KR100793571B1 - Device for interference cancellation of digital multimedia broadcasting - Google Patents

Abstract

The present invention relates to a wireless relay device for interference elimination of digital multimedia broadcasting, wherein the wireless relay device receiving a digital multimedia broadcasting (DMB) signal from a main transmission station in the wireless relay device amplifies the signal and transmits the signal to a transmission antenna. When the transmission and reception signals of the wireless relay device use the same frequency band, the transmission signal of the wireless relay device is input again to the receiving antenna of the relay device through the multipath fading channel and acts as an interference to the received signal from the main transmission station. If the incoming interference signal is above a certain level, the possibility of oscillation of the wireless relay device increases, causing system instability. The present invention provides a system synchronization unit for acquiring time synchronization and frequency synchronization of a digital multimedia broadcasting frame, and removes an interference signal which is reversely input after being transmitted to the outside, while eliminating a null symbol and a system synchronization unit. An interference cancellation apparatus for estimating an adaptive channel using a phase reference symbol and canceling an interference signal based on the adaptive channel is included. Accordingly, the present invention can provide a stable high quality signal to a user terminal receiving a broadcast service from a wireless relay apparatus by performing an effective adaptive interference cancellation function for the feedback signal between the transmission and reception antennas.

Wireless Repeater, Interference Cancellation, Digital Multimedia Broadcasting

Description

Wireless relay device for interference elimination of digital multimedia broadcasting {DEVICE FOR INTERFERENCE CANCELLATION OF DIGITAL MULTIMEDIA BROADCASTING}

1 is a configuration diagram briefly showing a wireless relay device for interference cancellation of digital multimedia broadcasting according to the present invention;

2 is a view showing in more detail the interference cancellation device of the wireless relay device for interference cancellation of digital multimedia broadcasting according to the present invention;

3 is a view for explaining a channel tap coefficient update process in a null symbol period and a phase reference symbol period in a DMB frame of a wireless relay device for interference cancellation in a digital multimedia broadcasting according to the present invention.

<Description of the code | symbol about the principal part of drawing>

10 receiving antenna 12 down converter

14 ADC 16 Interference Cancellation Device

18: system synchronization unit 20: control unit

22: automatic gain control unit 24: DAC

26 upconverter 28 transmit antenna

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless relay apparatus, and more particularly, to a wireless relay apparatus for removing interference of digital multimedia broadcasting that can provide a high quality digital multimedia broadcasting service by removing interference with respect to a feedback signal between transmitting and receiving antennas.

In general, a wireless relay device used in a communication system is installed to provide a service to a user in a shaded area that is difficult to transmit radio waves by a feature such as a mountain or a building. The wireless relay apparatus that receives the main transmission station signal received by the weak signal amplifies the received signal and provides a service to the user in the sound region.

In some of the conventional wireless relay device, in order to prevent the oscillation caused by the inflow signal between the transmitting and receiving antennas of the relay device, a function of canceling the inflow signal is provided, or the power of the retransmission signal is reduced to interfere with the inflow signal. Use a method to reduce this. Alternatively, a method of securing physical separation distances between the transmitting and receiving antennas or separating and installing two antennas between specific structures is used.

In order to eliminate the oscillation caused by the signal flowing back into the relay device, the wireless relay device emits a test signal from the transmitting antenna of the relay device and measures the signal component input to the receiving antenna, but radiates the test signal in the same frequency band. This can act as an interference signal in the existing system, and there is a problem in that the test signal must be frequently transmitted in order that the transmission rate of the test signal and the frequency estimation update frequency can be adapted to the change of the wireless channel.

Another method for removing the backflow signal to the wireless relay device is to use the adaptive filter to estimate the backflow signal and then remove it without radiating the test signal. The tap coefficient of the adaptive filter represents the feedback multipath channel coefficient between the radio relay antennas when the operation starts from the initial value 0 and the adaptive filter converges stably.

However, in the case of a null symbol transmission interval transmitted to provide frame synchronization, such as a DMB system, the signal retransmitted by the radio relay also becomes null, so that the feedback multipath signal between antennas is not input to the relay reception antenna. The tap coefficient of the filter converges to 0, and the feedback interference signal is input again in the phase reference symbol section input after the null symbol to enable channel estimation. Accordingly, such a sudden channel change in feedback channel estimation using an adaptive algorithm causes a large error in data estimation for a time before the tap coefficient converges.

In addition, since the phase reference symbol having a large residual interference signal due to the data estimation error is used as the phase reference of the DQPSK (Differential QPSK) modulation scheme in the DMB system, the error in the section is a user receiving the DMB signal from the wireless relay device. It greatly reduces the reception quality of the terminal.

In addition, when the power of the residual interference signal is large due to the error of the inverse signal estimated by using the adaptive filter, the transmission signal power of the radio relay apparatus is greatly increased.

Therefore, in the related art, in order to prevent oscillation caused by the inflow signal in some wireless relay devices, a function of canceling the signal flowed back to the wireless relay device is performed, but the inverse signal power between the antennas is the signal power of the main transmitter. It is still oscillating when it is larger than a certain standard, and the signal-to-interference ratio is greatly reduced when the channel variation rate of the inverse signal is large, as well as the generation of the inverse signal through the feedback channel estimation and the main transmission station. It is difficult to stably provide a null symbol and a phase reference symbol of a DMB frame to a user in estimating a received signal from the DMB frame.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems of the prior art, and by eliminating the interference of a signal introduced into an antenna of a wireless relay device, it is possible to service high quality digital multimedia broadcasting data to a terminal in a service area. The present invention provides a wireless relay device for interference cancellation in digital multimedia broadcasting.

In order to achieve the above object, the present invention provides a wireless relay apparatus for removing interference signals of digital multimedia broadcasting (DMB), the down converter for down-converting the signal received from the main transmission station to the intermediate frequency band, A converter for converting an output signal into a digital signal, a system synchronizer for acquiring time synchronization and frequency synchronization of a frame of a digital multimedia broadcasting, a null symbol of the system synchronizer, An interference cancellation device for estimating an adaptive channel using a phase reference symbol and removing interference signals, a converter for converting an output signal of the interference cancellation device to an analog signal, and an upconverting analog signal to a wireless signal for transmission It includes an up converter.

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.

1 is a block diagram schematically illustrating a wireless relay apparatus for interference cancellation of digital multimedia broadcasting according to the present invention.

As shown in FIG. 1, a wireless relay apparatus for eliminating interference of digital multimedia broadcasting according to the present invention includes a receiving antenna 10 for receiving a main transmission station signal and a down converter for downconverting a received signal into an intermediate frequency band. (12), an analog-to-digital converter (ADC) 14 for converting an output signal of the down converter 12 into a digital signal, and system synchronization by acquiring frame synchronization and symbol synchronization to the interference cancellation device 16. To control the system synchronizer 18, the interference canceling device 16 for canceling the interference signal reversely introduced between the antennas, the interference canceling device 16, the automatic gain control unit 22, and the system synchronizer 18. A control unit 20 for performing a function to perform the function, an automatic gain adjusting unit 22 connected to an output terminal of the interference eliminating device 16 and adjusting a signal gain of the interference eliminating device 16, and the interference eliminating device 16 Output signal to analog signal A digital to analog converter (DAC) 24, an upconverter 26 for upconverting an analog signal to a radio frequency (RF) signal, and an RF signal input through the upconverter 26. Transmit antenna 28).

Here, the interference canceling device 16 is based on the adaptive channel estimator 16a for estimating the feedback channel between the radio relay antennas, the inverse of the tap coefficient obtained from the channel estimator 16a, and the transmission signal of the relay device. An interference signal generator 16b for generating an introduced interference signal, and a signal of the main transmitter is reproduced by removing the interference signal from the received signal of the wireless relay device, and a null symbol or a phase reference symbol ) And a signal reproducing unit 16c for generating and transmitting.

The interference cancellation apparatus 16 receives the exact position of the null symbol and the start position of the phase reference symbol from the system synchronizer 18 through the adaptive channel estimator 16a. The adaptive channel estimator 16a stops the feedback channel estimation using the adaptive algorithm at the start position of the null symbol and restarts the feedback channel estimation at the start point of the phase reference symbol. In this case, the channel estimation in the null symbol interval converges all of the filter tap coefficients of the interference canceller 16 to 0 to have a large error of the feedback channel estimation in the phase reference symbol interval, but in the present invention, the channel estimation is performed in the null symbol interval. In case of stopping, when the feedback channel does not change significantly in the null symbol period, the channel estimation error can be kept small. In addition, the adaptive channel estimation is continued to stably obtain the feedback channel coefficients in the phase reference symbol interval, but the radio relay apparatus transmits its own generated phase reference symbol without regenerating the signal from the channel coefficients obtained in the interval. Provide the user with a stable phase reference symbol.

As described above, when the radio repeater provides self-generated phase reference symbols, the data reproducing section 16c receives channel information between the main transmission station signal and the wireless relay device from the system synchronizer 18 in the data symbol section after the phase reference symbol. In the reverse channel process to compensate for this.

The adaptive channel estimator 16a obtains stable feedback channel coefficients within the phase reference symbol interval, and estimates from the received signal of the radio relay apparatus in the data symbol interval through the interference signal generator 16b and the signal regenerator 16c. A signal received from the main transmission station is generated by removing the inflowed interference signal obtained through the convolution of the feedback channel and the radio relay transmission signal.

The system synchronizer 18 synchronizes the time by (a) estimating the approximate position of the null symbol section of the DMB frame within 10 samples using the energy estimation method of the general constant window section, and (b) from the main transmission station. Synchronize an integer multiple frequency for correcting a frequency error corresponding to an integer multiple of an orthogonal frequency division multiplexing (OFDM) subcarrier spacing by using a cross-correlation property between a received phase reference symbol and a phase reference symbol generated by a wireless repeater. (c) after synchronizing the fine time for estimating the exact time position of the null symbol and the phase reference symbol through fine time synchronization with respect to frame synchronization based on the received frequency reference phase shift of the phase reference symbol, (d) OFDM Corrects the fine frequency error less than 1% of the subcarrier spacing by using the autocorrelation of the cyclic prefix (CP) of the signal Synchronizing the fine frequency to the. In addition, the method includes measuring a channel between the main transmission station and the radio relay in the phase reference symbol period.

In more detail, interference cancellation of a digital multimedia broadcasting according to the present invention is as follows.

The received signal input to the receive antenna 10 of the wireless relay device is expressed by the following equation (1). Here, a multi-path of the feedback channels between the antennas to the receiving signal y _n of the wireless relay apparatus when the tab L, be described as a signal x _n receive the processing delay time of the relay apparatus from the N, the main transmitting station.

은 시간 샘플 ｎ에서 무선 중계 장치가 전송한 신호이고,

은 백색 잡음,

은 ｍ번째 궤환 채널 계수를 나타낸다. In Equation 1

Is the signal transmitted by the wireless relay device at time sample n,

Silver white noise,

Represents the m-th feedback channel coefficient.

을 통과하여 다시 중계 장치에 입력된다. The signal received before the processing delay time N of the relay device is the sum of the signal from the main transmission station and the white noise, and after the processing delay time of the relay device, the transmission signal of the relay device returns to the feedback channel between the antennas.

It passes through and enters the relay device again.

으 로 볼 때의 수신 신호는 중계 장치가 전송한 신호와 궤환 채널의 컨볼루션과 잡음과의 합으로 종래의 LMS 등의 적응 알고리듬을 이용하여 궤환 채널의 계수

을 추정할 수 있다.Sum of white noise and main station signal during feedback channel estimation

The received signal is the sum of the signal transmitted by the relay and the convolution and noise of the feedback channel, and the coefficient of the feedback channel using an adaptive algorithm such as a conventional LMS.

Can be estimated.

를 얻기 위한 일 예로서, LMS 알고리듬을 사용할 때의 채널 추정 계수 갱신 식을 나타낸다.Equation 2 is an adaptive feedback channel coefficient

As an example for obtaining, a channel estimation coefficient update equation when using the LMS algorithm is shown.

Μ represents the tap coefficient update unit size.

It is to remove the interference signal estimate from the received signal y _n of the radio relay apparatus for estimating a signal received at the primary transmitting station x _n as follows: Equation (3).

　　

　　

Accordingly, the wireless relay device for interference cancellation of digital multimedia broadcasting according to the present invention uses LMS (Least Mean Square), VSS- for the feedback multipath channel between antennas of the wireless relay device based on a signal transmitted from the wireless relay device. Estimation of the feedback channel using adaptive algorithms such as Variable Step Size LMS (LMS), and the interference signal introduced back through the convolution of the impulse response of the estimated feedback channel and the transmission signal of the relay device, Remove the interference signal from the reception signal of the relay device. At this time, the power level of the signal is limited through the automatic gain control unit 22 in order to prevent the reproduced signal from being output beyond the threshold compared to the average power of the signal received from the main transmission station.

2 is a view showing in more detail the interference cancellation device of the wireless relay device for interference cancellation of digital multimedia broadcasting according to the present invention.

As shown in FIG. 2, the apparatus for canceling interference in a wireless relay apparatus according to the present invention includes an adaptive feedback channel estimator 16a estimating an feedback channel between antennas using an adaptive algorithm, an estimated feedback channel, and a wireless relay. An interference signal generator 16b for generating an inverse interference signal based on the transmission signal of the apparatus, and a signal regenerator 16c for regenerating the signal of the main transmission station by removing the interference signal from the received signal of the radio relay apparatus. Include.

The signal regenerating unit 16c includes a canceller 160 which removes an interference signal transmitted from the interference signal generator 16b from the received signal, and a signal having a threshold value or more removed from the average power of the signal received from the main transmission station. Signal power limiter 162 for limiting the power of the signal when it is output from the 160 and the average power of the main station signal in the interval of receiving only the signal from the main station before the radio relay device transmits the signal The signal power measuring unit 164, the forward channel compensator 170 for compensating for the channel between the main transmission station and the radio relay device in the data symbol period after the radio relay device transmits the phase reference symbol generated by itself, Phase reference symbol generation that performs a function of generating a phase reference symbol to transmit a self generated phase reference symbol in the phase reference symbol period. And a selection switch 168 for selecting a signal of the phase reference symbol generator 166 generated in the phase reference symbol section and selecting and outputting a signal of the forward channel compensator 170 in the data section. .

As shown in Equation 1, the signal received by the wireless repeater in the section before the wireless relay transmits the signal is expressed as the sum of the transmission signal of the main transmitting station and the white noise, and the average power of the main transmitting station is measured in the section. Can be.

The interference signal is removed from the measured average power of the main transmission station in the interval where the interference signal of the wireless relay is input. If the estimated signal level of the main transmission station is greater than or equal to a predetermined threshold, the signal level is limited by determining the residual interference signal or noise component. .

에 대해 신호 전력 측정기(164)로부터 얻어진 평균 신호 전력을 바탕으로 신호 전력을 제한한다.The signal power limiter 162 is a signal transmitted from the remover 160 as shown in Equation 4.

Limit the signal power based on the average signal power obtained from the signal power meter 164 for.

는 최대 순간 전송 신호 크기로서 일 예로서, 수학식 5와 같이 신호 전력 측정기(164)에서 얻어진 평균 신호 전력으로부터 전송 신호의 피크대 평균 전력비(peak to average power ratio) 만큼 더해진 값을 사용할 수 있다.At this time,

As the maximum instantaneous transmission signal size, for example, a value obtained by adding the peak to average power ratio of the transmission signal from the average signal power obtained by the signal power meter 164 as shown in Equation 5 may be used.

Limiting the size of the transmission signal of the radio relay apparatus through Equation 4 and Equation 5 described above is estimated by the residual interference signal when the estimated feedback channel and the estimated interference signal are obtained without sufficient convergence of the adaptive algorithm. This is to prevent the possibility of oscillation increases because the power of the signal is greatly increased. Therefore, the power limiting method removes the interference signal while preventing oscillation using the same adaptive algorithm even if the power size of the interference signal through the feedback channel is increased by about 30 dB or more. In addition, it is possible to ensure the convergence of the adaptive algorithm, thereby restoring the signal of the main transmission station stably.

3 is a diagram illustrating a channel tap coefficient update process in a null symbol section and a phase reference symbol section in a DMB frame of a wireless relay device for interference cancellation in a digital multimedia broadcasting according to the present invention.

Referring to FIG. 3, a method of updating channel tap coefficients in a null symbol period and a phase reference symbol period in a DMB frame in a wireless relay apparatus according to the present invention is as follows.

As shown in (a) to (c) of FIG. 3, when estimating an interference signal of a relay apparatus using a conventional adaptive algorithm without distinguishing a null symbol section of a digital multimedia broadcasting frame (DMB frame), an adaptive channel The estimation signal includes (a) a section 304 stably estimating a feedback signal in a data symbol section before a null symbol, and (b) a main station signal is 0 in a null symbol section, and thus the transmission signal of the wireless relay device A transition section 305 for bringing all the coefficients of the feedback channel to 0 to 0, (c) a section 306 in which the channel tap coefficients have been stably converged to 0, and (d) a main transmission signal based on the phase While the symbol is transmitted, the feedback interference signal is also inputted to the receiving antenna of the wireless relay device and the transition period 307 for convergence from the state in which the channel tap coefficient is converged to 0 to the feedback channel coefficient value, and (e) the transition interval To reliably estimate the feedback channel comprises a zone (308) capable of removing the interference signal.

In the conventional method, when the interference signal is removed by the adaptive algorithm without distinguishing the transmission symbols, the transition period 305 and the phase reference symbol transmission interval 302 for convergence of the estimated channel tap coefficient to zero in the null symbol interval 301 are performed. The estimated channel tap coefficient has a large channel estimation error in transition period 307 for converging from 0 to a stable feedback channel tap coefficient. Therefore, in the service user side, a null symbol has information of a frame start point, and a phase reference symbol is a phase reference of a DQPSK modulation symbol, and a large error in the interval causes a great decrease in the quality of a signal serviced by the relay device.

On the other hand, as shown in (d) to (iii) of FIG. 3, according to the present invention, when the accurate position information of the null symbol and the phase reference symbol of the digital multimedia broadcasting frame (DMB frame) is used, the adaptive channel estimation signal is (a). A section 309 for stably estimating the feedback signal in the data symbol section before the null symbol, (b) a section 310 for stopping the adaptive channel tap coefficient update at the null symbol start position to maintain the channel coefficient, and (c A transition section 311 for resuming channel tap coefficient update at a phase reference symbol position and estimating a change in the feedback channel; and (d) a section for stably estimating the feedback channel after the transition section to remove the interference signal. ).

Therefore, the present invention maintains the coefficient of the feedback channel in the null symbol section 301 as compared to the conventional method, so that the transition section 311 in the phase reference symbol section 302 is shorter than the conventional transition section 307. As a result, in the data symbol section 303 after the phase reference symbol, a high quality signal from which an interference signal is removed can be transmitted more stably.

In addition, although the present invention continues updating the feedback channel coefficients from the received signal of the radio relay apparatus in the phase reference symbol interval 302, the received signal of the radio relay apparatus in the null symbol interval 301 and the phase reference symbol interval 302. The self-generated null symbol and phase reference symbol are transmitted without transmitting the estimated signal of the main transmission station obtained by removing the interference signal from the service area. Accordingly, since the relay apparatus regenerates and transmits the null symbol and the phase reference symbol by itself, the signal quality in the section can be maintained in terms of the service user.

As described above, the present invention applies an effective signal estimation method for the estimated signal power limitation and the null symbol and phase reference symbol interval of a DMB frame, and provides a high quality null symbol and a phase reference symbol to a user in a service area. This reduces the probability of error during system synchronization and data demodulation.

Therefore, the present invention can provide a high quality signal to the terminal in the service area by effectively removing the feedback signal input to the receiving antenna of the wireless relay device, and adaptively operates in the wireless environment through feedback channel estimation using an adaptive algorithm. can do.

Meanwhile, the present invention is not limited to the above-described embodiments, but various modifications are possible by those skilled in the art within the spirit and scope of the present invention described in the claims below.

Claims (7)

In the wireless relay device for removing interference signals of digital multimedia broadcasting (DMB), A down converter for down converting a signal received from a main transmission station into an intermediate frequency band, A converter for converting an output signal of the down converter into a digital signal; A system synchronizer for acquiring time synchronization and frequency synchronization of the frame of the digital multimedia broadcasting; An interference canceling apparatus for removing interference signals which have been inversely transmitted after being transmitted to the outside, estimating an adaptive channel using null symbols and phase reference symbols of the system synchronizer, and removing interference signals based on the interference signals; A converter for converting the output signal of the interference canceling device into an analog signal; An up-converter for upconverting and transmitting the analog signal to a wireless signal Wireless relay device for interference cancellation of a digital multimedia broadcasting comprising a. The method of claim 1, The system synchronizer, Estimate an approximate location of a null symbol interval in the frame, Correct the frequency error of integer multiple of OFDM subcarrier spacing, Fine time is synchronized to estimate the exact time position of frame synchronization and symbol synchronization, Synchronize the fine frequency to correct the fine frequency error of the subcarrier spacing, To estimate the channel response of the main station and the radio relay Wireless relay device for interference cancellation of digital multimedia broadcasting. The method of claim 1, The interference cancellation device, An adaptive channel estimator for estimating the feedback channel between antennas of the wireless relay device; An interference signal generator for estimating an interference signal based on the feedback channel estimate by the adaptive channel estimator; And a signal reproducing unit for estimating a main transmission station signal by removing the estimated interference signal from the received signal. The method of claim 3, wherein The signal reproducing unit, When the estimated signal by removing the interference signal is a signal of more than a threshold compared to the average signal power of the main transmission station, by limiting the power of the estimated signal to prevent oscillation and ensure convergence of the adaptive algorithm Wireless relay device for interference cancellation. The method of claim 4, wherein And using the threshold as a sum of the average power of the main transmission signal by the peak-to-average power ratio. The method of claim 3, wherein The signal reproducing unit, A canceller configured to cancel an interference signal from the received signal; A signal power limiter for limiting the power of the signal when a signal above a threshold is output from the canceller from the average power of the signal received from the main transmitting station; A signal power measuring device for measuring an average power of a main station signal in a section in which only the signal from the main station is received before the radio relay apparatus transmits the radio signal; A phase reference symbol generator for generating a phase reference symbol for transmitting a phase reference symbol generated by itself in a phase reference symbol section of the main transmission signal; A forward channel compensator for compensating a channel between the main transmitting station and a wireless relay device; A selection switch for selecting a signal of a phase reference symbol generator generated in the phase reference symbol section and selecting and outputting a signal of the forward channel compensator in a data section; Wireless relay device for interference cancellation of the digital multimedia broadcasting comprising a. The method of claim 3, wherein The signal reproducing unit, In the null symbol section and the phase reference symbol section in the frame of the digital multimedia broadcasting, An estimation section for stably estimating the feedback signal in the data symbol section before the null symbol; A channel coefficient holding period for stopping the updating of the adaptive channel tap coefficient at the null symbol start position to maintain the channel coefficient; A transition period for resuming updating of the channel tap coefficients at the phase reference symbol position to estimate a change in the feedback channel; And a section for stably estimating a feedback channel and removing the interference signal after the transition section.

Images