KR101203861B1 - method for channel estimation, channel estimator, mobile station and base station - Google Patents

Abstract

A channel estimation method is provided. The channel estimation method first obtains a first channel frequency response having a first frequency band from a pilot symbol. A second channel frequency response having a second frequency band including the first frequency band is obtained. The third channel frequency response is obtained by replacing the response of the frequency band corresponding to the first frequency band with the first frequency response in the second channel frequency response. The final channel response estimate is obtained using the third channel frequency response. Channel estimation with high precision is possible.

Channel Estimation, Pilot, Multicarrier, Communications, OFDM

Description

Method for channel estimation, channel estimator, mobile station and base station

1 is a graph comparing the channel frequency response estimation and the ideal channel frequency response according to the prior art.

2 is a block diagram illustrating a communication system according to an embodiment of the present invention.

3 is a block diagram illustrating the channel estimator of FIG. 2.

4 is a flowchart illustrating a channel estimation method using the channel estimator of FIG. 3.

5A to 5E are schematic diagrams illustrating the step-by-step response of the channel estimation method.

6A to 6F are graphs showing signals obtained by channel estimation steps.

7 is a graph illustrating channel response estimation results according to the number of repetitions.

FIG. 8 is a graph illustrating a block error rate versus a signal-to-noise ratio of transmission data according to the number of repetitions.

9 is a block diagram illustrating a channel estimator according to another embodiment of the present invention.

** Explanation of symbols in main part of drawing **

100: transmitter

200 receiver

280: channel estimator

The present invention relates to channel estimation, and more particularly, to a channel estimation method, a channel estimator, a terminal, and a base station for performing efficient channel estimation.

Digital wired / wireless communication systems are widely used to provide various types of communication such as voice and packet data.

In digital communication, information is converted into digital data in bits. The transmitter modulates the input bit stream into a signal for transmission, and the receiver demodulates the received signal into bits to recover information. In an ideal communication system the received signal is identical to the transmitted signal. In practice, however, the phase and amplitude of the signal change during the transmission of communication data from the transmitter to the receiver. This is because the channel is frequency-selective and time-varying. The transmitter must take these changes into account to recover the original data.

The change in phase and amplitude that occurs as a signal propagates along a channel is called the channel response. Channel response generally depends on frequency and time. If the receiver can determine the channel response, the received signal can be corrected to compensate for channel degradation. Determining the channel response at the receiver is called channel estimation. Channel estimation includes coherent detection and non-coherent detection. Coherent detection sends a compressed symbol called a pilot symbol along with a data symbol to estimate the channel. Non-coherent detection does not use any pilot symbols and estimates the difference between two consecutive symbols.

In general, coherent detection is performed by including a pilot symbol in a transmitted signal. That is, a signal including a pilot symbol having a known value (a priori) together with the data symbol is transmitted to the receiver. The receiver compares the received value of the pilot symbol with a known value to estimate the channel response.

For channel estimation using pilot symbols, see "JJ van de Beek, O. Edfors, M. Sandnell, SK Wilson, and PO Borjesson, On channel estimation in OFDM systems, In Proc. IEEE Vehicular Technology Conf., Vol. 2, July 1995, pp. 815-819 "or" O. Edfors, M. Sandnell, JJ van de Beek, SK Wilson, PO Borjesson, OFDM channel estimation by sigular value decomposition, IEEE Trans. Communications, Vol. 46, No. 7, July 1998 "and the like. These documents disclose LS (least square) estimation or minimum mean-square error (MMSE) estimation, which is a channel estimation method in the frequency domain.

Recently, as a multi-carrier communication system using a plurality of subcarriers has been developed, there is a need to increase the accuracy of channel estimation. In the multi-carrier communication system, the channel characteristics of each subcarrier are different, and the subcarriers undergoing large fading have a relatively high error rate.

Moreover, in a multi-carrier communication system, signals are transmitted using only some bands for various reasons among the total transmission bandwidths determined by the size of the Fourier transform. For example, only some subcarrier intervals are allocated for signal transmission for multiple access. In this case, since the pilot symbols are transmitted only in the transmission band, the initial channel frequency response obtained using the pilot symbols is limited to the transmission band.

1 is a graph comparing the channel frequency response estimation and the ideal channel frequency response according to the prior art. This is a case where the pilot symbols are limited to the subcarriers 53 to 203 and transmitted.

Since the pilot symbols are limited and transmitted within the transmission band, the initial channel frequency response obtained from the pilot symbols is discontinuous at frequencies between 52 and 53, 203 and 204, both ends. When the general Fourier transform channel estimation is performed on the initial channel frequency response, distortion is generated while transforming the channel frequency response estimation in the form of a continuous signal.

A channel estimation method using a Fourier transform will be described. First, an initial channel frequency response is inversely Fourier transformed to obtain a channel impulse response. Replace zero for any response other than the valid interval of the channel impulse response to remove thermal noise components. The Fourier transform can then be used to obtain a channel frequency response estimate with some thermal noise removed.

However, performing an Inverse Fourier Transform on a particular signal, performing a Fourier Transform after replacing some intervals with zero, results in low pass filtering of the signal. Therefore, the ideal channel frequency response (dotted line in Fig. 1) is transformed into a channel frequency response estimate (solid line in Fig. 1) in the form of a continuous continuous signal, thereby causing a problem of deepening distortion at both ends of the transmission band.

To increase the accuracy of channel estimation, the distortion at both ends of the transmission band should be reduced.

An object of the present invention is to provide a channel estimation method, a channel estimator, a terminal, and a base station with high precision using pilot symbols.

Another object of the present invention is to provide an efficient channel estimation method, a channel estimator, a terminal, and a base station.

According to an aspect of the present invention, a channel estimation method is provided. The channel estimation method obtains a first channel frequency response having a first frequency band from a pilot symbol, and obtains a second channel frequency response having a second frequency band including the first frequency band. The third channel frequency response is obtained by replacing the response of the frequency band corresponding to the first frequency band with the first frequency response in the second channel frequency response. The final channel response estimate is obtained using the third channel frequency response.

According to another aspect of the present invention, a channel estimation method using a pilot symbol is provided. The channel estimation method obtains an initial channel frequency response using a pilot symbol and obtains a final channel response estimate using a compensation channel frequency response including the initial channel frequency response.

According to still another aspect of the present invention, a repeated channel estimation method using a pilot symbol is provided. The iterative channel estimation method obtains an initial channel frequency response from the pilot symbol. From the initial channel frequency response, a temporary channel frequency response having a frequency band including the frequency band of the initial channel frequency response is obtained, and it is determined whether to repeat the operation of the temporary channel frequency response. In the case of the repetition, a compensation channel frequency response obtained by substituting the initial channel frequency response into a frequency band corresponding to the frequency band of the initial channel frequency response among the frequency bands of the temporary channel frequency response is obtained. Obtain the temporary channel frequency response.

According to another aspect of the present invention, a channel estimator is provided. The channel estimator is a repetition determination unit for determining whether to repeatedly calculate a temporary channel frequency response having a frequency band including a frequency band of an initial channel frequency response obtained from a pilot symbol, and the initial channel frequency response in the temporary channel frequency response. And a compensation generator for obtaining the compensation channel frequency response by substituting the initial channel frequency response in a frequency band corresponding to a frequency band of.

According to another aspect of the present invention, there is provided a channel estimation method in an OFDM based communication system. The channel estimation method obtains an initial channel frequency response for a transmission band by extracting a pilot symbol and obtains a channel impulse response from the initial channel frequency response. The response in the window region is taken from the channel impulse response to obtain a temporary channel frequency response having a frequency band wider than the transmission band. In the temporary channel frequency response, the initial channel frequency response is substituted into the frequency band corresponding to the transmission band to obtain a compensation channel frequency response, and the final channel response estimate is obtained using the compensation channel frequency response.

According to another aspect of the present invention, a terminal is provided. The terminal obtains a compensation channel frequency response including the initial channel frequency response from an antenna receiving a signal through a channel, a pilot extractor extracting a pilot symbol from the signal, and an initial channel frequency response obtained from the pilot symbol, And a channel estimator that obtains a final channel response estimate of the channel using the compensation channel frequency response.

According to another aspect of the present invention, a base station is provided. The base station obtains a compensation channel frequency response including the initial channel frequency response from an antenna receiving a signal through a channel, a pilot extractor extracting a pilot symbol from the signal, and an initial channel frequency response obtained from the pilot symbol, And a channel estimator that obtains a final channel response estimate of the channel using the compensation channel frequency response.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals designate like elements throughout the specification.

The following channel estimates can be used for various communication systems. The communication system is widely deployed to provide various communication services such as voice, packet data and the like. This technique can be used for downlink or uplink. The downlink means communication from a base station (BS) to a mobile station (MS), and the uplink means communication from a terminal to a base station. A base station generally refers to a fixed station that communicates with a terminal and may be referred to as other terminology, such as a base tranceiver system (BTS), an access point, or the like. The terminal may be fixed or mobile and may be called in other terms such as user equipment (UE), user terminal (UT), wireless device (wireless device), and the like.

Channel refers to a wireless communication channel, a wired communication channel, or both. Examples of wireless communication channels are satellite, voice communication channels. Examples of wired communication channels refer to, but are not limited to, optical wiring, copper wiring or other conductive wiring.

The technique disclosed below may be used in various multicarrier communication systems such as orthogonal frequency division multiplexing (OFDM). OFDM divides the total system bandwidth into a plurality of subcarriers having orthogonality. The subcarriers may be called subbands, tones, and the like.

2 is a block diagram illustrating a communication system according to an embodiment of the present invention. The communication system is based on orthogonal frequency division multiplexing (OFDM).

Referring to FIG. 2, a communication system includes a transmitter 100 and a receiver 200. The transmitter 100 may be part of a base station. The receiver 200 may be part of a terminal. Alternatively, the transmitter 100 may be part of a terminal and the receiver 200 may be part of a base station. The base station may include a plurality of receivers and a plurality of transmitters. The terminal may include a plurality of receivers and a plurality of transmitters.

The transmitter 110 includes a transmit processor 110, a pilot insertion unit 120, an IFFT unit 130, a CP insertion unit 140, a transmission unit 150, and a transmission antenna 160.

The transmission processor 110 receives data such as voice or packet data. The transmit processor 110 processes the input data (source coding, channel coding, mapping) to generate data symbols.

The pilot inserter 120 inserts a pilot symbol into the data symbol. Hereinafter, data symbols refer to modulation symbols for data and pilot symbols refer to modulation symbols for pilot signals. The modulation symbol refers to a complex value modulated by quadrature phase shift keying (QPSK) or 16 quadrature amplitude modulation (QAM). Pilot symbols are data known a priori to both the transmitter 100 and the receiver 200. Multiplexed data symbols and pilot symbols are called OFDM symbols. There is no restriction on the arrangement of data symbols and pilot symbols. An example of the arrangement of data symbols and pilot symbols is A.R.S. Bahai, B.R. See Saltzberg, M. Ergen, "Multi-Carrier Digital Communications: Theory and Applications of OFDM", 2nd Ed., Springer, 2004, pp. 122-124.

The inverse fast Fourier transform (IFFT) unit 130 performs IFFT on the OFDM symbol to generate symbols including time domain samples. The CP inserter 140 adds some samples of the previous symbol to the converted symbol. The added part is called a cyclic prefix and is also called a guard interval. The CP removes inter-symbol interference (ISI) to change the frequency-selective channel to a flat-fading channel. The transmitting unit 150 converts the sample signal output from the CP inserting unit 140 into an analog signal and transmits the analog signal through the transmitting antenna 160.

The receiver 200 includes a reception antenna 210, a reception unit 220, a CP remover 230, an FFT unit 240, a data detector 250, a reception processor 260, a pilot extractor 270, and a channel. Estimator 280.

The receiving antenna 210 receives the signal transmitted from the transmitter 100 and sends it to the receiving unit 220. The receiving unit 220 digitally converts the transmitted signal to provide a stream of samples.

The CP remover 230 removes the CP from the sample. The FFT unit 230 performs an FFT on the samples transmitted by the CP remover 230 to generate an OFDM symbol.

The pilot extractor 270 extracts a pilot symbol from the OFDM symbol. The pilot extractor 270 obtains an initial channel frequency response through a pilot symbol and inputs it to the channel estimator 280. Channel estimator 280 derives channel estimation between transmitter 100 and receiver 200 using the received initial channel frequency response as described below.

The data detector 250 extracts the data symbols from the OFDM symbols and performs data detection using the channel estimation of the channel estimator 280. The output of the data detector 250 is a data symbol estimate. Receive processor 260 processes (de-maps, decodes) the data symbol estimates to provide decoded data. In general, the receiving processor 230 is complementary to the transmitting processor 110 of the transmitter 100.

3 is a block diagram illustrating the channel estimator of FIG. 2.

Referring to FIG. 3, the channel estimator 280 includes a first transform unit 281, a response limiter 282, a second transform unit 283, an iteration determiner 284, and a compensation generator 285. do.

The input of the channel estimator 280 is an initial channel frequency response sent by the pilot extractor 270. In another embodiment, the input of the channel estimator 280 may be a pilot symbol itself, and may further include a separate module for obtaining an initial channel frequency in front of the first converter 281. In another embodiment, the channel estimator 280 may be integrated with the pilot extractor 270.

The channel response includes a channel frequency response in the frequency domain and a corresponding channel impulse response in the time domain. In general, the channel frequency response is obtained by Fourier transforming the channel impulse response. The channel impulse response is obtained by inverse Fourier transforming the channel frequency response.

The first converter 281 receives an initial channel frequency response obtained from the pilot symbol, and receives a compensation channel frequency response to be described later. The first converter 282 performs an IFFT on the initial channel frequency response or the compensation channel frequency response to convert the channel impulse response.

The response limiter 282 receives the channel impulse response from the first converter 281 and replaces the zero portion with respect to a portion outside the predetermined area. That is, the response limiting unit 282 outputs a zero-replaced channel impulse response by replacing zero with a response outside the preset window area. As another example, the response limiting unit 282 may pass only a response in the window region among the input channel impulse responses, and may prevent a response outside the window region from passing.

The second converter 283 performs an FFT on the zero-replaced channel impulse response input from the response limiter 282 to obtain a temporary channel frequency response.

The iteration determination unit 284 determines whether or not to repeatedly calculate the temporary channel frequency response. If the repetition operation is terminated, the repetition determination unit 284 outputs the temporary channel frequency response as a final channel response estimate. The final channel response estimate is the output of the channel estimator 280, which is an estimated final channel response. If the iteration operation continues, the iteration determination unit 284 outputs the temporary channel frequency response to the compensation generator 285. A method for determining whether to repeat operations will be described later with reference to a channel estimation method.

The compensation generator 285 obtains a compensation channel frequency response. The compensation channel frequency response is obtained by substituting the initial channel frequency response in a frequency band corresponding to the frequency band of the initial channel frequency response in the temporary channel frequency response. The compensation generator 285 outputs the compensation channel frequency response to the first converter 281.

The compensation channel frequency response inputted to the first converter 281 is repeatedly obtained through the first converter 281, the response limiter 282, and the second converter 283. Subsequently, the repetition determination unit 284 determines whether the repetition is repeated. This results in an iterative operation of the temporary channel frequency response.

In the present exemplary embodiment, the first transform unit 281 and the second transform unit 283 are included in the channel estimator 280, but the first transform unit 281 and the second transform unit 283 may be configured separately. It can be shared with other modules. For example, the second converter 283 may be an FFT unit 240. Alternatively, when both a receiver and a transmitter exist in one terminal, the second converter 283 may be an FFT unit 240, and the first converter 281 may be an IFFT unit 130.

4 is a flowchart illustrating a channel estimation method using the channel estimator of FIG. 3. 5A to 5E are schematic diagrams illustrating the step-by-step response of the channel estimation method.

Referring to FIG. 4, an initial channel frequency response Yi (k) (first channel frequency response) is obtained using information of a pilot symbol (S110). The initial channel frequency response Yi (k) is equal to Equation 1, and the response is schematically shown in FIG. 5A.

는 파일럿 심벌을 통해 구한 k₁부터 k₂ 사이의 초기 채널 주파수 응답이다. 초기 채널 주파수 응답 Yi(k)의 주파수 대역(frequency band) W1 (제1 주파수 대역)은 | k₂ - k₁ | 이다. 초기 채널 주파수 응답 Yi(k)의 주파수 대 역 W1은 수신기(200)에 전송된 전송 대역일 수 있다. 또는 초기 채널 주파수 응답 Yi(k)의 주파수 대역 W1은 각 사용자에게 할당된 할당 대역일 수 있다. here,

Is the initial channel frequency response between k ₁ and k ₂ obtained from the pilot symbols. The frequency band W1 (first frequency band) of the initial channel frequency response Yi (k) is | k ₂ -k ₁ | to be. The frequency band W1 of the initial channel frequency response Yi (k) may be a transmission band transmitted to the receiver 200. Alternatively, the frequency band W1 of the initial channel frequency response Yi (k) may be an allocated band allocated to each user.

Subsequently, IFFT is performed on the initial channel frequency response Yi (k) to obtain a channel impulse response y _p (n) (first channel impulse response) (S120). The channel impulse response y _p (n) is shown in Equation 2, and the response is schematically shown in FIG. 5B.

The zero-substituted channel impulse response y _zp (n) (second channel impulse response) is obtained by substituting the remaining portion except for the predetermined window area T in the channel impulse response y _p (n) (S130). The zero-replaced channel impulse response y _zp (n) is given by Equation 3, and the response is schematically shown in FIG. 5C.

In zero-replacement, if the size of the window region T is too small, the channel response due to the multipath delay spread cannot be obtained properly. If the window area T is too small, large distortion occurs at both ends of the transmission band. On the contrary, if the size of the window region T is too large, noise estimation or interference signals are included in the channel estimation in addition to the channel response due to the multipath delay spread, thereby degrading the channel estimation performance.

The size of the window area T may be equal to or greater than the maximum excess delay. In general, the maximum excess delay is the difference between the minimum delay at which the signal first arrives between the transmitter and receiver and the maximum delay at which the signal arrives through the multipath. The size of the window area T may be slightly larger than the maximum excess delay.

The size of the window area T may be a fixed value. In another embodiment, the size of the window area T may be adaptively changed. When the size of the window region T is changed, a closed loop may be formed between the receiver and the transmitter.

An FFT is performed on the zero-replaced channel impulse response y _zp (n) to obtain a temporary channel frequency response Yt (k) (second channel frequency response) on the frequency axis (S140). The temporary channel frequency response Yt (k) is obtained by K-point Fourier transform of the zero-substituted channel impulse response y _zp (n). The temporary channel frequency response Yt (k) is as shown in Equation 4, and the response is schematically shown in FIG. 5D.

는

에 대해 FFT를 수행한 것이고, K는 임의의 주파 수로 K>K₂>K₁ 의 관계가 성립한다. 초기치를 0이라 할 때, 임시 채널 주파수 응답 Yt(k)의 주파수 대역 W2 (제2 주파수 대역)는 K이다. 즉 임시 채널 주파수 응답 Yt(k)의 주파수 대역 W2은 초기 채널 주파수 응답 Yi(k)의 주파수 대역 W1보다 더 넓게 한다. 이 경우 임시 채널 주파수 응답 Yt(k)의 주파수 대역 W2은 초기 채널 주파수 응답 Yi(k)의 주파수 대역 W1을 포함한다. 초기 채널 주파수 응답 Yi(k)의 주파수 대역 W1은 임시 채널 주파수 응답 Yt(k)의 주파수 대역 W2의 일부분으로 볼 수 있다. 또는 초기 채널 주파수 응답 Yi(k)의 주파수 대역 W1 이 시스템의 전체 대역폭 중 일부만이 전송된 대역인 경우, 임시 채널 주파수 응답 Yt(k)의 주파수 대역 W2는 시스템의 전체 대역폭일 수 있다. here,

The

FFT is performed, and K is a relationship of K> K ₂ > K ₁ at any frequency. When the initial value is 0, the frequency band W2 (second frequency band) of the temporary channel frequency response Yt (k) is K. That is, the frequency band W2 of the temporary channel frequency response Yt (k) is wider than the frequency band W1 of the initial channel frequency response Yi (k). In this case, the frequency band W2 of the temporary channel frequency response Yt (k) includes the frequency band W1 of the initial channel frequency response Yi (k). The frequency band W1 of the initial channel frequency response Yi (k) can be seen as part of the frequency band W2 of the temporary channel frequency response Yt (k). Alternatively, when the frequency band W1 of the initial channel frequency response Yi (k) is a band in which only a part of the total bandwidth of the system is transmitted, the frequency band W2 of the temporary channel frequency response Yt (k) may be the entire bandwidth of the system.

Next, it is determined whether the channel estimation is performed M times (M≥1) (S150). Here, when the temporary channel frequency response Yt (k) is used as the final channel response estimate, it is repeated once (M = 1). If M≥2, the temporary channel frequency response Yt (k) is repeatedly obtained two or more times. M≥2 is preferred to sufficiently compensate for both ends of the transmission band.

The number of repetitions M can be designated as a preset value. Over and over again, the temporary channel frequency response Yt (k) is closer to the ideal channel frequency response.

In another embodiment, if the number of repetitions M is not specified in advance and a threshold is specified and the specified threshold is exceeded, the repetition operation may be stopped.

은 m회 반복하여 구한 임시 채널 주파수 응답 Yt(k)을 말하고,

은 m번째 오차값이다. 즉 현재 임시 채널 주파수 응답 Yt(k)과 이전 임시 채널 주파수 응답 Yt(k)의 차이인

이 문턱값보다 작으면 반복을 중지할 수 있다. 또 다른 실시예로,

이면 반복 연산을 중지할 수 있다. 또 다른 실시예로, 문턱값 설정과 반복 횟수 설정을 조합하여 할 수 있다. here,

Is the temporary channel frequency response Yt (k) obtained by repeating m times,

Is the m-th error value. That is, the difference between the current temporary channel frequency response Yt (k) and the previous temporary channel frequency response Yt (k)

If it is less than this threshold, iteration can be stopped. In another embodiment,

, You can stop the iteration. In another embodiment, the threshold value setting and the repetition frequency setting may be combined.

There is no limitation on the method of determining whether the repetition operation is performed and various other methods may be used by those skilled in the art.

If the number of repetitions M has not been reached yet, the compensation channel frequency response Yc (k) is obtained (S160). The compensation channel frequency response Yc (k) (third channel frequency response) is shown in Equation 6, and is schematically shown in FIG. 5E.

The compensation channel frequency response Yc (k) is obtained by replacing a portion of the temporary channel frequency response Yt (k) with the initial channel frequency response Yi (k). That is, the frequency band in which the response value of the initial channel frequency response Yi (k) exists in the temporary channel frequency response Yt (k) is replaced with the response value of the initial channel frequency response Yi (k). In the remaining frequency bands, the response value of the temporary channel frequency response Yt (k) is maintained. Thus, the compensation channel frequency response Yc (k) includes the initial channel frequency response Yi (k).

After obtaining the compensation channel frequency response Yc (k), using the compensation channel frequency response Yc (k), it is repeated again from step S120 to obtain a new temporary channel frequency response Yt (k).

Briefly describing obtaining a new temporary channel frequency response Yt (k), an IFFT is first performed on the compensation channel frequency response Yc (k) to obtain a channel impulse response y _p (n). The channel impulse response y _p (n) is replaced by zero except for the window region T, thereby obtaining a zero-replaced channel impulse response y _zp (n). FFT is performed on the zero-substituted channel impulse response y _zp (n) to obtain a new temporary channel frequency response Yt (k).

When the repetition operation is completed by the number of repetitions M, the temporary channel frequency response Yt (k) is determined as the final channel response estimate (S170). That is, the temporary channel frequency response Yt (k) becomes the output of the channel estimator 280.

According to the present invention, the final channel response estimate is obtained by using the compensation channel frequency response including the initial channel frequency response from the initial channel frequency response obtained from the pilot symbol. The compensation channel frequency response Yc (k) maintains the initial channel frequency response Yi (k) in the transmission band and has a continuous value near its boundary. By determining the final channel response estimate using the compensation channel frequency response Yc (k), performance degradation of the channel estimator 280 near the boundary of the transmission band can be minimized.

6A to 6F are graphs showing signals obtained by channel estimation steps. This example performs channel estimation when the pilot symbols are limited to subcarriers 53 to 90 and transmitted.

6A shows an initial channel frequency response Yi (k) obtained using information of a pilot symbol. There is a response between the transmission bands 53 and 90.

FIG. 6B shows the channel impulse response y _p (n) obtained by performing IFFT on the initial channel frequency response Yi (k).

FIG. 6C shows the zero-replaced channel impulse response y _zp (n) obtained by replacing the channel impulse response y _p (n) with zero except for the predetermined window region T. FIG.

FIG. 6D shows the temporary channel frequency response Yt (k) obtained by performing FFT on the zero-substituted channel impulse response y _zp (n). It is the result obtained by repeating once (M = 1).

6E shows the compensation channel frequency response Yc (k) obtained by replacing a portion of the temporary channel frequency response Yt (k) with the initial channel frequency response Yi (k). That is, the initial channel frequency response Yi (k) is replaced with the frequency band between 53 and 90 in the temporary channel frequency response Yt (k).

Finally, FIG. 6F shows the temporary channel frequency response Yt (k) obtained by repeating IFFT and FFT again for the compensation channel frequency response Yc (k). It is the result obtained by repeating twice (M = 2). In order to obtain the temporary channel frequency response Yt (k) again, an IFFT is first performed on the compensation channel frequency response Yc (k) to convert the channel impulse response. Obtain the channel impulse response by zero-substituting the channel impulse response for the window region. FFT is performed on the zero-replaced channel impulse response to obtain a temporary channel frequency response.

7 is a graph illustrating channel response estimation results according to the number of repetitions. Referring to FIG. 7, it can be seen that as the number of repetitions increases, the channel estimation response approaches the ideal channel response.

8 is a graph showing a channel response estimation result according to the number of repetitions as a block error rate (hereinafter referred to as BLER) to signal-to-noise ratio (hereinafter referred to as SNR) of transmission data.

Referring to FIG. 8, it can be seen that as the number of repetitions increases, the BLER is gradually improved. As the number of iterations increases, channel estimation performance improves. However, when the number of repetitions is 4 or more times, the performance improvement effect is insignificant, which teaches that an appropriate number of repetitions is required according to the characteristics of the channel.

According to the present invention, the channel response estimation through the channel estimator can be closer to the actual channel response. Therefore, channel estimation with high precision is possible, and the overall efficiency of the communication system can be improved.

9 is a block diagram illustrating a channel estimator according to another embodiment of the present invention.

9, the channel estimator 380 includes a filter 382, an iteration determination unit 384, and a compensation generator 385.

The filter unit 382 receives an initial channel frequency response obtained from a pilot symbol, and receives a compensation channel frequency response to be described later. The filter unit 382 passes only the response of the frequency band preset for the initial channel frequency response or the compensation channel frequency response. The filter unit 382 may be a low pass filter that passes only a frequency response within a predetermined range. The filter unit 382 may design a low pass filter according to a preset frequency range using a finite impulse response (FIR) filter or an finite impulse response (IIR) filter.

In comparison with the embodiment of FIG. 3, the response limiter 282 acts like a low pass filter in the time domain by substituting zero for a response outside the window region. Since the response limiter 282 operates in the time domain, a first converter 281 for converting a frequency response into a time response is required at an input of the response limiter 282, and a time is output at the output of the response limiter 282. A second converter 283 is needed to convert the response into a frequency response. However, filter portion 382 performs low pass filtering directly in the frequency domain. Thus, no separate means for converting between the time domain and the frequency domain is needed.

Since the operations of the iteration determination unit 384 and the compensation generation unit 285 are the same as those of the embodiment of FIG. 3, description thereof is omitted.

The channel estimation technique described above may be used in various OFDM based communication systems. For example, an OFDM-based communication system may utilize frequency hopping. Frequency hopping refers to the transmission of data through different subbands at different time intervals. In an OFDM-based communication system utilizing frequency hopping, pilot symbols and data symbols may be transmitted on different subbands. The technical idea of the present invention can be applied to an OFDM-based communication system using frequency hopping as it is.

The channel estimation technique described above may be used as it is for various OFDM based multiple access techniques. For example, orthogonal frequency division multiplexing access (OFDMA) provides each user with a portion of the available subcarriers to implement multiple access. OFDM-TDMA (time division multiple access) uses all subcarriers for a time slot that a user presets. Multi-carrier code division multiplexing access (MC-CDMA) is based on OFDM and CDMA technologies.

The channel estimation technique described above discloses a single-output single-input (SISO) system in which a transmitter and a receiver each have one antenna, but the present invention can be applied to a multi-antenna system as it is. For example, it may be a multi-input single-output (MISO), single-input multi-output (SIMO), multi-input multi-output (MIMO) system. The MISO system has multiple transmit antennas and one receive antenna. The SIMO system has one transmit antenna and multiple receive antennas. MIMO has a plurality of transmit antennas and a plurality of receive antennas.

The channel estimation technique described above may be implemented by various means. For example, the channel estimator may be implemented in hardware, software or a combination thereof. (DSP), a programmable logic device (PLD), a field programmable gate array (FPGA), a processor, a controller, a microprocessor, and the like, which are designed to perform the above- , Other electronic units, or a combination thereof. In a software implementation, the channel estimator may be implemented as a module that performs the functions described above. The software may be stored in a memory unit and executed by a processor. The memory unit or processor may employ various means well known to those skilled in the art.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention. You will understand.

As described above, the present invention enables channel estimation with high precision. Therefore, the reliability of the communication system is increased.

According to the present invention, accurate channel estimation can be performed even when pilot symbols are transmitted only for a portion of the entire system bandwidth. In addition, accurate channel estimation is possible only with pilot symbols, which is efficient.

Claims (23)

Obtaining a first channel frequency response having a first frequency band from the pilot symbol; Obtaining a second channel frequency response having a second frequency band including the first frequency band; Obtaining a third channel frequency response in which the response of the frequency band corresponding to the first frequency band is replaced with the first frequency response in the second channel frequency response; And Obtaining a final channel response estimate using the third channel frequency response. The method of claim 1, Obtaining the second channel frequency response Obtaining a first channel impulse response from the first channel frequency response; Obtaining a zero-replaced second channel impulse response in which zero is substituted for a response other than a predetermined window area in the first channel impulse response; And Obtaining the second channel frequency response from the second channel impulse response. The method of claim 2, And the window area is larger than a maximum excess delay. The method of claim 1, After obtaining the third channel frequency response, Substituting the third channel frequency response with the first channel frequency response to obtain the third channel frequency response. The method according to claim 1 or 4, Obtaining a final channel response estimate from the third channel frequency response Obtaining a third channel impulse response from the third channel frequency response; And performing a Fourier transform on the zero-replaced response in which the zero-replacement response is replaced with a response other than a predetermined window area in the third channel impulse response to obtain the final channel response estimate. delete In the channel estimation method using a pilot symbol, Obtaining an initial channel frequency response from the pilot symbol; And Obtaining a final channel response estimate using the compensation channel frequency response comprising the initial channel frequency response, The compensation channel frequency response is, Fourier transforming a zero-replaced response that takes a response within a predetermined window region in the channel impulse response of the compensation channel frequency response, and then substituting the initial channel frequency response for M times (an integer of M≥1) Obtain channel estimation method. In the repeated channel estimation method using a pilot symbol, Obtaining an initial channel frequency response from the pilot symbol; Obtaining a temporary channel frequency response having a frequency band including the frequency band of the initial channel frequency response from the initial channel frequency response; Determining whether to repeat the operation of the temporary channel frequency response; And When the repetition is performed, a compensation channel frequency response obtained by substituting the initial channel frequency response into a frequency band corresponding to the frequency band of the initial channel frequency response among the frequency bands of the temporary channel frequency response is obtained, and from the compensation channel frequency response, Iterative channel estimation method comprising the step of obtaining a temporary channel frequency response. 9. The method of claim 8, And if the repetition does not proceed, making the new temporary channel frequency response the final channel response estimate. 9. The method of claim 8, Determining whether to repeat the operation of the temporary channel frequency response A channel estimation method for determining based on a preset number of repetitions. 9. The method of claim 8, Determining whether to repeat the operation of the temporary channel frequency response And estimating the difference between the temporary channel frequency response and the new temporary channel frequency response. A first conversion unit obtaining a channel impulse response from an initial channel frequency response or a compensation channel frequency response obtained from a pilot symbol; A response limiter for obtaining a zero-replaced channel impulse response that takes a response within a predetermined window area from the channel impulse response; A second converter for obtaining a temporary channel frequency response from the zero-replaced channel impulse response; A repetition determination unit that determines whether to repeat the temporary channel frequency response, and outputs the temporary channel frequency response as a final channel response estimate when the repetitive operation ends; And And a compensation generator for obtaining the compensation channel frequency response by substituting the initial channel frequency response in a frequency band corresponding to the frequency band of the initial channel frequency response in the temporary channel frequency response. An iteration determining unit that determines whether to repeatedly compute a temporary channel frequency response having a frequency band including a frequency band of the initial channel frequency response obtained from the pilot symbol; And And a compensation generator for obtaining a compensation channel frequency response obtained by substituting the initial channel frequency response in a frequency band corresponding to the frequency band of the initial channel frequency response in the temporary channel frequency response. The method of claim 13, A first conversion unit obtaining a channel impulse response from the compensation channel frequency response; A response limiter for obtaining a zero-replaced channel impulse response that takes a response within a predetermined window area from the channel impulse response; And And a second converter for obtaining the temporary channel frequency response from the zero-replaced channel impulse response. The method of claim 13, And a filter unit for filtering the compensation channel frequency response for a preset frequency domain to obtain the temporary channel frequency response. The method of claim 13, And the repetition determiner outputs the temporary channel frequency response as a final channel response estimate when the repetition operation ends. A channel estimation method in an OFDM based communication system, Extracting a pilot symbol to obtain an initial channel frequency response for a transmission band; Obtaining a channel impulse response from the initial channel frequency response; Taking a response within a window region from the channel impulse response to obtain a temporary channel frequency response having a frequency band wider than the transmission band; Obtaining a compensation channel frequency response by substituting the initial channel frequency response in a frequency band corresponding to the transmission band in the temporary channel frequency response; And Obtaining a final channel response estimate using the compensated channel frequency response. The method of claim 17, The final channel response estimation method is a channel estimation method in an OFDM-based communication system to obtain a Fourier transform of the response within a predetermined window region from the impulse response of the compensation channel frequency response. delete An antenna receiving a signal through a channel; A pilot extractor extracting a pilot symbol from the signal; And A channel estimator obtaining a compensation channel frequency response including the initial channel frequency response from the initial channel frequency response obtained from the pilot symbol, and obtaining a final channel response estimate of the channel using the compensation channel frequency response; The channel estimator, An iteration determining unit that determines whether to repeatedly calculate a temporary channel frequency response having a frequency band including the frequency band of the initial channel frequency response; And And a compensation generator for obtaining the compensation channel frequency response from the temporary channel frequency response. 21. The method of claim 20, The channel estimator A first conversion unit obtaining a channel impulse response from the initial channel frequency response or the compensation channel frequency response; A response limiter for obtaining a zero-replaced channel impulse response that takes a response within a predetermined window area from the channel impulse response; And And a second converter for obtaining the temporary channel frequency response from the zero-replaced channel impulse response. 21. The method of claim 20, The channel estimator And a filter unit for filtering the compensation channel frequency response to a preset frequency range to obtain the temporary channel frequency response. delete

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