JP2005033638A - Multicarrier cdma interference canceller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology of solving problems of the effect of asynchronous reception on a reception section side and characteristic deterioration due to an inter-code interference at demodulation so as to extend application scopes of the frequency region spread multicarrier CDMA. <P>SOLUTION: A multicarrier CDMA interference canceller is obtained, which employs a novel channel estimate method for estimating a transmission characteristic of each transmission channel at the reception section side to compensate the characteristic in order to reduce the effect of the inter-code interference . Further, the characteristic deterioration above is reduced through the development of a repetitive multi-user detection method wherein multi-user detection is applied to the frequency region spread multicarrier CDMA and the result of application is repetitively converged. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an interference canceller of a multicarrier CDMA system applied to mobile communication.

  Multi-carrier CDMA (MC-CDMA), which combines Orthogonal Frequency Division Multiplexing (OFDM) and Code Division Multiple Access (CDMA), utilizes high tolerance to delayed waves and orthogonality of frequencies found in orthogonal frequency division multiplexing. In recent years, research and development has been actively promoted as having both the characteristics of high frequency utilization efficiency and the characteristics of high frequency utilization efficiency in a multi-cell environment found in CDMA. Multi-carrier CDMA is roughly classified into two types: time-domain spread multi-carrier CDMA using a direct-spreading-type spread spectrum technique (DSSS) and frequency-domain spread multi-carrier CDMA in which one chip of a spread code is assigned to each subcarrier. Can do.

  The former time-domain spread multi-carrier CDMA is obtained by converting direct-spread CDMA (DS-CDMA) into multi-carriers, and the despread output for each delay path in the receiving unit, which is also a problem in this method, is an interference component of other paths. Since multipath interference (MPI) is unavoidable, the characteristics deteriorate. In the latter frequency domain spread CDMA, when orthogonal frequency division multiplexing symbols are asynchronous between users, the characteristics deteriorate due to the influence of asynchronous reception at the receiving unit, and when frequency selective fading is different for each user, The cross-correlation (inter-code interference (ICI)) with different spreading codes included in the despread output at the receiving unit increases, and the characteristics deteriorate. In addition, frequency domain spread multicarrier CDMA is considered to have higher frequency utilization efficiency because frequency spectrum is more densely arranged than time domain spread multicarrier CDMA.

  From the above, in Non-Patent Documents 1 and 2 described later, it is reported that it is desirable to apply time domain spread multicarrier CDMA to the uplink and frequency domain spread multicarrier CDMA to the downlink. On the other hand, as reported in Non-Patent Document 3 described later, multiuser detection (MUD) is a technique for mitigating CDMA multiple access interference (MAI). In this method, the signals of all users are despread to derive interference components included in the received signal, and the characteristics are improved by subtracting them from the received signal.

E. A. Sourourand M. Nakagawa, "Performance of orthogonal multicarrier CDMA in a multipath fading channel," IEEE Trans.Commun. Vol.44, pp559-569, March 1996 S. Hara and R. Prasad, "Overview of multicarrier CDMA", IEEE Commun. Mag., Pp126-133, Dec. 1997 Marubayashi Gen, Nakagawa Masao, Kawano Ryuji, "Spread Spectrum Communication and its Applications" IEICE, 1998 Shingo Suwa, Hiroyuki Shin, and Mamoru Sawahashi, “Comparison of Link Capacity between Multi-carrier / DS-CDMA and MC-CDMA in Uplink Broadband Packet Radio Access” IEICE Radio Communication System Study Group, RCS2002-134, 2002 Takashi Shono, Tomoyuki Yamada, Kazuhiro Uehara, Katsuhiko Araki, “Quantitative evaluation of multiple access interference in uplink of frequency domain spread MC-CDMA” IEICE General Conference, 2003

As described above, frequency-domain spread multi-carrier CDMA has a problem of inter-code interference, but is expected to be applied to the uplink because of its high frequency utilization efficiency. However, in this case, orthogonal frequency division multiplexing symbols become asynchronous between users, and the characteristics deteriorate due to the influence of asynchronous reception in the reception unit. When despreading is performed, there is a problem that inter-code interference increases and characteristics are greatly deteriorated. In particular, in Non-Patent Document 4 mentioned above, it is pointed out that the influence of characteristic deterioration due to multiple access interference due to the latter inter-code interference becomes large. Incidentally, non-patent document 5 has performed quantitative evaluation on inter-code interference when frequency domain spread multi-carrier CDMA is applied to the uplink.
Therefore, an object of the present invention is to reduce inter-code interference that is a problem when frequency domain spread multi-carrier CDMA is applied to the uplink and is caused by different frequency selective fading for each user.

In order to achieve the above object, in claim 1 of the present invention,
A radio communication system including a radio base station and a radio terminal, and a signal point converter that converts a bit stream into a symbol stream that is a signal point in the transmission unit in the radio base station, and the symbol stream A serial-parallel converter that performs serial-parallel conversion, a replicator that replicates the symbol stream, a frequency-domain spreader that spreads by multiplying a spreading code in the frequency domain, and an inverse discrete Fourier transformer or inverse fast Fourier transformer And a guard interval inserter for inserting a guard interval, and in the radio reception unit in the radio base station, the received multicarrier symbol timing detection means and an error in local oscillation frequency between transmission and reception Automatic frequency controller that detects and corrects and guard-in that removes the guard interval A Tarval remover, either a discrete Fourier transformer or a fast Fourier transformer, a channel estimator that estimates and corrects distortion due to a propagation path, and multiplies the spreading code in the frequency domain, and then adds to despread And a multi-carrier CDMA transceiver employing frequency domain spreading, comprising: a frequency domain despreader that performs parallel to serial conversion of the symbol stream; and a reverse signal point converter that converts symbols to bits. A multi-carrier CDMA interference canceller for use in a wireless communication system, wherein the wireless base station includes a multiple access control unit for controlling multiple access of terminals having the multi-carrier CDMA transceiver employing the frequency domain spreading. The multiple access control unit, when the terminal transmits a frame, While transmitting a channel estimation preamble, the frame transmission of a terminal other than the terminal is paused, and after the preamble has been transmitted, the frame transmission of a terminal other than the terminal is resumed. It defines a multi-carrier CDMA interference canceller.

  In Claim 2, it is a radio communications system constituted by a radio base station and a radio terminal, and in the radio transmitter, a signal point converter for converting a bit stream into a symbol stream which is a signal point; A serial-parallel converter that performs serial-parallel conversion on the symbol stream, a replicator that replicates the symbol stream, a frequency-domain spreader that spreads by multiplying a spreading code in the frequency domain, and an inverse discrete Fourier transformer or inverse fast Any one of Fourier transformers and a guard interval inserter for inserting a guard interval, and the radio receiving unit in the radio base includes a means for detecting timing of received multicarrier symbols and local oscillation between transmission and reception An automatic frequency controller that detects and corrects frequency errors, and a guard that removes the guard interval. An interval remover, either a discrete Fourier transformer or a fast Fourier transformer, a channel estimator that estimates and corrects distortion due to a propagation path, and multiplies the spreading code in the frequency domain and adds it for further despreading. And a multi-carrier CDMA transceiver unit employing frequency domain spreading, comprising: a frequency domain despreader that performs parallel-serial conversion on the symbol stream; and a reverse signal point converter that converts symbols into bits. A multi-carrier CDMA interference canceller for use in the radio communication system, wherein the radio base station includes a plurality of radio terminals connected to the radio base station and having the transceiver unit And the multi-carrier CDMA control unit includes uplink and downlink. A time division duplex control unit that performs time division duplex and a pilot signal transmission control unit that transmits a pilot signal common to all users using a specific downlink slot at a specific period, The terminal includes a channel transfer function deriving unit that derives a channel transfer function based on a received pilot signal and a channel transfer function notifying unit that notifies the radio base station of the derived channel transfer function, thereby performing channel estimation. It defines a multi-carrier CDMA interference canceller configured to perform.

  In Claim 3, it is a radio | wireless communications system comprised by the radio base station and the radio | wireless terminal, Comprising: In the transmission part in the said radio base station, signal point conversion which converts a bit stream into the symbol stream which is a signal point , A serial-parallel converter that serial-parallel converts the symbol stream, a replicator that replicates the symbol stream, a frequency-domain spreader that spreads by multiplying a spreading code in the frequency domain, and an inverse discrete Fourier transformer Or an inverse fast Fourier transformer, and a guard interval inserter that inserts a guard interval. In the radio reception unit in the radio base, a means for detecting the timing of the received multicarrier symbol, An automatic frequency controller that detects and corrects an error in the local oscillation frequency of, and the guard interval A guard interval remover to be removed, either a discrete Fourier transformer or a fast Fourier transformer, a channel estimator for estimating and correcting distortion due to a propagation path, and multiplying the spreading code in the frequency domain, and further despreading Multi-carrier CDMA transmission / reception employing frequency domain spreading, comprising: a frequency domain despreader for summing, a parallel / serial converter for parallel-serial conversion of the symbol stream, and an inverse signal point converter for converting symbols to bits A multi-carrier CDMA interference canceller for use in a radio communication system comprising a plurality of units, wherein, in a radio base station, in the channel estimator of the radio receiver, for each sequence corresponding to one replicator, for each subcarrier A weight control unit that outputs a weight for each subcarrier, and a subcarrier. A multiplier that multiplies the input signal by the weight corresponding to the subcarrier of the weight control unit output, an adder that adds the multiplication output of the multiplier, and a multiplication for spreading the spreading code in the frequency domain. A multi-carrier CDMA interference canceller configured to perform channel estimation by performing control to determine a weight so that the adder output is coherent to an information symbol. It stipulates.

In a fourth aspect of the present invention, the multicarrier CDMA interference canceller according to any one of the first to third aspects of the present invention accommodates users 1 to N (N is a natural number of 2 or more). 1) By performing channel estimation, distortion correction, and despreading for each of the users 1 to N, approximate values (S _{1 to} S _N ) of the symbol data for each of the users 1 to N are calculated, and (2) the approximation By multiplying each value (S _{1 to} S _N ) by the inverse channel transfer function and spreading code of each of users 1 to N, terms (S ₁ ^{* to} S corresponding to each of users 1 to N in the received signal). _N ^*) is calculated, (3) user k (k from a received signal for all users: vector of _{1~N, i ≠ k): S} i * for all users except 1 to N) (i By subtracting the sum to calculate the removal of the interference component for user k estimates S _k ^*, (4) distortion correction for said S _k ^*, by despreading, the signal S _k with a reduced interference component (5) After the above process is executed for all users, the DU ratio, which is an index indicating the effect of interference removal, is measured. If the DU ratio> K with respect to the initial set value K, the above process is performed. If the DU ratio <K, the multi-carrier CDMA interference canceller having the interference canceling function configured to repeat the above processing is specified.
Furthermore, a multi-carrier CDMA interference canceller having an interference removal function configured to repeat the processes (1) to (4) at least once is defined.

In claim 5, the multi-carrier CDMA interference canceller according to any one of claims 1 to 3, wherein the user 1 to the user N (N is a natural number of 2 or more) are accommodated. (1) By performing channel estimation, distortion correction, and despreading for the user 1, the approximate value S _mi of the user 1 symbol data is calculated, and (2) the S By multiplying _mi by the channel transfer function and spreading code of user i, the term S _m1 ^* corresponding to user 1 in the received signal for all the users is calculated. _Smi ^* is also calculated for all users i, and (3) _rmi ^* is calculated as an input signal of user i by subtracting _Smi ^* from the received signal for all users, (4 ) The approximate value S ₁₂ of the symbol data of the user 2 is calculated by performing the channel estimation, the distortion correction, and the despreading on the user 2 for the r _mi ^* , and (5) the approximate value S ₁₂ Is multiplied by the channel transfer function and spreading code of user 2 to calculate the term S ₁₂ ^* corresponding to user 2 in r _mi ^* , (6) and the processing of (3) to (5) is further performed. S _{m (N + 1)} ^* Increase the user number by 1 and measure the UD ratio, which is an index showing the effect of interference cancellation, after making a round for all the users to be calculated. ratio> Exit K if above process repeats the above processing as the user ID i = 1 to 1 increases the UD ratio <K If the m, (7) the process for the user 1 the r _mi ^* Obtained by adding to the output S _{(m-1) 1} ^* (S _{(m-1) 1} ^* + r The processes (1) to (3) are executed with _mi ^* ) as the input of the m-th process for the user 1, and the user number is incremented by 1, and the above (S _{(m-1) 1} ^* + r _mi ^* ) Is input by the user i, and the processes (1) to (3) are performed. (8) The process (7) is repeated while incrementing the user number by 1. When i = N + 1 is reached in advance. The set UD ratio is measured. If UD ratio <K, the processes of (6) to (8) are repeated, m is increased by 1, and the processes of (6) to (8) are repeated. When the UD ratio> K, the multi-carrier CDMA interference canceller having an interference removal function is characterized in that all the processes are ended and the processes (3) to (8) are repeated at least once.

  According to the multicarrier CDMA interference canceller of the present invention, in the frequency domain spread multicarrier CDMA, it is possible to significantly reduce the inter-code interference caused by receiving different frequency selective fading for each user, and the time domain spread multicarrier It becomes possible to apply frequency domain spread multicarrier CDMA, which has better characteristics than CDMA, to the uplink.

An embodiment of a multicarrier CDMA apparatus according to the present invention will be described below with reference to the drawings. The communication system to which the present invention is applied is a system composed of a radio base station and a plurality of terminals, and is a combination of orthogonal frequency division multiplexing (OFDM) and code division multiple access (CDMA). Multi-carrier CDMA (MC-CDMA) is adopted. Here, the wireless base station in the present invention has a multiple access control unit for controlling connection between the base station and a plurality of terminals,
1) When a terminal transmits a frame, the multiple access control unit pauses frame transmission of terminals other than the terminal while transmitting a channel estimation preamble included in the frame, and completes transmission of the preamble. It has a function of resuming frame transmission of terminals other than the terminal.
2) A multi-carrier CDMA control unit that accommodates a plurality of terminals having transmission / reception units that can be connected to a radio base station is provided. At the same time, in the terminal, the multi-carrier CDMA control unit performs uplink and downlink. A time division duplex control unit that performs division duplex (TDD) and a pilot signal transmission control unit that transmits a pilot signal common to all users using a specific downlink slot at a specific period.
In addition, the wireless terminal
1) It has a channel transfer function deriving unit for deriving a channel transfer function based on the received pilot signal.
2) In addition, a channel transfer function notifying unit that notifies the radio base station of the derived channel transfer function is provided.

  FIG. 1 is a configuration diagram of a transmission unit of frequency domain spread MC-CDMA. In FIG. 1, a data stream (Information data) as an input signal is modulated by a modulator 11 to become a bit stream, and then multiplexed together with a pilot signal (Pilot) by a multiplexer 12. Since this multiplexed output is a bit stream of a serial signal, it is converted into Np series by a serial-to-parallel converter (S / P) 13, and further, each series corresponds to a spreading factor by duplicators 141 to 14n. To SF symbol streams. Thereafter, the duplicated symbol stream is multiplied by a spreading code from the spreader 15 in the frequency domain, and the multiplication result is inversely converted into a signal in the time domain by an inverse fast Fourier transformer (IFFT) 16. After that, a guard interval is inserted by a guard interval inserter (GI Insertion) 17 and transmitted as a transmission signal (Transmitted signal).

FIG. 2 is a configuration diagram of a receiving unit of frequency domain spread multicarrier CDMA. The received signal (Received signal) detects the timing of the symbol transmitted by the symbol timing detector 211, and then the guard interval remover 212 removes the guard interval. The signal thus obtained is converted into data in the frequency domain divided into _Nc pieces by a fast Fourier transformer (FFT) 22, and distortion in the propagation path is estimated by a channel estimator 23 and multiplied. This distortion is corrected by the processing. Thereafter, it is multiplied by a spreading code (spreading code) that is the output of the frequency domain despreader 24, and further combined into data in each SF frequency domain corresponding to the transmission side, and further added by adders 241 to 24n, respectively. A symbol stream is added to the parallel signal, and a parallel signal is converted into a serial bit stream by a parallel / serial converter (P / S) 25, and then recovered data is obtained by an inverse signal point converter (Demodulator) 26.

  FIG. 3 is a block diagram of the channel estimator 23 in FIG. 2 according to the present invention. In FIG. 3, a weight control unit (Weight Control) 31 uses data in the frequency domain that is the output of the fast Fourier transform (FFT) 22 so that the output of the adder 33 becomes coherent with respect to the information symbols. It is characterized in that channel estimation is performed by performing control for determining weights (weights). The output of the weight control unit 31 is multiplied by the output of the fast Fourier transformer 22 by the multiplier 32, and the multiplication result is fed back to the weight control unit 31 via the adder 33 so as to be coherent. By multiplying the spreading code (Spreading code) by the region despreader 24 in the multiplier 34, the data is grouped into data in each SF frequency region corresponding to the spreading factor and input to the adders 241 to 24n in FIG. The That is, for each series for one replicator, the input signal for each subcarrier is input, the weight control unit 31 outputs a weight for each subcarrier, and the multiplier 32 gives a weight to the input signal for each subcarrier. Multiply. The multiplier output is added to a plurality of adders 33, and the weight control unit 31 determines the weight so that the adder output becomes coherent with the information symbol.

  FIG. 4 is a block diagram of a receiving unit showing a first example corresponding to an iterative multiuser detector (IMUD) 41 according to the present invention, and FIG. 5 is an iterative multiuser detector (first example) used in this receiving unit. (IMUD) 41, FIG. 6 is a processing sequence diagram of the repeated multiuser detection of the first example. The iterative multiuser detector 51 of FIG. 5 operates according to the sequence of FIG.

In the situation where the systems of users 1 to N shown in FIG. 5 are accommodated,
(1) For each of users 1 to N (User 1 to User N), channel estimation, distortion correction, and despreading are performed by channel estimator 42 in FIG. Approximate values (S _{1 to} S _N ) of the symbol data corresponding to each are calculated (Step 601 in FIG. 6, hereinafter, the numbers in parentheses indicate steps in FIG. 6).
(2) The approximate values (S _{1 to} S _N ) are repeatedly input to the multi-user detector 41, and each of them is duplicated SF by the duplicator (Copier) 51 of FIG. The terms (S ₁ ^{* to} S _N ^* ) corresponding to the users 1 to N in the received signal by multiplying the N to N reverse channel transfer function 52 and the spreading code 53 respectively. Is calculated. (Step 602)
(3) By subtracting the vector sum of the above S _i ^* (i = 1 to N: i ≠ k) for all users excluding user k from the received signal for user k, S _k ^* is calculated (step 603 )
(4) By performing distortion correction and despreading for S _k ^*, a signal S _k with reduced interference components for user _k is calculated, and interference is removed by repeating the above process at least once. (Step 604)
This repetition is repeated until the required DU ratio (desired signal to interference signal power ratio) corresponding to the number of users specified at the time of circuit design is exceeded (step 605).

FIG. 6 summarizes the above sequence.
FIG. 7 is a block diagram of a receiving unit as a second example corresponding to an iterative multiuser detector (IMUD), FIG. 8 is a block diagram of the iterative multiuser detector (IMUD) 71 in the second example, and FIG. FIG. 10 is a circuit configuration diagram for explaining the operation of the interference canceller according to the invention, and FIG. 10 is an operation sequence diagram of repeated multi-user detection as the second example. In the case of the repetitive multiuser detector according to the second exemplary embodiment, the channel estimator is also included in the multiuser detector (IMUD) 71 for each user in the case of the first example. Is different. In accordance with the sequence of FIG. 10 (the numbers in parentheses below correspond to the steps described in FIG. 10), the iterative multiuser detector of FIG. 8 operates.

As shown in FIG. 9, in the situation where the present multicarrier CDMA interference canceller accommodates users i (i: 1 to N), interference cancellation is performed in the following procedure.
(1) The input signals dispersed in the frequency domain, which is the output of the fast Fourier transformer 22 in FIG. 2, are collected into SF lines corresponding to the dispersion rate and input to the correlator 91 of the user 1 in FIG. The In this correlator 91, the received signal r _i is subjected to processing such as channel estimation, distortion correction, and despreading, so that it corresponds to its own signal, that is, the user i from the coexistence with interference components from other users. Processing for extracting the approximate value S _mi of the symbol data to be performed is performed (step 1002). Here, the suffix m of S _mi is the number of times to repeat the following series of processes, and i is the user number. The S ₁₁ is immediately after the processing start.
(2) In the first converter (converter 1) 92, the approximate value S _mi is multiplied by the reverse channel transfer function (Reverse transfer function in FIG. 8) and spreading code (Spreading code in FIG. 8) of the user i. Thus, a term (S _mi ^* ) corresponding to the user _i in the received signal r _i is calculated (step 1003). For example, in the first processing for user 1, this term is S ₁₁ ^* where S _1T is the true value, and ΔS ₁₁ ^* is the error due to interference from other users, etc. S ₁₁ ^* = S _1T + ΔS given by ₁₁ ^*, and the S ₁₁ ^* is a that is consistent with the dimensions of the input side of the correlator 91, thereby enabling the following processes (3).
(3) Next, the fast Fourier by transformed subtractor 932 from the received signal r _i which contains the information of all the users have been by subtracting the signal S ₁₁ ^* obtained in the above process, the signal obtained by removing the influence of the user 1 r _mi ^* is calculated (step 1004), and the result is input to the correlator 94 of the user 2. At the same time, it is input to one of the input terminals of the correlator input side subtracter 933 for the user 3. The output of the converter 2 is applied to the other input of the subtracter 933. The output of the subtracter 933 is applied to the correlator input side of the user 3 as the next step, and simultaneously applied to one input of the subtracter on the correlator input side of the next stage user (in this case, the user 4). The
(4) The user 2 correlator 94 performs channel estimation, distortion correction, and despreading processing on the signal r _mi ^{* in} the same manner as in the case of the user 1, so that the symbol data of the user 2 to calculate the approximate value S _12.
(5) The approximate value S ₁₂ obtained thereby is multiplied by the inverse channel transfer function and the spreading code of the user 2 in the second converter 95, whereby the term corresponding to the user 2 in the signal r _mi ^* ( S ₁₂ ^*) is calculated.
(6) Hereinafter, the series of processes (3) to (5) is repeated by 1 at step 1005 until i is incremented by 1 (step 1006) and S _1N ^* is obtained. That is, by sequentially performing channel estimation, distortion correction, and despreading processes while shifting i from 1 to (N + 1) with respect to user i, S _{1 (i + 1), S 1 (i +} 2) ... S 1N and ^{_{S 1 (i + 1) *}} , S 1 (i + 2) *, ... calculates the S _1N ^* sequentially. In addition, the above processing is actually executed in order from the largest reception power regardless of the arrangement order of the user i.

Here, it is checked whether or not the effect of interference cancellation exceeds the required DU ratio corresponding to the number of users specified at the time of circuit design (step 1008). When the DU ratio (step 1007) does not satisfy the specification value K (No in step 1008), m = 2 and i = 1, and the next iteration is entered (step 1009 and step 1010).
(7) Through the series of processes described above, the first process (m = 1) is completed, and then the process returns to the first correlator 91 as the second process (m = 2). The input to the correlator 91 of the user 1 at the second time is the output of the first converter 92 (S _{(m-1) 1} ^* ) at the first time and the output of the subtractor 96, that is, the received signal. The sum (S _{(m−1) 1} ^* + R) of the residual component r _mi (= R) obtained by subtracting the signal of each user from the input to the first correlator 91 for the second time (m = 2) Then, the same processing as in the cases (3) to (6) is repeated (steps 1010 to 1012). However, in the second process, the signal (S _{(m-1) 1} ^* + R) becomes the input signal of the correlator 91 of the user 1, and this input signal and the first converter 92 output of the second time. Is subtracted by the subtractor 981, and the result of the calculation is added to the output of the first second converter 95 by the adder 992 to be input to the correlator 94 of the second user 2. This process is repeated also in the second time, and thereafter, i is incremented by 1 (step 1012) until the total number of users N + 1 is reached (S _{(m-1) 1} ^* + r _mi ^* ). Steps 1002, 1003, 1004 The same calculation is repeated (step 1014).
(8) In this way, one calculation process is completed for all users (i = 1 to N) (i = N + 1 in step 1014). Returning to step 1008, it is checked whether or not the initial set ratio of the DU ratio (desired signal to interference signal power ratio) is satisfied. If not reached (No in step 1008), the process proceeds to step 1009 and m is set to m + 1. Enter the loop. This is continued at least once until the result of step 1008 is Yes.

The block diagram of the transmission part of frequency domain spreading | diffusion MC-CDMA. The block diagram of the receiving part of frequency domain spreading | diffusion MC-CDMA. The block diagram of a channel estimation part. The block diagram of the receiving part corresponding to a 1st repetition multiuser detector. The block diagram of a 1st repetition multiuser detector. The sequence diagram which shows operation | movement of a 1st repetition multiuser detector. The block diagram of the receiving part corresponding to a 2nd repetition multiuser detector. The block diagram of a 2nd repetition multiuser detector. The circuit block diagram of the interference canceller by this invention. The sequence diagram which shows operation | movement of a 2nd repetition multiuser detector.

Explanation of symbols

11: Signal point converter (modulator) 12: Multiplexer 13: Series-parallel converter 141-14n: Duplicator 15: Spreader 16: Inverse fast Fourier transformer 17: Guard interval inserter
211: Symbol timing detector
212: Guard interval remover 22: Fast Fourier transformer 23: Channel estimator 24: Frequency domain despreader 241 to 24n: Adder 25: Parallel-serial converter 26: Inverse signal point converter 31: Weight control unit 32 : Multiplier 33: Adder 34: Multiplier 41: Repetitive multiuser detector 42: Channel estimator 51: Duplicator
52: Inverse channel transfer function generator 53: Spreading code generator
71: Iterative multiuser detector 72: Channel estimator
81: Inverse channel transfer function generator 91: User 1 correlator
92: First converter 93: Subtractor
94: Correlator of user 2 95: Second converter

Claims (5)

A wireless communication system including a wireless base station and a wireless terminal,
And in the transmitter in the radio base station,
A signal point converter for converting a bit stream into a symbol stream which is a signal point;
A serial-parallel converter for serial-parallel conversion of the symbol stream;
A duplicator for duplicating the symbol stream;
A frequency domain spreader that spreads by multiplying the spreading code in the frequency domain;
Either an inverse discrete Fourier transformer or an inverse fast Fourier transformer;
A guard interval inserter for inserting a guard interval;
In addition, in the radio receiver in the radio base station,
Means for detecting the timing of received multi-carrier symbols;
An automatic frequency controller that detects and corrects local oscillation frequency errors between transmission and reception;
A guard interval remover for removing the guard interval;
Either a discrete Fourier transformer or a fast Fourier transformer;
A channel estimator to estimate and correct distortion due to the propagation path;
A frequency domain despreader that multiplies the spreading code in the frequency domain and adds for further despreading;
A parallel to serial converter for parallel to serial conversion of the symbol stream;
A multicarrier CDMA interference canceller for use in a wireless communication system comprising a multicarrier CDMA transceiver employing frequency domain spreading comprising an inverse signal point converter for converting symbols into bits,
In the radio base station,
Comprising a multiple access control unit for controlling multiple access of a terminal having a multi-carrier CDMA transceiver employing the frequency domain spreading;
In the multiple access control unit,
When transmitting a frame, the terminal pauses frame transmission of a terminal other than the terminal while transmitting a channel estimation preamble included in the frame, and resumes frame transmission of a terminal other than the terminal after transmission of the preamble is completed. A multi-carrier CDMA interference canceller characterized by having a function to perform channel estimation. A wireless communication system including a wireless base station and a wireless terminal,
And in the said wireless transmission part,
A signal point converter for converting a bit stream into a symbol stream which is a signal point;
A serial-parallel converter for serial-parallel conversion of the symbol stream;
A duplicator for duplicating the symbol stream;
A frequency domain spreader that spreads by multiplying the spreading code in the frequency domain;
Either an inverse discrete Fourier transformer or an inverse fast Fourier transformer;
A guard interval inserter for inserting a guard interval;
In addition, in the radio receiver in the radio base,
Means for detecting the timing of received multi-carrier symbols;
An automatic frequency controller that detects and corrects local oscillation frequency errors between transmission and reception;
A guard interval remover for removing the guard interval;
Either a discrete Fourier transformer or a fast Fourier transformer;
A channel estimator to estimate and correct distortion due to the propagation path;
A frequency domain despreader that multiplies the spreading code in the frequency domain and adds for further despreading;
A parallel to serial converter for parallel to serial conversion of the symbol stream;
A multi-carrier CDMA interference canceller used in the wireless communication system comprising a multi-carrier CDMA transceiver unit employing frequency domain spreading, comprising an inverse signal point converter for converting symbols into bits,
In the radio base station,
A multi-carrier CDMA control unit accommodating the plurality of radio terminals having the transmission / reception unit connected to the radio base station;
In the multi-carrier CDMA control unit,
A time division duplex control unit that performs time division duplex on the uplink and downlink;
A pilot signal transmission control unit for transmitting a pilot signal common to all users using a specific downlink slot at a specific period;
In the wireless terminal,
A channel transfer function deriving unit for deriving a channel transfer function based on a received pilot signal and a channel transfer function notifying unit for notifying the radio base station of the derived channel transfer function are configured to perform channel estimation. A multi-carrier CDMA interference canceller characterized by being. A wireless communication system including a wireless base station and a wireless terminal,
And in the transmitter in the radio base station,
A signal point converter for converting a bit stream into a symbol stream which is a signal point;
A serial-parallel converter for serial-parallel conversion of the symbol stream;
A duplicator for duplicating the symbol stream;
A frequency domain spreader that spreads by multiplying the spreading code in the frequency domain;
Either an inverse discrete Fourier transformer or an inverse fast Fourier transformer;
A guard interval inserter for inserting a guard interval;
In addition, in the radio receiver in the radio base,
Means for detecting the timing of received multi-carrier symbols;
An automatic frequency controller that detects and corrects local oscillation frequency errors between transmission and reception;
A guard interval remover for removing the guard interval;
Either a discrete Fourier transformer or a fast Fourier transformer;
A channel estimator to estimate and correct distortion due to the propagation path;
A frequency domain despreader that multiplies the spreading code in the frequency domain and adds for further despreading;
A parallel to serial converter for parallel to serial conversion of the symbol stream;
A multicarrier CDMA interference canceller for use in a wireless communication system comprising a multicarrier CDMA transceiver employing frequency domain spreading comprising an inverse signal point converter for converting symbols into bits,
In the radio base station,
In the channel estimator of the radio reception unit,
For each series corresponding to one replicator, a weight control unit that receives an input signal for each subcarrier and outputs a weight for each subcarrier;
A multiplier that multiplies the input signal for each subcarrier by the weight corresponding to the subcarrier of the weight control unit output;
An adder for adding multiplication outputs of the multiplier;
A frequency domain spreader for multiplying the spreading code to spread in the frequency domain;
The multi-carrier CDMA interference canceller, wherein the weight control unit is configured to perform channel estimation by performing control to determine a weight so that the adder output is coherent with an information symbol. The multicarrier CDMA interference canceller according to any one of claims 1 to 3, wherein a user 1 to a user N (N is a natural number of 2 or more) are accommodated.
(1) By performing channel estimation, distortion correction, and despreading for each of the users 1 to N, approximate values (S _{1 to} S _N ) of the symbol data for each of the users 1 to N are calculated.
(2) A term corresponding to each of the users 1 to N in the received signal by multiplying each of the approximate values (S _{1 to} S _N ) by the inverse channel transfer function and spreading code of each of the users 1 to N ( S ₁ ^{* to} S _N ^* )
(3) Interference component for user k by subtracting the vector sum of S _i ^* (i: 1 to N, i ≠ k) for all users excluding user k (k: 1 to N) from the received signal for all users Calculate the estimated value S _k ^{* T from} which
(4) calculating a signal S _k with a reduced interference component by performing distortion correction and despreading on the S _k ^* ,
(5) After executing the above processing for all users, measure the DU ratio, which is an index indicating the effect of interference cancellation, and if the DU ratio> K with respect to the initial set value K, the above processing is terminated. A multi-carrier CDMA interference canceller having an interference cancellation function, wherein the above processing is repeated if DU ratio <K. The multi-carrier CDMA interference canceller according to any one of claims 1 to 3, wherein the user number is i and the processing number is N in a situation where users 1 to N (N is a natural number of 2 or more) are accommodated. Let m be the number of repetitions.
(1) By performing channel estimation, distortion correction, and despreading for the user 1, an approximate value S _mi of the symbol data of the user 1 is calculated,
(2) The term S _m1 ^* corresponding to user 1 in the received signal for all users is calculated by multiplying S _mi by the channel transfer function and spreading code of user i, and so on. to also calculate the S _mi ^* the remaining all users i as N,
(3) _rmi ^* is calculated as an input signal of user i by subtracting _Smi ^* from the received signals for all users;
(4) By performing the channel estimation, the distortion correction, and the despreading on the user 2 for the r _mi ^* , an approximate value S ₁₂ of the symbol data of the user 2 is calculated,
(5) Multiplying the approximate value S ₁₂ by the channel transfer function and spreading code of user 2 to calculate a term S ₁₂ ^* corresponding to user 2 in r _mi ^* ,
(6) Further, S _{m (N + 1)} ^* is calculated while incrementing the user number by 1 in the processes of (3) to (5), and the effect of interference cancellation is obtained after making a round for all users. DU ratio that is an index to be measured is measured, and if the DU ratio> K with respect to the initial set value K, the above processing is terminated, and if DU ratio <K, m is increased by 1 and the user number i = 1 is set. Repeat the above process,
(7) (S _{(m−1) 1} ^* + r _mi ^* ) obtained by adding the r _mi ^* to the processing output S _{(m−1) 1} ^* for the user 1 is the mth processing for the user 1 The processing of (1) to (3) is executed as an input, and the user number is further incremented by 1, and the above (S _{(m-1) 1} ^* + r _mi ^* ) is used as the input of user i (1) The process of (3) is performed and the process of (7) is repeated while incrementing the user number by 1. When the value reaches i = N + 1, the preset DU ratio is measured, and DU ratio <K In this case, the processes (6) to (8) are repeated, m is increased by 1 and the processes (6) to (8) are repeated. If DU ratio> K, all the processes are terminated, 3) to (8) are repeated at least once, and the multicarrier CDMA interference carrier having an interference cancellation function is provided. Sera.

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