, all of the D2D UE devices of the D2D group are OoC UE devices. In a partial coverage scenario, at least one of the UE devices of the D2D group is located in a service area of a single eNB and at least one D2D UE device of the group is outside all service areas. For the partial coverage scenario, therefore, at least one of the D2D UE devices of the D2D group is an InC UE device in a single service area and at least one UE device is an OoC UE device. Other coverage scenarios are possible. Since the UE devices of a group are mobile, there are situations where the coverage scenario of a D2D group changes. For example, where only one UE device of a D2D group is in coverage and moves out of coverage, the coverage scenario changes from a partial coverage scenario to an out of coverage scenario.

[0005] In order to maintain synchronization of communication within a D2D group, a synchronization signal is typically received by the UE devices in the group. In some situations, the synchronization signal is transmitted by the eNB. Such a situation occurs where all the D2D UE devices are in coverage. In some situations, a D2D synchronization signal (D2DSS) is transmitted by one or more of the D2D UE devices in the D2D group to maintain synchronization. When available to the D2DSS transmitting D2D UE device, the D2DSS is based on system timing obtained directly from the eNB. In some situations, however, the UE device cannot obtain the timing information directly from the eNB and the D2DSS is not based on timing directly obtained from the eNB. Proposals for 3GPP LTE revisions include a mechanism for indicating whether a D2DSS is based on timing directly obtained from the eNB or not. SUMMARY

[0006] In response to detecting a synchronization signal that is based directly on eNB timing, a device-to-device (D2D) User Equipment (UE) device transmits a notification to other D2D UE devices indicating that the D2D UE device will stop transmitting D2D synchronization signals that are not directly based on eNB timing. The UE D2D device stops transmitting D2D synchronization signals not directly based on eNB timing after a duration time period has elapsed. In one situation, the

synchronization signal is a D2DSS signal transmitted from a D2D UE device receiving timing information from an eNB. In another situation, the synchronization signal is at least one of a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) transmitted from an eNB.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is an illustration of a communication system where macrocell communication resources are used for device-to-device (D2D) communication and D2D synchronization signals (D2DSS) are used for D2D communication synchronization.

[0008] FIG. 2A is an illustration of the communication system for an example where a D2D user equipment (UE) device transmitting a D2DSS not based on eNB timing information.

[0009] FIG. 2B is an illustration of the communication system for an example where the D2D UE device transmitting the D2DSS not based on eNB timing information detects a D2DSS signal based on eNB timing information.

[0010] FIG. 2C is an illustration of the communication system for an example where a D2D UE device stops transmitting a D2DSS not based on eNB timing information after detection of the D2DSS that is based on timing information obtained directly from an eNB.

[0011] FIG. 3 is a block diagram of a wireless user equipment (UE) device suitable for use as the UE devices. [0012] FIG. 4 is a flow chart of a method of managing D2DSS transmission performed in a D2D UE device.

[0013] FIG. 5 is message diagram of communications between the UE devices.

DETAILED DESCRIPTION

[0014] As discussed above, a D2D UE device may sometimes transmit a D2DSS that is not based on timing information obtained directly from an eNB. In certain situations, such a D2DSS may cause interference since devices using the timing of the D2DSS may transmit signals into service areas where other UE devices are using synchronization timing that is derived from an eNB. For example, if an OoC D2D UE device is transmitting a D2DSS not directly based on system timing near a coverage area (cell), the transmissions by UE using the D2DSS may cause interference to UE devices within the cell since the transmission subframe boundaries of the transmissions may not coincide with subframe boundaries of transmissions of the UE devices within the coverage area. As a result, there is a need for a D2DSS management system that eliminates, minimizes or at least reduces interference. One potential solution includes a technique where the D2D UE device transmitting the D2DSS not directly based on eNB timing stops transmitting the D2DSS when a synchronization signal, such as a D2DSS, is detected that is directly based on eNB timing. If the D2D UE device stops transmitting immediately and without warning, the other D2D UE devices relying on the D2DSS may be unable to continue communication until an alternate synchronization source is established. As discussed herein, such undesired consequences are avoided by executing a D2DSS management technique where the D2D UE device notifies other D2D UE devices that the D2DSS transmission will be stopped and only stops transmitting the D2DSS after a time period. Such a technique provides time for the D2D UE devices to establish the alternate synchronization source before the D2D UE device stops transmitting the interfering D2DSS.

[0015] FIG. 1 is an illustration of a communication system 100 where macrocell communication resources are used for device-to device (D2D) communication. A eNB (base station, eNodeB, eNB) 102 provides wireless communication services to wireless comnnunication UE devices 104, 106, 108 within a geographical service area 1 10, sometimes referred to as a cell. Several eNBs are typically interconnected through a backhaul to provide several service areas to cover large areas. The various functions and operations of the blocks described with reference to the communication system 100 may be implemented in any number of devices, circuits, or elements. Two or more of the functional blocks may be integrated in a single device and the functions described as performed in any single device may be implemented over several devices. For example, at least some of the functions of the controller 1 12 may be performed by the eNB 102 and vice versa. A cellular communication system is typically required to adhere to a communication standard or specification. The Third-Generation Partnership Project Long-Term Evolution (3GPP LTE) communication specification is a specification for systems where base stations (eNodeBs) provide service to wireless communication devices (user equipment (UE) devices) using orthogonal frequency-division multiplexing (OFDM) on the downlink and single-carrier frequency-division multiple access (SC- FDMA) on the uplink. Although the techniques described herein may be applied in other types of communication systems, the exemplary systems discussed herein operate in accordance with a 3GPP LTE communication specification.

[0016] The eNB 102 is a fixed transceiver station, sometimes referred to as a base station, an evolved Node B or eNodeB, which may include a controller in some circumstances. The eNB 102 is connected to a controller 1 12 within a network 1 13 through a backhaul which may include any combination of wired, optical, and/or wireless communication channels. For the examples herein, the controller 1 12 includes the functionality of the Mobility Management Entity (MME) and the Packet Gateway (P- GW). Accordingly, the controller 1 12 includes a scheduler 1 14. In the example, the scheduler 1 14 allocates time-frequency resources for communication between the wireless communication devices 104, 106, 108, 109 as well as between the base station 102 and the wireless communication devices 104, 106, 108, 109. UE communication devices 1 16, 1 17, 1 18, 1 19 outside of the geographic service area 1 10 are capable of receiving wireless service from the eNB 102 when the devices 1 16, 1 17, 1 18, 1 19 are within the service area 1 10. Since, the devices 1 16, 1 17, 1 18, 1 19 however, are out of range of the eNB 102, they cannot receive timing information directly from the eNB 102. [0017] The wireless (UE) communication devices 104, 106, 108, 1 16, 1 17, 1 18, 1 19 (collectively UE devices 120) may be referred to as mobile devices, wireless devices, wireless communication devices, and mobile wireless devices, UEs, UE devices as well as by other terms. The UE devices 120 include electronics and code for communicating with base stations and with other wireless communication devices in device-to-device configurations. The wireless communication devices include devices such as cell phones, personal digital assistants (PDAs), wireless modem cards, wireless modems, televisions with wireless communication electronics, and laptop and desktop computers as well as other devices. The combination of wireless communication electronics with an electronic device, therefore, may form a UE device 120. For example, a UE device 120 may include a wireless modem connected to an appliance, computer, television, or other device.

[0018] The eNB 102 includes a wireless transceiver that can exchange wireless signals with the UE devices 104, 106, 108, 109 within the service area 1 10.

Transmissions from the base stations and from the UE devices 104, 106, 108, 109 are governed by a communication specification that defines signaling, protocols, and parameters of the transmission. The communication specification may provide strict rules for communication and may also provide general requirements where specific implementations may vary while still adhering to the communication specification.

Although the discussion below is directed to the 3GPP Long Term Evolution (LTE) communication specification, other communication specifications may be used in some circumstances. The communication specification defines at least a data channel and a control channel for uplink and downlink transmissions and specifies at least some timing and frequency parameters for physical downlink control channels from a base station to a UE device 120. System timing information provided to the UE devices allows for synchronization of communication.

[0019] As explained above, in some situations, two or more UE devices may communicate directly with each other without communication through a base station. Such device-to-device (D2D) communication may occur between UE devices within the service area of a base station or outside the service area. For the example discussed herein, the in coverage (InC) D2D UE devices 106, 108 in a first D2D group 122 are within the service area 1 10 and communicate with each other using D2D

communication. Out of Coverage (OoC) D2D UE devices 1 16, 1 18 in a second D2D group are outside of the service area 1 10 and communicate with each other using D2D communication. In a partial coverage scenario, at least one of the D2D UE devices of the D2D group is located in a service area of a single eNB and at least one D2D UE device of the group is outside all service areas. In a partial coverage scenario, therefore, at least one of the D2D UE devices of the D2D group is an InC UE device in a single service area and at least one UE device is an OoC UE device. The partial coverage D2D group 126 in FIG. 1 includes an InC D2D UE device 109, a first OoC D2D UE device 1 17 and a second OoC D2D UE device 1 19.

[0020] Typically, a D2D synchronization signal (D2DSS) is transmitted by one of the D2D UE devices in a D2D group to maintain synchronization. When available to the transmitting D2D UE device, the D2DSS is based on system timing obtained directly from the eNB. In some situations, however, the UE device cannot obtain the timing information directly from the eNB and the D2DSS is not based on timing directly obtained from the eNB. In system operating in accordance with a 3GPP LTE

specification (such as Release-12), the D2D timing information is provided using the D2DSS signaling. As is known, D2DSS is analogous to Primary Synchronization Signal/Secondary Synchronization Signal (PSS/SSS) channels that are transmitted from base stations to UE devices on downlink resources. D2DSS signals, however, are transmitted using SC-FDMA since D2D communication utilizes uplink communication resources. The UE devices use the D2DSS to determine frame and subframe boundaries, thereby, determining timing information. The D2DSS resources are available for all D2D data and control channel transmissions. Although a D2D UE device has available resources for transmitting the D2DSS as configured by the base station, however, there may be situations where at least some of the D2D UE devices in a D2D group do not transmit D2DSS (i.e., timing information). For example, if the D2D group is in the InC scenario, all D2D UE devices in the D2D group are receiving

PSS/SSS and are deriving timing information from the base station. As a result, there is no need to transmit D2DSS within the group. [0021] In OoC scenarios, the D2D timing cannot be derived directly from system timing since none of the UE devices are receiving PSS/SSS from a base station. At least one D2D UE device in the group transmits D2DSS.

[0022] For partial coverage scenarios, the D2D timing is preferably provided by a D2D UE device that derives the timing from an eNB connected to the network. More specifically, at least one of the UE devices within coverage transits D2DSS based on the system timing relieved via PSS/SSS.

[0023] Proposals for 3GPP LTE revisions include a mechanism for indicating whether a D2DSS is based on timing directly obtained from the eNB or not. For one technique, a D2DSS has a sequence selected from a one of two sets of sequences, where one set is for D2DSS having timing directly obtained from an eNB and the other set is for D2DSS having timing that is not directly obtained from an eNB . For the examples herein, the set of D2DSSs that can be transmitted by a UE device includes two groups where a D2DSSue_net set is a set of D2DSS sequence(s) transmitted by a UE device when the transmission timing reference is an eNB and where a

D2DSSue_oon set is a set of D2DSS sequence(s) transmitted by the UE device when the transmission timing reference is not an eNB. In some situations, the transmission timing reference must be obtained directly from an eNB in order to use the

D2DSSue_net set. In other situations, the D2DSSue_net set may be used where the transmission timing reference is obtained from another device that obtained the transmission timing from an eNB. Nonetheless, if the transmission timing is not obtained from the eNB, either directly or indirectly, the D2DSSue_net set cannot be used by the D2D UE device for transmitting the D2DSS.

[0024] When the D2D group is an OoC D2D group 124, therefore, one of the OoC D2D devices 1 18 transmits a D2DSS signal 128 selected from the D2DSSue_oon set. In the partial coverage scenario, the D2D UE device 109 within the service area 1 10 transmits a D2DSS using the sequence from D2DSSue_net set of sequences to the OoC D2D UE devices 1 17, 1 19. Since the D2D UE devices are mobile, it is possible for an OoC D2D UE device transmitting a D2DSS signal (from the D2DSSue_oon set) to move within range of a D2D UE device transmitting a D2DSS signal from the D2DSSue_net set such that the OoC D2D UE device can detect the D2DSS signal. In such a situation, the data transmission using the D2DSSue_oon set based timing could cause interference to the other data transmissions based on the PSS/SSS or

D2DSSue_net D2DSS timing within the cell (geographical service area) 1 10. For the examples herein, however, interference is eliminated, minimized, or at least reduced since the OoC D2D UE device stops transmitting after the D2DSSue_net signal is detected. Before stopping the transmission, the OoC D2D UE device notifies other D2D UE devices that the transmission will stop and waits a time period before ceasing the D2DSS transmissions.

[0025] FIG. 2A, FIG. 2B, and FIG. 2C are illustrations of the communication system 100 for an example where a D2D UE device transmitting a D2DSS not based on eNB timing information detects a D2DSS signal based on eNB timing information. In FIG. 2A, a first OoC D2D UE device 202 is transmitting a D2DSS 203 that is not based on timing information obtained directly from an eNB. The D2DSS 203 is received by a second OoC D2D UE device 204 and a third OoC D2D UE device 206 in the example. Any D2DSS transmitted by an InC D2D UE device 208 within a geographical service area (cell) of the eNB 102 is not detected by the first OoC D2D UE device 202. For the example, the D2DSS 203 is transmitted in accordance with at least one revision of the 3GPP specification and has a sequence selected from the D2DSSue_oon set of sequences.

[0026] In FIG. 2B, conditions have changed from the situation in FIG. 1 such that a D2DSS 210 transmitted by the InC D2D UE device 108 is detected by the first OoC D2D UE device 202. The D2DSS 210 is based on timing information 212 obtained by the InC D2D UE device 208 directly from the eNB 102. For the example, the InC D2D UE device 208 obtains the synchronization timing from synchronization signals transmitted from the eNB such as the Primary synchronization signal (PSS) and

Secondary synchronization signal (SSS). Other techniques may be used in some circumstances to determine the system timing from the eNB. The D2DSS 210 has a sequence selected from the D2DSSue_net set of sequences reserved for D2DSSs that are based on system timing obtained directly from an eNB. The first OoC D2D UE device received the D2DSS 210 and, based on the sequence, determines that it is based on system timing obtained directly from the eNB. In response to detection of the D2DSS 212, the first OoC D2D UE device 202 sends a Cease D2DSS Message 214 to other UE devices 204, 206 indicating that the first OoC D2D UE device 202 will stop transmitting the D2DSS 203. In some situations, the Cease D2DSS message is transmitted in a control message such as a scheduling assignment (SA) message. The Cease D2DSS message may also be transmitted in a discovery message. For example, an indicator field (indicator flag) in the SA or discovery message can be used to indicate that the D2DSS will no longer be transmitted. In some circumstances, a duration indicator can be transmitted to provide information regarding how long the D2DSS will continue to be transmitted. A two bit flag, for example, can be used to indicate four possible values assigned to different durations. In other circumstances, a SIB message including the duration can be used to configure all the D2D UE devices the duration of the D2DSS before transmission will be stopped. The duration may be based on a time period, the number of D2DSS cycles, the number of transmission periods, and other forms of duration measurements.

[0027] The first OoC D2D UE device 202 does not immediately stop transmitting the D2DSS but rather continues to transmit the D2DSS 203 for a time period. The time period may be measured from the time when the D2DSS 210 is received, when the cease D2DSS message is transmitted or from the last transmission of the D2DSS 203. In some situations, the time period may be based on the transmission period of the D2D communications. For example, the D2DSS 203 may be periodically transmitted in accordance with a convention schedule until the end of the current transmission period, to the end of the next transmission period or to any reference point within a

transmission period. As a result, the time period may vary since the time period is based on time the D2DSS 210 is detected relative to the boundaries of the transmission period.

[0028] In FIG. 2C, the first OoC D2D UE device 202 stops transmitting the D2DSS 203. As a result, the other OoC D2D UE devices must obtain a different timing source. In some situations, the second OoC D2D UE device or the third OoC D2D UE device transmits a D2DSS that is not based on tinning obtained directly from the eNB. In other situations, the first OoC D2D UE device transmits a D2DSS that is based on the D2DSS 210. In these situations, therefore the D2DSS transmitted by the first OoC D2D UE device is indirectly based on the system timing obtained from the eNB.

[0029] FIG. 3 is a block diagram of a user equipment (UE) device 300 suitable for use as the UE devices 120, 202, 204, 206, 208. Each of the UE devices includes a transceiver 302 a controller 304, as well as other components and circuitry (not shown) such as memory, for example. The transceiver 302 includes a transmitter 304 and a receiver 306. The transceiver 302 transmits uplink wireless signals to base stations and receives downlink wireless signals from the base stations. The transceiver can also be configured to transmit and receive D2D signals using allocated uplink communication resources. The controller 304 controls components of the mobile wireless

communication device to manage the functions of the device described herein as well as to facilitate the overall functionality of the device 300. The controller 304 is connected to the transceiver 302 and other components such as memory.

[0030] FIG. 4 is a flow chart of a method of managing D2DSS transmission performed in a D2D UE device. The example of FIG. 4, therefore, may be performed by the first OoC D2D UE 202 in FIG. 2A, FIG. 2B and FIG. 2C.

[0031] At step 402, the D2D UE device 202 transmits D2DSS signaling in accordance with conventional techniques where the D2DSS is based on timing/synchronization information that is not obtained directly from an eNB. For the example, the D2D UE device periodically transmits the D2DSS in accordance with a schedule where the D2DSS has a sequence selected from a D2DSSue_oon set or sequences.

[0032] At step 404, the D2D UE device determines whether a D2DSS has been received that is based on timing information obtained directly from an eNB. For the example, D2D UE device monitors the appropriate channels for D2DSS and determines if any received D2DSS has a sequence from the D2DSSue_net set of sequences. If a D2DSS based on eNB timing has been received, the procedure continues at step -406. Otherwise, the procedure returns to step 402 to continue transmitting the D2DSS and monitoring for D2DSS based on eNB timing [0033] At step 406, the D2D UE device 202 sends a Cease D2DSS notification message 214 indicating that the D2D UE device 202 will stop transmitting the D2DSS message.

[0034] At step 408, a timer is started. For the example, the timer value is a system parameter set during system configuration although the timer value may be dynamic or semi dynamic in some situations. The timer may be referenced from the time the

D2DSS based on eNB timing is detected, from the time the Cease D2DSS notification message was sent, or from other reference times.

[0035] At step 410, the D2D UE device 202 continues to transmit the D2DSS that is based on timing not obtained directly from the eNB. For the example, the D2D UE device 202 continues transmitting the D2DSS in accordance with conventional techniques.

[0036] At step 412, it is determined whether the timer has expired. If the timer has not expired, the procedure returns to step 410 to continue transmitting the D2DSS.

Otherwise, the procedure continues at step 414 where the D2D UE device stops transmitting the D2DSS that is based on timing/synchronization information not obtained directly from an eNB.

[0037] FIG. 5 is message diagram of communications between UE devices 202, 204, 206, 208. The example discussed with reference to FIG. 5 is an example of messaging for the examples of FIGs. 2A-2C and FIG. 4.

[0038] At event 502, the UE devices 202, 204, 206 are within D2D communication range but are not within range of any UE device transmitting a D2DSS based on timing information obtained directly from an eNB. At event 504, therefore, the first OoC D2D UE device is not receiving any D2DSS having a sequence selected from the

D2DSSue_net set.

[0039] At transmission 506, the first OoC D2D UE device 202 transmits a D2DSS that is not directly based on eNB timing information. For the example, the D2DSS has a sequence selected from the D2DSSue_oon set of sequences. The D2DSS is received by the second OoC D2D UE device 204 and the third OoC D2D UE device 206 [0040] At event 508, conditions change such that the first OoC D2D UE device is within range of an InC D2D device. At transmission 510, the InC D2D UE device 208 transmits a D2DSS that is based on timing information obtained directly from an eNB. The first OoC D2D UE device 202 receives the D2DSS and determines that it is based directly on eNB timing information. For the example, the first OoC D2D UE device 202 determines that the D2DSS has a sequence selected from the D2DSSue_net set of sequences.

[0041] At transmission 512, the first OoC D2D UE device 202 sends a Cease D2DSS notification message indicating that it will stop transmitting the D2DSS. For the example, the message is sent as within the next discovery message transmission or within the next SA transmission. The message is received by the second OoC D2D UE device 204 and the third OoC D2D UE device 206

[0042] At transmissions 514, 516, the first OoC D2D UE device 202 continues to transmit the D2DSS. Although two transmissions are shown in FIG. 5, there may be any number of transmissions depending in the circumstances. The D2DSS transmissions continue for a time period 518. After the time period is ended, the first OoC D2D UE device 202 no longer transmits the D2DSS that is based on timing information not directly obtained from the eNB.

[0043] At event 520, the D2D UE devices 202, 204, 206 establish an alternate synchronization source. In one example, one of the second OoC D2D UE device 204 or the third OoC D2D UE device 206 transmits a D2DSS. In some situations, the first OoC D2D UE device may transmit a D2DSS that is based on the timing provided in the D2DSS received from the InC D2D UE device 208.

[0044] In some situations, the synchronization signal that is based directly on eNB timing is a synchronization signal that is transmitted by an eNB. For example, the D2D UE device transmitting the D2DSS based on timing not directly obtained from an eNB may detect a PSS/SSS transmitted from an eNB. In such a situation, the D2D UE device notifies the other D2D UE devices that transmission of the non-eNB timing based D2DSS will be stopped and stops transmitting such D2DSSs. The D23D UE device may transmit a D2DSS that is based on the PSS/SSS. [0045] Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. The above description is illustrative and not restrictive. This invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.