JP2011199620A - Communication apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication apparatus capable of further improving channel estimation accuracy by suitably separating multiplexed reference signals.SOLUTION: A base station device 1 includes a channel estimation part 10 for estimating respective channel characteristics of a plurality of reception signals. The channel estimation part 10 subjects the transmission path frequency response of a reception multiple signal obtained by multiplexing a plurality of reference signals by cyclic shift to discrete cosine transform, and estimates the channel characteristics based on a transmission path time response obtained thereby.

Description

  The present invention relates to a communication apparatus having a function of estimating a channel by separating multiplexed reference signals.

In communication standards such as LTE (Long-Term Evolution), spatial scheduling (spatial division multiplexing) scheduling is performed in addition to time and frequency domain scheduling in uplink scheduling from a user terminal to a base station apparatus.
Spatial multiplexing scheduling is performed by multi-user MIMO (Multiple Input Multiple Output) in which the same frequency region is simultaneously allocated to a plurality of user terminals. For example, in LTE spatial multiplexing scheduling, the same resource block (RB; minimum unit for user allocation) is simultaneously allocated to a plurality of user terminals.

  When multi-user MIMO is performed in the uplink of LTE, reference signals of a plurality of user terminals are transmitted by code multiplexing using cyclic shift. Signals transmitted simultaneously from a plurality of user terminals are received by the base station apparatus as multiplexed signals. The base station apparatus separates the received multiplexed signal into signals for each user terminal and uses them for channel estimation for each user terminal (see Non-Patent Document 1, for example).

Takeshi Hattori, “OFDM / OFDMA Textbook”, First Edition, Impress R & D, Inc., 2008, p310-p312

  In order to separate the reference signal code-multiplexed by the cyclic shift, the base station apparatus normally converts the frequency response of the multiplexed reference signal to time by IDFT (Inverse Discrete Fourier Transform). Then, it is divided into transmission channel time responses for each user using a window function, DFT (Discrete Fourier Transform) is performed on the transmission channel time responses for each separated user, and the frequency is again obtained. By converting the signal into a region signal, the channel characteristics for each user are estimated.

  However, the channel characteristics estimated by separating signals multiplexed by the above method have a problem that distortion is likely to occur at both ends of the band. The reason is as follows. That is, when the transmission coefficient of the multiplexed reference signal is converted to the time domain by IDFT, a finite number of data is cut out and the period is extended, so the data becomes discontinuous at the boundary of the extended part, and higher order coefficients are generated As a result, it is conceivable that the delay spread in the data after conversion to the time domain becomes large. When the delay spread of data becomes large in this way, when data is divided into data for each user using a window function after that, the spread of data becomes larger than the window width, so that data outside the window width is lost. Therefore, it is considered that the estimated channel characteristics are distorted.

  As described above, if distortion occurs at both ends of the estimated channel characteristic band, it may adversely affect the demodulation processing using the channel characteristic. Therefore, such distortion is suppressed and channel estimation accuracy is further improved. The technology that can be used was envied.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a communication apparatus that can appropriately separate multiplexed reference signals and further improve channel estimation accuracy.

(1) The present invention provides a communication apparatus including a channel estimation unit that estimates channel characteristics of a plurality of received signals each including the plurality of reference signals from a received multiplexed signal in which a plurality of reference signals are multiplexed by cyclic shift. And the channel estimation unit performs channel characteristics of each of the plurality of received signals based on a channel time response of the received multiplexed signal obtained by performing discrete cosine transform on the channel frequency response of the received multiplexed signal. It is characterized by estimating.

(2) More specifically, the channel estimation unit performs a discrete cosine transform on a transmission channel frequency response of the received multiplexed signal to obtain a transmission channel time response of the received multiplexed signal, and the reception multiplexing A window processing unit that separates a transmission path time response of each of the plurality of reference signals from a transmission path time response of the signal, and an inverse discrete cosine transform of each of the separated transmission path time responses of the plurality of reference signals. A second converter that obtains a transmission path frequency response of each of the reference signals, and estimates channel characteristics of each of the plurality of received signals based on the transmission path frequency responses of the plurality of reference signals. Is preferred.

  According to the communication apparatus having the above configuration, the first conversion unit of the channel estimation unit converts the transmission channel frequency response of the received multiplexed signal into a transmission channel time response by discrete cosine transform, so that the period seen in the IDFT of the conventional example is used. It is possible to prevent a discontinuous portion of data at the time of expansion from occurring, and it is possible to prevent an increase in delay spread occurring in the transmission path time response of each of the plurality of reference signals in the transmission path time response of the received multiplexed signal. For this reason, it is possible to suppress data loss at the time of separation into transmission path time responses of a plurality of reference signals by the window processing unit, and as a result, it is possible to suppress distortion from occurring in channel characteristics to be estimated, Channel estimation accuracy can be increased.

(3) In addition, the present invention includes a channel estimation unit that estimates channel characteristics of a plurality of received signals including each of the plurality of reference signals from a received multiplexed signal obtained by multiplexing a plurality of reference signals by cyclic shift. A communication device, wherein the channel estimation unit estimates channel characteristics of each of the plurality of received signals based on a function to be processed obtained by performing even-symmetric extension processing on a transmission channel frequency response of the received multiplexed signal It is characterized by doing.

(4) More specifically, the channel estimator multiplies the transmission path frequency response of the received multiplexed signal by a complex constant based on a cyclic shift of each of the plurality of reference signals. A transmission frequency response of the received multiplexed signal obtained by shifting the transmission channel frequency response to the original frequency for each of the plurality of reference signals, and a transmission channel frequency response of the plurality of reference signals. An expansion processing unit that obtains the function to be processed for each of the plurality of reference signals by performing even-symmetric extension processing on the transmission line frequency response of the received multiplexed signal shifted to the frequency of A filter unit that obtains only transmission path frequency responses of the plurality of reference signals shifted to original frequencies from each of the functions to be processed, Based on the sending passage frequency response, it is preferable that estimates the plurality of received signals each channel characteristics.

According to the communication device having the above configuration, the extension processing unit of the channel estimation unit performs even-symmetrical extension processing on the transmission channel frequency response of the received multiplexed signal, so that the filter unit separates the transmission channel frequency responses of the plurality of reference signals. Data loss during acquisition can be suppressed. As a result, the channel characteristics to be estimated can be prevented from being distorted, and the channel estimation accuracy can be improved.
Further, in the communication apparatus of the present invention, since the transmission path frequency response of each of the plurality of reference signals is acquired in the frequency domain, it is not necessary to perform a process with a large amount of calculation such as IDFT, and the load on the apparatus can be reduced. can do.

(5) The plurality of extension processing units may include a group of the filter units before and after the frequency axis of the channel frequency response of the multiplexed signal obtained by shifting the channel frequency response of the plurality of reference signals to the original frequency. It is preferable to extend the data by the length of the delay, and in this case, data loss due to the filter unit can be more effectively suppressed while expanding with the minimum necessary data.

(6) Furthermore, since the transmission path time response acquired by the filter unit includes a delay component generated by passing through the filter unit, the channel estimation unit is acquired by the plurality of filter units. It is preferable to further include a plurality of removal units for removing delay components generated in the transmission channel frequency response portion of the plurality of reference signals, thereby acquiring the transmission channel time responses of the plurality of reference signals with higher accuracy. can do.

(7) Further, the present invention includes a channel estimation unit that estimates channel characteristics of a plurality of received signals each including the plurality of reference signals from a received multiplexed signal in which a plurality of reference signals are multiplexed by cyclic shift. In the communication apparatus, the channel estimation unit estimates channel characteristics of each of the plurality of received signals by performing processing based on even symmetry on a transmission channel frequency response of the received multiplexed signal. .
According to the communication apparatus having the above configuration, the channel estimation unit performs processing based on even symmetry with respect to the transmission channel frequency response of the received multiplexed signal, so that transmission of a plurality of reference signals from the transmission channel frequency response after the processing is performed. Data loss in separating and acquiring the road frequency response can be suppressed. As a result, the channel characteristics to be estimated can be prevented from being distorted, and the channel estimation accuracy can be improved.

(8) In addition, the present invention includes a channel estimation unit that estimates channel characteristics of a plurality of received signals each including the plurality of reference signals from a received multiplexed signal in which a plurality of reference signals are multiplexed by cyclic shift. The communication device, wherein the channel estimation unit multiplies a transmission path frequency response of the received multiplexed signal by a complex constant based on a cyclic shift of each of the plurality of reference signals. A multiplier that obtains a transmission path frequency response of the received multiplexed signal, the frequency response of which is shifted to the original frequency, for each of the plurality of reference signals, and a transmission path frequency response of the plurality of reference signals to the original frequency. Only the transmission line frequency response of the plurality of reference signals shifted to the original frequency is taken from each of the transmission line frequency responses of the received multiplexed signals that have been shifted. Comprising a filter unit for a, on the basis of the transmission channel frequency responses of the plurality of reference signals it is characterized by estimating the plurality of received signals each channel characteristics.

  According to the communication apparatus having the above configuration, since the transmission path frequency response of each of the plurality of reference signals is acquired in the frequency domain, it is not necessary to perform processing with a large amount of calculation such as IDFT, and the configuration can be simplified.

  According to the communication apparatus of the present invention, it is possible to favorably separate multiplexed reference signals and further improve channel estimation accuracy.

It is the schematic which shows the structure of the radio | wireless communications system in a LTE system. It is a block diagram which shows the principal part structure of the receiving system of a base station apparatus. It is a block diagram which shows the structure of a channel estimation part. It is a figure for demonstrating the aspect of the period expansion by discrete cosine transformation, (a) is the case of discrete cosine transformation, (b) has shown the case of IDFT. It is a figure for demonstrating the aspect when a transmission line frequency response is converted into a time domain, (a) shows an example in the case of discrete cosine transformation, (b) has shown an example in the case of IDFT. It is a block diagram which shows the structure of the channel estimation part with which the base station apparatus which concerns on 2nd embodiment of this invention is provided. (A) is the figure which showed typically an example of the to-be-processed function after performing even-symmetrical extension processing, (b) shows the transmission-line frequency response of one user terminal obtained by the LPF part. It is a schematic diagram. It is the graph showing the channel estimation result of each Example and the comparative example, (a-1) and (a-2) are Example 1, (b-1) and (b-2) are Example 2. , (C-1) and (c-2) are graphs showing the channel estimation results of the comparative example. It is an example which showed in the constellation map the data at the time of demodulating by the channel estimation result by Example 1 and the comparative example which were verified by the said simulation, (a) is based on Example 1, (b) is a comparative example. Shows that.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the present embodiment, LTE is described as an example of a communication method, but the present invention is not limited to this.

[First embodiment]
[1. Configuration of communication system]
FIG. 1 is a schematic diagram illustrating a configuration of a radio communication system in the LTE scheme. This wireless communication system includes a base station device 1 and user terminals 2a and 2b.
The base station apparatus 1 includes a plurality of antennas, and the base station apparatus 1 and the user terminals 2a and 2b have a function of performing multiuser MIMO transmission.

In this communication system, the downlink employs orthogonal frequency division division multiple access (OFDMA), and the uplink employs single carrier frequency division multiple access (SC-FDMA).
The LTE uplink frame is shared by a plurality of user terminals by frequency division division, and multiple access to the base station apparatus is possible. In addition to frequency multiplexing, spatial multiplexing is also performed.

In LTE, a minimum unit of user allocation called a resource block (RB) is set in a frame. As shown in FIG. 1, one resource block is 7 or 6 symbols × 12 subcarriers. In the uplink data channel of LTE, in the fourth symbol of one slot, all subcarriers are used as reference signals (Reference Signals) that are known signals, and are indicated by black circles in FIG. ing. Hereinafter, the reference signal is also referred to as a “pilot signal”.
Other symbols in one resource block are data signals (Data Signal), and are indicated by white circles in FIG.

Focusing on one resource block in which spatial multiplexing is performed, a plurality of user terminals 2a and 2b transmit simultaneously using signals x ₁ and x ₂ of the _one resource block.
Therefore, the base station apparatus 1 receives the transmitted signal _x 1, the _{signal x 2} is multiplexed (received signal y1, y2) a plurality of antennas 3 (3a, 3b), respectively. That is, the received signal _{y 1} by the antenna 3a is received, the received signal _{y 1x1} corresponding to the transmission signal _{x 1,} the received signal _{y 1x2} corresponding to the transmission signal _{x 2} are multiplexed, the received signal by the antenna 3b receives y ₂ is the received signal _{y 2x1} corresponding to the transmission signal _{x 1,} the received signal _{y 2x2} corresponding to the transmission signal _{x 2} are multiplexed.
The base station apparatus 1 acquires the received pilot signals included in the received signals y ₁ and y ₂ from the received signals y ₁ and y ₂ received by the plurality of antennas 3a and 3b, respectively. In this reception pilot signal, pilot signals corresponding to the transmission signals x ₁ and x ₂ are multiplexed.

User terminals 2a, 2b, for the pilot signal included in the transmitted signal _x 1, _{x 2,} and transmits the transmission signal _x 1, _{x 2} after performing cyclic shift processing. The cyclic shift process is a process of cyclically shifting the pilot signal by a different shift amount in the frequency axis direction for each user terminal, whereby the received pilot signal multiplexed and received by the base station apparatus 1 can be separated. It is.

Based on the multiplexed received pilot signal acquired from the received signals y ₁ and y ₂ , the base station apparatus 1 acquires the frequency responses of the received pilot signals corresponding to the transmitted signals x ₁ and x ₂ separately. Then, the channel estimation of the received signals corresponding to the transmission signals x ₁ and x ₂ is performed. The base station apparatus 1 separates the data signal for each user from the multiplexed other data signal using the estimated channel, and receives the received data signal x ^ ₁ , x corresponding to each user terminal 2a, 2b. ^ Is configured to obtain ₂ .

[2. Configuration of base station apparatus]
FIG. 2 is a block diagram illustrating a main configuration of the reception system of the base station apparatus 1.
A base station apparatus 1 as a communication apparatus according to the first embodiment of the present invention includes an FFT unit 5, a separation / equalization unit 6, an IDFT unit 7, a demodulation unit 8, in addition to a reception unit 4 to which an antenna 3 is connected. And a channel estimation unit 10. The base station apparatus 1 includes these units for each of the plurality of antennas 3 (3a, 3b) included in the base station apparatus 1.

The receiving unit 4 includes an amplifier, an A / D converter, and the like, and amplifies the received signal y received by the plurality of antennas 3 and converts the signal y (k) (k = 1, 2,...) Into a digital signal. .., L and L are output to the FFT unit 5 as the number of samples included in the sampling time.
The FFT unit 5 performs fast Fourier transform on the signal y (k), converts it from time domain to frequency domain data, demultiplexes subcarriers, etc., and separates and equalizes the data signal excluding the subcarriers. Output to. Further, the FFT unit 5 outputs the received pilot signal r (k) to the channel estimation unit 10 among the data signals converted into the frequency domain.

The channel estimation unit 10 estimates channel characteristics of received signals corresponding to the plurality of user terminals 2 a and 2 b based on the received pilot signal r (k), and outputs the estimation result to the separation / equalization unit 6.
Separating and equalizing unit 6, a plurality of user terminals 2a estimated by the channel estimation unit 10, 2b each of the received signals (e.g., if the received signal _{y 1,} the received signal _{y 1x1, y 1x2)} on the channel estimation result of Based on this, the frequency domain data signal given from the FFT unit 5 is separated into data signals for each user terminal, and equalization processing is performed.

  The data signal separated and equalized for each user terminal by the separation / equalization unit 6 is given to the IDFT unit 7, converted into time domain data, and demodulated by the demodulation unit 8.

[3. Configuration of channel estimation unit]
FIG. 3 is a block diagram illustrating a configuration of the channel estimation unit 10.
The channel estimation unit 10 includes a division unit 11, a DCT unit 12, a window processing unit 13, and a plurality of IDCT units 14, as shown in the figure.
The division unit 11 normalizes the received pilot signal r (k) given from the FFT unit 5 by dividing the basic pilot signal s (k), which is a known signal, and transmits the channel frequency of the received pilot signal r (k). A response h (k) is obtained.
The received pilot signal r (k) is a multiplexed signal obtained by multiplexing the pilot signals transmitted from each user terminal, and is represented by the following equation (1).

In Expression (1), h _n (k) (n = 1 to N) is a transmission path frequency response for each user terminal, N is the number of user terminals, and α _n is expressed by Expression (2) below. The shift amount in the frequency domain for each user terminal.
α _n = 2πn _cs / N (n _cs = 0, 1,..., N−1)
... (2)

  The division unit 11 divides the known basic pilot signal s (k) to obtain a transmission channel frequency response h (k) of the received pilot signal r (k) represented by the following equation (3).

  The DCT unit 12 as the first conversion unit performs discrete cosine transform (DCT: Discrete Cosine Transform) on the transmission channel frequency response h (k) of the received pilot signal r (k) obtained by the division unit 11. By converting to the time domain, a transmission path time response H (t) (k = 1, 2,... L, L is the number of samples included in the sampling time) shown in the following equation (4) is obtained.

As described above, the DCT unit 12 converts the frequency domain data into the time domain by expressing the frequency with a cosine function.
The window processing unit 13 performs window processing for separating the transmission channel time response H (t) of the received pilot signal r (k) obtained by the DCT unit 12 into the transmission channel time response of the received pilot signal for each user terminal. Do.
The transmission path time response H (t) of the received pilot signal r (k) is expressed by the following equation (5).

In the above equation (5), T is the symbol length.
The transmission channel time response H _n (t) (n = 1,... N) of the received pilot signal for each user terminal, which is the transmission channel time response of each of the plurality of reference signals, is expressed by the above equation (5). In this way, they are arranged at intervals of “T / N” in the time axis direction.
From the transmission channel time response H (t) of the received pilot signal r (k), the window processing unit 13 transmits the transmission channel time response H _n of the received pilot signal for each user terminal arranged in the time axis direction as described above. By cutting out (t) (hereinafter, also simply referred to as transmission path time response H _n (t)), it is separated into transmission path time responses H _n (t) for each user terminal.

Further, the window processing unit 13 calculates an offset amount in the time axis direction (“nT / N” in the above equation (5)) for each transmission path time response H _n (t) for each separated user terminal. By removing, the process of returning to the original position from the position (in the time axis direction) shifted by the cyclic shift process is also performed.

The window processing unit 13 outputs the transmission path time response H _n (t) for each separated user terminal to the IDCT unit 14.
The IDCT unit 14 as the second conversion unit converts the transmission channel time response H _n (t) of the user terminal into a frequency domain by performing inverse discrete cosine transform (IDCT: Inverse Discrete Cosine Transform). The transmission channel frequency response h _n (k) of the received pilot signal for each user terminal shown in (6) is obtained.

Each IDCT unit 14 separates the channel frequency response h _n (k) of the received pilot signal for each user terminal obtained as described above as the estimation result of the channel characteristics of the received signal corresponding to each user terminal. Output to the equalization unit 6.

According to the base station apparatus 1 having the above configuration, the DCT unit 12 of the channel estimation unit 10 performs transmission line time response h (k) of the multiplexed received pilot signal r (k) by means of discrete cosine transform. Since the response is converted into the response H (t), it is possible to prevent the occurrence of a discontinuous portion of the data at the time of the period extension seen in the IDFT of the conventional example, and the transmission path time response of the received pilot signal r (k). It is possible to prevent the delay spread occurring in the transmission path time response H _n (t) of each received pilot signal for each user terminal from increasing in H (t).

FIGS. 4A and 4B are diagrams for explaining a mode of period extension by discrete cosine transform. FIG. 4A shows a case of discrete cosine transform, and FIG. 4B shows a case of IDFT.
IDFT is an operation for performing conversion to the time domain by applying discrete-time Fourier transform to a countless infinite number of signal sequences obtained by periodically extending an original frequency domain signal whose data length is L. For this reason, as shown in FIG. 4B, data tends to be discontinuous at the boundary of the extended portion. This discontinuity causes an increase in higher-order coefficients and causes a delay spread after time domain conversion to be increased.
On the other hand, the discrete cosine transform is equivalent to applying the discrete Fourier transform to the signal generated by extending the original function signal whose data length is L to be even symmetric at the boundary point. is there. Therefore, in the discrete cosine transform, data continuity is maintained at the boundary of the extended portion as shown in FIG.
Due to the continuity at the boundary of the extended portion, the discrete cosine transform has a characteristic of concentrating signal components on the low frequency side. Accordingly, it is possible to suppress the delay spread in the data after being converted into the time domain.

FIGS. 5A and 5B are diagrams for explaining an aspect when the transmission line frequency response is converted into the time domain. FIG. 5A is an example in the case of discrete cosine transform, and FIG. 5B is an example in the case of IDFT. Show. In the figure, the horizontal axis represents time and the vertical axis represents power. Further, FIG. 5 shows data of two adjacent user terminals, which are drawn separately by black square marks and white square marks.
In the figure, in the case of discrete cosine transform, the spread in the time axis direction is smaller than in the case of IDFT, and the data of one user terminal falls within the window width range. On the other hand, in the case of IDFT, the spread in the time direction is large, and there is a signal having a relatively large value at a position exceeding the window width, and data located outside the window width is not acquired and lost. It becomes.

As described above, according to the present embodiment, since the delay spread in the data after being converted into the time domain can be suppressed to a small value, the transmission time response H _n (t) for each user terminal by the window processing unit 13. In the separation, the data portion can be prevented from spreading beyond the window width in the window processing, and data loss can be suppressed. As a result, distortion in the estimated channel characteristics can be suppressed, and the channel estimation accuracy can be increased.

Further, in this embodiment, when the transmission channel frequency response h (k) of the multiplexed received pilot signal r (k) is converted into the transmission channel time response H (t) by discrete cosine transform, FIG. As shown, a signal having a power lower than a predetermined threshold may be regarded as noise and removed. In this case, the influence of noise included in the data signal can be suppressed.
Note that the configuration in which a signal having power less than or equal to the predetermined threshold is regarded as noise and removed can also be used in channel estimation by IDFT.

[Second Embodiment]
FIG. 6 is a block diagram illustrating a configuration of the channel estimation unit 10 included in the base station device 1 according to the second embodiment of the present invention.
The channel estimation unit 10 of the present embodiment includes a division unit 11, a multiplication unit 21, an extension processing unit 22, an LPF (low-pass filter) 23, and a delay component removal unit 24.
The division unit 11 is multiplexed by dividing the basic pilot signal s (k), which is a known signal, from the received pilot signal r (k) given from the FFT unit 5 as in the first embodiment. A transmission channel frequency response h (k) of the received pilot signal r (k) is obtained.

The multiplier 21 calculates the shift amount (representing a complex constant e ^−jαNk ) based on the cyclic shift of each pilot signal set for each user terminal, and the transmission channel frequency response h (k) of the received pilot signal r (k). ) To obtain a transmission channel frequency response h _n ′ (k) obtained by shifting the transmission channel frequency response h _n (k) of each user terminal to the original frequency.
The multiplier 21 obtains the transmission channel frequency response h _n ′ (k) shifted to the original frequency corresponding to each received pilot signal of each user terminal.

The extension processing unit 22 causes the multiplication unit 21 to shift the transmission channel frequency response h _n (k) (hereinafter also simply referred to as transmission channel frequency response h _n (k)) of the received pilot signal of the user terminal to the original frequency. The even-numbered symmetric expansion processing is performed on the transmission channel frequency response h _n ′ (k), and the processed function that has been subjected to the even-symmetrical expansion processing is obtained for each user terminal.
FIG. 7A is a diagram schematically illustrating an example of the function to be processed h _n ″ (k) after the even symmetric extension processing is performed.

As shown in the figure, the function to be processed h _n ″ (k) has data D1 constituting the transmission line frequency response h (k) and extension data D2 and D3 arranged before and after the frequency axis. ing. The extension data D2 and D3 are provided so as to be line-symmetric with the data D1 with respect to the boundary with the data D1, and are even-symmetric with respect to the data D1.

The extension data D2 and D3 are provided so as to have the length of the group delay of the LPF 23. In the present embodiment, as will be described later, the LPF 23 is configured by an FIR (Finite Impulse Response) filter whose group delay length is ½ the tap length, and the extension data D2 and D3 are the tap lengths of the LPF 23. It is provided so that it may be 1/2. Therefore, when each element constituting the data D1 (transmission path frequency response h (k)) is expressed by the following formula (7),
Transmission path frequency response h (k) = [x (1), x (2),..., X (L)]
... (7)
Elements constituting the processed function processed function h _n ″ (k) obtained by subjecting the transmission line frequency response h (k) to the even symmetric extension processing can be expressed as the following formula (8).
Processed function h _n ″ (k) = [x (M / 2), x ((M / 2) −1),.
..., x (1), x (1), ..., x (L), x (L-1), ...
..., x (L- (M / 2) -1)]
... (8)

In the above formula (8), M is the tap length of the LPF 23.
In the above formula (8), the parts “x (M / 2), x ((M / 2) −1),..., X (1)” are the parts of the extension data D2, The part of “x (L−1),..., x (L− (M / 2) −1)” is the part of the extension data D3.

The LPF 23 is constituted by, for example, an FIR filter, and the transmission frequency response h _n () of the user terminal shifted to the original frequency from the processed function h _n ″ (k) obtained by the extension processing unit 22. k) has a function to acquire only.
That is, the object to be processed function h _{n ''} (k), since the transmission channel frequency response h _n of the one user terminal _(k) is shifted to the original frequency, passed through this part only, of the other By setting the cut-off value of the LPF 23 so as not to pass the portion, the LPF 23 can acquire only the transmission channel frequency response h _n (k) of the user terminal shifted to the original frequency.

The delay component removing unit 24 has a function of removing a delay component inevitably generated in the transmission channel frequency response h _n (k) of each user terminal obtained by the LPF 23.
FIG. 7B is a schematic diagram showing the transmission path frequency response h _n (k) of one user terminal obtained by the LPF 23. As shown in the figure, there is a delay component generated by passing through the LPF 23 on the low frequency side of the data d1 constituting the transmission line frequency response h _n (k) of one user terminal. This delay component generally occurs with a length corresponding to the tap length of the LPF 23, and is an element constituting the transmission path frequency response h _n (k) of one user terminal including the delay component after passing through the LPF 23. Is represented by the following formula (9).
Transmission path frequency response h _n (k) of one user terminal (including delay component) =
[H _n (1), h _n (2),..., H _n (L + M)]
... (9)

Further, transmission channel frequency response h _n of the one user terminal obtained by removing the delay component from the equation (9) transmission channel frequency response h _n of the one user terminal shown in _{(k) (k)} is the following formula (10) expressed.
Channel frequency response h _n (k) of one user terminal =
[H _n (M + 1), h _n (M + 2),..., H _n (M + L)]
... (10)

As described above, the present embodiment includes the delay component removing unit 24 that removes the delay component included in the transmission channel frequency response h _n (k) of one user terminal after passing through the LPF 23. The transmission path time response h _n (k) for each terminal can be acquired with higher accuracy.
As described above, the channel estimation unit 10 of the present embodiment obtains the transmission channel frequency response h _n (k) of the received pilot signal for each user terminal obtained by removing the delay component by the delay component removal unit 24, The estimation result of the channel characteristics of the received signal corresponding to each user terminal is output to the separation / equalization unit 6.

According to the base station apparatus 1 having the above configuration, the extension processing unit 22 of the channel estimation unit 10 performs the even symmetric extension processing on the transmission channel frequency response h (k) of the received pilot signal r (k). and it is possible to suppress the data loss at the time of obtaining separate transmission channel frequency responses h _n for each user terminal _(k) by the LPF 23. As a result, distortion in the estimated channel characteristics can be suppressed, and the channel estimation accuracy can be increased.
Further, in the base station apparatus 1 of the present embodiment, since the transmission path frequency response h _n (k) for each user terminal is acquired in the frequency domain, there is no need to perform processing with a large amount of calculation such as IDFT, etc. It can be set as the structure which can reduce the load with respect to.

  Further, in the present embodiment, the expansion processing unit 22 extends the even symmetrical expansion processing by the length of the group delay of the LPF 23 (extension data D2, D3). Data loss due to the LPF 23 can be more effectively suppressed.

  The present invention is not limited to the above embodiments. In each of the above embodiments, the case where the communication apparatus of the present invention is applied to the base station apparatus is illustrated, but it can also be applied to the user terminal side.

  In the second embodiment, the channel estimation unit 10 includes the division unit 11, the multiplication unit 21, the extension processing unit 22, the LPF 23, and the delay component removal unit 24. Of these, the channel estimator 10 can be configured by a form in which the extended processor 22 is omitted, that is, the divider 11, the multiplier 21, the LPF 23, and the delay component remover 24.

In this case, the transmission channel frequency response h _n ′ (k) obtained by the multiplication unit 21 and shifted to the original frequency for each received pilot signal of each user terminal is output to the LPF 23 as it is.
The LPF 23 acquires only the transmission channel frequency response h _n (k) of the user terminal shifted to the original frequency from the transmission channel frequency response h _n ′ (k) shifted to the original frequency. The delay component removing unit 24 removes a delay component included in the transmission path frequency response h _n (k) of each user terminal obtained by the LPF 23.
As described above, the channel estimation unit 10 configured as described above uses the channel frequency response h _n (k) of the received pilot signal for each user terminal as the estimation result of the channel characteristics of the received signal corresponding to each user terminal. Obtainable.

  According to the base station apparatus including the channel estimation unit 10 having the above-described configuration, the transmission path frequency response of each of the plurality of received pilot signals can be acquired in the frequency domain, and thus processing with a large amount of computation such as IDFT is performed. There is no need and a simple configuration can be obtained.

[About confirmation of effect]
The inventor performs a simulation for channel estimation by separating multiplexed received pilot signals by the base station apparatus according to each of the above embodiments, and verifies the effect as compared with the case where channel estimation is performed by a conventional method. Went.
As a comparative example, as described in the above-described conventional example, the transmission channel frequency response of the multiplexed received pilot signal is converted into a transmission channel time response by IDFT, separated, and then converted to the frequency domain by DFT. A base station apparatus that performs channel estimation was used.
As an example of the present invention, the base station apparatus 1 having the DCT unit and the IDCT unit shown in the first embodiment is used as Example 1, and the LPF unit shown in the second embodiment is provided. The base station apparatus 1 was set as Example 2.

  As a verification method, a received pilot signal in which pilot signals for two user terminals are multiplexed is used under the same conditions in the first and second embodiments and the comparative example, and then a simulation for channel estimation is performed. The comparison was made by representing the estimation results obtained by the simulation in a graph.

FIG. 8 is a graph showing the channel estimation results of each example and comparative example. (A-1) and (a-2) are Example 1, (b-1) and (b-2) are Example 2, (c-1) and (c-2) are graphs showing the channel estimation results of the comparative example. In FIG. 7, the horizontal axis indicates the frequency, and the vertical axis indicates the amplitude. The channel estimation result of one user terminal is shown on the left side of the drawing, and the channel estimation result of the other user terminal is shown on the right side.
In the figure, it can be seen that distortion occurs at both ends of the band when the channel estimation result according to the comparative example is seen.
On the other hand, in the channel estimation results according to the first and second embodiments, it can be seen that the channel estimation is performed with high accuracy without the distortion seen in the comparative example.

FIG. 9 is an example in which data when demodulated based on channel estimation results according to Example 1 and the comparative example verified by the above simulation are shown in a constellation map, (a) is according to Example 1, and (b). Indicates a comparative example.
In the comparative example, each data is scattered around each bit position, whereas in the first example, each data is accurately demodulated at each bit position.
Thus, under the conditions in this verification, it has become clear that the base station apparatus 1 according to the present embodiment can improve the channel estimation accuracy and the demodulation accuracy as compared with the conventional method.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Base station equipment (communication equipment)
10 channel estimation unit 12 DCT unit (first conversion unit)
13 Window processing unit 14 IDCT unit (second conversion unit)
21 Multiplying unit 22 Extended processing unit 23 LPF (filter unit)
24 Delay component removal unit (removal unit)

Claims (8)

A communication apparatus comprising a channel estimation unit that estimates channel characteristics of a plurality of received signals including each of the plurality of reference signals from a received multiplexed signal obtained by multiplexing a plurality of reference signals by cyclic shift,
The channel estimation unit estimates channel characteristics of each of the plurality of received signals based on a transmission channel time response of the received multiplexed signal obtained by performing discrete cosine transform on the channel frequency response of the received multiplexed signal. A communication device characterized by the above. The channel estimation unit
A discrete cosine transform of a transmission line frequency response of the received multiplexed signal, and a first conversion unit for obtaining a transmission path time response of the received multiplexed signal;
A window processing unit that separates a transmission path time response of the received multiplexed signal into a transmission path time response of each of the plurality of reference signals;
A second transform unit that performs inverse discrete cosine transform on each of the separated channel time responses of the plurality of reference signals to obtain a channel frequency response of each of the plurality of reference signals, and
The communication apparatus according to claim 1, wherein channel characteristics of each of the plurality of received signals are estimated based on transmission path frequency responses of the plurality of reference signals. A communication apparatus comprising a channel estimation unit that estimates channel characteristics of a plurality of received signals including each of the plurality of reference signals from a received multiplexed signal obtained by multiplexing a plurality of reference signals by cyclic shift,
The channel estimation unit estimates channel characteristics of each of the plurality of received signals based on a function to be processed obtained by performing even-symmetric extension processing on a transmission line frequency response of the received multiplexed signal. Communication device. The channel estimation unit
The transmission channel frequency response of the plurality of reference signals is shifted to the original frequency by multiplying the transmission channel frequency response of the received multiplexed signal by a complex constant based on the cyclic shift of each of the plurality of reference signals. A multiplier for obtaining a transmission line frequency response of the received multiplexed signal for each of the plurality of reference signals;
The function to be processed for each of the plurality of reference signals is obtained by performing even-symmetric extension processing on the channel frequency response of the received multiplexed signal obtained by shifting the channel frequency responses of the plurality of reference signals to the original frequency. An extension processing unit;
A filter unit that obtains only the transmission channel frequency response of the plurality of reference signals shifted to the original frequency from each of the functions to be processed for each of the plurality of reference signals,
The communication apparatus according to claim 3, wherein channel characteristics of each of the plurality of received signals are estimated based on transmission path frequency responses of the plurality of reference signals.   The plurality of extension processing units have a group delay length of the filter unit before and after the frequency axis of the channel frequency response of the multiplexed signal obtained by shifting the channel frequency responses of the plurality of reference signals to the original frequency. The communication apparatus according to claim 4, wherein the communication apparatus is expanded by a certain amount.   The communication device according to claim 4, wherein the channel estimation unit further includes a removal unit that removes a delay component generated in transmission path frequency responses of the plurality of reference signals acquired by the plurality of filter units. A communication apparatus comprising a channel estimation unit that estimates channel characteristics of a plurality of received signals including each of the plurality of reference signals from a received multiplexed signal obtained by multiplexing a plurality of reference signals by cyclic shift,
The communication apparatus, wherein the channel estimation unit estimates a channel characteristic of each of the plurality of received signals by performing a process based on even symmetry on a transmission path frequency response of the received multiplexed signal. A communication apparatus comprising a channel estimation unit that estimates channel characteristics of a plurality of received signals including each of the plurality of reference signals from a received multiplexed signal obtained by multiplexing a plurality of reference signals by cyclic shift,
The channel estimation unit
The transmission channel frequency response of the plurality of reference signals is shifted to the original frequency by multiplying the transmission channel frequency response of the received multiplexed signal by a complex constant based on the cyclic shift of each of the plurality of reference signals. A multiplier for obtaining a transmission line frequency response of the received multiplexed signal for each of the plurality of reference signals;
Only the transmission channel frequency response of the plurality of reference signals shifted to the original frequency from the transmission channel frequency response of the received multiplexed signal obtained by shifting the transmission channel frequency response of the plurality of reference signals to the original frequency. A filter unit for obtaining
A communication apparatus that estimates channel characteristics of each of the plurality of received signals based on transmission path frequency responses of the plurality of reference signals.