KR20100037905A - Ofdm receiver with co-channel interference estimation and efficient decoding - Google Patents

Abstract

PURPOSE: In OFDM(Orthogonal Frequency Division Multiplexing) receiver having the co-channel interference estimation and decoding performance improving function is the subcarrier location having interference, the stable performance of receiving % reception ability is guaranteed by accurately demodulating data. CONSTITUTION: A channel estimator(200) presumes the channel distortion by using the pilot symbol of the received signal. An equalizer(300) equalizes the channel distortion of the received signal by using the channel estimation value of the channel estimator. A P/S transform unit(400) changes the received signal which becomes equal as described above into the serial type. The co-channel interference estimating unit(500) obtains the distribution value toward the electricity of the received signal by using the channel estimation value. The location having the co-channel interference the co-channel interference estimating unit uses the distribution value is detected.

Description

OPDM receiver with co-channel interference estimation and efficient decoding

The present invention relates to an OFDM receiver that can be applied to a digital television receiver. In particular, the interference position and the amount of interference of the same channel are obtained based on channel estimation values, and then the soft decision weight is calculated using the same. The present invention relates to an OFDM receiver capable of improving co-channel interference estimation and decoding performance by decoding using decision weights.

In general, Orthogonal Frequency Division Multiplexing (OFDM), which is applied to terrestrial digital televisions, is known to be advantageous for high-speed data transmission, and is particularly robust to frequency-selective fading channel environments generated by multipaths and easy to implement equalizers. Therefore, attention has been paid in a manner suitable for a high speed communication environment.

Accordingly, the OFDM method is being used as a standard for next generation wired / wireless communication and broadcasting such as HIPERLAN / 2 (High PErformance Radio LAN) and DVB-T (Digital Video Broadcasting-Terrestrial).

However, the OFDM scheme has a disadvantage in that various fading and co-channel interference occurs that degrades the transmission performance according to wireless transmission, and a Doppler phenomenon and a fading phenomenon are basically generated in a DVB-T system, which is a European digital television standard. Due to interference with existing European analog television standards, Phase Alternating Line (PAL) and Sequential Color with Memory (SECAM), there are many limitations in the implementation.

Recently, as in the case of the DVB-T system, a method of increasing the efficiency of the frequency by using the same frequency band as the conventional analog method has been used. In this case, there is frequency interference caused by using the same frequency band. Done. This type of radio interference is called co-channel interference, and a lot of researches on a method of providing various services while avoiding co-channel interference with respect to a frequency efficiency problem have been discussed.

The DVB-T system is one of the European terrestrial TV standards and uses OFDM based multicarrier, and in the case of the DVB-T system, Reed-Solomon code is used as the outer coding. Inner coding is used again to use convolutional code for error correction (see [1] ETS 300 744: Digital broadcasting system for television, sound and data services; framing structure, channel coding and modulation for digital terrestrial television).

The structure of a typical OFDM transmitter is shown in FIG. 1. Referring to FIG. 1, a typical OFDM transmitter includes a channel encoder (CW) that convolutionally encodes transmission bits according to a predetermined convolution scheme. 11) an interleaver 12 for rearranging the coded bits from the channel encoder 11 in a predetermined order to prevent burst errors in the fading environment of the channel, and the interleaver 12; A symbol mapper 13 for converting the encoded bits from the symbol into complex symbols I and Q, and an S / P converter for S / P transforming the complex symbols from the symbol mapper 13 for multiplexing. 14, a pilot generator 15 for generating pilot symbols for channel estimation, and data symbols and pilot symbols from the symbol mapper 13 are assigned to each subcarrier, that is, a plurality of inputs of the IFFT unit; Each input port of the port An inverse Fourier transform on a subcarrier mapping part 16 allocated to a memory card and a symbol input from the subcarrier mapping part 16 to convert a symbol in a frequency domain into a sample in a time domain An IFFT unit 17 for converting into a symbol, a guard interval inserting unit 18 for inserting a guard period (CP) into an OFDM symbol from the IFFT unit 17, and the guard interval inserting unit 18 A P / S converter 19 for converting the OFDM symbols from the P / S converter 19 into serial symbols, and an RF unit 20 for converting the OFDM symbols from the P / S converter 19 into RF signals and transmitting them through an antenna ANT. It includes.

In this case, the IFFT unit 17 includes a plurality of input ports, each of which is matched with each of a plurality of subcarriers. Therefore, assigning the data symbols and pilot symbols to the input port of the IFFT unit 17 means that the data symbols and pilot symbols are assigned to the subcarriers, respectively.

Here, the number of input ports of the IFFT unit 17 may be set to a number corresponding to a multiple of 2 ^10. For example, the number of input ports of the IFFT unit 17 may be “1024” or “2048”. Can be.

On the other hand, considering convolutional coding, the reliability of the received signal for soft-decision is determined by the distance from the decision boundary. However, in the OFDM scheme, even in a selective fading channel environment, each subcarrier band has a non-selective characteristic. Therefore, if the confidence information of the signal-to-noise ratio in each subcarrier band can be known accurately, the performance can be improved by applying the decoder to the decoder ([2] Min-Young Park and Weon-Cheol Lee and Jong-Ho Kwak and Choul. -Hee Cho and Hyung-Mo Park, "A demapping method using the pilots in COFDM system", Consumer Electronics, IEEE Transactions on Volume 44, Issue 3, Page (s): 1150-1153, Aug. 1998).

If there is interference effect on each subcarrier by the proposed method to remove existing co-channel interference. There is an erasing method that determines that the data of the subcarrier is unreliable ([3] A soft decision decoding scheme for wireless COFDM with application to DVB-T Yong Wang; Jian Hua Ge; Bo Ai; Pei Liu ShiYong Yang; Consumer Electronics, IEEE Transactions on Volume 50, Issue 1, Page (s): 84-88, Feb 2004).

The process can be described by the following equations (1), (2) and (3).

는 OFDM의 FFT부(고속 퓨리에 변환부)의 출력신호이고,

는 채널 주파수 응답을 가리킨다.

는

의 추정치이다. 그리고,

는 등화된 수신신호이다.Here, "l" indicates the index of the OFDM symbol, "k" indicates the index of the subcarrier symbol,

Is an output signal of the FFT unit (fast Fourier transform unit) of OFDM,

Denotes the channel frequency response.

Is

Is an estimate of. And,

Is an equalized received signal.

>는 OFDM 심볼 인덱스 "l"에 대한 시간 평균 함수이다.

에서

는

의 경판정 값이다. 따라서

는

와

의 유클리드(Euclidean) 거리를 나타낸다.Here, for each subcarrier, a carrier to noise ratio (CNR) may be referred to as channel state information (CSI) for information on a subcarrier channel.

> Is the time averaged function for OFDM symbol index " l ".

in

Is

The hard decision value of. therefore

Is

Wow

Represents the Euclidean distance of.

는 비터비 복호부에서 비트 판정 매트릭을 가리키고, 각 부반송파의 채널 상태 정보가 가중치로 곱해져서 새로운 매트릭값이 된다 .here,

Denotes the bit decision metric in the Viterbi decoder, and the channel state information of each subcarrier is multiplied by the weight to become a new metric.

으로 설정하여 그 특정 부반송파가 가지고 있는 데이터는 연판정시 그 해당 부반송파의 연판정을 통해 얻어진 매트릭값을 무시하게 된다.Here, when the change of the estimated channel value for the OFDM symbol index " l " is larger than a certain threshold, the particular subcarrier is considered to be affected by the interference signal.

When the data is set by the specific subcarrier, the metric value obtained through the soft decision of the corresponding subcarrier is ignored.

However, when this method is applied, the data of the subcarrier is ignored when co-channel interference occurs. Therefore, the greater the influence of the interference, the greater the number of data lost.

Accordingly, there is a need for a technique that can more effectively eliminate co-channel interference by estimating the location and amount of interference.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and its object is to obtain the soft decision weight using the same, after obtaining the interference position and the interference amount of the same channel based on the channel estimate value, The present invention provides an OFDM receiver capable of improving co-channel interference estimation and decoding performance by decoding by using.

One technical aspect of the present invention for achieving the above object of the present invention comprises: a channel estimator for estimating channel distortion using a pilot symbol of a received signal; An equalizer for equalizing channel distortion of a received signal by using channel estimates of the channel estimator; A P / S converter converting the received signal equalized by the equalizer into a serial form; Obtain a variance of the power of the received signal using the channel estimation value from the channel estimator, detect the position where co-channel interference exists using the variance, and use the power of the received signal at that position An on-channel interference estimator for determining decision weights; And a soft demapper for quantizing the data symbols from the P / S converter into data bits using the soft decision weights of the co-channel interference estimation unit.

In one technical aspect of the present invention, the co-channel interference estimator may be configured to reduce the channel influence and noise effect by using the received signal, the channel estimate value, and the predetermined noise variance from the channel estimator. A dispersion value calculation unit for obtaining a dispersion value for each position; A comparison unit comparing the dispersion value from the dispersion value calculation unit with a preset reference value; An interference power amount calculating unit for recognizing a position where the dispersion value is larger than the reference value as a position where co-channel interference exists and obtaining an amount of interference power at the corresponding position; And a weight calculator configured to obtain the soft decision weight using the interference power amount of the interference power amount calculator.

In one technical aspect of the present invention, the soft demapper multiplies the data symbol from the P / S converter by the soft decision weight of the co-channel interference estimation unit, and multiplies the data symbol by which the soft decision weight is multiplied. It is characterized by quantizing with data bits.

In addition, another technical aspect of the present invention, the RF unit for receiving the RF signal and converts the RF signal into OFDM symbols; An S / P converter converting OFDM symbols of the RF unit into a parallel form; A guard interval removal unit for removing a guard interval between OFDM symbols from the S / P converter; An FFT unit performing fast Fourier transform on the OFDM symbol from the guard interval elimination unit and converting the OFDM symbol in the time domain into a complex symbol in the frequency domain; A subcarrier demapping unit for separating the symbols of the frequency domain from the FFT unit into data symbols and pilot symbols; A channel estimator estimating a channel distortion using a pilot symbol of a received signal from the subcarrier demapping unit; An equalizer for equalizing channel distortion of a received signal by using channel estimates of the channel estimator; A P / S converter converting the received signal equalized by the equalizer into a serial form; Obtain a variance of the power of the received signal using the channel estimation value from the channel estimator, detect the position where co-channel interference exists using the variance, and use the power of the received signal at that position An on-channel interference estimator for determining decision weights; And a soft demapper that multiplies the data symbols from the P / S converter by the soft decision weights of the co-channel interference estimation unit and quantizes the data symbols multiplied by the soft decision weights into data bits. .

In another technical aspect of the present invention, the co-channel interference estimator may be configured to reduce the channel influence and noise effect by using the received signal from the channel estimator, a channel estimate value, and a predetermined noise variance. A variance value calculator for calculating a variance value for each position with respect to the position; A comparison unit comparing the dispersion value from the dispersion value calculation unit with a preset reference value; An interference power amount calculating unit for recognizing a position where the dispersion value is larger than the reference value as a position where co-channel interference exists and obtaining an amount of interference power at the corresponding position; And a weight calculator configured to obtain the soft decision weight using the interference power amount of the interference power amount calculator.

In one technical aspect of the present invention, the OFDM receiver comprises: an interleaver for rearranging code bits output from the soft demapper in the reverse order of the arrangement order applied by an OFDM transmitter; And a channel decoder for decoding the convolutional coded bits from the inverber to recover the transmission data bits. In this case, the channel decoder may be a Viterbi decoder.

In one technical aspect of the present invention, the channel estimator, after initial channel estimation using LS (Least Square) at the pilot position, applies a smoothing technique, which is a channel estimation technique based on a Discrete Fourier Transform (DFT). And performing channel estimation.

According to the present invention, the interference position and the amount of interference of the same channel are obtained based on the channel estimation value, and the soft decision weight is obtained using the same, and the soft decision weight is decoded using the same to determine the same channel interference estimation and decoding performance. Can be improved.

In addition, when the OFDM receiver of the present invention is applied to an OFDM system in which co-channel interference exists, data can be more accurately demodulated even at subcarrier positions where interference exists, and interference between communication systems exists in an environment where frequency efficiency is important. In this case, more stable reception performance can be guaranteed.

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

The present invention is not limited to the embodiments described, and the embodiments of the present invention are used to assist in understanding the technical spirit of the present invention. In the drawings referred to in the present invention, components having substantially the same configuration and function will use the same reference numerals.

2 is a structural diagram of an OFDM receiver according to the present invention.

Referring to FIG. 2, the OFDM receiver according to the present invention includes an RF unit 110 for receiving an RF signal and converting the RF signal into an OFDM symbol, and converting the OFDM symbol of the RF unit 110 into a parallel form. Cyclic prefix remover 130 for removing a guard interval between the / P converter 120, the OFDM symbol from the S / P converter 120, and the guard interval remover 130 FFT unit 140 for performing fast Fourier transform on the OFDM symbols from the time domain to complex symbols in the frequency domain, and data symbols and pilot symbols in the frequency domain from the FFT unit 140. The subcarrier demapping unit 150 may be separated into symbols.

In addition, the OFDM receiver of the present invention uses a channel estimator 200 for estimating channel distortion using a pilot symbol from the subcarrier demapping unit 150 and a channel estimate value of the channel estimator 200. An equalizer 300 for equalizing channel distortion of the received signal, a P / S converter 400 for converting the received signal equalized by the equalizer 300 into a serial form, and the channel estimator 200 The variance of the power of the received signal is obtained by using the channel estimate value from). A soft device for quantizing the data symbols obtained from the same channel interference estimator 500 and the P / S converter 400 into data bits using soft decision weights of the cochannel interference estimator 500. Includes a mapper 600.

The channel estimator may perform channel estimation by applying a smoothing technique, which is a channel estimation technique based on Discrete Fourier Transform (DFT), after initial channel estimation using LS (Least Square) method at a pilot position.

The soft demapper 600 multiplies the data symbols from the P / S converter by the soft decision weights of the co-channel interference estimation unit, and quantizes the data symbols multiplied by the soft decision weights by data bits.

The OFDM receiver includes an interleaver 700 for rearranging the data bits output from the soft demapper 600 in a reverse order of the arrangement order applied by the OFDM transmitter, and the convolutional coding from the interleaver 700. And a channel decoder 800 for decoding the transmitted bits to recover the transmission data bits.

As the channel decoder 800, a Viterbi decoder may be employed.

3 is a block diagram of a co-channel interference estimation unit according to the present invention.

)을 구하는 간섭전력양 계산부(530)와, 상기 간섭전력량 계산부(520)의 간섭전력량(

)을 이용하여 상기 연판정 가중치를 구하는 가중치 계산부(540)를 포함한다.Referring to FIG. 3, the co-channel interference estimator 500 reduces a channel influence and a noise effect by using a received signal, a channel estimate value, and a predetermined noise dispersion from the channel estimator 200. A variance value calculator 510 for obtaining a variance value Var [Zm [k]] for each position of power and a variance value Var [Zm [k]] from the variance value calculator 510; And a comparison unit 520 for comparing the predetermined reference value, and a position where the variance value is larger than the reference value as a position where co-channel interference exists, and the amount of interference power at the corresponding position [k] (

) And the interference power amount of the interference power amount calculation unit 520

It includes a weight calculation unit 540 to obtain the soft decision weight using a).

In addition, the OFDM receiver includes an interleaver 700 for rearranging the data bits output from the soft demapper 600 in a reverse order of the arrangement order applied by the OFDM transmitter, and convolutional coding from the interleaver 700. And a channel decoder 800 for decoding the transmitted bits to recover the transmission data bits. Here, the channel decoder may be a Viterbi decoder.

FIG. 4 is a position estimation performance diagram of co-channel interference of the present invention when SIR is 3 dB, and the graph of FIG. 4 shows "signal-to-noise ratio (SNR) = 10 in a channel environment known as" COST 207 TU ". "," SIR (Signal-to-Interference Ratio) = 3dB "is a graph showing the dispersion value of the received signal power for each subcarrier when the condition is given.

FIG. 5 is a position estimation performance diagram of co-channel interference of the present invention when SIR is -3dB. The graph of FIG. 5 shows "SNR = 10" and "SIR = -3dB in a well-known channel environment called" COST 207 TU ". Is a graph showing the dispersion value of the received signal power for each subcarrier position.

4 and 5, it can be seen that in the present invention, even if the environment is different, the variance value of the reference value or more can be detected.

6 is a view showing the SNR-BER characteristic graph of the present invention when SIR is -3dB. In FIG. 6, G11 does not apply the soft decision weight, and G12 applies the soft decision weight according to the present invention. Is a graph of the case where the ideal weight is applied to the ideal channel.

7 is a view showing the SNR-BER characteristic graph of the present invention when SIR is 0dB. In FIG. 7, when G21 does not apply soft decision weight, G22 is applied when soft decision weight according to the present invention is applied. It is a graph of applying ideal weights to ideal channels.

Hereinafter, the operation and effects of the present invention will be described in detail with reference to the accompanying drawings.

2 to 7, the OFDM receiver of the present invention will be described. Referring to FIG. 2, in the OFDM receiver according to the present invention, a signal processing process from the RF unit 110 to the channel estimator 200 is performed. Explain first.

The RF unit 110 receives the RF signal through the antenna ANT2, converts the RF signal into an OFDM symbol, and outputs the RF signal to the S / P converter 120.

The S / P converter 120 converts the OFDM symbols of the RF unit 110 into a parallel form and outputs them to the guard interval removing unit 130.

The guard interval remover 130 removes the guard interval inserted in the transmission from the OFDM symbol from the S / P converter 120 to reduce the loss due to delay on the channel to the FFT unit 140. Output

The FFT unit 140 performs fast Fourier transform on the OFDM symbol from the guard interval elimination unit 130, converts the OFDM symbol in the time domain into a complex symbol in the frequency domain, and transmits it to the subcarrier demapping unit 150. Output

The subcarrier demapping unit 150 divides the symbols of the frequency domain from the FFT unit 140 into data symbols and pilot symbols and outputs the data symbols to the channel estimator 200.

In addition, the channel estimator 200 performs a DFT-based smoothing channel estimation using a pilot symbol from the subcarrier demapping unit 150 to obtain a channel estimate value for channel distortion, and then equalizes the 300. And the same channel interference estimator 500.

The equalizer 300 uses the channel estimate of the channel estimator 200 to equalize the channel distortion of the received signal by a ZF (Zero Forcing) method as shown in Equation 5 to convert the P / S converter 400. )

는 채널 추정값을 의미하고,

는 수신신호이고,

는 등화된 수신신호이다.here,

Means channel estimate,

Is the received signal,

Is an equalized received signal.

Next, the P / S converter 400 converts the received signal equalized by the equalizer 300 into a serial form and outputs the serial signal to the soft demapper 600.

Meanwhile, the co-channel interference estimator 500 obtains a variance value of the power of the received signal using the channel estimate value from the channel estimator 200, and uses the variance value to determine whether co-channel interference exists. The position is detected, and the soft decision weight is calculated and provided to the soft demapper 600 using the power of the received signal at the position.

The co-channel interference estimator 500 will be described in detail with reference to FIGS. 2 and 3.

In FIG. 3, first, the variance calculator 510 of the co-channel interference estimator 500 uses the received signal from the channel estimator 200, a channel estimate value, and a predetermined noise variance. And a dispersion value Var [Zm [k]] for each position of the power of the received signal having the reduced noise effect, and outputs it to the comparison unit 520.

), 채널 추정값(

) 및 기설정된 노이즈 분산(

)을 이용하여, 하기 수학식 6을 이용하여 구할 수 있다.In more detail, the dispersion value calculator 510 calculates the dispersion value Var [Zm [k]] from the received signal from the channel estimator 200 at the corresponding position.

), The channel estimate (

) And preset noise variance (

) Can be obtained using the following equation (6).

는 채널영향 및 노이즈 영향을 줄인 수신신호 전력,

는 수신신호,

는 채널 추정값, 그리고

는 기설정된 노이즈 분산.here,

Is the received signal power with reduced channel and noise effects,

Is the received signal,

Is the channel estimate, and

Is a preset noise variance.

)으로 추정할 수 있다.In this case, the variance value Var [Zm [k]] is represented by channel interference power (Equation 7).

) Can be estimated.

는 수신 신호에 대해 채널의 영향과 잡음 영향을 줄인 신호전력이고,

에 대해 분산을 구하게 되면 추가적인 간섭이 있는 곳에서만 그 값이 다른 부반송파 위치보다 크게 나오게 된다. In Equation 6,

Is the signal power which reduces the influence of the channel and noise on the received signal.

When variance is obtained, the value is larger than other subcarrier positions only where there is additional interference.

Accordingly, it is possible to detect the subcarrier position where the interference occurs through the equations (6) and (7).

Simulation for the performance verification of the co-channel interference estimation and decoding technique according to the present invention is carried out in the fading channel environment model COST (European Co-operation in the field of Scientific and Technical research) 207 TU (Typical Urban) Was taken, and was performed by recording statistical performance figures after a sufficient number of iterations, and the results are shown in FIGS. 4 to 7.

Referring to FIGS. 4 and 5, in the channel environment of "COST 207 TU," the conditions of "SNR" and "SIR" are differently applied to measure dispersion values of received signal power for each subcarrier location of the present invention. One result is shown in FIGS. 4 and 5.

4 is a graph showing dispersion values of received signal power for each subcarrier position when a condition of "SNR = 10" and "SIR = 3dB" is given, and the graph of FIG. 5 is "SNR = 10" and "SIR". When the condition of = -3dB "is given, it is a graph which shows the dispersion value of the received signal power for each subcarrier position.

의 분산값은 상기 수학식 7에 보인바와 같이 근사적으로 해당 부반송파 k의 위치에서 간섭량이라 할 수 있다. 4 and 5, in the present invention, even when the environment is given differently, it can be seen that in the case of interference in the same channel, a variance value of more than a reference value can be detected. In this case, the presence or absence of co-channel interference can be determined accurately and easily. That is, when the position of the interference signal is estimated by setting an appropriate reference value, the reference value may be set through Equation 6 on the assumption that there is no interference signal. When it is larger than the reference value, the subcarrier position is considered to be affected by the interference. In addition, obtained from Equation 6

As shown in Equation 7, the variance value of may be referred to as the amount of interference at the position of the corresponding subcarrier k.

Next, the comparison unit 520 compares the dispersion value Var [Zm [k]] from the dispersion value calculation unit 510 with a predetermined reference value, and if the dispersion value is larger than the reference value, the position ( k) is output to the interference power amount calculator 530.

)을 구하여 가중치 계산부(540)에 출력한다.Then, the interference power amount calculation unit 530 recognizes the position k where the variance value is larger than the reference value as a position where co-channel interference exists, and the amount of interference power at the corresponding position [k]. (

) Is obtained and output to the weight calculator 540.

)을 하기 수학식8 또는 수학식9를 이용하여 구할 수 있다.More specifically, the interference power amount calculation unit 530 checks whether the corresponding position k is the position of the data symbol or the position of the pilot symbol, and according to each identified position, the interference power amount (

) Can be obtained using Equation 8 or Equation 9 below.

를 추정하는 방식은 간섭의 영향을 받은 부반송파의 위치가 파일롯 부반송파인지 아니면 데이터를 담고 있는 부반송파 인지 여부에 따라 달라진다.As shown in Equations 8 and 9, the amount of instantaneous interference power at the estimated position of the co-channel interference

The method of estimating depends on whether the location of the subcarriers affected by the interference is a pilot subcarrier or a subcarrier containing data.

That is, when the subcarrier position obtained through Equations 6 and 7 is a subcarrier that contains data, the amount of interference power is obtained as shown in Equation 8. In contrast, when the subcarrier containing a pilot signal is obtained, Equation 9 is obtained.

Since the value of the data is not known when the co-channel interference position is the data subcarrier position, it is approximated as in Equation 8, and when the position is the pilot subcarrier position, the pilot signal is known in advance by the receiver. It can obtain | require by (9).

)을 이용하여 상기 연판정 가중치를 구하여 상기 소프트 디매 퍼(600)에 공급한다.In addition, the weight calculation unit 540, the interference power amount of the interference power amount calculation unit 520 (

The soft decision weight is obtained by using the above and supplied to the soft demapper 600.

)을 이용하여, 상기 연판정 가중치(

)를 하기 수학식10을 이용하여 구할 수 있다.In more detail, the weight calculator 540 may include the channel estimate value, the noise variance, and the interference power amount of the interference power calculator 520.

), The soft decision weight (

) Can be obtained using Equation 10 below.

)에서,

는 동일 채널 간섭의 영향을 받은 k번째 부반송파에 대한 간섭전력량으로서, 그 위치에 따라 상기 수학식 8 및 9에서 구할 수 있다.Soft decision weight of Equation 10

)in,

Is the amount of interference power for the k-th subcarrier affected by co-channel interference, and can be obtained from Equations 8 and 9 according to its position.

Next, the soft demapper 600 multiplies the data symbols from the P / S converter 400 by the soft decision weights of the co-channel interference estimation unit 500, and multiplies the soft decision weights. The quantized data symbols are quantized into data bits.

)는, 하기 수학식 11 및 12에 나태낸 바와같이 등화된 수신신호(

,

)에 곱해져서 양자화 된다.That is, the soft decision is made in the soft demapper 600, at this time, based on the position of the co-channel interference estimated by the co-channel interference estimator 500 and the amount of interference at the interference position is appropriate. The weight is obtained, and the soft decision weight (

) Is an equalized reception signal (as shown in Equations 11 and 12).

,

) Is multiplied and quantized.

In Equations 11 and 12, k denotes a subcarrier index of an OFDM symbol, and Z (x) denotes "round ((-x + 1) / 2 * QL)" (QL = 2 ² -1, n = quantization bit). Z (x) is a function that quantizes the number of bits n for soft decision.

,

는 16 QAM 변조 심볼의 인-페이즈(in-phase) 비트에 대한 연판정된 비트이고, 쿼드러처(quadrature) 성분의 연판정된 비트는 수학식 12와 같이

,

로 나타낸다.In Equation 11,

,

Is the soft-determined bit for the in-phase bit of the 16 QAM modulation symbol, and the soft-determined bit of the quadrature component is

,

Represented by

,

)에 연판정 가중치가 곱해지므로 QPSK나 64QAM에도 적용할 수 있다.Further, as shown in Equations 11 and 12, the equalized received signal (

,

) Is multiplied by the soft decision weighting, so it can also be applied to QPSK or 64QAM.

Thereafter, the data bits output from the soft demapper 600 are rearranged in the reverse order in which the data is arbitrarily arranged by the transmitter in the deinterleaver 700.

Next, in the Viterbi decoder 800 which is a channel decoder, convolutional coded bits are decoded.

On the other hand, the simulation for verifying the performance of the co-channel interference estimation and decoding technique according to the present invention is carried out in the fading channel environment model COST (European Co-operation in the field of Scientific and Technical research) 207 TU (Typical Urban) Considering 60 km / h, it was performed by recording a statistical performance value after a sufficient number of iterations, the results are shown in Figures 6 and 7.

6 and 7 will be described in detail.

6 and 7, after estimating an initial channel using LS (Least Square) at a pilot position, a channel estimation technique is performed by applying a smoothing technique, which is a channel estimation technique based on a Discrete Fourier Transform (DFT). The error due to the estimation is reduced and accurate co-channel interference estimation can be made.

In addition, the interference signal modeling generates a narrowband co-channel interference signal on the assumption that the signal has the same or different power as that of each signal through Gaussian Interference Modeling, and assigns it to each OFDM consecutive subcarrier. The performance of the present invention for estimating and compensating co-channel interference signals has been described. Here, the ratio of the interference power was set to SIR (-3, 0 dB) to evaluate whether the interference power estimation is accurately made according to the interference power.

The interleaver uses a random interleaver, uses 7 for the length of the binding length and 1/2 for the code rate. Viterbi decoding used a 4-bit soft decision after weighting.

In FIG. 6, in order to evaluate the performance of the same channel interference estimation method and the decoding method of the OFDM receiver according to the present invention, the upper limit performance is first used as a comparison target and the case where the interference location and amount are accurately known. Set.

In order to compare the estimation performance, under the LS and the smoothing channel estimation condition, if the interference location and the amount of power are actually known (G13), and using the estimation method proposed by the present invention (G12) and weights are obtained. Each decoded bit error performance was compared for the case where it does not apply (G11).

First, when using the channel estimation using LS and the smoothing method, and estimating the interference power and applying it as a weight (G12) compared with the case where the actual interference power and position are known (G13), The results showed a slight difference in BER performance within about 1dB. In addition, when the soft decision is made without weighting (G11), the weighting method proposed by the present invention (G12) shows a coded BER performance gain of about 2dB or more at high SNR.

FIG. 7 illustrates the same channel estimation performance by varying only the signal-to-interference power ratio by 0 dB under the same conditions as described above. Compared with the performance shown in FIG. 7, it can be seen that the difference with the upper limit performance is smaller at higher SNR. This is because there are relatively few performance degradation factors such as channel estimation error due to interference power.

That is, Figure 6 is a diagram showing the SNR-BER characteristic graph of the present invention when the SIR is -3dB, Figure 7 is a diagram showing the SNR-BER characteristic graph of the present invention when the SIR is 0dB, see Figures 6 and 7 In this case, it can be seen that "BER" is improved in the graphs G12 and G22 when the soft decision weight is applied according to the present invention, rather than the graphs G11 and G21 when the soft decision weight is not applied, which is an ideal channel. It can be seen that it is almost similar to "BER" in the graphs G13 and G23 when the ideal weight is applied to the graph.

In the present invention as described above, when co-channel interference exists in the OFDM receiver, the position and size of the interference signal are estimated and used as channel state information of each subcarrier. By using this estimated soft decision weight in soft decision in the soft demapper, the influence of co-channel interference can be reduced.

In addition, unlike the conventional erasing method, when there is interference on a specific subcarrier, the soft decision weight of the soft demapper is estimated by estimating the amount of interference at the co-channel interference location instead of simply discarding the data included in the subcarrier. In order to reduce the bit error probability, we can obtain more improved reception performance.

That is, according to the present invention, the OFDM receiver providing the same channel interference estimation and decoding scheme estimates the position and the amount of interference and estimates the information of the same interference in the reception environment based on the actual OFDM system in which the same channel interference exists. By applying the Viterbi decoder, it can be seen that improved BER performance can be obtained.

1 is a structural diagram of a typical OFDM transmitter.

2 is a structural diagram of an OFDM receiver according to the present invention;

3 is a block diagram of a co-channel interference estimation unit according to the present invention.

4 is a positional estimation performance diagram of co-channel interference of the present invention when SIR is 3 dB.

5 is a diagram of the position estimation performance of co-channel interference of the present invention when SIR is -3 dB.

6 is a graph showing the SNR-BER characteristic graph of the present invention when the SIR is -3 dB.

7 is a diagram showing a SNR-BER characteristic graph of the present invention when SIR is 0 dB.

Explanation of symbols on the main parts of the drawings

110: RF unit 120: P / S conversion unit

130: protection section insertion section 140: FFT section

150: subcarrier demapping unit 200: channel estimating unit

300: equalizer 400: P / S conversion unit

500: co-channel interference estimation unit 600: soft demapper

510: variance value calculation unit 520: comparison unit

530: interference power amount calculation unit 540: weight calculation unit

Claims (16)

A channel estimator for estimating channel distortion using a pilot symbol of a received signal; An equalizer for equalizing channel distortion of a received signal by using channel estimates of the channel estimator; A P / S converter converting the received signal equalized by the equalizer into a serial form; Obtain a variance of the power of the received signal using the channel estimation value from the channel estimator, detect the position where co-channel interference exists using the variance, and use the power of the received signal at that position An on-channel interference estimator for determining decision weights; And A soft demapper that quantizes the data symbols from the P / S converter by using the soft decision weights of the co-channel interference estimator to quantize the data symbols into data bits. OFDM receiver comprising a. The method of claim 1, wherein the co-channel interference estimation unit, A variance value calculator for calculating a variance value for each position of power of a received signal having reduced channel influence and noise effect by using the received signal from the channel estimator, a channel estimate value, and a predetermined noise variance; A comparison unit comparing the dispersion value from the dispersion value calculation unit with a preset reference value; An interference power amount calculating unit for recognizing a position where the dispersion value is larger than the reference value as a position where co-channel interference exists and obtaining an amount of interference power at the corresponding position; And A weight calculation unit that obtains the soft decision weight using the interference power amount of the interference power amount calculation unit. OFDM receiver comprising a. The method of claim 2, wherein the dispersion value calculation unit, And the variance value is obtained through the following equation using the received signal from the channel estimator, the channel estimate value, and a predetermined noise variance at the corresponding position. [Equation]

here,

Is the received signal power with reduced channel and noise effects,

Is the received signal,

Is the channel estimate, and

Is a preset noise variance. The method of claim 3, wherein the interference power amount calculation unit, And confirming whether the corresponding position is a position of a data symbol or a position of a pilot symbol, and obtaining the interference power amount according to Equation (a) or (b) according to each identified position. Equation a

[Equation b]

The method of claim 4, wherein the weight calculation unit, And using the channel estimate value, the noise variance, and the interference power amount of the interference power calculator, to obtain the soft decision weight value through the following equation. [Equation]

The method according to claim 1 or 5, wherein the soft demapper, And multiplying the data symbols from the P / S converter by the soft decision weights of the co-channel interference estimation unit and quantizing the data symbols multiplied by the soft decision weights into data bits. An RF unit which receives the RF signal and converts the RF signal into an OFDM symbol; An S / P converter converting OFDM symbols of the RF unit into a parallel form; A guard interval removal unit for removing a guard interval between OFDM symbols from the S / P converter; An FFT unit performing fast Fourier transform on the OFDM symbol from the guard interval elimination unit and converting the OFDM symbol in the time domain into a complex symbol in the frequency domain; A subcarrier demapping unit for separating the symbols of the frequency domain from the FFT unit into data symbols and pilot symbols; A channel estimator estimating a channel distortion using a pilot symbol of a received signal from the subcarrier demapping unit; An equalizer for equalizing channel distortion of a received signal by using channel estimates of the channel estimator; A P / S converter converting the received signal equalized by the equalizer into a serial form; Obtain a variance of the power of the received signal using the channel estimation value from the channel estimator, detect the position where co-channel interference exists using the variance, and use the power of the received signal at that position An on-channel interference estimator for determining decision weights; And A soft demapper that multiplies the data symbols from the P / S converter by the soft decision weights of the co-channel interference estimator, and quantizes the data symbols multiplied by the soft decision weights into data bits. OFDM receiver comprising a. The method of claim 7, wherein the co-channel interference estimation unit, A variance value calculator for calculating a variance value for each position of power of a received signal having reduced channel influence and noise effect by using the received signal from the channel estimator, a channel estimate value, and a predetermined noise variance; A comparison unit comparing the dispersion value from the dispersion value calculation unit with a preset reference value; An interference power amount calculating unit for recognizing a position where the dispersion value is larger than the reference value as a position where co-channel interference exists and obtaining an amount of interference power at the corresponding position; And A weight calculation unit that obtains the soft decision weight using the interference power amount of the interference power amount calculation unit. OFDM receiver comprising a. The method of claim 8, wherein the dispersion value calculation unit, And the variance value is obtained through the following equation using the received signal from the channel estimator, the channel estimate value, and a predetermined noise variance at the corresponding position. [Equation]

here,

Is the received signal power with reduced channel and noise effects,

Is the received signal,

Is the channel estimate, and

Is a preset noise variance. The method of claim 9, wherein the amount of interference calculation unit, And confirming whether the corresponding position is a position of a data symbol or a position of a pilot symbol, and obtaining the interference power amount according to Equation (a) or (b) according to each identified position. Equation a

[Equation b]

The method of claim 10, wherein the weight calculation unit, And using the channel estimate value, the noise variance, and the interference power amount of the interference power calculator, to obtain the soft decision weight value through the following equation. [Equation]

The method of claim 11, wherein the soft demapper, The soft decision weight (

) Equalizes the received signal (

,

OFDM multiplier to quantize using the following equation (a) and (b). Equation a

[Equation b]

Where k indicates the subcarrier index of the OFDM symbol, and Z (x) is "round ((-x + 1) / 2 * QL)" (QL = 2 ² -1, n = number of quantized bits) (x) is a function to quantize the number of bits (n) for soft decision. The method of claim 12, wherein the reference value, OFDM receiver characterized in that it is set assuming that there is no interference signal in the following equation. [Equation]

here,

Is the received signal power with reduced channel and noise effects,

Is the received signal,

Is the channel estimate, and

Is a preset noise variance. The method of claim 7 or 11, wherein the OFDM receiver, An interleaver for rearranging the data bits output from the soft demapper in the reverse order of the arrangement order applied by an OFDM transmitter; And A channel decoder for decoding the convolutional coded bits from the inverber to recover the transmitted data bits OFDM receiver, characterized in that it further comprises. The method of claim 14, The channel decoder, An OFDM receiver, which is a Viterbi decoder. The method of claim 15, wherein the channel estimator, After initial channel estimation using LS (Least Square) method in the pilot position, OFDM receiver characterized in that the channel estimation is performed by applying a smoothing technique, which is a channel estimation technique based on Discrete Fourier Transform (DFT).

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