JP2003069530A - Multicarrier cdma receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multicarrier CDMA receiver capable of keeping a reception signal quality and the accuracy of data demodulation in an excellent state even when fluctuations due to a frequency selective fading are fast. SOLUTION: This multicarrier CDMA receiver is provided with a first channel estimate section 103 and a second channel estimate section 104. The first channel estimate section 103 calculates a channel estimate after an interpolation in unit of subcarrier signal by using common pilot symbol of continuous plural slots, moreover, calculates the channel estimate after averaging in the direction of the frequency by averaging the channel estimate after the interpolation of each of subcarrier in the direction of the frequency. The second channel estimate section 104 calculates the channel estimate value corresponding to the number of repetition based on the data sequence applied re-decoding, re-modulating, and re-spreading processing to the decision data after error correction, each subcarrier signal after the channel fluctuation compensation, and the channel estimate.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a multi-carrier CDMA (Code Division Multiple Acces) as a communication system.
The present invention relates to a multi-carrier CDMA receiver adopting the s) method, and particularly to a multi-carrier CDMA used in a frequency selective fading environment such as mobile communication.
The present invention relates to a receiving device.

[0002]

2. Description of the Related Art A conventional multi-carrier CDMA receiver will be described below. An example of a transmitter / receiver of a mobile communication system that employs a multi-carrier CDMA system as a communication system is, for example, a document "Downlink Broadband Packet TD When Using Repeated Channel Estimation
-Characteristics of OFCDM, IEICE Technical Report RCS2
000-186 p.85-91 January 2001 ”. Hereinafter, the conventional technique described in the above document will be described with reference to the drawings.

FIG. 4 is a diagram showing the structure of a multicarrier CDMA transmitter. In FIG. 4, 200 is an encoding unit, 201 is a data modulation unit, 202 is a pilot symbol multiplexing unit, 203 is a serial / parallel conversion unit, 204 is a copying unit, and 205 is a copying unit.
-1, ..., 205-m are multipliers, 207 is another code multiplexing unit, and 208 is an IFFT (Inverse Fast F).
Ourier Transform) section, and 209 is a guard interval (GI) addition section. Note that FIG. 5 is a diagram showing a format of a transmission slot for each subcarrier, and the transmission slot is composed of a pilot symbol portion (known sequence) and a data portion.

In the multi-carrier CDMA transmission device, first, the coding unit 200 that receives binary data performs convolutional coding with a coding rate R = 1/2, and the data modulating unit 2
01 performs modulation processing according to a mapping rule corresponding to QPSK modulation. Since the pilot symbol multiplexing unit 202 that has received the output signal of the data modulation unit 201 generates the slots shown in FIG. 5 in subcarrier units,
N _p pilot symbols are placed before and after the slot, and N _d data symbols are placed in the slot.

The serial / parallel converter 203 converts the serial signal output from the pilot symbol multiplexer 202 into parallel symbols. The copy unit 204 performs a copy process of the received symbol. Multiplier 2
In 05-1 to 205-m, spreading based on the spreading factor SF is performed on the output of the copy unit 204 (multiplication of the spreading code and the output of the copy unit 204). In the other code multiplexing unit 207,
The symbols spread by other spreading codes are multiplexed. In the IFFT 208, the other code multiplexing unit 207
The output is converted to a quadrature multicarrier signal. The GI adding unit 209 adds a guard interval for each symbol output from the IFFT 208, and outputs the signal after the addition of the guard interval as a transmission signal.

FIG. 6 is a diagram showing the configuration of a conventional multicarrier CDMA receiver. In FIG. 6, 300 is a guard interval (GI) removing unit, and 301 is F
FT, 302 is a channel estimation unit, 303-
, ..., 303-m, 305-1, ..., 305-m are multipliers, 307-1, ..., 307-n are combiners, 309 is a parallel / serial conversion unit, 310
Is a data demodulation unit, 311 is a decoding unit, and 312
Is a re-encoding unit, 313 is a re-modulation unit, 314
Is a re-diffusion unit. Note that FIG. 7 is a diagram showing an example of an impulse response of a frequency selective fading transmission line in a mobile communication system. Frequency selective fading occurs when radio waves are reflected, diffracted, and scattered by surrounding buildings and topography, and the waves (multipath waves) arriving via a plurality of transmission paths interfere with each other.

In the multi-carrier CDMA receiver, first, the GI removing section 300, which receives a signal affected by frequency selective fading on the wireless communication path, removes the guard interval and outputs a signal continuous in symbol units. To do. Next, the FFT 301 performs Fourier transform processing to separate the received signal into each subcarrier signal component.

Channel estimating section 302 repeatedly performs channel estimation using the plurality of subcarrier signals separated as described above in the following procedure. First, the first time (1
The (second) channel estimation will be described. In channel estimation section 302, pilot symbol sections in slots are subjected to in-phase addition and then averaged to obtain a channel estimation value for each subcarrier according to the following equation (1).

[0009]

[Equation 1]

However, C_n(1) is the first subcarrier
Channel estimate for each_{n, 1}(I) is shown in FIG.
The first pilot symbol in the slot configuration of
Then Z _{n, 2}(I) shows the last pilot symbol
You Channel estimation value C obtained for each subcarrier
_n(1) is n + N centered on the nth subcarrier
_avgN-N from the th subcarrier_avgTh subcarriage
Channels obtained from adjacent subcarriers up to
And the n-th subcarrier
Averaged channel estimate X of_nFrom (1) according to the following equation (2)
Ask.

[0011]

[Equation 2]

However, N _c represents the total number of subcarriers.
Then, the channel estimation unit 302 calculates the compensation value w _n (1) for compensating the channel fluctuation due to the frequency selective fading based on the averaged channel estimation value obtained by the equation (2) by the following equation (3). ).

[0013]

[Equation 3]

After the first channel estimation by the channel estimation unit 302, the multipliers 303-1 to 303-m use the received channel variation compensation value w _n (1) to compensate the channel variation in subcarrier units. To do. Next, in the multipliers 305-1, ..., 305-m, # 0 to # SF-1 are applied to the signals after channel fluctuation compensation in subcarrier units.
Of the spread codes, and synthesizers 307-1 to 307-n
Then, the signals after the spreading code multiplication are combined to complete the despreading process. Next, the parallel / serial conversion unit 309 converts the despread signal, which is parallel data, into serial data. Next, the data demodulation unit 310 performs demodulation processing using the received serial data and outputs a soft decision value. Next, decoding section 311 performs Viterbi decoding on the received soft decision value and outputs a decision data symbol.

In the second and subsequent channel estimation, channel estimation is performed by adding the decision data symbols after error correction to the pilot symbols. Specifically, first, re-encoding section 312 re-encodes the Viterbi-decoded data symbol obtained based on the first channel estimation value. Next, the re-modulation unit 313 re-modulates the re-encoded data symbols. Next, the re-diffusion unit 3
In 14, the data after re-modulation is re-spread and the data sequence φ
_{Find n, q} (i). However, n represents a subcarrier number, and q (q = 2, 3, ...) Represents the number of repetitions.

The channel estimation section 302 removes the data modulation component by multiplying the corresponding received data symbol by the complex conjugate value φ _{n, q} ^* (i) of the data sequence, and then performs the in-phase addition of the pilot symbol section, Channel estimation value C _n (q) for each subcarrier when the number of repetitions is q
Is calculated according to the following equation (4).

[0017]

[Equation 4]

However, Z _n (i) represents the i-th received symbol of the n-th subcarrier group, and * represents a complex conjugate. Further, in the channel estimation unit 302, after obtaining the channel estimation value as described above, the averaged channel estimation value is calculated according to the following equation (5).

[0019]

[Equation 5]

Then, in the channel estimation unit 302, the channel fluctuation compensation value w _n necessary for compensating the channel fluctuation due to the frequency selective fading based on the averaged channel estimation value obtained by the equation (5). (Q) is calculated according to the following equation (6).

[0021]

[Equation 6]

Thereafter, the circuits after the multipliers 303-1 to 303-m operate in the same manner as after the first channel estimation, and finally generate the decision data symbol. further,
When iteratively estimating the channel, the re-encoding unit 312, the re-modulation unit 313, and the re-spreading unit 314 perform the processing recursively, and the channel fluctuation is calculated using the equations (4), (5), and (6). Calculate the amount of compensation.

[0023]

However, the above
The conventional multi-carrier CDMA receiver has the following problems.

In mobile communication, radio waves are reflected, diffracted, and scattered by surrounding buildings and topography, and a multipath wave that has passed through a plurality of transmission paths arrives at a mobile station. Then, these multipath waves interfere with each other, and frequency selective fading occurs in which the amplitude and phase of the received wave randomly change. Therefore, especially when the mobile station moves at high speed, the fluctuation due to the frequency selective fading becomes fast, so that in the channel estimation in the above-mentioned conventional multi-carrier CDMA receiver, the amplitude / phase fluctuation due to the fading is sufficient. However, there is a problem in that the received signal quality and the data demodulation accuracy deteriorate.

In the multi-carrier CDMA system, when the transmission signal from the base station is affected by frequency selective fading on the transmission line, a plurality of delayed waves exist depending on the transmission line condition. Therefore, there is also a problem that the signal reaching the mobile station is affected by multipath, interference occurs due to signals of other codes that are multiplexed and transmitted, and it becomes difficult to maintain good reception signal quality. there were.

Further, in the conventional multi-carrier CDMA receiving apparatus, when the channel estimation is repeatedly performed, the processing of re-encoding, re-modulation and re-spreading is performed, so that there is a problem that the signal processing scale becomes large. there were.

The present invention has been made in view of the above, and even when the mobile station moves at a high speed and the fluctuation due to the frequency selective fading becomes fast, the interference due to another code exists. Even in such a case, it is an object of the present invention to obtain a multi-carrier CDMA receiving device that can keep the received signal quality and the data demodulation accuracy excellent and can reduce the processing related to iterative channel estimation.

[0028]

[Means for Solving the Problems]
In order to achieve the object, in the multi-carrier CDMA receiver according to the present invention, the channel estimation value after interpolation is calculated using the common pilot symbols for a plurality of consecutive slots for each sub-carrier signal. Further, the channel estimation value after frequency interpolation is calculated by averaging the channel estimation values after interpolation for each subcarrier in the frequency direction (first channel estimation), and based on the channel estimation value. First channel estimation means for compensating for channel fluctuations of received data symbols in each subcarrier signal, and data obtained by performing re-encoding, re-modulation and re-spreading processing on decision data after despreading, demodulation and decoding processing. A sequence, each subcarrier signal after channel fluctuation compensation by the first channel estimation means, and a sequence calculated by the first channel estimation means. A channel estimation value corresponding to the number of repetitions is calculated based on the channel estimation value (the second and subsequent channel estimations), and then the first channel estimation means performs channel adjustment on the received data symbols after channel fluctuation compensation. And a second channel estimation means for performing fluctuation compensation.

Multicarrier CDM according to the next invention
In the A receiver, the second channel estimation means is
In order to perform channel fluctuation compensation from the second time onward, a channel estimation value calculated by averaging processing in the frequency direction for each subcarrier and a root mean square value calculated by averaging processing in the frequency direction for each subcarrier, Is used to calculate the channel estimation value.

Multicarrier CDM according to the next invention
In the A receiver, the second channel estimation means is
It is characterized in that the received data symbol is divided into a plurality of blocks to perform channel estimation and channel fluctuation compensation.

Multicarrier CDM according to the next invention
In the A receiver, the first channel estimation means is
After averaging in the frequency direction by performing channel estimation without using a pilot symbol in the rear part of the common pilot symbols for two consecutive slots and further averaging the channel estimation values for each subcarrier in the frequency direction. It is characterized in that the channel estimation value of is calculated.

Multicarrier CDM according to the next invention
In the A receiver, the first channel estimation means is
Channel estimation is performed by averaging common pilot symbols for two consecutive slots, and channel estimation values for each subcarrier are averaged in the frequency direction to calculate channel estimation values after frequency direction averaging. It is characterized by

Multicarrier CDM according to the next invention
In the A receiver, the channel estimation value after interpolation is calculated using the common pilot symbols for a plurality of consecutive slots for each subcarrier signal after despreading, and the interpolation interpolation is performed for each subcarrier. The channel estimation value after frequency direction averaging is calculated by averaging the subsequent channel estimation values in the frequency direction (first channel estimation), and based on the channel estimation value, spreading code multiplication for despreading is performed. First channel estimation means for compensating for channel fluctuations of received data symbols in a subsequent signal; a data sequence in which decision data after despreading, demodulation and decoding processing has been re-encoded and re-modulated; A signal after spreading code multiplication for despreading after channel fluctuation compensation by the first channel estimation means and a channel calculated by the first channel estimation means. A channel estimation value corresponding to the number of repetitions is calculated based on the estimation value (second and subsequent channel estimations), and then the first channel estimation means performs spread code multiplication for channel fluctuation compensation and despreading. Second channel estimation means for performing channel fluctuation compensation on the received data symbols.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a multicarrier CDMA receiver according to the present invention will be described in detail below with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1. FIG. 1 is a diagram showing a configuration of a first embodiment of a multicarrier CDMA receiving apparatus according to the present invention. In FIG. 1, 100 is a guard interval (GI) removing unit, 101 is an FFT, and 1
Reference numeral 02 is a channel estimation unit, 103 is a first channel estimation unit that performs the first channel estimation process, 104 is a second channel estimation unit that performs the second and subsequent channel estimation processes, 105-1, …, 105-m, 107-
1, ..., 107-m are multipliers, and 109-1 ,.
109-n is a synthesizer, 111 is a parallel / serial conversion unit, 112 is a data demodulation unit, 113
Is a decoding unit, 114 is a re-encoding unit, 115 is a re-modulation unit, and 116 is a re-spreading unit.

Since the processing on the transmitting side is basically the same as that of the conventional technique, its explanation is omitted. Also,
FIG. 2 is a diagram showing an example of a format of a transmission slot for each subcarrier. The transmission slot has a configuration in which two pilot portions exist with the data portion sandwiched therebetween.

Here, the operation of the multicarrier CDMA receiving apparatus of the first embodiment configured as described above will be explained in detail using the drawings.

In the multi-carrier CDMA receiving apparatus, first, the GI removing section 100, which receives a signal affected by frequency selective fading or the like on the wireless communication path, removes the guard interval and outputs a signal continuous in symbol units. To do. Next, the FFT 101 performs Fourier transform processing to separate the received signal into subcarrier signal components.

Channel estimation section 102 repeatedly performs channel estimation using the plurality of subcarrier signals separated as described above, in the following procedure. First, the first time (1
The (second) channel estimation will be described. In first channel estimation section 103, pilot symbol sections before and after the target slot are added in-phase for each subcarrier, and further averaged to calculate a channel estimation value for each subcarrier according to the following equation (7). To do.

[0040]

[Equation 7]

However, p _{n, 1} and p _{n, 2} are channel estimation values of the pilot part of the n-th subcarrier, and Z _{n, 1} (i) is of the target slot shown in FIG. Represents a pilot symbol that exists before, and Z _{n, 2} (i)
Represents a pilot symbol existing after the target slot.

Next, the first channel estimation unit 103 uses the channel estimation values p _{n, 1} and p _{n, 2} before and after the target slot obtained for each subcarrier to perform a primary interpolation on the target slot. Then, the channel estimation value after primary interpolation is calculated for each subcarrier. The channel estimation value V _n (k) after primary interpolation for each n-th subcarrier is calculated by the following equation (8), where N _d is the number of symbols in the data portion (k is the symbol number of the data portion). ).

[0043]

[Equation 8]

However, k = 0, 1, 2, ..., N _d −1, and Q ₁ and Q ₂ are respectively expressed by the following equation (9).

[0045]

[Equation 9]

Next, in the first channel estimation section 103, the channel estimation value V _n (k) after the primary interpolation of the nth subcarrier calculated as described above and the adjacent N
A channel estimation value calculated from _avg subcarriers is used to perform frequency-direction averaging processing, and a channel estimation value Y _n (1, k after frequency-direction averaging of the first n-th subcarrier is performed. ) Is calculated by the following equation (10) (where k is the symbol number of the data part).

[0047]

[Equation 10]

Then, in the first channel estimation section 103
Is the channel after averaging in the frequency direction calculated by equation (10).
Based on the estimate, the frequency selective fading
The nth subkey required to compensate for channel fluctuations.
Carrier channel fluctuation compensation value m _n(1, k) is given by the following equation (1
Calculate according to 1).

[0049]

[Equation 11]

After the first channel estimation by the first channel estimation unit 103, the multipliers 105-1 to 105-m receive the n-th channel fluctuation compensation value m.
Channel variation is compensated for each subcarrier using _n (1, k). The signal S _n (k) after channel fluctuation compensation for each subcarrier is expressed by the following equation (12). However,
Z _n (k) represents the kth received symbol of the nth subcarrier group.

[0051]

[Equation 12]

Next, the multipliers 107-1, ..., 107-
In m, the signal S _n (k) after channel fluctuation compensation in subcarrier units is multiplied by the spreading code, and the combiner 109
In -1 to 109-n, the signals after the spreading code multiplication are combined, and the despreading process is completed. Next, the parallel / serial conversion unit 111 converts the despread signal, which is parallel data, into serial data. Next, the data demodulation unit 112 performs demodulation processing using the received serial data and outputs a soft decision value. Next, the decoding unit 11
In 3, Viterbi decoding is performed on the received soft decision value and a decision data symbol is output.

In the second and subsequent channel estimation, channel estimation is performed by adding the decision data symbols after error correction to the pilot symbols. Specifically, first, re-encoding section 114 re-encodes the data symbol after Viterbi decoding obtained based on the first channel estimation value. Next, remodulation section 115 remodulates the recoded data symbols. Next, the re-diffusion unit 1
In 16, the data after re-modulation is re-spread and the data sequence φ
_{Find n, q} (i). However, n represents a subcarrier number, and q (q = 2, 3, ...) Represents the number of repetitions.

Next, in the second channel estimation section 104, the complex conjugate value φ _{n, q} ^* (i) of the data sequence is converted into the corresponding received data symbol (after channel fluctuation compensation in subcarrier units by the first channel estimation). By multiplying the signal S _n (k)) to remove the data modulation component, and then adding the absolute value of the channel estimation value for each subcarrier initially estimated, and calculating the time average value over N _d symbols. (See Expression (13)), the channel estimation value U _n (q) for each subcarrier in the case of the number of repetitions q is calculated.

[0055]

[Equation 13]

Next, the second channel estimation unit 104 calculates the root mean square value R _n (q) with respect to the channel estimation value U _n (q) of the n-th subcarrier according to the following equation (14). .

[0057]

[Equation 14]

Next, in the second channel estimation section 104, the channel estimation value U _{n of} the n-th subcarrier is _given.
(Q) and the channel estimation value calculated from the adjacent N _avg subcarriers are used to perform averaging processing in the frequency direction, and the averaging in the frequency direction after the second iteration (q = 2) is performed. The channel estimation value E _n (q) after conversion is given by
Calculated according to 5).

[0059]

[Equation 15]

Also, in the second channel estimation section 104,
The root mean square value R _n (q) of the n-th subcarrier
And 2 calculated from the adjacent N _avg subcarriers
The averaging process in the frequency direction is performed using the root mean square value and the mean square value F _n (q) after the averaging in the frequency direction after the second iteration (q = 2) is calculated by the following equation (16). Calculate by

[0061]

[Equation 16]

Then, the second channel estimation section 104, based on the channel estimation value and the root mean square value after the frequency direction averaging calculated by the equations (15) and (16), channel fluctuation due to frequency selective fading. The channel fluctuation compensation value m _n (q, k) of the n-th sub-carrier required to perform the compensation is calculated according to the following equation (17). However, q represents the number of repetitions, and the number of repetitions q is 2 or more.

[0063]

[Equation 17]

After that, the circuits after the multipliers 105-1 to 105-m operate in the same manner as after the first channel estimation, and finally generate the decision data symbol. further,
When iterative channel estimation is performed, processing is performed recursively by the re-encoding unit 114, the re-modulation unit 115, and the re-spreading unit 116, and equations (13), (14), (15), (1
The channel fluctuation compensation amount is calculated using 6) and (17).

As described above, in the present embodiment,
The channel estimation is performed for the first time by using the common pilot for two slots for each subcarrier, and then the channel variation is compensated by fading. In addition, the second and subsequent channel estimations include a data sequence obtained by re-encoding, re-modulating, and re-spreading the error-corrected data, a received data symbol after channel fluctuation compensation by the first channel estimation, and a first-time channel estimation. The absolute value (that is, the amplitude value) of the channel estimation value for each subcarrier by the channel estimation of 1) is used. The second and subsequent channel fluctuation compensations are performed on the received data symbols after the channel fluctuation compensation by the first channel estimation. By this means, it is possible to accurately compensate for channel fluctuations that could not be eliminated at the first time, and thus it is possible to obtain good data demodulation accuracy and received signal quality.

Further, in the present embodiment, the second and subsequent channel fluctuation compensations are calculated using the channel estimation value and the root mean square value after frequency averaging for each subcarrier. As a result, MMSE (Minimum Mean S
quare error) The despreading synthesis process can be performed according to the standard. In addition, even in a situation where interference increases due to an increase in the number of code multiplexes, good received signal quality can be obtained.

In this embodiment, the case where convolutional coding is adopted as the error correction method has been described.
Not limited to this, for example, the same effect can be obtained even when a turbo code is used.

Embodiment 2. The multicarrier CDMA receiving apparatus according to the second embodiment differs from the multicarrier CDMA receiving apparatus according to the first embodiment described above in the operation of second channel estimation section 104. Here, the first embodiment
The operation of the second channel estimation unit 104 different from that will be described in detail with reference to FIG.

In the second and subsequent channel estimations in the multicarrier CDMA receiving apparatus of the present embodiment, channel estimation is performed by adding the decision data symbols after error correction to the pilot symbols. Specifically, first, re-encoding section 114 re-encodes the data symbol after Viterbi decoding obtained based on the first channel estimation value. Next, remodulation section 115 remodulates the recoded data symbols. Next, the re-spreading unit 116 re-spreads the re-modulated data and outputs the data series φ.
_{Find n, q} (i). However, n represents a subcarrier number, and q (q = 2, 3, ...) Represents the number of repetitions.

Next, in second channel estimation section 104, the complex conjugate value φ _{n, q} ^* (i) of the data sequence is converted into the corresponding received data symbol (after channel fluctuation compensation for each subcarrier by the first channel estimation). The signal S _n (k)) is multiplied to remove the data modulation component, and then the absolute value of the channel estimation value for each subcarrier initially estimated is added to calculate the time average value over N _d / N _b symbols. By doing (see equation (18)), the channel estimation value U _{n, h} (q) for each subcarrier in the case of the number of repetitions q
To calculate. However, N _b represents the number of blocks for performing the channel estimation value calculation processing by dividing N _d symbols into a predetermined number of blocks.

[0071]

[Equation 18]

Note that h is a block number (h = 0, 1,
2, ..., N _b −1). Further, according to the following equation (19), the channel estimation value U of the nth subcarrier is calculated.
_The root mean square value R _{n, h} (q) for _{n, h} (q) is calculated.

[0073]

[Formula 19]

Next, in the second channel estimation section 104, the channel estimation value U of the nth subcarrier is obtained.
The averaging process in the frequency direction is performed using _{n, h} (q) and the channel estimation value calculated from the adjacent N _avg subcarriers, and the number of repetitions after the second (q = 2) The frequency direction averaged channel estimation value E _{n, q} (q) is calculated by the following equation (20).

[0075]

[Equation 20]

In the second channel estimation section 104,
The root mean square value R _{n, h} (q) of the n-th subcarrier
And 2 calculated from the adjacent N _avg subcarriers
The mean value in the frequency direction is used to calculate the mean square value F _{n, h} (q) after averaging in the frequency direction after the second iteration (q = 2). 21).

[0077]

[Equation 21]

Then, the second channel estimation unit 104, based on the channel estimation value and the root mean square value after frequency direction averaging calculated by the equations (20) and (21), channel fluctuation due to frequency selective fading. The channel fluctuation compensation value m _{n, h} (q, i) of the n-th sub-carrier required to perform the compensation is calculated according to the following equation (22).
However, q represents the number of repetitions, and the number of repetitions q is 2 or more. Further, i is 0, 1, 2, ..., N _d / N _b −1.

[0079]

[Equation 22]

Next, in the multipliers 105-1 to 105-m, the channel fluctuation compensation value m _{n, h} (q, i) is used to compensate the channel fluctuation for each subcarrier. Here, the signal S _n (k) after channel fluctuation compensation is made so as to correspond to the received data symbol number k = N _d / N _b · h + i.
Is calculated using the following equation (23). Where Z _n (k)
Represents the kth received symbol of the nth subcarrier group.

[0081]

[Equation 23]

As described above, in the present embodiment,
In the second and subsequent channel estimations, the data symbol portion is divided into a plurality of blocks for channel estimation, and then channel fluctuations are compensated. By this means, the averaging time in channel estimation can be reduced, so that channel fluctuations can be accurately compensated even when channel fluctuations are fast due to fading or the like.

Third Embodiment FIG. 3 is a diagram showing the configuration of the third embodiment of the multicarrier CDMA receiving apparatus according to the present invention. In FIG. 3, 402 is a channel estimation unit, 403 is a first channel estimation unit that performs the first channel estimation process, 404 is a second channel estimation unit that performs the second and subsequent channel estimation processes, 405-
1, ..., 405-l, 407-1, ..., 407-l, 4
09-1, ..., 409-l, 411-1, ..., 411-
l is a multiplier. The same components as those in the first embodiment described above are designated by the same reference numerals and the description thereof will be omitted.

The multi-carrier CDMA receiving apparatus of this embodiment is provided with a multiplier for spreading code multiplication at the time of despreading before a multiplier for channel fluctuation compensation so that the spreading code multiplication at the time of respreading is performed. No processing is required. Here, only the operation different from that of the first embodiment will be described.

The GI removing section 100, which has received a signal affected by frequency selective fading or the like on the wireless communication path, removes the guard interval and outputs a signal continuous in symbol units. Next, the FFT 101 performs Fourier transform processing to separate the received signal into subcarrier signal components.

Multipliers 405-1 to 405-l, 407-
In 1 to 407-1, the received subcarrier signals are multiplied (despread) by the corresponding spreading codes # 0 to # SF-1. That is, the multipliers 405-1 to 40-4
The outputs of 05-l and 407-1 to 407-l are signals of only the modulation component.

Multipliers 409-1 to 409-l, 411-
In 1 to 411-1, channel fluctuation compensation is performed on the received signal of the modulation component in subcarrier units.

Further, when the second and subsequent (q = 2) iterative channel estimation is performed, the estimation processing is performed using the signal that is not multiplied by the spreading code, that is, the signal of only the modulation component, as described above. Therefore, the remodulation unit 115
The data sequence subjected to the re-modulation processing in (3) is output to channel estimation section 402.

As described above, in the present embodiment,
The channel estimation is performed after multiplying each received subcarrier signal by a spreading code for the despreading process in advance, that is, after the despreading process. By this means, in the second and subsequent channel estimations, the data sequence input to the channel estimation unit may be the re-modulated data sequence, so that re-spreading processing can be omitted.

Fourth Embodiment In the multicarrier CDMA receiving apparatus according to the fourth embodiment, first channel estimating section 10
3 performs channel estimation without using the rear pilot symbols. In the present embodiment, only the operation of first channel estimation section 103 different from the above-described first embodiment will be explained.

The first channel estimation section 103 uses the channel estimation values p _{n, 1} and p _{n, 2} created based on the pilot symbols before and after the target slot obtained for each subcarrier, to determine the target slot. Linear interpolation for
A channel estimation value after primary interpolation for each subcarrier is calculated. The channel estimation value V _n (k) after the primary interpolation for each n-th subcarrier is calculated by the following equation (24), where N _d is the number of symbols in the data portion (k is the symbol number of the data portion). ).

[0092]

[Equation 24]

However, k = 0, 1, 2, ..., N _d −1, and Q ₁ and Q ₂ are respectively expressed by the following equation (25).

[0094]

[Equation 25]

As described above, in the present embodiment,
Even if the pilot is not added to the rear part of the slot, the channel fluctuation due to fading can be accurately estimated.

Embodiment 5. In the multicarrier CDMA receiving apparatus according to the fifth embodiment, first channel estimating section 10
3 performs channel estimation by averaging pilot symbols before and after. In the present embodiment, only the operation of first channel estimation section 103 different from the above-described first embodiment will be explained.

First channel estimation section 103 obtains channel estimation values p before and after the target slot obtained for each subcarrier.
_{Using n, 1} and _{pn, 2} , primary interpolation is performed on the target slot, and the channel estimation value after primary interpolation for each subcarrier is calculated. The channel estimation value V _n (k) after the primary interpolation for each n-th subcarrier is calculated by the following equation (26), where N _d is the number of symbols in the data portion (k is the symbol number of the data portion). ).

[0098]

[Equation 26]

However, k = 0, 1, 2, ..., N _d −1, and Q ₁ and Q ₂ are respectively expressed by the following equation (27).

[0100]

[Equation 27]

As described above, in the present embodiment,
Even if the received signal level is very low,
Since the weights of the same size are given (averaged) to the pilot symbols before and after, the channel fluctuation due to fading can be accurately estimated.

[0102]

As described above, according to the present invention, the channel estimation is performed for the first time by performing the primary interpolation by using the common pilot for two slots for each subcarrier, and then the channel fluctuation compensation by the fading is performed. It was configured. In addition, the second and subsequent channel estimations include a data sequence obtained by re-encoding, re-modulating, and re-spreading the error-corrected data, a received data symbol after channel fluctuation compensation by the first channel estimation, and a first-time channel estimation. The absolute value (that is, the amplitude value) of the channel estimation value for each subcarrier by the channel estimation of 1) is used. And 2
The channel fluctuation compensation after the first time is configured to be performed on the received data symbol after the channel fluctuation compensation by the first channel estimation. By this means, it is possible to accurately compensate for channel fluctuations that cannot be completely eliminated at the first time, and thus it is possible to obtain good data demodulation accuracy and received signal quality.

According to the next invention, the second and subsequent channel fluctuation compensations are calculated by using the channel estimation value and the root mean square value after frequency averaging for each subcarrier. As a result, MMSE (Minimum Mean Square Erro
r) There is an effect that the despreading synthesis process can be performed according to the standard. Further, it is possible to obtain good received signal quality even in a situation where interference increases due to an increase in the number of code multiplexes.

According to the next invention, in the second and subsequent channel estimation, the data symbol portion is divided into a plurality of blocks for channel estimation, and then the channel fluctuation is compensated. By this means, it is possible to reduce the averaging time in channel estimation, so even if the channel fluctuation is fast due to fading or the like,
The effect is that the channel fluctuation can be compensated with high accuracy.

According to the next invention, since channel estimation is performed only with pilot symbols in the front part of the slot, channel fluctuation due to fading can be accurately performed even when no pilot symbol is added in the rear part of the slot. The effect is that can be estimated.

According to the next invention, weights of the same size are given (averaged) to the pilot symbols before and after, even when the received signal level is extremely lowered.
Since the configuration is adopted, there is an effect that the channel fluctuation due to fading can be accurately estimated.

According to the next invention, the channel estimation is performed after multiplying each received subcarrier signal by the spreading code for the despreading process in advance, that is, after the despreading process. As a result, in the second and subsequent channel estimations, the data sequence input to the second channel estimation means may be the re-modulated data sequence, so that the re-spreading process can be omitted. .

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of first, second, fourth, and fifth embodiments of a multicarrier CDMA receiver according to the present invention.

FIG. 2 is a diagram showing an example of a format of a transmission slot.

FIG. 3 is a diagram showing the configuration of a third embodiment of a multicarrier CDMA receiver according to the present invention.

FIG. 4 is a diagram showing a configuration of a multicarrier CDMA transmission device.

FIG. 5 is a diagram showing a format of a conventional transmission slot.

FIG. 6 is a diagram showing a configuration of a conventional multicarrier CDMA receiver.

FIG. 7 is a diagram showing an example of an impulse response of a frequency selective fading transmission line.

[Explanation of symbols]

100 guard interval (GI) removal unit, 101
FFT, 102,402 channel estimation unit, 103,4
03 first channel estimation unit, 104, 404 second channel estimation unit, 105-1, 105-m, 107-1,
107-m, 405-1, 405-l, 407-1, 4
07-l, 409-1, 409-l, 411-1, 41
1-l multiplier, 109-1, 109-n combiner, 1
11 parallel / serial conversion unit, 112 data demodulation unit, 113 decoding unit, 114 re-encoding unit, 115 re-modulation unit, 116 re-spreading unit.

Claims (6)

[Claims] 1. A multicarrier CDMA receiver used in a frequency selective fading environment, in which a channel estimation value after interpolation is calculated using a common pilot symbol for a plurality of consecutive slots for each subcarrier signal. Further, the channel estimation value after frequency interpolation is calculated by averaging the channel estimation values after interpolation for each subcarrier in the frequency direction (first channel estimation), and based on the channel estimation value. First channel estimation means for compensating for channel fluctuations of received data symbols in each subcarrier signal, and data obtained by subjecting decision data after despreading, demodulation and decoding processing to re-encoding, re-modulation and re-spreading processing. Sequence, each subcarrier signal after channel fluctuation compensation by the first channel estimation means, and the first channel estimation A channel estimation value according to the number of repetitions is calculated based on the channel estimation value calculated by the step (second and subsequent channel estimation), and then the received data symbol after channel fluctuation compensation by the first channel estimation means. And a second channel estimation means for performing channel fluctuation compensation on the multi-carrier CDMA receiver. 2. The second channel estimation means performs channel fluctuation compensation from the second time onward, so that the channel estimation value calculated by averaging processing in the frequency direction for each subcarrier and the frequency direction for each subcarrier are used. The multi-carrier CDMA receiving apparatus according to claim 1, wherein the channel estimation value is calculated using the root mean square value calculated by the averaging process of. 3. The multi-carrier CDMA reception according to claim 1, wherein the second channel estimation means divides the received data symbol into a plurality of blocks to perform channel estimation and channel fluctuation compensation. apparatus. 4. The first channel estimation means, among the common pilot symbols for two consecutive slots,
A channel estimation is performed without using a rear pilot symbol, and the channel estimation values after frequency direction averaging are calculated by averaging the channel estimation values for each subcarrier in the frequency direction. Item 6. The multi-carrier CDMA receiver according to item 1, 2 or 3. 5. The first channel estimation means averages the continuous pilot symbols for two consecutive slots to perform channel estimation, and further averages channel estimation values for each subcarrier in the frequency direction. 4. The multi-carrier C according to claim 1, 2 or 3, wherein the channel estimation value after averaging in the frequency direction is calculated.
DMA receiver. 6. A multicarrier CDMA receiver used in a frequency selective fading environment, in which channel estimation after interpolation is performed by using a common pilot symbol for a plurality of consecutive slots for each subcarrier signal unit after despreading. The channel estimation value after the frequency direction averaging is calculated by calculating the value and further averaging the channel estimation values after the interpolating for each subcarrier in the frequency direction (first channel estimation). Based on the value
First channel estimation means for compensating for channel fluctuations of received data symbols in a signal after spread code multiplication for despreading, and re-encoding and re-modulation processing for decision data after de-spreading, demodulation and decoding processing Based on the data sequence subjected to the above, a signal after spreading code multiplication for despreading after channel fluctuation compensation by the first channel estimation means, and a channel estimation value calculated by the first channel estimation means. , A channel estimation value according to the number of repetitions (second and subsequent channel estimations), and then for the received data symbol after spreading code multiplication for channel fluctuation compensation and despreading by the first channel estimation means. And a second channel estimation means for compensating for channel fluctuations.