Data transmission/reception apparatus and method for achieving both multiplexing gain and diversity gain in a mobile communication system using space-time trellis code

A mobile communication system includes at least three transmission antennas of first to third transmission antennas, and uses an overlapped antenna scheme for grouping the first and second transmission antennas into a first transmission antenna group and grouping the second and third transmission antennas into a second transmission antenna group. First and second modulators modulate L information bit streams to be transmitted through the first transmission antenna group and output first and second modulation symbol streams. Third and fourth modulators modulate L other information bit streams to be transmitted through the second transmission antenna group and output third and fourth symbol streams. First to fourth puncturers puncture at least one modulation symbol in a predetermined position among the first to fourth modulation symbol streams. A multiplexer transmits a modulation symbol stream output from the first puncturer through the first transmission antenna, transmits modulation symbol streams output from the second and third puncturers through the second transmission antenna after summation, and transmits a modulation symbol stream output from the third puncturer through the third transmission antenna.

PRIORITY

This application claims priority under 35 U.S.C. § 119 to an application entitled “Data Transmission/Reception Apparatus and Method for Achieving Both Multiplexing Gain and Diversity Gain in a Mobile Communication System Using Space-Time Trellis Code” filed in the Korean Intellectual Property Office on Jan. 9, 2003 and assigned Ser. No. 2003-1452, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a mobile communication system, and in particular, to a data transmission/reception apparatus and method for achieving both multiplexing gain and diversity gain in a mobile communication system using a space-time trellis code (hereinafter referred to as “STTC”).

2. Description of the Related Art

With the rapid development of mobile communication systems, the amount of data serviced by the mobile communication system has also increased. Recently, a 3rdgeneration mobile communication system for transmitting high-speed data has been developed. For the 3rdgeneration mobile communication system, Europe has adopted an asynchronous wideband-code division multiple access (hereinafter referred to as “W-CDMA”) system as its radio access standard, while North America has adopted a synchronous code division multiple access-2000 (hereinafter referred to as “CDMA-2000”) system as its radio access standard. Generally, in these mobile communication systems, a plurality mobile stations (MSs) communicate with each other via a common base station (BS). However, during high-speed data transmission in the mobile communication system, a phase of a received signal may be distorted due to a fading phenomenon occurring on a radio channel. The fading reduces amplitude of a received signal by several dB to several tens of dB. If a phase of a received signal distorted due to the fading phenomenon is not compensated for during data demodulation, the phase distortion becomes a cause of information error of transmission data transmitted by a transmission side, causing a reduction in the quality of a mobile communication service. Therefore, in mobile communication systems, fading must be overcome in order to transmit high-speed data without a decrease in the service quality, and several diversity techniques are used in order to cope with the fading.

Generally, a CDMA system adopts a rake receiver that performs diversity reception by using delay spread of a channel. While the rake receiver applies reception diversity for receiving a multipath signal, a rake receiver applying the diversity technique using the delay spread is disadvantageous in that it does not operate when the delay spread is less than a preset value. In addition, a time diversity technique using interleaving and coding is used in a Doppler spread channel. However, the time diversity technique is disadvantageous in that it can hardly be used in a low-speed Doppler spread channel.

Therefore, in order to cope with fading, a space diversity technique is used in a channel with low delay spread, such as an indoor channel, and a channel with low-speed Doppler spread, such as a pedestrian channel. The space diversity technique uses two or more transmission/reception antennas. In this technique, when a signal transmitted via one transmission antenna decreases in its signal power due to fading, a signal transmitted via the other transmission antenna is received. The space diversity can be classified into a reception antenna diversity technique using a reception antenna and a transmission diversity technique using a transmission antenna. However, since the reception antenna diversity technique is applied to a mobile station, it is difficult to install a plurality of antennas in the mobile station in view of the mobile station's size and its installation cost. Therefore, it is recommended that the transmission diversity technique should be used in which a plurality of transmission antennas are installed in a base station.

Particularly, in a 4thgeneration mobile communication system, a data rate of about 10 Mbps to 150 Mbps is expected, and an error rate requires a bit error rate (hereinafter referred to as “BER”) of 10−3for voice, BER of 10−6for data, and BER of 10−9for image. The STTC is a combination of a multi-antenna technique and a channel coding technique, and is a technique bringing a drastic improvement of a data rate and reliability in a radio MIMO (Multi Input Multi Output) channel. The STTC obtains the receiver's space-time diversity gain by extending the space-time dimension of a transmitter's transmission signal. In addition, the STTC can obtain coding gain without a supplemental bandwidth, contributing to an improvement in channel capacity.

Therefore, in the transmission diversity technique, the STTC is used. When the STTC is used, coding gain having an effect of increasing transmission power is obtained together with diversity gain which is equivalent to a reduction in channel gain occurring due to a fading channel when the multiple transmission antennas are used. A method for transmitting a signal using the STTC is disclosed in Vahid Tarokh, N. Seshadri, and A. Calderbank, “Space Time Codes For High Data Rate Wireless Communication: Performance Criterion And Code Construction,” IEEE Trans. on Info. Theory, pp. 744-765, Vol. 44, No. 2, March 1998. In this reference, it is provided that if a code rate is defined as the number of symbols transmitted for a unit time, the code rate must be smaller than 1 in order to obtain diversity gain corresponding to the product of the number of transmission antennas and the number of reception antennas.

FIG. 1is a block diagram schematically illustrating a general structure of a transmitter using STTC. Referring toFIG. 1, when L information data bits d1, d2, d3, . . . , dLare input to the transmitter, the input information data bits d1, d2, d3, . . . , dLare provided to a serial-to-parallel (S/P) converter111. Here, the index L represents the number of information data bits to be transmitted by the transmitter for a unit transmission time, and the unit transmission time can become a symbol unit. The S/P converter111parallel-converts the information data bits d1, d2, d3, . . . , dLand provides its outputs to first to Lthencoders121-1to121-L. That is, the S/P converter111provides a parallel-converted information data bit d1, to the first encoder121-1, and in this manner, provides a parallel-converted information data bit dLto the Lthencoder121-L. The first to Lthencoders121-1to121-L each encode signals output from the S/P converter111in a predetermined encoding scheme, and then each provide their outputs to first to Mthmodulators131-1to131-M. Here, the index M represents the number of transmission antennas included in the transmitter, and the predetermined encoding scheme is an STTC encoding scheme. A detailed structure of the first to Lthencoders121-1to121-L will be described later with reference toFIG. 2.

The first to Mthmodulators131-1to131-M each modulate signals received from the first to Lthencoders121-1to121-L in a predetermined modulation scheme. The first to Mthmodulators131-1to131-M are similar to one another in operation except the signals applied thereto. Therefore, only the first modulator131-1will be described herein. The first modulator131-1adds up signals received from the first to Lthencoders121-1to121-L, multiplies the addition result by a gain applied to a transmission antenna to which the first modulator131-1is connected, i.e., a first transmission antenna ANT#1, modulates the multiplication result in a predetermined modulation scheme, and provides the modulation result to the first transmission antenna ANT#1. Here, the modulation scheme includes BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), QAM (Quadrature Amplitude Modulation), PAM (Pulse Amplitude Modulation), and PSK (Phase Shift Keying). It will be assumed inFIG. 1that since the number of encoders is L, 2L-ary QAM is used as a modulation scheme. The first to Mthmodulators131-1to131-M provide their modulation symbols S1to SMto first to Mthtransmission antennas ANT#1to ANT#M, respectively. The first to Mthtransmission antennas ANT#1to ANT#M transmit to the air the modulation symbols S1to SMoutput from the first to Mthmodulators131-1to131-M.

FIG. 2is a block diagram illustrating a detailed structure of the first to Lthencoders121-1to121-L ofFIG. 1. For simplicity, a description will be made of only the first encoder121-1. The information data bit d1output from the S/P converter111is applied to the first encoder121-1, and the first encoder121-1provides the information data bit d1to tapped delay lines, i.e., delays (D)211-1,211-2, . . . ,211-(K−1). Here, the number of the delays, or the tapped delay lines, is smaller by 1 than a constraint length K of the first encoder121-1. The delays211-1,211-2, . . . ,211-(K−1) each delay their input signals. That is, the delay211-1delays the information data bit d1and provides its output to the delay211-2, and the delay211-2delays an output signal of the delay211-1. In addition, input signals provided to the delays211-1,211-2, . . . ,211-(K−1) are multiplied by predetermined gains, and then provided to modulo adders221-1, . . . ,221-M, respectively. The number of the modulo adders is identical to the number of the transmission antennas. InFIG. 1, since the number of the transmission antennas is M, the number of the modulo adders is also M. Further, gains multiplied by the input signals of the delays211-1,211-2, . . . ,211-(K−1) are represented by gi,j,t, where i denotes an encoder index, j an antenna index and t a memory index. InFIG. 1, since the number of encoders is L and the number of antennas is M, the encoder index i increases from 1 to L, the antenna index j increases from 1 to M, and the memory index K increases from 1 to the constraint length K. The modulo adders221-1, . . . ,221-M each modulo-add signals obtained by multiplying the input signals of the corresponding delays211-1,211-2, . . . ,211-(K−1) by the gains. The STTC encoding scheme is also disclosed in Vahid Tarokh, N. Seshadri, and A. Calderbank, “Space Time Codes For High Data Rate Wireless Communication: Performance Criterion And Code Construction,” IEEE Trans. on Info. Theory, pp. 744-765, Vol. 44, No. 2, March 1998.

FIG. 3is a block diagram schematically illustrating a structure of an STTC transmitter having two encoders and 3 transmission antennas. Referring toFIG. 3, when 2 information data bits d1and d2are input to the transmitter, the input information data bits d1, and d2are applied to an S/P converter311. The S/P converter311parallel-converts the information data bits d1and d2, and outputs the information data bit d1to a first encoder321-1and the information data bit d2to a second encoder321-2. If it is assumed that the first encoder321-1has a constraint length K of 4 (constraint length K=4), an internal structure, illustrated inFIG. 2, of the first encoder321-1is comprised of 3 delays (1+2D+D3) and 3 modulo adders, wherein the number of delays and modulo adders is equal to a value smaller by 1 than the constant length K=4. Therefore, in the first encoder321-1, the undelayed information data bit d1applied to a first delay, a bit determined by multiplying a bit delayed once by the first delay by 2, and a bit delayed three times by a third delay are provided to a first modulo adder connected to a first modulator331-1of a first transmission antenna ANT#1. In this manner, outputs of the 3 modulo adders of the first encoder321-1are provided to the first modulator331-1, a second modulator331-2and a third modulator331-3, respectively. Similarly, the second encoder321-2encodes the information data bit d2output from the S/P converter311in the same encoding scheme as that used by the first encoder321-1, and then, provides its outputs to the first modulator331-1, the second modulator331-2and the third modulator331-3.

The first modulator331-1modulates the signals output from the first encoder321-1and the second encoder321-2in a predetermined modulation scheme, and then provides its output to a first transmission antenna ANT#1. It is assumed herein that a modulation scheme applied to the transmitter is QPSK. Therefore, if an output signal of the first encoder321-1is b1and an output signal of the second encoder321-2is b2, the first modulator331-1modulates the output signals in the QPSK modulation scheme, and outputs b1+b2*j, where j=√{square root over (−1)}. Like the first modulator331-1, the second modulator331-2and the third modulator331-3modulate output signals of the first encoder321-1and the second encoder321-2in the QPSK modulation scheme, and then, provide their outputs to a second transmission antenna ANT#2and a third transmission antenna ANT#3, respectively. The first to third transmission antennas ANT#1to ANT#3transmit to the air the modulation symbols S1to S3output from the first to third modulators331-1to331-3, respectively.

FIG. 4is a block diagram schematically illustrating a receiver structure corresponding to the transmitter structure using the STTC described above in conjunction withFIG. 1. Referring toFIG. 4, a signal transmitted to the air by a transmitter is received through reception antennas of the receiver. It is assumed inFIG. 4that there are provided N reception antennas. The N reception antennas each process signals received from the air. Specifically, a signal received through a first reception antenna ANT#1is provided to a channel estimator411and a metric calculator423. The channel estimator411performs channel estimation on signals output from the first to Nthreception antennas ANT#1to ANT#N, and then provides the channel estimation result to a hypothesis part412.

A possible sequence generator415generates all kinds of sequences which were possibly simultaneously encoded for information data bits transmitted by the transmitter, and provides the generated sequences to first to Lthencoders417-1to417-L. Since the transmitter transmits information data by the L information bits, the possible sequence generator415generates possible sequences {tilde over (d)}1. . . {tilde over (d)}Lcomprised of L bits. The L bits of the generated possible sequences are applied to the first to Lthencoders417-1to417-L, and the first to Lthencoders417-1to417-L encode their input bits in the STTC encoding scheme described in conjunction withFIG. 2, and then provide the encoded bits to first to Mthmodulators419-1to419-M. The first to Mthmodulators419-1to419-M each modulate the encoded bits output from the first to Lthencoders417-1to417-L in a predetermined modulation scheme, and provide their outputs to the hypothesis part412. The modulation scheme applied in the first to Mthmodulators419-1to419-M is set to any one of the BPSK, QPSK, QAM, PAM and PSK modulation schemes. Since a modulation scheme applied in the first to Mthmodulators131-1to131-M ofFIG. 1is 2L-ary QAM, the first to Mthmodulators419-1to419-M also modulate their input signals in the 2L-ary QAM modulation scheme.

The hypothesis part412receives signals output from the first to Mthmodulators419-1to419-M and the channel estimation value output from the channel estimator411, generates a hypothetic channel output at a time when a sequence consisting of the signals output from the first to Mthmodulators419-1to419-M has passed a channel corresponding to the channel estimation result, and provides the generated hypothetic channel output to the metric calculator423. The metric calculator423receives the hypothetic channel output provided from the hypothesis part412and the signals received through the first to Nthreception antennas ANT#1to ANT#N, and calculates a distance between the hypothetic channel output and the signals received through the first to Nthreception antennas ANT#1to ANT#N. The metric calculator423uses Euclidean distance when calculating the distance.

In this manner, the metric calculator423calculates Euclidean distance for all possible sequences the transmitter can transmit, and then provides the calculated Euclidean distance to a minimum distance selector425. The minimum distance selector425selects a Euclidean distance having the minimum distance from Euclidean distances output from the metric calculator423, determines information bits corresponding to the selected Euclidean distance as information bits transmitted by the transmitter, and provides the determined information bits to a parallel-to-serial (P/S) converter427. Although there are several possible algorithms used when the minimum distance selector425determines information bits corresponding to the Euclidean distance having the minimum distance, it is assumed herein that a Viterbi algorithm is used. A process of extracting information bits having the minimum distance by using the Viterbi algorithm is disclosed in Vahid Tarokh, N. Seshadri, and A. Calderbank, “Space Time Codes For High Data Rate Wireless Communication: Performance Criterion And Code Construction,” IEEE Trans. on Info. Theory, pp. 744-765, Vol. 44, No. 2, March 1998, so a detailed description thereof will not be provided for simplicity. Since the minimum distance selector425determines information bits corresponding to the Euclidean distance having the minimum distance for all sequences generated from the possible sequence generator415, it finally outputs L information bits of {circumflex over (d)}1, {circumflex over (d)}1, . . . , {circumflex over (d)}L. The P/S converter427then serial-converts the L information bits output from the minimum distance selector425, and outputs reception information data sequences {circumflex over (d)}1, {circumflex over (d)}1, . . . , {circumflex over (d)}L.

As described above, when the transmitter transmits a signal with a plurality of transmission antennas, the STTC can achieve coding gain having an effect of amplifying power of a received transmission signal, together with diversity gain, in order to prevent a reduction in channel gain occurring due to a fading channel. In Tarokh, it is provided that if a code rate is defined as the number of symbols transmitted for a unit time in a communication system using STTC, the code rate must be smaller than 1 in order to obtain diversity gain corresponding to the product of the number of transmission antennas and the number of reception antennas. That is, it is provided that if it is assumed that the number of information data bits in a symbol transmitted to the air through one transmission antenna at a particular transmission time is N, even though a transmitter uses a plurality of transmission antennas, the number of information data bits that can be transmitted to the air through the plural transmission antennas at a particular transmission time must be smaller than or equal to N in order to achieve diversity gain corresponding to the product of the number of transmission antennas and the number of reception antennas. The reason for providing that the number of information data bits that can be transmitted to the air through a plurality of transmission antennas should be smaller than or equal to N is to maintain diversity gain through the plural transmission antennas.

As mentioned above, a mobile communication system using STTC can achieve both the diversity gain and the coding gain, so the system is effective when using multiple antennas in a varying channel environment. However, since only one data stream is transmitted through multiple antennas, it is difficult to achieve multiplexing gain, which is equivalent to achieving gain in terms of a data rate. In order to solve this problem, there has been recently proposed a technique for applying multiplexing to multiple antennas before transmission in a transmitter in order to maximize a multiplexing gain, i.e., a data rate. In a technique for applying channel coding to the multiple antennas, a transmitter transmits a plurality of data streams through plural transmission antennas, thereby achieving both diversity gain and multiplexing gain.

Meanwhile, in a technique for applying STTC to the multiple antennas, if the number of transmission antennas of a transmitter is 3 and the number of reception antennas of a receiver is 3, it is possible in theory to obtain 9-level diversity gain. However, in practice in an actual mobile communication system, diversity gain of over 4 levels does not affect improvement in system performance, so there is a limitation on improvement in system performance. In a technique proposed to make up for the defects that result in system performance which cannot be improved further even though high-level diversity gain can be actually obtained, when the number of transmission antennas of a transmitter is larger than or equal to a predetermined number, the transmission antennas are classified into several groups for signal transmission. The technique for classifying the transmission antennas into several groups for signal transmission is called “combined array processing and diversity.” The combined array processing and diversity technique is disclosed in Vahid Tarokh, A. Naguib, N. Seshadri, and A. Calderbank, “Combined Array Processing And Space Time Coding.” IEEE Trans. Inform. Theory, Vol. 45, pp. 1121-1128, May 1999.

FIG. 5is a block diagram schematically illustrating a general structure of an STTC transmitter using the combined array processing and diversity technique. Referring toFIG. 5, the transmitter includes M transmission antennas, and classifies the M transmission antennas into P groups. That is, MPtransmission antennas constitute one group, and each group performs the transmission operation, i.e., encoding and modulation operations, described in conjunction withFIG. 1. Here, the sum of M1to MPis M. The combined array processing and diversity technique will now be described with reference to a first transmission antenna group and a Pthtransmission antenna group among the P transmission antenna groups.

First, the first transmission antenna group will be described. If L information data bits d11, d21, d31, . . . , dL1are input to a transmitter of the first transmission antenna group, the input information data bits d11, d21, d31, . . . , dL1are provided to an S/P converter511. Here, the index L represents the number of information data bits to be transmitted by the transmitter of the first transmission antenna group for a unit transmission time, and the unit transmission time can become a symbol unit. In addition, the index “1” succeeding the index L represents the first transmission antenna group. The S/P converter511parallel-converts the information data bits d11, d21, d31, . . . , dL1and provides its outputs to first to L1thencoders521-1to521-L1. That is, the S/P converter511provides a parallel-converted information data bit d11to the first encoder521-1, and in this manner, provides a parallel-converted information data bit dL1to the L1thencoder521-L1. The first to L1thencoders521-1to521-L1each encode signals output from the S/P converter511in a predetermined encoding scheme, and then provide their outputs to first to M1thmodulators531-1to531-M1. Here, the index M1represents the number of transmission antennas included in the transmitter of the first transmission antenna group, and the predetermined encoding scheme is an STTC encoding scheme.

The first to M1thmodulators531-1to531-M1each modulate signals received from the first to L1thencoders521-1to521-L1in a predetermined modulation scheme. The first to M1thmodulators531-1to531-M1provide modulation symbols S1to SM1to first to M1thtransmission antennas ANT#1to ANT#M1, respectively. The first to M1thtransmission antennas ANT#1to ANT#M1transmit to the air the modulation symbols S1to SM1output from the first to M1thmodulators531-1to531-M1.

Second, the Pthtransmission antenna group will be described. If L information data bits d1P, d2P, d3P, . . . , dLPare input to a transmitter of the Pthtransmission antenna group, the input information data bits d1P, d2P, d3P, . . . , dLPare provided to an S/P converter551. Here, the index “P” succeeding the index L represents the Pthtransmission antenna group. The S/P converter551parallel-converts the information data bits d1P, d2P, d3P, . . . , dLPand provides its outputs to first to LPthencoders561-1to561-LP. That is, the S/P converter551provides a parallel-converted information data bit d1Pto the first encoder561-1, and in this manner, provides a parallel-converted information data bit dLPto the LPthencoder561-LP. The first to LPthencoders561-1to561-LPeach encode signals output from the S/P converter551in a predetermined encoding scheme, and then provide their outputs to first to MPthmodulators571-1to571-MP. Here, the index MPrepresents the number of transmission antennas included in the transmitter of the Pthtransmission antenna group.

The first to MPthmodulators571-1to571-MPeach modulate signals received from the first to LPthencoders561-1to561-LPin a predetermined modulation scheme. The first to MPthmodulators571-1to571-MPprovide modulation symbols S1to SMPto (M−MP+1)thto Mthtransmission antennas ANT#(M−MP+1) to ANT#M, respectively. The (M−MP+1)thto Mthtransmission antennas ANT#(M−MP+1) to ANT#M transmit to the air the modulation symbols S1to SMPoutput from the first to MPthmodulators571-1to571-MP.

As described in conjunction withFIG. 5, the combined array processing and diversity classifies M transmission antennas into P transmission antenna groups, and then modulates input information data according to the groups before transmission, thereby increasing diversity gain efficiency. In addition, the combined array processing and diversity technique transmits a non-overlapping signal through transmission antennas.

FIG. 6is a block diagram schematically illustrating a receiver structure based on the combined array processing and diversity technique, and corresponding to the transmitter structure ofFIG. 5. Referring toFIG. 6, a signal transmitted to the air by a transmitter is received through reception antennas of the receiver. It is assumed inFIG. 6that there are provided N reception antennas. The N reception antennas each process signals received from the air. Specifically, signals received through first to Nthreception antennas ANT#1to ANT#N are provided to a channel estimator611and an interference suppressor613. The channel estimator611performs channel estimation on signals output from the first to Nthreception antennas ANT#1to ANT#N, and then provides the channel estimation result to the interference suppressor613. The interference suppressor613removes an interference component from each of the signals output from the first to Nthreception antennas ANT#1to ANT#N based on the channel estimation result output from the channel estimator611, and then provides its outputs to first to Pthdecoders615-1to615-P. Considering signals output from the first to Nthreception antennas ANT#1to ANT#N, of the N reception antennas, ΣMPp={2˜p} reception antennas are used to remove the interference component and the other reception antennas are used to increase diversity gain. A process of removing by the interference suppressor613an interference component from the signals received from the first to Nthreception antennas ANT#1to ANT#N is also disclosed in Vahid Tarokh, A. Naguib, N. Seshadri, and A. Calderbank, “Combined Array Processing And Space Time Coding.” IEEE Trans. Inform. Theory, Vol. 45, pp. 1121-1128, May 1999, so a detailed description thereof will be omitted for simplicity. The interference component-removed signals output from the interference compressor613are provided to the first to Pthdecoders615-1to615-P. The first to Pthdecoders615-1to615-P each perform STTC decoding on signals output from the interference compressor613, and output {circumflex over (d)}11{circumflex over (d)}21{circumflex over (d)}31. . . {circumflex over (d)}L1to {circumflex over (d)}1P{circumflex over (d)}2P{circumflex over (d)}3P. . . {circumflex over (d)}LP.

The combined array processing and diversity technique can simply trade off a diversity gain, i.e., a diversity order, with a data rate. In order to increase the diversity order, the number of transmission antenna groups of a transmitter must be increased. In addition, a receiver can relatively simply remove an interference component through the operation of removing the interference component. However, the combined array processing and diversity brings about a great loss in diversity gain in the process of trading off the diversity gain with the data rate. For example, it will be assumed that a transmitter has 3 transmission antennas and a receiver also has 3 reception antennas. The transmitter forms two transmission antennas into a first transmission antenna group, and forms the remaining one transmission antenna into a second transmission antenna group. Thus, it will be assumed that the transmitter transmits a first stream through the first transmission antenna group and a second stream through the second transmission antenna group. In this case, the receiver removes the second stream that acts as an interference component when decoding the first stream, thereby obtaining a diversity gain of a level 4. However, the receiver removes the first stream that acts as an interference component when decoding the second stream, so it has a diversity gain of a level 1, and this operates as if there is no diversity gain. Therefore, the combined array processing and diversity technique has a great loss of diversity gain when the number of transmission antennas of the transmitter is small.

In order to eliminate the diversity gain loss of the combined array processing and diversity technique, there has been proposed a technique for transmitting a signal by overlapping a plurality of transmission antennas, and the technique for transmitting a signal by overlapping the transmission antennas is called “overlapped combined array processing and diversity.” The overlapped combined array processing and diversity technique is disclosed in Korean patent application No. 2002-59621, filed on Sep. 30, 2002, and commonly assigned to the assignee of this application, the contents of which are incorporated herein by reference. This reference discloses a technique for transmitting/receiving a signal by grouping transmission antennas so that some transmission antennas among the transmission antennas overlap one another.

FIG. 7is a block diagram schematically illustrating a general structure of an STTC transmitter based on the overlapped combined array processing and diversity technique. Referring toFIG. 7, the transmitter includes M transmission antennas, and classifies the M transmission antennas into P groups. That is, MPtransmission antennas constitute one group, and each group performs the transmission operation, i.e., encoding and modulation operations, described in conjunction withFIG. 1. Here, the sum of M1to MPexceeds M. The reason that the sum of M1to MPexceeds M is because the overlapped combined array processing and diversity technique fundamentally overlaps transmission antennas. The overlapped combined array processing and diversity technique will now be described with reference to a first transmission antenna group and a Pthtransmission antenna group among the P transmission antenna groups.

First, the first transmission antenna group will be described. If L information data bits d11, d21, d31, . . . , dL1are input to a transmitter of the first transmission antenna group, the input information data bits d11, d21, d31, . . . , dL1are provided to an S/P converter711. Here, the index L represents the number of information data bits to be transmitted by the transmitter of the first transmission antenna group for a unit transmission time, and the unit transmission time can become a symbol unit. In addition, the index “1” succeeding the index L represents the first transmission antenna group. The S/P converter711parallel-converts the information data bits d11, d21, d31, . . . , dL1and provides its outputs to first to L1thencoders721-1to721-L1. That is, the S/P converter711provides a parallel-converted information data bit d11, to the first encoder721-1, and in this manner, provides a parallel-converted information data bit dL1to the L1thencoder721-L1. The first to L1thencoders721-1to721-L1each encode signals output from the S/P converter711in a predetermined encoding scheme, and then provide their outputs to first to M1thmodulators731-1to731-M1. Here, the index M1represents the number of transmission antennas included in the transmitter of the first transmission antenna group, and the predetermined encoding scheme is an STTC encoding scheme.

The first to M1thmodulators731-1to731-M1each modulate signals received from the first to L1thencoders721-1to721-L1in a predetermined modulation scheme. The first to M1thmodulators731-1to731-M1provide modulation symbols S1to SM1−1to a first summer741-1. Here, the summers are matched to the transmission antennas on a one-to-one basis, and the first summer741-1is connected to a first transmission antenna ANT#1. Of the modulation symbols S1to SM1, the modulation symbol SM1is provided even to the second summer741-2, and the reason is because a signal output from the M1thmodulator731-M1among output signals of the first transmission antenna group overlaps with output signals of a second transmission antenna group. The summer741-1sums up the modulation symbols S1to SM1and transmits the summation result to the air through the first transmission antenna ANT#1.

Second, the Pthtransmission antenna group will be described. If L information data bits d1P, d2P, d3P, . . . , dLPare input to a transmitter of the Pthtransmission antenna group, the input information data bits d1P, d2P, d3P, . . . , dLPare provided to an S/P converter751. Here, the index “P” succeeding the index L represents the Pthtransmission antenna group. The S/P converter751parallel-converts the information data bits d1P, d2P, d3P, . . . , dLPand provides its outputs to first to LPthencoders761-1to761-LP. That is, the S/P converter751provides a parallel-converted information data bit dip to the first encoder761-1, and in this manner, provides a parallel-converted information data bit dLPto the LPthencoder761-LP. The first to LPthencoders761-1to761-LPeach encode signals output from the S/P converter751in an STTC encoding scheme, and then provide their outputs to first to MPthmodulators771-1to771-MP. Here, the index MPrepresents the number of transmission antennas included in the transmitter of the Pthtransmission antenna group.

The first to MPthmodulators771-1to771-MPeach modulate signals received from the first to LPthencoders761-1to761-LPin a predetermined modulation scheme. The first to MPthmodulators771-1to771-MPprovide modulation symbols S1to SMPto an Mthsummer741-M. Of the modulation symbols S1to SMP, the modulation symbol S1is provided even to the second summer741-2, and the reason is because a signal output from the first modulator771-1among output signals of the Pthtransmission antenna group overlaps with output signals of the second transmission antenna group. The summer741-M sums up the modulation symbols S1to SM1and transmits the summation result to the air through the Mthtransmission antenna ANT#M.

FIG. 8is a block diagram schematically illustrating a receiver structure based on the overlapped combined array processing and diversity technique, and corresponding to the transmitter structure ofFIG. 7. Referring toFIG. 8, a signal transmitted to the air by a transmitter is received through reception antennas of the receiver. It is assumed inFIG. 8that there are provided N reception antennas. The N reception antennas each of which process signals received from the air. Specifically, signals received through first to Nthreception antennas ANT#1to ANT#N are provided to a channel estimator811and an interference suppressor813. The channel estimator811performs channel estimation on signals output from the first to Nthreception antennas ANT#1to ANT#N, and then provides the channel estimation result to the interference suppressor813. The interference suppressor813removes an interference component from each of the signals output from the first to Nthreception antennas ANT#1to ANT#N based on the channel estimation result output from the channel estimator811, and then provides its outputs to first to Pthdecoders815-1to815-P. Considering signals output from the first to Nthreception antennas ANT#1to ANT#N, of the N reception antennas, (M−MP) reception antennas are used to remove the interference component and the other reception antennas are used to increase diversity gain. A process of removing by the interference suppressor813an interference component from the signals received from the first to Nthreception antennas ANT#1to ANT#N is disclosed in Korean patent application No. 2002-59621, filed on Sep. 30, 2002, and commonly assigned to the assignee of this application, and is hereby incorporated by reference. A detailed description thereof will be omitted for simplicity. The interference component-removed signals output from the interference compressor813are provided to the first to Pthdecoders815-1to815-P. The first to Pthdecoders815-1to815-P each perform STTC decoding on signals output from the interference compressor813, and output {circumflex over (d)}11{circumflex over (d)}21{circumflex over (d)}31. . . {circumflex over (d)}L1to {circumflex over (d)}1P{circumflex over (d)}2P{circumflex over (d)}3P. . . {circumflex over (d)}LP. In the receiver based on the overlapped combined array processing and diversity technique illustrated inFIG. 8, a diversity gain becomes N−M+MP.

The overlapped combined array processing and diversity technique, as mentioned above, uses an overlapping method when grouping transmission antennas, so it can have a higher diversity gain as compared with the combined array processing and diversity technique. However, due to the overlapping method, even though the receiver eliminates an interference component, the interference component may exist, so that parallel transition is permitted in a trellis diagram. For example, when a transmitter has 3 transmission antennas and a receiver also has 3 reception antennas, a first stream is transmitted through a first transmission antenna and a second stream is transmitted through a second transmission antenna. In this case, information on the first transmission stream is added to information on the second transmission stream, and transmitted through the second transmission antenna. The receiver then performs interference suppression on a signal transmitted through a third transmission antenna only for a signal of the second stream when decoding the first stream, so the receiver has a diversity gain of a level 4 by achieving diversity gain for the 2 reception antennas. Likewise, the receiver is permitted to perform interference suppression on a signal transmitted from the first transmission antenna corresponding to only a signal of the first stream when decoding the second stream, so the receiver has a diversity gain of a level 4 by achieving diversity gain for the 2 reception antennas. However, as to a signal transmitted from the second transmission antenna according to the overlapping method, its modulation order is increased undesirably, since the first stream and the second stream overlap each other during transmission. For example, if modulation symbols of a transmission stream are 16QAM symbols, a signal transmitted from the second transmission antenna becomes a 256QAM signal obtained by overlapping 16QAM symbols. The 256QAM symbol and the 16QAM symbol are different from each other in their peak-to-average power ratio (hereinafter referred to as “PAPR”), and disadvantageously require design modification for a radio frequency (RF) processor. Finally, the overlapped combined array processing and diversity technique is disadvantageous in that it must consider parallel transition as mentioned above. A trellis structure that considers the parallel transition will be described with reference toFIG. 13.

FIG. 13illustrates a trellis structure based on the overlapped combined array processing and diversity technique. Since the overlapped combined array processing and diversity technique has the trellis structure that considers the parallel transition as illustrated inFIG. 13, an error rate may be increased undesirably due to the parallel transition, and in addition, an amount of trellis calculation is doubled undesirably due to the parallel transition.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a data transmission/reception apparatus and method for achieving both diversity gain and multiplexing gain in a mobile communication system using STTC.

It is another object of the present invention to provide a data transmission/reception apparatus and method for minimizing an error rate in an STTC mobile communication system using an overlapped combined array processing and diversity technique.

It is further another object of the present invention to provide a data transmission/reception apparatus and method having the same wireless standard in an STTC mobile communication system using an overlapped combined array processing and diversity technique.

To achieve the above and other objects, the invention provides an apparatus for transmitting data in a mobile communication system including at least three transmission antennas of first to third transmission antennas, and using an overlapped antenna scheme for grouping the first and second transmission antennas into a first transmission antenna group and grouping the second and third transmission antennas into a second transmission antenna group. The apparatus comprises first and second modulators for receiving L information bit streams to be transmitted through the first transmission antenna group, modulating each of the L information bit streams in a predetermined modulation scheme, and outputting first and second modulation symbol streams; third and fourth modulators for receiving L other information bit streams to be transmitted through the second transmission antenna group, modulating each of the L information bit streams in the modulation scheme, and outputting third and fourth modulation symbol streams; first to fourth puncturers for receiving the first to fourth modulation symbol streams, respectively, and puncturing at least one modulation symbol in a predetermined position among the received first to fourth modulation symbol streams; and a multiplexer for transmitting a modulation symbol stream output from the first puncturer through the first transmission antenna, transmitting a modulation symbol stream output from the second puncturer and a modulation symbol stream output from the third puncturer through the second transmission antenna after summing up the modulation symbol streams, and transmitting a modulation symbol stream output from the third puncturer through the third transmission antenna.

To achieve the above and other objects, the invention further provides an apparatus for receiving data in a mobile communication system which receives through N reception antennas modulation symbol streams transmitted through M transmission antennas from a transmitter. The apparatus comprises a channel estimator connected to each of the N reception antennas, for channel-estimating reception symbol streams output from the N reception antennas; an interference suppressor connected to each of the N reception antennas, for eliminating a reception symbol in at least one predetermined position as an interference component from each of reception symbol streams output from the N reception antennas; M modulators for modulating each of all information bit streams that can be possibly transmitted from the transmitter, in a predetermined modulation scheme, and outputting modulation symbol streams; M puncturers for puncturing at least one modulation symbol in a predetermined position from each of modulation symbol streams output from the M modulators; and a transmission symbol stream detector for detecting transmission symbol streams transmitted from the transmitter by considering parallel transition based on the reception symbol streams and a hypothetic channel output in a case where modulation symbol streams output from the M puncturers were transmitted through the same channel as a channel estimated by the channel estimator.

To achieve the above and other objects, the invention also provides a method for transmitting data in a mobile communication system including at least three transmission antennas of first to third transmission antennas, and using an overlapped antenna scheme for grouping the first and second transmission antennas into a first transmission antenna group and grouping the second and third transmission antennas into a second transmission antenna group. The method comprises the steps of receiving L information bit streams to be transmitted through the first transmission antenna group, modulating each of the L information bit streams in a predetermined modulation scheme, and outputting first and second modulation symbol streams; receiving L other information bit streams to be transmitted through the second transmission antenna group, modulating each of the L information bit streams in the modulation scheme, and outputting third and fourth modulation symbol streams; receiving the first to fourth modulation symbol streams, and puncturing at least one modulation symbol in a predetermined position among the received first to fourth modulation symbol streams, and outputting first to fourth punctured modulation symbol streams; and transmitting the first punctured modulation symbol stream through the first transmission antenna, transmitting the second and third punctured modulation symbol streams through the second transmission antenna after summing up the second and third punctured modulation symbol streams, and transmitting the fourth punctured modulation symbol stream through the third transmission antenna.

To achieve the above and other objects, the invention additionally provides a method for receiving data in a mobile communication system which receives through N reception antennas modulation symbol streams transmitted through M transmission antennas from a transmitter. The method comprises the steps of channel-estimating reception symbol streams output from the N reception antennas; eliminating a reception symbol in at least one predetermined position as an interference component from each of reception symbol streams output from the N reception antennas; modulating each of all information bit streams that can be possibly transmitted from the transmitter, in a predetermined modulation scheme, and outputting M modulation symbol streams; puncturing at least one modulation symbol in a predetermined position from each of the M modulation symbol streams; and detecting transmission symbol streams transmitted from the transmitter by considering parallel transition based on the reception symbol streams and a hypothetic channel output in a case where modulation symbol streams from which at least one modulation symbol was punctured were transmitted through the same channel as the channel-estimated channel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 9is a block diagram schematically illustrating a structure of a transmitter using a space-time trellis code (hereinafter referred to as “STTC”) according to an embodiment of the present invention. Referring toFIG. 9, the transmitter includes M transmission antennas, and classifies the M transmission antennas into P groups. That is, MPtransmission antennas constitute one group, and each group performs the transmission operation, i.e., encoding and modulation operations, described in conjunction withFIG. 1. Here, the sum of M1to MPexceeds M. The reason that the sum

∑P⁢MP
of M1to MPexceeds M is because the overlapped combined array processing and diversity technique fundamentally overlaps transmission antennas. In the overlapped combined array processing and diversity technique, the

∑P⁢MP
modulation symbols are overlapped and then transmitted to the air through the M transmission antennas. However, in the present invention, the

∑P⁢MP
modulation symbols are so punctured as to generate M modulation symbols, and then transmitted to the air through the M transmission antennas without being overlapped.

In this way, the P transmission antenna groups each perform a transmission operation, i.e., encoding and modulation operations, according to transmission antenna groups. Herein, 1˜M1represent transmission antennas of a first transmission antenna group, and 1˜MPrepresent transmission antennas of a Pthtransmission antenna group. In addition, it should be noted that the number of the 1stto M1thtransmission antennas can be different from the number of the 1stto MPthtransmission antennas. Further, the first to Pthtransmission antenna groups are identical in their transmission operation except the data applied thereto, so the invention will be described with reference to the first transmission antenna group and the Pthtransmission antenna group, for simplicity.

First, the first transmission antenna group will be described. If L information data bits d11, d21, d31, . . . , dL1are input to a transmitter of the first transmission antenna group, the input information data bits d11, d21, d31, . . . , dL1are provided to an S/P converter911. Here, the index L represents the number of information data bits to be transmitted by the transmitter of the first transmission antenna group for a unit transmission time, and the unit transmission time can become a symbol unit. In addition, the index “1” succeeding the index L represents the first transmission antenna group. The S/P converter911parallel-converts the information data bits d11, d21, d31, . . . , dL1and provides its outputs to first to L1thencoders921-1to921-L1. That is, the S/P converter911provides a parallel-converted information data bit d11to the first encoder921-1, and in this manner, provides a parallel-converted information data bit dL1to the L1thencoder921-L1. The first to L1thencoders921-1to921-L1each encode signals output from the S/P converter911in a predetermined encoding scheme, and then each provide their outputs to first to M1thmodulators931-1to931-M1. Here, the index M1represents the number of transmission antennas included in the transmitter of the first transmission antenna group, and the predetermined encoding scheme is an STTC encoding scheme.

The first to M1thmodulators931-1to931-M1each modulate signals received from the first to L1thencoders921-1to921-L1in a predetermined modulation scheme. The first to M1thmodulators931-1to931-M1provide modulation symbols S1to SM1to first to M1thpuncturers941-1to941-M1, respectively. The first to M1thmodulators931-1to931-M1are identical in their operation, so only the first modulator931-1will be described for simplicity. The first modulator931-1adds up signals received from the first to Lthencoders921-1to921-L, multiplies the addition result by a gain applied to a transmission antenna to which the first modulator931-1is connected, modulates the multiplication result in a predetermined modulation scheme, and provides the modulation result to the first puncturer941-1. Here, the modulation scheme includes BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), QAM (Quadrature Amplitude Modulation), PAM (Pulse Amplitude Modulation), and PSK (Phase Shift Keying). The first to M1thpuncturers941-1to941-M1each puncture the modulation symbols S1to SM1received from the first to M1thmodulators931-1to931-M1according to a predetermined puncturing matrix. The reason for puncturing the modulation symbols S1to SM1received from the first to M1thmodulators931-1to931-M1according to a predetermined puncturing matrix is to eliminate an interference component caused by overlapping of transmission signals onto particular transmission antennas in the overlapped combined array processing and diversity technique. That is, the modulation symbols S1to SM1of the first transmission antenna group are punctured according to the puncturing matrix, so that a transmission signal of the first transmission antenna group does not act as an interference component of another transmission antenna group.

A description will now be made of a procedure in which the first to M1thpuncturers941-1to941-M1puncture the modulation symbols S1to SM1output from the first to M1thmodulators931-1to931-M1, respectively.

The first to M1thpuncturers941-1to941-M1periodically puncture modulation symbols S1to SM1output from the first to M1thmodulators931-1to931-M1according to a corresponding transmission antenna. For example, if it is assumed that the number of transmission antennas of the first transmission antenna group is 2 and 4 symbols are transmitted through the 2 transmission antennas for a unit transmission period, then a puncturing matrix given by Equation (1) below is applied.

In Equation (1), P1represents a puncturing matrix. In the puncturing matrix P1, a column represents a transmission period, i.e., a symbol period, and a row represents a transmission antenna. In the puncturing matrix P1, an element “1” means that an input symbol is passed without being punctured, while an element “0” means that an input symbol is punctured, so that no symbol is transmitted for a corresponding period. That is, in the puncturing matrix P1, for a first column, or a first symbol period, a signal output from a first modulator connected to a first transmission antenna and a signal output from a second modulator connected to a second transmission antenna are passed without being punctured. Unlike this, in the puncturing matrix P1, for a second column, or a second symbol period, a signal output from the first modulator connected to the first transmission antenna is passed without being punctured, while a signal output from the second modulator connected to the second transmission antenna is punctured. In addition, in the puncturing matrix P1, for a third column, or a third symbol period, a signal output from the first modulator connected to the first transmission antenna and a signal output from the second modulator connected to the second transmission antenna are passed without being punctured. Unlike this, in the puncturing matrix P1, for a fourth column, or a fourth symbol period, a signal output from the first modulator connected to the first transmission antenna is passed without being punctured, while a signal output from the second modulator connected to the second transmission antenna is punctured.

The first to M1thpuncturers941-1to941-M1puncture the modulation symbols S1to SM1output from the first to M1thmodulators931-1to931-M1according to a predetermined puncturing matrix, and then provide their outputs to a first multiplexer (MUX#1)951-1and a second multiplexer (MUX#2)951-2, respectively. Here, the multiplexers are matched to the transmission antennas on a one-to-one basis, and the first multiplexer951-1is connected to a first transmission antenna ANT#1. Of the modulation symbols S1to SM1, the modulation symbol SM1is provided even to the second multiplexer951-2, and the reason is because a signal output from the M1thmodulator931-M1among output signals of the first transmission antenna group overlaps with output signals of a second transmission antenna group. The first multiplexer951-1multiplexes the modulation symbols S1to SM1and transmits the multiplexing result to the air through the first transmission antenna ANT#1.

Second, the Pthtransmission antenna group will be described. If L information data bits d1P, d2P, d3P, . . . , dLPare input to a transmitter of the Pthtransmission antenna group, the input information data bits d1P, d2P, d3P, . . . , dLPare provided to an S/P converter961. Here, the index “P” succeeding the index L represents the Pthtransmission antenna group. The S/P converter961parallel-converts the information data bits d1P, d2P, d3P, . . . , dLPand provides its outputs to first to LPthencoders971-1to971-LP. That is, the S/P converter961provides a parallel-converted information data bit dip to the first encoder971-1, and in this manner, provides a parallel-converted information data bit dLPto the LPthencoder971-LP. The first to LPthencoders971-1to971-LPeach encode signals output from the S/P converter961in an STTC encoding scheme, and then each provide their outputs to first to MPthmodulators981-1to981-MP. Here, the index MPrepresents the number of transmission antennas included in the transmitter of the Pthtransmission antenna group.

The first to MPthmodulators981-1to981-MPeach modulate signals received from the first to LPthencoders971-1to971-LPin a predetermined modulation scheme, and provide their outputs to first to MPthpuncturers991-1to991-MP, respectively. The first to MPthmodulators981-1to981-MPare identical in their operation, so only the first modulator981-1will be described for simplicity. The first modulator981-1adds up signals received from the first to LPthencoders971-1to971-LP, multiplies the addition result by a gain applied to a transmission antenna to which the first modulator981-1is connected, modulates the multiplication result in a predetermined modulation scheme, and provides the modulation result to the first puncturer991-1. The predetermined modulation scheme is identical to the modulation scheme applied to the first transmission antenna group. The first to MPthpuncturers991-1to991-MPeach puncture the modulation symbols S1to SMPreceived from the first to MPthmodulators981-1to981-MPaccording to a predetermined puncturing matrix, and then provide their outputs to a second multiplexer951-2and an Mthmultiplexer951-M, respectively. Also, the reason for puncturing the modulation symbols S1to SMPreceived from the first to MPthmodulators981-1to981-MPaccording to the puncturing matrix is to eliminate an interference component caused by overlapping of transmission signals onto particular transmission antennas in the overlapped combined array processing and diversity technique. That is, the modulation symbols S1to SMPof the Pthtransmission antenna group are punctured according to the puncturing matrix, so that a transmission signal of the Pthtransmission antenna group does not act as an interference component of another transmission antenna group.

A description will now be made of a procedure in which the first to MPthpuncturers991-1to991-MPpuncture the modulation symbols S1to SMPoutput from the first to MPthmodulators981-1to981-MP, respectively.

The first to MPthpuncturers991-1to991-MPperiodically puncture modulation symbols S1to SMPoutput from the first to MPthmodulators981-1to981-MPaccording to a corresponding transmission antenna. For example, if it is assumed that the number of transmission antennas of the Pthtransmission antenna group is 2 and 4 symbols are transmitted through the 2 transmission antennas for a unit transmission period, then a puncturing matrix given by Equation (1) above is applied. The first to MPthpuncturers991-1to991-MPpuncture the modulation symbols S1to SMPoutput from the first to MPthmodulators981-1to981-MPaccording to a predetermined puncturing matrix, and then provide their outputs to the second multiplexer (MUX#2)951-2and an Mthmultiplexer (MUX#M)951-M, respectively. The second to Mthmultiplexers951-2to951-M multiplex signals output from the first to MPthpuncturers991-1to991-MP, and transmit the multiplexing results to the air though the second to Mthtransmission antennas ANT#2to ANT#M. When the puncturing matrix is applied to the modulation symbols S1to SMPin this way, modulation symbols transmitted through the second to Mthtransmission antennas ANT#2to ANT#M do not act as an interference component for other transmission antennas.

FIG. 10is a block diagram schematically illustrating a receiver structure corresponding to the transmitter structure ofFIG. 9. Referring toFIG. 10, a signal transmitted to the air by a transmitter is received through reception antennas of the receiver. It is assumed inFIG. 10that there are provided N reception antennas, each of which process signals received from the air. Specifically, signals received through first to Nthreception antennas ANT#1to ANT#N are provided to a channel estimator1011and an interference suppressor1013. The channel estimator1011performs channel estimation on signals output from the first to Nthreception antennas ANT#1to ANT#N, and then provides the channel estimation result to the interference suppressor1013and first to Pthdecoders1015-1to1015-P. The interference suppressor1013eliminates an interference component from each of the signals output from the first to Nthreception antennas ANT#1to ANT#N based on the channel estimation result output from the channel estimator1011, and then provides its outputs to the first to Pthdecoders1015-1to1015-P. A process of performing by the channel estimator1011channel estimation on the signals output from the first to Nthreception antennas ANT#1to ANT#N and a process of eliminating by the inference suppressor1013an interference component from the signals output from the first to Nthreception antennas ANT#1to ANT#N are disclosed in V. Tarokh, A. Naguib, N. Seshadri, and A. R. Calderbank, “Space-Time Codes For High Data Rate Wireless Communications: Performance Criterion And Code Construction.”IEEE Trans. on Info. Theory, pp.744-765, Vol. 44, No. 2, March 1998, and V. Tarokh, A. Naguib, N. Seshadri, and A. R. Calderbank, “Combined Array Processing And Space Time Coding”IEEE Trans. Inform. Theory, Vol. 45, pp. 1121-1128, May 1999, the contents of both of which are incorporated herein by reference. These references introduce a method for classifying N transmission antennas into non-overlapping small groups with a size Niand using space-time codes called component codes in order to transmit information from antennas of each group, thereby remarkably reducing complexity of coding and decoding. Then, the first to Pthdecoders1015-1to1015-P each perform STTC decoding on signals output from the interference compressor1013based on the channel estimation result from the channel estimator1011, and output the information data bits transmitted by the transmitter. Since the transmitter punctures modulation symbols before transmission, the first to Pthdecoders1015-1to1015-P must consider this when decoding the modulation symbols, and an internal structure of the first to Pthdecoders1015-1to1015-P will be described with reference toFIG. 11.

FIG. 11is a block diagram illustrating an internal structure of the first to Pthdecoders1015-1to1015-P ofFIG. 10. The first to Pthdecoders1015-1to1015-P described in conjunction withFIG. 10all have the structure illustrated inFIG. 11, so only the first decoder1015-1will be described for simplicity. Referring toFIG. 11, a signal transmitted to the air by a transmitter is received through the reception antennas of the receiver. It is assumed inFIG. 11that there are provided N reception antennas. The N reception antennas each process signals received from the air. Specifically, signals received through first to Nthreception antennas ANT#1to ANT#N are provided to first to Nthdemultiplexers1111-1to1111-N, respectively. The first to Nthdemultiplexers1111-1to1111-N demultiplex signals output from the first to Nthreception antennas ANT#1to ANT#N in a demultiplexing scheme corresponding to the multiplexing scheme applied in the STTC transmitter, and then provide their outputs to a channel estimator1112and a metric calculator1131. The channel estimator1112channel-estimates signals output from the first to Nthdemultiplexers1111-1to1111-N by using a training sequence generated from a training sequence generator1115, and outputs the channel estimation result to a hypothesis part1113.

A possible sequence generator1120generates all kinds of sequences which were possibly simultaneously encoded for information data bits in the transmitter, and provides the generated sequences to first to Lthencoders1121-1to1121-L. Since the transmitter transmits information data by the L information bits, the possible sequence generator1120generates possible sequences {tilde over (d)}1. . . {tilde over (d)}Lcomprised of L bits. The L bits of the generated possible sequences are applied to the first to Lthencoders1121-1to1121-L, and the first to Lthencoders1121-1to1121-L encode the possible sequences {tilde over (d)}1. . . {tilde over (d)}Loutput from the possible sequence generator1120in an STTC encoding scheme, and then provide the encoded bits to first to Mthmodulators1123-1to1123-M. The first to Mthmodulators1123-1to1123-M each modulate the encoded bits output from the first to Lthencoders1121-1to1121-L in a predetermined modulation scheme, and provide their outputs to first to Mthpuncturers1125-1to1125-M. The modulation scheme applied in the first to Mthmodulators1123-1to1123-M is determined as any one of the BPSK, QPSK, QAM, PAM and PSK modulation schemes, and the first to Mthmodulators1123-1to1123-M apply a modulation scheme corresponding to the modulation scheme applied in the transmitter ofFIG. 9.

The first to Mthpuncturers1125-1to1125-M puncture signals output from the first to Mthmodulators1123-1to1123-M in accordance with a puncturing matrix identical to the puncturing matrix applied inFIG. 9, and then provide their outputs to the hypothesis part1113. The hypothesis part1113receives signals output from the first to Mthpuncturers1125-1to1125-M and the channel estimation result output from the channel estimator1112, generates a hypothetic channel output at a time when a sequence consisting of the signals output from the first to Mthpuncturers1125-1to1125-M passed the same channel as the channel estimation result did, and provides the generated hypothetic channel output to the metric calculator1131. However, in the present invention, when some of the modulation symbols to be transmitted through a particular transmission antenna are punctured in the transmitter, some of modulation symbols to be transmitted through another transmission antenna are multiplexed and inserted in the punctured symbol period. That is, in the present invention, a symbol stream transmitted from an overlapped antenna has a format formed such that not only its modulation symbols but also modulation symbols of another symbol stream are multiplexed and inserted in the transmission symbol stream. Therefore, a receiver must consider the modulation symbols of another symbol stream as parallel transition in a trellis during decoding, and inFIG. 11, a parallel transition part1114adds a value determined by multiplying a channel estimation result received at the receiver through a second transmission antenna ANT#2by all kinds of constellations that can be transmitted through other symbol streams, to an originally calculated metric. That is, when two symbol streams are alternately transmitted,2L2parallel transitions must be considered.

Meanwhile, the metric calculator1131receives the hypothetic channel output provided from the hypothesis part1113and the signals received through the first to Nthreception antennas ANT#1to ANT#N, and calculates a distance between the hypothetic channel output and the signals received through the first to Nthreception antennas ANT#1to ANT#N. The metric calculator1131uses Euclidean distance when calculating the distance. In this manner, the metric calculator1131calculates Euclidean distance for all possible sequences the transmitter can transmit, and then provides the calculated Euclidean distance to a minimum distance selector1133. The minimum distance selector1133selects a Euclidean distance having the minimum distance from Euclidean distances output from the metric calculator1131, determines information bits corresponding to the selected Euclidean distance as information bits transmitted by the transmitter, and provides the determined information bits to a parallel-to-serial (P/S) converter1135. Although there are several possible algorithms used when the minimum distance selector1133determines information bits corresponding to the Euclidean distance having the minimum distance, it is assumed herein that a Viterbi algorithm is used. A process of extracting information bits having the minimum distance by using the Viterbi algorithm is disclosed in Vahid Tarokh, N. Seshadri, and A. Calderbank, “Space Time Codes For High Data Rate Wireless Communication: Performance Criterion And Code Construction,” IEEE Trans. on Info. Theory, pp. 744-765, Vol. 44, No. 2, March 1998, so a detailed description thereof will not be provided for simplicity. The P/S converter1135then serial-converts the L information bits output from the minimum distance selector1133, and outputs reception information data sequences {circumflex over (d)}1, {circumflex over (d)}1, . . . , {circumflex over (d)}L.

An operation of the present invention will now be described with reference to the transmitter structure and the receiver structure described above.

First, it will be assumed that the transmitter has M transmission antennas and the receiver has N reception antenna. A signal received at the receiver through the N reception antennas is represented by
R=HS+NEquation (2)

In Equation (2), R denotes a signal received in an N×1 matrix, H denotes a channel characteristic, S denotes a transmission signal, and N denotes a noise component. The channel characteristic H is expressed in an N×M matrix, and each element of the N×M matrix is modeled with independent complex Gaussian. The noise component N is expressed in an N×1 vector, and represents a noise component received at the receiver. The transmission signal S is expressed in an M×1 vector, wherein an mthrow represents a modulation symbol transmitted from an mthtransmission antenna ANT#m. Here, the transmission signal S is comprised of P symbol streams, and each of the P streams is transmitted through MPtransmission antennas. In addition, the P streams are streams which were independently punctured according to a puncturing matrix as described in conjunction withFIG. 10, and as a result, it can be considered that in the puncturing operation, each of the P streams uses as many transmission antennas as the number determined by excluding the MPpunctured modulation symbols. Therefore, the present invention punctures

∑P⁢MP
modulation symbols generated from

∑P⁢MP
modulators according to a puncturing matrix so that the modulation symbols can be mapped to the M transmission antennas without being overlapped. Therefore, the transmission signal S is a signal which is mapped so that

∑P⁢MP
modulation symbols are mapped to the M transmission antenna without being overlapped.

In order to decode a Pthsymbol stream, the receiver must eliminate other symbol streams except the Pthsymbol stream, considering them as an interference component. For that purpose, N rows representative of a channel characteristic from a transmission antenna, through which the Pthsymbol stream was transmitted to the receiver, must be eliminated from the channel characteristic H. An N×(M−MP)-dimensional matrix determined by eliminating the N rows representing the channel characteristic from the transmission antenna to the receiver will be defined as an HPmatrix. Assuming that a null space of the HPmatrix is defined as ΩP, if the null space ΩPof the HPmatrix is multiplied by the reception signal R, a new reception signal R′ from which other symbol streams acting as an interference component except the Pthsymbol stream were eliminated can be generated.

Meanwhile, it is assumed that the Pthsymbol stream is transmitted using MPtransmission antennas and modulation symbols from q transmission antennas among the MPtransmission antennas were punctured. Although the modulation symbols from the q transmission antennas were punctured, the q transmission antennas each multiplex modulation symbols of other symbol streams except the Pthsymbol stream before transmission. Therefore, it is necessary to prevent the multiplexed other symbol streams from acting as an interference component. For example, when modulation symbols modulated in an L-ary modulation scheme are transmitted from each of the q transmission antennas, a receiver must decode the modulation symbols by considering q*2Lparallel transitions. That is, if it is assumed that one of symbol vectors corresponding to the q*2Lparallel transitions is Sc(c=1˜q*2L), the metric calculator1131of the receiver must subtract ΩPHPScfrom the calculated metric. C is a temporary variable whose range is 1˜q*2L.

A description will now be made of the reason why an interference component caused by actual overlapping of transmission antennas is eliminated using the puncturing pattern. Before the description is made, it should be noted that the parameters M, M1and MPgeneralized in the transmitter structure ofFIG. 10will be modified appropriately for the convenience of explanation. That is, in the transmitter structure ofFIG. 9, it will be assumed that the M is 3, and M1, MPand P are 2. In addition, it will be assumed herein that the transmitter applies BPSK as its modulation scheme, and transmits 4 symbols for a unit transmission time. Then, the first transmission antenna group consists of a first transmission antenna ANT#1and a second transmission antenna ANT#2, and the Pthtransmission antenna group becomes a second transmission antenna group, which consists of the second transmission antenna ANT#2and an Mthtransmission antenna ANT#M, i.e., a third transmission antenna ANT#3. Under the assumption stated above, the first and M1thmodulators931-1and931-M1of the first transmission antenna group become first and second modulators931-1and931-2, respectively, and the first and M1thpuncturers941-1and941-M1of the first transmission antenna group become first and second puncturers941-1and941-2, respectively. In addition, the first and MPthmodulators981-1and981-MPof the Pthtransmission antenna group become first and second modulators981-1and981-2, respectively, and the first and MPthpuncturers991-1and991-MPof the Pthtransmission antenna group become first and second puncturers991-1and991-2, respectively. Further, the Mthmultiplexer951-M becomes a third multiplexer951-3.

Modulation symbols output from the first and second modulators931-1and931-2are input to the first and second puncturers941-1and941-2, respectively, and the first and second puncturers941-1and941-2puncture the input modulation symbols by applying the puncturing matrix of Equation (1), and then provide the puncturing result to the first and second multiplexers951-1and951-2. When the puncturing matrix P1of Equation (1) is applied, the first puncturer941-1provides 4 input modulation symbols to the first multiplexer951-1without puncturing any of them, and the second puncturer941-2provides 4 input modulation symbols to the second multiplexer951-2after puncturing a second modulation symbol and a fourth modulation symbol while not puncturing a first modulation symbol and a third modulation symbol.

Meanwhile, modulation symbols output from the first and second modulators981-1and981-2are input to the first and second puncturers991-1and991-2, respectively, and the first and second puncturers991-1and991-2puncture the input modulation symbols by applying a puncturing matrix of Equation (3) below, and then provide the puncturing result to the second and third multiplexers951-2and951-3.

When the puncturing matrix P2of Equation (3) is applied, the first puncturer991-1punctures a first modulation symbol and a third modulation symbol from 4 input modulation symbols, and provides a second modulation symbol and a fourth modulation symbol to the second multiplexer951-2without puncturing, and the second puncturer991-2provides 4 input modulation symbols to the third multiplexer951-3without puncturing any of them.

The first multiplexer951-1transmits an intact signal output from the first puncturer941-1through the first transmission antenna ANT#1, the second multiplexer951-2transmits a signal output from the second puncturer941-2and a signal output from the first puncturer991-1through the second transmission antenna ANT#2after multiplexing, and the third multiplexer951-3transmits a signal output from the second puncturer991-2through the third transmission antenna ANT#3after multiplexing. Here, an output signal of the second multiplexer951-2will be described. The second multiplexer951-2multiplexes second and fourth modulation symbols output from the second puncturer941-2with second and fourth modulation symbols output from the first puncturer991-1, and outputs 4 modulation symbols in series. As a result, the 4 modulation symbols become non-overlapped modulation symbols. Conventionally, since modulation symbols transmitted through an overlapped antenna are also overlapped, when the transmitter applies QPSK as stated above, modulation symbols transmitted through the first transmission antenna ANT#1and the third transmission antenna ANT#3are BPSK modulation symbols, whereas modulation symbols transmitted through the second transmission antenna ANT#2which is the overlapped antenna become QPSK modulation symbols. However, in the present invention, since modulation symbols transmitted through an overlapped antenna, i.e., the second transmission antenna ANT#2, are not overlapped based on the puncturing procedure as described above, modulation symbols transmitted through the overlapped antenna become QPSK modulation symbols. Therefore, the transmitter can transmit symbols having the same constellation size according to transmission antennas.

The invention has been described with reference to a case where puncturing matrixes P1and P2are applied to a pair of first and second puncturers941-1and941-2and a pair of first and second puncturers991-1and991-2, respectively. Next, a description will be made of a case where the 4 puncturers, i.e., the first and second puncturers941-1and941-2and the first and second puncturers991-1and991-2, are all considered. In this case, puncturing matrixes are given by

It can be understood from Equation (4) and Equation (5) that the sums of element values of respective columns of a puncturing matrix P3and a puncturing matrix P4all become 3. This means that for each column, only 3 of 4 transmission symbols are transmitted at a particular symbol transmission time. First, describing rows of the puncturing matrix P3, a first row is mapped to a first transmission antenna ANT#1, second and third rows are mapped to a second transmission antenna ANT#2, and a fourth row is mapped to a third transmission antenna ANT#3. In the puncturing matrix P3, modulation symbols output from the second puncturer941-2and the first puncturer991-1are punctured according to elements in the second and third rows. As a result, a non-punctured symbol period is inserted in the mutually punctured symbol period. In the puncturing matrix P3, consideration is taken into not only an overlapped antenna, i.e., the second transmission antenna ANT#2, but also the other remaining transmission antennas, so only one interference component exists.

Second, describing rows of the puncturing pattern P4, a first row is mapped to a first transmission antenna ANT#1, a second row is mapped to the first transmission antenna ANT#1or a second transmission antenna ANT#2, a third row is mapped to the second transmission antenna ANT#2or a third transmission antenna ANT#3, and a fourth row is mapped to the third transmission antenna ANT#3. That is, elements of the puncturing matrix P4are mapped to the transmission antennas according to the following rule.

The transmission antenna mapping rule specifies how elements of the puncturing matrix P4should be mapped to the transmission antennas. That is, all elements in a first row of the puncturing matrix P4must be mapped to the first transmission antenna ANT#1, and elements in a second row of the puncturing matrix P4must be mapped to the first transmission antenna ANT#1if the transmission antenna mapping rule is represented by 1, and mapped to the second transmission antenna ANT#2if the transmission antenna mapping rule is represented by 2. Likewise, elements in a third row of the puncturing matrix P4must be mapped to the second transmission antenna ANT#2if the transmission antenna mapping rule is represented by 2, and mapped to the third transmission antenna ANT#3if the transmission antenna mapping rule is represented by 3. Finally, all elements in a fourth row of the puncturing matrix P4 must be mapped to the third transmission antenna ANT#3. By doing so, it is possible to insert a non-punctured symbol period in a mutually punctured symbol period.

A description will now be made of a trellis structure in the case where the transmitter applies BPSK.

First, a description will be made of a constellation in the case where BPSK is applied.

FIG. 12illustrates a general constellation for BPSK. As illustrated inFIG. 12, a constellation is shown on a real axis (I) and an imaginary axis (Q). In addition,FIG. 13, as described in the prior art section, illustrates a trellis structure based on the overlapped combined array processing and diversity, andFIG. 14illustrates a trellis structure according to the present invention. A comparison betweenFIG. 13andFIG. 14will be described. In the trellis structure ofFIG. 13, when a received signal is decoded, state transition is considered for all received symbols, i.e., parallel transition is considered. However, in the proposed trellis structure ofFIG. 14, parallel transition is not required to be considered, contributing to a reduction in an error rate.

As described above, the present invention eliminates overlapping of signals transmitted via an actual overlapped antenna through a puncturing operation even by using an overlapped antenna technique based on the overlapped combined array processing and diversity technique. Therefore, the present invention achieves both multiplexing gain and diversity gain due to the elimination of overlapping of the transmission signals. In addition, since the transmission signals are not overlapped, a receiver is not required to consider parallel transition when eliminating an interference component, thus minimizing an error rate. Further, since a signal transmitted via an overlapped antenna is not overlapped due to a puncturing operation, the present invention can transmit and receive a signal with the same wireless standard, contributing to a reduction in hardware complexity.