KR101488469B1 - Apparatus and method for synchronization in full duplex relay wtih frequency-domain feedback interfernece cancellation - Google Patents

Abstract

The present invention relates to a feedback interference cancellation method and a synchronization method using the same, and more particularly, to a downlink synchronization method for eliminating feedback interference in a full duplex relay, the method comprising: performing downlink initial synchronization with a base station; Resetting an FFT performance period for a received signal in order to minimize interference due to a mismatch in time synchronization between the received signal and the received feedback interference signal; and performing FFT on the received signal according to the reset FFT duration And estimating a feedback interference channel for the FFT-processed reception signal to remove the feedback interference signal.

Feedback, FDR, HDR, OFDM, Interference.

Description

Field of the Invention < RTI ID = 0.0 > [0001] < / RTI > A synchronization device and method in a full-

The present invention relates to a synchronization scheme considering feedback interference in an FDR (Full Duplex Relay) based on OFDM (Orthogonal Frequency Division Multiplexing), and more particularly, to a scheme for reducing interference between neighboring symbols and neighboring subcarriers Synchronization apparatus and method.

A relay (Realy, or relay station) is a type of wireless communication system for maximizing bandwidth efficiency by increasing transmission reliability or ensuring multiplexing gain by using one or more nodes dispersedly present between a transmitting end and a receiving end .

In a mobile communication system, direct communication between a base station and a mobile station is possible. However, terminals located in a cell boundary or in a radio wave shadow area communicate with a base station through a relay of a relay located at a specific location.

Through the relay function of the relay, not only the service area can be expanded to the service disabled area or the cell boundary, but also the yield can be improved by mitigating interference between adjacent cells.

In addition, the base station and the relay are connected wirelessly, and it is possible to spatially reuse frequency by recognizing which terminal is connected to these devices, and the base station centrally performs resource management for the terminals connected to the relay .

The types of relays can be divided into AF (Amplify and Forward) and DF (Decoding and Forward) relays according to data transmission methods.

The relay of the AF system simply amplifies and transmits the received signal, and the DF type relay decodes the received signal and transmits the signal to be transmitted from the relay. In this way, the noise propagates in the relay of the AF system, while the error due to the decoding can be propagated in the relay of the DF system.

Also, the relays can be divided into the relays of the HD (Half Duplex) and FD (Full Duplex) according to the duplex method. The relay of the FD scheme is superior to the HD scheme in transmission efficiency, but since the transmitted signal is fed back to serve as an interference to the receiving end, most relays now consider HD as a duplex scheme.

In the HDR (Half Duplex Relay), the downlink section is divided into an access zone and a relay zone. An access zone refers to a period during which a base station and a relay transmit signals to a terminal, and a relay zone refers to a period during which a relay receives signals from a base station.

However, a transition gap is required between the access zone and the relay zone, and an additional R-amble is required for the relay to synchronize with the base station. As described above, since the access zone and the relay zone are distinguished, the relay of the HD scheme has a lower transmission efficiency than the relay of the FD scheme.

In the FDR (Full Duplex Relay), since the access zone and the relay zone do not distinguish the DL frame period, the transmission efficiency can be increased as compared with the HD type relay.

However, since the base station and the relay use the same resources, there is a disadvantage that the interference between adjacent channels increases as compared with the relay of the HD type. In addition, there is a problem that the signal transmitted by the relay is fed back to the receiving end and acts as interference.

1 is a diagram illustrating signals input to a receiver when feedback interference is considered in the FDR.

Referring to FIG. 1, the FDR receivers 120 and 160 simultaneously receive feedback interference with signals transmitted from the base stations 110 and 150. 1 (a) shows a receiver 120 in a synchronous type, and FIG. 1 (b) shows a receiver 160 in an asynchronous type.

1 (a), since the feedback interference is received ahead of the signal transmitted from the base station 110 in the synchronous type, the FDR receiver 120 performs the FFT even though the base station 110 has acquired synchronization with the base station 110 It can be known that interference between adjacent symbol and interference between adjacent subcarriers occurs due to feedback interference by the FDR transmitter 130. [

1B, in the asynchronous type, since the feedback interference signal of the FDR transmitter 170 is generally received by the FDR receiver 160 later than the signal transmitted from the base station 150, the orthogonality of the signal in the FFT interval is destroyed It can be seen that interference between adjacent symbol interference due to feedback interference and interference between adjacent subcarriers do not occur.

FIG. 2 is a diagram illustrating a case where interference between adjacent symbols and interference between adjacent subcarriers are slightly generated by a feedback signal when a time synchronization error occurs in an asynchronous type relay.

Referring to FIG. 2, feedback interference from the FDR transmitter 230 may be received by the FDR receiver 220 by more than one sample in comparison with a signal transmitted from the base station 210 due to a time synchronization error.

In this case, interference between neighboring symbols due to feedback interference and interference between adjacent subcarriers occurs.

3 is a diagram illustrating a case where adjacent inter-symbol interference and adjacent sub-carrier interference by the feedback signal occur in the uplink transmission.

3, all the signals transmitted by the UEs in the FDR region are received at the same time by the FDR receiver 320, but the FDR is not timed advance before the timing synchronization inconsistency occurs in the base station receiving terminal, The feedback interference is received ahead of the signal transmitted from the terminals.

Therefore, adjacent symbol interference and adjacent subcarrier interference due to feedback interference from the FDR transmitter 330 to the FDR transmitter 320 occur in the same manner as the downlink synchronization type.

As described above, if the received signal is processed in the frequency domain after the relay acquires synchronization with the base station, the orthogonality of the feedback interference can be destroyed. The interference cancellation can not be correctly performed due to the influence of the adjacent inter-symbol interference due to the feedback interference and the interference between the adjacent sub-carriers, including the channel estimation of the feedback signal.

In general, the required signal-to-feedback-interference ratio (SFIR) is -40 dB to 10 dB. When the SFIR is less than -20 dB, it is impossible to demodulate the signal transmitted from the base station.

Therefore, in the OFDM-based FDR, there is a need for an apparatus and a method for minimizing adjacent symbol interference and adjacent subcarrier interference due to feedback interference.

It is an object of the present invention to provide a synchronization apparatus and method in a full-duplex relay performing frequency-domain feedback signal cancellation.

It is another object of the present invention to provide an apparatus and method for minimizing inter-symbol interference and adjacent subcarrier interference due to feedback interference in OFDM-based FDR.

According to a first aspect of the present invention, there is provided a downlink synchronization method for eliminating feedback interference in a full duplex relay, the method comprising the steps of: performing downlink initial synchronization with a base station; Resetting an FFT duration for a received signal to minimize interference due to a mismatch in time synchronization between a signal transmitted from the mobile station and a received feedback interfering signal, and performing FFT on the received signal according to the reset FFT duration. And estimating a feedback interference channel for the FFT-processed reception signal to remove the feedback interference signal.

According to a second aspect of the present invention, there is provided an apparatus for downlink synchronization through feedback interference cancellation in a full duplex relay, the apparatus comprising: a frequency synchronizer for performing downlink initial synchronization with a base station; An FFT section updater for resetting an FFT performance section for a received signal in order to minimize interference caused by a mismatch in time synchronization between a signal transmitted from the base station and a received feedback interference signal, And a channel estimator for estimating a feedback interference channel for the FFT-processed reception signal to remove the feedback interference signal.

According to a third aspect of the present invention, there is provided an uplink synchronization method for eliminating feedback interference in a full duplex relay, the method comprising: performing uplink initial synchronization with a terminal; Resetting an FFT duration for a received signal to minimize interference due to a mismatch in time synchronization between a signal transmitted from the mobile station and a received feedback interfering signal; and performing FFT on the received signal according to the reset FFT duration. And estimating a feedback interference channel for the FFT-processed reception signal to remove the feedback interference signal.

According to a fourth aspect of the present invention, there is provided an apparatus for uplink synchronization through elimination of feedback interference in a full duplex relay, the apparatus comprising: a frequency synchronizer for performing uplink initial synchronization with a terminal; An FFT section updater for resetting an FFT performance section for a received signal in order to minimize interference due to a mismatch in time synchronization between the signal transmitted from the terminal and the received feedback interference signal, And a channel estimator for estimating a feedback interference channel for the FFT-processed reception signal to remove the feedback interference signal.

The OFDM-based FDR of the present invention has an advantage of minimizing inter-symbol interference due to feedback interference and interference between adjacent subcarriers through a synchronization procedure considering feedback interference.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

In the present invention, an OFDM-based DF-type FDR is considered. The DF relays do not require transparent transmission with the base station. That is, the relay transmits the signal received from the base station in the n-th frame to the mobile station in the (n + 1) - th frame.

In the DF type relay, the process of removing, decoding, and forwarding the feedback interfering signal from the received signal must be completed within one frame. Therefore, in the DF method, the processing time for removing the feedback interference signal, which is the most important element in the existing relay, does not matter much.

The symbol streams input serially in OFDM are converted into a parallel form of block units composed of N symbols. Because the signal transmitted through each subchannel has frequency non-selective channel characteristics, it is possible to generate a feedback interfering signal through a single tap multiplication with low complexity for each subchannel at the receiving end. Therefore, it is efficient to process the feedback interference cancellation method in the OFDM-based DF FDR in the frequency domain.

However, when the feedback interference signal cancellation and decoding are performed in the frequency domain in the OFDM-based FDR, adjacent inter-symbol interference and adjacent sub-carrier interference occur due to time synchronization inconsistency between the feedback interfering signal and the signal transmitted from the base station. The present invention proposes a synchronization apparatus and method suitable for OFDM-based FDR in order to prevent the occurrence of such interference.

Hereinafter, the present invention will be described with respect to a synchronization apparatus and method in a full-duplex relay performing frequency-domain feedback signal cancellation.

4 is a diagram illustrating a process of removing an initial synchronization process, a feedback interference cancellation process in a downlink, and an uplink feedback interference in a receiving end of an FDR according to an embodiment of the present invention.

Referring to FIG. 4, step 100 shows an initial synchronization process after power is applied to the FDR 420. The FDR 420 performs time synchronization, frequency synchronization, and cell search between the BS 430 and the FDR 420 using the downlink synchronization signal transmitted from the BS 430.

When the cell search of the BS 430 is completed, the FDR 420 transmits an initial ranging signal to the BS 430. The base station 430 estimates time synchronization and power for uplink transmission using the initial ranging signal transmitted from the FDR 420 and transmits information on pre-compensation to the FDR 420, .

Step 200 is a step in the time domain before the FDR 420 performs the FFT on the downlink. The time domain interference between the feedback interference received at the receiver of the FDR 420 and the signal transmitted from the base station 430 In order to minimize the interference caused by the FFT.

The FDR 420 estimates the maximum delay of the feedback interfering channel and the propagation delay of the feedback interference using the downlink synchronization signal. Based on the estimated information, the FFT performing section is reset to perform the FFT. This is done for a reference signal (e.g., a pilot).

Step 300 is a process of removing the downlink feedback interference of the FDR 420. The FDR 420 estimates a feedback interference channel and generates a feedback interference signal. The generated feedback interfering signal is removed from the received signal in comparison to the received signal. The received signal with the feedback interference removed is divided into a preamble or a data signal for downlink synchronization.

If the received signal is a downlink synchronization signal, the FDR 420 estimates a symbol timing offset (hereinafter referred to as a tracking process) and performs decoding (demodulation) if the received signal is a data signal.

The symbol timing offset estimated through the tracking process is input to the FFT performance range update process in step 200, and the FFT performance interval is reset. The processes of steps 200 and 300 are repeatedly performed every frame in the downlink.

In order to minimize the interference due to the inconsistency of the time synchronization between the feedback interference received at the receiver of the FDR 420 and the signal transmitted from the terminal 410, an FFT This shows the process of resetting the performance interval.

The FDR 420 estimates the maximum delay and propagation delay of the feedback interference channel using a signal for uplink synchronization. Then, based on the estimated information, the FFT performing section is reset to perform the FFT.

Step 500 is a process for canceling the uplink feedback interference. The FDR 420 estimates a feedback interference channel and generates a feedback interference signal. The generated feedback interfering signal is removed from the received signal. The received signal from which the feedback interference is removed is divided into a signal for uplink synchronization (e.g., ranging, pilot) or a data signal.

The FDR 420 performs tracking if the received signal is a signal for uplink synchronization, and performs demodulation if the received signal is a data signal. The symbol timing offset estimated through the tracking process is input to the FFT performing range updating process in step 400, and the FFT performing interval is reset. Now, the synchronization process suitable for the FDR 420 will be described in more detail with reference to FIG.

5 is a flowchart detailing an initial synchronization process in an FDR according to an embodiment of the present invention.

5, in the initial synchronization process, a propagation delay estimation process 510 for estimating a propagation delay between the base station and the FDR, a frequency synchronization process for obtaining and compensating a carrier frequency offset between the base station and the FDR 520, Is performed.

Thereafter, a CP removing process 530 for removing the CP from the signal, an FFT performing process 540 for the CP-removed signal, and a cell search performing process 550 are performed. The signal received in the FDR is expressed by the following equation.

는 l-번째 시간영역 수신 신호 벡터를 나타낸다. 또한 n 개의 원소를 갖는

,

는 기지국으로부터 전송된 신호의 벡터, 잡음 벡터를 각각 나타낸다. h ^d 는 n 개의 열과 행으로 이루어진 기지국과 FDR간의 채널 행렬을 의미한다. 기지국과 FDR간의 전파 지연은 전파 지연 추정 과정(510 단계)에서 추정되며, 일 실시예로서 프리앰블의 반복패턴을 이용하여 하기 수식과 같이 추정될 수 있다. Here, a symbol having a length of n

Represents the 1 st time domain received signal vector. Also having n elements

,

Represents a vector of a signal transmitted from the base station, and a noise vector, respectively. and h ^d denotes a channel matrix between the base station and the FDR having n columns and rows. The propagation delay between the base station and the FDR is estimated in the propagation delay estimation process (step 510). In one embodiment, the propagation delay between the base station and the FDR can be estimated as follows using a repetition pattern of preambles.

는 자기상관 연산을 수행하는 윈도우의 크기, 윈도우간의 거리, 추정된 기지국과 FDR간의 전파 지연을 나타낸다. 주파수 동기화 과정(520) 및 CP 제거 과정(530)이 수행된 후, FFT 수행 과정(540)에서는 인접 심볼간 간섭과 인접 부 반송파간의 간섭이 발생하지 않도록 다음과 같은 범위내에서 FFT가 수행된다.here,

Represents the size of the window performing the autocorrelation operation, the distance between the windows, and the propagation delay between the estimated base station and the FDR. After the frequency synchronization process 520 and the CP removal process 530 are performed, in the FFT process 540, an FFT is performed within the following range in order to prevent interference between adjacent symbol interferences and adjacent subcarriers.

와 N_g 는 샘플 단위로 표시된 기지국과 FDR간 채널의 최대 지연과 OFDM 심볼의 CP 길이를 나타낸다. 주파수 영역 신호로 변환된 수신 신호에 대해, 셀 탐색 과정(550 단계)을 수행하여 기지국과의 하향 링크 동기를 완료한다. FDR과 기지국과의 동기화 과정이 완료되면 FDR는 단말에게 신호를 전송한다.here,

And N _g represent the maximum delay of the channel between the base station and the FDR indicated in the sample unit and the CP length of the OFDM symbol. The mobile station performs a cell search procedure (step 550) on the received signal converted into the frequency domain signal to complete the downlink synchronization with the base station. When the synchronization process between the FDR and the base station is completed, the FDR transmits a signal to the mobile station.

From this point on, the receiving end of the FDR simultaneously receives the feedback interference and the signal transmitted from the base station. Once feedback interference begins to be received, FDRs present in a low SFIR environment can not track the propagation delay between the base station and the FDR. Therefore, in order for the FDR to perform tracking, the elimination of feedback interference must precede.

When a feedback interfering signal is received, inter-symbol interference due to the feedback signal and interference between the adjacent sub-carriers may occur depending on the FFT performance period in the synchronous type and asynchronous type FDR.

Hereinafter, the influence between the adjacent symbol and the adjacent carrier according to the FFT start point will be described in more detail. As an embodiment, a case in which interference between adjacent symbols of a feedback signal or interference between adjacent subcarriers occurs according to an FFT performance period in a synchronous type will be described. First, if the orthogonality is not destroyed, the l - th time domain signal received in the FDR is given by

는 피드백 간섭, h ^f는 n 개의 열과 행을 갖는 FDR의 송신단과 수신단사이의 피드백 간섭 채널 행렬을 나타낸다. FFT의 수행구간을 상기 <수학식 3>과 같이 설정하였을 경우 피드백 신호에 의한 인접 심볼간 간섭과 인접 부 반송파간의 간섭이 발생하여 피드백 간섭의 채널 추정 및 제거를 수행할 수 없다. 피드백 간섭으로 인한 인접 심볼간 간섭 또는 인접 부 반송파간의 간섭이 발생한 경우, 수신 신호는 하기 수식과 같다.Here, having n elements

The feedback interference, h ^f represents a feedback interference channel matrix between the transmitter and the receiver of the FDR having columns and rows of n. If the performance interval of the FFT is set as Equation (3), interference between adjacent symbol interference due to the feedback signal and interference between neighboring subcarriers occurs, and channel estimation and removal of feedback interference can not be performed. When interference between adjacent symbols due to feedback interference or interference between adjacent subcarriers occurs, the received signal is expressed by the following equation.

는 l+1 번째 피드백 간섭을 나타낸다. h ^f, A, B는 하기 수식과 같다. Here, A having n columns and rows, B are having a channel matrix, the n elements representing the interference between the channel matrix, the adjacent symbols representing the interference between adjacent sub-carriers by the feedback interference

Lt; th &gt; feedback interference. h ^f , A , and B are as follows.

Here, h, L, and M represent the multipath feedback channel gain, the CP length of the OFDM symbol, and the maximum delay of the feedback interference channel. The received signal shown in Equation (5) can be expressed as a frequency domain signal as follows.

로 주어진다. 인접 심볼간 간섭 및 인접 부 반송파간의 간섭이 발생하면 채널 h ^f의 추정은 어려워지는 경향이 있다. 피드백 간섭이 제거된 수신 신호는 다음과 같이 주어진다. here,

. If inter-symbol interference and interference between adjacent sub-carriers occur, estimation of the channel h ^f tends to be difficult. The received signal with the feedback interference removed is given by

으로 근사화하면 상기 <수학식 8> 하기 수식과 같이 간략화된다. Assuming here that the feedback channel is correctly estimated

(8) can be simplified as shown in the following equation.

Y ₃ , and Y ₄ are interference caused by a mismatch between the feedback interference at the FDR receiving end and the time synchronization of the signal transmitted from the base station. The SISR (Signal to Interference due to Synchronization error Ratio) due to mismatch in signal-to-time synchronization is as follows.

6 is a diagram illustrating performance according to an embodiment of the present invention.

Referring to FIG. 6, BER performance of the received signal is shown in Equation (9), where SFIR = -40 dB. Simulation was performed in the ITU-R PedB channel between the transmitting end and the receiving end of the FDR and in the ITU-R Ped A channel between the base station and the FDR receiving end with an SNR of -20 to 10 dB.

The performance curve indicated by circles in FIG. 6 represents BER performance in the absence of feedback interference. It can be seen that the BER performance of the received signal is greatly degraded due to the interference caused by the inconsistency of the time synchronization.

As described above, in order to remove the feedback interference in the frequency domain in the OFDM-based FDR, it is necessary to further re-adjust the FFT performance period. Hereinafter, a method of resetting the FFT performance period proposed by the present invention during the synchronization process of the FDR will be described.

7 is a diagram illustrating a process of resetting an FFT performance period according to an embodiment of the present invention.

Referring to FIG. 7, the process of resetting the FFT duration includes a channel delay estimation process (step 710) and an FFT duration update process (step 720).

In the case of the received signal reference signal in the time domain (step 705), the above-described channel delay estimation process (step 710) and the FFT performing interval updating process (step 720) are performed, and then the FFT process according to the updated interval is performed (Step 730).

If the received signal is not the received signal reference signal in the time domain (step 705), the FFT process is performed without performing the channel delay estimation process (step 710) and the FFT performing interval updating process (step 720) ).

In the channel delay estimation process (step 710), the maximum delay of the channel between the base station and the FDR and the maximum delay of the channel between the transmitter and receiver of the FDR are estimated. In the FFT interval update process (step 720), FFT is performed considering the propagation delay between the base station and the FDR, the propagation delay between the transmitter and the receiver of the FDR, the maximum delay of the channel between the base station and the FDR, and the maximum delay of the channel between the transmitter and receiver. The interval is determined.

In the FFT process (step 730), it is necessary to minimize the inter-symbol interference due to the feedback signal and the interference between the adjacent subcarriers. That is, the FFT is performed in the interval in which the SISR is minimized as follows.

는 채널 지연 추정 과정(710 단계)에서 추정된 샘플 단위로 표시된 기지국과 FDR간 채널의 최대 지연, 보호구간의 길이, FFT 시작점을 나타낸다. Here, the constraint means a range in which FFT can be performed so that a signal to be demodulated does not cause interference between adjacent symbols.

Represents the maximum delay of the channel between the base station and the FDR indicated in the sample unit estimated in the channel delay estimation process (step 710), the length of the guard interval, and the FFT start point.

It is necessary to estimate the FFT duration range in which interference due to the feedback signal does not occur within the FFT duration range given in Equation (11). In the channel delay estimation process (step 710), the maximum delay of the channel between the transmitting end and the receiving end of the relay is estimated. The correlation can be estimated by the following equation through cross-correlation calculation between the reception signal and the preamble.

는 시간영역의 프리앰블 시퀀스, 상호상관 수행 윈도우의 크기, 연산된 상호상관 결과, 릴레이의 송신단과 수신단 사이의 전파 지연을 나 타낸다. here,

Shows the preamble sequence in the time domain, the size of the cross-correlation window, the calculated cross-correlation result, and the propagation delay between the transmitter and receiver of the relay.

The maximum delay of the channel can be estimated using the calculated cross correlation result. That is, an index having a correlation value greater than or equal to a predetermined threshold value is compared with a maximum value among the correlation values, and a maximum value of the estimated indexes is regarded as a maximum delay of the feedback interference channel.

는 기지국과 릴레이 사이의 전파 지연만큼 앞당겨 얻어진다.Since the maximum delay of the estimated feedback interference includes the propagation delay between the base station and the relay, the maximum delay of the feedback interference actually considered

Is obtained ahead of the propagation delay between the base station and the relay.

을 이용하여 SISR을 최소화하기 위한 FFT의 수행 구간은 동기 타입의 경우 하기 수식과 같은 범위를 얻을 수 있다.In the case where the above-

The range of execution of the FFT for minimizing the SISR can be obtained in the range of the following equation in the case of the synchronous type.

는 SISR을 최소화하는 FFT의 시작점을 나타낸다. 또한 비동기 타입의 경우에 FFT 수행 구간은 하기 수식과 같은 범위를 갖는다.here

Represents the starting point of the FFT that minimizes the SISR. In the case of the asynchronous type, the FFT execution interval has the same range as the following equation.

는 하기 기술하는 트랙킹 과정을 통해 갱신된다.&Quot; (13) &quot; and &quot; (14) &quot;

Is updated through the tracking process described below.

FIG. 8 is a flowchart illustrating a feedback interference cancellation process and a tracking process after performing an FFT according to an embodiment of the present invention.

Referring to FIG. 8, the feedback interference cancellation and tracking process includes a feedback interference channel estimation process 810, a feedback interference signal generation process 820, a feedback interference cancellation process 830, a propagation delay estimation process 840, , A channel estimation process (step 850), and a demodulation process (step 860).

The feedback interference channel estimation process (step 810), the feedback interference signal generation process (step 820), and the feedback interference signal removal process (step 830) are performed on the received signal. If the processed signal is the reference signal, A propagation delay estimation process (step 840) and an FFT execution interval update process (step 870) are performed on the processed signal.

If the processed signal is not a reference signal (step 835), channel estimation (step 850) and demodulation (step 860) are performed on the processed signal.

When the FFT is performed on the received signal so that the adjacent symbol interference due to the feedback signal and the adjacent subcarrier interference do not occur in the downlink, the frequency domain received signal is as follows.

As an example for explaining the feedback interference cancellation and tracking process, it is assumed that the FFT performance period is performed in accordance with the feedback interference, and interference between adjacent symbol interference due to feedback interference and interference between adjacent subcarriers do not occur at this time.

는 피드백 간섭 신호와 기지국으로부터 전송된 신호의 시간동기 불일치에 의한 위상회전이다. 채널 추정 과정(810 단계)을 통해 피드백 간섭 채널

을 추정한다. Here, having N element

Is the phase rotation due to the time synchronization inconsistency between the feedback interfering signal and the signal transmitted from the base station. Through the channel estimation process (step 810)

.

The feedback interference signal generation process (step 820) generates feedback interference using the estimated feedback interference channel and the transmitted signal. The generated feedback interference is removed through a feedback interference cancellation process (step 830). The received signal from which the feedback interference signal is removed is expressed by the following equation.

는 피드백 간섭이 제거된 수신 신호를 나타낸다. 피드백 간섭이 제거된 수신 신호는 동기화 과정을 위해 전송된 프리앰블 또는 데이터 신호로 구분된다. 수신 신호가 데이터 신호이면 복조화 과정을 수행하고, 프리앰블이면 전파 지연 추정 과정(840 단계)를 통해 기지국로부터 전송된 신호와 피드백 간섭사이의 전파 지연의 차를 추정한다. 기지국로부터 전송된 신호와 피드백 간섭간의 전파 지연의 차는 다음과 같은 과정을 통해 추정된다. here

Represents a received signal from which feedback interference is canceled. The received signal with the feedback interference removed is divided into a preamble or a data signal transmitted for the synchronization process. If the received signal is a data signal, a demodulation process is performed. If the preamble is a preamble, a difference between propagation delays between a signal transmitted from the base station and feedback interference is estimated through a propagation delay estimation process (step 840). The difference in propagation delay between the signal transmitted from the base station and the feedback interference is estimated through the following procedure.

는 기지국에서 전송한 프리앰블, 추정된 전파 지연의 차를 나타낸다. 추정된 전파 지연의 차를 이용하여 기지국과 릴레이 수신단 사이의 전파 지연은 다음과 같이 갱신된다.here,

Represents the difference between the preamble transmitted by the base station and the estimated propagation delay. The propagation delay between the base station and the relay receiving end is updated as follows using the difference of the estimated propagation delay.

는 t-번째 프레임에 적용되는 기지국과 릴레이 수신단 사이의 전파 지연, t-1번째 프레임에서 추정된 전파 지연을 나타낸다.here,

Represents the propagation delay between the base station and the relay receiver applied to the t -th frame, and the propagation delay estimated from the t -th frame.

Interference between adjacent symbol interference due to feedback interference and interference between adjacent subcarriers may occur in the uplink interval as in the downlink. In the uplink section, all the signals transmitted by the terminals belonging to the relay are received at the same time in the relay receiving terminal.

However, the relay transmits a signal based on the information of the uplink control channel transmitted from the base station so that the time synchronization inconsistency does not occur at the base station receiving terminal. In this case, the feedback interference is received at the relay receiving terminal ahead of the signal transmitted from the terminals.

Therefore, the process of removing the feedback interference generated in the uplink and resetting the FFT performing interval is performed in the same manner as the downlink synchronization process described in the embodiment.

9 is a block diagram of an FDR according to an embodiment of the present invention.

Referring to FIG. 9, FIG. 9 illustrates a block configuration of a receiving end of an FDR, and the transmitting process is transmitted through an inverse process of a receiving process. The FDR receiver includes an RF processor 910, a frequency synchronizer 920, a CP remover 930, an FFT 940, an FFT interval updater 945, a channel estimator 950, and a decoder 960 .

The received signal is subjected to baseband processing via the RF processor 910 and then input to a frequency synchronizer 920. The frequency synchronization unit 920 estimates the maximum delay of the feedback interference channel and the propagation delay of the feedback interference channel using the synchronization signal of the link with respect to the input signal, and performs a frequency synchronization process. The estimated information is input to the FFT interval update unit 945. The FFT interval update unit 945 resets the FFT interval based on the FFT interval update unit 945 and the FFT unit 940 performs FFT according to the reset interval . The synchronized signal is input to the CP remover 930 to remove the CP.

That is, the frequency synchronization unit 920 estimates the maximum delay of the channel between the base station and the relay, the maximum delay of the channel between the transmitting end and the receiving end of the relay, and inputs the maximum delay to the FFT interval updater 945.

The FFT interval updater 945 estimates the propagation delay between the base station and the FDR, the propagation delay between the transmitter and the receiver of the FDR, the maximum delay of the channel between the base station and the FDR, and the maximum delay of the channel between the transmitter and the receiver, Determine the performance interval. This process is performed on the reference signal.

Under the control of the FFT interval updater 945, the FFT unit 940 performs an FFT on the received signal so that adjacent inter-symbol interference due to the feedback signal and adjacent sub-carrier interference do not occur.

The channel estimator 950 performs channel estimation on a signal other than a feedback interference channel and a reference signal. Then, a signal of the estimated feedback channel channel is generated, and a signal such as this signal is removed from the received signal. The removed signal is input to the decoding unit 960 and input to an upper layer after decoding (decoding, interleaving, etc.).

FIG. 10 is a graph illustrating the performance when the interference between adjacent inter-symbol interference and adjacent subcarriers due to feedback interference is minimized through the FFT reset process in the asynchronous type FDR according to the embodiment of the present invention and when the FFT reset process is not performed FIG.

Referring to FIG. 10, FIG. 9 (a) is a by channel delay (n-1) th feedback interference symbol n - is the illustration for looking at the interference effects of on the second symbol, Figure 9 (b) are: Fig. 8 is a graph for explaining the influence of adjacent symbol interference due to feedback interference symbols.

The simulation environment is ITU-R Ped A channel between the base station and the relay receiver, ITU-R Ped B channel between the transmitter and receiver of the relay, -40 ~ 0 dB for the signal to feedback interference ratio and -20 ~ 10dB noise. .

As shown in FIG. 10 (a), even though the FFT starts within the guard interval, it is confirmed that the interference between the adjacent symbols and the adjacent carrier interference occur due to the influence of the channel delay, .

Figure 10 (b) is the n (n + 1) th feedback interference symbol - is to look at the influence of interference on the second symbol. It can be seen that the influence of the interference is greater when the interference due to the next symbol occurs due to the time synchronization error as shown here.

FIG. 11 is a graph showing performance curves when interference between adjacent inter-symbol interference and adjacent subcarriers due to feedback interference is minimized through the FFT reset process in the synchronous type FDR according to an embodiment of the present invention, and when the FFT reset process is not performed Fig.

Referring to FIG. 11, when the synchronous type as the feedback interference from relay receiver shown diagram that assumes a situation in which received prior five samples compared to the signal transmitted from the base station is not performing the FFT reset process (n + 1 ) Th feedback interference symbol on the n - th symbol is very large, so that the BER performance is greatly degraded.

10 and 11, it can be seen that, in the case of the synchronous type, interference between adjacent symbol interference due to feedback interference and interference between adjacent subcarriers is more significantly affected as compared with the asynchronous type.

Therefore, it can be seen that the process of resetting the performance period of the FFT is effective for minimizing the interference between the adjacent symbol interference due to the feedback interference and the adjacent subcarriers through the synchronization process of the present invention.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but is capable of various modifications within the scope of the invention. Therefore, the scope of the present invention should not be limited by the illustrated embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

1 is a diagram illustrating a signal input to a receiver when feedback interference is considered in the FDR,

FIG. 2 is a diagram illustrating a case where interference between adjacent inter-symbol interference and adjacent subcarriers is slightly generated by a feedback signal when a time synchronization error occurs in an asynchronous relay;

3 is a diagram illustrating a case where adjacent inter-symbol interference and adjacent sub-carrier interference due to a feedback signal occur in uplink transmission,

FIG. 4 is a diagram illustrating a process of removing an initial synchronization process, a feedback interference cancellation process in a downlink, and an uplink feedback interference in a receiving end of an FDR according to an embodiment of the present invention;

5 is a flowchart detailing an initial synchronization process in an FDR according to an embodiment of the present invention,

Figure 6 illustrates performance in accordance with an embodiment of the present invention;

FIG. 7 is a flowchart illustrating a process of resetting an FFT performance period according to an embodiment of the present invention. FIG.

FIG. 8 is a flowchart illustrating a feedback interference cancellation process and a tracking process after performing an FFT according to an embodiment of the present invention.

9 is a block diagram of an FDR according to an embodiment of the present invention.

FIG. 10 is a graph illustrating the performance when the interference between adjacent inter-symbol interference and adjacent subcarriers due to feedback interference is minimized through the FFT reset process in the asynchronous type FDR according to the embodiment of the present invention, and when the FFT reset process is not performed The drawings,

FIG. 11 is a graph showing performance curves when interference between adjacent inter-symbol interference and adjacent subcarriers due to feedback interference is minimized through the FFT reset process in the synchronous type FDR according to an embodiment of the present invention, and when the FFT reset process is not performed FIG.

Claims (20)

A method for downlink synchronization through feedback interference cancellation in a full duplex relay, Performing downlink initial synchronization with a base station; Resetting an FFT duration for a received signal to minimize interference caused by a mismatch in time synchronization between a signal transmitted from the base station and a received feedback interfering signal; Performing an FFT on the received signal according to a reset FFT performing interval; And estimating a feedback interference channel for the FFT-processed reception signal to remove the feedback interference signal. The method according to claim 1, In the process of resetting the FFT performance interval, Estimating a maximum delay time and a propagation delay of a feedback interference channel using a signal for downlink synchronization; And resetting the FFT performance period using the maximum delay time and the propagation delay of the estimated feedback interference channel. 3. The method of claim 2, Wherein the signal for downlink synchronization comprises a pilot signal. The method according to claim 1, The received signal with the feedback interference removed Data or a signal for downlink synchronization. 5. The method of claim 4, And performing demodulation if the received signal with the feedback interference removed is data. An apparatus for downlink synchronization through feedback interference cancellation in a full duplex relay, A frequency synchronizer for performing downlink initial synchronization with a base station, An FFT interval updater for resetting an FFT performance interval for a received signal in order to minimize interference caused by a mismatch in time synchronization between a signal transmitted from the base station and a received feedback interference signal; An FFT for performing an FFT on the received signal according to a reset FFT performing interval, And a channel estimator for estimating a feedback interference channel with respect to the received signal subjected to the FFT to remove the feedback interference signal. The method according to claim 6, The FFT interval updater, when resetting the FFT duration, Estimates a maximum delay time and a propagation delay of a feedback interference channel using a signal for downlink synchronization, And resets the FFT performance period using the maximum delay time and the propagation delay of the estimated feedback interference channel. 8. The method of claim 7, Wherein the signal for downlink synchronization comprises a pilot signal. The method according to claim 6, The received signal with the feedback interference removed Data or a signal for downlink synchronization. 10. The method of claim 9, Further comprising a decoding unit that performs demodulation when the received signal from which the feedback interference is removed is data. A method for uplink synchronization through feedback interference cancellation in a full duplex relay, Performing uplink initial synchronization with a terminal; Resetting an FFT duration for a received signal to minimize interference due to a time synchronization inconsistency between a signal transmitted from the terminal and a received feedback interfering signal; Performing an FFT on the received signal according to a reset FFT performing interval; And estimating a feedback interference channel for the FFT-processed reception signal to remove the feedback interference signal. 12. The method of claim 11, In the process of resetting the FFT performance interval, Estimating a maximum delay time and a propagation delay of a feedback interference channel using a signal for uplink synchronization; And resetting the FFT performance period using the maximum delay time and the propagation delay of the estimated feedback interference channel. 13. The method of claim 12, Wherein the signal for uplink synchronization includes a ranging signal. 12. The method of claim 11, The received signal with the feedback interference removed Data or a signal for uplink synchronization. 15. The method of claim 14, And performing demodulation if the received signal with the feedback interference removed is data. An apparatus for uplink synchronization through feedback interference cancellation in a full duplex relay, A frequency synchronizer for performing uplink initial synchronization with a terminal, An FFT interval updater for resetting an FFT performance interval for a received signal in order to minimize interference caused by a mismatch in time synchronization between a signal transmitted from the terminal and a received feedback interference signal; An FFT for performing an FFT on the received signal according to a reset FFT performing interval, And a channel estimator for estimating a feedback interference channel with respect to the received signal subjected to the FFT to remove the feedback interference signal. 17. The method of claim 16, The FFT interval updater, when resetting the FFT duration, Estimates a maximum delay time and a propagation delay of a feedback interference channel using a signal for uplink synchronization, And resets the FFT performance period using the maximum delay time and the propagation delay of the estimated feedback interference channel. 18. The method of claim 17, Wherein the signal for uplink synchronization comprises a ranging signal. 17. The method of claim 16, The received signal with the feedback interference removed Data or a signal for uplink synchronization. 20. The method of claim 19, Further comprising a decoding unit that performs demodulation when the received signal from which the feedback interference is removed is data.

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