KR100387234B1 - Channel estimation apparatus cosidering I/Q mismatching error and digital signal receiver comprising it - Google Patents

Abstract

The present invention relates to a channel estimating apparatus considering an I / Q mismatch error and a digital signal receiver having the same. In a channel estimator for estimating a channel from a reference signal received through a predetermined channel, the received reference signal is sampled. A preprocessor for synchronizing and converting the synchronized sample signal into a fast Fourier transform; And when the frequency n of the reference signal having the symbol size N is 0 <n <N / 2, the odd-numbered signal X _n of the reference signal is 0, and when the N / 2 <n <N, the even-numbered signal X _n is 0. And a channel estimator for estimating a channel for the signal component and a channel for the distortion component due to the I / Q mismatch error by performing a predetermined calculation with an output value of the preprocessor.

According to the present invention, SNR is improved compared to the prior art by estimating and correcting channel distortion due to I / Q mismatch error. In addition, the present invention is suitable for a communication system such as OFDM unlike the prior art in which the channel distortion is corrected in the frequency domain after the FFT of the received signal.

Description

A channel estimation apparatus considering an I / i mismatch error and a digital signal receiver having the same {channel estimation apparatus cosidering I / Q mismatching error and digital signal receiver comprising it}

The present invention relates to a channel estimating apparatus considering an I / Q mismatch error and a digital signal receiver having the same. In particular, an apparatus for estimating a signal distortion channel due to an I / Q mismatch error and a signal estimated by correcting the estimated channel are detected. To a receiver.

In order to transmit and receive signals in a typical wireless communication system, upconvert a complex baseband signal to convert it into a passband signal, or conversely, downconvert the passband signal by Convert to a complex baseband signal. The complex baseband signal is separated into an in-phase (I) signal and a quadrature-phase (Q) signal, respectively, through a digital-to-analog converter (DAC), a lowpass filter, and a mixer. In this process, if the I and Q signal transmission characteristics are not the same, severe signal distortion occurs and system performance is degraded. I / Q mismatch is not the same because the I / Q signal transmission characteristics are called. The causes are the amplitude and phase imbalance of the mixer, the I / Q phase error of the oscillator in the mixer, and the I / Q mismatch. Q lowpass filter imbalance, DAC and ADC errors, and time delay differences. The larger the bandwidth of the signal, the greater the error that occurs in hardware implementation, so the I / Q mismatch error also increases.

Prior arts on I / Q mismatch include Karl Gerlach's "The effect of I, Q mismatch errors on adaptive cancellation, IEEE Transactions on Aerospace and Electronic." System, Vol. 28, No. 3, pp.729-740, July 1992) and K. Gerlach and MJ Steiner, "Adaptive Matching Filters to Correct I / Q Mismatch Errors" (An adaptive matched filter that compensates for I, Q mismatch erroes, IEEE Transactions on Signal Processing, Vol. 45, No. 12, pp. 3102-3107, December 1997). In the prior arts, the I / Q mismatch phenomenon is analyzed in the time domain, and the correction methods also operate in the time domain. However, these prior arts do not explain how to optimally obtain the value of a filter for correcting I / Q mismatch, respectively, and there is a problem that a complicated matrix operation must be performed for each iteration.

Other conventional techniques for I / Q mismatch errors include "Performance analysis of a DCQPSK-OFDM modem using an analog BB filter" by M. Benedetto and P. Mandarini. analog BB filters, Proceedings of Acts mobile summit '96, pp. 346-367, 1996) and Benedetto et al. (MGDBenedetto et. al), "Effects of in-phase and quadrature path mismatch and phase noise in QDCPSK-OFDM modems." (Effects of a mismatch in the In-phase and Quadrature paths, and of phase noise, in QDCPSK-OFDM modems, Proceedings of Acts mobile summit '97, pp. 769-774, 1997). These prior arts analyze the effects of I / Q mismatch on OFDM signals but do not suggest a correction method.

In addition, it is necessary to estimate and correct a channel in the frequency domain as in an orthogonal frequency division multiplexing (OFDM) system.

The present invention is directed to a channel estimator for estimating signal distortion due to an I / Q mismatch error in a fast Fourier transform (FFT) of a received signal, and a digital signal receiver having the same.

1 illustrates a digital signal transmission / reception apparatus in which I / Q mismatch occurs.

2 is a block diagram of a digital signal receiver according to the present invention.

FIG. 3 shows the comparison of the SNR of a signal whose distortion due to gain mismatch is corrected and the SNR of an uncorrected signal according to the present invention.

4 is a diagram illustrating a comparison between the SNR of a signal whose distortion due to timing phase error is corrected and the SNR of an uncorrected signal according to the present invention.

FIG. 5 shows a comparison between the SNR of a signal whose distortion due to oscillation phase error is corrected and the SNR of an uncorrected signal according to the present invention.

In order to accomplish the above technical problem, the present invention provides a channel estimator for estimating the channel from a reference signal received through a predetermined channel, wherein the received reference signal is sampled, synchronized, and fast Fourier transformed from the synchronized sample signal. Pretreatment unit; And if the frequency n of the reference signal having the symbol size N is 0 <n <N / 2, the odd-numbered signal X _n of the reference signal is 0, and if N / 2 <n <N, the even-numbered signal X _n 0, and a channel estimator for estimating a channel for the signal component and a channel for the distortion component due to the I / Q mismatch error by a predetermined calculation with the output value of the preprocessor.

In order to accomplish the above technical problem, the present invention provides a channel estimator for estimating the channel from a reference signal received through a predetermined channel, wherein the received reference signal is sampled, synchronized, and fast Fourier transformed from the synchronized sample signal. Pretreatment unit; And a distortion signal X _Nn for X _nn ^* = X _n and an odd frequency n for signal X _n of even frequency n of the reference signal having a symbol size N, and X _Nn ^* = -X _n for a signal of odd frequency n. And a channel estimator configured to estimate a channel of a signal component and a channel of a distortion component due to an I / Q mismatch error by performing a predetermined calculation with an output of the preprocessor.

According to an aspect of the present invention, there is provided a signal receiver for estimating the channel from a reference signal received through a predetermined channel and correcting the estimated channel with respect to the reference signal to detect the reference signal. A preprocessor for sampling and synchronizing the reference signal, and for performing fast Fourier transform on the synchronized sample signal; When the frequency n of the reference signal having the symbol size N is 0 <n <N / 2, the odd-numbered signal X _n of the reference signal is 0, and when N / 2 <n <N, the even-numbered signal X _n is A channel estimator for estimating a channel for a signal component and a distortion component due to an I / Q mismatch error by a predetermined calculation with an output value of the preprocessor; An equalizer for correcting a channel for the signal component estimated by the channel estimator and a channel for the distortion component at an output of the preprocessor; And a detector for detecting data from the output of the equalizer.

According to an aspect of the present invention, there is provided a signal receiver for estimating the channel from a reference signal received through a predetermined channel and correcting the estimated channel with respect to the reference signal to detect the reference signal. A preprocessor for sampling and synchronizing the reference signal, and for performing fast Fourier transform on the synchronized sample signal; The distortion signal X _{Nn is set} to X _Nn ^* = X _n and the signal of odd frequency n is X _Nn ^* =-X _n for the signal X _n of the even frequency n of the reference signal having a symbol size N, A channel estimator estimating a channel of a signal component and a channel of a distortion component due to an I / Q mismatch error by a predetermined calculation with an output of the preprocessor; An equalizer for correcting a channel for the signal component estimated at the output of the preprocessor and a channel for the distortion component; And a detector for detecting data from the output of the equalizer.

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

1 illustrates a digital signal transmission / reception apparatus in which I / Q mismatch occurs. Signal transmitting and receiving apparatus according to Figure 1, the first and the 2DAC (11, 12), the first statue low-pass filter (F _I 14), a first quadrature low-pass filter (F _Q: 15), first and second mixer 16, 17, first adder 18, transmit antenna 19, receive antenna 20, third and fourth mixers 21 and 22, second in-phase low pass filter (G _I : 23), A second orthogonal low pass filter (G _Q : 24) and first and second ADCs 26 and 27 are provided.

The operation is as follows. The transmission digital signal x _k is converted into an analog signal through the first and second DACs 11 and 12 after the I signals x _{k, I} and the Q signals x _{k, Q} are separated. F _I 14 and F _Q 15 low pass filter the transformed signal. At this time, the Q signal is compared with the I signal. There may be a time delay. The first and second mixers 16 and 17 convert each low pass filtered result into a passband signal. At this time, the phases of the oscillation signals supplied to the first and second mixers 16 and 17 are compared with the ideal values. As far as the difference can be. The outputs of the first and second mixers 16, 17 are added by the adder 18 and then transmitted via the transmit antenna 19.

On the receiving side, the third and fourth mixers 21 and 22 convert the signal received through the receiving antenna 20 into a baseband signal. At this time, the phases of the oscillation signals supplied to the third and fourth mixers 21 and 22 are compared with the ideal values. As far as the difference can be. Each output signal of the third and fourth mixers 21, 22 is low pass filtered at G ₁ (23) and G _q (24). At this time, the Q signal is compared with the I signal. As long as time delay can occur. The first and second ADCs 26 and 27 convert the low pass filtered signal into a digital signal.

2 is a block diagram of a digital signal receiver according to the present invention. The receiver according to FIG. 2 includes a synchronizer 201, a fast Fourier transform (FFT) 203, a channel estimator 205, a tap calculator 206 of the equalizer, an equalizer 207, and a detector 209. Include.

The synchronization unit 201 synchronizes the reception signal r _k . Here, r _k is a signal input to the synchronization unit 201 after the received analog signal is sampled, and a reference signal, which is also known in advance on the receiving side, is transmitted through a predetermined channel and received. The FFT unit 203 performs N-point FFT on the synchronized signal. The output R _n of the FFT unit 203 may be expressed as in the following equation.

X _n is the FFT result of the reference signal, H _{s, n} is the signal channel, H _{d, n} is the distortion channel, Is the complex conjugate of the FFT result of the signal distorted by I / Q mismatch, and N _n is the noise in the frequency domain.

According to Equation 1, the received signal R _n is a result of FFT of the received signal r _k , and the original signal. Interfered and distorted signal by I / Q mismatch in Plus noise N _n . The channel estimator 205 estimates the signal channel and the distortion signal channel due to I / Q mismatch, respectively, from the FFT signal R _n and X _n , the FFT result of the reference signal. and Outputs The tap calculator 206 of the equalizer estimates the estimated channel and The tap value of the equalizer 207 is calculated from the equation. The equalizer 207 corrects the signal distortion of the received signal R _n using the obtained tap value. The detector 209 detects the reference signal X _n from the corrected value Z _n .

The operation of the channel estimator 205, the tap calculator 206 of the equalizer, and the equalizer 207 will be described in detail as follows.

The channel estimator 205 sets the odd-numbered signal to 0 when the frequency n is 0 <n <N / 2 in the reference signal X _n , and sets the even-numbered signal to 0 when n is N / 2 <n <N. From the output signal R _n of the FFT unit 203, the signal channels H _{s, n} and the distortion channels H _{d, m} are estimated as follows.

Low pass filtering of the output value of Equation 2 reduces the effects of noise, and estimates the characteristics of the signal and distortion channels for all n and Can be obtained. The same result can be obtained even if the position where 0 value is designated in the reference signal is reversed from that of Equation 2.

Channel estimation can be done in other ways. That is, the even signal in the reference signal is The odd numbered signal In this case, the channel characteristics can be estimated as follows.

The low pass filtering of the output value of Equation 3 can reduce the influence of noise, and estimate the signal channel and distortion channel characteristics for all n. and Can be estimated. In contrast to Equation 3 above, the odd-numbered signal The even signal is Even the same result can be obtained.

The tap calculator 206 of the equalizer estimates the channel characteristic and The tap W _n of the equalizing unit 207 is obtained from the following equation. In this case, the equalizer 207 is preferably a minimum mean square error equalizer.

here,

SNR _est is an estimate of the signal-to-noise ratio (SNR). H ^* is the conjugate transpose matrix of H , and E {| X _n | ² } and E {| N _n | ² } is the average power of X _n and N _n , respectively.

If the channel estimation is not performed from the reference signal and the SNR cannot be estimated from the actual received signal, the tap value of the equalizer 207 is calculated as follows.

The equalizer 207 can obtain a value Z _n whose distortion is corrected from the output R _n of the FFT unit 203 and the tap value W _n of the equalizer 207 as follows.

The channel estimator 205, the tap calculator 206, and the equalizer 207 of the equalizer may be implemented in software in a digital signal processor or a computer, or in a hardware form such as a logic circuit. It may be implemented as, and may be implemented by firmware.

3 to 5 illustrate the SNR of a signal whose I / Q mismatch error is corrected and the SNR of a signal whose I / Q mismatch error is not corrected according to the present invention. That is, 16 QAM (Quadrature Amplitude Modulation) Orthogonal Frequency Division Multiplexing (OFDM) signals are required to achieve a Bit Error Rate (BER) = 1E-4 in an AWGN channel when I / Q mismatch is present. The input SNR is shown. The FFT size of the OFDM signal is N = 256 and subsymbol X _n = 16QAM.

3 shows the performance change when the gain mismatch G is present. When there is a gain mismatch G, the received signal r _k can be expressed as follows.

As shown, when the gain mismatch G = 2dB is improved by about 2dB compared to the results according to the present invention and the results of the prior art, when G = 5dB is improved by about 16dB.

4 shows the performance change with respect to the timing phase error. Total Timing Phase Error When is present, the reception signal r _k can be expressed as follows.

As shown, the timing phase error When = 0.1T, the result according to the present invention is improved by about 1 dB compared to the result of the prior art. It is about 7dB improvement when = 0.2T.

Fig. 5 shows the performance change when the oscillation phase error Φ is constantly present. For example, assuming that Φ ₁ = Φ and the rest are ideal, the frequency value R _n of the received signal r _k may be expressed as follows.

As shown, when the oscillation phase error Φ = 10 °, the results according to the present invention were improved by about 1.5dB compared to the results of the prior art, and when Φ = 20 °, about 5.5dB was improved.

According to the present invention, SNR is improved compared to the prior art by estimating and correcting channel distortion due to I / Q mismatch error. In addition, the present invention is suitable for a communication system such as OFDM unlike the prior art in which the channel distortion is corrected in the frequency domain after the FFT of the received signal.

Claims (10)

In the channel estimator for estimating the channel from the reference signal received through a predetermined channel, A preprocessing unit for sampling the received reference signal, synchronizing, and converting the synchronized sample signal by a fast Fourier transform; And When the frequency n of the reference signal having the symbol size N is 0 <n <N / 2, the odd-numbered signal X _n of the reference signal is 0, and when N / 2 <n <N, the even-numbered signal X _n is And a channel estimator for estimating a channel for the signal component and a channel for the distortion component due to the I / Q mismatch error by a predetermined calculation with an output value of the preprocessor. Channel estimator. The method of claim 1, wherein the channel estimator When the output of the preprocessing unit is R _n and the distortion signal for X _n is X _Nn , an estimated value of the channel for the signal component And a channel estimate value for the distortion component due to the I / Q mismatch error. Then the expression Means for obtaining; And Obtained estimate And And a low pass filter for low pass filtering. In the channel estimator for estimating the channel from the reference signal received through a predetermined channel, A preprocessing unit for sampling the received reference signal, synchronizing, and converting the synchronized sample signal by a fast Fourier transform; And The distortion signal X _{Nn is set} to X _Nn ^* = X _n and the signal of odd frequency n is X _Nn ^* =-X _n for the signal X _n of the even frequency n of the reference signal having a symbol size N. And a channel estimator for estimating a channel for the signal component and a channel for the distortion component due to the I / Q mismatch error by performing a predetermined calculation with the output of the preprocessor. 4. The apparatus of claim 3, wherein the channel estimator When the output of the preprocessing unit is R _n and the distortion signal for X _n is X _Nn , an estimated value of the channel for the signal component And a channel estimate value for the distortion component due to the I / Q mismatch error. Then the expression Means for obtaining; And Obtained estimate And And a low pass filter for low pass filtering. A signal receiver for estimating the channel from a reference signal received through a predetermined channel and correcting the estimated channel with respect to the reference signal to detect the reference signal, A preprocessing unit for sampling the received reference signal, synchronizing, and converting the synchronized sample signal by a fast Fourier transform; When the frequency n of the reference signal having the symbol size N is 0 <n <N / 2, the odd-numbered signal X _n of the reference signal is 0, and when N / 2 <n <N, the even-numbered signal X _n is A channel estimator for estimating a channel for a signal component and a distortion component due to an I / Q mismatch error by a predetermined calculation with an output value of the preprocessor; An equalizer for correcting a channel for the signal component estimated by the channel estimator and a channel for the distortion component at an output of the preprocessor; And And a detector for detecting data from an output of the equalizer. The method of claim 5, wherein the channel estimator When the output of the preprocessing unit is R _n and the distortion signal for X _n is X _Nn , an estimated value of the channel for the signal component And a channel estimate value for the distortion component due to the I / Q mismatch error. Then the expression Means for obtaining; And Obtained estimate And And a low pass filter for low pass filtering. The method of claim 6, wherein the equalizing unit The low pass filter outputs are respectively , When, the expression here, , SNR _est is the estimate of the signal-to-noise ratio (SNR), H ^* is the conjugate transpose matrix of H , E {| X _n | ² } and E {| N _n | ² } is the average power of X _n and N _n , respectively. Means for obtaining equalization tap coefficients as follows; And From the equalization tap coefficient Digital signal receiver characterized in that it comprises an equalizer for correcting the channel distortion as shown. A signal receiver for estimating the channel from a reference signal received through a predetermined channel and correcting the estimated channel with respect to the reference signal to detect the reference signal, A preprocessing unit for sampling the received reference signal, synchronizing, and converting the synchronized sample signal by a fast Fourier transform; The distortion signal X _{Nn is set} to X _Nn ^* = X _n and the signal of odd frequency n is X _Nn ^* =-X _n for the signal X _n of the even frequency n of the reference signal having a symbol size N, A channel estimator estimating a channel of a signal component and a channel of a distortion component due to an I / Q mismatch error by a predetermined calculation with an output of the preprocessor; An equalizer for correcting a channel for the signal component estimated at the output of the preprocessor and a channel for the distortion component; And And a detector for detecting data from an output of the equalizer. The method of claim 8, wherein the channel estimator When the output of the preprocessing unit is R _n and the distortion signal for X _n is X _Nn , an estimated value of the channel for the signal component And a channel estimate value for the distortion component due to the I / Q mismatch error. Then the expression Means for obtaining; And Obtained estimate And And a low pass filter for low pass filtering. The method of claim 9, wherein the equalizing unit The low pass filter outputs are respectively , When, the expression here, , SNR _est is the estimate of the signal-to-noise ratio (SNR), H ^* is the conjugate transpose matrix of H , E {| X _n | ² } and E {| N _n | ² } is the average power of X _n and N _n , respectively. Means for obtaining equalization tap coefficients as follows; And From the equalization tap coefficient Digital signal receiver characterized in that it comprises an equalizer for correcting the channel distortion as shown.