KR100793789B1 - An apparatus for estimating channel and a method thereof - Google Patents

Abstract

The present invention relates to a channel estimating apparatus and a channel estimating method. The present invention provides an apparatus for estimating a channel of a transmission signal having a training signal having a cyclic structure, comprising: a correlator for correlating and outputting a received signal in a time domain, a training signal in a generated time domain, and correlation values output by the correlator Receives a correlation value between the signals of the first section including 255 consecutive signals in the training signal section of the received signal and the generated training signal, and generates a correlation value exceeding a reference value among the received correlation values A channel determining unit detecting and outputting position information of the signal of the first section; And a channel selector which selects and outputs a correlation value located in the position information output by the channel selector among the correlation values output by the correlator. According to the channel estimating apparatus and the channel estimating method according to the present invention, a channel can be accurately estimated in a system for transmitting a training signal having a cyclic structure.

Channel Estimation, PN, OFDM, CIR, Channel Impulse Response

Description

An apparatus for estimating channel and a method

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

2 is a diagram showing a structure of a frame having a guard interval of 1/9 of a frame of a TDS-OFDM transmission signal;

3 is a structural diagram of an example of a broadcast receiving apparatus that may include a channel estimating apparatus according to the present invention;

4 is a diagram illustrating a transmission path of a transmission signal for explaining a concept of a channel estimation method according to the present invention.

5A is a diagram illustrating a frame structure of a frame sync among transmission signals of a TDS-OFDM.

FIG. 5B is a diagram illustrating an example of a channel impulse response calculated by a PN sequence of a predetermined section and a receiving end included in a frame sync. FIG.

5C is a diagram illustrating an example of a channel impulse response calculated by a PN sequence of a frame sync section and a receiving end.

6 is a structural diagram showing an embodiment of a channel estimating apparatus according to the present invention with reference to FIG.

<Explanation of symbols in the main part of the drawing>

10: channel encoding unit 15: TPS generation unit

20 modulator 30 reverse DFT

40: PN generation unit 50: multiplexer

60: filter unit 70: RF transmission unit

110: tuner 120: automatic gain control unit

130: A / D converter 140: phase separator

145: Multiplier 150: Resampler

160: filter unit 170: frame synchronization unit

171: PN correlation unit 172: signal acquisition unit

174: signal tracking unit 177: automatic frequency control unit

179: multiplier 180,182: DFT unit

190: equalizer

210: correlator 220: channel determination unit

230: channel selector

The present invention relates to a channel estimating apparatus and a channel estimating method, and more particularly, to a channel estimating apparatus and a channel estimating method capable of accurate channel estimation when receiving a transmission signal including a training signal of a cyclic structure.

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 signal modulation scheme called Time Domain Synchronous OFDM (hereinafter referred to as TDS-OFDM) is used.

A signal transmitted after being modulated at the transmitting end of the TDS-OFDM is applied with an Inverse Discrete Fourier Transform (IDFT) as in the cyclic prefix OFDM (CP-OFDM) scheme.

However, the transmission signal is used as a training signal by inserting a pseudonoise (PN) in place of the CP in the guard interval.

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 bitstream 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 the encoded bit stream and modulates the bit stream by quadrature amplitude modulation (QAM), such as 4-, 16-, or 64-values.

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 general, 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.

The filter unit 60 outputs the bandwidth of the multiplexed DMB-T signal by limiting the bandwidth. 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. A transmission frame structure having a guard interval of 1/9 will be described with reference to FIG. 2.

The frame includes 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.

The frame sync consists of a PN sequence, and the PN sequence used for the frame sync 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 may vary from 0 to 254 according to the initial state of the PN sequence.

When the guard interval is 1/9, the preamble and the postamble may be added to the 255 PN sequences before and after to configure a frame sink including 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.

In order to receive the transmitted signal as above, correct channel estimation is preceded to compensate for the channel of the received signal. However, when estimating a channel with the PN sequence, since the training signal including the PN sequence has a cyclic structure, there is a problem in that the channel impulse response due to the cyclic structure can be accurately calculated.

An object of the present invention is to provide a channel estimating apparatus and a channel estimating method capable of accurately estimating a channel in a system for transmitting a training signal having a cyclic structure as described above.

In order to achieve the above object, the present invention provides an apparatus for estimating a channel of a transmission signal having a training signal of a cyclic structure, comprising: a correlator for correlating and outputting a received signal in a time domain and a generated training signal in a time domain; Receives a correlation value between the generated training signal and the signals of the first interval including the continuous 255 signals in the training signal interval of the received signal of the correlation values output by the correlator, the received correlation value A channel determination unit which detects and outputs position information of the signal of the first section for generating a correlation value exceeding a reference value among the signals; And a channel selector which selects and outputs a correlation value located in the position information output by the channel selector among the correlation values output by the correlator.

In another aspect, the present invention provides a method for estimating a channel of a transmission signal having a training signal having a cyclic structure, comprising: (a) generating a first correlation value correlated with a training signal interval included in a generated training signal and a received signal; Outputting a second correlation value correlated with a first section of one training signal and the included training signal of the received signal; (b) outputting position information on a signal section of a correlation value having a value exceeding a reference value among the second correlation values; And (c) selecting one correlation value among the first correlation values of step (a) from the position information.

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

3 is a structural diagram of an example of a broadcast receiving apparatus that may include a channel estimating apparatus according to the present invention. The operation of the TDS-OFDM broadcast signal receiving apparatus will now be described with reference to FIG. 3.

When the TDS-OFDM broadcast signal receiver is divided into a signal receiver and a frame synchronizer, the signal receiver includes a tuner 110, an automatic gain controller (AGC) 120, an analog to digital converter 130, A phase splitter 140 and a filter unit 160 are included.

The tuner 110 of the TDS-OFDM broadcast signal receiving apparatus converts an RF transmission band signal into a base band signal and outputs it. The automatic gain controller (AGC) 120 normalizes and outputs the power of the output signal.

An analog-to-digital converter (130) converts an analog signal output from the automatic gain controller (AGC) 120 into a digital signal and outputs it. 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 filter unit 160 may perform a filter role of limiting the bandwidth of the broadcast signal compensated for the frequency error estimated by the automatic frequency control unit (AFC) 177, thereby limiting and outputting the bandwidth of the received signal. .

A square root rasied cosine (SRRC) filter may be used for the filter unit 60. In this case, a roll-off factor α used for bandwidth limitation is generally 0.05.

On the other hand, the frame synchronization unit may include an automatic frequency control unit (AFC) 177, a signal acquisition unit 172, and a signal tracking unit 174.

The automatic frequency controller (AFC) 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 do.

The signal acquisition unit 172 synchronizes the PN sequence sent by the transmitter. The signal tracking unit 174 may compensate for the symbol error by using the captured PN sequence. All frame synchronization units of the received signal may use the result of the PN correlator 171.

The data estimated as a result of the frame synchronization unit is transformed into the frequency domain through the fast fourier transform (FFT) process in the DFT units 180 and 182, and the channel is compensated through the equalizer 190 to the channel decoder (not shown). Is output.

Channel estimation may be performed prior to input of equalizer 190 compensating for the channel. In TDS-OFDM, channel estimation may be performed in the frequency domain, and if the channel is accurately estimated, fine frame synchronization may be performed so that inter-frame interference does not occur.

On the other hand, if the frame-to-frame synchronization is incorrectly estimated, inter-frame interference (IFI) may occur. In order to remove the inter-frame interference, the DFT operation may be performed from the frame of the signal of the path reaching the receiver among the signals received through the multi path. As described above, accurate channel estimation is required to accurately estimate frame synchronization to remove interframe interference.

The present invention relates to selecting a channel impulse response for channel estimation before being input to the DFT unit 182 above.

4 shows a transmission path of a transmission signal for explaining the concept of a channel estimation method according to the present invention. Referring to FIG. 4 and the following equation, a channel estimation method according to the present invention will be described as follows.

Subcarriers of the transmit signal X _k d, and when said filters of the transmitter h _T, the filter of the receiver h _R, a transmission channel h _C, the value after applying a Fourier transform to the noise n, the receiving terminal R _K R _K is then Same as

The transmission signal X _k undergoes an Inverse Fourier Transform (IFFF) process and a filter process (h _R (t)) at the transmitter. And, the transmission signal undergoes the transmission channel h _C (t), and noise (n (t)) may be mixed during the transmission. The receiver undergoes a filter process (h _R (t)) and a Fourier transform (FFT) process.

If the PN sequence is included in the transmission signal, if the PN sequence is correlated with the PN sequence generated by the receiver after passing through the transmission channel and the filter, the result can be expressed by the following equation.

는 상관(correlation)을 나타낸다.Symbol in equation (2)

Denotes correlation.

PN^＊) 결과는 델타(delta)함수가 된다. 일 예로 TDS-OFDM의 훈련 신호인 PN 시퀀스는 순환 구조를 가지는데 정확한 채널 추정을 위해 PN 시퀀스간의 상관결과를 사용할 수 있다.Correlation of PN Sequence and PN Sequence in Equation 2 (PN

PN ^* ) results in a delta function. For example, the PN sequence, which is a training signal of the TDS-OFDM, has a cyclic structure, and a correlation result between the PN sequences may be used for accurate channel estimation.

5A to 5C illustrate a concept for estimating a channel in the channel estimation method according to the present invention. A channel estimation method according to the present invention will be described with reference to FIGS. 5A to 5C as follows.

FIG. 5A is a diagram illustrating a frame structure of a frame sync among TDS-OFDM transmission signals. FIG. In the following, the section (① + ② + ③) that combines ① section, ② section and ③ section is p (n), ② section, ③ section and section ④ sum section (② + ③ + ④) is PN (n) ( PN sequence) and denotes c (n) in the sections 1 to ⑤.

One frame of the transmission signal includes a PN sequence (PN (n)) sections (2, 3, 4) and a postamble section (5), which is the same sequence as ②, and a preamble section (1), which is the same sequence as (4).

As shown in the example of FIG. 5B, when the PN sequence generated by the receiver correlates with p (n), which is a sum of the ① section, ② section, and ③ section, the first correlation peak value (| p (n) |), section ④ The second correlation peak value may be represented as a channel impulse response by the intervals and ⑤.

The first correlation peak value for p (n) is greater than the second correlation peak value, and the two correlation peak values are separated by 255 data, which is the length of the PN sequence, and the interval is the sum of ①, ②, and ③ sections. Corresponds to the length of the interval.

On the other hand, since it is generally preferable to use a lot of channel information for channel estimation, in the channel estimation method according to the present invention, it is preferable to use all the signals in the frame sync as the channel impulse response, which is channel estimation information.

When the PN sequence generated by the receiver and the c (n) section, which is the received frame sync section, are correlated as the channel estimation information, c (n) also has a periodic structure therein, that is, the sections ①, ④, and ②. Since and ⑤ are the same, the channel impulse response to the PN sequence of the receiver may have three correlation peak values as shown in FIG. 5C.

Three correlation peak values are shown in FIG. 3C as a result of the correlation value for c (n). The channel impulse responses, which are correlated peak values, are spaced apart by 255 data intervals, and the center correlated peak value is the channel impulse response (| c (n) |) having the largest peak value, and its position is | p (n in FIG. 5B. Matches the position of the maximum correlation peak of) |.

Therefore, for accurate channel estimation, it is desirable to remove two small peaks of the three peaks of the channel impulse response before converting the signal to the frequency domain and performing channel estimation.

6 is a structural diagram showing an embodiment of a channel estimating apparatus according to the present invention. The embodiment includes a correlator 210 that correlates a received signal, a channel determiner 220 and a channel selector 230 respectively connected to the correlator 210.

Referring to FIG. 6, the operation of an embodiment of a channel estimating apparatus according to the present invention will be described.

The correlator 210 correlates the received signal with the PN sequence generated by the receiver for the received signal from which frame synchronization is detected. The correlator 210 outputs c (n) and p (n), respectively, as a result of correlating the PN sequences generated at the receiver. c (n) represents a correlation result between the PN sequence of the receiver and 420 data for the frame sync, and p (n) represents a correlation result of the first 255 data of the PN sequence and frame sync of the receiver. Hereinafter, the first 255 data sections of the frame sync of the received signal are referred to as a first section.

For more accurate channel estimation, it is preferable to use the correlation result c (n) corresponding to the frame sync. On the other hand, to remove the small peak among the correlation results of c (n), the position of the correlation peak value of the correlation result p (n) can be used.

In the case of using the channel impulse response using c (n), in order to eliminate the possibility of estimating the channel using a small peak value, the largest correlation value among the correlation values of c (n) is used by using the position of the peak value of p (n). You can choose only.

The channel determiner 220 may store the position and size of the peak of the correlation value with respect to p (n) among the correlation values output by the correlator 210. The channel determination unit 220 may store a threshold value for the peak value in advance to determine whether the correlation value output from the correlator 210 exceeds the reference value.

In addition, the channel determiner 220 may store a position on the correlation peak value signal as a logic value whether the predetermined correlation value is exceeded among the output correlation values. For example, a logical value may be represented as a flag at a position where a correlation peak of | p (n) | appears.

If the correlation peak value of | p (n) | is a correlation peak value exceeding a predetermined reference value, the flag value of the position is set to true or 1, even if the peak value does not appear or the peak value appears. If a correlation peak value is shown, the flag value for that location may store a value of false or zero.

As described above, the channel determiner 220 may inform the channel selector 230 about the position of the correlation peak value.

The channel selector 230 receives a correlation value c (n) from the correlator 210 and receives position information indicating the peak value of the correlation value from the channel determination unit 220.

5b and 5c, the position of the largest correlation peak value among the peak values of | p (n) | of FIG. 5b and the position of the largest correlation peak value among the peak values of | c (n) | The same on the output value of the correlation value.

Therefore, when the channel determination unit 220 transmits the position information of the large correlation peak value among the peak values of | p (n) |, the channel selection unit 230 receives the transmission value and at the position | c ( The correlation peak value of n) | can be output as a channel impulse response.

Therefore, even if the PN sequence, which is a training signal, has a cyclic structure, the result of the channel impulse response can be estimated accurately, and channel estimation can be performed using this.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of the present invention.

The effects of the channel estimating apparatus and the channel estimating method according to the present invention described above are as follows. According to the channel estimating apparatus and the channel estimating method according to the present invention, a channel can be accurately estimated in a system for transmitting a training signal having a cyclic structure.

Claims (7)

An apparatus for estimating a channel of a transmission signal having a training signal of a circular structure, A correlator for correlating and outputting the received signal in the time domain and the training signal in the generated time domain; Receives a correlation value between the generated training signal and the signals of the first interval including the continuous 255 signals in the training signal interval of the received signal of the correlation values output by the correlator, the received correlation value A channel determination unit which detects and outputs position information of the signal of the first section for generating a correlation value exceeding a reference value among the signals; And And a channel selector for selecting and outputting a correlation value located in the position information output by the channel selector among the correlation values output by the correlator. The method of claim 1, And the training signal is pseudonoise (PN). The method of claim 1, The first interval is a channel estimation device, characterized in that the first 255 signal intervals of the training signal of the received signal. The method of claim 1, And the position information is a logical value. A method for estimating a channel of a transmission signal having a training signal of a cyclic structure (a) a first correlation value that correlates the training signal interval included in the generated training signal in the time domain and the received signal in the time domain; Outputting second correlation values correlated with a first period including a signal; (b) outputting position information on a signal section of a correlation value having a value exceeding a reference value among the second correlation values; And and (c) selecting one of the first correlation values of step (a) from the position information. The method of claim 5, The training signal is a channel estimation method, characterized in that the pseudonoise (PN). The method of claim 5, And a first section of step (a) is the first 255 signal sections of the training signal.

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