KR20120129815A - Method and terminal for performing direct communication between terminals - Google Patents

Abstract

PURPOSE: A method for performing direct communications between terminals and the terminal supporting the same are provided to obtain synchronization between the terminals performing direct communications by improving a synchronization channel structure. CONSTITUTION: Direct communications is performed with one or more second terminals using allocated resources for the direct communications between terminals. The resources include a synchronous channel which is used for frequency synchronization and time synchronization between the terminals. The synchronization channel includes a synchronization channel preamble which is used for either preamble detection, time offset estimation, frequency offset estimation, or channel estimation. The synchronization channel preamble is either a first sequence repeating a basic pattern or a second sequence combining the basic pattern with a pattern multiplying the basic pattern by (-1). One or more OFDM(orthogonal frequency division multiplexing) symbols are used for transmitting the synchronization channel preamble.

Description

Method for performing direct communication between terminals and a terminal supporting the same {METHOD AND TERMINAL FOR PERFORMING DIRECT COMMUNICATION BETWEEN TERMINALS}

The present invention relates to a method for performing direct communication between terminals and a terminal supporting the same.

A method of supporting direct communication between terminals using resources allocated to cellular communication, the method of allocating some of the resources for cellular communication as a dedicated resource for direct communication between terminals for terminals in cell coverage and resources for cellular communication There is a method to be used simultaneously for this cellular communication and direct communication.

Here, direct communication between terminals within cell coverage of the base station is assumed. In addition, it is assumed that a terminal intending to perform direct communication between terminals can know location information of resources used for direct communication between terminals through a control channel of cellular communication.

However, in a disaster environment or the like, some or all of the terminals to perform direct communication may be located outside the cell coverage of the base station. In this case, the terminal located outside the cell coverage of the base station cannot receive the control channel of the base station. Such a terminal cannot obtain information on resources used for direct communication between terminals.

In general, direct communication between terminals is achieved using some of the resources for cellular communication. Accordingly, a signal of a terminal performing cellular communication and a signal of a terminal performing direct communication may be mixed in the cell coverage of the base station. If synchronization between the base station and all or part of the terminal performing the direct communication is not achieved, adjacent channel interference may occur between the cellular communication signal and the direct communication signal. In the receiving terminal, inter-symbol interference and inter-carrier interference may occur.

An object of the present invention is to provide a method for performing direct communication between terminals. In particular, it is intended to provide a method for obtaining synchronization between terminals performing direct communication.

According to an aspect of the present invention, a method for performing direct communication between terminals of a first terminal includes performing direct communication with at least one second terminal using resources allocated for direct communication between terminals. The resource includes a synchronization channel used for frequency synchronization and time synchronization between terminals, and the synchronization channel includes a synchronization channel preamble used for at least one of preamble detection, time offset estimation, frequency offset estimation, and channel estimation.

According to another aspect of the present invention, a method for performing direct communication between terminals of a first terminal includes performing direct communication with at least one second terminal using resources allocated for direct communication between terminals. The resource includes a dedicated channel for transmitting a data packet or for transmitting a dedicated channel preamble used for time offset estimation or frequency offset estimation.

According to another aspect of the present invention, a method for performing direct communication between terminals of a first terminal includes performing direct communication with at least one second terminal using resources allocated for direct communication between terminals, The resource includes an auxiliary channel for mapping and transmitting at least one of a ranging channel, a channel quality information (CQI) channel, and a feedback channel.

A terminal according to an aspect of the present invention includes a radio frequency (RF) module and a processor, wherein the processor is configured to perform direct communication with at least one second terminal using resources allocated for direct communication between terminals. The resource may include a synchronization channel used for frequency synchronization and time synchronization between terminals, and the synchronization channel may include a synchronization channel preamble used for at least one of preamble detection, time offset estimation, frequency offset estimation, and channel estimation. Include.

A terminal according to another aspect of the present invention includes a radio frequency (RF) module and a processor, wherein the processor is configured to perform direct communication with at least one second terminal using resources allocated for direct communication between terminals. The resource may include a dedicated channel for transmitting a data packet or transmitting a dedicated channel preamble used for time offset estimation or frequency offset estimation.

A terminal according to another aspect of the present invention includes a radio frequency (RF) module and a processor, wherein the processor is configured to perform direct communication with at least one second terminal using resources allocated for direct communication between terminals. The resource is configured, and the resource includes an auxiliary channel for mapping and transmitting at least one of a ranging channel, a channel quality information (CQI) channel, and a feedback channel.

According to another aspect of the present invention, a method for performing direct communication between terminals by a first terminal includes estimating a frequency offset, setting a transmission frequency or a reception frequency using the estimated frequency offset, and transmitting or Performing direct communication with at least one second terminal using a reception frequency, and when the first terminal is located within cell coverage of the base station, the frequency offset is estimated according to the frequency of the base station.

According to another aspect of the present invention, a method for performing direct communication between terminals by a first terminal includes performing ranging with a base station, and a second terminal performing direct communication with the first terminal by the first terminal. Transmitting the direct communication signal to the second terminal such that a difference between the time point at which the direct communication signal is received and the time point at which the second terminal receives the cellular communication signal between the base station and the third terminal is within a cyclic prefix (CP). It includes.

According to an embodiment of the present invention, a method of performing direct communication between terminals can be obtained.

In particular, it is possible to reduce the interference between the cellular communication signal and the direct communication signal, and to efficiently match frequency synchronization and time synchronization between terminals performing direct communication.

In addition, it is possible to obtain a structure of a synchronization channel and a preamble transmission scheme for synchronization acquisition between terminals performing direct communication. In addition, a structure of a dedicated channel and a structure of an auxiliary channel allocated for direct communication can be obtained.

1 is a diagram illustrating an environment supporting direct communication between terminals according to an embodiment of the present invention.
2 is a diagram illustrating a transmission frequency setting process according to an embodiment of the present invention.
3 and 4 are diagrams illustrating an embodiment of performing direct communication between terminals using uplink resources.
5 and 6 illustrate another embodiment of performing direct communication between terminals by using an uplink resource.
7 is a flowchart illustrating a method of synchronizing time in direct communication between terminals according to an embodiment of the present invention.
8 and 9 illustrate an embodiment of performing direct communication between terminals using downlink resources.
10 is a diagram illustrating a frame structure including resources for direct communication between terminals according to an embodiment of the present invention.
11 shows a structure of a synchronization channel according to an embodiment of the present invention.
12 shows a structure of a synchronization channel according to another embodiment of the present invention.
13 is a structure of a PRBS generator.
14 is a diagram illustrating a method of allocating a dedicated channel preamble to a dedicated channel resource according to an embodiment of the present invention.
15 is a diagram illustrating a resource allocation structure for an auxiliary channel according to an embodiment of the present invention.
16 illustrates a method of allocating a ranging channel to auxiliary channel resources according to an embodiment of the present invention.
17 illustrates a method of allocating a CQI channel to auxiliary channel resources according to an embodiment of the present invention.
18 illustrates a method of converting CQI information into a CQI code according to an embodiment of the present invention.
19 illustrates a terminal that can be applied to an embodiment of the present invention.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement 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 the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and like reference numerals designate like parts throughout the specification.

Throughout the specification, when a part is said to "include" a certain component, it means that it can further include other components, without excluding other components unless specifically stated otherwise.

Throughout the specification, a mobile station (MS) is a terminal, a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (access) It may refer to a terminal (AT), a user equipment (UE), or the like, and may include all or some functions of the terminal, MT, SS, PSS, AT, UE, and the like.

In addition, a base station (BS) includes a node B, an evolved node B, an eNodeB, an access point (AP), a radio access station (RAS) a base transceiver station (BTS), a mobile multihop relay (MMR) -BS, or the like, and may include all or some of functions of a Node B, an eNodeB, an AP, a RAS, a BTS, and an MMR-BS.

In the present specification, it is intended to efficiently support direct communication between terminals using a terminal and resources used for orthogonal frequency division multiple access (OFDMA) based cellular communication.

1 is a diagram illustrating an environment supporting direct communication between terminals according to an embodiment of the present invention. Hereinafter, the direct communication between terminals may be mixed with direct communication.

Referring to FIG. 1, at least one terminal 300, 310, 320, 330, 340, 350, 360, or 370 is located within or outside cell coverage A of the base station 100.

In the scenario of direct communication between terminals, when the two terminals 300 and 310 performing direct communication are both within cell coverage of the same base station (scenario 1), the two terminals 320 and 330 performing direct communication are different from each other. When in the cell coverage of the base station (scenario 2), one of the two terminals (340, 350) performing direct communication is within the cell coverage, the other is outside the cell coverage (scenario 3) and performing the direct communication There are cases where both terminals 360 and 370 are out of cell coverage (scenario 4).

Meanwhile, the terminals 300, 310, and 320 in the cell coverage A may perform cellular communication with the base station 100, and the terminals 330 and 340 in the cell coverage B may perform cellular communication with the base station 200. Can be performed.

≪ Example 1 >

In Embodiment 1 of the present invention, in order to reduce interference between cellular communication and direct communication, a method of synchronizing frequency synchronization with time synchronization is considered.

First, a method of synchronizing frequency will be described. Specifically, frequency synchronization may be performed by minimizing a frequency offset generated due to a frequency difference between oscillators of the transmitting terminal and the receiving terminal.

The transmission frequency setting method for each direct communication scenario between terminals is as follows.

In scenario 1, the frequency offset estimated according to the frequency of the base station 100 is corrected in advance, and data for direct communication is transmitted. In this case, each of the terminals 300 and 310 estimates a frequency offset based on the frequency of the same base station 100. Accordingly, when performing direct communication using a downlink resource, the receiving terminal 300 or 310 transmits a cellular communication signal transmitted by the base station 100 and a direct communication signal transmitted by the transmitting terminal 300 or 310 to a subcarrier. It can be received without interference. Even when performing direct communication using an uplink resource, the receiving terminal 300 or 310 may transmit a cellular communication signal transmitted by a terminal performing cellular communication and a direct communication signal transmitted by the transmitting terminal 300 or 310 as a subcarrier. It can be received without interference.

In scenario 2, the terminal 320 corrects the frequency offset estimated according to the frequency of the base station 100 in advance, the terminal 330 corrects the frequency offset estimated according to the frequency of the base station 200 in advance, and direct communication Send data for At this time, the frequency offset between the oscillators of each of the base stations 100 and 200 is insignificant. Accordingly, when performing direct communication using a downlink resource, the receiving terminal 300 or 310 is a subcarrier of the cellular communication signal transmitted by the base station 100 and the direct communication signal transmitted by the transmitting terminal 320 or 330. It can be received without interference. Even when performing direct communication using an uplink resource, the receiving terminal 320 or 330 may subcarrier the cellular communication signal transmitted by the terminal performing cellular communication and the direct communication signal transmitted by the transmitting terminal 320 or 330. It can be received without interference.

In scenario 3, the terminal 340 corrects the frequency offset estimated according to the frequency of the base station 200 in advance, and transmits a synchronization signal so that the terminal 350 outside the cell coverage can estimate the frequency reference. The terminal 350 outside the cell coverage corrects the frequency offset estimated using the synchronization signal in advance and transmits data for direct communication.

In scenario 4, the terminals 360 and 370 store the frequency offset estimated in the process of performing cellular communication with the base station when it is within cell coverage of the base station. When performing direct communication outside the cell coverage, the pre-stored frequency offset is corrected in advance, and the direct communication data is transmitted. In this case, since the frequency offset between the oscillators of each of the base stations 100 and 200 is insignificant, the base station 100 has almost the same frequency offset even if cellular communication is performed. Therefore, even if the frequency offset is stored in advance, it is possible to perform direct communication without significant deviation.

In summary, a process of setting a transmission frequency of a terminal performing direct communication may be illustrated in FIG. 2. Referring to FIG. 2, the terminal estimates a frequency offset (S200), sets a transmission frequency using the estimated frequency offset (S210), and performs direct communication using the transmission frequency (S220). In this case, when the terminal is located within the cell coverage of the base station, the frequency offset may be estimated according to the frequency of the base station. When the terminal is not located within the cell coverage of the base station, the frequency offset may be estimated according to a synchronization signal received from another terminal located within the cell coverage or a frequency stored in advance when the terminal is located within the cell coverage of the base station.

The transmission frequency setting method may be similarly applied to the reception frequency setting. That is, when the terminal is within the cell coverage of the base station, the terminal estimates the frequency offset according to the frequency of the base station, and corrects the estimated frequency offset in advance to receive the direct communication data.

If the terminal is outside the cell coverage of the base station, if the synchronization signal can be received from another terminal within the cell coverage, the frequency offset is estimated using the received synchronization signal, and the estimated frequency offset is corrected in advance to direct communication data. Receive. If the terminal cannot receive the synchronization signal from another terminal within the cell coverage, the terminal pre-corrects using the frequency offset stored during cellular communication and receives the direct communication data.

Next, a time synchronization method will be described to reduce interference between cellular communication and direct communication. To this end, the arrival time of the interference signal and the data signal may be set to be within the CP (Cyclic Prefix) length.

3 and 4 are diagrams illustrating an embodiment of performing direct communication between terminals using uplink resources.

Referring to FIG. 3, HR-BS means a base station, AMS means a terminal performing cellular communication, HR-MS1 means a transmitting terminal during direct communication, and HR-MS2 means reception during direct communication Means the terminal. The ratio of the distance between links of HR-BS, AMS, HR-MS1, and HR-MS2 is as shown.

Some of the uplink resources used for cellular communication may be used for direct communication between terminals according to a frequency division multiplex (FDM) scheme. To this end, the HR-MS1 performs ranging with the HR-BS and transmits a communication signal for direct communication to the HR-MS2 according to an uplink time criterion set through ranging.

Not only HR-BS but also HR-MS2 may receive a communication signal (AMS Tx) that AMS transmits to HR-BS. At this time, the communication signal ④ transmitted by the AMS to the HR-BS may act as an interference signal ① to the HR-MS2. In addition, the HR-MS1 may receive a communication signal (HR-MS1 Tx) transmitted from the HR-MS2 to the HR-MS2 as well as the HR-BS. At this time, the communication signal ② transmitted by the HR-MS1 to the HR-MS2 may act as an interference signal ③ to the HR-BS.

If the difference between the arrival time of the interference signal and the arrival time of the communication signal is out of the cyclic prefix (CP) at the receiving side, interference may occur. That is, as shown in FIG. 4, when the HR-BS receives the communication signal ④ transmitted by the AMS to the HR-BS and the interference signal ③ transmitted by the HR-MS1 at the same time, the interference between subcarriers due to a time synchronization error The problem does not occur. However, when HR-MS2 does not simultaneously receive the communication signal ② transmitted by HR-MS1 to HR-MS2 and the interference signal ① transmitted by AMS, that is, the communication signal ② and the interference signal ①. When the difference T _offset of the arrival time is out of the CP, an interference problem between subcarriers may occur. Therefore, the difference T _offset between the arrival time of the communication signal ② and the interference signal ① can be adjusted to be within CP.

Equation 1 is an example of calculating a T _offset .

Here, d _{I - MM} is the propagation distance between AMS and HR-MS2, d _{Cell - MB} is the propagation distance between AMS and HR-BS, d _{I - MB} is the propagation distance between HR-MS1 and HR-BS, d _{dm - MM} is the propagation distance between HR-MS1 and HR-MS2 and c is the speed of light.

The maximum value of T _offset is shown in Equation 2.

Table 1 shows the maximum value of T _offset according to cellular coverage and direct mode coverage size.

Coverage 1000 m 2000 m 3000m 4000 m 1000 m 6.7㎲ 10.0㎲ 13.3㎲ 16.7㎲ 2000 m 10.0㎲ 13.3㎲ 16.7㎲ 20.0 ㎲ 3000m 13.3㎲ 16.7㎲ 20.0 ㎲ 23.0 ㎲ 4000 m 16.7㎲ 20.0 ㎲ 23.3㎲ 26.7㎲

Here, the horizontal axis represents direct communication coverage and the vertical axis represents cellular communication coverage.

By adjusting the transmission time of the communication signal transmitted by HR-MS1 such that the maximum value of T _offset is within the CP length, it is possible to minimize the interference problem between subcarriers in the base station.

However, if the CP length is short, the propagation distances of the two interference signals (①, ③) are both short, and the distance between AMS and HR-BS and the distance between HR-MS1 and HR-MS2 are both long, The interference problem can be great. Therefore, even if interference in HR-MS2 occurs, it is necessary to reduce the size thereof.

To this end, it is possible to adjust the transmission time of the communication signal so that the interference signal and the communication signal can be simultaneously received at the receiving terminal in the direct communication.

5 and 6 illustrate another embodiment of performing direct communication between terminals by using an uplink resource.

Referring to FIG. 5, HR-BS means a base station, AMS means a terminal performing cellular communication, HR-MS1 means a transmitting terminal during direct communication, and HR-MS2 means reception during direct communication Means the terminal. The ratio of the distance between links of HR-BS, AMS, HR-MS1, and HR-MS2 is as shown.

The HR-MS2 may transmit a message to the HR-MS1 that adjusts the timing at which the HR-MS1 transmits a communication signal. Accordingly, as shown in FIG. 6, the HR-MS2 may simultaneously receive the interference signal ① transmitted by the AMS and the communication signal ② transmitted by the HR-MS1 to the HR-MS2.

However, according to this, the difference (T _offset ) between the arrival time between the communication signal ④ transmitted by the HR-BS to the HR-BS and the interference signal ③ transmitted by the HR-MS1 may occur.

Equation 3 is an example of calculating T _offset .

Here, d _{I - MM} is the propagation distance between AMS and HR-MS2, d _{Cell - MB} is the propagation distance between AMS and HR-BS, d _{I - MB} is the propagation distance between HR-MS1 and HR-BS, d _{dm - MM} is the propagation distance between HR-MS1 and HR-MS2 and c is the speed of light. The maximum value of T _offset is shown in Equation 2. However, since the propagation distances of the communication signals ② and ④ are shorter than the propagation distances of the interference signals ① and ③, the SINR is high and the influence of the interference is not large.

When performing direct communication between terminals using uplink resources, the methods described with reference to FIGS. 3 and 4 and the methods described with reference to FIGS. 5 and 6 may be used or combined.

7 is a flowchart illustrating a method of synchronizing time in direct communication between terminals according to an embodiment of the present invention. A case in which the method described with reference to FIGS. 3 and 4 and the method described with reference to FIGS. 5 and 6 are combined.

Referring to FIG. 7, the HR-MS1 performs ranging with the HR-BS (S700), and accordingly, the HR-MS1 transmits the difference between the reception time of the communication signal and the reception time of the interference signal within the CP according to the result. The viewpoint is set (S710). The HR-MS1 transmits a direct communication signal at the set time (S720).

On the other hand, the AMS transmits a cellular communication signal to the HR-BS (S730). In this case, the cellular communication signal may act as an interference signal to the HR-MS2.

The HR-MS2 sets a transmission time adjustment value by using a difference between the reception time points of the communication signal received from the HR-MS1 and the interference signal received from the AMS (S740). For example, when the difference between the reception time of the interference signal transmitted by the AMS and the communication signal transmitted by the HR-MS1 exceeds the CP length, the transmission time adjustment value is set so as to fall within the CP. The adjustment value can be set to zero. As another example, when the interference signal transmitted by the AMS is not received, the transmission time adjustment value may be set to receive the communication signal at the same time. As another example, when the size of the communication signal transmitted by HR-MS1 is larger than a predetermined level compared to the interference signal transmitted by the AMS, the transmission time adjustment value may be set to zero.

When the HR-MS1 receives the transmission time adjustment message including the transmission time adjustment value from the HR-MS2 (S750), the transmission time is adjusted, and a communication signal is transmitted to the HR-MS2 at the time of the adjustment (S760).

8 and 9 illustrate an embodiment of performing direct communication between terminals using downlink resources.

Referring to FIG. 8, HR-BS means a base station, AMS means a terminal performing cellular communication, HR-MS1 means a transmitting terminal during direct communication, and HR-MS2 means reception during direct communication Means the terminal. The ratio of the distance between links of HR-BS, AMS, HR-MS1, and HR-MS2 is as shown.

Some of the uplink resources used for cellular communication may be used for direct communication between terminals according to a frequency division multiplex (FDM) scheme.

The HR-BS may transmit a communication signal (HR-BS Tx) transmitted to the AMS as well as the HR-MS2. At this time, the communication signal ④ transmitted by the HR-BS to the AMS may act as an interference signal ① to the HR-MS2. In addition, the HR-MS1 may receive a communication signal (HR-MS1 Tx) transmitted from the HR-MS2 to the HR-MS2 as well as the AMS. In this case, the communication signal ② transmitted by the HR-MS1 to the HR-MS2 may act as an interference signal ③ to the AMS.

If the difference between the arrival time of the interference signal and the arrival time of the communication signal is out of the cyclic prefix (CP) at the receiving side, interference may occur. That is, as shown in FIG. 9, when the difference (T _offset1 ) between the time when the AMS receives the communication signal ④ transmitted by the HR-BS to the AMS and the interference signal ③ transmitted by the HR-MS1 is greater than the CP length. As a result, interference between subcarriers may occur due to time synchronization error. When the difference T _offset2 between the time point at which the HR-MS2 receives the communication signal ② transmitted from the HR-MS1 to the HR-MS2 and the interference signal ① transmitted from the HR-BS is out of the CP, the subcarrier Interference problems may occur. T _offset1 and T _offset2 may be represented by Equations 4 and 5, respectively.

Here, d _{I - BM _ tx} means a distance between HR-MS1 and HR-BS. When the distance between HR-MS1 and HR-BS is separated by d _{I - BM _ tx} , the downlink reference signal of HR-MS1 is delayed by d _{I-BM_tx} / c relative to the base station. Therefore, if d _{i - BM _ tx} / c is reduced, time error can be reduced.

To this end, HR-MS1 transmits a direct communication signal to HR-MS2 at the same time as the downlink transmission time of HR-BS. In this case, the ranging result with the base station or GPS may be used. Accordingly, T _offset1 and T _offset2 can be reduced as shown in Equations 6 and 7, respectively.

As such, by adjusting the time synchronization error during the uplink transmission or the downlink transmission, interference between the cellular communication signal and the direct communication signal can be reduced.

Second Embodiment

In a second embodiment of the present invention, there is a method of allocating some of resources allocated for direct communication to a synchronization channel in order to obtain time synchronization and frequency synchronization between terminals performing direct communication. The sync channel includes a preamble promised between terminals. Terminals performing direct communication may synchronize time synchronization and frequency synchronization between terminals by using a preamble included in a synchronization channel.

Hereinafter, a preamble transmission method and a sequence generation method used for the preamble will be described for efficiently matching time synchronization and frequency synchronization between terminals performing direct communication.

To this end, a frame structure including direct communication resources between terminals will be described.

10 is a diagram illustrating a frame structure including resources for direct communication between terminals according to an embodiment of the present invention.

Referring to FIG. 10, a superframe 1000 includes a plurality of frames (eg, four frames), and each frame includes a resource 1010 for direct communication between terminals. Resources for direct communication between terminals may be allocated over a plurality of subframes (eg, three subframes) for each frame (eg, a total of seven subframes). Resources for direct communication between terminals may be allocated, for example, in an FDM scheme.

The resource 1010 for the direct communication may include at least one of a synchronization channel 1020, a dedicated channel 1030, and a supplementary channel 1040.

The synchronization channel 1020 includes synchronization information for direct communication between terminals. One sync channel 1020 may occupy one subframe. The synchronization channel 1020 is a synchronization channel preamble (SYNC-CH preamble), which is a reference signal required for frequency synchronization or time synchronization between terminals, and hop count information, base station information, and synchronization on how many hops are connected to the base station. And a synchronization channel message (SYNC-CH message) including at least one of terminal information for transmitting a channel, terminal information for receiving a synchronization channel, and information on a frame structure (eg, arrangement of a dedicated channel and an auxiliary channel). The sync channel preamble and the sync channel message may be transmitted in a TDM manner. The sync channel preamble may be used for at least one of preamble detection, time offset estimation, frequency offset estimation, and channel estimation.

The dedicated channel 1030 is a channel for sending and receiving data packets. The dedicated channel 1030 may include a plurality of dedicated subchannels each having a predetermined size of physical resource. The unit of the dedicated subchannel may be at least one mRB. One mRB may be configured in units of (6 subcarriers * 6 OFDM symbols).

The auxiliary channel 1040 is an additional channel corresponding one-to-one to each dedicated subchannel constituting the dedicated channel 1030. The auxiliary channel 1040 uses CSMA-CA or the like to obtain a right to use each dedicated subchannel. The auxiliary channel transmits and receives RTS and CTS to reserve a dedicated channel, transmits an indicator indicating that a specific MAC message is being transmitted on a corresponding dedicated channel, and transmits an ACK / NACK to indicate whether packet decoding is successful during packet transmission. Transmission, transmission of CQI, CSI, RI (Rank Information) necessary for link adaptation, synchronization channel reception response message, ranging response, ranging signal necessary for maintaining and acquiring synchronization of MCS transmission It is for the purpose of transmission, transmission of a short length MAC management message, and transmission of other physical layer signaling signals. The auxiliary channel may be located in a slot different from the dedicated subchannel so as to receive feedback information on the dedicated subchannel corresponding to one-to-one. As a link adaptation method of an auxiliary channel, there is a method of adjusting transmission power by using a fixed modulation method and a code rate. Repeat coding may be performed on the auxiliary channel.

11 shows a structure of a synchronization channel according to an embodiment of the present invention.

Referring to FIG. 11, in the time domain of the synchronization channel 1020, the first time domain preamble 1100 is transmitted with a cyclic prefix (CP), and the second and third time domain preambles 1102 and 1104 are without a CP. Is sent. The same sequence is repeatedly transmitted to the first time domain preamble 1100 and the second and third time domain preambles 1102 and 1104. Here, the preamble having a length of 1024 samples may be repeated 3 + α times in the time domain. The same sequence may be repeatedly transmitted in the frequency domain.

12 shows a structure of a synchronization channel according to another embodiment of the present invention.

Referring to FIG. 12, when resources for cellular communication and resources for direct communication are divided according to the FDM scheme, 72 consecutive subcarriers may be allocated for the synchronization channel 1020. The sync channel preamble is transmitted through 36 subcarriers among 72 consecutive subcarriers, and the same preamble pattern can be repeated in three OFDM symbol intervals. To this end, a 36-bit long binary sequence may be allocated to 72 subcarriers on a frequency axis, and converted into a time domain preamble using an inverse fast fourier transform (IFFT). At this time, the size of the IFFT is the same as the size of the IFFT used in cellular communication.

Accordingly, when the receiving terminal estimates time synchronization in the frequency domain using the synchronization channel preamble, interference between carriers due to frequency error can be reduced. That is, the accuracy of estimating time synchronization in the frequency domain can be increased.

Meanwhile, the sync channel preamble may be defined as two patterns, for example, sequence 0 1200 or sequence 1 1210, and may be expressed as a basic pattern having a length of 512 samples in the time domain. In the case of the sequence 0 1200, the basic pattern B of 512 samples length is repeated twice to form a time domain preamble of 1024 samples length. In the case of the sequence 1 (1210), a time domain preamble having a length of 1024 samples is formed by combining a base pattern (C) having a length of 512 samples and a pattern (-C) multiplied with the base pattern (C) by (1). In this case, the time domain preamble of 1024 sample length may be repeated (3 + α) times so that the length of the synchronization channel preamble becomes 3 OFDM symbols. The first time domain preamble (or the first OFDM symbol) may be transmitted together with a cyclic prefix (CP) 1220 and the second and third time domain preambles may be transmitted without the CP. In this case, α may be defined as shown in Equation 8.

Here, N _cp is the length of CP and N _FFT means the FFT size.

As such, if only the first time domain preamble is transmitted with the CP and the remaining time domain preamble is repeatedly transmitted without the CP, the phase of the preamble sequence has cyclic continuity. Accordingly, it is advantageous for the receiving terminal to estimate time synchronization. In addition, since the preamble sequence is repeated in the frequency domain, the frequency error can be easily estimated using the preamble sequence.

In addition, if the basic pattern of the synchronization channel preamble is reduced to 512 samples in length, it is possible to reduce the time error estimation complexity in the receiver as compared with 1024 samples in length. And, the frequency error estimation range can be widened twice.

A structure of a pseudo random binary sequence (PRBS) generator for generating a sequence used for a sync channel preamble according to an embodiment of the present invention is shown in FIG. The polynomial for the PRBS generator is given by 1+ X ¹ + X ⁴ + X ⁷ + X ¹⁵ . The initial register value of the PRBS is defined as in Equation 9.

Here, b0 means a LSB (least significant bit) of the PRBS seed. Sequence 0 (S _k ⁰ ) and sequence 1 (S _k ¹ ) of the sync channel preamble are defined as in Equations 10 and 11, respectively. As such, the preamble sequence different from the existing ranging code can be generated by setting the initial register value differently while using the existing ranging code generator as it is. This allows the same terminal to support both cellular and direct communication, while minimizing the modem's modem structure change.

Here, C _k is a binary code generated by the PRBS generator of Figure 13, C ₀ is the first output of the PRBS. S _k ^j represents the k th bit of the j th sequence. The k th bit may be transmitted on the k th subcarrier among the 72 consecutive subcarriers allocated for the synchronization channel 1020.

S _k ⁰ may transmit 1 or -1 through an odd subcarrier among 72 consecutive subcarriers allocated for the synchronization channel 1020, and may transmit no signal through an even subcarrier.

S _k ¹ may transmit 1 or -1 through an even subcarrier among 72 consecutive subcarriers allocated for the synchronization channel 1020, and may transmit no signal through an odd subcarrier.

A transmitting terminal that participates in direct communication between terminals and transmits a synchronization channel 1020 may select and transmit one of sequence 0 or sequence 1. Since the receiving terminal cannot know what sequence the transmitting terminal has transmitted, it must be able to detect both sequences.

The two sequences can be used for various purposes.

For example, terminals participating in direct communication in the same region may be divided into two groups, the first group may use sequence 0, and the second group may use sequence 1. FIG. Through this, it is possible to increase the probability of detecting a collision caused by two or more terminals transmitting the synchronization channel at the same time.

As another example, a terminal using a GPS signal as a reference signal may use sequence 0, and a terminal using a base station signal as a reference signal may use sequence 1. FIG. Through this, the receiving terminal can know the reference signal used by the transmitting terminal.

As another example, the terminal having the accuracy of the synchronization signal higher than the reference value may use the sequence 0, and the terminal having the accuracy of the synchronization signal lower than the reference value may use the sequence 1. Through this, the receiving terminal can know the accuracy of the time synchronization and frequency synchronization of the synchronization channel.

As another example, a terminal supporting IEEE 802.16m may use sequence 0, and a terminal supporting only IEEE 802.16e-2009 may use sequence 1. FIG. Through this, the receiving terminal can distinguish the communication standard of the transmitting terminal.

<Example 3>

As described in Embodiment 2, in order to acquire time synchronization and frequency synchronization between terminals during direct communication between terminals, a synchronization channel may be transmitted. However, unlike cellular communication which periodically receives a preamble for synchronization acquisition from a base station, time synchronization error or frequency synchronization error may be large in direct communication. In addition, when terminals performing direct communication move during data transmission and reception, a distance between terminals may be changed to increase a time synchronization error.

In a third embodiment of the present invention, a data packet or a predefined dedicated channel preamble is transmitted through a dedicated channel. The structure of the dedicated channel and the structure of the frame including the dedicated channel can refer to FIG. 10.

Here, the data packet is a packet generated according to a channel coding scheme and a modulation scheme previously promised between the transmitting terminal and the receiving terminal. The dedicated channel preamble is a signal that is requested by the receiving terminal or irregularly transmitted when the transmitting terminal determines that transmission is necessary. The dedicated channel preamble may be used for at least one of time synchronization error estimation, frequency synchronization error estimation, and channel state estimation.

A structure of a pseudo random binary sequence (PRBS) generator for generating a sequence used for a dedicated channel preamble according to an embodiment of the present invention is shown in FIG. The polynomial for the PRBS generator is given by 1+ X ¹ + X ⁴ + X ⁷ + X ¹⁵ . The initial register value of the PRBS may be defined as shown in Equation 12.

Here, b0 means a LSB (least significant bit) of the PRBS seed.

The sequence S _k of the dedicated channel preamble is defined as in Equation 13.

Here, C _k is a binary code generated by the PRBS generator of Figure 13, C ₀ is the first output of the PRBS.

14 is a diagram illustrating a method of allocating a dedicated channel preamble to a dedicated channel resource according to an embodiment of the present invention.

Referring to FIG. 14, a dedicated channel preamble having a length of 72 subcarriers is divided into 12 subcodes by 6 subcarriers. Each subcode is assigned to 12 mRBs, respectively. The same sequence is repeatedly transmitted during six OFDM symbol intervals.

When a predetermined event occurs, the transmitting terminal may stop transmitting the data packet and transmit the dedicated channel preamble.

As an example, when the estimated timing offset (timing offset) in the ranging signal transmitted from the receiving terminal to the transmitting terminal through the auxiliary subchannel exceeds the reference value, the transmitting terminal may transmit a dedicated channel preamble.

As another example, even if a packet error rate (PER) exceeds a reference value, the transmitting terminal may transmit a dedicated channel preamble.

As another example, when the transmitting terminal receives the preamble transmission request signal through the auxiliary channel, the transmitting terminal may transmit the dedicated channel preamble.

On the other hand, if the data packet transmitted before the dedicated channel preamble transmission includes information on whether the dedicated channel preamble is transmitted and the dedicated channel preamble transmission time, the receiving terminal may receive the dedicated channel preamble by decoding the dedicated channel at the corresponding time point. .

Even if the data packet does not include information on whether the dedicated channel preamble is transmitted and when the dedicated channel preamble is transmitted, when the receiving terminal fails to decode the dedicated channel, the dedicated channel may be regarded as the dedicated channel preamble. The receiving terminal may detect whether the dedicated channel preamble is received using the correlator.

The receiving terminal may estimate the frequency offset or estimate the time offset using the dedicated channel preamble.

<Fourth Embodiment>

In a fourth embodiment of the present invention, there is a method of allocating some of resources allocated for direct communication to an auxiliary channel in order to obtain time synchronization and frequency synchronization between terminals performing direct communication.

15 is a diagram illustrating a resource allocation structure for an auxiliary channel according to an embodiment of the present invention.

Referring to FIG. 15, a unit of an auxiliary channel includes at least one tile (eg, 4 tiles) distributed in a frequency domain. One tile may be configured in units of (2 subcarriers * 5 OFDM symbols). Accordingly, performance gain and frequency diversity gain through redundant transmission in the time domain can be obtained.

The ranging channel, the channel quality information (CQI) channel, and the feedback channel may be time-divided on the auxiliary channel and transmitted alternately.

16 illustrates a method of allocating a ranging channel to auxiliary channel resources according to an embodiment of the present invention.

Referring to FIG. 16, a ranging channel having an eight subcarrier length is divided into four subcodes by two subcarriers. Each subcode is assigned to four tiles, respectively. The same sequence is repeatedly transmitted during five OFDM symbol intervals. The sequence S _k of the ranging channel is defined as in Equation 14.

The transmitting terminal periodically transmits the ranging channel, and the receiving terminal estimates time synchronization, frequency synchronization, and signal-to-noise ratio using the ranging channel.

The receiving terminal may increase the accuracy of the estimation using the cumulative result of the ranging channel transmitted periodically.

The receiving terminal may correct the time synchronization or the frequency synchronization using the estimation result or determine the CQI value transmitted in the opposite direction of the ranging channel.

In addition, the receiving terminal may request a dedicated channel preamble from the transmitting terminal using the estimation result. The transmission start time of the ranging channel (for example, the position of the slot to start the transmission of the ranging channel) and the transmission period may be determined during the initialization process when establishing a link between the terminals.

17 illustrates a method of allocating a CQI channel to auxiliary channel resources according to an embodiment of the present invention.

Referring to FIG. 17, four CQI codes of length 10 may be mapped to four tiles.

18 illustrates a method of converting CQI information into a CQI code according to an embodiment of the present invention.

Referring to FIG. 18, a sequence corresponding to CQI information (CQI payload) is generated based on the definition of Table 2 (Sequence Generation) (S1800).

Index Sequence Usage 0 1111111111 level 0 One 0010110001 level 1 2 0100100110 level 2 3 1001101000 level 3 4 1011000100 level 4 5 0110001010 level 5 6 0000011101 level 6 7 1101010011 level 7 8 1100011000 Reserved 9 0001010110 Reserved 10 0111000001 Reserved 11 1010001111 Reserved 12 1000100011 Reserved 13 0101101101 Reserved 14 0011111010 Reserved 15 1110110100 Reserved

Here, the index may be determined using the signal-to-noise ratio of the terminal transmitting the CQI channel. The signal-to-noise ratio may be estimated through a dedicated channel preamble, a dedicated channel pilot, a ranging channel, and the like. Table 2 shows an example of transmitting 3-bit information through the CQI channel, but this may be variously modified.

The sequence is modulated and repetition (S1810) and mapped to a symbol s [k] (Symbol sequence to subcarrier mapping) (S1820). For example, sequence 0 can be modulated with symbol 1 and sequence 1 can be modulated with symbol -1.

The symbol is generated as a CQI code according to Equation (15).

In this case, K _i [j] refers to the j th element of K _i , and K _i corresponding to four tiles is defined as in Equations 16 to 19.

Accordingly, the CQI channel may include up to 4 bits of information.

The CQI channel may be transmitted periodically. The transmission start time and transmission period of the CQI channel may be determined in an initialization process when establishing a link between terminals. At this time, the ranging channel and the CQI channel should be set not to overlap each other.

The receiving terminal receiving the CQI channel may decode the index using a non-coherent demodulation method. In order to increase the decoding performance, the correlation value between sequences should be minimum (eg, 2 or less). The correlation value between the m th sequence and the n th sequence may be defined as in Equation 20.

Here, b _{i , k} means k-th bit of the i-th sequence.

Meanwhile, the feedback channel may be allocated to the auxiliary channel resource in the same manner as the CQI channel. The feedback channel is an ACK indicating normal decoding of a data packet received through a dedicated channel, a NAK indicating failure to decode a data packet received through a dedicated channel (indicated by a transmission frame in accordance with HARQ), and a normal reception of an MCS change request message. MCS change confirm (MCS change confirm) for notifying the user, resource change (RCHG) indication for notifying the normal reception of the resource change request, and Send Indication for notifying the transmission of broadcast messages such as RTS and CTS in advance. It may include.

Table 3 shows a sequence corresponding to information included in the feedback channel.

Index Sequence Usage 0 1111111111 ACK One 0010110001 NAK for frame 0 2 0100100110 NAK for frame 1 3 1001101000 NAK for frame 2 4 1011000100 NAK for frame 3 5 0110001010 MCS Change Confirm 6 0000011101 RCHG Indication 7 1101010011 Reserved 8 1100011000 Send Indication 9 0001010110 Reserved 10 0111000001 Reserved 11 1010001111 Reserved 12 1000100011 Reserved 13 0101101101 Reserved 14 0011111010 Reserved 15 1110110100 Reserved

Here, when one of the sequences of the feedback channel is used for Send Indication, the same sequence should not be used for the CQI channel. For example, if index 8 of the feedback channel is allocated for the transmission indication, index 8 of the CQI channel should not be used. This is because the transmission start time and transmission period of the CQI channel are not known when the terminal is not directly transmitting and receiving the RTS or the CTS, and thus the CQI channel and the feedback channel cannot be distinguished.

As described above, the auxiliary channel transmits a ranging channel, a CQI channel, and a feedback channel. Accordingly, the terminal receiving the auxiliary channel should distinguish whether it is a ranging channel, a CQI channel, or a feedback channel. If the UE knows the transmission start time and transmission period of at least one of the ranging channel, the CQI channel and the feedback channel, it may be classified accordingly.

In the case of a ranging channel, the terminal may detect the ranging code using the structure of FIG. 16. The terminal may estimate a time error or a frequency error using the detected ranging code and estimate the signal-to-noise ratio.

In the case of a CQI channel, the UE may decode the information included in the CQI channel by using the correspondence between the CQI information and the sequence of Table 1.

In the case of a feedback channel, the terminal may decode the information included in the feedback channel by using the correspondence between the feedback information and the sequence of Table 3.

On the other hand, when the terminal is not directly transmitting and receiving the RTS or CTS, the transmission start time and transmission period of at least one of the ranging channel, the CQI channel and the feedback channel are not known. Therefore, the terminal receiving the auxiliary channel can distinguish the channels using the sequence. That is, the CQI sequence and the ranging sequence defined in Table 1 are compared with the received signal, and the sequence closest to the received signal is found. Here, the ranging sequence may be defined as in Equation 21.

Here, the ranging sequence may be obtained by allocating the sequence S _k of the ranging channel defined in Equation 14 as shown in FIG. 16. The ranging sequence is only an example and may be set so that the correlation value and the sequence used for the CQI channel or the feedback channel are minimum.

When the received signal of the terminal is closest to Equation 21, the terminal may determine the auxiliary channel as the ranging channel.

On the other hand, if the received signal of the terminal is closest to the sequence corresponding to the Send Indication of Table 2, the terminal may determine that the auxiliary channel as a feedback channel. The transmission indication means that a broadcast message including an RTS or CTS is transmitted, so that a corresponding dedicated channel can be received.

In other cases, the UE may determine that the auxiliary channel is a CQI channel or a feedback channel.

19 illustrates a terminal that can be applied to an embodiment of the present invention.

Referring to FIG. 19, the terminal 1300 includes a processor 1310, a memory 1320, and a radio frequency (RF) unit 1330. The processor 1310 may be configured to implement the procedures and / or methods proposed by the present invention. The memory 1320 is connected to the processor 1310 and stores various information related to the operation of the processor 1310. The RF unit 1330 is connected with the processor 1310 and transmits and / or receives a radio signal. The terminal 1300 may have a single antenna or multiple antennas.

The embodiments of the present invention described above are not implemented only by the apparatus and method, but may be implemented through a program for realizing the function corresponding to the configuration of the embodiment of the present invention or a recording medium on which the program is recorded.

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 (27)

In a method for performing direct communication between terminals of a first terminal,
Performing direct communication with at least one second terminal using resources allocated for direct communication between terminals;
Including,
The resource includes a synchronization channel used for frequency synchronization and time synchronization between terminals,
And the synchronization channel comprises a synchronization channel preamble used for at least one of preamble detection, time offset estimation, frequency offset estimation and channel estimation. The method of claim 1,
The sync channel preamble is one of a first sequence in which a basic pattern having a N _FFT / 2 sample length is repeated or a second sequence in which a pattern obtained by multiplying the basic pattern and the basic pattern by (-1) is combined, and the N _FFT Is the size of the FFT. The method of claim 2,
At least one OFDM symbol is used for transmission of the synchronization channel preamble,
The base pattern is repeated twice or a time-domain preamble consisting of a combination of the base pattern and the pattern multiplied by (-1) is repeated several times during the at least one OFDM symbol. The method of claim 3,
Wherein the time domain preamble is repeated (3 + α) times during the at least one OFDM symbol, wherein α is 2N _CP / N _FFT and N _CP is the length of CP. The method of claim 2,
The first sequence or the second sequence is defined by a binary code generated by the PRBS used for ranging code generation, the initial value of the PRBS is b14, ..., b0 = 1, 1, 0, Method that is 1,0,1,0,0,0,0,0,0,0,0,0. The method of claim 5,
The first sequence is

Wherein the second sequence is

Where C _k is a binary code generated by the PRBS and C ₀ is the first output of the PRBS. The method of claim 2,
And wherein the first terminal selects one of the first sequence and the second sequence to generate the sync channel preamble, and the second terminal can detect both the first sequence and the second sequence. The method of claim 1,
Three OFDM symbols are used to transmit the sync channel preamble,
A first OFDM symbol of the three OFDM symbols includes a cyclic prefix (CP), and a second OFDM symbol and a third OFDM symbol do not include the CP. The method of claim 1,
If 72 consecutive subcarriers are assigned to the sync channel, the sync channel preamble is mapped to 36 subcarriers. In a method for performing direct communication between terminals of a first terminal,
Performing direct communication with at least one second terminal using resources allocated for direct communication between terminals;
Including,
The resource includes a dedicated channel for transmitting a data packet or for transmitting a dedicated channel preamble used for time offset estimation or frequency offset estimation. The method of claim 10,
The dedicated channel preamble has a 72 subcarrier length and is divided into 12 subcodes having 6 subcarriers. The method of claim 10,
The dedicated channel preamble is repeatedly transmitted through six OFDM symbols. The method of claim 10,
The sequence of the dedicated channel preamble is defined by a binary code generated by a PRBS used for generating a ranging code, and an initial value of the PRBS is b14, ..., b0 = 1,1,0,1,0 The method of 1,0,0,0,0,0,0,0,0,0. The method of claim 13,
The sequence of the dedicated channel preamble is

And C _k is the binary code generated by the PRBS and C ₀ is the first output of the PRBS. In a method for performing direct communication between terminals of a first terminal,
Performing direct communication with at least one second terminal using resources allocated for direct communication between terminals;
Including,
The resource includes a secondary channel for mapping and transmitting at least one of a ranging channel, a channel quality information (CQI) channel, and a feedback channel. 16. The method of claim 15,
At least one of the ranging channel, the channel quality information (CQI) channel, and the feedback channel is transmitted in a time division manner. 16. The method of claim 15,
The CQI code transmitted on the CQI channel is determined using a signal-to-noise ratio estimated over at least one of a dedicated channel preamble, a dedicated channel pilot, and the ranging channel. 16. The method of claim 15,
At least one of the ranging channel, the CQI channel, and the feedback channel is periodically transmitted according to a transmission start time and transmission period determined during link initialization. 16. The method of claim 15,
The feedback channel is transmitted in a different time domain than the ranging channel or the CQI channel. 16. The method of claim 15,
The feedback channel includes at least one of ACK, NAK, MCS change confirmation, RCHG request indication, transmission indication. RF (Radio Frequency) module, and
Includes a processor,
The processor is configured to perform direct communication with at least one second terminal using resources allocated for direct communication between terminals,
The resource includes a synchronization channel used for frequency synchronization and time synchronization between terminals, and the synchronization channel includes a synchronization channel preamble used for at least one of preamble detection, time offset estimation, frequency offset estimation, and channel estimation. Terminal. RF (Radio Frequency) module, and
Includes a processor,
The processor is configured to perform direct communication with at least one second terminal using resources allocated for direct communication between terminals,
The resource includes a dedicated channel for transmitting a data packet or a dedicated channel preamble used for time offset estimation or frequency offset estimation. RF (Radio Frequency) module, and
Includes a processor,
The processor is configured to perform direct communication with at least one second terminal using resources allocated for direct communication between terminals,
The resource includes a secondary channel for mapping and transmitting at least one of a ranging channel, a channel quality information (CQI) channel, and a feedback channel. In a method for performing direct communication between terminals by a first terminal,
Estimating a frequency offset,
Setting a transmission frequency or a reception frequency using the estimated frequency offset, and
Performing direct communication with at least one second terminal using the transmission frequency or the reception frequency
Including,
If the first terminal is located within cell coverage of a base station, the frequency offset is estimated according to the frequency of the base station. 25. The method of claim 24,
When the first terminal is not located within the cell coverage of the base station, the frequency offset is a synchronization signal received from the at least one second terminal or a frequency stored in advance when the first terminal is located within the cell coverage of the base station. Estimated according to the method. In a method for performing direct communication between terminals by a first terminal,
Performing ranging with the base station, and
The difference between the time point at which the second terminal performing direct communication with the first terminal receives the direct communication signal of the first terminal and the time point at which the second terminal receives the cellular communication signal between the base station and the third terminal is CP ( Transmitting the direct communication signal to the second terminal to be within a Cyclic Prefix)
&Lt; / RTI &gt; The method of claim 26,
Receiving a transmission time adjustment message from the second terminal, and
Adjusting a time point at which the direct communication signal is transmitted according to the transmission time adjustment message;
&Lt; / RTI &gt;

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