Synchronization management based on device characteristics for D2D devices

Abstract

A device-to-device, D2D, communication device (10) receives a first synchronization signal from a first other D2D communication device (10) and a second synchronization signal from a second other D2D communication device (10). If the first other D2D communication device (10) and the second other D2D communication device (10) have the same priority level for selection as a synchronization reference, the D2D communication device (10) compares a characteristic of the first other D2D communication device (10) with a characteristic of the second other D2D communication device (10). Based on the comparison, the D2D communication device (10) selects between synchronizing to the first synchronization signal and synchronizing to the second synchronization signal.

Description

Technical Field

[0001] The present invention relates to a method for controlling device-to-device (D2D) communication, and a corresponding device, system and computer program. Background Art

[0002] Current wireless communication networks, for example, based on 4G (4th generation) LTE (Long Term Evolution) or 5G (5th generation) NR technologies as specified by 3GPP (3rd Generation Partnership Project), also support D2D communication modes to enable direct communication between UEs (User Equipment), sometimes also referred to as sidelink communication. Such D2D communication modes can be used, for example, for vehicular communications, for example, including communications between vehicles, between vehicles and roadside communication infrastructure, and possibly between vehicles and cellular networks. Due to the various different types of devices that may be involved in communications with vehicles, vehicle-to-everything (V2X) communication is another term used to refer to such communications. Vehicular communications have the potential to increase traffic safety, reduce energy consumption, and enable new services related to intelligent transportation systems.

[0003] Due to the nature of the basic road safety services, the LTE V2X functionality has been designed as a broadcast transmission, i.e., all receivers within a certain range of the transmitter can receive the transmission of the message from the transmitter, i.e., can be considered as the intended recipients. In fact, the transmitter may not know or be able to control the intended receiver group. The V2X functionality for NR technology is described in 3GPP TR 38.885 V16.0.0 (2019-03), for example. In NR technology, more targeted V2X services are also considered by also supporting groupcast, multicast or unicast transmissions, where the intended receivers of the message consist of only a subset of receivers within a certain range of the transmitter (multicast) or a single receiver (unicast). For example, in a platoon service for vehicles, some messages may only be of interest to the member vehicles of the platoon, and can then be effectively targeted to the member vehicles of the platoon through multicast transmission. In another example, a perspective function in which one vehicle provides video data from a front camera to a following vehicle may only involve V2X communication with a pair of vehicles, for which unicast transmission may be a preferred choice. In addition, NR sidelink communications support D2D communications for UEs with and without network coverage, with varying degrees of interaction between UE and network, including the possibility of standalone, network-free operation.

[0004] In D2D communication, the synchronization of UE can be used to establish D2D communication or to enhance the performance of D2D communication. Synchronization generally involves providing synchronization information to the UE. For example, in the sidelink discovery process of LTE technology, the synchronization information may include a sidelink synchronization signal (Sidelink Synchronization Signal, SLSS), timing information and / or some additional configuration parameters, such as a MasterlnformationBlock-SL message or a MasterlnformationBlock-SL-V2X message. In NR technology, the synchronization information may include a sidelink synchronization signal block (Sidelink Synchronization Signal Block, S-SSB). The synchronization information sent by the UE may be derived from information or signals received from the network when within coverage, from information or signals received by the UE as a synchronization reference for the sending UE, or from information or signals received from a global navigation satellite system (GNSS). S-SSB includes a sidelink synchronization signal (SLSS) and a physical sidelink broadcast channel (PSBCH). SLSS is a synchronization sequence that depends on an SLSS identifier (SLSSID). The S-SSB is sent in a time slot and spans 7 to 14 orthogonal frequency division multiplexing (OFDM) symbols, including the unused last OFDM symbol, and constitutes a guard period (GP). The S-SSB is transmitted periodically according to the S-SSB period, for example every 160ms. It can be transmitted once or more times within a period, that is, there may be S-SSB repetitions. The SLSS identifier (SLSS-ID) indicated by the SLSS provides an indication of the priority associated with the S-SSB in some cases together with the content of the PSBCH. In the absence of an external, more reliable synchronization source, such as GNSS-derived or NW-derived synchronization, the UE typically searches for and synchronizes with the S-SSB transmission indicating the highest priority.

[0005] Typically, a UE is configured with two resources where it can send an S-SSB. It typically transmits on one and listens on the other. In this way, it can send and receive S-SSB signals in a period of, for example, 160ms. Of the two resources, it is determined which one is used for transmission based on the synchronization state of the transmitting UE, such as the priority value of the synchronization reference used, and some (pre-)configured parameters. Reception of the S-SSB is attempted in the other resource. The SLSS-ID used for transmission is typically different from the one (or more) SLSS-IDs that the UE may expect to receive. In some cases, three resources may be configured, the third of which is used by the UE to derive synchronization directly from the GNSS.

[0006] Regarding its functionality as a transmitter of S-SSB, the UE can be configured to send the S-SSB once per period (e.g. 160 ms) or a (pre-)configured number of times in one of the two resources, using the value of the SLSS-ID determined based on the UE's synchronization state and the content of the PSBCH. Regarding the UE's reception of the S-SSB, the purpose of receiving the S-SSB is to determine the synchronization reference used by other UEs in their transmissions. Depending on the priority of the synchronization reference used by the receiving UE and the priority of the synchronization reference indicated by the received S-SSB, as well as on the measurement of the received power of the received S-SSB, the receiving UE decides whether to maintain its current synchronization reference or switch to a new reference indicated by the S-SSB. As explained previously, the change of the synchronization reference in turn affects the behavior of the UE as a transmitter of S-SSB. For example, it determines the value of the SLSS-ID and the content of the PSBCH to be used for the transmission of the S-SSB.

[0007] A distributed protocol is used to ensure that different UEs using the same synchronization reference transmit S-SSBs simultaneously with exactly the same content, including SLSS-ID and PSBCH content. As a result, the receiver typically observes a linear superposition of the signals transmitted from multiple UEs. This is sometimes referred to as the SFN combination of the received signals.

[0008] If the LTE procedure is followed, there is no standard procedure to decide which one prevails once there are two synchronization references with the same priority. One solution created for LTE is that each UE can track multiple synchronization references and therefore be able to synchronize with several UEs with different synchronization references at the same time. However, the problem with this solution is scalability and the increase in UE complexity and cost in order to obtain it. Therefore, in the case where a pair of UEs do not have any other synchronization reference other than their internal clock, there is no mechanism to achieve synchronization consensus. As a result, each UE will maintain its own synchronization reference. When considering out-of-coverage UEs, i.e. UEs that are not within the coverage of the eNB / gNB or GNSS, the situation is similar to that of NR SL. Figure 1 The diagram illustrates a table showing the existing synchronization priority classification for NR SL Release 16. It can be seen that in the out of coverage scenario of multiple UEs, there will be no unified synchronization reference for the UEs, because each UE will use the same priority synchronization reference (P6 or P6') so that no UE will switch to another synchronization reference. Figure 2 A corresponding example is illustrated, where a group of UEs having a T2 synchronization reference cannot communicate with another group of UEs having a T1 synchronization reference.

[0009] Therefore, there is a need for techniques that allow selection of a synchronization reference for D2D communications. Summary of the invention

[0010] According to an embodiment, a method for controlling D2D communication is provided. According to the method, a D2D communication device receives a first synchronization signal from a first other D2D communication device. Further, the D2D communication device receives a second synchronization signal from a second other D2D communication device. If the first other D2D communication device and the second other D2D communication device have the same priority level for selection as a synchronization reference, the D2D communication device compares a characteristic of the first other D2D communication device with a characteristic of the second other D2D communication device. Based on the comparison, the D2D communication device selects between synchronizing to the first synchronization signal and synchronizing to the second synchronization signal.

[0011] According to another embodiment, a method for controlling D2D communication is provided. According to the method, a D2D communication device sends a synchronization signal, and the synchronization signal is used to synchronize one or more other D2D communication devices using the D2D communication device as a synchronization reference. Further, the D2D communication device indicates a characteristic of the D2D communication device to the one or more other D2D communication devices.

[0012] According to a further embodiment, a D2D communication device is provided. The D2D communication device is configured to receive a first synchronization signal from a first other D2D communication device. Further, the D2D communication device is configured to receive a second synchronization signal from a second other D2D communication device. Further, the D2D communication device is configured to compare a characteristic of the first other D2D communication device with a characteristic of the second other D2D communication device if the first other D2D communication device and the second other D2D communication device have the same priority level for selection as a synchronization reference, and based on the comparison, select between synchronizing to the first synchronization signal and synchronizing to the second synchronization signal.

[0013] According to a further embodiment, a D2D communication device is provided. The D2D communication device comprises at least one processor and a memory. The memory contains instructions executable by the at least one processor, whereby the D2D communication device operates to receive a first synchronization signal from a first other D2D communication device. Further, the memory contains instructions executable by the at least one processor, whereby the D2D communication device operates to receive a second synchronization signal from a second other D2D communication device. Further, the memory contains instructions executable by the at least one processor, whereby the D2D communication device operates to: if the first other D2D communication device and the second other D2D communication device have the same priority level for selection as a synchronization reference, compare the characteristics of the first other D2D communication device with the characteristics of the second other D2D communication device, and based on the comparison, select between synchronizing to the first synchronization signal and synchronizing to the second synchronization signal.

[0014] According to a further embodiment, a D2D communication device is provided. The D2D communication device is configured to send a synchronization signal, the synchronization signal being used to synchronize one or more other D2D communication devices using the D2D communication device as a synchronization reference. Further, the D2D communication device is configured to indicate a characteristic of the D2D communication device to the one or more other D2D communication devices.

[0015] According to a further embodiment, a D2D communication device is provided. The D2D communication device comprises at least one processor and a memory. The memory contains instructions executable by the at least one processor, whereby the D2D communication device operates to transmit a synchronization signal, the synchronization signal being used to synchronize one or more other D2D communication devices using the D2D communication device as a synchronization reference. Further, the memory contains instructions executable by the at least one processor, whereby the D2D communication device is used to indicate a characteristic of the D2D communication device to the one or more other D2D communication devices.

[0016] According to another embodiment of the present invention, a computer program or a computer program product is provided, for example in the form of a non-transitory storage medium, which includes program code to be executed by at least one processor of a D2D communication device. The execution of the program code causes the D2D communication device to receive a first synchronization signal from a first other D2D communication device. Further, the execution of the program code causes the D2D communication device to receive a second synchronization signal from a second other D2D communication device. Further, the execution of the program code causes the D2D communication device to compare the characteristics of the first other D2D communication device with the characteristics of the second other D2D communication device if the first other D2D communication device and the second other D2D communication device have the same priority level for selection as a synchronization reference, and based on the comparison, select between synchronizing to the first synchronization signal and synchronizing to the second synchronization signal.

[0017] According to another embodiment of the present invention, a computer program or computer program product is provided, for example in the form of a non-transitory storage medium, which includes program code to be executed by at least one processor of a D2D communication device. Execution of the program code causes the D2D communication device to send a synchronization signal, the synchronization signal being used to cause one or more other D2D communication devices to synchronize using the D2D communication device as a synchronization reference. Further, execution of the program code causes the D2D communication device to indicate a characteristic of the D2D communication device to the one or more other D2D communication devices.

[0018] Details of such and further embodiments will be apparent from the following detailed description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The priority order of synchronization references for D2D communication devices is schematically illustrated.

[0020] Figure 2 An example of a scenario in which there are multiple synchronization references having the same priority and resulting in a non-single selection of a synchronization reference is schematically illustrated.

[0021] Figure 3 An exemplary V2X scenario in which D2D communication may be controlled according to an embodiment of the present invention is schematically illustrated.

[0022] Figure 4 An exemplary scenario according to an embodiment of the present invention is schematically illustrated, wherein D2D communication may be controlled according to an embodiment of the present invention.

[0023] Figure 5 The priority order of synchronization references for D2D communication devices according to an embodiment of the present invention is schematically illustrated.

[0024] Figure 6 An exemplary scenario according to an embodiment of the present invention is schematically illustrated, wherein a D2D communication device selects its synchronization reference according to an embodiment of the present invention.

[0025] Figure 7 A flow chart for schematically illustrating a method according to an embodiment of the present invention is shown.

[0026] Figure 8 A flow chart for schematically illustrating a method according to an embodiment of the present invention is shown.

[0027] Fig. 9 The structure of a D2D communication device according to an embodiment of the present invention is schematically illustrated. DETAILED DESCRIPTION

[0028] Hereinafter, the concept of exemplary embodiments according to the present invention will be explained in more detail with reference to the accompanying drawings. The illustrated embodiments relate to the control of D2D communication by wireless communication devices. These wireless communication devices may include various types of UE or other wireless devices (WD). As used herein, the term "wireless device" (WD) refers to a device capable of, configured, arranged and / or operable to communicate wirelessly with a network node and / or other WD. Unless otherwise specified, the term WD may be used interchangeably with UE in this article. Wireless communication may involve the use of electromagnetic waves, radio waves, infrared waves and / or other types of signals suitable for transmitting information through the air to send and / or receive wireless signals. In some embodiments, WD may be configured to send and / or receive information without direct human interaction. For example, WD may be designed to send information to the network on a predetermined schedule when triggered by an internal or external event, or in response to a request from the network. Examples of WD include, but are not limited to, smart phones, mobile phones, cellular phones, voice over IP (VoIP) phones, wireless local loop phones, desktop computers, personal digital assistants (PDAs), wireless cameras, game consoles or devices, music storage devices, playback devices, wearable terminal devices, wireless endpoints, mobile stations, tablet computers, laptop computers, laptop embedded devices (LEEs), laptop mounted devices (LMEs), smart devices, wireless customer premises equipment (CPEs), vehicle-mounted wireless terminal devices, connected vehicles, etc. In some examples, in the Internet of Things (IoT) scenario, WD can also represent a machine or other device that performs monitoring and / or measurement and transmits the results of such monitoring and / or measurement to another WD and / or network node. WD in this case can be a machine-to-machine (M2M) device, which is referred to as a machine type communication (MTC) device in the 3GPP context. As a specific example, WD can be a UE that implements the 3GPP narrowband IoT (NB-IoT) standard. Specific examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, household or personal appliances (e.g., refrigerators, televisions, etc.), or personal wearable devices (e.g., watches, fitness trackers, etc.). In other scenarios, a WD may represent a vehicle or other device capable of monitoring and / or reporting its operating status or other functions associated with its operation. A WD as described above may represent an endpoint of a wireless connection, in which case the device may be referred to as a wireless terminal. In addition, a WD as described above may be mobile, in which case it may also be referred to as a mobile device or mobile terminal. The concepts shown focus particularly on WDs that support D2D communications, such as by implementing 3GPP standards for sidelink communications, vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and vehicle-to-everything (V2X).A WD supporting D2D communication is also referred to herein as a D2D communication device. D2D communication can be based, for example, on LTE radio technology or NR radio technology as specified by 3GPP, for example, on the PC5 SL interface of LTE or NR technology. However, it should be noted that the concepts explained can also be applied to other radio technologies, such as WLAN (Wireless Local Area Network) technology.

[0029] In the illustrated concept, one or more characteristics of the D2D communication device are considered when deciding whether to select a D2D communication device as a synchronization reference. Specifically, in the case where a certain D2D communication device receives a first synchronization signal from a first other D2D communication device and receives a second synchronization signal from a second other D2D communication device, and the first and second other D2D communication devices have the same priority for selection as a synchronization reference, for example, because they both correspond to Figure 1 In the priority order of P6 or P6', the D2D communication device will decide whether to synchronize to the first other D2D communication device or the second other D2D communication device based on at least one characteristic of the first other D2D communication device and the second other D2D communication device. The D2D communication device may correspond to various types of UEs, and the synchronization signal may correspond to the S-SSB of the NR technology. Various characteristics of the D2D communication device may be considered, such as the quality of the internal clock of the D2D communication device, the device type of the D2D communication device, the capabilities of the D2D communication device, the resources available to the D2D communication device, the number of other D2D communication devices using the D2D communication device as a synchronization reference, etc. In some cases, the characteristic may be fixed, such as the device type or the quality of the internal clock. In other cases, the characteristic may be variable, such as the number of other synchronized D2D communication devices using the D2D communication device as a synchronization reference. Note, however, that the characteristics of the D2D communication device may not be confused with the characteristics of the synchronization signal received from the D2D communication device, such as the received power or the received signal quality.

[0030] In the described concept, synchronization consensus can be achieved for UEs outside the coverage or influence of GNSS, eNB, gNB, so that no other synchronization source is available except the internal clock of the UE. Synchronization consensus means that UEs in a certain area will eventually select the same UE as a synchronization reference, or at least reduce the number of synchronization references used in the area. The selection scheme of the described concept can converge to a stable situation while using one-hop information. For example, when the selection of the synchronization reference is based on the quality of the internal clock of the UE, (one or more) UEs with the best internal clock quality will be selected as the common synchronization reference for all UEs in a specific area. Information about the characteristics can be shared between UEs, for example, by including it in the information transmitted by the transmitted synchronization signal. There is no need to define additional priority levels for synchronization reference selection. The described concept can also be applied to scenarios when there are two or more UE groups, each UE group uses different synchronization references of the same priority to enable at least some of the groups to select the same synchronization reference.

[0031] As described above, the described concepts may be applied to synchronization of D2D communication devices in out-of-coverage scenarios, for example, UEs that are out of coverage of a 4G network, a 5G network, or a future 6G network. In addition, the described concepts may also be applied to D2D communication devices that do not support cellular network connectivity or synchronization with GNSS, or in scenarios where cellular network connectivity and / or GNSS connections are lost or unreliable, for example, when considering vehicle communications or public safety applications in tunnels or inside buildings. Another scenario in which synchronization of D2D communication devices based on the described concepts may be beneficial is an application involving a group of devices, for example, a group of drones or autonomous sensors. For such devices, synchronization with a GNSS or cellular network may be limited or unavailable due to environmental conditions or capabilities of the device. Another scenario in which synchronization with a GNSS or cellular network may be limited or unavailable includes the operation of the D2D communication device at high altitudes or under high mobility of the D2D communication device.

[0032] Figure 3 An exemplary scenario involving V2X communications is illustrated. In particular, Figure 3 Various UEs 10 are shown, which may participate in V2X communications or other D2D communications, illustrated by solid arrows. Figure 3 An access node 100 of a wireless communication network is shown, such as an eNB of LTE technology or a gNB of NR technology, or an access point of a WLAN. At least some of the UEs 10 are also capable of communicating by using DL radio transmissions and / or UL radio transmissions, illustrated by dashed arrows.

[0033] Figure 3The UE 10 illustrated in the figure includes a vehicle, a drone, a mobile phone, and a person, such as a pedestrian, a cyclist, a driver of a vehicle, or a passenger of a vehicle. Here, it is noted that in the case of a vehicle, the radio transmission may be performed by a communication module installed in the vehicle, and in the case of a person, the radio transmission may be performed by a radio device carried or worn by the person, such as a wristband device or a similar wearable device. In addition, it is noted that Figure 3 The UEs shown in the figure are merely exemplary, and other types of V2X communication devices or D2D communication devices may also be utilized in the illustrated concepts, such as RSU (roadside unit) or other infrastructure-based V2X communication devices, V2X communication devices in aircraft such as airplanes or helicopters, V2X communication devices in spacecraft, in trains or train cars, in ships, in motorcycles, in bicycles, in mobile scooters, or in any other kind of mobile or transportation devices. V2X communication may also involve utilizing the illustrated mechanisms and processes to implement DRX operations for V2X communication between UEs 10, thereby improving the energy efficiency of V2X communication.

[0034] Figure 4 An exemplary D2D communication scenario is illustrated. In particular, Figure 4 A plurality of UEs 10 are shown, which are connected to each other via radio links implementing direct wireless links (illustrated by double-headed arrows). In addition, one of the UEs 10 is connected to an access node 100 of a wireless communication network via a radio link, for example, to an eNB of LTE technology or a gNB of NR technology. The access node 100 is part of a RAN (Radio Access Network) of a wireless communication network, which typically also includes further access nodes to provide coverage of the desired wireless communication network. In addition, Figure 4 A core network (CN) 210 of the wireless communication network is shown. The CN 210 may provide connectivity of the UE 10 to other data networks, for example, through a GW 220 provided in the CN 210. In addition, the CN 210 may also include various nodes for controlling the operation of the UE 10.

[0035] The radio link can be used for D2D communication between UEs 10. In addition, the radio link to the wireless communication network can be used to control or otherwise assist the D2D communication. In addition, D2D communication and / or data communication with the wireless communication network can be used to provide various types of services to UE 10, such as voice services, multimedia services, data services, intelligent transportation systems (ITS) or similar vehicle management or coordination services, NSPS services and / or NCIS services. Such services can be based on applications executed on UE 10 and / or on devices linked to UE 10. Therefore, in the illustrated concept, D2D transmissions may convey or correspond to V2X messages, ITS messages, or some other kind of messages related to the service. In addition, Figure 4 The application service platform 250 in the CN 210 of the wireless communication network is shown. Figure 4 One or more application servers 300 provided outside the wireless communication network are illustrated. (One or more) applications executed on the UE 10 and / or on one or more other devices linked to the UE 10 can use a radio link with one or more other UEs 10, an application service platform 250 and / or (one or more) application servers 300, thereby enabling corresponding (one or more) services on the UE 10. In some scenarios, the services utilized by the UE 10 can therefore be hosted on the network side, for example, on the application service platform 250 or on (one or more) application servers 300. However, some services may also be network-independent, so that they can be utilized without requiring an active data connection to the wireless communication network. This can be applied, for example, to certain V2X services or NSPS (National Security and Public Safety) services. Such services can be used in out-of-coverage situations, but can still be assisted from the network side when the UE 10 is within the coverage of the wireless communication network, for example, by configuring the UE 10 with respect to the use of the service. The application service platform 250 and the server(s) 300 may also be viewed as host computers that host services provided by applications executed on the UE 10 and utilize DL transmissions, UL transmissions, and / or D2D transmissions. Figure 4 In the scenario, UE 10 may apply DRX operation to D2D communication to improve energy efficiency.

[0036] exist Figure 4 In the example of , the UE 10 is assumed to be a mobile phone and a vehicle or vehicle-based communication device, such as an onboard or vehicle-integrated communication module, or a smartphone or other user equipment linked to a vehicle system. However, it should be noted that other types of UEs may also be used, such as devices carried by pedestrians, or infrastructure-based devices, such as, for example, Figure 3 The roadside unit shown in .

[0037] As described above, in the claimed solution, one or more of the UEs 10 may use another of the UEs 10 as a synchronization reference, and the selection of the one of the UEs 10 as the synchronization reference is based on one or more characteristics of the UE 10, also denoted as "device characteristics" hereinafter. Therefore, synchronization consensus may be achieved in scenarios where no higher priority synchronization source is available. It may be possible for a larger group of UEs 10 to select the same UE 10 as a common synchronization source, thereby avoiding the formation of isolated synchronization clusters. Moreover, such synchronization consensus may be achieved without requiring excessive signaling between the UEs 10.

[0038] In some scenarios, characteristics considered when selecting a UE 10 to be used as a synchronization reference include the quality of the UE 10's internal clock, i.e., the internal clock from which the UE 10 will derive the synchronization signal being sent. Thus, a synchronization consensus can be based on the quality of the respective internal clocks of the UEs 10 in a certain area. The quality of the internal clock can be evaluated, for example, in terms of clock stability, for example, as represented by clock drift. In this way, it can be achieved that among multiple internal clocks, one with the best quality is selected as a common synchronization reference for the UE 10. As a result, D2D transmissions between UEs 10 can be better aligned, which helps to achieve higher performance. Synchronization with high-quality clocks is also beneficial in applications where the relative timing of multiple devices needs to be controlled in a deterministic manner, such as in advanced Industrial Internet of Things (IIoT) applications.

[0039] The quality of the internal clock may be taken into account, for example, by configuring each UE 10 to include information about its own internal clock into the broadcasted synchronization signal, for example, into the S-SSB broadcasted by the UE 10. For example, such information may be included in the PSBCH. The information may be contained, for example, in an information field of a message conveyed by the PSBCH or in the SLSS. The UE 10 may then autonomously select a synchronization signal as a synchronization reference based on the indicated information about the internal clock, for example, by selecting the UE 10 as the synchronization reference, wherein the information indicates a clock with the lowest frequency tolerance or frequency drift parameter.

[0040] Therefore, the UEs 10 may include information about their own internal clock in the transmitted synchronization signals. In some scenarios, the UE 10 may include such information in a selective manner into the transmitted synchronization signals, for example in response to detecting that no other synchronization source is available other than the UE 10's own internal clock. This may have the following effect: for example, when the UE 10 enters a certain area with other UEs 10, the information about the internal clock will be transmitted once in the initial synchronization. Furthermore, the information may be sent in response to detecting that the UE 10 itself has the best internal clock in the area and therefore becomes the dominant synchronization reference.

[0041] In addition or as an alternative to indicating information about its own internal clock in the broadcasted synchronization signal, the UE 10 may also exchange information about the internal clock of the UE 10 during connection establishment, for example, in RRC (Radio Resource Control) signaling for establishing a SL connection between two UEs 10. This information may then, for example, indicate the UE 10 which has the best internal clock in the area based on previously received information. In an information-related embodiment, different parameters about the synchronization reference, such as the clock with the lowest frequency tolerance or drift parameter, are exchanged between different UEs during a connection establishment procedure, such as an RRC signaling interaction.

[0042] The above-described consensus-based selection of a synchronization reference may be integrated into existing schemes for prioritizing between different types of synchronization references. For example, the consensus-based selection may be applied at a lower priority than the selection of a synchronization reference derived directly or indirectly from a GNSS or gNB / eNB. Figure 5 A table illustrating an example of this priority order is shown in FIG. Figure 5 In the example, the priority order corresponds to Figure 1 The consensus-based selection is added in GNSS-based synchronization as a new priority level P6a below UEs indirectly synchronized with gNB / eNB (P5), and in gNB / eNB-based synchronization as a new priority level P6-a' below UEs indirectly synchronized with GNSS, corresponding to the priority order as currently specified for NR technology. The lowest priority levels (P6-b, P6-b') are given to any other UE, i.e. to UEs that are not synchronized to GNSS or gNB / eNB and do not use consensus-based synchronization.

[0043] As described above, information about the internal clock of the UE 10 can be explicitly indicated by including it in the signaling sent by the UE 10. Alternatively or additionally, such information can also be indicated in an implicit manner. Specifically, information about the internal clock of each UE 10 can be indicated based on a UE identifier (UE-ID). For example, configuration information can be provided to the UE 10, which maps the UE-ID to different levels of internal clock quality, for example, by defining a subset of UE-IDs that are known to have accurate clock quality. This configuration can be provided from the wireless communication network when the UE 10 is in coverage, or can be pre-configured in the UE 10, for example, based on manufacturer or operator settings. In some scenarios, the UE-ID used to indicate the internal clock quality can also be a UE-ID dedicated to synchronization purposes and associated with a specific level of internal clock quality.

[0044] In some scenarios, information about the quality of the internal clock of the UE 10 may also be included in the discovery signaling. Specifically, in order to discover other UEs 10 that are potential peers for D2D communication, the UE 10 may send a discovery message. Such discovery messages are, for example, specified by the SL discovery process for NR technology and LTE technology. Such discovery messages may be supplemented by information about the quality of the internal clock. Then, for example, when there is a UE-to-network (UE2NW) relay or a UE-to-UE (UE2UE) relay, a consensus-based synchronization process may be initiated. During the discovery process, a handshake for achieving consensus-based synchronization may be performed.

[0045] Another device characteristic that may be considered as an alternative or additional solution to the internal clock quality is the number of existing synchronizations of the UE 10. For example, for a first UE 10, the number of other UEs 10 using the first UE 10 as a synchronization reference may already be high, while for a second UE 10, the number of other UEs 10 using the second UE 10 as a synchronization reference is lower. When another UE 10 needs to choose between using the first UE 10 and the second UE 10 as a synchronization reference, it may be more advantageous to choose the first UE 10 because it has the majority of other synchronized UEs 10. This may reduce the number of resynchronizations required to achieve synchronization consensus and speed up the process of convergence of all UEs 10 in the considered area to a common synchronization reference. This choice may also be expressed as synchronization consensus based on synchronization majority.

[0046] As described above, in the case of synchronization consensus based on synchronization majority, the selection of the synchronization reference is based on a majority value associated with each UE 10. The majority value for a given UE 10 may correspond to the number of other UEs 10 that use that UE 10 as a synchronization reference. However, other types of majority values ​​may also be used, for example the number of other UEs 10 that use the same synchronization source as the UE 10 under consideration.

[0047] In some scenarios, the UE 10 that needs to select a synchronization source can also determine the majority value required for the selection. For example, if the UE 10 receives multiple synchronization signals derived from the same synchronization reference during a period, the UE 10 can select the synchronization signal corresponding to the synchronization reference used by the highest number of peer UEs 10.

[0048] In some scenarios, an indication of the number of UEs 10 using the same synchronization reference may also be included in the received synchronization signal, for example, in a field of the PSBCH or SLSS. For example, the field may include a parameter denoted "number_of_synch" indicating the number of other UEs 10 using the same synchronization reference. A UE 10 receiving a synchronization signal with such an indication may then select a synchronization signal indicating a higher value of the parameter "number_of_synch". Each UE 10 may determine and store its own value of the parameter "number_of_synch" and indicate it to other UEs 10 if necessary.

[0049] In a scenario where multiple UEs 10 are out of coverage, each UE 10 that uses the dominant synchronization reference in the current period (which means that the UE has not changed the synchronization reference and the synchronization signals received by the UE 10 are derived from the same synchronization reference or from a lower priority synchronization reference) can determine the parameter "number_of_synch" by recording the number of synchronization signals received during a period and derived from the same synchronization reference as itself. The UE 10 can then include this parameter in the synchronization signals it transmits itself, for example, in the PSBCH or SLSS.

[0050] When considering a multi-hop scenario, the UE 10 may also calculate its parameter "number_of_synch" based on the value of this parameter as indicated in synchronization signals received from other UEs 10. Specifically, the UE 10 may consider the values ​​of this field of those received synchronization signals derived from the same synchronization reference, determine the maximum value, and increase this maximum value by one before forwarding this value as the parameter "number_of_synch" to the next hop.

[0051] In the case that the UE 10 receives more than one synchronization signal per cycle from the same other UE 10, the receiving UE 10 can check a field in the received synchronization signal indicating the synchronization signal index corresponding to the position of the synchronization signal within the current synchronization cycle. When determining the value of its parameter "number_of_synch", the UE 10 can discard synchronization signals with indices higher than 1.

[0052] In some scenarios, the UE 10 may also select between different values ​​for indicating the parameter "number_of_synch". For example, such a selection may depend on changes in the quality of the device clock due to changes in the battery level or the device temperature. For example, if the battery level is low, the UE 10 may indicate a lower value for the parameter "number_of_synch", and if the battery level is high, a higher value for the parameter "number_of_synch". Similarly, if the device temperature is high, the UE 10 may indicate a lower value for the parameter "number_of_synch", and if the device temperature is low, a higher value for the parameter "number_of_synch".

[0053] Figure 6 An example is illustrated in which the UE 10 may select its synchronization source based on a majority value as explained above. Figure 6 In the example of , the first group of UEs 10 uses synchronization reference T1 and the second group of UEs 10 uses synchronization reference T2. Due to having different synchronization references, D2D communication between UEs 10 of different groups is generally not possible. In the above process, the UEs 10 of the first group transmit a synchronization signal indicating the value of the parameter "number_of_synch" = 4. The UEs 10 of the second group transmit a synchronization signal indicating the value of the parameter "number_of_synch" = 2. If a UE 10 of the second group receives a synchronization signal from a UE 10 of the first group, it will resynchronize to this synchronization signal received from the UE 10 of the first group. In addition, it will extend this synchronization reference to the remaining UEs 10 of the second group, and the value of the parameter "number_of_synch" is increased by one. The peer UE increases the value of number_of_synch. As a result, the UEs 10 of the second group will change their synchronization reference to T1, so that there is a common synchronization reference for all UEs 10.

[0054] In some scenarios, the characteristics considered in the consensus-based selection of the synchronization reference may also be based on the capabilities of the UE 10. For example, in a flexible topology or mesh network, there may be UEs 10 with different capabilities. For example, energy-saving devices, reduced-capability (RedCap) devices, or vehicles may be located near each other and participate in D2D communications. In such scenarios, it may be beneficial to consider device capabilities alternatively or additionally in the consensus-based selection of the synchronization reference.

[0055] Similar to the internal clock quality, the UE 10 may explicitly include information about their capabilities in the transmitted synchronization signals. Alternatively or additionally, such information may also be included in other signaling, such as in discovery messages, in signaling performed during connection establishment such as RRC signaling, or in dedicated capability exchange signaling.

[0056] In some scenarios, power limited UEs 10 or RedCap UEs 10 may be configured to transmit their respective synchronization signals less frequently than other UEs 10. Such behavior may be configured from the wireless communication network, or may be pre-configured, for example, based on manufacturer operator settings.

[0057] Other device characteristics that may be considered in the consensus-based selection of a synchronization reference may include transmission parameters of the signaling described above, in particular transmission parameters of the synchronization signal. Examples of such transmission parameters include:

[0058] - The bandwidth or resource blocks available or actually used for synchronization signal transmission. If the bandwidth used to send synchronization signals is smaller, the synchronization operation to be performed by other UEs 10 may be more challenging, so it may be preferable to select a synchronization source that uses a higher bandwidth to send synchronization signals.

[0059] - A signal sequence that can be used or is actually used to transmit a synchronization signal.

[0060] - Periodicity of the synchronization signal. For example, power limited UEs or RedCap UEs may send their synchronization signals less frequently.

[0061] - The transmission power available or actually used for synchronization signal transmission. Power-limited UEs or RedCap UEs may use less power to transmit synchronization signals to synchronize them.

[0062] In some scenarios, when out of coverage of GNSS and eNB / gNB, the UE 10 may be configured to apply a maximum periodicity to receive synchronization signaling. The maximum periodicity may be limited by device design, standardization, or manufacturer or operator settings. In this way, it may be achieved that the UE 10 will listen to or receive the maximum number of synchronization signals to which it can potentially synchronize, for example, using a consensus-based selection of a synchronization reference. In addition, the UEs 10 may be configured to be in a full search mode for synchronization, i.e., they send their own synchronization signals according to the configured periodicity, and listen to the synchronization signals of peer UEs 10 for the remaining periods.

[0063] In some scenarios, for example, due to the mobility of the UE 10, the UE 10 may move out of the coverage of the D2D communication, or a new UE 10 may appear in the coverage of the D2D communication. In the consensus-based selection of the synchronization reference, such disappearing or newly appearing UE 10 may be considered based on a timer. The UE 10 may maintain the obtained consensus-based synchronization for the duration of the timer. When the timer expires, a consensus synchronization process may be newly initiated, so that an updated consensus-based synchronization may be obtained.

[0064] Figure 7 A flow chart is shown for illustrating a method that can be used to implement the described concepts. Figure 7 The method may be used to implement the illustrated concept in a D2D communication device corresponding to, for example, any of the above-mentioned UEs 10. In some scenarios, the D2D communication device may be a vehicle or a vehicle-mounted device, but other types of WDs, such as those mentioned above, may also be used.

[0065] If a processor-based implementation of a D2D communication device is used, then Figure 7 At least some steps of the method may be executed and / or controlled by one or more processors of the D2D communication device. Such a D2D communication device may also include a memory storing program code, the program code being used to implement the following description Figure 7 at least some of the functions or steps of the method.

[0066] At step 710 , the D2D communication device receives a first synchronization signal from a first other D2D communication device, and at step 720 , the D2D communication device receives a second synchronization signal from a second other D2D communication device.

[0067] At step 730 , if the first other D2D communication device and the second other D2D communication device have the same priority level for selection as a synchronization reference, the D2D communication device compares the characteristics of the first other D2D communication device with the characteristics of the second other D2D communication device.

[0068] In some scenarios, the characteristic of the first other D2D communication device includes the quality of an internal clock of the first other D2D communication device, and the characteristic of the second other D2D communication device includes the quality of an internal clock of the second other D2D communication device.

[0069] In some scenarios, the characteristic of the first other D2D communication device includes a frequency tolerance of an internal clock of the first other D2D communication device, and the characteristic of the second other D2D communication device includes a frequency tolerance of an internal clock of the second other D2D communication device.

[0070] In some scenarios, the characteristic of the first other D2D communication device includes a frequency drift of an internal clock of the first other D2D communication device, and the characteristic of the second other D2D communication device includes a frequency drift of an internal clock of the second other D2D communication device.

[0071] In some scenarios, the characteristic of the first other D2D communication device includes the number of D2D communication devices synchronized with the first other D2D communication device, and the characteristic of the second other D2D communication device includes the number of D2D communication devices synchronized with the second other D2D communication device.

[0072] In some scenarios, the characteristics of the first other D2D communication device include the number of D2D communication devices using the same synchronization reference as the first other D2D communication device, and the characteristics of the second other D2D communication device include the number of D2D communication devices using the same synchronization reference as the second other D2D communication device.

[0073] In some scenarios, the characteristic of the first other D2D communication device includes the type of the first other D2D communication device, and the characteristic of the second other D2D communication device includes the type of the second other D2D communication device. Examples of such types of D2D communication devices are: vehicles, sensors, power-constrained devices or reduced-capability devices, relay devices, roadside units, industrial devices, or wearable devices.

[0074] In some scenarios, the characteristics of the first other D2D communication device include capabilities of the first other D2D communication device, and the characteristics of the second other D2D communication device include capabilities of the second other D2D communication device.

[0075] In some scenarios, the characteristic of the first other D2D communication device includes the capability of the first other D2D communication device to send a first synchronization signal, and the characteristic of the second other D2D communication device includes the capability of the second other D2D communication device to send a second synchronization signal.

[0076] In some scenarios, the characteristic of the first other D2D communication device includes a bandwidth available for the first other D2D communication device to send the first synchronization signal, and the characteristic of the second other D2D communication device includes a bandwidth available for the second other D2D communication device to send the second synchronization signal.

[0077] In some scenarios, the characteristic of the first other D2D communication device includes radio resources available to the first other D2D communication device for sending the first synchronization signal, and the characteristic of the second other D2D communication device includes radio resources available to the second other D2D communication device for sending the second synchronization signal.

[0078] In some scenarios, the characteristic of the first other D2D communication device includes a sequence type used by the first other D2D communication device to send a first synchronization signal, and the characteristic of the second other D2D communication device includes a sequence type used by the second other D2D communication device to send a second synchronization signal.

[0079] In some scenarios, the characteristic of the first other D2D communication device includes a periodicity applied by the first other D2D communication device to send a first synchronization signal, and the characteristic of the second other D2D communication device includes a periodicity applied by the second other D2D communication device to send a second synchronization signal.

[0080] In some scenarios, the characteristics of the first other D2D communication device include a transmit power used by the first other D2D communication device to send a first synchronization signal, and the characteristics of the second other D2D communication device include a transmit power used by the second other D2D communication device to send a second synchronization signal.

[0081] In some scenarios, the first synchronization signal indicates a characteristic of the first other D2D communication device. Alternatively or additionally, the D2D communication device may receive additional signaling from the first other D2D communication device and such additional signaling may indicate the characteristic of the first other D2D communication device. The additional signaling may, for example, include a discovery message or an RRC signaling. The characteristic of the first other D2D communication device may be indicated as information sent explicitly or in an implicit manner. For example, the characteristic may be indicated by an identifier of the first other D2D communication device. In some scenarios, the D2D communication device may determine the characteristic of the first other D2D communication device based on the identifier of the first other D2D communication device, for example, based on a mapping of the characteristic of the first other D2D communication device to the identifier of the first other D2D communication device. The identifier of the first other D2D communication device may include an identifier dedicated to synchronization purposes, an identifier also used for other purposes, or both.

[0082] In some scenarios, the second synchronization signal indicates the characteristics of the second other D2D communication device. Alternatively or additionally, the D2D communication device may receive additional signaling from the second other D2D communication device and such additional signaling may indicate the characteristics of the second other D2D communication device. The additional signaling may, for example, include a discovery message or an RRC signaling. The characteristics of the second other D2D communication device may be indicated as information sent explicitly or in an implicit manner. For example, the characteristic may be indicated by an identifier of the second other D2D communication device. In some scenarios, the D2D communication device may determine the characteristics of the second other D2D communication device based on the identifier of the second other D2D communication device, for example, based on a mapping of the characteristics of the second other D2D communication device to the identifier of the second other D2D communication device. The identifier of the second other D2D communication device may include an identifier dedicated to synchronization purposes, an identifier also used for other purposes, or both.

[0083] At step 740, the D2D communication device selects between synchronizing to the first synchronization signal and synchronizing to the second synchronization signal. The selection is based on the comparison of step 730. Having synchronized to the selected one of the first synchronization signal or the second synchronization signal, the D2D communication device may maintain synchronization with the selected one of the first synchronization signal and the second synchronization signal until the timer expires.

[0084] At step 750, the D2D communication device may transmit a third synchronization signal, the third synchronization signal being used to enable one or more additional D2D communication devices to synchronize using the D2D communication device as a synchronization reference. The third synchronization signal may, for example, include an S-SSB.

[0085] At step 760, the D2D communication device may indicate the characteristics of the D2D communication device to one or more additional D2D communication devices. In some scenarios, the third synchronization signal may indicate the characteristics of the D2D communication device. In some cases, the third synchronization signal may indicate the characteristics of the D2D communication device only in a subset of instances of periodic transmission of the third synchronization signal. Alternatively or additionally, the D2D communication device may send additional signaling indicating the characteristics of the D2D communication device, such as a discovery message or RRC signaling. The characteristics of the D2D communication device may be indicated as information sent explicitly or in an implicit manner. For example, the characteristics may be indicated by an identifier of the D2D communication device. The identifier of the D2D communication device may include an identifier dedicated to synchronization purposes, an identifier also used for other purposes, or both.

[0086] The characteristic of the D2D communication device may include the quality of the internal clock of the D2D communication device, for example, the frequency tolerance of the internal clock of the D2D communication device and / or the frequency drift of the internal clock of the D2D communication device.

[0087] Alternatively or additionally, the characteristic of the D2D communication device may include the number of D2D communication devices synchronized with the D2D communication device. Alternatively or additionally, the characteristic of the D2D communication device may include the number of D2D communication devices using the same synchronization reference as the D2D communication device. Alternatively or additionally, the characteristic of the D2D communication device may include the type of the D2D communication device. Examples of the type of such D2D communication devices are: vehicles, sensors, power-limited devices or reduced-capacity devices, relay devices, roadside units, industrial devices, or wearable devices. Alternatively or additionally, the characteristic of the D2D communication device may include the capabilities of the D2D communication device, for example, the ability of the D2D communication device to transmit a third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a bandwidth that the D2D communication device can use to send the third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a radio resource that the D2D communication device can use to send the third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a sequence type applied by the D2D communication device to send the third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a periodicity applied by the D2D communication device to send the third synchronization signal.Alternatively or additionally, the characteristic of the D2D communication device may include a transmission power applied by the D2D communication device to send the third synchronization signal.

[0088] Figure 8 A flow chart is shown for illustrating a method that can be used to implement the described concepts. Figure 8 The method may be used to implement the illustrated concept in a D2D communication device, for example corresponding to any of the above-mentioned UEs 10. In some scenarios, the D2D communication device may be a vehicle or a vehicle-mounted device, but other types of WDs, such as those mentioned above, may also be used.

[0089] If a processor-based implementation of a D2D communication device is used, then Figure 8 At least some steps of the method may be executed and / or controlled by one or more processors of the D2D communication device. Such a D2D communication device may also include a memory storing program code, the program code being used to implement the following description Figure 8 at least some of the functions or steps of the method.

[0090] At step 810, the D2D communication device may select a synchronization reference, such as its internal clock or another D2D communication device. After synchronizing with the synchronization reference, the D2D communication device may maintain synchronization with the synchronization reference until a timer expires.

[0091] At step 820, the D2D communication device sends a synchronization signal, which is used to enable one or more other D2D communication devices to synchronize using the D2D communication device as a synchronization reference. The synchronization signal may include, for example, an S-SSB.

[0092] At step 830, the D2D communication device indicates the characteristics of the D2D communication device to one or more other D2D communication devices. In some scenarios, the synchronization signal may indicate the characteristics of the D2D communication device. In some cases, the synchronization signal may indicate the characteristics of the D2D communication device only in a subset of instances of periodic transmission of the third synchronization signal. Alternatively or additionally, the D2D communication device may transmit additional signaling indicating the characteristics of the D2D communication device, such as a discovery message or RRC signaling. The characteristics of the D2D communication device may be indicated as information sent explicitly or in an implicit manner. For example, the characteristics may be indicated by an identifier of the D2D communication device. The identifier of the D2D communication device may include an identifier dedicated to synchronization purposes, an identifier also used for other purposes, or both.

[0093] The characteristic of the D2D communication device may include the quality of the internal clock of the D2D communication device, for example, the frequency tolerance of the internal clock of the D2D communication device and / or the frequency drift of the internal clock of the D2D communication device.

[0094] Alternatively or additionally, the characteristic of the D2D communication device may include the number of D2D communication devices synchronized with the D2D communication device. Alternatively or additionally, the characteristic of the D2D communication device may include the number of D2D communication devices using the same synchronization reference as the D2D communication device. Alternatively or additionally, the characteristic of the D2D communication device may include the type of the D2D communication device. Examples of such types of D2D communication devices are: vehicles, sensors, power-limited devices or reduced-capacity devices, relay devices, roadside units, industrial devices, or wearable devices. Alternatively or additionally, the characteristic of the D2D communication device may include the capabilities of the D2D communication device, for example, the ability of the D2D communication device to transmit a third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a bandwidth that the D2D communication device can use to send the third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a radio resource that the D2D communication device can use to send the third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a sequence type applied by the D2D communication device to send the third synchronization signal. Alternatively or additionally, the characteristic of the D2D communication device may include a periodicity applied by the D2D communication device to send the third synchronization signal.Alternatively or additionally, the characteristic of the D2D communication device may include a transmission power applied by the D2D communication device to send the third synchronization signal.

[0095] Fig. 9 9 illustrates a processor-based implementation of a D2D communication device 900 that can be used to implement the above concepts. Fig. 9 The structure illustrated in may be used to implement the concepts in any of the UEs 10 described above.

[0096] As illustrated, the D2D communication device 900 includes one or more radio interfaces 910. The radio interface(s) 910 may be based on NR technology or LTE technology, for example. However, other radio technologies such as WLAN or Bluetooth may also be used. The radio interface(s) 910 may support D2D communication, for example, using SL communication as specified for NR technology or LTE technology.

[0097] Further, the D2D communication device 900 may include a processor 950 coupled to (one or more) radio interfaces 910 and a memory 960 coupled to (one or more) processors 950. For example, the (one or more) radio interfaces 910, the (one or more) processors 950 and the memory 960 may be coupled via one or more internal bus systems of the D2D communication device 900. The memory 1560 may include a read-only memory (ROM) such as a flash ROM, a random access memory (RAM) such as a dynamic RAM (DRAM) or a static RAM (SRAM), a large-capacity memory such as a hard disk or a solid-state disk, and the like. As illustrated, the memory 960 may include software 970 and / or firmware 980. The memory 960 may include appropriately configured program code to be executed by the (one or more) processors 950 in order to implement the above-mentioned functions for controlling D2D communication, such as in conjunction with Figure 7 or as explained in 8.

[0098] It should be understood that Fig. 9 The structure illustrated in is merely schematic, and the D2D communication device 900 may actually include additional components that have not been illustrated for clarity, such as an internal clock, additional interfaces, or additional processors. In addition, it should be understood that the memory 960 may include additional program codes for implementing known functions of the UE. According to some embodiments, a computer program may also be provided for implementing the functions of the wireless communication device 900, for example, in the form of a physical medium storing program code and / or other data to be stored in the memory 960, or by making the program code downloadable or by streaming.

[0099] As can be seen, the concepts described above can be used to improve the selection of synchronization references by D2D communication devices. Synchronization consensus can be achieved without adding excessive complexity to existing hierarchical schemes of synchronization references.

[0100] It should be understood that the embodiments and implementation schemes explained above are merely illustrative and are susceptible to various modifications. For example, the concepts shown can be applied in combination with various radio technologies and D2D communications, not limited to the SL mode of LTE technology or NR technology, for example, in combination with WLAN technology or other wireless ad hoc network technologies. In addition, the concepts can be applied with respect to various types of UEs. In addition, the concepts can be applied in combination with various services supported by D2D communications. In addition, it should be understood that the above concepts can be implemented using correspondingly designed software executed by one or more processors of an existing device or apparatus, or by using dedicated device hardware. In addition, it should be noted that the devices or apparatus shown can each be implemented as a single device, or as a system of multiple interactive devices or modules.

Claims

1. A method for controlling device-to-device (D2D) communication, the method comprising: D2D communication device (10; 900) receiving a first synchronization signal from a first other D2D communication device; The D2D communication device (10; 900) receiving a second synchronization signal from a second other D2D communication device (10; 900); If the first other D2D communication device (10; 900) and the second other D2D communication device (10; 900) have the same priority level for selection as a synchronization reference, the D2D communication device compares a characteristic of the first other D2D communication device (10; 900) with a characteristic of the second other D2D communication device (10; 900); as well as Based on the comparison, the D2D communication device (10; 900) selects between synchronizing to the first synchronization signal and synchronizing to the second synchronization signal.

2. The method according to claim 1, wherein: The characteristics of the first other D2D communication device (10; 900) include the quality of the internal clock of the first other D2D communication device (10; 900), and the characteristics of the second other D2D communication device (10; 900) include the quality of the internal clock of the second other D2D communication device (10; 900).

3. The method according to claim 2, wherein: The characteristic of the first other D2D communication device (10; 900) includes a frequency tolerance of an internal clock of the first other D2D communication device (10; 900), and the characteristic of the second other D2D communication device (10; 900) includes a frequency tolerance of an internal clock of the second other D2D communication device (10; 900).

4. The method according to claim 2 or 3, wherein: The characteristic of the first other D2D communication device (10; 900) includes a frequency drift of an internal clock of the first other D2D communication device (10; 900), and the characteristic of the second other D2D communication device (10; 900) includes a frequency drift of an internal clock of the second other D2D communication device (10; 900).

5. A method according to any one of the preceding claims, wherein: The characteristics of the first other D2D communication device (10; 900) include the number of D2D communication devices (10; 900) synchronized with the first other D2D communication device (10; 900), and the characteristics of the second other D2D communication device (10; 900) include the number of D2D communication devices (10; 900) synchronized with the second other D2D communication device (10; 900).

6. A method according to any one of the preceding claims, wherein: The characteristics of the first other D2D communication device (10; 900) include the number of D2D communication devices (10; 900) using the same synchronization reference as the first other D2D communication device (10; 900), and the characteristics of the second other D2D communication device (10; 900) include the number of D2D communication devices (10; 900) using the same synchronization reference as the second other D2D communication device (10; 900).

7. A method according to any one of the preceding claims, wherein: The characteristic of the first other D2D communication device (10; 900) comprises the type of the first other D2D communication device (10; 900), and the characteristic of the second other D2D communication device (10; 900) comprises the type of the second other D2D communication device (10; 900).

8. A method according to any one of the preceding claims, wherein: The characteristics of the first other D2D communication device (10; 900) include the capabilities of the first other D2D communication device (10; 900), and the characteristics of the second other D2D communication device (10; 900) include the capabilities of the second other D2D communication device (10; 900).

9. The method according to claim 8, wherein: The characteristics of the first other D2D communication device (10; 900) include the ability of the first other D2D communication device (10; 900) to send the first synchronization signal, and the characteristics of the second other D2D communication device (10; 900) include the ability of the second other D2D communication device (10; 900) to send the second synchronization signal.

10. The method according to claim 8 or 9, wherein: The characteristics of the first other D2D communication device (10; 900) include a bandwidth that the first other D2D communication device (10; 900) can use to send the first synchronization signal, and the characteristics of the second other D2D communication device (10; 900) include a bandwidth that the second other D2D communication device (10; 900) can use to send the second synchronization signal.

11. The method according to any one of claims 8 to 10, wherein: The characteristics of the first other D2D communication device (10; 900) include radio resources that the first other D2D communication device (10; 900) can use to send the first synchronization signal, and the characteristics of the second other D2D communication device (10; 900) include radio resources that the second other D2D communication device (10; 900) can use to send the second synchronization signal.

12. The method according to any one of claims 8 to 11, wherein: The characteristics of the first other D2D communication device (10; 900) include the sequence type applied by the first other D2D communication device (10; 900) to send the first synchronization signal, and the characteristics of the second other D2D communication device (10; 900) include the sequence type applied by the second other D2D communication device (10; 900) to send the second synchronization signal.

13. The method according to any one of claims 8 to 12, wherein: The characteristics of the first other D2D communication device (10; 900) include the periodicity used by the first other D2D communication device (10; 900) to send the first synchronization signal, and the characteristics of the second other D2D communication device (10; 900) include the periodicity used by the second other D2D communication device (10; 900) to send the second synchronization signal.

14. The method according to any one of claims 8 to 13, wherein: The characteristics of the first other D2D communication device (10; 900) include the transmission power used by the first other D2D communication device (10; 900) to send the first synchronization signal, and the characteristics of the second other D2D communication device (10; 900) include the transmission power used by the second other D2D communication device (10; 900) to send the second synchronization signal.

15. A method according to any one of the preceding claims, wherein: The first synchronization signal indicates a characteristic of the first other D2D communication device (10; 900).

16. A method according to any one of the preceding claims, comprising: The D2D communication device (10; 900) receives the first other D2D communication device (10; 900) receives further signalling indicating characteristics of said first other D2D communication device (10; 900).

17. A method according to any one of the preceding claims, wherein: The second synchronization signal indicates a characteristic of the second other D2D communication device (10; 900).

18. A method according to any one of the preceding claims, comprising: The D2D communication device (10; 900) receives further signaling from the second other D2D communication device (10; 900) indicating characteristics of the first other D2D communication device (10; 900).

19. A method according to any one of the preceding claims, comprising: The D2D communication device (10; 900) determines a characteristic of the first other D2D communication device (10; 900) based on the identifier of the first other D2D communication device (10; 900).

20. The method according to claim 19, comprising: The D2D communication device (10; 900) determines the characteristic of the first other D2D communication device (10; 900) based on a mapping of the characteristic of the first other D2D communication device (10; 900) to an identifier of the first other D2D communication device (10; 900).

21. A method according to any one of the preceding claims, comprising: The D2D communication device (10; 900) determines a characteristic of the second other D2D communication device (10; 900) based on the identifier of the second other D2D communication device (10; 900).

22. The method according to claim 21, comprising: The D2D communication device (10; 900) determines the characteristic of the second other D2D communication device (10; 900) based on a mapping of the characteristic of the second other D2D communication device (10; 900) to an identifier of the second other D2D communication device (10; 900).

23. A method according to any one of the preceding claims, comprising: The D2D communication device (10; 900) maintains synchronization with the selected one of the first synchronization signal and the second synchronization signal until a timer expires.

24. A method according to any one of the preceding claims, comprising: The D2D communication device (10; 900) transmits a third synchronization signal, the third synchronization signal being used to enable one or more other D2D communication devices (10; 900) to synchronize using the D2D communication device (10; 900) as a synchronization reference.

25. The method according to claim 24, wherein: The third synchronization signal indicates a characteristic of the D2D communication device (10; 900).

26. The method according to claim 25, wherein: The third synchronization signal indicates a characteristic of the D2D communication device (10; 900) only in a subset of instances of periodic transmission of the third synchronization signal.

27. A method according to any one of claims 24 to 26, comprising: The D2D communication device (10; 900) transmits further signaling indicating characteristics of the D2D communication device (10; 900).

28. A method according to any one of claims 25 to 27, wherein: The characteristics of the D2D communication device (10; 900) are indicated by an identifier of the D2D communication device (10; 900).

29. The method according to any one of claims 25 to 28, wherein: The characteristics of the D2D communication device (10; 900) include the quality of an internal clock of the D2D communication device (10; 900).

30. The method of claim 29, wherein: The characteristics of the D2D communication device (10; 900) include a frequency tolerance of an internal clock of the D2D communication device (10; 900).

31. The method according to claim 29 or 30, wherein: The characteristic of the D2D communication device (10; 900) includes a frequency drift of an internal clock of the D2D communication device (10; 900).

32. The method according to any one of claims 25 to 31, wherein: The characteristics of the D2D communication device (10; 900) include the number of D2D communication devices (10; 900) synchronized with the D2D communication device (10; 900).

33. A method according to any one of claims 25 to 32, wherein: The characteristics of the D2D communication device (10; 900) include the number of D2D communication devices (10; 900) that use the same synchronization reference as the D2D communication device (10; 900).

34. A method according to any one of claims 25 to 33, wherein: The characteristics of the D2D communication device (10; 900) include the type of the D2D communication device (10; 900).

35. The method according to any one of claims 25 to 34, wherein: The characteristics of the D2D communication device (10; 900) include the capabilities of the D2D communication device (10; 900).

36. The method of claim 35, wherein: The characteristics of the D2D communication device (10; 900) include the ability of the D2D communication device (10; 900) to send the third synchronization signal.

37. The method according to claim 35 or 36, wherein: The characteristics of the D2D communication device (10; 900) include a bandwidth that the D2D communication device (10; 900) can use to send the third synchronization signal.

38. A method according to any one of claims 35 to 37, wherein: The characteristics of the D2D communication device (10; 900) include radio resources available to the D2D communication device (10; 900) for sending the third synchronization signal.

39. The method according to any one of claims 35 to 38, wherein: The characteristics of the D2D communication device (10; 900) include a sequence type applied by the D2D communication device (10; 900) for sending the third synchronization signal.

40. The method according to any one of claims 35 to 39, wherein: The characteristics of the D2D communication device (10; 900) include a periodicity applied by the D2D communication device (10; 900) for sending the third synchronization signal.

41. The method according to any one of claims 35 to 40, wherein: The characteristics of the D2D communication device (10; 900) include a transmission power used by the D2D communication device (10; 900) to transmit the third synchronization signal.

42. A method for controlling device-to-device (D2D) communication, the method comprising: D2D communication device (10; 900) sends a synchronization signal, wherein the synchronization signal is used to enable one or more other D2D communication devices (10; 900) synchronizing using the D2D communication device (10; 900) as a synchronization reference; as well as The D2D communication device (10; 900) indicates characteristics of the D2D communication device (10; 900) to the one or more further D2D communication devices (10; 900).

43. The method of claim 42, wherein: The synchronization signal indicates a characteristic of the D2D communication device (10; 900).

44. The method of claim 43, wherein: The synchronization signal indicates a characteristic of the D2D communication device (10; 900) only in a subset of instances of periodic transmission of the third synchronization signal.

45. A method according to any one of claims 42 to 44, comprising: The D2D communication device (10; 900) transmits further signaling indicating characteristics of the D2D communication device (10; 900).

46. ​​A method according to any one of claims 42 to 45, wherein: The characteristics of the D2D communication device (10; 900) are indicated by an identifier of the D2D communication device (10; 900).

47. A method according to any one of claims 42 to 46, wherein: The characteristics of the D2D communication device (10; 900) include the quality of an internal clock of the D2D communication device (10; 900).

48. The method of claim 47, wherein: The characteristics of the D2D communication device (10; 900) include a frequency tolerance of an internal clock of the D2D communication device (10; 900).

49. The method according to claim 47 or 48, wherein: The characteristic of the D2D communication device (10; 900) includes a frequency drift of an internal clock of the D2D communication device (10; 900).

50. The method according to any one of claims 42 to 49, wherein: The characteristics of the D2D communication device (10; 900) include the number of D2D communication devices (10; 900) synchronized with the D2D communication device (10; 900).

51. The method according to any one of claims 42 to 50, wherein: The characteristics of the D2D communication device (10; 900) include the number of D2D communication devices (10; 900) that use the same synchronization reference as the D2D communication device (10; 900).

52. The method according to any one of claims 42 to 51, wherein: The characteristics of the D2D communication device (10; 900) include the type of the D2D communication device (10; 900).

53. The method according to any one of claims 42 to 52, wherein: The characteristics of the D2D communication device (10; 900) include the capabilities of the D2D communication device (10; 900).

54. The method of claim 53, wherein: The characteristics of the D2D communication device (10; 900) include the ability of the D2D communication device (10; 900) to send the synchronization signal.

55. The method of claim 53 or 54, wherein: The characteristics of the D2D communication device (10; 900) include a bandwidth that the D2D communication device (10; 900) can use to send the synchronization signal.

56. A method according to any one of claims 53 to 55, wherein: The characteristics of the D2D communication device (10; 900) include radio resources available to the D2D communication device (10; 900) for sending the synchronization signal.

57. The method according to any one of claims 53 to 56, wherein: The characteristics of the D2D communication device (10; 900) include a type of sequence used by the D2D communication device (10; 900) to send the synchronization signal.

58. A method according to any one of claims 53 to 57, wherein: The characteristics of the D2D communication device (10; 900) include a periodicity applied by the D2D communication device (10; 900) for sending the synchronization signal.

59. The method according to any one of claims 53 to 58, wherein: The characteristics of the D2D communication device (10; 900) include a transmission power used by the D2D communication device (10; 900) to transmit the synchronization signal.

60. A D2D communication device (10; 900), the D2D communication device (10; 900) being configured as: - receiving a first synchronization signal from a first other D2D communication device (10; 900); - receiving a second synchronization signal from a second other D2D communication device (10; 900); - if the first other D2D communication device (10; 900) and the second other D2D communication device (10; 900) have the same priority level for selection as synchronization reference, comparing the characteristics of the first other D2D communication device (10; 900) with the characteristics of the second other D2D communication device (10; 900); and - based on said comparison, selecting between synchronizing to said first synchronization signal and synchronizing to said second synchronization signal.

61. The D2D communication device (10; 900) according to claim 60, wherein: The D2D communication device (10; 900) is configured to perform the method according to any one of claims 2 to 41.

62. The D2D communication device (10; 900) according to claim 60 or 61, comprising: at least one processor (950), and a memory (960) containing program code executable by the at least one processor (950), Thus, the program code is executed by the at least one processor (950) so that the D2D communication device (10; 900) performs the method according to any one of claims 1 to 41.

63. A D2D communication device (10; 900), the D2D communication device (10; 900) being configured to: - sending a synchronization signal for causing one or more further D2D communication devices (10; 900) to synchronize using the D2D communication device (10; 900) as a synchronization reference; and - indicating characteristics of the D2D communication device (10; 900) to the one or more further D2D communication devices (10; 900).

64. The D2D communication device (10; 900) according to claim 63, wherein: The D2D communication device (10; 900) is configured to perform a method according to any one of claims 43 to 59.

65. The D2D communication device (10; 900) according to claim 60 or 61, comprising: at least one processor (950), and a memory (960) containing program code executable by the at least one processor (950), Thus, the execution of the program code by the at least one processor (950) causes the D2D communication device (10; 900) to perform the method according to any one of claims 42 to 59.

66. A computer program or a computer program product, comprising program code to be executed by at least one processor (950) of a D2D communication device (10; 900), wherein execution of the program code causes the D2D communication device (10; 900) to perform a method according to any one of claims 1 to 59.

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