KR100767695B1 - Broadcast receiving device and broadcast receiving method - Google Patents

Abstract

The present invention relates to a broadcast receiving apparatus and a broadcast receiving method that are robust to a mobile receiving environment.

According to an embodiment of the present invention, a demodulator for demodulating a modulated broadcast reception signal, a different threshold value is applied to each channel symbol in a signal demodulated by the demodulator, and a channel smaller than the predetermined threshold value in each channel symbol. And a decoder for equalizing a received signal by removing a subcarrier having a transfer function power, and a decoder for decoding the equalized signal by the channel equalizer.

Description

An apparatus and a method for receiving broadcast

Fig. 1 (a) is a CTF power characteristic diagram which experienced the actual fast fading channel.

FIG. 1 (b) is an enlarged view of a portion where the size of CTF power of FIG. 1 (a) is small

2 is a broadcast receiving apparatus according to the present invention

3 is a detailed structural diagram of a channel state information estimator according to the present invention;

4 is a detailed structural diagram of a reliability determiner according to the present invention;

5 is an overall signal flow diagram of a broadcast receiving method according to the present invention;

* Description of the symbols for the main parts of the drawings *

100: channel equalizer 200: decoder

10: equalizer 20: reliability determiner

30 demapping machine 40 quantizer

50: decoder 60: channel estimator

70: channel state information estimator

The present invention relates to a broadcast receiving apparatus and a broadcast receiving method, and more particularly, to a broadcast receiving apparatus and a broadcast receiving method for improving channel reliability in consideration of characteristics of channel symbols during channel equalization.

Orthogonal Frequency Division Multiplexing (OFDM) technology can be seen as a special form of multi-carrier transmission, in which one data string is transmitted on a subcarrier having a lower data rate. One of the important reasons for using OFDM is that it increases the robustness against frequency selection fading or narrowband interference. In a single carrier system, the entire link may fail due to one fade or interference, but in a multicarrier system, only some subcarriers are affected. Therefore, the use of forward error correction can correct a small number of error subcarriers.

The OFDM scheme has many advantages over the single carrier scheme. However, the OFDM scheme is sensitive to various synchronization errors such as frequency offset. Therefore, when designing an OFDM receiver for a European portable receiver, it is necessary to thoroughly study each element technology. Among the various synchronization elements, frequency synchronization is a function of matching an RF carrier frequency between a transmitter and a receiver.

The carrier frequency difference between a transmitter and a receiver is called a frequency offset. In particular, the OFDM scheme has a disadvantage of being sensitive to frequency offset. Therefore, the COFDM receiver developed by CCETT uses an AFC (Automatic Frequency Controdl) loop to compensate for inaccurate components of the tuning oscillator or frequency offset caused by Doppler shift.

The frequency offset compensation and the FFT window offset compensation are essential, where sampling clock frequency offset compensation due to oscillator inaccuracy must also be made. After performing this series of synchronous recovery, channel estimation is performed and channel equalization is performed to obtain an accurate scatter sent from the transmitter. The scatterer thus obtained performs Transmission Parameter Signaling (TPS) recovery, followed by Forward Error Correction (FEC).

In the channel equalization step, if the equalization is performed in consideration of the characteristics of the channel symbol, more accurate channel equalization is possible, and a solution for this is necessary.

SUMMARY OF THE INVENTION The present invention has been made to solve the necessity, and an object of the present invention is to provide a broadcast receiving apparatus which extracts channel state information through a channel transfer function value of a broadcast reception signal and thereby removes symbols having low reliability. will be.

Another object of the present invention is to provide a broadcast receiving method for extracting channel state information through a channel transfer function value of a broadcast reception signal and thereby removing a symbol having low reliability.

In order to achieve the above object, the present invention provides a demodulator for demodulating a modulated broadcast reception signal, equalizes a signal demodulated by the demodulator, and applies a predetermined threshold value to each channel symbol in the equalized signal. And a channel equalizer for removing and outputting a subcarrier having a channel transfer function power smaller than the predetermined threshold value in each channel symbol, and a decoder for decoding a signal output from the channel equalizer. Provide the device.

According to another embodiment of the present invention, in the broadcast receiving apparatus that receives and demodulates a broadcast signal, equalizes the demodulated signal, and decodes the transmitted signal, the present invention receives a demodulated signal and receives a channel of each channel symbol. A channel estimator for estimating a state of a channel by measuring a transfer function power, an equalizer for equalizing a demodulated signal by receiving an output of the channel estimator and the demodulated signal, and a channel estimator of each channel symbol measured by the channel estimator A channel state information estimator for estimating channel state information by receiving a channel transfer function power, and a channel state information value estimated by the channel state information estimator is predetermined for each channel symbol in a signal equalized by the equalizer. A method of equalizing the demodulated broadcast signal in a channel equalizer including a reliability determiner for removing a subcarrier smaller than a threshold. It provides a receiving apparatus.

According to still another embodiment of the present invention, the present invention provides a method for estimating a channel state by measuring a channel transfer function of a demodulated broadcast reception signal, equalizing a broadcast reception signal due to the estimated channel state, and estimating the channel state. Extracting channel state information due to the established channel state, and determining reliability by removing subcarriers whose channel state information is smaller than a predetermined threshold value from each channel symbol due to the channel state information, It provides a broadcast signal receiving method comprising the step of decoding a signal whose reliability is determined.

Therefore, according to the present invention, a robust receiver can be produced in a mobile reception environment.

Orthogonal Frequency Division Multiplexing (OFDM) technology of the DVB broadcasting system can be regarded as a special form of multi-carrier transmission, and one data string is transmitted through a subcarrier having a lower data rate. One of the important reasons for using OFDM is that it increases the robustness against frequency selective fading or narrowband interference. In a single carrier system, the entire link may fail due to one fade or interference, but in a multicarrier system, only some subcarriers are affected. Therefore, the use of forward error correction can correct a few error subcarriers.

    However, the channel frequency response of the distorted subcarrier becomes small under deep multi-path fading. The reduction in power appearing in some subcarriers makes the reliability of the received coded data different, and for this reason, the performance of the Viterbi Decorder is degraded. Therefore, it is essential to measure the reliability of the coded data received at each subcarrier location.

 In general, information indicating the reliability of coded data received by each subcarrier is called channel state information (CSI), and Soft Decision of a Viterbi Decoder is performed using CSI. . As a result, reliability using CSI improves bit error rate (BER) performance.

There are several ways to calculate the existing channel state information (CSI). One of them is a method of interpolating Mean Square Error (MSE) of a pilot subcarrier. This method requires a long time to obtain valid channel state information (CSI). Mobile reception is not suitable because fast time varying fading occurs. In addition, the implementation using Euclidean distance, which is another method, also makes it difficult to convert the distance between the point and the point when the speed of the receiver is fast, and is not suitable for the mobile environment because the average value is used.

The present invention provides a broadcast receiving device and a broadcast receiving method for improving bit error rate performance by measuring channel state information (CSI) using a channel transfer function (CTF) to suit a mobile environment.

As a result, it can be seen from the following Equations 1 to 4 that the higher the CNR, the higher the reliability of the coded data carried on the subcarrier. In the equation, N _{k , l} is Gaussian noise, H _{k , l} is the actual channel, H` <sub>k , l</sub> is the channel predicted by the Channel Estimator, and X <sub>k , l</sub> is the transmission. Coded Data, and finally, X`k _{, l} represents Coded Data restored through Equalizer. Where k denotes the position of a subcarrier and l denotes the order of symbols.

(If )

(If)

As described in the above equation, it can be seen that the higher the CNR, the higher the reliability. CNR means a carrier to noise ratio (CNR). Here, since the CNR is proportional to the power of the channel transfer function (CTF), the large CTF power means that the coded data on the subcarrier has high reliability, and the small CTF power means that the CTF power is coded. It can be seen that the reliability of the data) is small.

Therefore, if a subcarrier having a CTF power less than an arbitrary threshold is found, and coded data transmitted on the subcarrier is removed and input to the decoder, the bit error rate (BER) performance is improved. It can be improved.

Figure 1 (a) shows the CTF power that actually experienced the fast fading channel. FIG. 1 (b) shows an enlarged view of a small portion of the CTF power of FIG. 1 (a).

As can be seen in FIG. 1, in a fast fading channel environment, channel characteristics are different for each symbol. If the channel state information (CSI) is determined using a uniform threshold in dotted lines in FIG. 1 (a), too much coded data is removed from symbol 1. Since much coded data is removed, most of the information to be used in the decoder stage is lost. Therefore, when CSI is applied, the bit error rate (BER) performance is degraded. Therefore, in consideration of the channel characteristics of the symbol, a different threshold is applied to each symbol.

In this patent, the threshold is changed using the average channel transfer function (CTF) power in the symbol.

A variable threshold that varies from symbol to symbol can be derived from the following equation.

P _gain is calculated in the same manner as in Equation 5. P _gain reflects the channel characteristics of the symbol.

If P _gain is less than 1, the channel in the symbol has a bad CNR overall.

Therefore, when P _gain is less than 1, the threshold should be made smaller, and when it is larger than 1, the reference threshold should be maintained. This is shown in Equation 6.

IF

IF

ELSE

The Variable Threshold obtained in Equation 6 is compared with the CTF power of each subcarrier, and according to Equation (7), the CSI _FLAG at the position of the subcarrier having a CTF power larger than the Variable threshold is 1, and in other cases, 0.

As a result, a value of 1 for CSI _FLAG means high reliability, and a value of 0 means low reliability. Therefore, finally, the signal input to the decoder (decoder) is determined by the equation (8). That is, when the CSI _FLAG is 0, the total value is zero, if the CSI _FLAG is 1, X _{l, k} is the value of the final output value. This may be represented by Equation 8.

The present patent calculates channel state information (CSI) of each subcarrier using a channel transfer function (CTF), through which coded data having low reliability is removed and inputted to a Viterbi decoder. Improved bit error rate (BER).

2 illustrates a configuration of a broadcast receiving apparatus for improving reliability by using CSI proposed in the present patent.

The broadcast reception device according to the present invention includes a demodulator (not shown), a channel equalizer 100, and a decoder 200.

The demodulator (not shown) reproduces the signal received in the data communication to the original signal. Since the digital signal is not suitable to pass through the transmission line, when the transmitting side modulates it into an analog signal, the receiving side reproduces the original digital signal.

The channel equalizer 100 equalizes the signal demodulated by the demodulator.

Equalization is an operation that weakens amplitude or phase distortion by providing a circuit for compensating attenuation and propagation time delay variation for each frequency in the transmission band.

In the signal demodulated by the demodulator, a predetermined threshold value is differently applied to each channel symbol, and a subcarrier having a channel transfer function power smaller than the predetermined threshold value is removed from each channel symbol to the decoder. Output

Detailed description thereof is as described above.

The decoder 200 converts the data, which is converted into code according to a certain rule, into its original form. The decoder 200 includes a demapper 30, a quantizer 40, and a decoder 50.

The channel equalizer 100 includes an equalizer 10, a channel estimator 60, a channel state information extractor 70, and a reliability determiner 20.

The channel estimator 60 receives the demodulated signal and estimates the channel state by measuring the power of the channel transfer function (CTF) of each channel symbol.

The equalizer 10 receives the channel state information, which is the output of the channel estimator 60, and the demodulated signal, and equalizes the demodulated signal.

The channel state information estimator 70 receives the channel transfer function power of each channel symbol measured by the channel estimator 60 to estimate channel state information.

The reliability determiner 20 removes, for each channel symbol, the subcarrier whose channel state information value estimated by the channel state information estimator is smaller than a predetermined threshold value from the signal equalized by the equalizer.

Detailed structures of the channel state estimator 70 and the reliability determiner 20 will be described below.

3 shows a detailed structure of the channel state information estimator 70.

Referring to FIG. 3, the state estimator 70 stores a symbol in response to a channel frequency. And a channel state information detector 72, a threshold changer 73, and a channel state information generator 74.

The channel state information detector 72 outputs P _gain as a block for calculating Equation (5).

The threshold changer 73 outputs a variable threshold value according to a symbol characteristic through Equation (6).

During this process, one symbol is required, and thus a symbol store 71 is needed to store the channel transfer function of one symbol. The channel state information generator 74 performs equation (7), and as a result, outputs the CSI _FLAG .

4 is a detailed structural diagram of the reliability determiner 20.

2, 3, and 4, the reliability determiner 20 is composed of a symbol store 21 and a multiplier 22. Since 1 symbol is passed to output the CSI _FLAG by using the channel state information estimator 70, the coded data compensated by the equalizer 10 must be adjusted through the symbol storage 21. Finally, multiplier 22 performs equation (8).

5 is a signal flow of a broadcast receiving method according to the present invention.

Estimating a channel state by measuring a channel transfer function of a demodulated broadcast received signal, equalizing a broadcast received signal due to the estimated channel state, and extracting channel state information due to the estimated channel state And determining reliability by removing subcarriers whose channel state information is smaller than a predetermined threshold value in each channel symbol due to the channel state information, and decoding the signal in which the reliability is determined.

The action at each step is as described above.

Through this process, the Soft Decision of the decoder can be implemented using the channel state information (CSI) proposed in the present patent.

According to the present invention, it is possible to make a receiver more robust to a mobile environment while simultaneously satisfying the DVB-T / H specification.

The present invention is not limited to the above-described embodiments, and can be modified by those skilled in the art as can be seen from the appended claims, and such modifications are within the scope of the present invention. .

The effects of the broadcast receiving apparatus and the broadcast receiving method according to the present invention described above are as follows.

According to the present invention, a receiver robust to a mobile reception environment can be made.

Claims (6)

A demodulator for demodulating a modulated broadcast reception signal; Equalize the demodulated signal by the demodulator and apply a variable threshold value having a different threshold value for each channel symbol to remove subcarriers having a channel transfer function power smaller than the predetermined variable threshold value in each channel symbol. A channel equalizer for outputting; It includes a decoder for decoding the signal output from the channel equalizer, And the channel equalizer obtains the predetermined variable threshold value using average channel transfer function power in a symbol. A broadcast receiving device that receives and demodulates a broadcast signal, equalizes the demodulated signal, and decodes it into a transmission signal. A channel estimator for receiving a demodulated signal and measuring channel transfer function power of each channel symbol to estimate a state of a channel; An equalizer which equalizes the demodulated signal by receiving the output of the channel estimator and the demodulated signal; A channel for estimating channel state information by receiving the channel transfer function power of each channel symbol measured by the channel estimator, and extracting a predetermined variable threshold value using the average channel transfer function power of the symbol. State information estimating unit; And a reliability determination unit for removing subcarriers whose channel state information values estimated by the channel state information estimator are smaller than the extracted variable threshold value for each channel symbol from the equalized signal by the equalizer. And a broadcast receiving device. 3. The channel state information estimator of claim 2, wherein the channel state information estimator A channel state information detector for detecting channel state information by obtaining an average value of channel transfer function power of each channel symbol measured by the channel estimator; A threshold changer for outputting a variable threshold according to a symbol characteristic based on the detected channel state information; A symbol store for storing one symbol in response to a channel frequency; And a channel state information generator for generating a CSI _FLAG by comparing the variable threshold value with a channel transfer function value. The method of claim 2, wherein the reliability determination unit, A symbol store configured to synchronize an elapsed symbol with an output of the channel state information estimator; And a multiplier configured to determine reliability by removing subcarriers whose channel state information is smaller than a predetermined threshold based on the determined channel state information. Estimating a channel state by measuring a channel transfer function of the demodulated broadcast received signal; Equalizing a broadcast reception signal due to the estimated channel state; Estimating channel state information by receiving the measured channel transfer function power of each channel symbol, and extracting a predetermined variable threshold value using an average channel transfer function power of the symbol; Determining reliability for each symbol by removing a subcarrier whose estimated channel state information value is smaller than the extracted variable threshold value for each channel symbol; And decoding the signal of which the reliability is determined. The method according to claim 1 or 2, The predetermined variable threshold value is obtained by extracting a gain value from the following equation, And comparing the extracted gain value with a magnitude of 1 to determine whether to maintain a reference threshold value or to make it smaller than the reference threshold value.

Where P _gain (l) represents the gain value, P _reference represents the reference threshold)

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