KR100651913B1 - Equalizer in receiver of orthogonal frequency division multiplexed signals - Google Patents

Abstract

An equalizer of an OFDM modulation signal receiver is provided to improve channel compensation performance by compensating a channel without using a null carrier. In an equalizer of an apparatus for receiving an OFDM(Orthogonal Frequency Division Multiplexing) signal using a PN(Pseudonoise) sequence, a TPS(Time Domain Synchronous) dispersion calculation part(200) calculates a dispersion value of noise with an error of received TPS data and reference TPS data. A first equalizer part(190) compensates a channel with the dispersion value of noise outputted from the dispersion calculation part.

Description

Equalizer in receiver of orthogonal frequency division multiplexed signals

1 is a configuration diagram showing a brief configuration of a transmission device of the DMB-T

FIG. 2 is a view showing a structure of a frame having a guard interval of 1/9 among the frames of signals transmitted by the DMB-T transmitting apparatus of FIG.

3 is a structural diagram of a conventional TDS-OFDM receiver

4 is a structural diagram of an embodiment of an equalizer of a TDS-OFDM receiver according to the present invention;

5 is a structural diagram of an embodiment of a TPS dispersion calculation unit in an equalizer of a TDS-OFDM receiver according to the present invention;

Figure 6 illustrates the concept of TPS variance on a constellation of an equalizer according to the present invention.

<Description of Symbols for Main Parts of Drawing>

10: channel encoding unit 15: TPS generation unit

20 modulator 30 reverse DFT

40: PN generation unit 50: multiplexer

60: SRRC unit 70: RF transmission unit

110: tuner 120: automatic gain control unit

130: A / D converter 140: phase separator

145: Multiplier 150: Resampler

160: SRRC unit 170: synchronization unit

171: PN correlation unit 172: signal acquisition unit

174: signal tracking unit 177: automatic frequency control unit

180: first DFT unit 182: second DFT unit

190: first equalizer 192: minimum error generator

195: first operator 200: TPS dispersion calculation unit

210: TPS decoder 220: reference TPS generator

230: second operator 240: third operator

The present invention relates to an equalizer of an apparatus (hereinafter, referred to as an OFDM receiver) for receiving a broadcast signal modulated by orthogonal frequency division multiplexing (OFDM), and more specifically, to compensate for a channel. The present invention relates to an equalizer of an OFDM receiver having good performance.

Recently, Tsinghua University has proposed a new standard for terrestrial digital television (“Terrestrial DTV”) broadcasting to China. The proposal relates to a broadcast standard called Terrestrial Digital Multimedia / Television Broadcasting (DMB-T). In DMB-T, a new modulation scheme called Time Domain Synchronous OFDM (hereinafter referred to as TDS-OFDM) is used.

Data transmitted after being modulated at the transmitting end of the TDS-OFDM is applied with an Inverse Discrete Fourier Transform (IDFT) like the method used in the Cyclic Prefix OFDM (CP-OFDM) method.

However, a pseudonoise (PN) is inserted in the guard interval instead of CP and used as a training signal.

The above-described method can reduce overhead when transmitting a broadcast signal, improve channel usage efficiency, and improve performance of a synchronizer and a channel estimator of a broadcast signal receiver.

1 is a block diagram showing a brief configuration of a transmission apparatus of a DMB-T. Referring to FIG. 1, the operation of the transmitter of the DMB-T will be described.

The channel encoder 10 outputs a bit stream encoded by the channel in order to detect an error at the receiving end.

The TPS generation unit 15 generates and outputs TPS data including information of a frame group number, a Forward Error Correction (FEC) code error ratio, a time-deinterleaver mode, and the like.

The modulator 20 receives a bit stream of the channel encoder 20 and TPS data of the TPS generator and receives quadrature amplitude modulation (QAM) of 4, 16, or 64 values of the bit stream. Modulate in such a manner.

The inverse DFT unit 30 modulates a signal modulated by the OFDM scheme in the frequency domain into an OFDM signal in the time domain. In particular, the DMB-T method converts a frequency domain signal of 3780 points of transmission data into a time domain signal.

The PN generator 40 generates a PN sequence to be used as a training signal of a broadcast signal to be transmitted.

The multiplexer 50 distributes the generated PN sequence and the OFDM signal converted by the inverse DFT unit 30 in a time domain, and multiplexes the same.

And, SRRC (Square Root Cosine Rasied; hereinafter SRRC) section 60, and outputs the limited bandwidth of the multiplexed DMB-T signal. In general, the roll-off factor α used for the bandwidth limit is 0.05.

In addition, the RF transmitter 70 up-converts the output signal of which the bandwidth is limited to an RF (Radio Frequency) transmission band of frequency fc to transmit a broadcast signal.

FIG. 2 shows a structure of a frame in which a guard interval is 1/9 of a frame of a signal transmitted by the DMB-T transmitting apparatus of FIG. 1. Referring to FIG. 2, the transmission frame structure will be described with an example in which the guard interval is 1/9 in the OFDM scheme.

The frame consists of frame sync and frame body.

The frame body is a place where data to be transmitted is a DFT block to which a Discrete Fourier Transform (DFT) is applied, and the DFT block generally includes 3780 stream data.

In general, the 3780 stream data of the frame body is divided into four nine TPS data sections and three 936 transmission data sections between the sections, so that a total of 3780 data are included in one frame body.

The frame sink is composed of a PN sequence, and the PN used for the frame sink may use a sequence having an order of 8 (m = 8). When m = 8, 255 different sequences can be generated. The sequences are extended to preambles and postambles for use in guard intervals.

The preamble and the postamble are repetition intervals of the PN sequence for cyclic extension of the PN sequence.

Of the 255 PN sequences of the frame sync, the first 115 PNs of the PN sequence are added as a postamble to the end of the 255 PN sequence, and the last 50 PNs of the PN sequence are added as preambles before the 255 PN sequence. To expand.

The polynomial of the PN sequence is P (x) = x ⁸ + x ⁶ + x ⁵ + x + 1, and the generated phase varies from 0 to 254 according to the initial state of the PN sequence.

When the guard interval is 1/9, the preamble and the post emblem are added to the 255 PN sequences before and after to form a frame sync composed of 420 data. In other words, 420 data, which is 1/9 of 3780 data of the DFT block, are used for frame sync. One OFDM frame is composed of a frame sink of 420 data and a frame body of 3780 data.

The structure of the data frame may vary depending on the protection period, and the number of data distributed in each frame may also be distributed differently.

In addition, the protective section may be defined as 1/4 or 1/9, in addition to the 1/6 protective section may be used, and thus, the length of the protective section may be formed differently depending on the standard forming the system.

3 shows a structure diagram of a conventional TDS-OFDM receiver. Referring to FIG. 3, the operation of the TDS-OFDM receiver will be described.

The tuner 110 of the conventional TDS-OFDM receiver converts a signal of an RF transmission band into a base band signal and outputs it.

The automatic gain controller (AGC) 120 normalizes and outputs the power of the output signal.

The analog-to-digital converter 130 converts an analog signal output from the automatic gain controller into a digital signal and outputs the digital signal.

The phase splitter 140 divides an inphase component signal (hereinafter referred to as I signal) and a quadrature component signal (hereinafter referred to as Q signal) from the signal output from the A / D converter 130. Print separately.

The automatic frequency control (FCC) unit 177 compensates for the estimated frequency error of the separated I and Q signals, and the SRRC unit 160 controls the bandwidth of the received signal as in the transmitter. Perform a filter role to limit

The synchronization unit of the received signal can be largely divided into three parts.

First, the AFC unit 177 calculates the frequency error of the received signal as described above, and calculates the product of the received signal and the signal whose frequency error is calculated by the multiplier 145 to compensate for the frequency error of the received signal. Can be.

Second, the acquisition unit 172 synchronizes the PN sequence sent by the transmitter.

Finally, the signal tracking unit 174 compensates for the symbol error using the captured PN sequence.

The signal acquisition unit 172, the signal tracking unit 174, and the AFC unit 177 of the received signal synchronization unit all use the results of the PN correlation unit 171.

The channel and data estimated as a result of the synchronization unit for synchronizing the received signal are transformed into the time domain through the fast fourier transform (FFT) process in the DFT units 180 and 182, and the channel is compensated through the equalizer 190 and then the channel is compensated. Output to the decoder.

Conventional equalizers may use either a zero-forcing equalizer or a minimum mean square error equalizer. The minimum mean square error (MMSE) equalizer outperforms the zero-forcing equalizer in terms of mean square error (MSE).

However, in order to implement the MMSE equalizer, the power of noise should be measured. The conventional equalizer measures the power of noise from a null carrier. However, since the DMB-T does not use a null carrier, there is a problem that the equalizer of the OFDM receiver cannot compensate the channel by a conventional method.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an equalizer of an OFDM receiver capable of compensating a channel without using a null carrier and having good channel compensating performance.

In order to achieve the above object, the present invention provides an equalizer of an apparatus for receiving an orthogonal frequency division multiplexing (OFDM) signal using a pseudonoise (PN) sequence as a training signal. A TPS variance calculator for calculating a variance of noise based on an error between time domain synchronous (TPS) data and reference TPS data; And a first equalizer for compensating a channel with a dispersion value of noise output from the dispersion calculator.

The first equalizer includes: a minimum error generator configured to receive a dispersion value output from the TPS dispersion calculator and generate a minimum mean square error value for the channel impulse response in response to the dispersion value and the frequency of the channel impulse; And a first operator for outputting a channel-compensated symbol by the product of the minimum mean square error value of the minimum error generation unit and the received data response.

The TPS dispersion calculator includes: a TPS decoder configured to decode and output the received TPS symbol; A reference TPS generation unit for generating reference TPS data transmitted by a transmitter; A second calculator for obtaining a difference between the TPS data of the reference TPS generating unit and the TPS data output from the TPS decoding unit; And a third operator that squares the calculated value of the second calculator to obtain a noise variance value.

The noise variance value is preferably a noise variance value of TPS data included in one frame of the OFDM transmission signal.

The received TPS data may include 36 pieces in one frame of the OFDM transmission signal.

The received TPS data may include information of any one or more of a frame group number, a forward error correction code rate, and a time-deinterleaver mode.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described.

4 shows an embodiment of an equalizer of an OFDM receiver according to the present invention. An embodiment of the equalizer of the OFDM receiver according to the present invention includes a first equalizer 190 and a TPS dispersion calculator 200.

The first equalizer 190 includes a minimum error generator 192 and a first operator 195.

Referring to Figure 4 describes the operation of the first equalizing unit 190 of an embodiment according to the present invention.

The two signals output from the signal synchronization unit, that is, the data signal from which the frequency error and the symbol timing error of the received signal are removed and the impulse response signal of the channel are respectively transmitted to the first DFT unit 180 and the second DFT unit 182, respectively. Is entered.

The first DFT unit 180 and the second DFT unit 182 convert signals into a frequency domain, respectively.

The signal output from the second DFT 182 is input to the minimum error generation unit 192.

The minimum error generator 192 calculates an inverse of the TPS dispersion value output from the TPS dispersion calculator 200 and the channel response of the channel impulse output by the second DFT 182 to have a minimum mean square error. Calculate the channel compensation function (hereafter Gmmse).

The channel compensation function is applied to a frequency response of the data to output a channel compensated symbol of the frequency response of the data.

Hereinafter, a concept in which the equalizer compensates for a channel will be described.

If the k th symbol of data is called Y (k) and the symbol sent from the transmitter is X (k), then Y (k) is as follows.

If the k-th symbol of the frequency response signal of the data is referred to as Y (k) and the symbol sent from the transmitter is referred to as X (k), then Y (k) is as follows.

Is the noise component of the kth symbol.

라고 하면, 등화기로부터 출력되는 심벌은 수학식의 2와 같다.Channel compensated data

In this case, the symbol output from the equalizer is equal to 2 in the equation.

In equation (2), if G (k) is the best G (k) at which the minimum mean square error (MMSE) of G (k) becomes the minimum, Gmmse is equal to equation (3).

는 채널 임펄스의 주파수 응답신호의 k번째 심벌,

는

의 켤레복소수를 의미한다.here

Is the kth symbol of the frequency response signal of the channel impulse,

Is

Means the complex conjugate of.

Here, it is assumed that X (k) and η (k) are white noise, and the variance of the signal is assumed to be normalized to one.

In Equation 3, R _x is an autocorrelation matrix of a transmitted signal, and Rη is an autocorrelation matrix of noise. Then, Equation 3 may be written as Equation 5 using Equation 4.

In Equation 5, σ ² _N is the variance of noise. It can be seen from Equation 5 that the noise variance must be accurately calculated to prevent degradation of reception performance. Substituting Equation 5 into Equation 2 can be written as Equation 6.

The equalizer of the OFDM receiver according to the present invention uses the TPS data to measure the variance of the noise.

The TPS data includes information such as a frame group number, a forward error correction code rate, a time-deinterleaver mode, and the like.

The TPS data is quadrature phase shift keying (QPSK), and since the receiver can easily detect the TPS data signal and the value of the TPS data is often unchanged, the pilot signal is in the frequency domain. Can be used like

In addition, when the TPS data signal is transmitted with a greater magnitude of power than other signals, the receiving device can more reliably detect and use the TPS data signal.

5 shows an embodiment of a TPS variance calculation unit 200 for extracting a TPS variance in an equalizer of an OFDM receiver according to the present invention.

The TPS dispersion calculator 200 may include a TPS decoder 210, a reference TPS generator 220, and a second operator 230 and a third operator 240 that calculate a variance of the TPS. The TPS decoder 210 decodes a symbol corresponding to TPS data among channel compensated symbols of data output from the first equalizer 190.

The reference TPS generation unit 220 generates reference TPS data transmitted by the OFDM transmitter by using that the TPS data hardly changes.

The second operator 230 calculates a difference between the decoded symbol of the TPS decoder 210 and the reference TPS data of the reference TPS generator 220.

The third calculator 240 may calculate a variance of noise by squaring the difference calculated by the second calculator 230.

In general, there may be 36 TPS data in one frame, and the variance of the power of noise may be obtained in units of frames by using the average of the variances of the 36 frames.

The process of calculating the variance of the power of the noise is shown in equation (7). In Equation 7, subscript T indicates a TPS data interval, and as an example, N _T indicates the number of TPS data.

는 채널 보상된 TPS 데이터이다. 노이즈의 분산은 수학식 7에서 계산되는 것처럼 36개의 TPS 데이터의 평균치를 사용하는 것이 바람직하다.In Equation 7, Y _T is received TPS data,

Is channel compensated TPS data. The variance of the noise is preferably used as the average value of 36 TPS data, as calculated in the equation (7).

FIG. 6 is a diagram illustrating that the amount of noise variance can be obtained from the TPS symbol received on the constellation and the reference TPS data transmitted from the transmitter. The horizontal axis corresponds to an in-phase signal (I signal) and the vertical axis corresponds to a quadrature phase signal (Q signal).

The signal difference of the noise may be output due to an error between the TPS data output by the first equalizer 190 and the reference TPS data of the reference TPS generator 220.

Referring to the effect of the equalizer of the apparatus for receiving the broadcast signal modulated by the orthogonal frequency multiplexing method according to the present invention described above are as follows.

According to the equalizer according to the present invention, the channel can be compensated without using a null carrier, and the compensation performance of the channel can be improved.

Claims (6)

In an equalizer of an apparatus for receiving a signal of an orthogonal frequency division multiplexing (OFDM) using a pseudonoise (PN) sequence as a training signal, A TPS dispersion calculator for calculating a variance of noise based on an error between the received time domain synchronous data and the reference TPS data; And And a first equalizer for compensating for a channel by a dispersion value of noise output from the dispersion calculator. The method of claim 1, The first equalizer includes: a minimum error generator configured to receive a dispersion value output from the TPS dispersion calculator and generate a minimum mean square error value for the channel impulse response in response to the dispersion value and the frequency of the channel impulse; And And a first operator for outputting a channel-compensated symbol by the product of the minimum mean square error value of the minimum error generation unit and the received data response. The method of claim 1, The TPS dispersion calculator includes: a TPS decoder configured to decode and output the received TPS symbol; A reference TPS generation unit for generating reference TPS data transmitted by a transmitter; A second calculator for obtaining a difference between the TPS data of the reference TPS generating unit and the TPS data output from the TPS decoding unit; And And a third operator that squares the calculated value of the second calculator to obtain a noise variance value. The method of claim 1, And the noise variance value is a noise variance value of the TPS data included in one frame of the OFDM transmission signal. The method of claim 1, The received TPS data equalizer of the OFDM modulated signal receiving apparatus, characterized in that 36 pieces are included in one frame of the OFDM transmission signal. The method of claim 1, The received TPS data includes at least one of a frame group number, a FEC code rate or a time-deinterleaver mode. Equalizer for modulated signal receiver.

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