KR100504525B1 - Channel State Information Generation Circuit for Orthogonal Frequency Division Multiplexing System - Google Patents

Abstract

The present invention relates to a channel state information (CSI) generation circuit of an OFDM system using multiple carriers, wherein the normalized value of an input signal corresponds to one of a plurality of areas, and the conversion state of data is changed according to the result. By outputting the channel state information data with a great change to the demapper stage, all channel state information data is changed to the demapper stage without changing the data value beyond the range of data to be delivered. The output eliminates data loss and improves the performance of the receiver system.

Description

Channel State Information Generation Circuit for Orthogonal Frequency Division Multiplexing System

The present invention relates to an Orthogonal Frequency Division Multiplexing (OFDM) system using multiple carriers, and more particularly, to a CSI generation circuit of an OFDM system that controls generation of Channel State Information (CSI) data. will be.

The OFDM transmission system is a multicarrier transmission scheme in which data is transmitted using a plurality of carriers having orthogonality to each other, unlike a single carrier scheme in which data is transmitted using one carrier. Each carrier has a very small bandwidth, which is affected by the channel change. However, in the case of the entire frequency band, in the case of the multi-interference channel, each carrier transmitted is only affected by the channel, and only the amplitude is reduced.

In this case, the amplitude of each carrier is commonly referred to as channel state information (CSI). In an OFDM system, information indicating reliability of a received signal may be obtained using the CSI.

In addition, in the case of DVB-T (Digital Video Broadcasting-Terrestrial), which is determined by European digital TV standards, the transmitter transmits a pilot signal between data to be transmitted using a PN sequence in addition to the data to be transmitted by the transmitter. After comparing with the original pilot value transmitted from the transmitter (i.e., the pilot value that the receiver already knows), the status of the transmitted channel can be known. Usually, the transmitted pilot signal is divided by the known pilot value. Use power as CSI.

In the case of the Rayleigh channel thus obtained, the CSI is shown in FIG. 1.

As can be seen in Figure 1, in the case of a multipath Rayleigh channel, that is, the size of the signals coming in the multipath is similar to the state of the channel is very poor and it can be seen that the change of the value is also very rapid. The CSI value is normalized to a mean of 1.

2 is a general block diagram of a DVB-T system, in which a fast Fourier transform (FFT) is performed on a tuner 21 receiving an OFDM signal through an antenna and channel data tuned by the tuner 21. OFDM demodulator 22, a channel estimator 23 for extracting a pilot signal inserted at the transmitter side from the FFT signal and outputting a channel impulse response for estimating a channel state by comparing with a pilot value which is already known; An equalizer 24 that divides the FFT signal into a channel impulse response to compensate for carriers distorted by the channel, a demapper 25 that demaps the equalized data inversely according to the mapping method of the transmitted data, and the channel The CSI generator 26 converts the channel impulse response output from the estimator 23 into channel state information (CSI) values, and outputs the CSI values of the demapper 25 and the CSI generator 26. Using decision and A soft decision generation unit 27 that performs quantization, an internal deinterleaver 28 that performs symbol deinterleaving and bit deinterleaving on the quantized data, and a 1 or 0 on internal deinterleaved data is determined. It consists of the Viterbi decoder 29.

3 is a detailed block diagram of the CSI generation unit 26, which includes a squarer 31 that squares a channel impulse response, a normalizer 32 that normalizes output data of the squarer 31, and the normalizer. And a limiter 33 for limiting the output data at 32 and outputting the CSI value.

4 is a graph illustrating a method generally used to generate a CSI value in the CSI generator 26.

The DVB-T receiving system configured as described above first receives an OFDM signal through the tuner 21 and then performs an FFT in the OFDM demodulator 22.

That is, when transmitting the desired data by the OFDM method, the transmitting side maps the data to be transmitted according to the modulation method, passes through an Inverse Fast Fourier Transform (IFFT), and then inserts a guard interval to transmit the data. On the other hand, the receiving side undergoes the reverse process of the transmitting end. First, FFT is performed and then demapping is reversed according to the mapping method of the transmitted data.

Meanwhile, the channel state estimator 23 extracts a pilot signal inserted by the transmitter from the FFT data output from the OFDM demodulator 22 and divides the pilot signal into a known pilot value to output a channel impulse response.

The equalizer 24 receives the FFT signal from the OFDM 22 and divides it into the channel impulse response to compensate for the carriers distorted by the channel, and then outputs the demapper 25 to the demapper 25. Demap the equalized data in reverse according to the mapping method of the transmitted data.

In addition, the CSI generator 26 receives the channel impulse response of the channel estimator 23 and squares it in the squarer 31 to convert the power into a form of power. In other words, the channel impulse response is the amplitude of each carrier, which is squared to obtain the signal power.

In this case, when the amplitude difference of each active carrier increases due to noise, a large amount of information is required when the amplitude difference of each active carrier is used as it is. Therefore, the normalizer 32 normalizes the output of the squarer 31 and then the limiter 33. Will output

That is, normalization is performed for one OFDM symbol and is usually performed by dividing each data by a value obtained by dividing the total sum of channel power data by the total number of data during one symbol period. Normally, normalization is performed so that the average of symbol CSI values is one. By using this method, the result data as shown in FIG. 1 can be obtained.

The limiter 33 outputs only the value of ± α to the soft decision generator 27 based on the average value m of the normalized values as shown in FIG. 4, and the value greater than or equal to or less than or equal to -α is saturated. (saturation).

The soft decision generator 27 multiplies the de-mapped data by the CSI value output from the CSI generator 26 and quantizes the difference between the multiplied values and outputs the difference to the internal deinterleaver 28. . The internal deinterleaver 28 performs symbol deinterleaving and bit deinterleaving on the quantized data and outputs the result to the Viterbi decoder 29, and the Viterbi decoder 29 1 or 0 with respect to the internal deinterleaved data. Determine.

However, as shown in FIG. 1, the CSI value output from the normalizer 32 of the conventional CSI generator 26 has a value from 0 to 4, and the CSI value output from the limiter 33 is 0 to. Only values up to 2 (if m = 1) are output, and all CSI values above 2 are output as 2. When using this method, since CSI values are not different from each other when CSI is 2 or more, even if the CSI values are output to the demapping stage, they are de-mapped to the same value, thereby degrading the performance of the Viterbi decoder. In other words, the resolution falls.

On the other hand, if the limiter 33 outputs the data as it is without limitation, the difference between the maximum value and the minimum value of the channel state information is very large. The output should be difficult, which makes it difficult to process the next stage.

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 CSI generation circuit of an OFDM system for transmitting all values to the demapping stage without loss of channel state information (CSI) data.

In the CSI generation circuit of the OFDM system according to the present invention for achieving the above object, the channel impulse response obtained by the channel estimator is normalized by squaring, and the result of determining the normalized value corresponds to which area of the plurality of areas is the result. According to the present invention, the data is converted into channel state information through a limiter after changing the data conversion state.

The present invention is characterized in that when the area is divided into two, the value normalized and output is determined as area 1 when the value is smaller than the average value of the normalized values, and as area 2 when it is large.

The present invention is characterized by outputting the input value as a limiter as it is determined as the area 1, and outputting it as a limiter after converting the data according to a predetermined conversion equation when it is determined as the area 2.

This CSI generation circuit can eliminate the data lost by the limiter, thereby improving the performance of the system.

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

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 5 is a block diagram illustrating a CSI generation circuit of an OFDM system according to the present invention, wherein a squarer 51 and a squarer 51 for obtaining signal power of a channel impulse response output from the channel estimator 22 of FIG. A normalizer 52 that normalizes the squared value of the square), an area discriminator 53 that determines whether the normalized value belongs to the area 1 or the area 2, and the area discriminator ( The data converter 54 converts the data output from the normalizer 52 according to the area determined by 53), and the limiter 55 restricts the converted data to a predetermined range and outputs the data.

In the present invention configured as described above, the squarer 51 obtains signal power by squaring the channel impulse response of the channel estimator 23 and outputs the signal power to the normalizer 52. That is, when the difference in the channel impulse response of each active carrier due to noise is used as the channel state information as it is, a lot of information is required, so after normalizing in the normalizer 52, the region discriminator 53 and the data converter ( 54).

The region discriminator 53 determines region 1 when the normalized value x is smaller than m (m is an average value of normalized values) and region 2 when x is larger than m. If the normalizer 52 is normalized such that the average of symbol CSI values is 1 (m = 1), the area discriminator 53 discriminates the area 1 when the input data x is smaller than 1. If x is larger than 1, it is determined as area 2 and output to the data converter 54.

When the data output from the normalizer 52 is determined as the area 1 by the area discriminator 53, the data converter 54 outputs the input value to the limiter 55 as it is, and when it is determined as the area 2. The data is converted into the limiter 55 after the data is converted according to a predetermined conversion equation. That is, the data converter 54 receives the determination result of the area discriminator 53, converts the data x input by the relational expression corresponding thereto, and outputs the y value.

At this time, data conversion according to each region is shown in Equation 1 below.

y = x x ≤ m (area 1)

y = β (x-m) + m x> m (area 2)

In Equation 1, m is an average value of normalized values, x is normalized data to be input, and it is determined to what extent the CSI value is not saturated by adjusting β (indicating slope).

That is, when β = 1, the same method as in the prior art, for example, means that the input data is output to the limiter 55 as it is. Gives the effect of mapping m to m + α.

The smaller the β value, the larger the CSI can be delivered to the demapping stage without data loss.

As can be seen in Figure 1 it can be seen that most of the channel information is below m = 1.0. Therefore, when x <1.0, the input value is output as it is, as in Equation 1, and the resolution of the data is maintained as it is. This reduces the resolution slightly but prevents data loss due to saturation. By doing so, the performance of the system can be improved by eliminating data lost by the limiter in the CSI generation unit.

That is, the data output by this method is output to the demapper only the value defined by the limiter as in the prior art, but since the data is already compressed in front of the limiter, there is no data lost by the limiter.

As described above, according to the CSI generation circuit of the OFDM system according to the present invention, by determining which area among the plurality of areas the normalized value for the input signal corresponds to the output state by differently converting the data according to the result, In outputting the channel state information data with a great change to the demapper stage, all channel state information data is output to the demapper stage without changing the data value beyond the range of data to be delivered to the demapper stage. It is effective to improve the performance of the receiver system by eliminating the loss.

1 is a waveform diagram illustrating an example Rayleigh channel impulse response with 20 multiple paths.

2 is a block diagram illustrating an overall configuration of a typical DVB-T receiver.

3 is a detailed block diagram of a CSI generation unit of FIG. 2;

4 is a graph illustrating a CSI generation process in FIG.

5 is a block diagram illustrating a CSI generation circuit in accordance with the present invention.

6 is a graph illustrating a CSI generation process according to the present invention;

Explanation of symbols for main parts of the drawings

21 tuner 22 OFDM demodulator

23: channel estimator 24: equalizer

25: demapper 26: CSI generation unit

27: soft decision generating unit 28: internal deinterleaver

29: Viterbi decoder 51: squarer

52: normalizer 53: region discriminator

54: Data Converter 55: Limiter

Claims (3)

In an OFDM system for demodulating a received orthogonal frequency division multiplex (OFDM) signal into an original signal through a fast Fourier transform (FFT), an equalizer, a demapper, a deinterleaver, and a Viterbi decoder, A channel estimator for extracting pilot information from a fast Fourier transform (FFT) signal and outputting a channel impulse response by comparing the pilot information with known pilot information; A power calculator which calculates a signal power by squaring the channel impulse response output from the channel estimator, and normalizes the signal power; An area determination unit determining which area of the plurality of areas the value output from the power calculation unit corresponds to; A data converter converting and outputting data output from the power calculator according to the determination result of the area discriminator; And a limiter configured to limit the output data of the data determination unit to a predetermined range and output the channel state information to the demapper as a channel state information value. The method of claim 1, wherein the area discrimination unit In the case of having two divided regions, when the value normalized and output by the power calculation unit is smaller than the average value of the normalized values, the divided region is determined as region 1, and when the divided region is large, region 2 is output to the data converter. Channel state information generating circuit. The method of claim 2, wherein the data conversion unit When the data output from the power calculation unit is determined as the area 1 by the area determination unit, the input value is outputted as a limiter as it is, and when it is determined as the area 2, the data is converted according to the following conversion formula and then the limiter. And a channel state information generating circuit, characterized in that the output to the. y = β (x-m) + m x> m (area 2) Here, x is normalized input data, m is an average value of normalized values, and β is an adjustable slope value.