KR20160031954A - Method and terminal for synchronization in distributed wireless communication - Google Patents

Abstract

Disclosed are a synchronization method in a distributed wireless communication system and a terminal supporting the same. In the synchronization method, the terminal divides a synchronization period into a plurality of back-off slots and randomly selects a back-off counter by using a contention window. The terminal checks if a channel is idle, during at least one of the back-off slots, and changes the back-off counter depending on whether the channel is idle.

Description

[0001] METHOD AND TERMINAL FOR SYNCHRONIZATION IN DISTRIBUTED WIRELESS COMMUNICATION [0002]

The present invention relates to a synchronization method in a distributed wireless communication system and a terminal supporting the same.

Wireless communication systems can be largely classified into synchronous and asynchronous systems.

A synchronous wireless communication system refers to a system in which terminals operate according to a common reference time. In a synchronous wireless communication system, since a certain operation is performed at a predetermined time, the efficiency of use of radio resources can be increased and a system with excellent performance can be easily designed. Also, the power consumption of the terminals can be reduced through a power save mode. For example, terminals operating in the power saving mode operate in the reception mode only for a predetermined time, and power consumption of the receiver can be reduced by turning off the power in the remaining time. A terminal that desires to transmit data to a terminal operating in a power consumption reduction mode can transmit data or transmit a control message during a predetermined reception mode time to release the power consumption reduction mode.

The synchronous wireless communication system can be further divided into a centralized synchronization method and a distributed synchronization method. A typical example of a centrally controlled synchronization method is a cellular system. In a cellular system, terminals in a cell perform synchronization based on a timing reference signal provided by a base station. The distributed synchronization method is a method in which a synchronization signal is not transmitted in a specific device but a terminal in a network participates in transmission of a synchronization signal to synchronize the terminals. This distributed synchronization method is suitable for device-to-device communications (D2D communications) networks or ad hoc networks.

The asynchronous wireless communication system means a system in which terminals perform transmission and reception operations without a predetermined reference time. In an asynchronous wireless communication system, terminals always monitor a wireless channel to receive packets of other terminals in the network. When a packet is detected during monitoring, the terminals use the preamble signal included in the packet to estimate the start point of the packet and then read the information of the packet. The asynchronous method is mainly used in a system which does not have a predetermined reference time, and is simple in implementation and does not require high resource efficiency. However, there is a disadvantage in that power consumption is large because terminals must always monitor a wireless channel.

One of the distributed synchronization methods is as follows. Each terminal periodically transmits a synchronization signal using its time synchronization (i.e., reference time). Then, each terminal receives the synchronous signal transmitted from peripheral terminals and adjusts its own time synchronization using the received synchronous signal. Thus, all terminals can have a common reference time. At this time, the synchronizing signal to be used is a pulse signal, a ZC sequence (Zadoff-Chu sequence), an am sequence (m-sequence), a chirp signal, or the like. This method assumes that terminals simultaneously receive a synchronization signal while transmitting a synchronization signal. However, in such a scheme, if the terminals are densely packed, the synchronization signals transmitted by the terminals can be received overlapping with each other, so that an error may occur in the estimation of the reception time of the synchronization signal or an estimation of the reception time may not be possible. Also, in the unlicensed frequency band, when the same radio channel is used by the neighboring heterogeneous network, the synchronization signal can not be transmitted or the transmitted synchronization signal can not be received due to interference.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a distributed synchronization method in a wireless communication system.

According to an embodiment of the present invention, a synchronization method of a first terminal in a distributed wireless communication system is provided. The method includes dividing a synchronization interval into a plurality of backoff slots, establishing a contention window, arbitrarily selecting a backoff counter using the contention window, selecting at least one of the plurality of backoff slots Checking whether the channel is idle during a backoff slot of the channel, and modifying the backoff counter depending on whether the channel is idle.

The modifying may include decreasing the backoff counter if the channel is idle, and not decreasing the backoff counter if the channel is busy.

The synchronization method may further include transmitting a synchronization signal when the backoff counter is smaller than a predetermined value.

Wherein the selecting comprises: if {0, 1, 2, ..., , CW-1} as the backoff counter.

Whether or not the channel is idle can be checked through CCA (Clean Channel Access).

The synchronization method may further include setting a first counter that is a counter different from the backoff counter, and decreasing the first counter if the channel is idle.

The synchronization method may further include updating (updating) the contention window if the first counter is smaller than a predetermined value.

The synchronization method may further include updating the contention window if the channel is idle for a predetermined time after transmitting the synchronization signal.

The changing step may include not decreasing the backoff counter when the channel determines that the synchronization signal transmission can not be completed for the remaining period of the idle period or the synchronization period.

Wherein the setting of the contention window comprises calculating an average reception time difference between the first synchronization signals received by the first terminal and calculating an average reception time difference between the first terminal and the other terminals Calculating a contention window, and setting the contention window using the average reception time difference and the average contention window.

The synchronization method may further include adjusting the synchronization timer using the first synchronization signal when the first terminal receives the first synchronization signal from the second terminal.

The step of adjusting the synchronization timer may include the step of, when the phase of the synchronization timer is between the first value and the second value, changing to a predetermined constant value regardless of the first synchronization signal.

The first synchronization signal may include a backoff indicator indicating a frame start time of the first terminal, and the step of adjusting the synchronization timer may include: using a phase value of the synchronization timer corresponding to the backoff indicator And adjusting the phase value of the synchronization timer.

According to another embodiment of the present invention, a method for synchronizing a first terminal in a distributed wireless communication system is provided. The synchronization method includes receiving first synchronization signals from second terminals that are terminals different from the first terminal, calculating an average reception time difference between the synchronization signals, using the first synchronization signals, Setting a first contention window, which is a contention window of the first terminal, using the average reception time difference and the average contention window, calculating an average contention window for the second terminals, And determining whether to transmit the synchronization signal in response to the contention window.

The method of claim 1, wherein the determining comprises: selecting a backoff counter using the first contention window; during a backoff slot where a synchronization interval is divided into a plurality of intervals, if the channel is idle, And if the backoff counter is zero, transmitting the synchronization signal.

Wherein the synchronization method comprises: setting a predetermined value of the backoff counter after transmitting the synchronization signal; and updating the first contention window when the set backoff counter is zero (Updating) the data.

According to another embodiment of the present invention, a terminal is provided. The terminal includes an RF module for performing transmission and reception of a synchronization signal and a synchronization section for dividing a synchronization section into a plurality of backoff slots and arbitrarily selecting a backoff counter using a contention window, And decreasing the backoff counter if the channel is idle during an off-slot.

The processor may transmit the synchronization signal if the backoff counter is zero.

The processor may set the backoff counter to a predetermined value after transmitting the synchronization signal, and may update the contention window if the set backoff counter is zero.

The processor calculates an average reception time difference between the received synchronization signals, calculates an average contention window for the terminal and the other terminals using the received synchronization signals, and uses the average reception time difference and the average contention window Thereby setting the contention window.

According to an embodiment of the present invention, synchronization can be obtained in a distributed manner while reducing signaling overhead between terminals.

According to another embodiment of the present invention, a network can be configured in a distributed synchronous manner in a multi-hop wireless environment as well as a single-hop wireless environment.

According to another embodiment of the present invention, a terminal is synchronized with a peripheral terminal, thereby improving efficiency of radio resource use, reducing power consumption through a sleep mode, and improving network performance.

)의 관계를 나타내는 도면이다.
도 18은 본 발명의 실시예에 따른 단말이 동기 신호를 송수신하면서 동기를 맞추는 방법을 나타내는 도면이다.
도 19는 본 발명의 실시예에 따른 동기 타이머 갱신 방법을 나타내는 도면이다.
도 20은 본 발명의 다른 실시예에 따른 동기 타이머 갱신 방법을 나타내는 도면이다.
도 21은 본 발명의 실시예에 따른, 랜덤 백오프로 인해 동기 신호가 프레임의 시작 시점으로부터 시간 지연이 되는 경우, 동기 타이머의 위상을 갱신하는 방법을 나타내는 도면이다.
도 22는 본 발명의 실시예에 따른 초기 동기화 절차를 나타낸다.
도 23은 본 발명의 실시예에 따른 단말을 나타내는 도면이다. 1 is a diagram illustrating time resources according to an embodiment of the present invention.
FIG. 2 shows a case where three terminals (terminal A, terminal B, and terminal C) are out of synchronization with each other. FIG. 3 shows a case where three terminals Fig.
4 is a flowchart illustrating a synchronization method according to an embodiment of the present invention.
5 is a diagram illustrating a configuration of a sync signal according to an embodiment of the present invention.
6 is a diagram illustrating a structure of a synchronization section 110 according to an embodiment of the present invention.
7 is a diagram showing an example of a position at which a synchronization signal is transmitted.
8 is a diagram showing a case where transmission of a synchronization signal is not completed within a synchronization section.
9A and 9B are flowcharts showing a random access method according to an embodiment of the present invention.
10 is a flowchart showing a random access method according to another embodiment of the present invention.
11 is a flowchart showing the case where T = 0 in the random access method of FIG.
FIG. 12 is a flowchart showing a case where T = 0 in the random access method of FIG.
13 is a diagram showing transmission of a synchronization signal on the time axis when the random access scheme of FIG. 9 is applied.
FIG. 14 is a diagram showing transmission of a synchronous signal on the time axis when the random access scheme of FIG. 11 is applied.
FIG. 15 is a diagram showing transmission of a synchronization signal on the time axis when the random access scheme of FIG. 12 is applied.
FIG. 16 is a diagram showing that when the random access scheme of FIG. 12 is used, the terminal A transmits the synchronization signal while performing the CCA at the discontinuity of the synchronization interval.
FIG. 17 shows the phase of the frame and the synchronous timer

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FIG. 18 is a diagram illustrating a method of synchronizing a terminal while transmitting and receiving a synchronization signal according to an embodiment of the present invention.
19 is a diagram illustrating a synchronization timer update method according to an embodiment of the present invention.
20 is a diagram illustrating a synchronization timer update method according to another embodiment of the present invention.
21 is a diagram illustrating a method of updating the phase of a synchronization timer when a synchronization signal is delayed from a start time of a frame due to a random backoff signal according to an embodiment of the present invention.
22 shows an initial synchronization procedure according to an embodiment of the present invention.
23 is a diagram illustrating a terminal according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Throughout the specification, a terminal is referred to as a mobile terminal (MT), a mobile station (MS), an advanced mobile station (AMS), a high reliability mobile station ), A subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), a user equipment (UE) AMS, HR-MS, SS, PSS, AT, UE, and the like.

Also, a base station (BS) is an advanced base station (ABS), a high reliability base station (HR-BS), a node B, an evolved node B, eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR) BS, RS, HR, RS, etc.) may be referred to as a high reliability relay station (HR-RS) -RS, and the like.

Now, a method of synchronizing (i.e., a distributed synchronization method) in a distributed communication system according to an embodiment of the present invention and a terminal supporting the method will be described in detail. Hereinafter, a distributed wireless communication system environment will be described on the assumption that a distributed wireless communication system environment is present, and a detailed description of the distributed wireless communication system will be omitted if it is known to those skilled in the art. The distributed synchronization method described below will be described based on the operation of the terminal.

1 is a diagram illustrating time resources according to an embodiment of the present invention.

As shown in FIG. 1, a time resource according to an embodiment of the present invention includes a frame 100 that is periodically repeated. In Fig. 1, it is assumed that the length of the frame 100 is predetermined.

The frame 100 is subdivided into a plurality of intervals, and in FIG. 1, only a synchronization period 110 is shown among a plurality of intervals. That is, FIG. 1 shows that the time resources are divided into the frames 100, and the frame 100 is further divided into the synchronization period 110 and the remaining intervals 120. The remaining slots 110 may be divided into a data interval, a search interval, and the like, but they are not shown in FIG. 1 for the sake of convenience. The synchronization interval 110 may be located anywhere in the frame, and for convenience, the synchronization interval 110 is shown at the beginning of the frame in FIG. A guard period may be located between the sections constituting the frame 100.

The synchronization period 110 is a period during which terminals transmit a synchronization signal. The UEs can know the positions of the start and end of the frame using the sync signal received in the sync period 110. [

FIG. 2 shows a case where three terminals (terminal A, terminal B, and terminal C) are out of synchronization with each other. FIG. 3 shows a case where three terminals Fig.

As shown in FIG. 2, the start times of the frames of the terminals A, B, and C do not coincide with each other.

The purpose of synchronization is to synchronize the terminals synchronized with each other. If the two terminals' frames start at the same time, the two terminals are said to be "in sync." In a situation where a plurality of terminals exist in a predetermined network, when a plurality of terminals in the network are synchronized, the network is said to be "synchronous ".

As shown in FIG. 3, the start times of the frames of the terminals A, B, and C coincide with each other. In an actual network, it may not be possible to accurately synchronize the terminals. Therefore, even if the difference between the start points of the frames is smaller than the error range, the synchronization is correct.

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

4, the synchronization method according to an embodiment of the present invention includes an initial synchronization procedure S410, a synchronization and maintenance procedure S430, and a re-synchronization procedure S430. ).

A terminal that is not synchronized synchronizes with the initial synchronization procedure (S410). For example, when the terminal is powered on, the terminal synchronizes with the initialization synchronization procedure. A terminal successfully performing initial synchronization performs a synchronization maintenance and management procedure (S420). If it is determined that the terminal that has performed the synchronization maintenance and management procedure has lost synchronization, the mobile terminal performs a resynchronization procedure (S430) or performs an initial synchronization procedure (S410).

The initial synchronization procedure (S410), the synchronization maintenance and management procedure (S420), and the resynchronization procedure (S430) consist of a combination of three operations: transmission of a synchronization signal, reception of a synchronization signal, and update of synchronization time.

Meanwhile, a timing reference signal is a signal transmitted by the UEs to synchronize with each other.

5 is a diagram illustrating a configuration of a sync signal according to an embodiment of the present invention.

As shown in FIG. 5, the sync signal according to the embodiment of the present invention includes a preamble field, a backoff indicator field, and a contention window (CW) indicator field. Where the contention window indicator field is an optional field. On the other hand, the synchronization signal may include fields other than those shown in FIG.

The preamble field may be used for detection of a synchronization signal, automatic gain control (AGC) of a reception unit, estimation of a reception time of a synchronization signal, and estimation of a wireless channel when the synchronization signal arrives at the reception unit of the terminal. This preamble is located at the front of the synchronization signal.

The back off indicator field indicates a difference between a start point of the synchronization section 110 and a time point at which the synchronization signal is transmitted. As shown in FIG. 1, when the synchronization section 110 is positioned at the front of the frame 100, the start point of the synchronization section is the same as the start point of the frame. On the other hand, the backoff indicator field is located after the preamble field.

The terminals do not transmit the synchronization signal in the synchronization period of all the frames. If all terminals transmit a synchronization signal in the synchronization interval of every frame, there may be a conflict between the synchronization signals because there are too many synchronization signals transmitted in the synchronization interval in the dense region of the terminal. Accordingly, when the terminals are dense, the probability that the terminals transmit the synchronous signal in the synchronization section is small, and when the terminals are not concentrated, the terminals increase the probability of transmitting the synchronous signal in the synchronization section, . The Contention Window (CW) indicator field contains the contention window value of the terminal that transmitted the synchronization signal. For example, a method similar to CSMA / CA (carrier sense multiple access with collision avoidance) used in DCF (Distributed Coordination Function) of IEEE 802.11 can be used as a method for determining a synchronization signal transmission probability of a UE. If such a method is used, the contention window indicator field may contain a contention window size value. On the other hand, the synchronization signal may not include the contention window indicator field. If there is a contention window field, the contention window indicator field is located after the preamble field. And the contention window indicator field may be located before or behind the backoff indicator field.

6 is a diagram illustrating a structure of a synchronization section 110 according to an embodiment of the present invention.

As shown in FIG. 6, the synchronization interval 110 according to the embodiment of the present invention includes N backoff slots (111). The size of the backoff slot may be less than or equal to the size of the synchronization signal.

In order to reduce the probability of collision with a synchronous signal transmitted from another terminal, a random access method is used for transmission of the synchronous signal. The start of transmission of the synchronization signal is performed at the beginning of the backoff slot.

7 is a diagram showing an example of a position at which a synchronization signal is transmitted.

7 shows a case where the synchronizing signal is transmitted beginning at the starting point 9 of the second back-off slot ^{(beginning of 9 th backoff slot)} . As shown in Fig. 7, the synchronization signal 112 is transmitted at the start point of the ninth backoff slot. In FIG. 7, it is assumed that the length of the synchronization signal is equal to the length of three backoff slots.

8 is a diagram showing a case where transmission of a synchronization signal is not completed within a synchronization section.

The transmission of the synchronization signal needs to be completed before the end of the synchronization period 110. [ As shown in FIG. 8, when the transmission of the synchronization signal is completed after the synchronization section 110 ends, the synchronization signal is not transmitted. On the other hand, as described below, when the synchronization signal is not transmitted because the transmission of the synchronization signal is not completed, the backoff counter is not reduced even if the corresponding backoff slot is idle.

A random access scheme is used for transmission of a synchronization signal according to an embodiment of the present invention, and a random access scheme is a contention-based random access scheme using a contention window (CW). Hereinafter, this will be described in detail.

9A and 9B are flowcharts showing a random access method according to an embodiment of the present invention. A random access scheme according to an embodiment of the present invention is a random backoff procedure using a contention window CW.

First, terminals store their own contention window size values. Here, the size of the contention window CW is initialized at the start of the random backoff procedure (S900).

The terminals select a backoff counter value based on the current contention window size (S910). For example, if the size of the contention window of the terminal is W _C , the corresponding terminal may transmit {0, 1, 2, ... , W _C -1}. When the integer n is selected, the terminal sets its back-off counter value to n.

If n = 0, the corresponding terminal transmits a synchronization signal at the next backoff slot (S920, S960). If the value of n is not zero, the following step S930 is performed.

The terminal that has transmitted the synchronization signal performs a clear channel assessment (CCA) during the next backoff slot (S961). The method for performing the CCA by the terminal will be apparent to those skilled in the art to which the present invention pertains, and a detailed description thereof will be omitted.

The terminal performs CCA and checks whether the corresponding backoff slot is idle (S962). If the corresponding backoff slot is not idle, the UE repeats the CCA during the next backoff slot (S962, S961) until the CCA result becomes idle. If the corresponding backoff slot is idle, the terminal further performs the CCA for a predetermined time T (S962, S963). Here, the predetermined time T may be T = 0 or T > 0.

If T > 0 in step S963 and the result of the CCA is not idle, step S961 is performed (steps S964 and S961). If the result of the CCA is idle or T = 0 in step S963, the terminal may decrease or not decrease the backoff counter value of its own by one (S964, S965). That is, step S965 is optional.

The MS having performed step S965 updates its own contention window size and moves to step S910 (steps S970 and S910).

On the other hand, if n > 0 in step S920, the terminal performs the CCA during the next backoff slot (S930).

If the corresponding backoff slot is idle as a result of performing the CCA in step S930, the terminal decrements the backoff counter value by one (S940, S950). The terminal moves to step S920. If the corresponding backoff slot is not idle as a result of the CCA in step S930, the terminal performs the CCA again in the next backoff slot (steps S940 and S980).

If the corresponding backoff slot is not an idle as a result of the CCA in step S980, the terminal repeats the CCA during the next backoff slot until the CCA result becomes idle (S990, S980). If the corresponding backoff slot is idle as a result of performing the CCA in step S980, the terminal further performs the CCA for a predetermined time T (S990, S992). Here, the predetermined time T may be T = 0 or T > 0.

If T > 0 in step S992 and the result of the CCA is not idle, step S980 is performed (steps S994 and S980). If the result of the CCA is idle or T = 0 in step S992, the terminal may reduce or not decrease the backoff counter value of its own by one (S994, S996). That is, step S996 is optional. The terminal having performed step S996 moves to step S920.

10 is a flowchart showing a random access method according to another embodiment of the present invention. The random access method according to another embodiment of the present invention is a procedure for improving the inter-terminal fairness as compared to FIG. In other words, in the random access method according to another embodiment of the present invention, after the UE transmits a synchronization signal, it resets its counter to Wc-n slot and updates the contention window size when the reset counter becomes zero.

The terminals store their own contention window size values. Here, the size of the contention window CW is initialized when the random backoff procedure is started (S1000).

The UEs select a backoff counter value based on the current contention window size (S1010). For example, if the size of the contention window of the terminal is W _C , the corresponding terminal may transmit {0, 1, 2, ... , W _C -1}. When the integer n is selected, the terminal sets its back-off counter value to n. And N is set to the contention window size (W _c ). Here, N is a counter for counting the number of backoffs after updating the backoff counter value to an arbitrary integer.

If n = 0, the corresponding terminal transmits a synchronization signal in the next backoff slot (S1020, S1070). If the value of n is not zero, the following step S1030 is performed.

The terminal that has transmitted the synchronization signal performs a clear channel assessment (CCA) during the next backoff slot (S1080).

The UE performs CCA and checks whether the corresponding backoff slot is idle (S1090). If the corresponding backoff slot is idle, the terminal further performs the CCA for a predetermined time T (S1090, S1092). Here, the predetermined time T may be T = 0 or T > 0. If the corresponding backoff slot is not idle, the terminal moves to step S1080.

If it is determined in step S1092 that T> 0 and the CCA result is not idle, step S1080 is performed (steps S1094 and S1080). If the result of the CCA is idle or T = 0 in step S1092, the terminal may reduce or not decrease the back-off counter value and N of the CCA respectively by one (S1094, S1096). That is, step S1096 is optional.

If N = 0, the UE updates the size of its contention window, and then moves to step S1010 (S1060, S1062). If the value of N is not 0, the process moves to step S1020 (S1060, S1020).

If n > 0 in step S1020, the UE performs the CCA during the next backoff slot (S1030).

If the corresponding backoff slot is idle as a result of performing the CCA in step S1020, the terminal decrements the backoff counter value and the N value by one (S1040, S1050). Then, the terminal moves to step S1060. If the corresponding backoff slot is not idle as a result of performing the CCA in step S1030, the terminal moves to step S1080.

11 is a flowchart showing the case where T = 0 in the random access method of FIG. That is, FIG. 11 is a simplified flow chart, using T = 0 and optional steps S965 and S996 in FIG. Therefore, the random access method of FIG. 11 is the same as that of FIG. 9, and a detailed description thereof will be omitted.

FIG. 12 is a flowchart showing a case where T = 0 in the random access method of FIG. That is, FIG. 12 is a simplified flow chart, using T = 0 and optional step S1096 in FIG. Therefore, the random access scheme of FIG. 12 is the same as that of FIG. 10, and a detailed description thereof will be omitted.

13 is a diagram showing transmission of a synchronization signal on the time axis when the random access scheme of FIG. 9 is applied. More specifically, FIG. 13 illustrates a case where T is equal to the length of one backoff slot in the random access scheme of FIG. 9, and the optional steps S965 and S996 are not used, the synchronization signals of terminals A, B, The transmission is represented by a time axis. In Fig. 13, it is assumed that the length of the synchronization signal is twice the backoff slot.

At time t _1, it is assumed that terminals A, B, C have a backoff counter value is 9, 7, 3, respectively.

At time t _2, the backoff counter value of the terminal C, and a zero (zero), the terminal C starts the transmission of the synchronization signal. At this time, the backoff counter values of terminals A and B are 6 and 4, respectively. That is, since the back-off slot is idle between t ₁ and t _2, Fig. 9 by the S920, S930, S940, S950, terminal backoff counter value of A, B, C is reduced gradually.

At time t _3, the terminal C is completed, the synchronization signal transmitted.

In (a back-off slot + T) the time after the time t ₄ for the terminal C is randomly determined back-off counter value. In FIG. 13, it is assumed that the terminal C sets the back-off counter value to 8. That is, the terminal C updates the back-off counter value to 8 in steps S961, S962, S963, S964, S970, and S910 in Fig. At this time, the terminal A and the terminal B maintain the backoff counter values at 6 and 4 respectively by the steps S980, S990, S992, and S994 of FIG.

At time t ₅ , the backoff counter value of the terminal B becomes zero, and the terminal B starts transmission of the synchronization signal.

At time t _6, as determined 4 backoff counter value is randomly selected B terminal. At this time, the backoff counter values of terminal A and terminal C are 2 and 4, respectively.

At time t _7, it is that this back-off counter value of the terminal A zero (zero), and the terminal A starts the transmission of the synchronization signal.

And the time at t _8, 8 as the determined backoff counter value is randomly selected A terminal. At this time, the backoff counter values of the terminal B and the terminal C are 2 and 2, respectively.

At time t _9, all of the back-off counter value of the terminal B and the terminal C becomes zero (zero), the terminal B and the terminal C is at the same time start the transmission of the synchronization signal. That is, the synchronization signals of the terminal B and the terminal C collide with each other.

At time t ₁₀ , terminal B sets 5 as a backoff counter value arbitrarily selected, and terminal C sets 0 as a backoff counter value arbitrarily selected. At this time, since the backoff counter value of the terminal C is zero, the terminal C starts transmission of the synchronization signal at time t ₁₀ . The terminal B does not idle the CCA result by the synchronization signal of the terminal C, and thus does not decrease the backoff counter value.

And the time t _11, the terminal C is a random backoff counter value is determined to select the nine. At this time, the backoff counter values of terminal A and terminal B are 6 and 5, respectively.

FIG. 14 is a diagram showing transmission of a synchronous signal on the time axis when the random access scheme of FIG. 11 is applied. That is, FIG. 14 shows the synchronization signal transmission of the terminals A, B and C on the time axis when T = 0 in the random access method of FIG. 9 and optional steps of S965 and S996 are used. In Fig. 14, the length of the synchronization signal is assumed to be twice the backoff slot.

At time t _1, it is assumed that terminals A, B, C have a backoff counter value is 9, 7, 3, respectively.

At time t _2, the backoff counter value of the terminal C, and a zero (zero), the terminal C starts the transmission of the synchronization signal. At this time, the backoff counter values of terminals A and B are 6 and 4, respectively. That is, t ₁ and so back-off slot is idle between t _2, by the S1120, S1130, S1140, S1150 in Fig. 11, the terminal backoff counter value of A, B, C is reduced gradually.

At time t _3, the terminal C is completed, the synchronization signal transmitted.

Since T = 0, at time t ₄ after a time corresponding to one backoff slot, the terminal C arbitrarily selects the backoff counter value. In FIG. 14, it is assumed that the terminal C sets the backoff counter value to 8. That is, the terminal C arbitrarily selects the backoff counter value from 8 by steps S11611, S1162, S1165, S1170, and S1110 in Fig. At this time, the terminal A and the terminal B decrease the backoff counter values to 5 and 3 respectively by the steps S1120, S1130, S1140, and S1150 in FIG.

At time t ₅ , the backoff counter value of the terminal B becomes zero, and the terminal B starts transmission of the synchronization signal.

At time t _6, as determined 4 backoff counter value is randomly selected B terminal. At this time, the backoff counter values of terminal A and terminal C are decreased to 1 and 4, respectively.

At time t _7, it is that this back-off counter value of the terminal A zero (zero), and the terminal A starts the transmission of the synchronization signal.

And the time at t _8, 8 as the determined backoff counter value is randomly selected A terminal. At this time, the backoff counter values of the terminal B and the terminal C are reduced to 2 and 2, respectively.

At time t _9, all of the back-off counter value of the terminal B and the terminal C becomes zero (zero), the terminal B and the terminal C is at the same time start the transmission of the synchronization signal. That is, the synchronization signals of the terminal B and the terminal C collide with each other.

At time t ₁₀ , terminal B sets 6 as a backoff counter value arbitrarily selected, and terminal C sets 0 as a backoff counter value arbitrarily selected. At this time, since the backoff counter value of the terminal C is zero, the terminal C starts transmission of the synchronization signal at time t ₁₀ . Then, the terminal B detects that the CCA result is not idle by the synchronization signal of the terminal C

At time t ₁₁ , the terminal C sets 9 as the arbitrarily selected backoff counter value. At this time, the backoff counter values of terminal A and terminal B are reduced to 4 and 3, respectively.

At time t _12, the backoff counter value of the terminal A is zero (zero), the terminal A starts the transmission of the synchronization signal.

At time t ₁₃ , terminal A sets 7 as the arbitrarily selected backoff counter value. At this time, the backoff counter values of the terminal B and the terminal C are decreased to 0 and 4, respectively. Since the backoff counter value of the terminal B is zero, the terminal B starts transmission of the synchronization signal at t ₁₃ .

FIG. 15 is a diagram showing transmission of a synchronization signal on the time axis when the random access scheme of FIG. 12 is applied. That is, FIG. 15 shows the synchronization signal transmission of the terminals A, B, and C on the time axis when T = 0 and the optional step S1096 is used in the random access method of FIG. In FIG. 15, it is assumed that the length of the synchronization signal is twice the backoff slot and the contention window size is 16. The size of the contention window of the terminals A, B, and C may be changed to 16 (the size of the contention window of the terminals A, B, and C) .

At time t _1, the terminal A, B, C are assumed to have each of the (n, N) to a value (9, 12), (7, 13), (3, 7). Here, n is a backoff counter value, and N is a counter for counting the number of backoffs after updating the backoff counter value to an arbitrary integer.

At time t _2, the backoff counter value of the terminal C, and a zero (zero), the terminal C starts the transmission of the synchronization signal. At this time, the terminal C has N = 4, and the terminal A and the terminal B have (n, N) = (6, 9) and (n, N) = (4, 10), respectively. That is, t ₁ and t ₂ Since the idle (idle) in the back-off slot between, by the S1220, S1230, S1240, S1250, S1260 in Fig. 12, the terminals A, B, C (n, N) is reduced more and more.

At time t _3, the terminal C is completed, the synchronization signal transmitted.

(N, N) = (5, 8), (n, N) = (3, 9) at time t ₄ after time corresponding to one backoff slot. ), And (n, N) = (*, 3). That is, terminal A and terminal B decrease (n, N) to (5, 8) and (3, 9) by S1220, S1230, S1240, S1250 and S1260. Then, the terminal C sets (n, N) to (*, 3) by S1230, S1240, and S1250. Here, the meaning of "*" means that n can be any value except for n = 0. That is, at time t ₄ , the terminal C can perform a process of decreasing only the counter N value without setting the backoff counter value to an arbitrary integer value.

At time t ₅ , the backoff counter value of the terminal B becomes zero, and the terminal B starts transmitting the synchronization signal. At this time, the terminal B has N = 6. Then, the time from t _5, the value N of the terminal C, and a zero (zero), which causes the terminal C updates the contention window size (S1260, S1262, S1210). The terminal C arbitrarily sets the value of the backoff counter to 8 using the updated contention window size (contention window value). In Fig. 15, it is assumed that the updated contention window size is 16. On the other hand, the terminal A has (n, N) = (2, 5).

The time from t _6, the terminal A, B, C, respectively (n, N) = (1 , 4), (n, N) = (*, 5), and (n, N) = (7 , 15) Have.

At time t ₇ , the backoff counter value of the terminal A becomes zero, and the terminal A starts transmission of the synchronization signal.

From the time t _8, the terminal A, B, C, respectively (n, N) = (* , 2), (n, N) = (*, 3), and (n, N) = (5 , 13) Have.

At time t _9, the terminal A is the N value becomes zero (zero), the terminal A is updated (update) the contention window size. Then, the terminal A arbitrarily sets the backoff counter value to 6 using the updated contention window size.

At time t ₁₀ , the value of N in the terminal B becomes zero, and the terminal B updates the contention window size (contention window value). The terminal B arbitrarily sets the backoff counter value to 7 using the updated contention window size.

At time t _11, the backoff counter value of the terminal C is zero (zero), the terminal C starts the transmission of the synchronization signal.

At time t ₁₂ , the terminals A, B, and C are set to (n, N) = (2, 12), (n, N) = (4, 13) Have.

At time t _13, a backoff counter value of the terminal A is 0, the terminal A starts the transmission of the synchronization signal.

At time t _14, the terminal A, B, C, respectively (n, N) = (* , 9), (n, N) = (1, 10), and (n, N) = (* , 4) the Have.

At time t15, the backoff counter value of the terminal B becomes zero, and the terminal B starts transmission of the synchronization signal.

13, 14, and 15, a method of transmitting a synchronization signal using a random access method by the UEs in the synchronization interval has been described. However, since the synchronization section is repeatedly present at a specific position in the frame, discontinuity occurs on the time axis.

FIG. 16 is a diagram showing that when the random access scheme of FIG. 12 is used, the terminal A transmits the synchronization signal while performing the CCA at the discontinuity of the synchronization interval. In FIG. 16, it is assumed that the size of the contention window CW is always 8 after the size of the contention window CW is updated. However, the size of the contention window may be changed along with the update.

At time t _1, the terminal A is assumed to have a value (n, N) (4, 6).

At time t _2, the terminal A detects a busy channel (channel busy) through the CCA, and the terminal A will stop the decrease of n and N.

Haejimyeon channel is idle (idle) at the time t _3, the mobile station A resumes the decrease of n and N from the time t4.

At time t ₅ , the backoff counter value of the terminal A becomes zero, and the terminal A starts transmission of the synchronization signal.

At time t _6, the terminal A has first a value of N, and starts the reduction of N that has been stopped with the transmission of the synchronization signal. Then, the terminal A performs a process of decreasing only the counter N value without setting the backoff counter value to an arbitrary integer value (i.e., n = *).

At time t ₇ , the N value of the terminal A becomes zero, and the terminal A updates the size of the contention window. Then, the terminal A arbitrarily sets the backoff counter value to 3 using the size (8) of the updated contention window. Further, at t ₇ , the terminal A senses channel busy through the CCA, and the terminal A stops decreasing n and N.

The channel is idle (idle) in a single bag-in-t ₈ time the off-slot has elapsed as a state, the terminal A n, to decrease the value of N again, but the transfer is complete, the sync signal in the sync interval time remaining Can not be. Accordingly, the terminal A does not start decreasing n and N at t8.

The time t ₉ is the start point of the synchronization interval of the next frame. At t ₉ , the terminal A has n = 2 and N = 7. And terminal A starts decreasing n and N again.

At time t ₁₀ , the backoff counter value of the terminal A becomes zero, and the terminal A starts transmission of the synchronization signal.

At time t11, the terminal A has 4 as the value of N, and restarts the decrease of N that was interrupted with the synchronization signal transmission. Then, the terminal A performs a process of decreasing only the counter N value without setting the backoff counter value to an arbitrary integer value (i.e., n = *).

At time t _12, and zero the value N of the terminal A, the terminal A to update the size of the contention window. The terminal A arbitrarily sets the backoff counter value to 4 using the updated contention window size (8).

At time t ₁₃ , the terminal A senses channel busy through the CCA and stops decreasing n and N.

The time t ₁₄ is the start point of the synchronization section of the next frame, and at t ₁₄ , the terminal A has n = 0 and N = 4. Since the terminal A is n = 0, the terminal A starts transmission of the synchronization signal.

At time t _15, the terminal A has a value of N = 3, the terminal A starts a reduction of the stop with the transmission of the synchronizing signal N again.

Meanwhile, the size of the contention window described above (used in combination with 'contention window' and 'contention window value' in this specification) can be determined by reflecting the number of peripheral terminals. In order to reduce the probability of collision of the synchronous signal, if there are many terminals in the vicinity, the terminals lower the transmission frequency of the synchronous signal, and if there are not many terminals in the vicinity, the terminals increase the transmission frequency of the synchronous signal. However, even if it is difficult to grasp the number of terminals located nearby, the overhead may be large. Therefore, the embodiment of the present invention described below does not directly use the number of peripheral terminals to determine the value of the contention window. That is, the embodiment of the present invention uses a method of maintaining the transmission frequency of the synchronization signal constant regardless of the number of terminals in a specific area.

A method for maintaining the frequency of a synchronous signal transmitted in a specific area constantly includes a receiving time difference (hereinafter referred to as 'IAT (inter-arrival time)') which is a difference between a time when a predetermined synchronous signal is received and a time when a next synchronous signal is received, Quot;). For example, after the terminal determines a target reception time difference (hereinafter, referred to as a target inter-arrival time (TIAT)), the terminal calculates a reception time difference (hereinafter referred to as MIAT measured inter-arrival time). The UE updates the contention window value in a direction in which the difference between the TIAT value and the MIAT value decreases. Alternatively, instead of the reception time difference, an idle time may be used, which is the length of time the channel idle until a next synchronization signal is received after a predetermined synchronization signal is received. At this time, the value obtained by subtracting the length of the synchronization signal from the reception time difference is equal to the idle time. In the present invention, the case where IAT is used will be described.

The terminals use the measured IAT for a certain period of time to calculate the MIAT of the area in which they are located. For example, the terminals can calculate the MIAT by setting the time window of the size W _A and then the average value of the IAT measured from the past to the present W _A. Alternatively, each time a UE receives a new synchronization signal, a method of updating the MIAT using Equation (1) can be used.

이며, IAT는 마지막에 수신된 동기 신호를 이용한 측정한 수신 시간차를 나타낸다. In Equation (1)

And IAT represents the measured reception time difference using the last received synchronization signal.

On the other hand, the terminals can determine the increase / decrease of their own contention window values using the reception pattern of the received synchronization signals. However, since the reception patterns of the synchronization signals for the terminals located close to each other are very similar, if the values of the competition windows of the two terminals differ greatly, the difference value may not be narrowed. In this case, the synchronization signal transmission rates of two terminals located close to each other may be significantly different. In order to solve this problem, each terminal can estimate the average contention window value (hereinafter referred to as 'CW _oth ') of neighboring terminals and use the estimated CW _oth to update its contention window value. A method of updating the contention window value of the terminal using the estimated CW _oth is described in Table 1 below.

As described above with reference to FIG. 5, the synchronization signal may include a contention window value of the terminal that transmitted the synchronization signal. The terminal receiving the synchronization signal estimates an average contention window value (CW _oth ) of neighboring terminals using the contention window value included in the received synchronization signal. For example, the terminal may calculate the CW _oth value by averaging the CW received during W _B from the past to the present, after setting the time window W _B. Alternatively, each time a new sync signal is received, the terminal may use a method of updating the CW _oth value using the following equation (2).

이며, CW는 마지막으로 수신된 동기 신호에 포함된 경쟁 윈도우 값을 나타낸다. In Equation (2)

And CW denotes a contention window value included in the last received synchronization signal.

As another method of updating the CW _oth , it can be updated using the following equation (3).

이고

이며,

와

는 각각

와

를 만족한다. 그리고 CW는 마지막으로 수신된 동기 신호에 포함된 경쟁 윈도우 값을 나타낸다. In Equation (3)

ego

Lt;

Wow

Respectively

Wow

. And CW represents the contention window value included in the last received synchronization signal.

(n=1, 2, 3,….16)은 경쟁 윈도우 값을 갱신할 시 곱해주는 상수이다.

은 갱신 후 경쟁 윈도우의 값이 커져야 할 경우에는 1보다 큰 값을 가지며 갱신 후 경쟁 윈도우의 값이 작아져야 할 경우에는 1보다 작은 값을 갖는다. 만약 단말이 주변 단말의 평균 경쟁 윈도 값의 추정 값(CWoth)을 모르는 경우,

, 그리고

이 만족된다. Table 1 below shows rules for updating the value of the contention window of the terminal when the terminal knows the estimated value (CW _oth ) of the average contention window value of the peripheral terminal. In Table 1, C ₁ , C ₂ , D ₁ , and D ₂ are real numbers greater than one.

(n = 1, 2, 3, ... 16) is a constant that multiplies the time to update the contention window value.

Has a value larger than 1 when the value of the contention window after the update has to be increased and is smaller than 1 when the value of the contention window after the update has to be decreased. If the terminal does not know the estimated value (CWoth) of the average contention window value of the neighboring terminal,

, And

Is satisfied.

이고

,

,

,

,

인 경우에 간단하게 정리한 표이다. Table 2, below,

ego

,

,

,

,

Is a simple summary table.

When a terminal receives a synchronization signal, it can perform the following three operations. The three actions are MIAT update, CW _oth value update, and their timing. Here, the timing indicates the update of the phase value of the synchronization timer. The updating of the MIAT and the updating of the CW _oth value have been described above and the timing will be described below. A method for the terminal to update its own timing uses the reception time of the received synchronization signal.

)이 360도가 되는 순간이 프레임의 끝 또는 시작 시점이다. 도 17은 프레임과 동기 타이머의 위상(

)의 관계를 나타내는 도면이다. 도 11에 나타낸 바와 같이, 동기 타이머의 위상이 360도가 되는 순간이 프레임의 끝 또는 시작 점이 된다. The UE has a synchronization timer and the phase of the synchronization timer (

) Is 360 degrees is the end or start of the frame. FIG. 17 shows the phase of the frame and the synchronous timer

). ≪ / RTI > As shown in Fig. 11, the moment when the phase of the synchronization timer reaches 360 degrees becomes the end or start point of the frame.

FIG. 18 is a diagram illustrating a method of synchronizing a terminal while transmitting and receiving a synchronization signal according to an embodiment of the present invention. In FIG. 18, it is assumed that the terminal B is at a distance capable of communicating with the terminal A and the terminal C, and that the terminal A and the terminal C are at a distance that can not communicate with each other.

As shown in FIG. 18, terminals A, B, and C are in a state in which synchronization does not coincide with each other at time 0.

At time t _1, a phase alignment timer of the mobile station A, and 360 degrees and transmits the synchronization signal. At this time, the terminal B receives the synchronization signal transmitted from the terminal A and updates its synchronization timer to match the synchronization timer of the terminal A. However, since the terminal C does not receive the synchronization signal of the terminal A, it does not update its synchronization timer.

At time t _2, the phase alignment timer of the UE B is 360 degrees and transmits the synchronization signal. At this time, after receiving the synchronization signal transmitted from the terminal B, the terminal C updates its synchronization timer to match the synchronization timer of the terminal B. At this time, the terminal A receives the synchronous signal transmitted from the terminal B, but does not update the synchronous timer because it is already synchronized with the terminal B.

On the other hand, as shown in FIG. 18, terminals do not always transmit a synchronization signal when their synchronization timer phase is 360 degrees. The transmission of the synchronization signal is performed through contention-based random access as described above. Therefore, the transmission of the synchronization signal may occur not at the beginning of the frame at which the phase of the synchronization timer is 360 degrees but at a delay of an arbitrary backoff slot. In FIG. 18, it is assumed that the synchronization signal is transmitted at the start of the frame without indicating the transmission delay of the synchronous signal due to the random back-off for convenience of explanation. The synchronization signal transmission delay due to the random back-off will be described in detail below with reference to FIG.

를 가지고 있는 단말이 동기 신호를 수신하는 경우 아래에서 설명하는 과정을 통해 동기 타이머 위상 값을

로 갱신한다. 19 is a diagram illustrating a synchronization timer update method according to an embodiment of the present invention. As the synchronous timer phase value

The mobile terminal receives the synchronization signal, the synchronization timer phase value

.

을 가지고 있는 것을 가정한다. In FIG. 19, when the terminal receives a synchronization signal,

. ≪ / RTI >

The terminal obtains x ₁ as shown in the following Equation (4).

는 미리 정해진 (0,0)과 (1.1)을 지나고 0< x <1에서

이고

인 함수이다. In Equation (4)

Passes through predetermined (0, 0) and (1.1), and 0 < x < 1

ego

Function.

Then, the terminal obtains x ₂ as shown in the following equation (5).

는 미리 정해진 상수이다. In Equation (5)

Is a predetermined constant.

를 구한다. Then, the terminal finally obtains the following Equation 6

.

인 경우

로 갱신하다. 그리고,

의 관계가 성립을 알 수 있다. 즉, 동기 타이머의 위상 값의 갱신은 동기 신호를 수신할 시의 동기 타이머 위상 값에 따라 다르게 결정된다. As shown in Fig. 19, in the same way as described above, the terminal calculates its own synchronization timer phase value

If

To renew. And,

And the relationship between the two. That is, the update of the phase value of the synchronization timer is determined differently according to the synchronization timer phase value at the time of receiving the synchronization signal.

Unlike FIG. 19, the following method can be used as a method for updating the phase value of the synchronization timer when the terminal receives the synchronization signal. Another method of updating the phase value of the synchronization timer when the terminal receives the synchronization signal is to use the method illustrated in Fig.

20 is a diagram illustrating a synchronization timer update method according to another embodiment of the present invention.

As shown in FIG. 20, when the terminal receives a synchronization signal, if the phase value of its synchronization timer is a value between f _m and f _{m + 1} , the phase value is updated to f _{new, m} . For example, if the phase value of the terminal is between f ₁ and f ₂ , the terminal updates it to f _{new, 1, which} is a predetermined value regardless of the value of the received synchronization signal.

In the special case of the method illustrated in FIG. 20, when the terminal receives the synchronization signal, if the phase value of its own synchronization timer is less than 180 degrees, the terminal maintains the current synchronization timer phase value and the terminal receives the synchronization signal There is a method of updating its own synchronization timer phase value to 360 degrees when its own synchronization timer phase value is larger than 180 degrees.

21 is a diagram illustrating a method of updating the phase of a synchronization timer when a synchronization signal is delayed from a start time of a frame due to a random backoff signal according to an embodiment of the present invention. In FIG. 21, it is assumed that the terminals A, B, C, and D are all in a communicable position.

At time t ₁ , the synchronization timer phase value of terminal A is 360 degrees. Because according to a random back-off procedure of the sync signal transmission is performed (timing reference signal), the synchronization signal transmission of the terminal A is generated at t ₂ later than the time t _1. Here, the time t ₂ is located between time t ₁ and time t _3.

At time t ₂ , the terminal B receives the synchronization signal transmitted by the terminal A. At this time, the terminal B can know that the start point of the frame of the terminal A is not t ₂ but t ₁ using the backoff indicator included in the synchronization signal received from the terminal A (see arrow 2010). UE B is using their phase alignment timer value at time t _1, and updates the phase value of the synchronous timer (see arrow 2020). At this time, the method of updating the phase value of the synchronization timer may be the method of FIG. 19 and FIG. Then, as shown by the arrow 2030, the terminal B calculates the synchronous timer phase value of the current time t ₂ using the updated synchronous timer phase value at the time t ₁ . Accordingly, after updating the phase value of the synchronization timer, the terminal B is synchronized with the terminal A.

At time t ₂ , the terminal C receives the synchronization signal transmitted by the terminal A. At this time, the terminal C can know that the start point of the frame of the terminal A is t ₁ instead of t ₂ (see arrow 2040) by using the backoff indicator included in the synchronization signal received from the terminal A. C is the terminal by using their phase alignment timer value at time t _1, and updates the phase value of the synchronous timer (see arrow 2050). At this time, the method of updating the phase value of the synchronization timer may be the method of FIG. 19 and FIG. And, as indicated by arrow 2060, the terminal C by using a phase alignment timer value updated at the time t ₁ and calculates the phase alignment timer value at the current time t _2. Thus, after updating the phase value of the synchronization timer, the terminal C is synchronized with the terminal A.

At time t ₂ , the terminal D receives the synchronization signal transmitted by the terminal A. At this time, the terminal D can know that the start point of the frame of the terminal A is t ₁ instead of t ₂ (see arrow 2070) by using the backoff indicator included in the synchronization signal received from the terminal A. Terminal D, using their phase alignment timer value at time t _1, and updates the phase value of the synchronization timer. At this time, the method of FIG. 19 and the method of FIG. 20 can be used for updating the phase value of the synchronization timer. As shown in FIG. 21, the reception of the synchronization signal may occur at an arbitrary position in the synchronization section 110. Accordingly, when the terminal updates the phase of its own synchronization timer using the received synchronization signal after receiving the synchronization signal, the remaining time in the synchronization section of the frame may not be sufficient to transmit the synchronization signal . In this case, the UE can perform a random access procedure for transmitting a synchronization signal in the next frame without performing a random access procedure for transmitting the synchronization signal in the corresponding frame.

The terminal performs an initial synchronization procedure (S410 in FIG. 4) as part of the initialization procedure. Initialization of the terminal may occur when the terminal is powered on, or when all communications are interrupted and the terminal is in an inactive state and then in an inactive state. Hereinafter, an initial synchronization procedure according to an embodiment of the present invention will be described with reference to FIG.

22 shows an initial synchronization procedure according to an embodiment of the present invention.

First, the terminal operates in a reception mode for a predetermined time before transmitting a synchronization signal (S2100). The terminal operates in a reception mode and determines whether there is a synchronization signal transmitted by peripheral terminals (S2110).

If the synchronization signal is detected in step S2110, the terminal determines whether the detected synchronization signal is a synchronization signal transmitted from terminals (for example, terminals constituting a network) that are in synchronization with each other (step S2120). For example, if the synchronization signal is periodically received and the start time of the frame from the synchronization signal is consistently and consistently estimated, the terminal may determine that it has been transmitted from synchronized terminals.

In step S2120, if the synchronization signal is transmitted from the synchronized terminals, the terminal adjusts its synchronization timer phase to the synchronization timer phase included in the received synchronization signal, and transmits the synchronization signal through the random access procedure described above (S2130). At this time, since the UE has joined the synchronized UEs, the UE can perform the synchronization maintenance and management procedure (S420) of FIG.

 If the synchronization signal is not detected in step S2110, the terminal determines that there is no terminal transmitting the synchronization signal in the vicinity. At this time, the terminal arbitrarily selects the phase value of its own synchronization timer (S2140). Then, the terminal can start the transmission of the synchronization signal using the above-described random access procedure and perform the synchronization maintenance and management procedure (S420) of FIG.

If it is determined in step S2120 that the synchronization signal is not the synchronization signal transmitted by the synchronized terminals, the terminal randomly selects its own synchronization timer phase value (S2150). Then, the terminal performs a procedure for synchronizing with neighboring terminals. For example, if the start time of the frame estimated from the received sync signal is inconsistent or the start time of the estimated frame is plural, the terminal can determine that the detected sync signal is transmitted from the terminals that are not synchronized . A method for the terminal to arbitrarily select its own synchronization timer phase value may be a method for selecting a random real number and may be a method for selecting any one of the phase values of the received synchronization signal.

On the other hand, the terminal transmits a synchronization signal in a synchronization interval according to its own synchronization timer using the above-described random access method. The terminal operates in the reception mode except for transmitting the synchronization signal, and receives the synchronization signal transmitted by the peripheral terminals. At this time, the synchronization signal is not synchronized with peripheral terminals, so that the synchronization signal can be received at an arbitrary position in the frame as well as in the synchronization section. When the synchronization signal is received, the terminal performs the above-described update of the MIAT, update of the CW _oth value, and update of the phase value of its own synchronization timer. The updating of the phase value of the synchronization timer may be performed by the method of FIG. 19 or another method may be used. The terminal that has updated the synchronous timer phase value does not transmit the synchronous signal using the random access in the current frame (i.e., the frame newly determined by updating the synchronous timer phase) but transmits the synchronous signal using the random access Can be performed. If the UE repeats these processes and determines that the neighboring UEs are synchronized with each other, the UE can perform the synchronization maintenance and management procedure S420 of FIG. For example, if a synchronous signal is periodically received for a predetermined period of time, and the starting point of the frame estimated from the received synchronous signal is consistently and consistently within the error range, the terminal can determine that it is synchronized with neighboring terminals have.

The terminal performs synchronization maintenance and management procedures (corresponding to S430 in FIG. 4) when the terminals synchronize with neighboring terminals through an initial synchronization procedure. The synchronization maintenance and management procedure can prevent synchronization inconsistency due to timing drift caused by the error of the oscillators of the terminals, interference of a new terminal that is not synchronized or interference with a heterogeneous wireless network . Through synchronous maintenance and management procedures, it is possible to detect inconsistent situations. Hereinafter, the synchronization maintenance and management procedure according to the embodiment of the present invention will be described.

A terminal transmits a synchronization signal in a synchronization section in a frame using the above-described random access method. The terminal operates in the reception mode except for transmitting the synchronization signal, and receives the synchronization signal transmitted by the peripheral terminals. At this time, since the terminal has already synchronized with peripheral terminals, the terminal receives the synchronization signal in the synchronization section. Accordingly, in order to reduce power consumption, the terminal can turn off some functions of the terminal in a section in which simultaneous signals are not received.

When receiving the synchronization signal, the terminal updates the MIAT, updates the CW _oth value, and updates the phase value of its own synchronization timer. The phase value update of the synchronous timer can be performed by the method of FIGS. 19 and 20 above. In the synchronization maintenance and management procedure, the phase value of the synchronization timer after the update does not greatly differ from the phase value of the synchronization timer before the update. The terminal continues the random access for the synchronization signal transmission in the current frame even after updating the phase value of the synchronization timer.

The mobile station repeats these processes and continually monitors whether or not the synchronization with neighboring mobile stations is out of the error range. If the synchronization error deviates from a certain error range, the terminal may initiate an initial synchronization procedure and may begin the resynchronization procedure described below. A terminal operating in the power saving mode may periodically release the power saving mode and perform a full scan in at least one frame to detect whether synchronization has been lost. Meanwhile, if the terminal enters the power consumption detection mode after starting the synchronization signal transmission in step S2140 of FIG. 22 through the periodic full scan, the terminal can detect terminals having different motions from the terminal.

The initial synchronization procedure and maintenance and management procedures described above may use frames having different lengths. For example, to shorten the synchronization time between terminals performed in the initial synchronization procedure, the frame used in the initial synchronization procedure may be shorter than the frame used in the synchronization maintenance and management procedure.

If the synchronized terminal loses synchronization due to timing drift, interference of the neighboring heterogeneous wireless network, or the like, the terminal performs the re-synchronization procedure (S430) of FIG. This resynchronization procedure is similar to the initial synchronization procedure, but differs in the following points. The frame used in the initial synchronization procedure may be different in length from the frame used in the synchronization maintenance and management procedure. However, the frame used in the resynchronization procedure uses the same length as the frame used in the synchronization maintenance and management procedure. In the initial synchronization procedure, a scan of a wireless channel is performed for a predetermined time to determine whether a synchronization signal exists. However, in the resynchronization procedure, the scan may not be performed or may be performed for a shorter time than the initial assimilation procedure.

23 is a diagram illustrating a terminal according to an embodiment of the present invention.

23, a terminal 2200 according to an embodiment of the present invention includes a processor 2210, a memory 2220, and an RF module 2230.

The processor 2210 may be configured to implement the procedures, methods, and functions described in FIGS. 1-21.

The memory 2220 is coupled to the processor 2210 and stores various information related to the operation of the processor 2210.

The RF module 2230 is connected to an antenna (not shown) and transmits or receives radio signals. The antenna may be implemented as a single antenna or multiple antennas (MIMO antennas).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It belongs to the scope of right.

Claims (20)

A method for synchronizing a first terminal in a distributed wireless communication system,
Dividing the synchronization interval into a plurality of backoff slots,
Setting a contention window,
Optionally selecting a backoff counter using the contention window,
Checking if the channel is idle during at least one backoff slot of the plurality of backoff slots, and
And changing the backoff counter according to whether the channel is idle. The method according to claim 1,
Wherein the modifying comprises:
Decreasing the backoff counter if the channel is idle, and
And not decreasing the backoff counter if the channel is busy. The method according to claim 1,
And if the backoff counter is less than a predetermined value, transmitting a synchronization signal. The method according to claim 1,
Wherein the selecting comprises: if {0, 1, 2, ..., , &Lt; / RTI &gt; CW-1} as an arbitrary integer as the backoff counter. The method according to claim 1,
Wherein whether the channel is idle is checked via Clean Channel Access (CCA). The method according to claim 1,
Setting a first counter that is a counter different from the backoff counter, and
Further comprising decreasing the first counter if the channel is idle. The method according to claim 6,
And updating (updating) the contention window if the first counter is smaller than a predetermined value. The method of claim 3,
And updating the contention window if the channel is idle for a predetermined time after transmitting the synchronization signal. The method according to claim 1,
Wherein the changing step comprises not decreasing the backoff counter when the channel determines that the synchronization signal transmission is not completed for the remaining period of the idle period or the synchronization period. The method according to claim 1,
Wherein the setting of the contention window comprises:
Calculating an average reception time difference between first synchronization signals received by the first terminal,
Calculating an average contention window for the first terminal and another terminal using the first synchronization signals; and
And setting the contention window using the average reception time difference and the average contention window. The method according to claim 1,
And adjusting the synchronization timer using the first synchronization signal when the first terminal receives the first synchronization signal from the second terminal. 12. The method of claim 11,
Wherein the step of adjusting the synchronization timer includes changing a predetermined constant value regardless of the first synchronization signal when the phase of the synchronization timer is between a first value and a second value
How to synchronize. 12. The method of claim 11,
Wherein the first synchronization signal includes a backoff indicator indicating a frame start point of the first terminal,
Wherein adjusting the synchronization timer comprises adjusting a phase value of the synchronization timer using a phase value of the synchronization timer corresponding to the backoff indicator. A method for synchronizing a first terminal in a distributed wireless communication system,
Receiving first synchronization signals from second terminals that are different from the first terminal;
Calculating an average reception time difference between the synchronization signals,
Calculating an average contention window for the second terminals using the first sync signals,
Setting a first contention window, which is a contention window of the first terminal, using the average reception time difference and the average contention window; and
And determining whether to transmit a synchronization signal in response to the first contention window. 15. The method of claim 14,
Wherein the determining comprises:
Optionally selecting a backoff counter using the first contention window,
Decreasing the backoff counter if the channel is idle during a backoff slot where the synchronization interval is divided into a plurality of intervals,
And if the backoff counter is zero, transmitting a synchronization signal. 16. The method of claim 15,
Setting a predetermined value of the backoff counter after transmitting the synchronization signal, and
And updating (updating) the first contention window if the set backoff counter is zero. An RF module for transmitting and receiving a synchronization signal, and
The method comprising: dividing a synchronization interval into a plurality of backoff slots, randomly selecting a backoff counter using a contention window, and if the channel is idle during a first backoff slot of the plurality of backoff slots, The processor comprising: 18. The method of claim 17,
Wherein the processor transmits the synchronization signal when the backoff counter is zero. 19. The method of claim 18,
Wherein the processor updates the contention window when the backoff counter is set to a predetermined value after transmitting the synchronization signal and when the set backoff counter is zero. 18. The method of claim 17,
The processor calculates an average reception time difference between the received synchronization signals, calculates an average contention window for the terminal and the other terminals using the received synchronization signals, and uses the average reception time difference and the average contention window And sets the contention window.

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