Wireless communication system, receiving apparatus with a plurality of antennas, demodulating method for such wireless communication system, receiving apparatus, and program for such demodulating method

A receiving apparatus has two or more reception antennas, a data reproducer, and a likelihood information generator. The receiving apparatus operates selectively in a first reception mode and a second reception mode depending on the features of signals sent from a transmitting apparatus. In the first reception mode, the receiving apparatus reproduces data and generates likelihood information. In the second reception mode, the receiving apparatus reproduces data using the likelihood information generated in the first reception mode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, and more particularly to a receiving apparatus having a plurality of antennas.

2. Description of the Related Art

Extensive research and development efforts are under way with regard to reception processes for coded MIMO (Multiple Input Multiple Output) systems. One of those reception processes is based on a combination of a complexity-reduced MLD (Maximum Likelihood Detection) process, which has reduced the calculation complexity of the MLD process, and soft-decision decoding, for achieving simple, high-performance reception characteristics. The method disclosed in Hiroyuki KAWAI, Kenichi HIGUCHI, Noriyuki MAEDA, Mamoru SAWAHASHI, Takumi ITO, Yoshikazu KAKURA, Akihisa USHIROKAWA, Hiroyuki SEKI, “Likelihood Function for QRM-MLD Suitable for Soft-Detection Turbo Decoding and Its Performance for QFCDM MIMO Multiplexing in Multipath Fading Channel,” IEICE TRANS. Commun., Vol. E88-B, No. 1, January 2005 will be described below with reference toFIG. 1of the accompanying drawings. For the sake of brevity, it is assumed that propagation paths between receiving and transmitting apparatus comprise flat-fading channels.

FIG. 1is a block diagram of a conventional wireless communication system for carrying out the method disclosed in the above document.

Bit likelihood calculator101will be described in detail below. Bit likelihood calculator101calculates a likelihood that the transmitted bit is 0 and a likelihood that the transmitted bit is 1.

FIG. 2of the accompanying drawings is a block diagram of bit likelihood calculator101. As shown inFIG. 2, bit likelihood calculator101comprises averager1011, buffer1012, and selectors3221-1,3221-2,3221-3.

Averager1011is supplied with symbol candidate and likelihood pairs (S1, e1) . . . (S256, e256). If both symbol candidates, where each of the bits included in the transmitted three signals is 0, and symbol candidates where each of the bits included in the transmitted three signals is 1, can be selected, then averager1011selects the maximum likelihoods of the symbol candidates, averages smaller ones of likelihoods that the bit is 0 and likelihoods that the bit is 1, and outputs average value q.

Each of selectors3221-1,3221-2,3221-3is supplied with symbol candidate and likelihood pairs (S1, e1) . . . (S256, e256) that have been buffered by buffer1012and average value q. For calculating a bit likelihood, each selector selects a symbol candidate where each bit is 0 and a symbol candidate where each bit is 1, selects a maximum symbol likelihood of the symbol candidates, and outputs the selected maximum symbol likelihood as a bit likelihood. If there are no symbol candidates including bits0or bits1and hence each selector is unable to select a bit likelihood, then the selector uses supplied average value q as a bit likelihood of bit1.

Bit likelihood calculator101can widen an averaging interval in averager1011to increase the averaging accuracy.

However, the conventional scheme has suffered the following problems:

The first problem is that the scheme causes a large processing delay because of the buffering of the data until the averaging process is over.

Accordingly, it has been difficult to apply the conventional scheme to wireless communication systems which pose strict limitations on any delay times.

The second problem is that the number of samples used for averaging cannot be determined in advance because it is not possible to determine in advance how many symbols that have both bit0and bit1are present among symbol characteristics that are supplied for the averaging process.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a means for calculating a bit likelihood without causing a processing delay in a receiving process based on a combination of complexity-reduced MLD and likelihood calculation.

According to the present invention, there is provided a receiving apparatus for carrying out a demodulating process. The receiving apparatus has N antennas (N is an integer of 2 or greater) for receiving signals transmitted from a transmitting apparatus having M antennas (M is an integer of 2 or greater) each for transmitting K types (K is an integer of 2 or greater) of signals composed of at most M spatially multiplexed signals. The receiving apparatus comprises:

data reproducing means so as to be supplied with a received signal received by the N antennas and bit likelihood information, detecting a feature of a signal which is spatially multiplexed on a kth signal (k is an integer of 2 or greater) to switch between a first reception mode and a second reception mode, operating in the first reception mode directly calculating likelihoods where each bit is 1 and likelihoods where each bit is 0 from the received signals as first bit likelihood pairs and outputting a reproduced bit string and the first bit likelihood pairs, and operating in the second reception mode for, if likelihoods where each bit is 1 and likelihoods where each bit is 0 can be directly calculated, directly calculating likelihoods where each bit is 1 and likelihoods where each bit is 0, and for, if likelihoods where each bit is 1 and likelihoods where each bit is 0 cannot directly be calculated, calculating likelihoods from the bit likelihood information as second likelihood pairs, performing soft decision decoding on the second likelihood pairs, and outputting a reproduced bit string; and

likelihood information calculating means for being supplied with the received signals and the first bit likelihood pairs, calculating a physical quantity with respect to smaller bit likelihoods of the first likelihood pairs, and outputting the calculated physical quantity as the bit likelihood information.

The data reproducing means may receive the signals in the second reception mode if the product of modulation multi-valued numbers of the signal which is spatially multiplexed on the kth signal is greater than a predetermined value P1(P1is 2Mor greater), and the data reproducing means may receive the signals in the first reception mode otherwise.

The likelihood information calculating means may average only the smaller bit likelihoods of the first likelihood pairs, and convert an average value into the bit likelihood information using at least one of a transmission parameter of the transmitted signals and a parameter of propagation paths between the antennas.

The likelihood information calculating means may use a layout of constellation points as the transmission parameter.

If the average squared distance between minimum signal points of the kth signal transmitted from an mth antenna is represented by d2k,m,minand if K1types of signals (K1is 1 or greater and less than K) are received in the first reception mode and (K−K1) types of signals are received in the second reception mode, then the likelihood information calculating means may generate the bit likelihood information Q as:

Q=q⁢∑k=1K-K1⁢∑m=1M⁢ⅆk,m,min2∑k=1K1⁢∑m=1M⁢ⅆk,m,min2
where q represents an average value of smaller ones of the first bit likelihood pairs.

Alternatively, if the average squared distance between minimum signal points of the kth signal transmitted from an mth antenna is represented by d2k,m,minand K1types of signals (K1is 1 or greater and less than K) are received in the first reception mode and (K−K1) types of signals are received in the second reception mode, then the likelihood information calculating means may generate the bit likelihood information Q as:

Q=q⁢⁢1∑n=1N⁢∑m=1M⁢hnm2·∑m=1M⁢1∑n=1N⁢hnm2·∑k=1K-K1⁢∑m=1M⁢ⅆk,m,min2∑k=1K1⁢∑m=1M⁢ⅆk,m,min2
where hnmrepresents the propagation path between an nth reception antenna and the mth transmission antenna, and q an average value of smaller bits of the first bit likelihood pairs.

The wireless communication system according to the present invention includes the receiving apparatus described above, and a program according to the present invention controls the receiving apparatus to perform the above process.

The first wireless communication system according to the present invention has two or more receiving antennas, a data reproducer, and a likelihood information generator. The receiving apparatus operates selectively in a first reception mode and a second reception mode depending on the features of signals sent from a transmitting apparatus. In the first reception mode, the receiving apparatus reproduces data and generates likelihood information. In the second reception mode, the receiving apparatus reproduces data using the likelihood information generated in the first reception mode.

Based on the above arrangement, a delay due to buffering does not occur, and transmitted data can quickly be reproduced.

The second wireless communication system according to the present invention generates likelihood information depending on the parameter of transmission paths between the transmitting apparatus and the receiving apparatus. Based on the above arrangement, a delay due to buffering does not occur, and transmitted data can be received with high performance. Furthermore, the accuracy of bit likelihood information can be prescribed in advance.

According to the present invention, the receiving apparatus operates selectively in reception modes depending on the feature of transmitted signals. Using bit likelihood, that is calculated in one of the reception modes, in the other reception mode, the receiving apparatus can quickly receive signals without causing a processing delay due to buffering.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3shows in block form a wireless communication system according to the present invention.

Receiving apparatus1comprises data reproducing device12, likelihood information generator13, and recording medium14. Data reproducing device12comprises first data reproducer121and second data reproducer122. Second data reproducer122comprises complexity-reduced MLD device1221, bit likelihood calculator1222, and decoder1223. When receiving apparatus1is in a first reception mode, first data reproducer121and likelihood information generator13operates. When receiving apparatus1is in a second reception mode, second data reproducer122operates. Receiving apparatus1switches between the first reception mode and the second reception mode using control signals and data signals in the received signals.

FIG. 4is a flowchart of a processing sequence of the wireless communication system shown inFIG. 3. Operation of receiving apparatus1will be described below with reference toFIG. 4. The processing sequence shown inFIG. 4is performed by a processor (not shown) which executes a program stored in recording medium14of receiving apparatus1. The scope of the present invention covers such a program.

In data reproducing device12, first data reproducer121is supplied with received signals r1, r2, . . . , rN, reproduces signals dU+1, dU+2, . . . , dU+vfrom control signals contained in the reception signals, and outputs likelihoods where a certain pit is 0 and likelihoods where a certain pit is 1 as bit likelihood pairs (L0U+1, L1U+1), (L0U+2, L1U+2), . . . ((L0V, L1V) in step S101.

As described above, bit likelihood information is generated from bit likelihood pairs calculated in the first reception mode, and the generated bit likelihood information is used to reproduce and output signals in the second reception mode. In the above description, the two data reproducing devices are employed and operate in the first and second reception modes, respectively. However, the present invention is not limited to the arrangement shown inFIG. 3. One data reproducing device may be employed and applicable demodulating parameters may be controlled to operate the data reproducing device selectively in first and second reception modes.

FIG. 5shows in block form a wireless communication system according to a first embodiment of the present invention. The wireless communication system according to the first embodiment is of basically the same arrangement as the wireless communication system shown inFIG. 3.

As shown inFIG. 5, the wireless communication system according to the first embodiment comprises transmitting apparatus4having three antennas21-1,21-2,21-3, and receiving apparatus3having three antennas11-1,11-2,11-3.

Receiving apparatus3comprises data reproducing device31, likelihood information generator32, and recording medium33. Data reproducing device31comprises first data reproducer311and second data reproducer312.

First data reproducer311comprises channel estimator3111, maximum ratio combiner3112, bit likelihood calculator3113, and decoder3114. Second data reproducer312comprises channel estimator3111′, QR decomposition MLD device3121, bit likelihood calculator3122, and decoder3123. Likelihood information generator32comprises comparator and averager321and converter322.

FIG. 6shows the format of signals that are transmitted by transmitting apparatus4. As shown inFIG. 6, transmitting apparatus4sends data signal1and a control signal from antenna21-1, data signal2and a control signal from antenna21-2, and data signal3and a control signal from antenna21-3. Therefore, transmitting apparatus4sends two types of signals, or in other words, data signals and control signals. The data signals are sent as three multiplexed signals, and the control signals are sent as non-multiplexed signals. It is assumed that data signals1,2,3are modulated, i.e., have constellation points arranged, according to 16QAM, and the control signals are modulated, i.e., have constellation points arranged, according to QPSK.

With respect to all the embodiments described below, it is assumed that propagation paths between the receiving and transmitting apparatus comprise flat-fading channels and undergo sufficiently gradual variations. The assumption is introduced for illustrative purposes only and is not intended to limit the scope of the invention in any way.

It is also assumed that the modulating process (constellation) for the control signals and the data signals is known in the receiving apparatus. This assumption is also introduced for illustrative purposes only. If the modulating process is changed by an adaptive control process such as an adaptive modulation process, then it may be handled in the same manner as described below by giving a function to reproduce information about the modulating process change to the likelihood information generator.

In any one of the embodiments, there are two types of transmission signals, one being a control signal and the other a data signal. However, those two types of transmission signals are given for illustrative purpose only and should not limit the scope of the present invention. In addition, though two reception modes are realized by different devices, i.e., the first data reproducer and the second data reproducer in the embodiments, such an arrangement should not limit the scope of the present invention. The two reception modes may be realized by controlling parameters used for reproducing signals.

The difference between control signals which are transmitted as identical signals from the respective antennas and data signals which are transmitted as different signals from the respective antennas will be described below.

It is assumed that control signals are represented by sc[t]. Since the same control signals are transmitted from the respective antennas, the signals received by the reception antennas are expressed as:
r1c[t]=h11sc[t]+h12sc[t]+h13sc[t]+n1[t]=(h11+h12+h13)sc[t]+n1[n]=h1sc[t]+n1[t]
r2c[t]=h21sc[t]+h22sc[t]+h23sc[t]+n2[t]=(h21+h22+h23)sc[t]+n2[n]=h2sc[t]+n2[t]
r3c[t]=h31sc[t]+h32sc[t]+h33sc[t]+n3[t]=(h31+h32+h33)sc[t]+n3[n]=h3sc[t]+n3[t]
where r1c[t], r2c[t], r3c[t] represent received signals at the respective reception antennas, and hijthe propagation path between transmission antenna j and reception antenna i. It is assumed that transmission path fluctuations are sufficiently shorter than signal transmission intervals.

The above equations indicate that if the same signals are transmitted from a plurality of transmission antennas, they can be handled as a signal transmitted from one transmission antenna. Reception processes in such an environment are introduced by many documents. In those reception processes, the best characteristics can be achieved by a maximum ratio combination as described in the present embodiment.

It is assumed that data signals1,2,3are represented by sd1[t], sd2[t], sd3[t], respectively. In this case, the signals received by the reception antennas are expressed as:
r1c[t]=h11s1c[t]+h12s2c[t]+h13s3c[t]+n1[t]
r2c[t]=h21s1c[t]+h22s2c[t]+h23s3c[t]+n2[t]
r3c[t]=h31s1c[t]+h32s2c[t]+h33s3c[t]+n3[t]
In order to demodulate and decode data signals1,2,3from a received MIMO signal, a reception process such as QR decomposition MLD as disclosed in the non-patent document referred to above is required.

FIG. 7is a flowchart of a demodulating process performed by receiving apparatus3according to the first embodiment. The processing sequence of receiving apparatus3according to the first embodiment will be described below with reference toFIG. 7. The processing sequence shown inFIG. 7is performed by a processor (not shown) in receiving apparatus3which executes a program stored in recording medium33of receiving apparatus3.

Received signals r1, r2, r3that are received by respective three antennas11-1,11-2,11-3are sent to receiving apparatus3.

Bit likelihood calculator3113is supplied with demodulated signal zc[t], calculates bit likelihood pair (L04, L14), and outputs calculated bit likelihood pair (L04, L14). Bit likelihood pair (L04, L14) may be calculated according to 3GPP, TR25.848(HSDPA), A1.4, for example. Decoder3123is supplied with bit likelihood pair (L04, L14), decodes it, and outputs reproduced data d4.

Likelihood information generator32will be described below. Likelihood information generator32is supplied with bit likelihood pair (L04, L14) and received signals r1, r2, r3.

In likelihood information generator32, comparator and averager321is supplied with bit likelihood pair (L04, L14), compares likelihoods where each bit is 0 and likelihoods where each bit is 1, selects smaller likelihoods in step S303, averages the selected likelihoods, and outputs the averaged likelihood as average second likelihood q in step S304.

Converter322is supplied with average second likelihood q and received signals r1, r2, r3, generates bit likelihood information Q1therefrom, and outputs generated bit likelihood information Q1in step S305.

FIG. 8shows converter322in block form. As shown inFIG. 8, converter322comprises channel estimator3111, a plurality of adding/squaring circuits3221, a pair of adding circuits3222, a plurality of squaring/reciprocal generating circuits3223, a pair of multiplying circuits3224, and reciprocal generating circuit3225.

Q1=q⁢3αβ⁢ⅆ1,min2ⅆ2,min2
where d22.min, d21.minrepresent average squared distances between minimum signal points of the control signals and the data signals. An average squared distance between minimum signal points refers to an average value of squared distances between minimum signal points from a certain symbol to another symbol that has a one bit difference from the certain symbol. If Gray coding is assumed, then d2minis equal to the square of a minimum signal converted distance because the constellation points for QPSK are symmetrical.

Bit likelihood information Q1described above is peculiar to the system having three transmission antennas and three reception antennas. If K types (K is an integer of 2 or greater) of signals, composed of at most M spatially multiplexed signals, are transmitted to each of M transmission antennas (M is an integer of 2 or greater) and received by N antennas (N is an integer of 2 or greater), and if the average squared distance between minimum signal points of the kth signal transmitted from the mth antenna is represented by dk,m,minand if K1types of signals (K1is 1 or greater and less than K) are received in the first reception mode and (K−K1) types of signals are received in the second reception mode, then general bit likelihood information Q is expressed as:

Q=q⁢⁢1∑n=1N⁢∑m=1M⁢hnm2·∑m=1M⁢1∑n=1N⁢hnm2·∑k=1K-K1⁢∑m=1M⁢ⅆk,m,min2∑k=1K1⁢∑m=1M⁢ⅆk,m,min2
where hnmrepresents the propagation path between the nth reception antenna and the mth transmission antenna, and q an average value of smaller bits of the first bit likelihood pairs.

According to 16QAM, an average value is produced based on the positions of constellation points even if Gray coding is assumed.

FIG. 21shows a portion of a pattern of constellation points according to 16QAM that are only in the first quadrant. There are four symbols in positions that are nearest constellation point1111which have a different from 1 bit therefrom. There is one such symbol in a position other than the positions nearest each of constellation points1110,1011, and there are two such symbols in positions other than the positions nearest constellation point1010. These symbols are averaged to provide:

d1,min2={4⁢dmin2+2⁢(3⁢d⁢min2+4⁢d⁢min2)+2⁢d⁢min2+8⁢d⁢min2}·116=2816⁢d⁢min2
where d2minrepresents the distance between minimum signals according to 16QAM.

Second data reproducer312will be described below. Second data reproducer312is supplied with received signals r1, r2, r3and bit likelihood information Q1.

Channel estimator3111′ is supplied with received signals r1, r2, r3, estimates channels therefrom, and outputs estimated channel values h11, h12, h13, h21, h22, h23, h31, h32, h33in step S306. QR decomposition MLD device3121is supplied with received signals r1, r2, r3, and estimated channel values h11, h12, h13, h21, h22, h23, h31, h32, h33from channel estimator3111′, symbol candidates and likelihoods of the symbols with respect to data signals1,2,3, and outputs symbol candidate and likelihood pairs (S11, e11) . . . (S1256, e1256) in step S307. In the present embodiment, the number of symbol candidates is 256. The amount of calculations required is much smaller than if the MLD process is applied to calculate 4096 symbol candidate and likelihood pairs.

Each of selectors31221-1,31221-2,31221-3is supplied with symbol candidate and likelihood pairs (S11, e11) . . . (S1256, e1256) and bit likelihood information Q1. Each of selectors31221-1,31221-2,31221-3selects, from 256 symbols, symbol candidates where each bit is 0 and symbol candidates where each bit is 1, and selects the maximum symbol likelihood among the selected symbol candidates as bit likelihood for bit0or bit1. If there is no symbol candidate for bit0or no symbol candidate for bit1, then each of selectors31221-1,31221-2,31221-3selects the bit likelihood information as bit likelihood. Accordingly, bit likelihood calculator3122can reliably calculate the likelihood for each bit0and each bit1regardless of the existence of symbol candidates.

According to the present embodiment, since the bit likelihood calculator, which links the complexity-reduced MLD device, does not need to perform an averaging process in calculating bit likelihood, the bit likelihood calculator does not suffer a processing delay due to an averaging process and hence can quickly calculate the bit likelihood. In addition, because bit likelihood information is calculated by the first data reproducer, the averaging accuracy of the bit likelihood information is determined by the first data reproducer. Therefore, the accuracy of the bit likelihood information is determined in advance until the second data reproducer starts to calculate the bit likelihood.

The processing operation of likelihood information generator32has been described above by way of example only for the purpose of illustrating the above embodiment. Specific operational details of likelihood information generator32are not limited to the processing operation described above.

FIG. 12shows in block form a wireless communication system according to a second embodiment of the present invention. The wireless communication system according to the second embodiment is similar in structure to the wireless communication system shown inFIG. 3.

As shown inFIG. 12, the wireless communication system according to the second embodiment comprises transmitting apparatus6having three antennas21-1,21-2,21-3, and receiving apparatus5having three antennas11-1,11-2,11-3.

Receiving apparatus5comprises data reproducing device51, likelihood information generator53, and recording medium52. Data reproducing device51comprises first data reproducer511and second data reproducer512.

FIG. 13shows the format of signals that are transmitted by transmitting apparatus6. As shown inFIG. 13, transmitting apparatus6sends data signal1and control signal1from antenna21-1, data signal2and control signal2from antenna21-2, and data signal3and control signal3from antenna21-3. Therefore, transmitting apparatus6sends two types of signals, or in other words, data signals and control signals. The data signals are sent as three multiplexed signals, and the control signals are also sent as three multiplexed signals. It is assumed that data signals1,2,3are modulated, i.e., have constellation points arranged according to 16QAM, and control signals1,2,3are modulated, i.e., have constellation points arranged according to QPSK.

FIG. 14is a flowchart of a demodulating process performed by receiving apparatus5according to the second embodiment. The processing sequence of receiving apparatus5according to the second embodiment will be described below with reference toFIG. 14. The processing sequence shown inFIG. 15is performed by a processor (not shown) in receiving apparatus5which executes a program stored in recording medium52of receiving apparatus5.

Second data reproducer312is supplied with received signals r1, r2, r3and bit likelihood information Q1, decodes them, and outputs data signals d1, d2, d3in step S505in the same manner as in the first embodiment. The wireless communication system according to the second embodiment differs from the wireless communication system according to the first embodiment with regard to first data reproducer511and likelihood information generator53. Therefore, first data reproducer511and likelihood information generator53will be described in detail below.

As shown inFIG. 15, first data reproducer511comprises channel estimator3111, maximum likelihood estimator5111, bit likelihood calculator5112, and decoder3123.

Channel estimator3111is supplied with received signals r1, r2, r3, estimates transmission paths therefrom, and outputs estimated channel values h11, h12, h13, h21, h22, h23, h31, h32, h33. Maximum likelihood estimator5111calculates likelihoods for all symbol candidates which have possibly been transmitted, calculates symbol candidates and likelihoods for the symbols, and outputs symbol candidate and likelihood pairs (S21, e21), . . . , (S264, e264) according to the maximum likelihood estimating method disclosed in Ohgane, Nishimura, Ogawa “Space Division Multiplexing and its Basic Characteristics in MIMO Channels,” IEICE Transactions B, J87-B, No. 9, p. 1162-1173, September 2004.

Bit likelihood calculator5112is supplied with symbol candidate and likelihood pairs (S21, e21), . . . , (S264, e264) and calculates and outputs bit likelihood pairs (L04, L14), (L05, L15), (L06, L16). The product according to the modulating process for control signals is 64, which is sufficiently smaller than the product 4096 according to the modulating process for data signals. In such a case, signals can easily be received with high performance by using the maximum likelihood estimating method. According to the maximum likelihood estimating method, since symbol likelihoods for all symbol candidates are output, candidates where each bit is 0 and candidates where each bit is 1 are included without fail. By selecting maximum symbol likelihood for symbol candidates where each bit is 0 or 1 as bit likelihood, the bit likelihood can be directly calculated.

Comparator and averager531is supplied with bit likelihood pairs (L04, L14), (L05, L15), (L06, L16), compares likelihoods where each bit is 0 and likelihoods where each bit is 1, selects smaller likelihoods in step S523(FIG. 14), averages the selected likelihoods, and outputs the averaged likelihood as average second likelihood q in step S503.

Converter532is supplied with average second likelihood q and received signals r1, r2, r3, generates bit likelihood information Q1therefrom, and outputs generated bit likelihood information Q1in step S504.

Reciprocal generating circuit3225is supplied with average squared distance d22,minbetween minimum signal points of control signals, and outputs the reciprocal thereof. Multiplying circuit3224multiplies the reciprocal, average squared distance d21,minbetween minimum signal points of data signals, and average second likelihood q, and outputs the product as bit likelihood information Q1. Bit likelihood information Q1is expressed as:

Bit likelihood information Q1described above is peculiar to a system having three transmission antennas and three reception antennas. If K types (K is an integer of 2 or greater) of signals composed of at most M spatially multiplexed signals are transmitted to each of M transmission antennas (M is an integer of 2 or greater) and received by N antennas (N is an integer of 2 or greater), and if the average squared distance between minimum signal points of the kth signal transmitted from the mth antenna is represented by d2k,m,minand if K1types of signals (K1is 1 or greater and less than K) are received in the first reception mode and (K−K1) types of signals are received in the second reception mode, then general bit likelihood information Q is expressed as:

Q=q⁢∑k=1K-K1⁢∑m=1M⁢ⅆk,m,⁢min2∑k=1K1⁢∑m=1M⁢ⅆk,m,⁢min2
where q represents an average value of smaller bits of the first bit likelihood pairs.

In the first embodiment, the conversion is based on the estimated propagation path response and the constellation points layout. According to the present embodiment, the conversion is based on only the constellation points layout because both the control signals and the data signals are transmitted through MIMO channels.

According to the present embodiment, even through control signals are transmitted through MIMO channels, bit likelihood information can reliably be generated by applying the demodulating process which is capable of reliably calculating bit likelihood. As a result, since no averaging process is required for calculating bit likelihood with the second data reproducer, the second data reproducer does not suffer a processing delay due to an averaging process and hence can quickly calculate bit likelihood.

The processing operation of likelihood information generator53has been described above by way of example only for the purpose of illustrating the above embodiment. Specific operational details of likelihood information generator53are not limited to the processing operation described above.

According to a third embodiment of the present invention, three data signals and three control signals are transmitted as shown inFIG. 13as in the second embodiment. In the present embodiment, it is assumed that the data signals are modulated according to one modulating process, and the control signals are modulated according to respective different modulating processes.

According to the third embodiment, converter532shown inFIG. 16is replaced with converter732shown inFIG. 18. Stated otherwise, the receiving apparatus according to the third embodiment differs from the receiving apparatus according to the second embodiment only with regard to converter732. Details of converter732will be described below.

Converter732is supplied with average second likelihood q. In converter732, adding circuit3222, reciprocal generating circuit3225, and multiplying circuit3224calculate bit likelihood information Q1as follows:

According to the present embodiment, even though the control signals are modulated according to respective different modulating processes, bit likelihood information can be generated from the average second likelihood by a weighting process that is performed by converter732depending on the layout of constellation points of the control signals.

According to a fourth embodiment of the present invention, three data signals and three control signals are transmitted as shown inFIG. 13as with the second embodiment. In the present embodiment, it is assumed that the data signals and the control signals may not necessarily be modulated according to one modulating process.

According to the fourth embodiment, converter532shown inFIG. 16is replaced with converter832shown inFIG. 19. Stated otherwise, the receiving apparatus according to the fourth embodiment differs from the receiving apparatus according to the second embodiment only as regards converter832. Details of converter832will be described below.

In converter732, reciprocal generating circuit3225, adding circuit3222, and multiplying circuit3224convert the average second likelihood q into bit likelihood information Q1according to the equation:

Q1=ⅆ1,min2⁢+ⅆ2,min2⁢+ⅆ3,min23⁢ⅆ4,min2⁢q
and output calculated bit likelihood information Q1, where d21,min, d22,min, d23,minrepresent respective average squared distances between minimum signal points of data signals1,2,3, and d24,minrepresent an average squared distance between minimum signal points of the control signals.

According to the present embodiment, even though the layout of signal points of data signals is not constant, bit likelihood information can be determined.

According to a fifth embodiment, three data signals and one control signal are transmitted as with the first embodiment.

According to the fifth embodiment, bit likelihood calculator3122shown inFIG. 5is replaced with bit likelihood calculator9122shown inFIG. 20. Stated otherwise, the receiving apparatus according to the fifth embodiment differs from the receiving apparatus according to the first embodiment only as regards bit likelihood calculator9122. Details of converter732will be described below.

Details of bit likelihood calculator9122will be described below.

Only when both likelihoods for bit0and likelihood for bit1can be selected from symbol candidate and likelihood pairs, averager91221can have smaller likelihoods to be averaged, and sequentially averages them using bit likelihood information Q1as an initial value, and outputs an average value p.

Each of selectors3221-1,3221-2,3221-3is supplied with symbol candidate and likelihood pairs (S1, e1) . . . (S256, e256) and average value p. If likelihoods for either bit0or bit1can be selected from symbol candidate and likelihood pairs, then each of selectors3221-1,3221-2,3221-3selects a maximum value of the symbol likelihoods as a bit likelihood. If likelihoods for either bit0or bit1can be selected from symbol candidate and likelihood pairs, then each of selectors3221-1,3221-2,3221-3selects average value p instead as the bit likelihood.

Since averager91221sequentially averages the smaller likelihoods using bit likelihood information Q1as an initial value, no buffer is required in the converter, thereby eliminating the delay caused by the conventional bit likelihood calculator shown inFIG. 2.

In addition, the second embodiment is also advantageous in that the sequentially averaged value approaches, over, the average value calculated by the conventional bit likelihood calculator shown inFIG. 2.