KR102458590B1 - Method and apparatus for synchronization in D2D communication network - Google Patents

Abstract

A method for synchronizing a D2D terminal in a D2D communication network through the steps of receiving a first D2D synchronization signal from at least one D2D synchronization source, and synchronizing according to a synchronization time reference provided through the first D2D synchronization signal, and at least one When the D2D synchronization signal and the D2D synchronization channel are received from the D2D synchronization source, determining whether to maintain the role as an independent synchronization source based on negotiation information for negotiation between synchronization sources included in the D2D synchronization channel, and as an independent synchronization source If the role is not maintained, a method of negotiating whether to perform the role of the synchronization source with another D2D synchronization source through the step of operating as a relay synchronization source is provided.

Description

Direct communication network synchronization method and apparatus {Method and apparatus for synchronization in D2D communication network}

The present invention relates to a method and apparatus for synchronizing a D2D terminal with another D2D terminal in a direct communication network.

In a long term evolution (LTE) mobile communication system, research is underway to support device to device (D2D) communication. In D2D communication, a terminal may directly transmit/receive data to/from an adjacent terminal without going through a base station. In LTE D2D, which is being discussed at the 3GPP standardization meeting, a method for a D2D terminal to provide synchronization to support D2D communication is being discussed, and according to an agreement, some of the D2D terminals operate as a D2D synchronization source. can do. The D2D synchronization source transmits a synchronization signal (D2D Synchronization Signal, D2DSS) for synchronizing and a physical D2D Synchronization Channel (PD2DSCH) for transmitting additional information for synchronization to adjacent D2D UEs by timing the synchronization time. reference) can be provided. Upon receiving the D2D synchronization signal and the D2D synchronization channel from the adjacent D2D synchronization source, the D2D terminal sets the synchronization time reference based on the received D2D synchronization signal and information included in the D2D synchronization channel.

A method for a terminal supporting D2D communication to synchronize with a neighboring D2D terminal may vary depending on whether the D2D terminal is controlled by the base station. When the D2D terminal can be directly controlled from the base station, the D2D terminal is a downlink of the base station through a synchronization signal (eg, a primary synchronization signal and a secondary synchronization signal) transmitted by the base station. Synchronous time criteria may be provided. In addition, in order to provide a synchronization time to an adjacent D2D terminal, the base station instructs a specific D2D terminal to operate as a D2D synchronization source.

An object of the present invention is to provide a method and apparatus for transmitting synchronization information to an adjacent D2D terminal and synchronizing with the adjacent D2D terminal when the D2D terminal cannot be controlled by a base station.

According to an embodiment of the present invention, there is provided a synchronization method of a D2D terminal performing D2D communication. The synchronization method includes receiving a first D2D synchronization signal from at least one D2D synchronization source, and synchronizing according to a synchronization time reference provided through the first D2D synchronization signal.

The synchronization method may further include receiving a first D2D synchronization channel from at least one D2D synchronization source, and adjusting a synchronization time reference based on delay information on propagation delay included in the D2D synchronization channel. can

In the synchronization method, the delay information may be a bit string determined to have a predetermined length based on a type of CP supported by D2D communication and a synchronization adjustment interval.

The synchronization method may further include broadcasting a second D2D synchronization signal according to the adjusted synchronization time reference.

The synchronization method may further include broadcasting information about a second hierarchical level in which 1 is increased from a first hierarchical level included in the first D2D synchronization channel through a second D2D synchronization channel.

The adjusting in the synchronization method may include adjusting the synchronization time reference so that the accumulated time of propagation delay is not longer than the CP supported by D2D communication.

The synchronizing in the synchronization method includes estimating a propagation delay based on the reception strength of the first D2D synchronization signal, and adjusting a synchronization time reference provided through the first D2D synchronization signal based on the estimated propagation delay. may include.

According to another embodiment of the present invention, a method for synchronizing a D2D terminal performing D2D communication is provided. The synchronization method includes receiving a first D2D synchronization signal from at least one D2D synchronization source, and estimating a round-trip delay (RTD) with at least one D2D synchronization source based on the first D2D synchronization signal. and transmitting the D2D synchronization channel including delay information configured based on the round trip delay.

The synchronization method may further include transmitting a second D2D synchronization signal to at least one D2D synchronization source, wherein the first D2D synchronization signal may be a synchronization signal generated based on a synchronization time reference of the second D2D synchronization signal. .

According to another embodiment of the present invention, there is provided a synchronization source negotiation method of an independent synchronization source included in a D2D communication network. The synchronization source negotiation method, when receiving a D2D synchronization signal and a D2D synchronization channel from at least one D2D synchronization source, maintains a role as an independent synchronization source based on negotiation information for negotiation between synchronization sources included in the D2D synchronization channel determining whether to do so, and operating as a relay synchronization source if it does not maintain its role as an independent synchronization source.

In the synchronization source negotiation method, the negotiation information may include a negotiation constant determined when the independent synchronization source selects a role as the independent synchronization source.

The determining in the synchronization source negotiation method includes comparing the negotiation constant of the independent synchronization source with the negotiation constant of at least one D2D synchronization source, and determining whether to maintain the role as the independent synchronization source based on the comparison result may include.

In the synchronization source negotiation method, the negotiation information may include a time stamp indicating a time when the independent synchronization source operates as the independent synchronization source.

The determining in the synchronization source negotiation method includes comparing a time stamp of an independent synchronization source with a time stamp of at least one D2D synchronization source, and determining whether to maintain a role as an independent synchronization source based on the comparison result may include.

The synchronization source negotiation method may further include increasing the hierarchical level by one when the role as an independent synchronization source is not maintained.

The determining in the synchronization source negotiation method includes: determining the hierarchical level of at least one D2D synchronization source; and determining whether to maintain the role as an independent synchronization source when the hierarchical level of the at least one D2D synchronization source is 0 or 1 may include the step of

The determining in the synchronization source negotiation method may further include maintaining a role as an independent synchronization source when the hierarchical level of at least one D2D synchronization source is 2 or higher.

According to an embodiment of the present invention, a D2D terminal may perform synchronization with an adjacent D2D terminal through a hierarchical structure without the control of the base station outside the coverage of the base station. In this case, the D2D terminal according to an embodiment of the present invention can avoid signal collision or signal interference due to propagation delay by adjusting the synchronization time reference. In addition, in the case of an independent synchronization source, the D2D terminal appropriately adjusts the number of independent synchronization sources through negotiation with other synchronization sources, thereby solving the problems of battery consumption and computational complexity increase of the D2D terminal.

1 is a diagram illustrating a topology of a D2D communication network according to an embodiment of the present invention.
2 is a diagram illustrating a topology of a D2D communication network according to another embodiment of the present invention.
3 is a diagram illustrating interference and collision of D2D data according to another embodiment of the present invention.
4 is a flowchart illustrating a synchronization signal transmission method according to an embodiment of the present invention.
5 is a flowchart illustrating a method of measuring delay information according to an embodiment of the present invention.
6 is a flowchart illustrating a synchronization signal transmission method according to another embodiment of the present invention.
7 is a conceptual diagram illustrating a negotiation method between synchronization sources according to an embodiment of the present invention.
8 is a flowchart illustrating a negotiation method between synchronization sources according to an embodiment of the present invention.
9 is a block diagram illustrating a wireless communication system according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, a terminal is a mobile station (MS), a mobile terminal (MT), an advanced mobile station (AMS), a high reliability mobile station (HR-MS) , a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), user equipment (UE), etc. may refer to, and the like, MT, MS, AMS , HR-MS, SS, PSS, AT, UE, etc. may include all or some functions.

In addition, the base station (base station, BS) is an advanced base station (advanced base station, ABS), a high reliability base station (high reliability base station, HR-BS), a Node B (node B), an advanced node B (evolved node B, eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR)-BS, a relay serving as a base station station, RS), a relay node (RN) serving as a base station, an advanced relay station (ARS) serving as a base station, and a high reliability relay station (HR) serving as a base station -RS), small base station [femoto base station (femoto BS), home node B (home node B, HNB), home eNodeB (HeNB), pico base station (pico BS), macro base station (macro BS), micro base station (micro BS) ), etc.] and the like, and may include all or some functions of ABS, NodeB, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc. have.

1 is a diagram illustrating a topology of a D2D communication network according to an embodiment of the present invention.

When the D2D terminal can receive a downlink synchronization signal from the base station, or can receive a D2D synchronization signal and a D2D synchronization channel from an adjacent D2D synchronization source, the D2D terminal can obtain a synchronization time reference through the provided synchronization signal. .

When the D2D terminal directly receives the synchronization time reference from the base station, the D2D terminal transmits a synchronization signal (eg, a primary synchronization signal (PSS) or a secondary synchronization signal (SSS)) broadcasted by the base station. ) to obtain the synchronization time reference. In this case, the quality of the synchronization signal provided by the base station may be greater than or equal to a threshold of a predetermined size.

When a D2D UE receives a synchronization time reference from an adjacent D2D synchronization source, the D2D UE receives a synchronization time reference from an adjacent D2D synchronization source. The synchronization time reference may be obtained through the D2D synchronization signal and the D2D synchronization channel transmitted from the synchronization source. In this case, the synchronization time reference may be directly provided to the D2D synchronization source through the synchronization signal of the base station, or may be provided from an adjacent D2D synchronization source to which the synchronization time reference of the base station is applied. In this case, the D2D terminal indirectly acquires the synchronization time reference of the base station.

Alternatively, the synchronization time reference provided to the D2D synchronization source may be provided directly from the independent synchronization source, or may be provided from another D2D synchronization source provided with the synchronization time reference from the independent synchronization source. In this case, the D2D terminal directly or indirectly acquires the time reference of the independent synchronization source.

When the D2D terminal receives a D2D synchronization signal and a D2D synchronization channel from another D2D terminal controlled by the base station or provided with a synchronization time reference by the base station, the D2D terminal may obtain a common synchronization time reference provided by the base station. However, when the D2D terminal cannot receive the synchronization time reference of the base station, the D2D terminal may apply the synchronization time reference provided from the independent synchronization source. The D2D terminal according to an embodiment of the present invention may have priority with respect to the synchronization time reference as follows.

- First, the D2D synchronization signal provided by the base station has the highest priority.

- The indirectly received D2D synchronization signal of the base station has a higher priority than the D2D synchronization signal provided from an independent synchronization source. That is, when the source of the synchronization time reference is the base station, the priority of the D2D synchronization signal including information on the synchronization time reference is high.

- When there is only the D2D synchronization signal received from the independent synchronization source, the synchronization time standard of D2D communication for public safety has higher priority than other cases. In addition, when the D2D synchronization channel includes information on the number of hops or a stratum level, a synchronization signal transmitted from a D2D synchronization source having a low number of hops or a low hierarchy level has higher priority.

- Finally, when at least two synchronization signals have the same priority, the signal with the stronger reception strength has a higher priority.

When both D2D communication for public safety and D2D communication for data transmission and exchange between terminals other than public safety are supported in the D2D communication network according to an embodiment of the present invention, D2D communication for public safety is It takes precedence over D2D communication for purposes other than public safety. Therefore, the D2D terminal may set the highest priority for the D2D synchronization signal of the D2D communication for public safety when setting the synchronization time reference.

In order for the D2D terminal to give high priority to the D2D synchronization signal for public safety, it should be able to distinguish the D2D synchronization signal for public safety from the D2D synchronization signal of other D2D communication. According to an embodiment of the present invention, a sequence of a D2D synchronization signal for public safety and a sequence of other D2D synchronization signals may be divided into groups to distinguish the D2D synchronization signal. Alternatively, it may indicate that the D2D synchronization signal is for public safety through the D2D synchronization channel.

In a method in which the sequence of the D2D synchronization signal for public safety and the sequence of other D2D synchronization signals are divided into groups, some sequences among the entire sequence that can be used as the D2D synchronization signal may be designated for the D2D synchronization signal for public safety. have. Therefore, if the D2D terminal receiving the D2D synchronization signal correctly receives the D2D synchronization signal, the D2D terminal determines whether the synchronization time reference is used in D2D communication for public safety through the received D2D synchronization signal, and data with other D2D terminals. It can be determined whether it is used in communication.

In a method in which the purpose of the D2D synchronization signal is known through the D2D synchronization channel, an indicator indicating the purpose of the D2D synchronization signal (eg, public safety indicator), or D2D communication for public safety and other D2D A delimiter capable of distinguishing communication may be included in the D2D synchronization channel. In this case, the indicator and the delimiter may consist of a small number of bits. For example, the D2D synchronization source sets the public safety identifier included in the D2D synchronization channel to 1 when providing the synchronization time reference of D2D communication for public safety, and public safety when providing the synchronization time reference of other D2D communication. You can set the safety delimiter to 0. After receiving the D2D synchronization channel, the D2D terminal may know the purpose of using the synchronization time reference provided through the public safety identifier (whether for public safety or for other purposes).

When the D2D terminal cannot receive the downlink synchronization signal of the base station or the D2D synchronization signal from the adjacent D2D synchronization source, the D2D terminal provides a synchronization time reference to other adjacent D2D terminals under a predetermined condition. source, I-SS). The independent synchronization source may determine a synchronization time reference and broadcast the determined synchronization time reference to an adjacent D2D terminal. In this case, the synchronization time reference determined by the independent synchronization source may be provided to the independent synchronization source through a timer inside the terminal or a global positioning system (GPS). In an embodiment of the present invention, when the D2D terminal does not receive a synchronization signal (a downlink synchronization signal of the base station or a D2D synchronization signal and a D2D synchronization channel) from a base station or an adjacent D2D terminal, the strength of the provided synchronization signal is the synchronization time reference. It may operate as an independent synchronization source when a specific threshold for ensuring quality is not satisfied or when the minimum value of the number of different synchronization time references required to stably provide a synchronization time reference is not satisfied.

The D2D terminal, which has been provided with the synchronization time reference from the independent synchronization source, may deliver its synchronization time reference to its lower D2D terminal through the D2D synchronization signal and the D2D synchronization channel. In this case, the D2D terminal operates as a relay synchronization source (R-SS). The relay synchronization source may transmit a synchronization time reference provided from an upper independent synchronization source (independent synchronization source or an adjacent relay synchronization source) to an adjacent D2D terminal through the D2D synchronization signal and the D2D synchronization channel generated by the relay synchronization source.

According to the hierarchical synchronization procedure according to an embodiment of the present invention, the relay synchronization source may transmit the synchronization time reference provided from the upper D2D synchronization source to the lower D2D terminal through the D2D synchronization signal and the D2D synchronization channel. The D2D synchronization signal and the D2D synchronization channel may be transmitted from at least one resource pool designated for the D2D synchronization signal and the D2D synchronization channel, and each resource pool may have a predetermined period. When a D2D terminal operating as a relay synchronization source receives a D2D synchronization signal and a D2D synchronization channel from one D2D synchronization resource pool, the D2D terminal randomly selects one of the remaining D2D synchronization resource pools to generate a D2D synchronization signal and D2D synchronization channel can be transmitted. For example, when there are two D2D synchronization resource pools, the relay synchronization source receives a D2D synchronization signal and a D2D synchronization channel from one of the resource pools, and its own D2D synchronization signal and a D2D synchronization channel through the other resource pool. can be transmitted. The relay synchronization source may determine the synchronization time reference through the D2D synchronization signal provided from the upper D2D synchronization source according to the priority of the operation reference and synchronization time reference as the synchronization source described above, and transmit the D2D synchronization signal and the D2D synchronization channel. . The relay synchronization source transmits the D2D synchronization signal and the D2D synchronization channel as follows.

First, the relay synchronization source may transmit the same D2D synchronization signal (ie, the same sequence) as the D2D synchronization signal provided from the upper D2D synchronization source. In this case, the same D2D synchronization signal is a synchronization time reference provided from the same D2D synchronization source. For example, when the D2D terminal receives the n-th D2D synchronization signal from the upper D2D synchronization source and operates as the relay synchronization source, the D2D terminal may transmit the same n-th D2D synchronization signal as the provided synchronization signal. In addition, the D2D terminal may check the synchronization group to which it belongs through the received D2D synchronization signal. When a sequence divided by a specific group (public safety or not, within/out of the coverage of the base station, etc.) is used as the D2D synchronization signal, the D2D terminal receiving the D2D synchronization signal receives the D2D synchronization signal to receive information such as the synchronization group ( In the future, 'group information') may be additionally provided.

Meanwhile, the relay synchronization source may transmit a D2D synchronization signal different from the D2D synchronization signal provided from the upper D2D synchronization source. In this case, the relay synchronization source may randomly select one of the remaining selectable D2D synchronization signals except for a D2D synchronization signal receivable from a D2D synchronization source adjacent to the D2D synchronization signal providing the synchronization time reference, and transmit the selected D2D synchronization signal. . A sequence used for a D2D synchronization signal has orthogonality, and different D2D synchronization sources use different sequences as much as possible as a D2D synchronization signal. Therefore, a D2D terminal that is not yet synchronized has a D2D synchronization signal transmitted from an adjacent D2D synchronization source. may increase the probability of successfully receiving In order to additionally provide information (group information) about a group providing a synchronization time reference of the D2D synchronization signal, the sequence of the D2D synchronization signal may be classified for each predetermined group, or group information may be included in the D2D synchronization channel.

As the synchronization time reference provided as the relay synchronization source is transmitted to the adjacent D2D terminal, the synchronization time reference may accumulate propagation delay, multi-path fading, processing delay of the D2D terminal, etc. and the error may increase due to the accumulated delay. In an embodiment of the present invention, a stratum level may be used to reduce a time error that may occur as the number of hops through which the synchronization time reference is transmitted increases. For example, one synchronization source according to an embodiment of the present invention may transmit a D2D synchronization channel including a hierarchical level. One D2D synchronization source obtains a synchronization time reference through a D2D synchronization signal and a D2D synchronization channel provided from an upper D2D synchronization source, and generates a D2D synchronization signal and a D2D synchronization channel, so that the generated D2D synchronization signal and the D2D synchronization channel are adjacent to each other. It can be transmitted to the D2D terminal. At this time, the value of the hierarchical level included in the D2D synchronization channel of the D2D synchronization source is increased. The hierarchical level is information for transferring information on the number of hops, and may be included in the D2D synchronization channel. Each time the D2D synchronization signal for D2D synchronization passes through one hop, the value of the layer level may also increase by one. In a D2D sync channel broadcast from an independent sync source, the hierarchical level is set to zero. Since the smaller the hierarchical level value, the smaller the time error due to the accumulated delay. Therefore, when the D2D UE selects the synchronization time reference, the hierarchical level value is equal to or greater than the threshold value indicating the D2D synchronization signal strength (the threshold for properly receiving the D2D synchronization signal). century) is preferred. And, when the D2D terminal receives the synchronization time reference from a plurality of higher D2D synchronization sources, the priority of the synchronization time reference may be increased as the hierarchical level of the D2D synchronization source providing the synchronization time reference is lower. When the synchronization time reference is provided from a plurality of D2D synchronization sources of the same hierarchical level, the D2D terminal may synchronize according to the synchronization time reference of the D2D synchronization source providing the D2D synchronization signal having a stronger received signal strength.

Referring to FIG. 1 , UE1110 is an independent synchronization source, and the hierarchical level is 0. UE2 120 , UE3 130 , UE4 140 , and UE5 150 are relay synchronization sources, the layer level of UE2 120 is 1, and the layer level of UE3 130 and UE4 140 is 2 , the layer level of UE5 150 is three. The layer level of UE6 160 is four. Among the two concentric circles shown around the UE1110, the solid line 111 indicates a range in which the signal transmitted from the UE1110 is received with the received signal strength X [dBm], and the dotted line 112 is the UE1110. indicates the available range in which the synchronization time reference of

UE4 140 may receive a D2D synchronization signal and a D2D synchronization channel from UE2 120 having a hierarchical level of 1 and UE3 130 having a hierarchical level of 2 . In this case, the UE4 140 may perform synchronization according to the synchronization time reference received from the UE2 120 having a lower hierarchical level. UE5 150 receives a D2D synchronization signal and a D2D synchronization channel from UE3 130 and UE4 140, which are at the same hierarchical level, in this case, a synchronization time reference of UE4 140 providing a stronger D2D synchronization signal. You can set your own motives accordingly.

2 is a diagram illustrating a topology of a D2D communication network according to another embodiment of the present invention, and FIG. 3 is a diagram illustrating interference and collision of D2D data according to another embodiment of the present invention.

Referring to FIG. 2 , when a D2D terminal performs synchronization through a hierarchical structure according to an embodiment of the present invention, as the D2D synchronization signal is transmitted through hops, propagation delay and multi-path delay are accumulated, resulting in synchronization time error. may occur. That is, a synchronization time error between an independent synchronization source providing one synchronization time reference and a synchronization D2D terminal may increase, which may cause interference and collision during transmission of D2D data between D2D terminals. In particular, when the sum of the accumulated delays is longer than the length of a cyclic prefix (CP) supported by D2D communication, the D2D terminal cannot properly receive interference or collision data.

2 and 3 , when UE1 110 is an independent synchronization source and UE2 120 is a relay synchronization source, the synchronization time difference between UE3 130 and UE1 110 is Equation 1 below. .

In this case, Δ ₁ is a propagation delay between UE1 110 and UE2 120 , and Δ ₂ is a propagation delay between UE2 120 and UE3 130 . In one embodiment of the present invention, the signal transmitted from UE3 130 to UE1 110 is due to the propagation delay (Δ ₃ ) between UE3 130 and UE1 110 Δ ₁ +Δ ₂ +Δ ₃ late UE1 ( 110) can be reached.

The D2D synchronization source according to an embodiment of the present invention can solve a signal interference or signal collision problem that may occur due to an error of a synchronization signal by appropriately adjusting the synchronization time reference. For example, the D2D synchronization source according to an embodiment of the present invention sets the synchronization time criterion so that the accumulated time of the propagation delay and the multi-path delay according to the increase in the number of hops (or layer level) is not longer than the time length of the CP. can be adjusted At this time, the D2D synchronization source sets a time reference based on the received D2D synchronization signal of the upper layer, and when transmitting the D2D synchronization signal, the information on the accumulated propagation delay (hereinafter referred to as 'delay information') is reflected to reflect the synchronization time standards can be adjusted. The D2D synchronization source may include delay information in the D2D synchronization channel or provide delay information for adjusting the synchronization signal to another terminal by estimating the delay through the reception strength of the D2D synchronization signal. In this case, the concept of upper and lower levels is intended to describe the transfer process of the synchronization time reference provided from the adjacent D2D synchronization source, and when the hierarchical level is not applied, the priority between the transmitting terminal and the receiving terminal of the synchronization time reference does not exist. can

4 is a flowchart illustrating a synchronization signal transmission method according to an embodiment of the present invention.

Referring to FIG. 4 , a method in which a D2D synchronization source provides delay information to a D2D synchronization source of a lower layer through a D2D synchronization channel is illustrated.

First, the upper layer D2D synchronization source 410 transmits delay information on the D2D synchronization channel when transmitting the D2D synchronization signal (S401). At this time, the delay information included in the D2D synchronization channel is a bit of a predetermined length based on the transmission strength of the D2D synchronization signal, the type of CP (eg, normal or extended) and the synchronization adjustment interval, etc. It can be determined by heat. The D2D synchronization source of the upper layer may be an independent synchronization source or a relay synchronization source.

Thereafter, the D2D synchronization sources 421 and 422 of the lower layer set a synchronization time reference using the D2D synchronization signal received from the D2D synchronization source 410 of the upper layer, and delay information included in the D2D synchronization channel is used. to adjust the synchronization time reference (S402). That is, the D2D synchronization sources 421 and 422 set a synchronization time reference through the D2D synchronization signal provided from the source set through the D2D synchronization signal based on the delay information included in the D2D synchronization channel, and include in the D2D synchronization channel. Based on the delay information, the set synchronization time reference can be adjusted.

Thereafter, the lower layer D2D synchronization sources 421 and 422 may provide the adjusted synchronization time reference to the adjacent D2D terminal by broadcasting the D2D synchronization signal ( S403 ).

5 is a flowchart illustrating a method of measuring delay information according to an embodiment of the present invention.

Delay information included in the synchronization channel according to an embodiment of the present invention is embedded in the D2D terminal (pre-configured) by applying information such as the transmission strength of the D2D synchronization signal and the coverage of the D2D synchronization source, or directly by the base station can be configured. When the delay information is configured by the base station, the base station may provide the delay information to the D2D synchronization source through a system information block (SIB) message or a radio resource control (RRC) message. When delay information is not set by the base station or when the delay information set by the base station has expired, the D2D synchronization source brings built-in delay information in consideration of the transmission strength of the D2D synchronization signal. The D2D synchronization source may transmit delay information built into the terminal or set by the base station by reflecting it on the D2D synchronization channel.

According to another embodiment of the present invention, the delay information may be set through path loss calculation. The D2D synchronization source may transmit a D2D synchronization channel including information on the reference strength of the D2D synchronization signal transmitted by the D2D synchronization source (hereinafter referred to as 'reference strength information'). Since the amount of data that can be transmitted through the D2D synchronization channel is not large, the D2D synchronization source may select one of a plurality of reference strengths that may be used as reference strengths of the D2D synchronization signal. The reference strength of the D2D synchronization signal may vary depending on the situation of the D2D synchronization source transmitting the D2D synchronization signal (inside/outside the coverage of the base station, public safety, the number of receivable adjacent D2D synchronization sources, etc.). Accordingly, the reference strength of the D2D synchronization signal selectable by the D2D synchronization source may be set by the base station, or may be pre-configured or built-in. The method of setting delay information through path loss calculation is as follows.

First, the D2D synchronization source transmits a provided synchronization time reference or a synchronization time reference generated by itself. In this case, reference strength information of the D2D synchronization signal included in the D2D synchronization channel may be selected according to the transmission strength of the synchronization signal, and a default value is stored as delay information.

Thereafter, among the D2D terminals that have received the D2D synchronization signal and the D2D synchronization channel, a terminal to operate as a relay synchronization source (ie, a D2D synchronization source of a lower layer) applies the received synchronization time reference, and performs the D2D synchronization signal and the D2D synchronization. broadcast the channel. At this time, the D2D synchronization source of the lower layer transmitting the D2D synchronization signal and the D2D synchronization channel includes reference strength information included in the D2D synchronization channel received from the D2D synchronization source of the upper layer (independent synchronization source or relay synchronization source of the upper layer). It is applied to broadcast a D2D synchronization signal and a D2D synchronization channel.

The independent synchronization source receiving the D2D synchronization signal and the D2D synchronization channel from the relay synchronization source of the lower layer or the relay synchronization source of the upper layer receives the reference strength information of the received strength of the D2D synchronization signal and the D2D synchronization signal provided through the D2D synchronization channel. By calculating the path loss based on the background, delay information can be set. Thereafter, the independent synchronization source or the relay synchronization source of the upper layer reflects the set delay information to the D2D synchronization channel, and transmits the D2D synchronization signal and the D2D synchronization channel.

A synchronization source of a lower layer that has received a D2D synchronization channel including delay information from an independent synchronization source or a relay synchronization source of an upper layer may adjust the synchronization time reference by reflecting the delay information.

According to another embodiment of the present invention, the delay information may be set through a hand-shake method. In the handshake method, one or a plurality of D2D synchronization sources to which a synchronization time reference is provided from the same D2D independent synchronization source directly or through a relay synchronization source and the reference is applied operates in the same group, and each D2D synchronization source has its own You can check the group it belongs to. For example, a D2D synchronization source having the same synchronization time reference uses the same D2D synchronization signal, uses a grouped D2D synchronization signal, or checks a group to which it belongs through a group identifier included in a D2D synchronization channel. can A D2D synchronization source of an upper layer according to an embodiment of the present invention measures a round-trip delay (RTD) by transmitting and receiving a D2D synchronization signal and a D2D synchronization channel with a D2D synchronization source of a lower layer, and the measured round trip Delay information can be configured based on the delay. The method of configuring delay information through handshake may be applied according to a predetermined period, and in this application period, a measurement period for the D2D synchronization signal of the D2D terminal and power consumption of the D2D terminal may be considered.

According to another embodiment of the present invention, a method of configuring delay information through a handshake between terminals when the same D2D synchronization signal is used will be described.

First, the D2D synchronization source broadcasts a provided synchronization time reference or a self-generated synchronization time reference. In this case, delay information included in the D2D synchronization channel may be set as an initial value.

Among the D2D terminals that have received the D2D synchronization signal and the D2D synchronization channel, the terminal to operate as the relay synchronization source (ie, the D2D synchronization source of the lower layer) applies the received synchronization time reference and the same signal as the received D2D synchronization signal. (ie the same sequence). Then, the relay synchronization source broadcasts the selected D2D synchronization signal and the D2D synchronization channel. In this case, the D2D synchronization signal and the D2D synchronization channel may be transmitted through at least one resource pool as described above.

The D2D synchronization source of the upper layer decodes the D2D synchronization signal of the D2D synchronization source of the lower layer by searching for the D2D synchronization signal received from the adjacent D2D synchronization source and the D2D synchronization signal provided from the D2D synchronization source of the lower layer among the D2D synchronization channels, , it is possible to obtain a synchronous time reference. In addition, the D2D synchronization source of the upper layer may calculate a round-trip time delay based on the obtained synchronization time reference, and reflect the calculated round-trip time delay in delay information to be included in its own D2D synchronization channel. In this case, when the upper layer D2D synchronization source receives D2D synchronization signals from a plurality of lower layer D2D synchronization sources and calculates a plurality of round trip time delays, the upper layer D2D synchronization source calculates an average value of the plurality of round trip time delays and the average value of the round trip time delay may be reflected in the D2D synchronization channel.

Thereafter, the D2D synchronization source of the lower layer receiving the D2D synchronization signal and the D2D synchronization channel from the D2D synchronization source of the upper layer may adjust the synchronization time reference based on the delay information in which the round trip time delay is reflected.

According to another embodiment of the present invention, delay information is configured through handshake between terminals when a D2D synchronization signal is used for each group or group-related information (eg, group index, etc.) is included in the D2D synchronization channel. explain how.

When the D2D synchronization signal is divided into groups, one group includes a part of sequences usable as the D2D synchronization signal. Accordingly, the terminal receiving the D2D synchronization signal can know to which group the corresponding synchronization reference belongs to the sequence of the D2D synchronization signal. When each group is not distinguished by a D2D synchronization signal, the D2D synchronization source includes information about the group (eg, group index) in the D2D synchronization channel and provides information on which group the synchronization criterion belongs to. .

First, the D2D synchronization source transmits a provided synchronization time reference or a synchronization time reference generated by itself. In this case, delay information included in the D2D synchronization channel may be set as an initial value.

Among the D2D terminals receiving the D2D synchronization signal or the D2D synchronization channel transmitted from another D2D synchronization source, the terminal to operate as the relay synchronization source (ie, the D2D synchronization source of the lower layer) applies the received synchronization time reference. And when the D2D synchronization source of the lower layer uses the D2D synchronization signal divided by groups, one of the sequences available as the D2D synchronization signal in the corresponding group is selected as the synchronization signal, and the group index included in the D2D synchronization channel is used as the synchronization signal. In case of classification, the corresponding group index is included in the D2D synchronization channel. In this case, the D2D synchronization signal and the D2D synchronization channel may be transmitted through at least one resource pool as described above.

The D2D synchronization source of the upper layer may decode the D2D synchronization signal received from the adjacent D2D synchronization source and the D2D synchronization signal provided by the D2D synchronization source of the lower layer among the D2D synchronization channels to obtain a synchronization time reference. Then, the D2D synchronization source of the upper layer calculates a round-trip time delay based on the obtained synchronization time reference, and reflects the calculated round-trip time delay in delay information included in the D2D synchronization channel. At this time, when the upper layer D2D synchronization source receives D2D synchronization signals from a plurality of lower layer D2D synchronization sources and calculates a plurality of round trip time delays, the upper layer D2D synchronization source delays the average value of the plurality of round trip time delays information can be reflected.

Thereafter, the D2D synchronization source of the lower layer receiving the D2D synchronization signal and the D2D synchronization channel from the D2D synchronization source of the upper layer may adjust the synchronization time reference based on delay information included in the D2D synchronization channel.

Referring to FIG. 5 , first, a D2D synchronization source 510 of an upper layer broadcasts a D2D synchronization signal ( S501 ). The relay synchronization sources 521 and 522 that have received the D2D synchronization signal from the D2D synchronization source 510 of the upper layer determine the synchronization time reference (or reference timing) of the D2D synchronization source 510 of the upper layer. Derives (S502), generates a D2D synchronization signal based on the estimated reference timing, and broadcasts the generated D2D synchronization signal (S503).

Upon receiving the D2D synchronization signal broadcast from the D2D synchronization sources 521 and 522 of the lower layer, the D2D synchronization source 510 of the upper layer estimates the average RTD of the round trip delay (S504), and the average The D2D synchronization channel is transmitted by including the delay information configured based on the round trip delay in the D2D synchronization channel (S505).

The D2D synchronization sources 521 and 522 of the lower layer that have received the D2D synchronization channel from the D2D synchronization source 510 of the upper layer may modify the synchronization time reference based on delay information of the D2D synchronization channel ( S506).

6 is a flowchart illustrating a synchronization signal transmission method according to another embodiment of the present invention.

Referring to FIG. 6 , the D2D synchronization source may estimate the delay based on the reception strength of the D2D synchronization signal, and the synchronization time reference may be adjusted based on the estimated delay time length. That is, when the D2D synchronization source 610 of the upper layer transmits the D2D synchronization signal (S601), the D2D synchronization sources 621 and 622 of the lower layer estimate the propagation delay based on the reception strength of the received D2D synchronization signal. , it is possible to adjust the synchronization time reference provided through the D2D synchronization signal based on the estimated propagation delay ( S602 ).

In this case, the propagation delay may be estimated based on the strength of the received signal and a table in which propagation delay values according to the strength of the received signal are described, or the propagation delay may be estimated from the strength of the received signal through a predetermined algorithm.

According to an embodiment of the present invention, in order to more precisely estimate the propagation delay, the D2D synchronization source may include reference strength information of the D2D synchronization signal transmitted by the D2D synchronization source in the D2D synchronization channel. In this case, since the amount of data that can be transmitted through the D2D synchronization channel is not large, the D2D synchronization source may transmit the D2D synchronization signal by selecting one of a plurality of reference strength options. The strength of the D2D synchronization signal may vary depending on the situation of the D2D synchronization source that transmits the D2D synchronization signal (inside/outside the coverage of the base station, public safety, the number of receivable adjacent D2D synchronization sources, etc.). Accordingly, a plurality of reference strength options that can be selected by the D2D synchronization source may be set by the base station or may be pre-configured in advance. The D2D receiving terminal (or relay synchronization source) that has received the D2D synchronization channel including the reference strength information and the D2D synchronization signal transmitted with the reference strength compares the reception strength of the D2D synchronization signal with the reference strength information included in the D2D synchronization channel. Thus, the path loss can be calculated, and a time error due to propagation delay can be estimated based on the calculated path loss value. In addition, the D2D receiving terminal (or relay synchronization source) that has received the D2D synchronization signal may adjust the synchronization time reference based on the estimated time error.

On the other hand, when the strength of the D2D synchronization signal is preset by the base station or the like to be transmitted at a predetermined strength regardless of the situation of the D2D group, etc. (ie, the D2D synchronization source and the receiving D2D terminal know the predetermined strength), the D2D synchronization channel In , a bit for reference strength information of the D2D synchronization signal may not be used, and this bit may be used to additionally provide other information.

Thereafter, the lower layer D2D synchronization sources 621 and 622 may broadcast the D2D synchronization signal to provide the adjusted synchronization time reference to the adjacent D2D terminal ( S603 ).

In an embodiment of the present invention, the delay information included in the D2D synchronization channel includes the propagation delay accumulated in the D2D terminal or the relay synchronization source when the D2D synchronization source provides the synchronization time reference through the D2D synchronization signal and the D2D synchronization channel. Due to this, it is possible to prevent a synchronization time error from occurring, and to prevent interference or collisions such as inter-symbol interference (ISI) and inter-carrier interference (ICI) due to the time error. In this case, it is more effective to apply the delay information to a D2D terminal or relay synchronization source located far from the D2D synchronization source enough to cause a propagation delay of a sufficient length, rather than being applied to a D2D terminal or relay synchronization source close to the D2D synchronization source. can And, so that the delay information according to an embodiment of the present invention can be effectively used, the D2D synchronization source provides D2D additional information (hereinafter referred to as 'additional information') for determining whether to use the delay information together with the delay information. It can be transmitted through a sync channel.

In an embodiment of the present invention, the additional information may provide a criterion for determining whether to use the delay information based on the reception strength of the D2D synchronization signal provided by the D2D synchronization source. That is, as additional information, the D2D synchronization source may transmit the signal strength from the perspective of the D2D receiving terminal through the D2D synchronization channel. If the signal strength information from the D2D receiving terminal's point of view is the received signal strength information Y (in dB or dBm), the D2D receiving terminal or the relay synchronization source is a D2D synchronization channel when the reception strength of the received D2D synchronization signal is less than Y. The synchronization time reference can be adjusted by using the delay information included in the . In this case, the received signal strength information Y may be set in consideration of the transmission strength of the D2D synchronization signal transmitted from the D2D synchronization source, whether a normal CP or an extended CP is used, whether an adjacent D2D synchronization source exists, and the like.

According to an embodiment of the present invention, additional information may be used in a D2D synchronization source of a lower layer or a D2D terminal as follows. First, a D2D synchronization source of a higher layer transmits delay information and additional information through a D2D synchronization channel in consideration of a transmission strength of a D2D synchronization signal to be transmitted, a length of a CP, and the like. The D2D synchronization source of the lower layer that has received the D2D synchronization channel compares the received strength of the received D2D synchronization signal with the signal strength provided through the additional information. If the reception strength of the received D2D synchronization signal is smaller than the signal strength provided through the additional information, the D2D synchronization source of the lower layer may adjust its synchronization time reference by applying the provided delay information.

7 is a conceptual diagram illustrating a negotiation method between synchronization sources according to an embodiment of the present invention, and FIG. 8 is a flowchart illustrating a negotiation method between synchronization sources according to an embodiment of the present invention.

In the synchronization procedure of the D2D terminal using the hierarchical structure, since a plurality of different independent synchronization sources may exist, different synchronization time references may be provided to one D2D terminal. When there are a plurality of different synchronization time references by a plurality of independent synchronization sources, battery consumption and computational complexity of the D2D terminal tracking synchronization may increase, and synchronization performance may also decrease in terms of the entire D2D network. Accordingly, in order to synchronize the D2D terminals using the hierarchical structure, each independent synchronization source needs to negotiate with each other in order to reduce the number of independent synchronization sources.

In one embodiment of the present invention, one independent synchronization source is an adjacent independent synchronization source or a relay synchronization source having a hierarchical level of 1 (that is, a D2D synchronization signal and synchronization in which the independent synchronization source directly broadcasts the synchronization time reference of the independent synchronization source) Upon receiving the D2D synchronization signal and the D2D synchronization channel from the synchronization source provided through the channel), each independent synchronization source may reduce the number of independent synchronization sources by maintaining or giving up its role as a synchronization source. In this case, appropriate negotiation information may be provided to each independent synchronization source for negotiation. An independent synchronization source or a relay synchronization source having a hierarchical level of 1 according to an embodiment of the present invention provides information for negotiation between synchronization sources (hereinafter referred to as 'negotiation information') to an adjacent D2D synchronization source through a D2D synchronization channel can do.

Negotiation information may be established through the following two methods. First, according to the first method, when one D2D terminal selects a role as an independent synchronization source, the D2D terminal may arbitrarily select a negotiation number for negotiation between independent synchronization sources. In this case, the negotiation constant may be determined as a bit string of a predetermined length. An independent synchronization source that has selected the negotiation constant may include the negotiation constant in its D2D synchronization channel.

According to the following second method, a time stamp indicating a time when the independent synchronization source operates as the independent synchronization source may be transmitted through the D2D synchronization channel. In this case, the time stamp information may be an integer increasing according to a predetermined time interval or an integer indicating a time at which an independent synchronization source starts to operate.

Thereafter, the D2D synchronization source of the lower layer receiving the negotiation information from the independent synchronization source transmits the negotiation information through a D2D synchronization signal or a D2D synchronization channel. Accordingly, the independent synchronization source may receive negotiation information by receiving the D2D synchronization signal and the D2D synchronization channel when an independent synchronization source or a relay synchronization source having a hierarchical level of 1 is located in an adjacent area. Referring to FIG. 7 , UE4, which was operating as an independent synchronization source, changed its role to a relay synchronization source after negotiation.

Referring to FIG. 8 , first, an independent synchronization source according to an embodiment of the present invention searches for a D2D synchronization signal and a D2D synchronization channel provided from an adjacent D2D synchronization source (S801). Then, the independent synchronization source determines whether the D2D synchronization source broadcasting the D2D synchronization signal and the D2D synchronization channel is an independent synchronization source or a relay synchronization source having a hierarchical level of 1 (S802). For example, the independent synchronization source may know the hierarchical level of the D2D synchronization source broadcasting the D2D synchronization channel through information about the hierarchical level included in the D2D synchronization channel. If the D2D sync source broadcasting the received D2D sync signal and D2D sync channel is not an independent sync source or a relay sync source with hierarchical level 1 (i.e., hierarchical level 2 or higher), the independent sync source acts as an independent sync source. maintain (S803).

However, if the D2D synchronization source broadcasting the D2D synchronization signal and the D2D synchronization channel is an independent synchronization source or a relay synchronization source with a hierarchical level of 1 (that is, the hierarchical level of the D2D synchronization channel is 0 or 1), the independent synchronization source is a D2D synchronization source The negotiation constant or time stamp included in the channel is compared with its own negotiation constant or time stamp (S804). As a result of comparison, if the priority of its own negotiation constant is higher than or equal to the priority of the negotiation constant of an adjacent D2D synchronization source, the independent synchronization source maintains its role as the independent synchronization source. Alternatively, as a result of comparison, if the time indicated in its own time stamp is relatively older than the time indicated in the time stamp provided to the D2D synchronization channel of the adjacent D2D synchronization source, the independent synchronization source maintains its role as the independent synchronization source.

However, if the priority of its negotiated integer or timestamp is lower than that of the adjacent D2D synchronization source, the independent synchronization source gives up the role of the independent synchronization source (ie, stops operating as an independent synchronization source), and the adjacent D2D synchronization source Synchronizes itself to the synchronization time reference of (that is, serves as a relay synchronization source) (S805). Thereafter, the D2D synchronization source, which has given up the role of the independent synchronization source, increases the hierarchical level by one, and broadcasts the D2D synchronization signal and the D2D synchronization channel based on the modified synchronization time reference ( S806 ).

As described above, according to an embodiment of the present invention, a D2D terminal may perform synchronization with an adjacent D2D terminal through a hierarchical structure outside the coverage area of the base station without the control of the base station. In this case, the D2D terminal according to an embodiment of the present invention can avoid signal collision or signal interference due to propagation delay by adjusting the synchronization time reference. In addition, in the case of an independent synchronization source, the D2D terminal appropriately adjusts the number of independent synchronization sources through negotiation with other synchronization sources, thereby solving the problems of battery consumption and increased computational complexity of the D2D terminal.

9 is a block diagram illustrating a wireless communication system according to an embodiment of the present invention.

Referring to FIG. 9 , a wireless communication system according to an embodiment of the present invention includes a transmitting terminal 910 and a receiving terminal 920 .

The transmitting terminal 910 includes a processor 911 , a memory 912 , and a radio frequency unit (RF unit) 913 . The memory 912 may be connected to the processor 911 to store various information for driving the processor 911 . The wireless communication unit 913 may be connected to the processor 911 to transmit and receive wireless signals. The processor 911 may implement a function, process, or method proposed in an embodiment of the present invention. In this case, in the wireless communication system according to an embodiment of the present invention, the air interface protocol layer may be implemented by the processor 911 . The operation of the transmitting terminal 910 according to an embodiment of the present invention may be implemented by the processor 911 .

The reception terminal 920 includes a processor 921 , a memory 922 , and a wireless communication unit 923 . The memory 922 may be connected to the processor 921 to store various information for driving the process 921 . The wireless communication unit 923 may be connected to the processor 921 to transmit and receive wireless signals. The processor 921 may implement a function, step, or method proposed in an embodiment of the present invention. In this case, in the wireless communication system according to an embodiment of the present invention, the air interface protocol layer may be implemented by the processor 921 . The operation of the receiving terminal 920 according to an embodiment of the present invention may be implemented by the processor 921 .

In an embodiment of the present invention, the memory may be located inside or outside the processor, and the memory may be connected to the processor through various known means. The memory is various types of volatile or non-volatile storage media, and for example, the memory may include a read-only memory (ROM) or a random access memory (RAM).

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improved forms of the present invention are also provided by those skilled in the art using the basic concept of the present invention as defined in the following claims. is within the scope of the right.

Claims (18)

delete delete delete delete delete delete delete delete delete A synchronization source negotiation method of an independent synchronization source included in a device to device (D2D) communication network, the method comprising:
When receiving a D2D synchronization signal and a D2D synchronization channel from at least one D2D synchronization source, determining whether to maintain the role as an independent synchronization source based on negotiation information for negotiation between synchronization sources included in the D2D synchronization channel; And
operating as a relay synchronization source when not maintaining its role as the independent synchronization source
including,
The negotiation information is
a timestamp indicating the time the independent synchronization source operated as an independent synchronization source;
The determining step is
comparing a timestamp of the independent synchronization source with a timestamp of the at least one D2D synchronization source; and
determining whether to maintain the role as the independent synchronization source based on the comparison result
A synchronous source negotiation method comprising: delete delete delete delete In claim 10,
increasing the hierarchical level by 1 when not maintaining the role as the independent synchronization source;
A synchronous source negotiation method further comprising a. In claim 10,
The step of determining whether to maintain a role as an independent synchronization source based on negotiation information for negotiation between synchronization sources included in the D2D synchronization channel includes:
checking the hierarchical level of the at least one D2D synchronization source; and
determining whether to maintain the role as the independent synchronization source when the hierarchical level of the at least one D2D synchronization source is 0 or 1
A synchronous source negotiation method comprising: 17. In claim 16,
The step of determining whether to maintain a role as an independent synchronization source based on negotiation information for negotiation between synchronization sources included in the D2D synchronization channel includes:
maintaining the role as the independent synchronization source when the hierarchical level of the at least one D2D synchronization source is 2 or higher
A synchronous source negotiation method further comprising a. A synchronization source negotiation method of an independent synchronization source included in a device to device (D2D) communication network, the method comprising:
When receiving a D2D synchronization signal and a D2D synchronization channel from at least one D2D synchronization source, determining whether to maintain the role as an independent synchronization source based on negotiation information for negotiation between synchronization sources included in the D2D synchronization channel; And
operating as a relay synchronization source when not maintaining its role as the independent synchronization source
including,
The negotiation information is
a negotiation number determined when the independent synchronization source selects a role as the independent synchronization source;
The determining step is
comparing the negotiation constant of the independent synchronization source with the negotiation constant of the at least one D2D synchronization source; and
determining whether to maintain the role as the independent synchronization source based on the comparison result
A synchronous source negotiation method comprising:

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