KR20070094314A - Broadcast signal demodulation device - Google Patents

Abstract

The present invention relates to a broadcast signal demodulation device. The present invention includes a Fourier transform unit for converting the received signal in the time domain to the frequency domain; A channel detector for outputting whether the channel environment of the received signal is a time-varying channel or a delay spread channel; And a sampling frequency synchronizer configured to estimate and compensate a sampling frequency offset from any one of a continuous pilot signal or a distributed pilot signal among signals in a frequency domain output by the Fourier transform unit according to channel information output by the channel detector. A broadcast signal demodulation device is provided. According to the broadcast signal demodulation device according to the present invention, an accurate sampling frequency offset may be compensated for in consideration of a reception environment of a transmission signal.

Description

Apparatus for receiving broadcasting

1 is a structural diagram of an example of a broadcast signal demodulation apparatus capable of receiving a transmission signal of DVB-H

2 illustrates an example of a structure of a transmission signal of DVB-H.

3 is a structural diagram showing an embodiment of a broadcast signal demodulation device according to the present invention;

4 is a structural diagram showing an embodiment of a sampling frequency synchronization unit in a broadcast signal demodulation device according to the present invention;

5 is a block diagram illustrating a process of estimating a sampling frequency offset by a first error detector;

6 is a block diagram illustrating a process of estimating a sampling frequency offset by a second error detector;

7 and 8 illustrate S-curve when calculating the gain of the sampling frequency offset from the continuous pilot signal and the distributed pilot signal, respectively.

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

11: tuner 13: filter section

15: automatic gain control unit 17: analog / digital conversion unit

21: symbol timing recovery unit 22: decimal part carrier wave register

23: Fourier transform unit 24: integer portion carrier wave register

25: Sampling frequency offset recovery section 26: Fine symbol timing recovery section

27: channel equalizer 110: analog / digital conversion unit

120: resampler 130: protection section removal unit

140: Fourier transform unit 150: Guard band removal unit

160: equalization unit 500: channel detection unit

510: first pilot extractor 520: first error detector

521: first symbol delay unit 523: second multiplier

525: phase calculating unit 527: phase adding unit

528: first adder 529: second multiplier

530, second pilot extracting unit 540, second error detecting unit

541: second symbol delay unit 550: multiplexer

560: filter portion 570: oscillation portion

The present invention relates to a broadcast signal demodulation device, and more particularly, to a broadcast signal demodulation device capable of accurately estimating a sampling frequency offset even when a broadcast signal reception environment is changed.

Digital video broadcasting-handheld (DVB-H), which has emerged as a competitive model for terrestrial digital multimedia broadcasting (DMB), is being evaluated as a model that can converge broadcasting and communication. DVB-H is a transmission system that extends the mobile portable terminal area of a broadcasting area and transmits transmission information as an IP datagram.

IP datagram refers to a signal processing method of sending a signal in a packet by an internet protocol. DVB-H has an IP protocol for transmitting voice and video signals (audio / video) by packet unit and compressing them.

DVB-H uses a time slicing multiplexing method, which is a multiplexing method that divides a channel's capacity into a predetermined time slot and loads a packetized broadcast signal in each time slot. .

For example, when the transmitter of DVB-H compresses a signal having a transmission time of 10 seconds and transmits it with a new width of 3 seconds of transmission time, the receiver temporarily stores the compressed signal transmitted as described above in a buffer and then sequentially Play the multimedia video while decompressing.

As described above, the DVB-H transmits a compressed signal using a time division multiplexing method and a timeslot, thereby reducing power consumption of the signal receiving terminal and performing a seamless handover of the transmission signal.

1 is a diagram illustrating an example of a broadcast signal demodulation apparatus capable of receiving a transmission signal of DVB-H. The broadcast signal demodulation device of the DVB-H format of FIG. 1 may include an analog signal receiver 10 and a broadcast signal demodulator 20. An example of a broadcast signal demodulation device in a typical DVB-H format will be described with reference to FIG. 1.

When the antenna of the RF signal receiver 10 receives a transmission signal, the tuner 11 may convert an intermediate frequency signal into an RF signal and output the RF signal.

For example, the filter unit 13 operates as a surface acoustic wave (SAW) filter, and may filter and output the converted signal in a predetermined frequency band.

Since the signal passing through the filter unit 13 is weak in power, the auto gain controller 15 compensates and outputs the gain of the signal passing through the filter unit 13.

The analog / digital converter 17 may convert the gain-compensated analog signal into a digital signal and output the digital signal.

 The broadcast signal demodulator 20 includes a symbol timing recovery unit 21, a fractional carrier carrier 22, a Fourier transform unit 23, an integer carrier carrier 24, a sampling frequency offset recovery unit 25, and a fine symbol The timing recovery unit 26 and the channel equalizer 27 may be included.

The symbol timing recovery unit 21 extracts and outputs only a signal of a data section excluding a guard section of a frame of the transmission signal.

The fractional carrier wave unit 22 may estimate and output a frequency offset of less than half of the interval between the subcarriers. The Fourier transformer 23 converts the compensated signal in the time domain to the frequency domain. The integer carrier recovery unit 24 may estimate and output a frequency offset corresponding to an integer multiple of a subcarrier interval using a pilot signal of a signal in the frequency domain.

The sampling frequency offset recovery unit 25 may compensate the sampling frequency offset of the received signal by using a resampler (not shown).

The fine symbol timing recovery unit 26 may compensate for the fine symbol timing error remaining in the compensated signal.

The channel equalizer 27 may compensate for distortion of the transmission signal passing through the multipath.

The channel compensated signal is input to a channel decoder to perform error correction of the signal.

However, since the broadcast signal demodulation apparatus estimates the sampling frequency offset without considering the reception environment of the transmission signal, the reception performance is deteriorated depending on the reception environment of the signal.

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 a broadcast signal demodulation apparatus capable of estimating and compensating for an accurate sampling frequency offset.

Another object of the present invention is to provide a broadcast signal demodulation device capable of compensating for an accurate sampling frequency offset in consideration of a reception environment of a transmission signal.

In order to achieve the above object, the present invention includes a Fourier transform unit for converting the received signal in the time domain to the frequency domain; A channel detector for outputting whether the channel environment of the received signal is a time-varying channel or a delay spread channel; And a sampling frequency synchronizer configured to estimate and compensate a sampling frequency offset from any one of a continuous pilot signal or a distributed pilot signal among signals in a frequency domain output by the Fourier transform unit according to channel information output by the channel detector. A broadcast signal demodulation device is provided.

The sampling frequency synchronization unit may include: a first pilot extracting unit extracting a continuous pilot signal from a received signal when the channel information is a time-varying channel; A first error detector for calculating a sampling frequency offset from the continuous pilot signal of the first pilot extractor; A filter unit for removing the calculated sampling frequency offset; And an oscillator for outputting an oscillation signal at a sampling frequency output by the filter unit.

The first error detector may normalize and output the calculated sampling frequency offset.

The sampling frequency synchronization unit comprises: a second pilot extractor extracting a distributed pilot signal from a received signal when the channel information is a delay spread channel; A second error detector configured to calculate a sampling frequency offset from the distributed pilot signal of the second pilot extractor; A filter unit for removing the calculated sampling frequency offset; And an oscillator for outputting an oscillation signal at a sampling frequency output by the filter unit.

The second error detector may normalize and output the calculated sampling frequency offset.

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

2 is a diagram illustrating a transmission signal structure of DVB-H. The transmission signal structure of the DVB-H will be described with reference to FIG. 2.

2 is a diagram illustrating a pattern of a transmission signal of DVB-H including a distributed pilot. The transmission signal pattern of the DVB-H will be described with reference to FIG. 2.

2 is a direction in which the frequency of subcarriers transmitted at the same time is increased (frequency axis), and a vertical direction is a direction in which time progresses (time axis). Circles arranged in a horizontal line indicate the positions of subcarriers forming an OFDM symbol.

The distributed pilot is repeated at every 12 subcarrier positions in the OFDM symbol transmitted at the same time. In the OFDM symbol transmitted at the next time, the distributed pilot may be located at a position where the subcarrier frequency interval is separated by 3 from the subcarrier position of the distributed pilot in the OFDM symbol transmitted at the previous time. Thus, the same distributed pilot pattern may be repeated every four OFDM symbols consecutive in time.

In FIG. 2, Tu represents the number of usable subcarriers, Dt represents the distance between distributed pilots on the time axis, and Df represents the distance between distributed pilots on the frequency axis, respectively.

The distance Df between the distributed pilots in the frequency domain determines the delay range of the ghost that can be estimated in the channel.

Since the same pilot pattern appears every four input symbols, time interpolation can be performed at the same pilot position. That is, the first input symbol (t = 1) represents the same symbol pattern as the symbol input at t = 5, and the time interpolation for the symbol input at t = 2, 3, 4 at the distributed pilot of the symbols is Can be performed.

The symbol input at t = 6 has the same distributed pilot pattern as the symbol input at t = 2, and t = 3,4,5 on the distributed pilot position of the symbol input at t = 6 and the symbol input at t = 2. Time interpolation may be performed on the symbols of.

Therefore, if a symbol is input at t = 7 and then time interpolated in the above manner, the symbols input at t = 4 are distributed in the frequency domain of the input symbol at t = 4 since distributed pilots are located at four subcarrier positions. The spacing between pilots is originally reduced to one quarter of the spacing between distributed pilots, and a symbol input at t = 4 has a pattern in which distributed pilots are located every four subcarrier positions.

In the distributed pilot, the position k of the frequency axis is as follows.

Where p is a positive integer and k ranges from 0 ≦ k ≦ Kmax.

Here, Kmax has a value of 1704 in the 2K transmission mode, 3408 in the 4K transmission mode, and 6816 in the 8K transmission mode. In addition, l is a symbol index constituting an OFDM symbol and means a position in a symbol of a subcarrier.

The continuous pilot has a pattern located at a subcarrier location of a certain position in an OFDM symbol. Therefore, the continuous pilot is repeated at the same subcarrier position for each OFDM symbol and continues in time at that position.

In the DVB-H, the continuous pilot position is a continuous pilot signal of the transmission signal at K = 0, 48, 54, 87, ..., 1704 of the positions K of 1706 subcarriers in the 2K mode.

In the 8K mode, there are 6816 OFDM subcarriers, and a continuous pilot signal is located at subcarrier positions K = 0, 48, 54, 87, ... 2229, 2235, 2322, ..., 6816.

3 is a structural diagram showing an embodiment of a broadcast signal demodulation device according to the present invention. Referring to FIG. 3, an operation of an embodiment of a broadcast signal demodulation device according to the present invention will be described.

When the broadcast signal demodulation device receives the transmission signal of the DVB-H format, the analog-to-digital conversion unit 110 samples the analog signal into a digital signal and outputs the digital signal.

The resampler 120 may receive a signal from which the sampling frequency offset of the output signal is compensated from the sampling frequency synchronizer 500, and output the sampled signal according to the signal.

The guard interval removing unit 130 may receive the sampled signal and may remove and output a signal from which a guard interval is removed from a transmission signal of the DVB-H.

The Fourier transform unit 140 may convert the signal from which the guard interval has been removed into the frequency domain and output the converted signal. Preferably, the Fourier transform unit 140 may convert the signal into the frequency domain using a fast fourier transform algorithm. .

The guard band removing unit 150 may remove and output the guard band padded with zero among the signals converted into the frequency domain.

The equalizer 160 compensates for the distortion of the signal from which the guard band is removed and outputs the compensated signal.

4 is a diagram illustrating an embodiment of a sampling frequency synchronization unit 500 of a broadcast signal demodulation device according to the present invention. Referring to Figure 4 describes the operation of an embodiment of the sampling frequency synchronization unit 500 according to the present invention.

 The sampling frequency synchronizer 500 according to the present invention may select and output a pilot frequency offset by selecting a pilot signal according to a reception environment of a transmission signal output from the channel detector 600.

Upon receiving the signal converted into the frequency domain from the Fourier transform unit 140, the first pilot extractor 510 may extract and output a continuous pilot signal from the OFDM symbol converted into the frequency domain. On the other hand, the second pilot extractor 530 may extract and output the distributed pilot signal.

The first error detector 520 may calculate and output a sampling frequency offset from the continuous pilot signal of the first pilot extractor 510.

The second error detector 540 may calculate and output a sampling frequency offset from the distributed pilot signal of the second pilot extractor 530.

The channel detector 600 may detect and output a channel of the received signal. That is, the channel detector 200 may determine and output whether the channel environment of the received signal is a time-varying channel according to mobile reception or a delay spread channel according to fixed reception. The channel detecting unit 600 determines a channel environment of a received signal in various ways. As an example, it may be determined whether the channel environment of the received signal is a time-varying channel or a delay spread channel due to fixed reception in consideration of changes in the CTF signal.

The multiplexer 550 may select and output a sampling frequency offset output by the first error detector 520 or the second error detector 540 according to the channel information of the channel detector 600.

That is, the multiplexer 550 may output the sampling frequency offset of the continuous pilot signal calculated by the first error detector 520 when the channel of the received signal is a time-varying channel according to the mobile reception mode.

Alternatively, the multiplexer 550 may output the sampling frequency offset of the distributed pilot signal calculated by the second error detector 540 when the channel of the received signal is a delay spread channel according to the fixed reception mode.

Since the time-varying channel is difficult to estimate the channel, when the channel of the received signal is determined to be a time-varying channel, calculating channel information from a continuous pilot symbol at a fixed position in the OFDM symbol can minimize distortion of the channel information.

On the other hand, if the delay spread channel according to the fixed reception channel information is calculated as a distributed pilot channel, it is preferable to compensate the sampling frequency offset due to the long delay spread channel according to the signal received in the multipath.

The filter unit 560 may compensate and output a sampling frequency offset that is selected and output by the multiplexer 550. The oscillator 570 outputs a signal oscillated at a sampling frequency output from the filter unit 560.

The process of the first error detection unit 520 calculating the sampling frequency offset as the continuous pilot signal is shown in Equations 2 to 4.

과

은 각각 l번째와 l-1번째 OFDM 심볼의 연속 파일럿 신호, k는 연속 파일럿 신호의 인덱스, N은 한 심볼에 속한 데이터의 개수, Ng는 보호구간의 데이터 개수, n은 노이즈를 각각 나타낸다.

and

Are the continuous pilot signals of the l-th and l-1 th OFDM symbols, k is the index of the continuous pilot signal, N is the number of data belonging to one symbol, Ng is the number of data in the protection interval, and n is noise.

의 위상은 각 부반송파 인덱스(

), 샘플링 주파수 오프셋에 따른 타이밍 에러(

) 및 반송파의 주파수 오프셋(

)의 관계로 표현할 수 있다. remind

The phase of each subcarrier index (

), Timing error due to sampling frequency offset (

) And the frequency offset of the carrier (

Can be expressed as

의 범위를 가진다. Here, the subcarrier index k is for the data interval included in one symbol

Has a range of.

)는 수학식 4에서 보인 것처럼 입력되는 하나의 심볼 내 부반송파 인덱스 중 음의 주파수 영역의 부반송파 인덱스(

)에 대한

의 합을 양의 주파수 영역의 부반송파 인덱스(

)에 대한

의 합으로부터 감산하여 산출할 수 있다.Timing Error with Sampling Frequency Offset for Continuous Pilot (

) Is a subcarrier index of the negative frequency domain of the subcarrier index in one symbol input as shown in Equation (

For)

The sum of the subcarrier indexes in the positive frequency domain (

For)

It can be calculated by subtracting from the sum of.

)를 이하의 수학식 5부터 수학식 7에 따라 산출할 수 있다. 상기

는 샘플링 주파수 오프셋 산출 이득을 나타낸다.On the other hand, the second error detection unit 540 has a timing error according to a sampling frequency offset from a distributed pilot located at four subcarrier index intervals.

) Can be calculated according to Equation 5 to Equation 7 below. remind

Denotes the sampling frequency offset calculation gain.

FIG. 5 is a block diagram illustrating a process in which the first error detector 520 calculates a sampling frequency offset from Equation 2 to Equation 5. FIG.

The first symbol delay unit 521 delays and outputs the real part and the imaginary part of the continuous pilot by one symbol period. The first multiplier 523 conjugates and outputs consecutive pilots in neighboring symbols.

The phase calculator 525 may calculate a phase at a position on the constellation of the result of the conjugate multiple operation.

The phase summing unit 527 may calculate the sum of phases of the subcarrier indexes of the negative frequency domain and the sum of phases of the subcarrier indexes of the positive frequency domain among the symbol subcarrier indexes.

The first adder 528 sums the sum of the phases of the two symbol index regions, and the second multiplier 529 adjusts the gain of the result of the first adder 528 to adjust the sampling frequency offset. It can be estimated.

On the other hand, the second error detector 540 may calculate a sampling frequency offset from the distributed pilot signal.

A process of calculating the sampling frequency offset from the distributed pilot signal will be described with reference to Equations 5 to 7 below.

Since the distributed pilot signal is located at the same subcarrier position every four OFDM symbols, the complex conjugate for the continuous distributed pilot signal is represented by Equation 5. n 'represents noise.

은 수학식 6과 같다. Phase of the complex conjugate result in equation (5)

Is the same as Equation 6.

의 범위를 가진다.Here, the subcarrier index k is the data interval included in one symbol

Has a range of.

, 양의 주파수 영역의 부반송파 인덱스에 대한 위상의 합을

로 표현하면, 샘플링 주파수 오프셋에 따른 타이밍 에러(

)는 수학식 7과 같다.Sum of phases for subcarrier indexes in the negative frequency domain of the range

Sum the phases for the subcarrier indexes in the positive frequency domain.

In this case, the timing error according to the sampling frequency offset (

) Is the same as Equation 7.

는 추정하는 샘플링 주파수 오프셋의 이득을 나타낸다.

Denotes the gain of the estimated sampling frequency offset.

6 is a block diagram illustrating a process in which the second error detector 540 estimates a sampling frequency offset from the distributed pilot signal. Each block of FIG. 6 is similar to each block of FIG. 5, but the second symbol delay unit 541 of FIG. 6 may delay and output four symbols. Since the remaining blocks of FIG. 6 correspond to the blocks of FIG. 5, a detailed description thereof will be omitted.

,

)을 산출할 수 있는 S-curve이다. 도 7 및 도 8의 수평축은 샘플링 주파수 오프셋을, 수직축은 그 샘플링 주파수 오프셋에 따른 타이밍 에러를 나타낸다. 그리고, 상기 샘플링 주파수 오프셋의 이득(

,

)은 각 각 S-curve의 기울기의 역수에 해당한다. 상기 이득은 필터부(560)가 샘플링 주파수 오프셋에 따른 타이밍 에러를 정규화하는데 사용될 수 있다. 7 and 8 show the gain of the sampling frequency offset from the continuous pilot signal and the distributed pilot signal, respectively.

,

) Is an S-curve that can be calculated. 7 and 8 represent the sampling frequency offset, and the vertical axis represents the timing error according to the sampling frequency offset. And, the gain of the sampling frequency offset (

,

) Corresponds to the inverse of the slope of each S-curve. The gain may be used by the filter unit 560 to normalize timing error according to the sampling frequency offset.

It is easy for a person skilled in the art to change or modify the present invention from the present specification. Therefore, although an embodiment of the present invention has been described above clearly, various modifications thereof should be made without departing from the spirit and the scope of the present invention.

The effects of the broadcast signal demodulation device according to the present invention described above are as follows. According to the broadcast signal demodulation device according to the present invention, an accurate sampling frequency offset may be estimated to compensate for this. In addition, an accurate sampling frequency offset may be compensated for in consideration of a reception environment of a transmission signal.

Claims (5)

A Fourier transform unit for converting the received signal in the time domain into the frequency domain; A channel detector for outputting whether the channel environment of the received signal is a time-varying channel or a delay spread channel; And And a sampling frequency synchronizer configured to estimate and compensate a sampling frequency offset from any one of a continuous pilot signal or a distributed pilot signal among signals in a frequency domain output by the Fourier transform unit according to channel information output by the channel detector. Broadcast signal demodulation device. The method of claim 1, The sampling frequency synchronization unit may include: a first pilot extracting unit extracting a continuous pilot signal from a received signal when the channel information is a time-varying channel; A first error detector for calculating a sampling frequency offset from the continuous pilot signal of the first pilot extractor; A filter unit for removing the calculated sampling frequency offset; And And an oscillator for outputting an oscillation signal at a sampling frequency output from the filter unit. The method of claim 2, And the first error detection unit normalizes the calculated sampling frequency offset and outputs the normalized sampling frequency offset. The method of claim 1, The sampling frequency synchronization unit comprises: a second pilot extractor extracting a distributed pilot signal from a received signal when the channel information is a delay spread channel; A second error detector configured to calculate a sampling frequency offset from the distributed pilot signal of the second pilot extractor; A filter unit for removing the calculated sampling frequency offset; And And an oscillator for outputting an oscillation signal at a sampling frequency output from the filter unit. The method of claim 4, wherein And the second error detection unit normalizes the calculated sampling frequency offset and outputs the normalized sampling frequency offset.

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