KR20060069019A - Method for tracing symbol location using channel impulse response(cir) in dmb receiver - Google Patents

Abstract

The present invention is to provide a symbol location tracking method that can minimize the reduction in performance that can occur in the structure that can reduce the hardware complexity of the signal synchronization unit in the DMB receiver, an impulse response through a phase reference symbol (PRS) Obtaining a (CIR), estimating a timing offset value of each frame using the CIR, and removing a value overlapping the timing offset value estimated in a previous frame from the estimated timing offset value, Estimating the timing offset value, and applying the estimated total timing offset value to the next frame to perform symbol position tracking and improvement.

OFDM demodulator, DMB receiver, CIR, timing offset

Description

Method for tracing symbol location using Channel Impulse Response (CIR) in DMB receiver}

1 is a conceptual block diagram of a receiver according to a general DMB scheme;

2 is a diagram illustrating a structure of a symbol position tracker for tracking symbol positions using CIR currently used;

3 is a diagram illustrating a frame structure of a general OFDM transmission signal.

4A is a diagram illustrating an example of a timing offset of a general input signal.

4b is a view showing a process of a symbol location tracking method using a CIR in general

5A is a diagram illustrating an example of a timing offset of a general input signal.

5B is a view showing a process of a general symbol position tracking method using CIR according to the present invention.

* Explanation of symbols for main parts of the drawings

100: antenna 101: tuner

102: AGC 103: A / D converter

104: I / Q distributor 105: mode detector

106: signal synchronization unit 107: OFDM demodulator

108: frequency reverse interleaving 109, 114: channel divider

110: FIC decoder 111: time deinterleaving

112: convolutional decoder 113: energy descramble

115: convolutional deinterleaving 116: RS decoder

117: FIC data decoder 118: audio / video decoder

119: video decoder 201: time domain synchronizer

202: protection section eliminator 203: FFT / IFFT

204: PRS generator 205: QPSK demodulator

206: path delay detector

The present invention relates to digital multimedia broadcasting (DMB), and more particularly, to an efficient symbol location tracking method using channel impulse response (CIR) in a DMB receiver.

Digital multimedia broadcasting (DMB), adopted in Korea, is based on Eureka-147 digital radio broadcasting (DAB), which has been adopted as the European terrestrial radio standard. Also added to improve the multimedia broadcasting performance is a RS code and a convolutional interleaver, which are robust against burst errors that can occur on a transmission channel.

The two additional blocks are applied to the DAB Ensemble input signal at the transmitter and provide an error rate low enough for video service even in a mobile receiving environment.

In addition, the transmission channel of the DMB broadcast is a wireless mobile reception channel, and the amplitude of the received signal is not only time-varying, but also the Doppler Spreading of the spectrum of the received signal due to the influence of the mobile receiver. This happens.

In consideration of the transmission and reception in such a channel environment, the DMB transmission scheme is based on Orthogonal Frequency Division Multiplexing.

In addition, interleaving of signals in the time domain and the frequency domain may be performed to correct an error occurring in a transmission channel.

In addition, the DMB transmission signal is transmitted with a very small signal strength compared to the existing analog radio broadcasting signal, and considering the mobile reception like in a car in a severe fading channel environment such as downtown, the signal strength of the actual received signal is very high. small.

Therefore, the DMB receiver should be able to correct the transmission error by receiving the received signal as much as possible in such a poor reception environment.

In addition, considering the fact that it is a mobile terminal, providing the maximum reception performance at a limited cost is a key requirement of the DMB receiver configuration.

Accordingly, the present invention has been made to solve the above problems, and provides a symbol location tracking method that can minimize the performance reduction that can occur in a structure that can reduce the hardware complexity of the signal synchronization unit in the DMB receiver. The purpose is.

Another object of the present invention is to provide a symbol location tracking method using a channel impulse response (CIR) that can reduce the overall hardware cost of the DMB receiver.

A feature of the symbol location tracking method using the CIR in the DMB receiver according to the present invention for achieving the above object is to obtain an impulse response (CIR) through a phase reference symbol (PRS), and using this CIR Estimating a timing offset value, removing a value overlapping with a timing offset value estimated in a previous frame from the estimated timing offset value, and estimating the total timing offset value of the corresponding frame; And applying the value to the next frame to perform symbol position tracking and improvement.

로 계산되는 것이 바람직하며, 는 n번째 프레임에서의 총 타이밍 오프셋 값을, 는 n번째 프레임에 새롭게 생긴 타이밍 오프셋 값을 나타낸다.In this case, the total timing offset value tofs _n is expressed by

It is preferable that is calculated as, where is the total timing offset value in the n-th frame, and denotes the timing offset value newly generated in the n-th frame.

In addition, estimating a timing offset value includes generating a transfer function (CTF) of a transport channel through a phase reference symbol (PRS) through FFT operation and QPSK demodulation, and performing an inverse Fourier transform (IFFT) on the generated CTF. And obtaining a response (CIR) and estimating a timing offset value of each frame using the CIR.

In addition, the IFFT is preferably performed in the null symbol period of the next frame.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments with reference to the accompanying drawings.

A preferred embodiment of the symbol position tracking method using the CIR in the DMB receiver according to the present invention will be described with reference to the accompanying drawings.

1 is a conceptual block diagram of a receiver according to a general DMB scheme.

Referring to FIG. 1, the received signal input to the antenna 100 is converted into a pass-band signal of a desired intermediate frequency via the tuner 101. The AGC 102 serves to multiply the gain value calculated according to the reference signal size in order to keep the size of the signal input to the A / D converter 103 constant.

Accordingly, the A / D converter 103 performs sampling to transform the digital signal into a digital signal regardless of the magnitude of the received signal.

Subsequently, the I / Q divider 104 restores the real part of the received complex signal to a complex signal, and the mode detector 105 detects a transmission mode of the received signal. The OFDM demodulator 107 removes unnecessary guard intervals, and then converts a signal in the time domain into a frequency domain through fast fourier transform (FFT). Next, the signal synchronizer 106 extracts information necessary for synchronization in the time / frequency domain of the signal using the input and output signals of the OFDM demodulator 107. The frequency de-interleaving 108 then restores the positions of the sub-carrier signals interleaved at the transmitter.

Next, the channel divider 1 109 separates the control channel FIC channel and the data channel MSC channel.

Then, the FIC decoder 110 receives the FIC channel as an input and extracts information necessary to decode the MSC channel.

In addition, the time deinterleaving 111 receives the MSC channel as an input and restores 16 logical frames interleaved by the transmitter in the original frame order. Subsequently, the time deinterleaved MSC channel corrects a random error occurring in the transport channel through a convolutional decoder 112. The error-corrected data is restored to the original data via the energy descramble 113.

Then, channel divider 2 114 discriminates and separates whether the transmitted data channel is a data / audio signal for DAB service or a video signal for DMB service.

The signal for the DAB service is decoded through the corresponding audio / data decoders 118, and the signal for the DMB service is input to the convolutional de-interleaving 115.

In this case, the separate data transmitted through the FIC channel is recovered by the FIC data decoder 117.

Subsequently, the convolutional deinterleaving 115 rearranges the data additionally interleaved by the transmitter in the original order, and the RS decoder 116 restores the RS-encoded data by the transmitter.

Finally, the video decoder 119 restores the video signal for the DMB service.

The present invention relates to a synchronization unit in the time domain among the signal synchronization units 106.

That is, the OFDM method, which is a transmission method used by the DMB system, has a disadvantage of being very sensitive to signal synchronization errors in the time domain and the frequency domain. In particular, the synchronization error in the time domain causes inter-symbol interference (ISI) to deteriorate the performance of the entire receiver.

Therefore, the performance of the synchronization part of the time domain becomes an important factor that determines the performance of the entire DMB receiver.

The synchronization process of the time domain can be roughly divided into a symbol position obtaining process for roughly estimating the position of a symbol at a synchronization start point, and a symbol position tracking process for maintaining synchronization while continuously tracking the position of the acquired symbol.

The symbol position acquisition process used in a DMB system generally performs initial acquisition of symbol positions by estimating the position of a null symbol transmitted every frame.

In addition, the symbol position tracking process used in the DMB system uses a guard interval that is additionally transmitted every symbol, and phase shift of a sub-carrier in a frequency domain. The method is divided into a method of using a channel impulse response (CIR) using a pilot symbol transmitted every frame.

In this case, the method using the protection interval and the phase shift method have low hardware complexity, are easy to implement, and show good performance in the Additive White Gaussian Noise (AWGN) channel environment, but are multi-path. Tracking performance is disadvantageous in mobile reception environment in urban area such as environment or fading channel.

On the other hand, the method of tracking the position of a symbol by estimating the CIR reduces the estimation error to less than one OFDM sample, thereby showing excellent tracking performance even in a multipath fading channel.

FIG. 2 is a diagram illustrating a structure of a symbol position tracker for tracking symbol positions using a CIR currently used.

Referring to FIG. 2, the time domain synchronizer 201 informs the OFDM demodulator 107 where the start position of an OFDM symbol is located in the output data stream of the I / Q divider 104.

Then, the guard period remover 202, which is one of the two blocks constituting the OFDM demodulator 107, removes the guard interval additionally transmitted for every OFDM symbol and outputs a symbol in which data is actually transmitted.

The other FFT / IFFT 203 performs a Fourier transform that transforms an OFDM received symbol in the time domain from which the guard interval is removed to the frequency domain.

At this time, the output of the FFT 203 operation is a frequency domain transmitted in a signal frame structure having information of a null symbol, a phase reference symbol (PRS), FIC, and MSC, as in the signal frame structure shown in FIG. Consists of subcarriers.

The symbol position tracking process in the time domain synchronization process consists of estimating a channel using subcarriers of a received pilot symbol. In this case, the pilot symbol is a phase reference symbol (PRS), and is a signal in which transmission between transmission and reception terminals is promised in advance.

Accordingly, the PRS generator 204 generates a promised reference pilot symbol during transmission between the transceivers, and the QPSK demodulator 205 demodulates a modulated phase of each subcarrier of the received pilot symbol by using the generated reference pilot symbol. .

The output of the QPSK demodulator 205 becomes a channel transfer function (CTF) of a transport channel. Therefore, the FFT / IFFT 203 calculates the CIR of the time domain by inverse FFT transforming the CTF of the frequency domain into the time domain.

Finally, the path delay detector 206 finds an important signal path that is determined to cause ISI from the estimated CIR, and detects a timing offset from the start of the current symbol. .

The offset information thus detected is fed back to the time domain synchronizer 201 so as to track the change in the symbol position according to the change of the transmission channel.

The symbol position tracking method using the CIR reduces the position estimation error within one OFDM sample not only in the AWGN channel but also in the time-varying multipath fading mobile reception channel environment, thereby enabling accurate symbol position tracking. .

However, there is a problem in the structure of an OFDM demodulator using the sharing of an FFT operation for obtaining subcarrier information of an OFDM signal and the sharing of an IFFT operation for obtaining a CIR from a CTF.

The problem is that the IFFT operation for obtaining the CIR from the phase reference symbol of the currently input OFDM signal frame is performed in the null symbol section of the next frame. That is, the symbol position tracking value of the current frame can be obtained in the next frame and must be applied to the next frame to modify the symbol position to reflect this value.

4A illustrates an example of a timing offset of a general input signal, and FIG. 4B illustrates a process of a symbol position tracking method using a CIR.

In this case, it is assumed that timing offsets a, b, c, d, e, and f are generated for each frame of the input OFDM signal, and it is assumed that no symbol position tracking and improvement process is performed. Then, the timing offset of the input signal can make the signal shown in the example.

Referring to FIG. 4B, first, when the first frame (frame1) is received, the CRS is generated through the FFT operation, the PRS generator, and the QPSK demodulation in the PRS section. Then, IFFT is taken using the null symbol interval of the second frame (frame2) to obtain the CIR, and the timing offset is obtained through this. This value is then applied to the next third frame (frame3) to complete the symbol location tracking and refinement process. This process can be expressed by the following equations (1) and (2).

: n 번째 프레임에서의 총 타이밍 오프셋 값only,

: Total timing offset value in nth frame

: n 번째 프레임에 새롭게 생긴 타이밍 오프셋 값

: New timing offset value in nth frame

This method has only the timing offset value that is necessarily generated due to the latency of the symbol position tracking process according to Equation 1 for the odd numbered frames, but also the latency of the improved step after tracking the symbol position for the even numbered frames. In the fourth frame, the sixth frame, the eighth frame, ..., three timing offset values generated in the three frames appear earlier, which causes a decrease in performance.

Accordingly, the present invention proposes a method of extracting the timing offset value reflecting the improvement value by predicting the timing offset value which will be improved later in this process in order to solve the performance reduction.

5A illustrates an example of a timing offset of a general input signal, and FIG. 5B illustrates a process of a general symbol position tracking method using a CIR according to the present invention.

In this case, it is assumed that timing offsets a, b, c, d, e, and f are generated for each frame of the input OFDM signal, and it is assumed that no symbol position tracking and improvement process is performed.

Referring to FIG. 5B, first, when a first frame (frame1) is received, a CTF is generated through an FFT operation, a PRS generator, and QPSK demodulation in a PRS section. Then, IFFT is taken using the null symbol interval of the second frame (frame2) to obtain the CIR, and the timing offset is obtained through this. This value is then applied to the next third frame (frame3) to complete the symbol location tracking and refinement process.

In addition, when the second frame (frame2) is received, the CRS is generated through the FFT operation, the PRS generator, and the QPSK demodulation in the PRS section. Then, IFFT is taken using the null symbol interval of the third frame (frame3) to obtain the CIR, and the timing offset is obtained through this. This value is then applied to the next fourth frame (frame4) to complete the symbol location tracking and improvement process.

In this way, the timing offset is estimated every frame.

In this case, when the timing offset is estimated every frame, the second offset is applied to the second frame. Therefore, the timing offset generated in the third frame, which is the next frame, is detected twice.

That is, in the third frame, the timing offset value a estimated in the first frame and the timing offset value a + b estimated in the second frame are applied to complete the symbol position tracking and improvement process. There will be duplicated errors detected. This error will continue to occur every frame.

To solve this problem, we use Δ to predict in advance the timing offset to be improved in the future when detecting the timing offset for the current frame.

That is, the timing offset measured in the first frame (frame1) is a, the timing offset measured in the second frame (frame2) is a + b, and the Δ value is a.

As such, when the timing offset detected at the first time is improved, it is actually applied a. However, when the timing offset detected at the second frame is improved, the value actually applied is a value previously predicted at the detected timing offset a + b. To be b.

This may be represented by the following equation (3).

: n번째 프레임에서의 총 타이밍 오프셋 값only,

: Total timing offset value in nth frame

: n번째 프레임에 새롭게 생긴 타이밍 오프셋 값

: New timing offset value in nth frame

Compared to the conventional method described above, the timing offset value necessarily generated due to the latency of the symbol location tracking process may be applied to each frame regardless of the latency of the symbol location improvement step. That is, only two timing offset values generated from the second frame to the previous frame appear to prevent the reduction of symbol position tracking performance.

In addition, when this method is implemented in real hardware, as shown in Equation 3, the process of obtaining the predicted timing offset value is very simple, so it does not require a separate hardware cost, so it is suitable for a hardware-saving OFDM demodulator through FFT / IFFT sharing. Do.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

As described above, the symbol location tracking method using the impulse response (CIR) of the channel in the DMB receiver according to the present invention has the following effects.

It is suitable for the low power and low cost structure pursued by the OFDM demodulator of the FFT / IFFT shared structure because there is no additional hardware burden while improving the symbol position tracking performance compared to the conventional method, but the maximum reception is achieved by improving the symbol position tracking performance using the CIR. Performance can be secured.

Claims (4)

Obtaining an impulse response (CIR) through a phase reference symbol (PRS), and estimating a timing offset value of each frame using the CIR; Estimating a total timing offset value of the corresponding frame by removing a value overlapping with the timing offset value estimated in a previous frame from the estimated timing offset value; And performing symbol position tracking and improvement by applying the estimated total timing offset value to a next frame. The method of claim 1, The total timing offset value tofs _n is a formula

Symbol position tracking method characterized in that it is calculated by. (only,

is the total timing offset value in the nth frame,

: New timing offset value in nth frame) The method of claim 1, Estimating a timing offset value, generating a transmission function (CTF) of a transport channel through a phase reference symbol (PRS) through FFT operation and QPSK demodulation; Taking an inverse Fourier transform (IFFT) on the generated CTF to obtain an impulse response (CIR), Estimating a timing offset value of every frame using the CIR. The method of claim 3, wherein And wherein the IFFT is in a null symbol interval of a next frame.

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