WO2015111851A1

WO2015111851A1 - Method for implementing synchronization between d2d devices and a d2d device

Info

Publication number: WO2015111851A1
Application number: PCT/KR2014/013025
Authority: WO
Inventors: Shichang Zhang; Yingyang Li; Chengjun Sun; Yunchuan YANG; Jingxing Fu
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2014-01-24
Filing date: 2014-12-30
Publication date: 2015-07-30
Also published as: CN104812058A

Abstract

Embodiments of the present invention provide a method for implementing synchronization between D2D devices, for a D2D device which is able to detect the synchronization source of the cellular network and is located at the edge of the cellular cell, if the D2D synchronization signal of the same level D2D device cannot be detected within a certain area, D2D signal is continuously transmitted with a particular period. And according to a detected result of the synchronization signal of the next level device, the transmission density of the D2D synchronization signal is adjusted. For a D2D synchronization device which is able to detect the synchronization source of the cellular cell, D2D synchronization signal is transmitted in response to a trigger synchronization signal triggered by a D2D device outside the coverage of the synchronization source of the cellular network. For a D2D device which is outside the coverage of the synchronization source of the cellular cell, synchronization signal is transmitted/detected or trigger synchronization signal is transmitted according to actions of the D2D device in the coverage of the synchronization source of the cellular cell. According to the technical solution provided by the present disclosure, synchronization between D2D devices may be implemented effectively.

Description

METHOD FOR IMPLEMENTING SYNCHRONIZATION BETWEEN D2D DEVICES AND A D2D DEVICE

The present invention relates to mobile communication techniques, and more particularly, to a method and an apparatus for implementing synchronization between D2D devices.

At present, device to device (D2D) communications technique has been accepted by 3GPP standards due to its huge potential benefits in common security field and common civil communications field. It is a candidate evolution trend of LTE advanced (LTE-A) systems.

According to current 3GPP conclusions, D2D devices implement D2D communications via a half-duplex manner. When the D2D device is covered by a wireless network, the D2D communication occupies only uplink carrier (FDD systems) or uplink subframes (TDD systems). A working assumption of the current 3GPP is as follows: PUSCH structure in current LTE system is utilized in the communications between D2D devices, i.e., information bits of the communications between the D2D devices are born by wireless signals generated based on SC-FDMA multiplexing technique.

However, corrected reception of the SC-FDMA wireless signals requires strict time and frequency synchronization between a transmitting end and a receiving end. This means multiple D2D devices in the D2D communications must be synchronous in time and frequency. But in a practical D2D communication environment, multiple D2D devices participating in the D2D communications may form a D2D group. There may be no common synchronization source for the D2D devices in the D2D group. For example, some or all D2D devices in the D2D group are outside the coverage area of a wireless cell, or, D2D devices in the D2D group are within coverage areas of different asynchronous wireless cells. Therefore, under the D2D communications environment, some D2D devices have to transmit synchronization signals as synchronization source, so as to realize the time and frequency synchronization between the D2D devices in the D2D group.

In a cellular communications environment, eNB transmits synchronization signals with a fixed time period. Terminals in a cell realize an initial time and frequency synchronization with the eNB through detecting the synchronization signals transmitted by the eNB. However, different from the eNB, power of the D2D devices are usually provided by batteries, the power and capability for continuously transmitting synchronization signals are limited. In addition, in a D2D group, problems such as the D2D device in what environment should transmit the synchronization signal, when should the D2D device stop transmitting the synchronization signal and how the D2D device detects the synchronization signal to realize synchronization with other D2D devices in the D2D group will affect the synchronization between the D2D devices and finally affect the communications between the D2D devices. There is no solution for the above problems yet.

The present invention is to solve at least one of the above defects. In particular, a method for implementing synchronization between D2D devices in a D2D group is provided.

A method for implementing synchronization between D2D devices, including:

detecting, by a D2D device, a synchronization source of a cellular network, and determining a transmitting/detecting configuration of the D2D synchronization signal; wherein the transmitting/detecting configuration includes a transmitting/detecting period, a transmitting window and a detecting window corresponding to each level synchronization device; and

transmitting/detecting, by an IC device which detects the synchronization source of the cellular network and an OOC device which does not detects the synchronization source of the cellular network, the D2D synchronization signal according to the transmitting/detecting configuration.

Preferably, the transmitting/detecting the D2D synchronization signal by the IC device includes:

a1, if the IC device is located at the edge of the cellular cell or the IC device receives a D2D synchronization signal detecting indication from a base station, selecting, by the IC device, a window w _l,i from transmitting windows of same level synchronization devices in each long period according to the transmitting/detecting configuration of the D2D synchronization signal, and detecting D2D synchronization signal of the same level synchronization device in the window w _l,i; or, if the IC device reports a detected result of the D2D synchronization signal of the same level synchronization device to the base station and receives a D2D synchronization signal transmitting indication from the base station, executing step a2; wherein the transmitting/detecting configuration includes a long period and a basic period, the long period includes M basic periods, M is an integer, i denotes an index of the basic period in the long period P_l; and l denotes a identifier of the long period in the transmitting/detecting configuration; and

a2, transmitting the D2D synchronization signal in the window w _l,i for use of synchronization of a next level synchronization device.

Preferably, the IC device transmitting/detecting the D2D synchronization signal includes:

a1, if the IC device is located at the edge of the cellular cell or receives a D2D synchronization signal detecting indication from a base station, detecting, by the IC device, D2D synchronization signal of the same level synchronization device in subframe n of each long period; if the IC device does not detect the D2D synchronization signal of the same level synchronization device, or if the IC device reports a detected result of the D2D synchronization signal of the same level synchronization device to the base station and receives a D2D synchronization signal transmitting indication from the base station, executing step a2; wherein mod (n-Δ, P _u)=0, the transmitting/detecting configuration comprises a long period P_l and a basic period P_u, the long period P_l comprises N basic periods P_u, l denotes a identifier of the long period in the transmitting/detecting configuration, Δdenotes a long period detecting window offset defined in advance; and

a2, transmitting the D2D synchronization signal in the window w _l,i of each long period for use of synchronization of a second level synchronization device; wherein a subframe number corresponding to a subframe where the windoww _l,i is located meets: mod (n _l-Δ, P _l)=0, or mod (n _l-Δ- N_ID×P _u, P _l)=0, wherein N_ID=mod(RNTI, N), RNTI denotes an ID of the IC device in the cell.

Preferably, after step a2, the method further includes:

detecting, by the IC device, the synchronization signal of the same level synchronization device in transmitting/detecting window

, and after detecting the synchronization signal of the same level synchronization device, stopping transmitting the D2D synchronization signal; if the synchronization signal of the same level synchronization device is not detected, returning to step a2;

wherein a subframe number corresponding to the subframe where

is located meets: mod(

-Δ, P _u)=0 and

_≠ n _l.

Preferably, the IC device determines whether it is located at the edge of the cellular cell by:

if a receiving power of a reference signal of the cellular cell detected by the IC device is lower than a preconfigured threshold TH_cc, determining that the IC device is located at the edge of the cellular cell.

Preferably, after step a2, the method further includes:

detecting, by the IC device according to the transmitting/detecting configuration of the D2D synchronization signal, D2D synchronization signal of a next level synchronization device in a transmitting window of a second level synchronization device of a basic period where the window w _l,i belongs, and detecting D2D synchronization signal of the same level synchronization device in a transmitting window of the same level synchronization device except for w _l,i; if the D2D synchronization signal of the next level synchronization device is detected, increasing a transmission density of the D2D synchronization signal.

Preferably, the increasing the transmission density of the D2D synchronization signal includes:

transmitting, by the IC device, the D2D synchronization signal in the window w _l,i and a transmission window w _l,j in which no D2D synchronization signal of the same level synchronization device is detected; wherein j denotes an index of the transmitting window in which no D2D synchronization signal of the same level synchronization device is detected in the long period l.

Preferably, after increasing the transmission density of the D2D synchronization signal, detecting, by the IC device, the D2D synchronization signal of the next level synchronization device in the transmitting window of the second level synchronization device in the basic period of the window in which the IC device transmits the D2D synchronization signal, and returning to step a2 if the D2D synchronization signal of the next level synchronization device is not detected in all transmitting windows of second level synchronization devices.

Preferably, the transmitting the D2D synchronization signal by the IC device includes:

after detecting a trigger synchronization signal transmitted by a second level synchronization device, transmitting, by the IC device, the D2D synchronization signal in a transmitting window of a first level synchronization device with a period P_IC indicated in the transmitting/detecting configuration.

Preferably, the IC device detects the trigger synchronization signal in each detecting window of the first synchronization device according to the transmitting/detecting configuration.

Preferably, after transmitting the D2D synchronization signal in the transmitting window of the first level synchronization device, the method further includes:

detecting, by the IC device in the detecting window corresponding to the transmitting window of the first level synchronization device, D2D synchronization signal of the next level synchronization device, and stopping transmitting the D2D synchronization signal if no D2D synchronization signal of the next level synchronization signal is detected.

Preferably, the transmitting/detecting the D2D synchronization signal by the OOC device includes:

performing, by the OOC device according to pre-stored priorities of carriers corresponding to the cellular cell, the D2D synchronization signal transmitting/detecting operation on each carrier supported by the OOC device in turn.

Preferably, for any carrier, after the OOC detects the D2D synchronization signal on the carrier within a preconfigured time period T_OOC, performing, by the OOC device, synchronization operation according to the D2D synchronization signal with the highest priority among the detected D2D synchronization signals.

Preferably, after detecting the D2D synchronization signal on any carrier, the method further includes:

b1, selecting, by the OOC device, a window w _k,i in which the highest priority D2D synchronization signal is detected among all windows in which synchronization signals are detected, determining a synchronization level of the OOC device k+1 according to level information k in the D2D synchronization signal detected in the window w _k,i, and detecting the D2D synchronization signal of the same level synchronization device in a transmitting window w _t,i of the same level synchronization device in the basic period of the window w _k,i; wherein the transmitting/detecting configuration includes a long period and a basic period, the long period includes M basic periods, M is an integer, i denotes an index of the basic period in which the synchronization signal with the highest priority is detected;

b2, if the OOC device is a lowest level device and the OOC device does not detect the D2D synchronization signal of the same level device in the window w _t,i; or, if the OOC device is located at the edge of the coverage of the synchronization signal of an upper level synchronization device, and the OOC device is not a lowest level device and the receiving power of the D2D synchronization signal of the same level synchronization device detected by the OOC device in the window w _t,i is lower than a preconfigured threshold TH_b; or if the OOC device is far away from the edge of the coverage of the upper level synchronization device, and the OOC device is not a lowest level device and the OOC device does not detects the D2D synchronization signal of the same level device in the window w _t,i, executing step b3; and

b3, transmitting, by the OOC device, the D2D synchronization signal in the window w _t,i.

Preferably, after step b3, the method further includes:

if the OOC device is located at the edge of the coverage of the upper level synchronization device, and the OOC device is not the lowest level device, detecting, by the OOC device in a transmitting window of a next level synchronization device in the basic period where the window w _t,i belongs, the D2D synchronization signal of the next level synchronization device, and detecting the D2D synchronization signal of the same level synchronization device in the transmitting window of the same level synchronization device except for the window w _t,i; and increasing the transmission density of the D2D synchronization signal if the D2D synchronization signal of the next level synchronization device is detected.

transmitting, by the OOC device, the D2D synchronization signal in the window w _t,i and a transmission window w _t,j in which no D2D synchronization signal of the same level synchronization device is detected; wherein j denotes an index of the transmitting window in which no D2D synchronization signal of the same level synchronization device is detected in the long period l.

Preferably, after increasing the transmission density of the D2D synchronization signal, detecting, by the OOC device, the D2D synchronization signal of the next level synchronization device in the transmitting window of the next level synchronization device in the basic period of the window in which the OOC device transmits the D2D synchronization signal, and returning to step b3 if the D2D synchronization signal of the next level synchronization device is not detected in all transmitting windows of next level synchronization devices.

c1, selecting, by the OOC device, a window w _k,i in which the highest priority synchronization signal is detected among the detected D2D synchronization signals, determining a synchronization level of the OOC device k+1 according to level information k in the D2D synchronization signal detected in the window w _k,i, if the OOC device is located at the edge of the coverage of the synchronization signal of the upper level synchronization device and is not the lowest level device, selecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, a window w _l,ii from transmitting windows corresponding to the same level synchronization devices of each long period l, and detecting synchronization signal of the same level synchronization device in the window w _l,ii; wherein the transmitting/detecting configuration includes a long period and a basic period, the long period includes M basic periods, M is an integer, i denotes an index of the basic period in which the synchronization signal with the highest priority is detected; ii denotes an index of the basic period where the transmitting window belongs in the long period l; and

c2, if no D2D synchronization signal of the same level synchronization device is detected in the window , transmitting, by the OOC device, the D2D synchronization signal in the window w _l,ii of each long period l.

Preferably, for any carrier, if the OOC device does not detect any D2D synchronization signal on any carrier within the preconfigured period of time, selecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, a window w _l,i from transmitting window of first or second level synchronization device of each long period l, and transmitting independent D2D synchronization signal in the window w _l,i with the period l for use of synchronization by the next level synchronization device; wherein the transmitting/detecting configuration includes a long period and a basic period, the long period includes M basic periods, M is an integer, i denotes an index of the basic period in the long period.

Preferably, for any carrier, if the OOC device does not detect any D2D synchronization signal on any carrier within the preconfigured period of time, transmitting, by the OOC device, the trigger synchronization signal and detecting the D2D synchronization signal on the carrier in a time-division manner, if no D2D synchronization signal is detected with a preconfigured time period T_tr after the trigger synchronization signal is transmitted, executing step d; and

d, selecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, a window w _l,i from transmitting window of first or second level synchronization device of each long period P_l, and transmitting independent D2D synchronization signal in the window w _l,i with the period P_l for use of synchronization by the next level synchronization device; wherein the transmitting/detecting configuration includes a long period and a basic period, the long period includes M basic periods, M is an integer, i denotes an index of the basic period in the long period.

Preferably, after step d, the method further includes:

detecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, the D2D synchronization signal of the next level synchronization device in a transmitting window of a second or third level synchronization device of the basic period where the window w _l,i belongs, and detecting D2D synchronization signal of the same level synchronization device in a transmitting window of the same level synchronization device except for w _l,i; if the D2D synchronization signal of the next level synchronization device is detected, increasing a transmission density of the D2D synchronization signal.

transmitting, by the OOC device, the D2D synchronization signal in the window w _l,i and a transmission window w _l,j in which no D2D synchronization signal of the same level synchronization device is detected; wherein j denotes an index of the transmitting window in which no D2D synchronization signal of the same level synchronization device is detected in the long period P_l.

Preferably, after increasing the transmission density of the D2D synchronization signal, detecting, by the OOC device, the D2D synchronization signal of the next level synchronization device in the transmitting window of the second or third level synchronization device in the basic period of the window in which the OOC device transmits the D2D synchronization signal, and returning to step d if the D2D synchronization signal of the next level synchronization device is not detected in all transmitting windows of second or third level synchronization devices.

Preferably, for any carrier, if the OOC device does not detect any D2D synchronization signal on any carrier within the preconfigured period of time T_OOC, transmitting, by the OOC device, the trigger synchronization signal and detecting the D2D synchronization signal on the carrier in a time-division manner, if no D2D synchronization signal is detected with a preconfigured time period T_tr after the trigger synchronization signal is transmitted, stopping transmitting the trigger synchronization signal and detecting the D2D synchronization signal in the time-division manner; and executing steps b1~b3.

An apparatus for implementing synchronization between D2D devices, includes: a cellular network synchronization source detecting unit, a configuration receiving unit, an IC device synchronizing unit and an OOC device synchronizing unit; wherein

the cellular network synchronization source detecting unit is to detect a synchronization source of the cellular network, indicate the IC device synchronizing unit to perform a synchronizing processing if the synchronization source of the cellular network is detected, and indicate the OOC device synchronizing unit to perform a synchronizing processing if no synchronization source is detected;

the configuration receiving unit is to receive transmitting/detecting configuration of the D2D synchronization signal; the transmitting/detecting configuration includes a transmitting/detecting period, a transmitting window and a detecting window corresponding to each level synchronization device;

the IC device synchronizing unit is to transmit/detect D2D synchronization signal according to the transmitting/detecting configuration after receiving a notification of the cellular network synchronization source detecting unit; and

the OOC device synchronizing unit is to transmit/detect D2D synchronization signal according to the transmitting/detecting configuration after receiving a notification of the cellular network synchronization source detecting unit.

According to the technical solution provided by the embodiments of the present disclosure, for a D2D device which is able to detect the synchronization source of the cellular network and is located at the edge of the cellular cell, if the D2D synchronization signal of the same level D2D device cannot be detected within a certain area, D2D signal is continuously transmitted with a particular period. And according to a detected result of the synchronization signal of the next level device, the transmission density of the D2D synchronization signal is adjusted. For a D2D synchronization device which is able to detect the synchronization source of the cellular cell, D2D synchronization signal is transmitted in response to a trigger synchronization signal triggered by a D2D device outside the coverage of the synchronization source of the cellular network. For a D2D device which is outside the coverage of the synchronization source of the cellular cell, synchronization signal is transmitted/detected or trigger synchronization signal is transmitted according to actions of the D2D device in the coverage of the synchronization source of the cellular cell. According to the technical solution provided by the present disclosure, synchronization between D2D devices may be implemented effectively.

FIG. 1 is a flowchart illustrating a solution according to various embodiments of the present disclosure.

FIG. 2 is a schematic diagram illustrating a transmitting/detecting configuration according to various embodiments of the present disclosure.

FIG. 3 is a flowchart illustrating a first embodiment of the present disclosure.

FIG. 4 is a flowchart illustrating a second embodiment of the present disclosure.

FIG. 5 is a flowchart illustrating a third embodiment of the present disclosure.

FIG. 6 is a flowchart illustrating a fourth embodiment of the present disclosure.

FIG. 7 is a flowchart illustrating a fifth embodiment of the present disclosure.

FIG. 8 is a flowchart illustrating a sixth embodiment of the present disclosure.

FIG. 9 is a flowchart illustrating a seventh embodiment of the present disclosure.

FIG. 10 is a schematic diagram illustrating a basic structure of a D2D device according to various embodiments of the present disclosure.

The present invention will be described in further detail hereinafter with reference to accompanying drawings and embodiments to make the objective, technical solution and merits therein clearer.

In D2D communications environment, the D2D devices in a D2D group may have no common synchronization source. Therefore, in the D2D communications environment, D2D devices having potential communication requirement may fail to be synchronized to the same synchronization source (e.g. eNB in cellular communications) under some circumstances. As described in the background, synchronization is a premise for implementing any communications between the D2D devices. In order to solve the above problem, various embodiments of the present disclosure provide a method for implementing synchronization between D2D devices in a D2D group. As shown in FIG. 1, the method includes the following.

At block 110, a D2D device detects a synchronization source R of a cellular network, and determines a transmitting/detecting configuration of D2D synchronization signal.

The D2D device may detect signals transmitted by a cellular network cell (such as synchronization signal, cell downlink reference signal (CRS), etc.), and determines whether the synchronization source R of the cellular network can be successfully detected according to strength of the signal detected or other criterion. If a particular D2D device is able to successfully detect the synchronization source R of the cellular network, the D2D device is referred to as an IC device. Otherwise, if a particular D2D device cannot successfully detect the synchronization source R of the cellular network, the D2D device is referred to as an OOC device.

It should be noted that, the IC device and the OOC device are with respect to a particular cellular network synchronization source R. For example, suppose D2D device A is within the coverage of the cellular network synchronization source R, D2D device B is within the coverage of a cellular network synchronization source different from R. Thus, for R, D2D device B is referred to as OOC device.

If the IC device is referred to as a first level synchronization device, an OOC device which realizes synchronization directly based on D2D synchronization signal forwarded by the IC device is referred to as a second level synchronization device, and an OOC device which realizes synchronization directed based on the D2D synchronization signal forwarded by the second level synchronization device is referred to as a third level synchronization device, and so on, until the lowest level synchronization device.

The above transmitting/detecting configuration may be defined by a standard directly or be configured by the cellular network or a D2D central control node, including transmitting/detecting period, a transmitting window and a detecting window corresponding to each level synchronization device.

In particular, the transmitting/detecting period may include a basic period transmitting/detecting configuration and a long period transmitting/detecting configuration. The basic period transmitting/detecting configuration includes any one or any combination of the following: basic period P_u, time offset Δ of the transmitting/detecting window within P_u, corresponding relationship between the transmitting window and the detecting window within P_u, and a transmitting/detecting carrier CF. If the transmitting/detecting configuration includes the corresponding relationship between the transmitting window and the detecting window within P_u, each transmitting/detecting time offset corresponds to one D2D synchronization signal transmitting/detecting window within P_u. Each P_u may include one or more transmitting/detecting windows.

The long period transmitting/detecting configuration includes a transmitting/detecting window period P_l. The transmitting/detecting window period P_l includes M basic transmitting/detecting periods P_u, wherein M may be 1 or any random value, or a value defined by a particular standard or a cellular network cell or a D2D central control node. If M=1, the long period is the same as the basic period, i.e., there is just one transmitting/detecting period at this time.

One possible long period transmitting/detecting configuration (example 1) is as shown in FIG. 2. In FIG. 2, period P_l includes two basic periods, each basic period includes four transmitting/detecting windows respectively corresponding to each level synchronization device. The window corresponding to Δ_wi (0≤wi≤2) is a transmitting window of the wi+1 level synchronization device. A next window adjacent to this window is a detecting window corresponding to it. The window corresponding to Δ₃ is a transmitting window of a lowest level device. In FIG. 2, the transmitting window of a next level device is the detecting window of a current level synchronization device. In a practical application, such a relationship may be followed. However, the transmitting window of a particular level device is not always followed by a detecting window of the same level.

Another possible long period transmitting/detecting configuration (example 2) is as shown in FIG. 2. In FIG. 2, the period includes two basic periods, each basic period includes four transmitting/detecting windows respectively corresponding to each level of synchronization devices. The window corresponding to Δ_wi (0≤wi≤2) is a transmitting window of the wi+1 level synchronization device. The window corresponding to Δ₃ is a transmitting window of a lowest level device. The transmitting/detecting configuration does not include definitions for the corresponding relationship between the transmitting window and the detecting window.

At block 120, the IC device and the OOC device transmits/detects synchronization signal in a corresponding format according to their corresponding transmitting/detecting configurations.

The D2D synchronization signal transmitted by each level D2D device carries level information of the D2D device. A lowest level synchronization device may forward synchronization signal, but the synchronization signal will not be used by other D2D devices for synchronizing with the synchronization source R. Whether a window is a transmitting window or a detecting window is determined with respect to the level of the synchronization device. The transmitting window of a particular level synchronization device or also be a detecting window for another level synchronization device, and vice versa.

For facilitating the understanding of the present disclosure, the above technical solution is described in further detail hereinafter with reference to some detailed application scenarios and interaction modes of the devices.

Embodiment 1

In this embodiment, a target device is able to successfully detect a synchronization source of a cellular network cell, i.e., the device is an IC device. The device determines, according to strength of detected cell reference signal of the cellular network, whether it is at edge of the cellular cell. If it is at edge of the cellular cell, the device further detects power of D2D synchronization signal of a same level synchronization device. If the power of the detected synchronization signal is lower than a particular threshold, the device begins to transmit D2D reference signal with long period in the transmitting/detecting configuration. Alternatively, the IC device may also receive an indication from the base station, starts to detect the D2D synchronization signal of a same level synchronization device, reports the detected result to the base station, and determines whether to transmit D2D synchronization signal according to an instruction of the base station.

The IC device which transmits the D2D synchronization signal with the long period detects D2D synchronization signal from next level synchronization device in the transmitting window of the next level synchronization device, and detects D2D reference signal from other same level synchronization device in the transmitting window of the other same level synchronization device. If the D2D synchronization signal from the next level synchronization device is detected, the IC device increases transmission density of the D2D synchronization signal, i.e., transmits the D2D synchronization signal in all idle transmitting windows of the same level synchronization devices within the long period. The detailed implementation is as shown in FIG. 3. The process includes the following.

At block 310, the IC device obtains transmitting/detecting configurations C_l and C_uof the D2D synchronization signal.

C_l and C_uare respectively the transmitting/detecting configurations of the long period and the basic period. Some parameters in the two configurations may be the same. In one embodiment, the two configurations may be completely the same. C_l and C_u may be broadcasted by the cellular network or a D2D central control node, or is defined by standard.

At block 320, the IC device detects signals of the cellular network, determines whether the IC device is at the edge of the cellular cell. If yes, block 330 is executed; otherwise, this block is repeated; or the IC device determines whether a D2D synchronization signal detecting instruction is received from the base station, if yes, block 330 is executed; otherwise, this block is repeated.

The IC device may determine whether it is at the edge of the cellular cell via various conventional methods. For example, the determination may be made based on whether the receiving power of the reference signal of the cellular network is lower than a threshold TH_cc, if the receiving power is lower than TH_cc, it is determined that the IC device is at the edge of the cellular cell; wherein the reference signal detected by the IC device may include any one or any combination of: primary synchronization channel signal of the cellular cell, secondary synchronization channel signal of the cellular cell, cell reference signal of the cellular cell. The receiving power of the reference signal may be one detected result or an average of detection results during a period of time. The value of TH_cc may be configured by the cellular network or the D2D central control node, or defined by standard.

At block 330, if it is determined in block 320 that the IC device is at the edge of the cellular cell, the IC device selects a windoww _l,i from the transmitting windows of first level synchronization devices in each long period, detects synchronization signal from synchronization device of the same level in the windoww _l,i. Or, the IC device receives an indication for detecting the D2D synchronization signal from the eNB, and selects the window w _l,i to detect the synchronization signals from the same level synchronization device.

Wherein w _l,i is a transmitting window corresponding to Δ_l in basic period P_u, _i of P_l. Δ_l is the time offset of the transmitting window of the first level synchronization device in the basic transmitting/detecting period, wherein i is a value between 0 and M-1, denoting an index of the basic period in the long period, and M denotes the number of basic periods in the long period. The value of i (i.e., the selection of the window w _l,i) may be selected randomly or following another manner, which is not intended to be restricted in the present disclosure. P_l denotes the transmitting/detecting window period determined by the configuration C_l, i.e., long period.

At block 340, if the IC device fails to detect the synchronization signal from the same level synchronization device in the windoww _l,i, the IC device transmits synchronization signal in the window w _l,i of each period P_l. Otherwise, the IC device continues to detect the synchronization signal from the same level synchronization device in the window w _l,i. Or, the IC device reports the detected result to the base station, and determines whether to transmit D2D synchronization signal according to an instruction of the base station. If transmit, the IC device transmits the D2D synchronization signal in the window w _l,i of each period P_l. Otherwise, the IC device continues to detect the synchronization signal from the same level synchronization device in the window w _l,i.

Herein, if the IC device does not detect the synchronization signal from the same level synchronization device in the windoww _l,i, it indicates that there is no other IC device transmitting D2D synchronization signal in the window w _l,i within the coverage of the synchronization signal of the IC device. Thus, the IC device may transmit D2D synchronization signal in the windoww _l,i, such that a second level synchronization device within the coverage of the IC device synchronization signal may realize synchronization using the D2D synchronization signal.

Preferably, the IC device may determine whether synchronization signal from same level synchronization device is successfully detected through determining whether the receiving power of the synchronization signal is lower than TH_cd. The above receiving power may be one detected result of the synchronization signal power from the same level synchronization device in the transmitting window corresponding to Δ_l, or an average value of the detected results of the synchronization signal power of the same level synchronization device in the transmitting window corresponding to Δ_lwithin a period of time T_cd. T_cd may be one or more long periods, or a value configured by the cellular network or the D2D central control node, or defined by standard. The value of TH_cd may be configured by the cellular network or the D2D central control node (e.g., issued via a cell broadcast message), or defined by standard.

In one embodiment, the IC device may not determine the receiving power of the synchronization signal. The detected result of the synchronization signal is directly reported to the base station in block 330 and it is determined whether to transmit the D2D synchronization signal according to an instruction of the base station.

The IC device may start to transmit the synchronization signal in the transmitting window w _l,i of the m ^th long period after determining to transmit the D2D synchronization signal, and re-transmits the D2D synchronization signal in the transmitting windoww _l,i of each long period. Thus, in each long period, the IC device transmits the D2D synchronization signal in merely one window, this manner is referred to as a scattered manner.

At block 350, if the IC device transmits the D2D synchronization signal in the scattered manner, the IC device detects, in the transmitting window of a second level synchronization device in the basic period where the window w _l,i belongs, D2D synchronization signal from a next level synchronization device, and detects synchronization signal from same level synchronization device in the transmitting window w _l,j corresponding to Δ_l in the basic period P_u, _j.

The IC device transmits the D2D synchronization signal in the scattered manner for synchronization of next level synchronization device. If detecting the D2D synchronization signal transmitted by the IC device, the second level synchronization device may use it for synchronization of itself. Meanwhile, the OOC device which detects the D2D synchronization signal of the IC device may transmit D2D synchronization signal in the transmitting window corresponding to the OOC device, to respond the D2D synchronization signal transmitted by the IC device. Therefore, the IC device may determine whether there is a next level synchronization device receives the D2D synchronization signal by the IC device through detecting D2D synchronization signal in the transmitting window of the next level synchronization device.

In this embodiment, the detecting window of a current level synchronization device is the transmitting window of the next level synchronization device. Therefore, in this block, the IC device detects the D2D synchronization signal of the next level synchronization device in the detecting windowcorresponding to w _l,i, i.e., the transmitting window of the second level synchronization device in the basic period where w _l,i belongs, so as to determine whether there is a next level synchronization device receives the synchronization signal transmitted by the IC device, wherein 0≤j≤M-1 and j≠i.

Besides detecting the D2D synchronization signal of next level synchronization device in the transmitting window of the next level synchronization device, the IC device further detects D2D synchronization signal from a same level synchronization device in the transmitting windoww _l,j of the same level synchronization device except for w _l,i.

At block 360, the IC device adjusts transmission manner of the D2D synchronization signal according to the detected result of the D2D synchronization signal of next level synchronization device and the detected result of D2D synchronization signal of the same level synchronization device in w _l,j.

Preferably, the IC device may determine whether the receiving power of the synchronization signal is higher than TH_dd, to determine whether the D2D synchronization signal of the next level or same level synchronization device is successfully detected. For the detection of the D2D synchronization signal of the next level synchronization device, the receiving power may be one detected result of the synchronization signal power of the next level synchronization device in the detecting window corresponding to window w _l,i, or an average of detected results of the synchronization signal power of the next synchronization device in the detecting window corresponding to window w _l,i within a period of time T_dd. For the detection of the D2D synchronization signal of the same level synchronization device, the receiving power may be one detected result of the synchronization signal power of the same level synchronization device in the transmitting window corresponding to window w _l,j, or an average of detected results of the synchronization signal power of the same synchronization device in the transmitting window corresponding to window w _l,j within a period of time T_dd.

If the IC device detects the D2D synchronization signal of the next synchronization device, it indicates that there is a second level synchronization device is implementing synchronization utilizing the D2D synchronization signal of the IC device. Thus, the IC device adds the transmission density of the D2D synchronization signal, transmits the D2D synchronization signal in the idle transmitting windows of first level synchronization devices in the long period, i.e., transmits the D2D synchronization signal in window {w _l} of each long period P_l, wherein {w _l} includes the transmitting windows in w _l,i and w _l,jin which no D2D synchronization signal from the same level synchronization device is detected. Thus, in each long period, the IC device may transmit D2D synchronization signal in multiple windows, this manner is referred to as a dense manner.

At block 370, if the IC device transmits the D2D synchronization signal in the dense manner, the IC device detects D2D synchronization signals from next level synchronization device in transmitting windows of second level synchronization devices corresponding to the {w _l}.

Similarly as the scattered manner, the IC device determines D2D synchronization signal from next level synchronization device in transmitting window of second level synchronization device corresponding to the {w _l}, so as to determine whether there is a second level synchronization device receives and utilizes the D2D synchronization signal transmitted by the IC device.

At block 380, if the IC device does not detect D2D synchronization signal from next level synchronization device in transmitting window of second level synchronization device corresponding to the {w _l}, the IC device transmits the D2D synchronization signal in the scattered manner, and blocks 350 ~ 380 are repeated; otherwise, the IC device continues to detect D2D synchronization signal from next level synchronization device in transmitting window of second level synchronization devices corresponding to the {w _l}.

Preferably, the IC device may determine whether the receiving power of the synchronization signal is higher than TH_dd, to determine whether the D2D synchronization signal of the next level synchronization device is successfully detected. The receiving power may be one detected result of the synchronization signal power of the next level synchronization device in the detecting window corresponding to {w _l}, or an average of detected results of the synchronization signal power of the next synchronization device in the detecting window corresponding to {w _l} within a period of time T_dd. Preferably, the position of the transmitting window that the IC device transmits the D2D synchronization signal in the scattered manner is the same as block 340.

Now this embodiment is finished. In this embodiment, if the IC device is at the edge of the cellular cell, and there is no other IC device around this IC device transmitting D2D synchronization signal in the same basic period, the IC device continuously transmits D2D synchronization signal with period P_l, and increases the transmission density of the D2D synchronization signal after detecting feedback of a next level synchronization device. Although this manner may increase power consumption of the IC device transmitting the D2D synchronization signal, it can reduce complexity for the OOC device to detect the synchronization signal.

Embodiment 2

In this embodiment, the target device is able to successfully detect the synchronization source of the cellular cell, i.e., it is an IC device. The device detects a trigger synchronization signal from an OOC device in a particular period, and starts to transmit D2D synchronization signal in response to detecting the above trigger synchronization signal. The IC device transmitting the D2D synchronization signal detects D2D synchronization signal from a next level synchronization device. If the IC device fails to detects the D2D synchronization signal from next level synchronization device, the IC device stops transmitting the D2D synchronization signal. The detailed implementation is as shown in FIG. 4. The process includes the following.

At block 410, the IC device obtains a transmitting/detecting configuration C_IC of the D2D synchronization signal.

C_IC is the transmitting/detecting configuration, the structure of which is similar to that described in the above embodiment. Especially, the transmitting/detecting configuration may define just one period P_IC. C_IC may be broadcasted by the cellular network or defined by standard.

At block 420, the IC device detects a trigger synchronization signal.

The trigger synchronization signal is in form of a sequence transmitted by a second level synchronization device. Carrier frequency of the trigger synchronization signal is the same as the detecting frequency of the IC device, i.e., is designated by the transmitting/detecting configuration. Detailed design of the trigger synchronization signal is not intended to be restricted in the present disclosure. The detailed format and transmission manner of the trigger synchronization signal may be defined by a system and is known by all D2D devices. The IC device detects the trigger synchronization signal according to the defined format and transmission manner.

For example, since the D2D synchronization signal transmitting/detecting configuration has indicated the detecting window of the first level synchronization device (i.e., the IC device), it is possible to that the IC device is triggered if there is a trigger synchronization signal in the detecting window. Accordingly, the IC device may detect the trigger synchronization signal in the detecting window w _ccorresponding to Δ_c. Δ_cis a time offset corresponding to the detecting window of the first level synchronization device determined by the configuration C_IC, w _c∈{w _1c}, wherein {w _1c} is a set of detecting windows of the first level synchronization device determined by the configuration C_IC.

At block 430, if the IC device detects the trigger synchronization signal, the IC device transmits the D2D synchronization signal with period P_IC, and executes block 440; otherwise, the method returns to block 420.

After the IC device detects the trigger synchronization signal, it indicates that there is a second synchronization device within the coverage of the synchronization signal of the IC device desiring to implement synchronization based on the D2D synchronization signal of the IC device. Therefore, in this block, after detecting the trigger synchronization signal, the IC device transmits the D2D synchronization signal periodically. The period P_IC is a transmitting/detecting window period determined by the configuration C_IC. At this time, the transmitting/detecting configuration defined just one transmitting/detecting window period, it is the same in the following.

Preferably, the IC device may determine whether the trigger synchronization signal is successfully detected through determining whether the receiving power of the trigger synchronization signal is higher than TH_ct. The above receiving power may be one detected result of the trigger synchronization signal power, or an average value of the detected results of the trigger synchronization signal power within a period of time T_bd. T_bd may be one or more periods (the periods may be discontinuous), or a value configured by the cellular network or the D2D central control node, or defined by standard. The value of TH_ct may be configured by the cellular network or the D2D central control node (e.g., issued via a cell broadcast message), or defined by standard.

When a certain period of time elapsed after the above condition is met, the IC device transmits the D2D synchronization signal in the transmitting window w _t (e.g., the m ^th transmitting window corresponding to w _c after the above condition is met) of the first level synchronization device, and re-transmits the D2D synchronization signal in the transmitting window w _tof each period. The value of m may be 1 or any random value, or is defined by the standard, or broadcasted by the cellular cell or configured by the D2D central control node. The relationship between the detecting window w _c and the transmitting window w _t is determined by C_IC.

At block 440, if the IC device transmits the D2D synchronization signal with period P_IC, from the r ^th period after the first time transmission, the IC device detects D2D synchronization signal from a next level synchronization device in the transmitting window of the next level synchronization device corresponding to Δ_c.

Similarly to the first embodiment, after transmitting the D2D synchronization signal, the IC device detects the D2D synchronization signal of the next level synchronization device in the transmitting window of the next synchronization device, so as to determine whether there is a next level synchronization device receiving and utilizing the D2D synchronization signal transmitted by the IC device. The value of r may be 0 (indicating the period that the D2D synchronization signal is firstly transmitted), or any random number, or defined by standard, or broadcasted by the cellular cell or configured by the D2D central control node.

At block 450, if the IC device does not detect D2D synchronization signal from the next level synchronization device in block 440, the IC device stops transmitting the D2D synchronization signal, and repeats blocks 420 ~ 450; otherwise, the method returns to block 440 to keep on transmitting the D2D synchronization signal.

If the IC device does not detect the D2D synchronization signal from the next level synchronization device, it indicates that there is no second level synchronization device within the coverage of the synchronization signal of the IC device which receives and utilizes the D2D synchronization signal of the IC device. In this case, it is not required to transmit the D2D synchronization signal any more.

Preferably, the IC device may determine whether the synchronization signal of the next level synchronization device is successfully detected through determining whether the receiving power of the synchronization signal of the next level synchronization device is lower than TH_dd. The above receiving power may be one detected result of the synchronization signal power from the next level synchronization device in the detecting window corresponding to Δ_l, or an average value of the detected results of the synchronization signal power of the next level synchronization device in the detecting window corresponding to Δ_lwithin a period of time T_dd.

Now this embodiment is finished. In this embodiment, the IC device starts to transmit the D2D synchronization signal merely after detecting the trigger synchronization signal. This manner is able to reduce power consumption of the IC device, but increases complexity of the OOC device for detecting the synchronization signal.

Embodiment 3

In this embodiment, the target device cannot detect the synchronization source of the cellular cell, i.e., the device is an OOC device. The OOC device detects D2D synchronization signal transmitted by a D2D device by a manner similar as cell search in the cellular network system. For a D2D device which has detected the D2D synchronization signal, if the device is not a lowest level device and is far away from the edge of the coverage of the D2D synchronization signal, or the device is a lowest level device, the device transmits D2D synchronization signal in an idle window with a long period. If the device is not a lowest level device and is at the edge of the coverage of the D2D synchronization signal, the device transmits D2D synchronization signal in an idle window with the long period, and starts to detect synchronization signal of a next level synchronization device in a transmitting window of the next level synchronization device corresponding to the above idle window. After detecting the synchronization signal of the next level synchronization device, the device increases transmission density of the D2D synchronization signal, and transmits the D2D synchronization signal in all idle windows of the same level synchronization devices in the long period. The detailed implementation is as shown in FIG. 5, including the following.

At block 510, the OOC device obtains transmitting/detecting configurations C_l and C_uof the D2D synchronization signal.

At block 520, the OOC device detects D2D synchronization signal on each supported carrier cf according to the configuration C_l.

Wherein cf∈CF, CF denotes a set consists of carriers supported by UE. The OOC device may save carrier information of adjacent cellular cells and sort non-used cellular cells according priorities based on information such as access time or measured time, cell signal quality, etc. According to the sorted result, the OOC device detects the D2D synchronization signal on the corresponding carriers. For each carrier, the detection of het D2D synchronization signal of the OOC device is the same. Hereinafter, a carrier cf is taken as an example.

At block 530, if the OOC device detects D2D synchronization signal on carrier cf within time T_OOC, the OOC device selects a window w _k,i in which the highest priority synchronization signal is detected among all windows in which synchronization signals are detected, detects synchronization signal of same level synchronization device in the transmitting window w _t,i of the next level synchronization device corresponding to the window w _k,i according to the configuration C_l, and executes block 540; if the OOC device does not detect any D2D synchronization signal within time T_OOC, block 531 is executed.

If the OOC device detects the D2D synchronization signal within the time T_OOC, the D2D synchronization signal may be detected in one or more windows, thus, the OOC device needs to select, among all windows in which the D2D synchronization signal is detected, a window w _k,i in which the highest priority synchronization signal is detected.

The window w _k,i denotes the selected window in which the highest priority synchronization signal is detected, wherein k denotes a synchronization level when the window acts as a transmitting window, i denotes an index of a basic period where the window w _k,i belongs, w _t,i denotes a transmitting window corresponding to the k+1 level synchronization device in the basic period P_u, _i where the window w _k,i belongs in the long period P_l.

After the OOC device selects the window w _k,i, the D2D synchronization signal detected in this window is taken as the D2D synchronization signal transmitted by an upper level synchronization device, and synchronization processing is performed according to this synchronization signal. The upper level synchronization device may be an IC device or an upper level OOC device.

In addition, similarly as the first embodiment, after transmitting the D2D synchronization signal, the upper level synchronization device A detects the D2D synchronization signal transmitted by a next level synchronization device in the transmitting window of the next level synchronization device, so as to determine whether there is a next level synchronization device which has received and utilized the D2D synchronization signal transmitted by the device A. For this situation, it is only required that there is one D2D synchronization signal fed back by the next level synchronization device. Not all next level synchronization devices receiving the D2D synchronization signal transmitted by the upper level synchronization device have to transmit. Therefore, in this block, after detecting the D2D synchronization signal of the upper level synchronization device, the OOC device further detects the D2D synchronization signal of the same level synchronization device, so as to determine whether to transmit D2D synchronization signal to respond to the D2D synchronization signal transmitted by the upper level synchronization device.

Preferably, the OOC device may determine whether the power of the D2D synchronization signal detected in the window w _k,i is higher than TH_dd, so as to determine whether the D2D synchronization signal is successfully detected. In addition, an OOC device located at the edge of the coverage of the synchronization signal of the upper level synchronization device is referred to as a NDB device. On the contrary, an OOC device which is far away from the edge of the coverage of the synchronization signal of the upper level synchronization device is referred to as a FDB device. For example, if the power of the D2D synchronization signal detected by the OOC device in the window w _k,i is lower than a threshold TH_b, wherein TH_dd≤TH_b, it is determined that the OOC device is located at the edge of the coverage of the synchronization signal of the upper level synchronization device and the OOC device is called a NDB device. Otherwise, the OOC device is called a FDB device. The above receiving power may be one detected result of the D2D synchronization signal power in the window w _k,i, or an average of detected result of the D2D synchronization signal power in the window w _k,i during a period of time TH_dd. TH_dd≤TH_b. the values of them may be configured by the cellular network or a D2D central control node (e.g., issued by a cell broadcast message) or defined by standard.

At block 531, the OOC device transmits independent D2D synchronization signal in a scattered manner in the basic period P_u, _ii of each long period according to the configuration C_l.

If the OOC device does not detect any D2D synchronization signal within the time T_OOC, the OOC device acts as a synchronization source and transmits independent D2D synchronization signal for synchronization of other OOC devices within the coverage of the synchronization signal of the OOC device.

Wherein P_u, _ii is defined by the configuration C_u, and is one of M basic periods of the long period P_l, wherein i is any value between 0 and M-1. The manner that the OOC device determines the value of ii is not intended to be restricted in the present disclosure. Preferably, the OOC device transmits the synchronization signal in the transmitting window of the first level or second level synchronization device in the basic period P_u, _ii. P_l denotes a transmitting/detecting window period determined by the configuration C_l. the value of T_OOC may be defined by standard or configured by the cellular network or the D2D central control node (e.g., issued by a cell broadcast message).

At block 540, the OOC device determines a synchronization level of itself, transmits or detects corresponding D2D synchronization signal according to a corresponding configuration based on the detected result of the synchronization signal of same level D2D device in the window w _t,i.

The OOC device retrieves the level of the upper level synchronization device according to the D2D synchronization signal detected in the window w _k,i in block 530, so as to determine the synchronization level of itself. Then, according to the synchronization level of itself and the detected result of the D2D synchronization signal of the same level D2D device in the window w _t,i, the OOC device transmits or detects D2D synchronization signal.

In particular, the OOC device transmits D2D synchronization signal in the transmitting window corresponding to itself, to realize one of the following objectives: 1, transmit the D2D synchronization signal to respond the synchronization signal transmitted by the upper level synchronization device; 2, transmit the D2D synchronization signal, such that a lower level synchronization device realizes synchronization according to this D2D synchronization signal.

Based on the above two objectives, the D2D synchronization signal may be transmitted under the following conditions.

1. If the OOC device is a lowest level device and the device does not successfully detect the D2D synchronization signal of the same level synchronization device in the window w _t,i, it indicates that there is no other same level synchronization device responds the synchronization signal of the upper level synchronization device. Therefore, the OOC device transmits the D2D synchronization signal in a scattered manner, i.e., the OOC device transmits the D2D synchronization signal in the window w _t,i of each long period in the scattered manner. If the power of the detected synchronization signal from the same level D2D device is lower than TH_dd, it may be regarded that the D2D synchronization signal of the same level synchronization device is not successfully detected.

2. If the OOC device is a NDB device, it indicates that the OOC device is located at the edge of the coverage of the synchronization signal of the upper synchronization device, it may be required to provide D2D synchronization signal to the next level synchronization device. If the OOC device is both a NDB device and is not the lowest level device, and the power of the synchronization signal from the same level D2D device detected by the device in the window w _t,i is lower than the threshold TH_b, it indicates that although there is a same level D2D device transmitting synchronization signal, the OOC device is at the edge of the coverage of the synchronization signal of the same level synchronization device, it is required to provide D2D synchronization signal for the next level device. Therefore, the OOC device transmits D2D synchronization signal in the window w _t,i of each long period in the scattered manner.

3. If the OOC device is a FDB device, it indicates that the OOC terminal is far away from the edge of the coverage of the synchronization signal of the upper level synchronization device. Therefore, it is not required to provide D2D synchronization signal for other devices within the coverage of its synchronization signal. If the OOC device is both a FDB device and is not a lowest level device, and the device does not detect synchronization signal of the same level synchronization device in the window w _t, it indicates that there is no other same level synchronization device responds the D2D synchronization signal of the upper level synchronization device. Therefore, the OOC device transmits the D2D synchronization signal in the scattered manner to respond the D2D synchronization signal transmitted by the upper level synchronization device, i.e., the OOC device transmits the D2D synchronization signal in the window w _t,i of each long period in the scattered manner. If the power of the detected synchronization signal from the same level D2D device is lower than TH_dd, it may be regarded that the D2D synchronization signal of the same level synchronization device is not successfully detected.

The above receiving power may be one detected result of the D2D synchronization signal power within the window w _t,i, or an average of detected results of the D2D synchronization signal power in the window w _t,i during a period of time T_dd.

If the OOC device cannot meet any of the above three conditions, repeat the detection of the synchronization signal of the same level synchronization device in block 530.

When the D2D synchronization signal is transmitted due to one of the three conditions is met, the D2D synchronization signal transmitted when the

conditions

1 and 3 are met are in response to the upper level synchronization device, whereas the D2D synchronization signal transmitted when the condition 2 is met is transmitted to provide a synchronization signal for other synchronization devices. Therefore, for the D2D synchronization signal transmitted under the condition 2, similar to the blocks 350 ~ 380 in the first embodiment, it is also required to determine whether the next level synchronization device has received the synchronization signal, and increases the transmission density if the next level synchronization device receives the synchronization signal. The detailed implementation is described with reference to blocks 550 ~ 580.

At block 550, if the OOC device is a NDB device and is not a lowest level device, and the OOC device transmits the D2D synchronization signal in the scattered manner, the OOC device detects D2D synchronization signal from a next level synchronization device in the detecting window corresponding to the window w _t,i, and detects synchronization signal of the same level synchronization device in the transmitting window w _t,j corresponding to Δ_t in the basic period P_u, _j.

The corresponding relationship between the above window and the detecting window is determined by the configuration C_l, 0≤j≤M-1 and j≠i.

At block 560, if the OOC device is a NDB device and transmits D2D synchronization signal in the scattered manner, the device adjusts transmission manner of the D2D synchronization signal according to the detected result of the D2D synchronization signal of next level synchronization device and the detected result of D2D synchronization signal of the same level synchronization device in w _t,j.

Preferably, the device may determine whether the receiving power of the synchronization signal is higher than TH_dd, to determine whether the D2D synchronization signal of the next level or same level synchronization device is successfully detected. For the detection of the D2D synchronization signal of the next level synchronization device, the receiving power may be one detected result of the synchronization signal power of the next level synchronization device in the detecting window corresponding to window w _t,i, or an average of detected results of the synchronization signal power of the next synchronization device in the detecting window corresponding to window w _t,i within a period of time T_dd. For the detection of the D2D synchronization signal of the same level synchronization device, the receiving power may be one detected result of the synchronization signal power of the same level synchronization device in the transmitting window corresponding to window w _t,j, or an average of detected results of the synchronization signal power of the same synchronization device in the transmitting window corresponding to window w _t,j within a period of time T_dd.

If the device detects the D2D synchronization signal of the next synchronization device, the device transmits the D2D synchronization signal in the dense manner in window {w _t} of each long period P_l, wherein {w _t} includes the transmitting windows in w _t,i and w _t,jin which no D2D synchronization signal from the same level synchronization device is detected.

At block 570, if the OOC device transmits the D2D synchronization signal in the dense manner, the OOC device detects D2D synchronization signals from next level synchronization device in transmitting window corresponding to the {w _t}.

At block 580, if the OOC device transmits the D2D synchronization signal in the dense manner, and does not detect D2D synchronization signal from next level synchronization device, the OOC device transmits the D2D synchronization signal in the scattered manner, and blocks 350 ~ 380 are repeated.

Preferably, the OOC device may determine whether the receiving power of the synchronization signal is higher than TH_dd, to determine whether the D2D synchronization signal of the next level is successfully detected. The receiving power may be one detected result of the synchronization signal power of the next level synchronization device in the detecting window corresponding to {w _t}, or an average of detected results of the synchronization signal power of the next synchronization device in the detecting window corresponding to{w _t} within a period of time T_dd. At this time, the position of the transmitting window that the OOC device transmits the D2D synchronization signal is the same as block 540.

Now this embodiment is finished. In this embodiment, actions of the OOC device correspond to those of the IC device in the first embodiment. The biggest advantage of this manner is: the OOC device may re-use the searching function in current cellular network to realize the searching of the D2D synchronization signal. As such, the implementation of the D2D device is simplified.

Embodiment 4

In this embodiment, the target device cannot detect the synchronization source of the cellular cell, i.e., it is an OOC device. The OOC device detects the D2D synchronization signal transmitted by D2D device in a manner similar as cell searching in the cellular network system. If no D2D synchronization signal is detected, a trigger synchronization signal is transmitted, so as to trigger a potential IC device to transmit D2D synchronization signal. The detailed implementation is as shown in FIG. 6. The process includes the following.

At block 600, the OOC device obtains a transmitting/detecting configuration C_OC of the D2D synchronization signal.

C_OC is the transmitting/detecting configuration, the structure of which is similar to that described in the above embodiment. It includes a long period transmitting/detecting configuration and a basic period transmitting/detecting configuration. C_OC may be defined by standard or configured by a D2D central control node.

At block 610, the OOC device detects D2D synchronization signal on each supported carrier cf according to the configuration C_OC.

At block 611, if the OOC device detects D2D synchronization signal on carrier cf within time T_OOC, the OOC device transmits/detects D2D synchronization signal according to blocks 520 ~ 580 in embodiment 3.

At block 620, if the OOC device does not detect any D2D synchronization signal on carrier cf within time T_OOC, the OOC device transmits a trigger synchronization signal on the carrier cf and detects the D2D synchronization signal on the carrier cf in a time-division manner.

The trigger synchronization signal is in form of a sequence transmitted by a second level synchronization device. Carrier frequency of the trigger synchronization signal is the same as the detecting frequency of the IC device, i.e., is designated by the transmitting/detecting configuration. Detailed design of the trigger synchronization signal is not intended to be restricted in the present disclosure.

After the transmission of the trigger synchronization signal and the detection of the D2D synchronization signal in the time-division manner, the following operations are performed according to the detected result of the D2D synchronization signal.

At block 621, if the OOC device does not detect any D2D synchronization signal within time T_tr, the OOC device transmits independent D2D synchronization signal in the transmitting window of the first or second level synchronization device in the basic period P_u, _i of each long period in the scattered manner according to the configuration C_OC, and transmits/detects D2D synchronization signal following blocks 350 to 380 in the first embodiment.

The value of T_tr may be defined by standard or configured by the cellular network or a D2D central control node (e.g., issued by a cell broadcast message). During the processing according to blocks 350 ~ 380, the execution body is replaced by the OOC device.

At block 630, if the OOC device detects D2D synchronization signal within time T_tr, the OOC device stops transmitting the trigger synchronization signal and detecting the D2D synchronization signal in the time-division manner, and transmits/detects D2D synchronization signal according to blocks 520 ~ 580 in embodiment 3.

Now this embodiment is finished. In this embodiment, the actions of the OOC device are corresponding to those of the IC device in the embodiment 2. It helps to reduce the power consumption of the IC device. However, the OOC device has to transmit the trigger synchronization signal on different carriers to trigger the IC device, which increases complexity of the OOC device.

Embodiment 5

In this embodiment, a target device is able to successfully detect a synchronization source of a cellular network cell, i.e., the device is an IC device. The device determines, according to strength of detected cell reference signal of the cellular network, whether it is at edge of the cellular cell. If it is at edge of the cellular cell, the device further detects power of D2D synchronization signal of a synchronization device of the same level with it. If the power of the detected synchronization signal is lower than a particular threshold, the device begins to transmit D2D reference signal with long period in the transmitting/detecting configuration. Alternatively, the IC device may also receive an indication from the base station, starts to detect the D2D synchronization signal of a synchronization device of the same level, reports the detected result to the base station, and determines whether to transmit D2D synchronization signal according to an instruction of the base station. The detailed implementation is as shown in FIG. 7. The process includes the following.

At block 710, the IC device obtains transmitting/detecting configurations C_l and C_uof the D2D synchronization signal.

At block 720, the IC device detects signals of the cellular network, determines whether the IC device is at the edge of the cellular cell. If yes, block 730 is executed; otherwise, this block is repeated; or, the IC device determines whether a D2D synchronization signal detecting instruction is received from the base station, if yes, block 730 is executed; otherwise, this block is repeated.

The IC device may determine whether it is at the edge of the cellular cell via various conventional methods. For example, the determination may be made based on whether the receiving power of the reference signal of the cellular network is lower than a threshold TH_cc, if the receiving power is lower than TH_cc, it is determined that the IC device is at the edge of the cellular cell; wherein the reference signal detected by the IC device may include any one or any combination of: primary synchronization channel signal of the cellular cell, secondary synchronization channel signal of the cellular cell, cell reference signal of the cellular cell. The receiving power of the reference signal may be one detected result or an average result of detected results during a period of time. The value of TH_cc may be configured by the cellular network or the D2D central control node, or defined by standard.

At block 730, if it is determined in block 720 that the IC device is at the edge of the cellular cell, the IC device receives an indication for detecting the D2D synchronization signal from the eNB, the IC device selects a windoww _l,i from the transmitting windows of first level synchronization devices in each long period, detects synchronization signal from the same level synchronization device in the windoww _l,i.

At block 740, if the IC device does not detect the synchronization signal from the same level synchronization device in the windoww _l,i, the IC device transmits D2D synchronization signal in the window w _l,i of each period P_l. Otherwise, block 730 is repeated. Or, the IC device reports the detected result to the base station, and determines whether to transmit D2D synchronization signal according to an instruction of the base station. If transmit, the IC device transmits the D2D synchronization signal in the window w _l,i of each period P_l. Otherwise, block 730 is repeated.

Herein, if the IC device fails to detect the synchronization signal from the same level synchronization device in the windoww _l,i, it indicates that there is no other IC device transmitting D2D synchronization signal in the window w _l,i within the coverage of the synchronization signal of the IC device. Thus, the IC device may transmit D2D synchronization signal in the windoww _l,i, such that a second level synchronization device within the coverage of the IC device synchronization signal may realize synchronization using the D2D synchronization signal.

Preferably, the IC device may determine whether synchronization signal from same level synchronization device is successfully detected through determining whether the receiving power of the synchronization signal is lower than TH_cd. The above receiving power may be one detected result of the synchronization signal power of the same level synchronization device in the transmitting window corresponding to Δ_l, or an average of the detected results of the synchronization signal power of the same level synchronization device in the transmitting window corresponding to Δ_lwithin a period of time T_cd. T_cd may be one or more long periods, or a value configured by the cellular network or the D2D central control node, or defined by standard. The value of TH_cd may be configured by the cellular network or the D2D central control node (e.g., issued via a cell broadcast message), or defined by standard.

In one embodiment, the IC device may not determine the receiving power of the synchronization signal. The detected result of the synchronization signal is directly reported to the base station in block 730 and it is determined whether to transmit the D2D synchronization signal according to an instruction of the base station.

Now this embodiment is finished. In this embodiment, if the IC device is at the edge of the cellular cell, and there is no other IC device around this IC device transmitting D2D synchronization signal in the same basic period, the IC device always continuously transmits D2D synchronization signals with period P_l. Although this manner may increase power consumption of the IC device transmitting the D2D synchronization signal, it can reduce complexity for the OOC device to detect the synchronization signal.

Embodiment 6

In this embodiment, the target device cannot detect the synchronization source of the cellular cell, i.e., the device is an OOC device. The OOC device detects D2D synchronization signal transmitted by a D2D device by a manner similar as cell search in the cellular network system. For a D2D device which has detected the D2D synchronization signal, after realizing synchronization utilizing the D2D synchronization signal, if the device is not a lowest level device and is at the edge of the coverage of the above D2D synchronization signal, the device transmits D2D synchronization signal in an idle window with a long period. The detailed implementation is as shown in FIG. 8, including the following.

At block 810, the OOC device obtains transmitting/detecting configurations C_l and C_uof the D2D synchronization signal.

At block 820, the OOC device detects D2D synchronization signal on each supported carrier cf according to the configuration C_l.

At block 830, if the OOC device detects D2D synchronization signal on carrier cf within time T_OOC, block 840 is executed; otherwise, block 831 is executed.

The window w _k,i denotes the selected window in which the highest priority synchronization signal is detected, wherein k denotes a synchronization level when the window acts as a transmitting window, i denotes an index of a basic period where the window w _k,i belongs.

The OOC device retrieves the level of the upper level synchronization device according to the D2D synchronization signal detected in the window w _k,i in block 830, so as to determine the synchronization level of itself.

At block 831, the OOC device transmits independent D2D synchronization signal in a scattered manner in the basic period P_u, _j of each long period according to the configuration C_l.

Wherein P_u, _j is defined by the configuration C_l, and is one of M basic periods of the long period P_l, wherein j is any value between 0 and M-1. The manner that the OOC device determines the value of j is not intended to be restricted in the present disclosure. Preferably, the OOC device transmits the synchronization signal in the transmitting window of the first level or second level synchronization device in the basic period P_u, _j. P_l denotes a transmitting/detecting window period determined by the configuration C_l. the value of T_OOC may be defined by standard or configured by the cellular network or the D2D central control node (e.g., issued by a cell broadcast message).

At block 840, the OOC device determines a synchronization level and status of itself, detects corresponding D2D synchronization signal according to corresponding configuration.

Based on the above objective, if the OOC device is a NDB device and is not a lowest level device, it indicates that the OOC is within the coverage of the synchronization signal of the upper level synchronization device and may be required to provide D2D synchronization signal for the next level synchronization device. The OOC device selects a window w _l,ii from transmitting windows corresponding to the same level synchronization devices of each long period, and detects synchronization signal of the same level synchronization device in the window w _l,ii.

Wherein w _l,ii is a transmitting window corresponding to Δ_l in basic period P_u, _ii of P_l. Δ_l is the time offset of the transmitting window of the first level synchronization device in the basic transmitting/detecting period, wherein ii is a value between 0 and M-1, denoting an index of the basic period in the long period, and M denotes the number of basic periods in the long period. The value of ii (i.e., the selection of the window w _l,ii) may be selected randomly or following another manner, which is not intended to be restricted in the present disclosure. P_l denotes the transmitting/detecting window period determined by the configuration C_l, i.e., long period.

If the OOC device is a FDB device and is not a lowest level device, the device continuously detects its status, and executes the operations of the NDB non-lowest level device when the device becomes a NDB device.

If the OOC device is a lowest level device, operations after it detects the D2D synchronization signal is not restricted in the present disclosure.

At block 850, if the OOC device is non-lowest level NDB device, and fails to detect synchronization signal from the same level synchronization device in w _l,ii, the OOC device transmits D2D synchronization signal in the window w _l,ii of each long period in the scattered manner.

If the receiving power of the synchronization signal detected in the window w _l,ii is lower than the threshold TH_b, it may be determined that the synchronization signal from the same level D2D synchronization device is not detected. The above receiving power may be one detected result of the D2D synchronization signal power in the window w _l,ii, or an average of the detected results of the D2D synchronization signal power in the window w _l,ii during a period of time T_dd.

If the OOC device does not meet the above conditions, detection of the synchronization signal from the same level synchronization device in block 840 is repeated.

Embodiment 7

In this embodiment, a target device is able to successfully detect a synchronization source of a cellular network cell, i.e., the device is an IC device. The device determines, according to strength of detected cell reference signal of the cellular network, whether it is at edge of the cellular cell. If it is at edge of the cellular cell, the device further detects power of D2D synchronization signal of a synchronization device of the same level with it. If the power of the detected synchronization signal is lower than a particular threshold, the device begins to transmit D2D reference signal with long period in the transmitting/detecting configuration in particular transmitting/detecting window. Then, the IC device continues to detect D2D synchronization signal in transmitting/detecting windows other than the above transmitting/detecting window, and stops transmitting the synchronization signal when detecting D2D synchronization signal or is far away from the edge of the cell. The detailed implementation is as shown in FIG. 9. The process includes the following.

At block 910, the IC device obtains transmitting/detecting configurations C_l and C_uof the D2D synchronization signal.

C_l and C_uare respectively the transmitting/detecting configurations of the long period and the basic period. Some parameters in the two configurations may be the same. In one embodiment, the two configurations may be completely the same. C_l and C_u may be broadcasted by the cellular network or a D2D central control node, or is defined by standard. In this embodiment, the period length corresponding to C_u is P _u, C_l corresponds to P_l=N×P _u, wherein 1≤N, which is configured by the base station or standards.

Position of the transmitting/detecting window is uniquely determined by the offset Δ and the basic period P _u. If the following condition is met, subframe n (0≤n＜10240) is the transmitting/detecting window:

Mod (n-Δ，P _u)=0;

In this embodiment, C_l and C_u correspond to the same Δ value, i.e., the set of transmitting/detecting windows belonging to the long period is a subset of the set of transmitting/detecting windows belonging to the short period.

At block 920, the IC device detects signals of the cellular network, determines whether the IC device is at the edge of the cellular cell. If yes, block 930 is executed; otherwise, this block is repeated; or, the IC device determines whether a D2D synchronization signal detecting instruction is received from the base station, if yes, block 930 is executed; otherwise, this block is repeated.

At block 930, if it is determined in block 920 that the IC device is at the edge of the cellular cell or the IC device receives an indication for detecting the D2D synchronization signal from the eNB, the IC device detects in the transmitting/detecting window determined in block 910 the synchronization signal of the same level synchronization device.

At block 940, if the IC device does not detect the synchronization signal from the same level synchronization device in the above transmitting/detecting window, the IC device transmits D2D synchronization signal with period P_l. Otherwise, block 930 is repeated. Or, the IC device reports the detected result to the base station, and determines whether to transmit D2D synchronization signal according to an instruction of the base station. If transmit, the IC device transmits the D2D synchronization signal with the period P_l. Otherwise, block 930 is repeated.

Herein, if the IC device fails to detect the synchronization signal from the same level synchronization device in the transmitting/detecting window, it indicates that there is no other IC device transmitting D2D synchronization signal within the coverage of the synchronization signal of the IC device. Thus, the IC device may transmit D2D synchronization signal with the period P_l, such that a second level synchronization device within the coverage of the IC device synchronization signal may realize synchronization using the D2D synchronization signal.

Preferably, the IC device may determine whether synchronization signal from same level synchronization device is successfully detected through determining whether the receiving power of the synchronization signal is lower than TH_cd. The above receiving power may be one detected result of the synchronization signal power of the same level synchronization device in the transmitting window, or an average of the detected results of the synchronization signal power of the same level synchronization device in the transmitting window within a period of time T_cd. T_cd may be one or more long periods, or a value configured by the cellular network or the D2D central control node, or defined by standard. The value of TH_cd may be configured by the cellular network or the D2D central control node (e.g., issued via a cell broadcast message), or defined by standard.

In one embodiment, the IC device may not determine the receiving power of the synchronization signal. The detected result of the synchronization signal is directly reported to the base station in block 930 and it is determined whether to transmit the D2D synchronization signal according to an instruction of the base station.

The IC device may start to transmit the synchronization signal in the transmitting window w _l of the m ^th long period after determining to transmit the D2D synchronization signal, and re-transmits the D2D synchronization signal in the transmitting windoww _l of each long period. Thus, in each long period, the IC device transmits the D2D synchronization signal in merely one window, this manner is referred to as a scattered manner, wherein the subframe number n _l corresponding to the subframe where the transmitting window w _l is located meets:

Mod (n _l-Δ，P _l)=0; or mod (n _l-Δ- N_ID×P _u, P _l)=0;

wherein N_ID=mod(RNTI, N), RNTI denotes an ID of the IC device in the cell.

At block 950, if the IC device transmits the D2D synchronization signal in the transmitting/detecting window w _l with the periodP _l, the device detects the synchronization signal of the same level synchronization device in the transmitting/detecting window

, and stops transmitting the D2D synchronization signal after detecting the synchronization signal of the same level synchronization device. If the synchronization signal of the same level synchronization device is not detected, block 940 and 950 are continued to be executed.

The subframe number

corresponding to the subframe where the window

is located meets:

Mod(

-Δ,P _u)=0 and

_≠ n _l;

Now this embodiment is finished. In this embodiment, if the IC device is at the edge of the cellular cell, and there is no other IC device around this IC device transmitting D2D synchronization signal in the same basic period, the IC device transmits the D2D synchronization signal with the long period P _l, and stops transmitting the D2D synchronization signal when there is a device transmitting D2D synchronization signal with short period around the IC device. If there is no device transmitting synchronization signal with short period at the edge of the cell, this manner may provide timing for other D2D devices outside the coverage of the cell, and avoids interferences to the devices in the cell which are brought out by the D2D device during the D2D communication in the asynchronous manner (with respect to the above cell).

The above describes the method for implementing synchronization between D2D devices. Various examples of the present disclosure also provide a D2D device, capable of implementing the above method. FIG. 10 shows a structure of the D2D device according to various embodiments of the present disclosure. As shown in FIG. 10, the device includes: a cellular network synchronization source detecting unit, a configuration receiving unit, an IC device synchronizing unit and an OOC device synchronizing unit.

The cellular network synchronization source detecting unit is to detect a synchronization source of the cellular network, indicates the IC device synchronizing unit to perform a synchronizing processing if the synchronization source of the cellular network is detected, and indicate the OOC device synchronizing unit to perform a synchronizing processing if no synchronization source is detected.

The configuration receiving unit is to receive transmitting/detecting configuration of the D2D synchronization signal. The transmitting/detecting configuration includes a transmitting/detecting period, a transmitting window and a detecting window corresponding to each level synchronization device.

The IC device synchronizing unit is to transmit/detect D2D synchronization signal according to the transmitting/detecting configuration after receiving a notification of the cellular network synchronization source detecting unit. In particular, the processing manners in the first and second embodiments may be utilized.

The OOC device synchronizing unit is to transmit/detect D2D synchronization signal according to the transmitting/detecting configuration after receiving a notification of the cellular network synchronization source detecting unit. In particular, the processing manners in the third and fourth embodiments may be utilized.

Those skilled in the art would know that some or all blocks included in the method of the present disclosure may be implemented by a program executed by relevant hardware. The program may be stored in a machine readable storage medium. When the program is executed, one or some of the blocks in the method of the present disclosure are performed.

In addition, the functional units in each embodiment of the present disclosure may be integrated into one processing module or exist as independent units. Two or more units may be integrated into one module. The integrated module may be implemented by hardware or by software functional modules. If the integrated module is implemented by software functional module and is sold or used as an independent product, the product may be stored in a machine readable storage medium.

The foregoing descriptions are only preferred embodiments of this invention and are not for use in limiting the protection scope thereof. Any changes and modifications can be made by those skilled in the art without departing from the spirit of this invention and therefore should be covered within the protection scope as set by the appended claims.

Claims

A method for implementing synchronization between D2D devices, comprising:detecting, by a D2D device, a synchronization source of a cellular network, and determining a transmitting/detecting configuration of the D2D synchronization signal; wherein the transmitting/detecting configuration comprises a transmitting/detecting period, a transmitting window and a detecting window corresponding to each level synchronization device; andtransmitting/detecting, by an IC device which detects the synchronization source of the cellular network and an OOC device which does not detects the synchronization source of the cellular network, the D2D synchronization signal according to the transmitting/detecting configuration.
The method of claim 1, wherein the transmitting/detecting the D2D synchronization signal by the IC device comprises:a1, if the IC device is located at the edge of the cellular cell or the IC device receives a D2D synchronization signal detecting indication from a base station, selecting, by the IC device, a window w _l,i from transmitting windows of same level synchronization devices in each long period according to the transmitting/detecting configuration of the D2D synchronization signal, and detecting D2D synchronization signal of the same level synchronization device in the window w _l,i; or, if the IC device reports a detected result of the D2D synchronization signal of the same level synchronization device to the base station and receives a D2D synchronization signal transmitting indication from the base station, executing step a2; wherein the transmitting/detecting configuration comprises a long period and a basic period, the long period comprises M basic periods, M is an integer, i denotes an index of the basic period in the long period P_l; and l denotes a identifier of the long period in the transmitting/detecting configuration; anda2, transmitting the D2D synchronization signal in the window w _l,i for use of synchronization of a second level synchronization device.
The method of claim 1, wherein the IC device transmitting/detecting the D2D synchronization signal comprises:a1, if the IC device is located at the edge of the cellular cell or receives a D2D synchronization signal detecting indication from a base station, detecting, by the IC device, D2D synchronization signal of the same level synchronization device in subframe n of each long period; if the IC device does not detect the D2D synchronization signal of the same level synchronization device, or if the IC device reports a detected result of the D2D synchronization signal of the same level synchronization device to the base station and receives a D2D synchronization signal transmitting indication from the base station, executing step a2; wherein mod (n-Δ, P _u)=0, the transmitting/detecting configuration comprises a long period P_l and a basic period P_u, the long period P_l comprises N basic periods P_u, l denotes a identifier of the long period in the transmitting/detecting configuration, Δdenotes a long period detecting window offset defined in advance; anda2, transmitting the D2D synchronization signal in the window w _l,i of each long period for use of synchronization of a second level synchronization device; wherein a subframe number corresponding to a subframe where the windoww _l,i is located meets: mod (n _l-Δ, P _l)=0, or mod (n _l-Δ- N_ID×P _u, P _l)=0, wherein N_ID=mod(RNTI, N), RNTI denotes an ID of the IC device in the cell.
The method of claim 3, wherein after step a2, the method further comprises:detecting, by the IC device, the synchronization signal of the same level synchronization device in transmitting/detecting window
, and after detecting the synchronization signal of the same level synchronization device, stopping transmitting the D2D synchronization signal; if the synchronization signal of the same level synchronization device is not detected, returning to step a2;wherein a subframe number corresponding to the subframe where
is located meets: mod(
-Δ, P _u)=0 and
_≠ n _l.
The method of claim 2 or 3, wherein the IC device determines whether it is located at the edge of the cellular cell by:if a receiving power of a reference signal of the cellular cell detected by the IC device is lower than a preconfigured threshold TH_cc, determining that the IC device is located at the edge of the cellular cell.
The method of claim 2, wherein after step a2, the method further comprises:detecting, by the IC device according to the transmitting/detecting configuration of the D2D synchronization signal, D2D synchronization signal of a next level synchronization device in a transmitting window of a second level synchronization device of a basic period where the window w _l,i belongs, and detecting D2D synchronization signal of the same level synchronization device in a transmitting window of the same level synchronization device except for w _l,i; if the D2D synchronization signal of the next level synchronization device is detected, increasing a transmission density of the D2D synchronization signal.
The method of claim 6, wherein the increasing the transmission density of the D2D synchronization signal comprises:transmitting, by the IC device, the D2D synchronization signal in the window w _l,i and a transmission window w _l,j in which no D2D synchronization signal of the same level synchronization device is detected; wherein j denotes an index of the transmitting window in which no D2D synchronization signal of the same level synchronization device is detected in the long period l.
The method of claim 6 or 7, wherein after increasing the transmission density of the D2D synchronization signal, detecting, by the IC device, the D2D synchronization signal of the next level synchronization device in the transmitting window of the second level synchronization device in the basic period of the window in which the IC device transmits the D2D synchronization signal, and returning to step a2 if the D2D synchronization signal of the next level synchronization device is not detected in all transmitting windows of second level synchronization devices.
The method of claim 1, wherein the transmitting the D2D synchronization signal by the IC device comprises:after detecting a trigger synchronization signal transmitted by a second level synchronization device, transmitting, by the IC device, the D2D synchronization signal in a transmitting window of a first level synchronization device with a period P_IC indicated in the transmitting/detecting configuration.
The method of claim 9, wherein the IC device detects the trigger synchronization signal in each detecting window of the first synchronization device according to the transmitting/detecting configuration.
The method of claim 9, after transmitting the D2D synchronization signal in the transmitting window of the first level synchronization device, the method further comprises:detecting, by the IC device in the detecting window corresponding to the transmitting window of the first level synchronization device, D2D synchronization signal of the next level synchronization device, and stopping transmitting the D2D synchronization signal if no D2D synchronization signal of the next level synchronization signal is detected.
The method of claim 1, wherein the transmitting/detecting the D2D synchronization signal by the OOC device comprises:performing, by the OOC device according to pre-stored priorities of carriers corresponding to the cellular cell, the D2D synchronization signal transmitting/detecting operation on each carrier supported by the OOC device in turn.
The method of claim 12, wherein for any carrier, after the OOC detects the D2D synchronization signal on the carrier within a preconfigured time period T_OOC, performing, by the OOC device, synchronization operation according to the D2D synchronization signal with the highest priority among the detected D2D synchronization signals.
The method of claim 13, wherein after detecting the D2D synchronization signal on any carrier, the method further comprises:b1, selecting, by the OOC device, a window w _k,i in which the highest priority D2D synchronization signal is detected among all windows in which synchronization signals are detected, determining a synchronization level of the OOC device k+1 according to level information k in the D2D synchronization signal detected in the window w _k,i, and detecting the D2D synchronization signal of the same level synchronization device in a transmitting window w _t,i of the same level synchronization device in the basic period of the window w _k,i; wherein the transmitting/detecting configuration comprises a long period and a basic period, the long period comprises M basic periods, M is an integer, i denotes an index of the basic period in which the synchronization signal with the highest priority is detected;b2, if the OOC device is a lowest level device and the OOC device does not detect the D2D synchronization signal of the same level device in the window w _t,i; or, if the OOC device is located at the edge of the coverage of the synchronization signal of an upper level synchronization device, and the OOC device is not a lowest level device and the receiving power of the D2D synchronization signal of the same level synchronization device detected by the OOC device in the window w _t,i is lower than a preconfigured threshold TH_b; or if the OOC device is far away from the edge of the coverage of the upper level synchronization device, and the OOC device is not a lowest level device and the OOC device does not detects the D2D synchronization signal of the same level device in the window w _t,i, executing step b3; and b3, transmitting, by the OOC device, the D2D synchronization signal in the window w _t,i.
The method of claim 14, wherein after step b3, the method further comprises:if the OOC device is located at the edge of the coverage of the upper level synchronization device, and the OOC device is not the lowest level device, detecting, by the OOC device in a transmitting window of a next level synchronization device in the basic period where the window w _t,i belongs, the D2D synchronization signal of the next level synchronization device, and detecting the D2D synchronization signal of the same level synchronization device in the transmitting window of the same level synchronization device except for the window w _t,i; and increasing the transmission density of the D2D synchronization signal if the D2D synchronization signal of the next level synchronization device is detected.
The method of claim 15, wherein the increasing the transmission density of the D2D synchronization signal comprises:transmitting, by the OOC device, the D2D synchronization signal in the window w _t,i and a transmission window w _t,j in which no D2D synchronization signal of the same level synchronization device is detected; wherein j denotes an index of the transmitting window in which no D2D synchronization signal of the same level synchronization device is detected in the long period l.
The method of claim 15 or 16, wherein after increasing the transmission density of the D2D synchronization signal, detecting, by the OOC device, the D2D synchronization signal of the next level synchronization device in the transmitting window of the next level synchronization device in the basic period of the window in which the OOC device transmits the D2D synchronization signal, and returning to step b3 if the D2D synchronization signal of the next level synchronization device is not detected in all transmitting windows of next level synchronization devices.
The method of claim 13, wherein after detecting the D2D synchronization signal on any carrier, the method further comprises:c1, selecting, by the OOC device, a window w _k,i in which the highest priority synchronization signal is detected among the detected D2D synchronization signals, determining a synchronization level of the OOC device k+1 according to level information k in the D2D synchronization signal detected in the window w _k,i, if the OOC device is located at the edge of the coverage of the synchronization signal of the upper level synchronization device and is not the lowest level device, selecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, a window w _l,ii from transmitting windows corresponding to the same level synchronization devices of each long period l, and detecting synchronization signal of the same level synchronization device in the window w _l,ii; wherein the transmitting/detecting configuration comprises a long period and a basic period, the long period comprises M basic periods, M is an integer, i denotes an index of the basic period in which the synchronization signal with the highest priority is detected; ii denotes an index of the basic period where the transmitting window belongs in the long period l; andc2, if no D2D synchronization signal of the same level synchronization device is detected in the window w _l,ii, transmitting, by the OOC device, the D2D synchronization signal in the window w _l,ii of each long period l.
The method of claim 12, wherein for any carrier, if the OOC device does not detect any D2D synchronization signal on any carrier within the preconfigured period of time, selecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, a window w _l,i from transmitting window of first or second level synchronization device of each long period l, and transmitting independent D2D synchronization signal in the window w _l,i with the period l for use of synchronization by the next level synchronization device; wherein the transmitting/detecting configuration comprises a long period and a basic period, the long period comprises M basic periods, M is an integer, i denotes an index of the basic period in the long period.
The method of claim 12, wherein for any carrier, if the OOC device does not detect any D2D synchronization signal on any carrier within the preconfigured period of time, transmitting, by the OOC device, the trigger synchronization signal and detecting the D2D synchronization signal on the carrier in a time-division manner, if no D2D synchronization signal is detected with a preconfigured time period T_tr after the trigger synchronization signal is transmitted, executing step d; andd, selecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, a window w _l,i from transmitting window of first or second level synchronization device of each long period P_l, and transmitting independent D2D synchronization signal in the window w _l,i with the period P_l for use of synchronization by the next level synchronization device; wherein the transmitting/detecting configuration comprises a long period and a basic period, the long period comprises M basic periods, M is an integer, i denotes an index of the basic period in the long period.
The method of claim 20, wherein after step d, the method further comprises:detecting, by the OOC device according to the transmitting/detecting configuration of the D2D synchronization signal, the D2D synchronization signal of the next level synchronization device in a transmitting window of a second or third level synchronization device of the basic period where the window w _l,i belongs, and detecting D2D synchronization signal of the same level synchronization device in a transmitting window of the same level synchronization device except for w _l,i; if the D2D synchronization signal of the next level synchronization device is detected, increasing a transmission density of the D2D synchronization signal.
The method of claim 21, wherein the increasing the transmission density of the D2D synchronization signal comprises:transmitting, by the OOC device, the D2D synchronization signal in the window w _l,i and a transmission window w _l,j in which no D2D synchronization signal of the same level synchronization device is detected; wherein j denotes an index of the transmitting window in which no D2D synchronization signal of the same level synchronization device is detected in the long period P_l.
The method of claim 21 or 22, wherein after increasing the transmission density of the D2D synchronization signal, detecting, by the OOC device, the D2D synchronization signal of the next level synchronization device in the transmitting window of the second or third level synchronization device in the basic period of the window in which the OOC device transmits the D2D synchronization signal, and returning to step d if the D2D synchronization signal of the next level synchronization device is not detected in all transmitting windows of second or third level synchronization devices.
The method of claim 14 or 15 or 16, wherein for any carrier, if the OOC device does not detect any D2D synchronization signal on any carrier within the preconfigured period of time T_OOC, transmitting, by the OOC device, the trigger synchronization signal and detecting the D2D synchronization signal on the carrier in a time-division manner, if no D2D synchronization signal is detected with a preconfigured time period T_tr after the trigger synchronization signal is transmitted, stopping transmitting the trigger synchronization signal and detecting the D2D synchronization signal in the time-division manner; and executing steps b1~b3.
An apparatus for implementing synchronization between D2D devices, comprising: a cellular network synchronization source detecting unit, a configuration receiving unit, an IC device synchronizing unit and an OOC device synchronizing unit; whereinthe cellular network synchronization source detecting unit is to detect a synchronization source of the cellular network, indicate the IC device synchronizing unit to perform a synchronizing processing if the synchronization source of the cellular network is detected, and indicate the OOC device synchronizing unit to perform a synchronizing processing if no synchronization source is detected;the configuration receiving unit is to receive transmitting/detecting configuration of the D2D synchronization signal; the transmitting/detecting configuration includes a transmitting/detecting period, a transmitting window and a detecting window corresponding to each level synchronization device;the IC device synchronizing unit is to transmit/detect D2D synchronization signal according to the transmitting/detecting configuration after receiving a notification of the cellular network synchronization source detecting unit; andthe OOC device synchronizing unit is to transmit/detect D2D synchronization signal according to the transmitting/detecting configuration after receiving a notification of the cellular network synchronization source detecting unit.