JP2005176325A - Method for increasing transmit diversity gain in wireless communication system, and wireless communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adaptive transmit diversity scheme using simple feedback for a wireless system. <P>SOLUTION: A wireless communication system includes a transmitter and a receiver. The transmitter includes multiple groups of transmit antennas. Input symbols are generated and then an orthogonal space-time block is encoded to produce a data stream for each group of transmit antennas. Each data stream is adaptively linear space encoded to produce an encoded signal for each transmit antenna of each group according to feedback information for the group. The receiver includes a single receive antenna, a module for measuring a phase of a channel impulse response for each transmit antenna. The feedback information is determined independently for each group of transmit antennas from the channel impulse responses. The feedback information for each group of transmit antennas is sent to the transmitter. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates generally to transmit diversity gain in wireless communication networks, and more particularly to adaptively maximizing diversity gain at a transmitter.

  In next generation wireless communication systems, there is a need to provide high quality voice services as well as broadband data services having data rates that far exceed the limits of current wireless systems. For example, High Speed Downlink Packet Access (HSDPA) approved by the 3rd Generation Partnership Project (3GPP) standard of the Wideband Code Division Multiple Access (WCDMA) system is called EDGE (enhanced data rate for GSM evolution, so-called 2.5G communication). The standard) supports a data rate of up to 10 Mbps or more on the downlink channel, up to 384 Kbps. For 3GPP, 3GPP TR25.848 v4.0.0 “3GPP technical report: Physical layer aspects of ultra high speed downlink packet access” (March 2001) and ETSI. See GSM 05.05 “Radio transmission and reception” (ETSI EN 300 910 V8.5.1, November 2000).

  Data rate can be increased by antenna diversity. Antenna diversity effectively suppresses the adverse effects of multipath fading on the channel by providing multiple copies of the transmitted signal at the receiver. Because typical end-user devices (eg, mobile phones and handheld computers) are limited in size and cost, downlink transmission gives priority to transmit diversity over receiver diversity.

  One of the most common transmit diversity techniques is space-time coding. Alamouti “A simple transmit diversity technique for wireless communications” (IEEE J. Select. Area Commun., Vol.16, pp.1451-1458, October 1998), Tarokh et al. “Space-time codes for high data rate wireless communication : performance criterion and code construction "(IEEE Trans. Info. Theory, vol.44, pp.744-765, March 1998), Tarokh et al." Space-time block codes from orthogonal designs "(IEEE Trans. Info. Theory, vol.45, pp.1456-1467, July 1999) and “Space-time diversity systems based on linear constellation precoding” by Xin et al. (IEEE Trans. Wireless Commun., vol.2, pp.294-309, March 2003) Please refer to).

  When space-time coding is used, data symbols are coded in both the time domain (transmission interval) and the space domain (transmit antenna array). For systems with exactly two transmit antennas, Alamouti et al. Describe an orthogonal space-time block code (STBC). The overall diversity order is achieved by simple algebraic operations.

  Space-time trellis coding takes advantage of the full potential of multiple antennas by trying to maximize both the diversity gain and coding gain of the system. Better performance is achieved at the cost of a relatively high encoding and decoding complexity.

  The above technique is designed under the assumption that the transmitter has no knowledge of the fading channel. Thus, the above technique can be classified as having open loop transmit diversity.

  System performance can be further enhanced if some channel information is available at the transmitter from feedback information from the receiver. These systems are classified as having closed loop transmit diversity. The feedback information can be used to maximize the gain at the receiver in a transmit diversity system. “Combining beamforming and orthogonal space-time block coding” by Jongren et al. (IEEE Trans. Info. Theory, vol.48, pp.611-627, March 2002), “Optimal transmitter eigen-beamforming and space-time block by Zhou et al.” coding based on channel mean feedback "(IEEE Trans. Signal Processing, vol.50, pp.2599-2613, October 2002), Rohani et al." A comparison of base station transmit diversity methods for third generation cellular standards "(Proc. IEEE Veh. Techno. Conf. VTC '99 Spring, pp.351-355, May 1999), "Transmit diversity in 3G CDMA systems" by Derryberry et al. (IEEE Commun. Mag., Vol.40, pp.68-75, April) 2002), Lo “Maximum ratio transmission” (IEEE Trans. Commun., Vol.47, pp.1458-1461, October 1999), Huawe “STTD with adaptive transmitted power allocation” (TSGR1-02-0711, May, 2002) and Horng et al., “Adaptive space-time transmit diversity for MIMO systems” (Proc. IEEE Veh. Techno. Conf. VTC '03 Spring, pp.1070-1073, April 2003). I want.

  Space-time block coding can be combined with linear optimal beamforming. The linear coding matrix can be optimized based on fading channel feedback information. A transmit adaptive array (TxAA) is another closed-loop transmit diversity system in which transmitted symbols are encoded only in the spatial domain. If the fading channel vector is known to the transmitter, an improvement in performance can be achieved. The concept of spatially coded transmit diversity can be generalized as maximum ratio transmission (MRT).

  In all the above closed loop systems, the feedback information needs to be an M × N complex-valued matrix, where M and N are the number of antennas at the transmitter and receiver, respectively. The elements of the matrix are either channel impulse response (CIR) or CIR statistics (eg, mean or covariance). Since the feedback matrix contains 2MN real-valued scalars, considerable bandwidth is consumed by the reverse link feedback information from the receiver to the transmitter.

  To overcome this problem, a suboptimal method with less feedback information is possible. Adaptive space-time block coding (ASTTD) uses a real-valued vector consisting of the power ratio of the fading channel as feedback information. In this case, the feedback information is used to adjust the power of each transmission antenna. This technique still consumes a large number of bits.

  Therefore, it is desirable to maximize the transmit diversity gain while reducing the number of bits sent back to the transmitter.

  The present invention provides an adaptive transmit diversity scheme with simple feedback for wireless communication systems.

  It is an object of the present invention to achieve better system performance with less feedback information and less computation than conventional transmit diversity methods.

  Using simple linear operations at both the transmitter and receiver, the method provides 1-bit feedback for a system with two antennas (M = 2) at the transmitter and one antenna at the receiver. Only information is needed.

  When there are more antennas in the transmitter (M> 2), the number of feedback bits is 2 (M−1) bits. This is still significantly less than the number of bits required by most conventional closed loop transmit diversity techniques.

  When the above quadrant phase constraint method is combined with an orthogonal space-time block code, the amount of feedback information can be further reduced. For systems with 3 or 4 transmit antennas, the amount of feedback can be only 1 and 2 bits, respectively.

  The computational complexity of the method of the present invention is much lower compared to the optimal quantized TxAA closed loop technique using the same amount of feedback.

  Furthermore, the method outperforms some closed-loop transmit diversity techniques that transmit more information in the feedback channel.

  FIG. 1 shows a baseband representation of a diversity system 100 according to the present invention. The system includes M antennas 101 at a transmitter 10 (for example, a base station) and one antenna 102 at a receiver 20 (for example, a mobile phone).

At time k, the modulated symbol s _k 103 is linearly encoded in the spatial domain at the transmitter according to the spatial encoding vector 111 of the following equation (110).

The encoded transmission data 112 is expressed by the following equation, and x _m (k) indicates data transmitted by the m-th transmission antenna 101.

In the adaptive transmission diversity method of the present invention, the transmitter obtains the spatially encoded vector p _k 111 according to the feedback information 121 obtained from the spatial decoding 130 of the received signal 105 at the receiver (120).

  Specifically, the feedback information 121 relates to a phase difference between received signal pairs in the fading transmission channel 115. It is desirable to minimize the phase difference between the signals so that the diversity gain is maximized at the receiver. Furthermore, it is desirable to minimize the number of bits required to indicate the phase difference. It is also desirable to reduce the amount of calculation associated with the generation of feedback information in the receiver 20.

Received signal, the propagation signals from all the transmit antennas to be the channel impulse response, is the sum obtained by adding the additive white Gaussian noise (AWGN) 104 having a dispersion N _0/2 per dimension. In the receiver, the sample r _k 113 of the received signal R _x can be expressed by the following equation (1).

Here, E _s is the sum of the transmission energy of all of the transmitting antennas, M is the number of antennas, z _k is the additive noise 104. A channel impulse response (CIR), which is a time function of each fading channel, is expressed as follows.

Here, h _m (k) is the CIR of the fading channel between the m-th transmitting antenna and the receiving antenna, and (·) ^T indicates matrix transposition.

In the system model defined by the equation (1), the optimal spatial encoding vector p (hat) _k for maximizing the output SNR is expressed by the following equation (2).

Here, (·) ^H represents a Hermitian matrix operator. This scheme is called a transmit adaptive array (TxAA). However, in order to form an optimal spatial coding vector, it is necessary to fully understand the CIR vector h _k containing 2M real scalar values. Therefore, it is impractical to implement the TxAA scheme in an actual system where resources allocated to the feedback channel are limited.

  In order to reduce the amount of feedback information, an optimal quantization feedback scheme for TxAA will be described. A spatially encoded vector is obtained from a thorough search algorithm such as the following equation (3).

Where P is the set of all possible quantized spatial coding vectors. This set contains 2 ^{b (M−1)} possible vectors for systems using b-bit quantization and M transmit antennas. In order to determine the optimal quantized feedback vector p (hat) _k , the receiver can determine for all possible 2 ^{b (M−1)} encoded vectors before it can select the optimal encoded vector. ^{_{, p k h k h k H}} p k value must be thoroughly seek the ^H.

Each calculation of the cost function involves approximately M ² complex multiplications. Thus, the total amount of computational complexity caused by feedback information alone is approximately O (2 ^{b (M−1)} × M ² ), which increases exponentially with the number of transmit antennas and the number of antennas. Becomes extremely large when the number is 3 or more.

  To balance system performance, feedback information size, and system computational complexity, the adaptive transmit diversity method according to the present invention uses a quadrant phase constraint method to determine feedback information. Therefore, both the feedback amount and the computational complexity can be greatly reduced.

Method Description The adaptive transmit diversity method of the present invention will first be described for the simplest system having two transmit antennas and one receive antenna. In this simple case, exactly one bit of feedback information is required to generate the spatially encoded vector 111 used by the spatial encoding 110. In a general method for a system with more than two M transmit antennas, 2 (M−1) bits of feedback information are required to determine 120 the spatially encoded vector 111.

System with Two Transmitting Antennas In the case of a system with two transmitting antennas, the spatially encoded vector 111 of the present invention is defined as the following equation (4).

Here, b _k ε {0, 1} is the quantized binary feedback information 121 sent from the receiver. One feedback bit b _k (0 or 1) is based on the estimated phase shift in CIR h _k as shown in the following equation (5).

Here, h _m (k) is a channel impulse response which is a time function, (•) ^* indicates a complex conjugate, and operation R (•) returns the real part of the operand. In other words, if the product of the complex conjugate of the CIR of one channel and the CIR of the other channel is positive, the bit is zero, otherwise it is 1, and thus the spatially encoded vector p111 is [ 1, 1] or [1, -1].

Using the definition of the spatial encoding vector p _{k in} Equation (3), the transmission signal vector 112 is x _k = [s _k , (−1) ^bk s _k ]. By replacing the vector x _k in equation (1), the received sample can be expressed as in the following equation (6).

At the receiver using coherent detection, the received sample _{r (k) (p k h} k) H = h 1 * (k) + h 2 * (k) (- 1) is multiplied by the ^bk, following formula (7) Form a decision variable y (k).

Here, v _k is expressed by the following equation and is a noise component of the decision variable.

The variance of the noise component v _k is expressed as the following equation (8).

  From formula (5), it can be seen that the following formula (9) holds.

  Therefore, the instantaneous output SNRγ at the receiver can be written as in the following equations (10) and (11).

Here, γ ₀ = E _s / N ₀ is the SNR without diversity. The conventional diversity gain g _c and the feedback diversity gain g _b can be defined as the following equations (12) and (13).

The conventional diversity gain g _c is the same as the orthogonal space-time block coding (STBC) diversity gain, but the feedback diversity gain g _b is an additional diversity gain contributed by the binary feedback information 121.

From the above equation, in the closed-loop system, by using only the 1-bit _bk feedback information 121, the transmission signal of the present invention also considers the feedback diversity gain even though the transmission signal is encoded only in the spatial domain. It can be seen that the output SNR of the scheme is always better than when only the orthogonal STBC gain is considered in an open loop system.

System with 3 or more transmit antennas The process described above is for a system with 2 transmit antennas. If the transmitter has more than two antennas (M> 2), a modified transmit diversity method using 2 (M-1) bits of feedback information is used.

  In the present invention, for a system having more than two M transmission antennas, the spatially encoded vector 111 is defined as in the following equation (14).

Here, i ² = −1, and q _m (k) ∈ {0, 1, 2, 3} is feedback information from the receiver when m = 2, 3,. . For consistency of expression, let q ₁ (k) = 0 for any k.

Such definitions, each q _{m (k)} includes 2 bits of information, feedback information used to form the space encoding vector p _k becomes 2 (M-1) bits in total. Combining the equations (1) and (14), the received sample r (k) can be written as the following equation (15).

In the decoder 130, the decision variable y (k) is obtained by multiplying the received sample r (k) by (p _k h _k ) ^H. This can be written as the following equation (16).

Here, v _k = (p _k h _k ) ^H · z _k is a noise component having a variance | p _k h _k | ² · N ₀ , and the conventional diversity gain g _c and the feedback diversity gain g _b are They are defined as the following equations (17) and (18), respectively.

In the above equation, the conventional diversity gain g _c is fixed for a constant value of M, but the feedback diversity gain is maximized by appropriately selecting feedback information based on q _m (k). The

Using 2 (M−1) bits of information, g _b can be maximized by selecting q _m (k) such that all the total elements of g _b are positive. One of the total elements of g _b can be expressed as the following equation (19).

Here, θ _m ε [0, 2π) is the phase of h _m (k).

  When the condition of the following equation (20) is satisfied for an arbitrary m ≠ n, the term of the equation (19) is positive.

  That is, the absolute value of the phase difference between the two signals is less than 90 degrees.

In order to satisfy this maximization condition of the equation (20), the phase θ _m + {q _m (k) / 2} · π with respect to m = 1, 2,... Q _m (k) is adjusted to be within a degree. This method is called quadrant phase constraint method.

Without losing generality, the phase θ ₁ of the signal of the first subchannel h ₁ (k) is not changed. This is called the reference phase of the reference signal. The reference phase can be arbitrarily selected from any of the M transmit antennas or the CIR with the highest power.

  Here, the goal is to make the phase difference between all signals less than π / 2, or to constrain all shift phases to quadrant phase sectors (ie 90 degree sectors).

Therefore, the phase θ _m of all other subchannel signals is rotated {q _m (k) / 2} · π counterclockwise at the transmitter so that the absolute value of the phase difference is less than 90 degrees. There is a need to. Thereby, the information necessary to form each q _m (k) is only 2 bits.

  One way to satisfy the quadrant phase constraint is to place all phases in the same coordinate quadrant as the reference phase. As shown in FIG. 2, the four quadrants I-IV of the Cartesian coordinate system of real number (Re) and imaginary number (Im) are labeled. The quadrant number of an arbitrary angle φ∈ [0, 2π) is expressed by the following equation, and the symbol in this equation indicates that the value is rounded up to the nearest integer.

Using the above analysis, the receiver obtains feedback information q _m (k) in the case of m = 2, 3,..., M based on the phase difference of an arbitrary received signal pair.

The example 200 of FIG. 2 has θ ₁ in quadrant II and θ _m in quadrant IV. Using equation (21), q _m (k) = − 2 is obtained. This corresponds to rotating θ _m clockwise by π radians (180 °), in which case the rotated phase θ _m − {q _m (k) / 2} · π is in quadrant II. .

Alternatively, as shown in FIG. 3, all phases are placed in a 90 degree sector 300 centered on the reference phase. All phases are normalized so that θ (tilde) _m = θ _m −θ _l + 2lπ with respect to the reference phase. Here, the integer l is selected such that the normalized phase θ (tilde) _m is in the range of [0, 2π). The normalized phase θ (tilde) _m is rotated counterclockwise by an angle of q _m · (π / 2), and the rotated angle θ (tilde) _m + q _m · (( π / 2) is in the quadrant phase sector of [−π / 4, π / 4] of the coordinate system. From the above description, the feedback information q _m can be calculated as follows.

Here, the symbols in this expression return the closest smaller integer. An example is shown in FIG. 3, where θ (tilde) _m = 9π / 8.

q _m = 2 and the corresponding rotated angle is θ (tilde) _m −q _m · (π / 2) = π / 8, which is the [− π / 4, π / 4] quadrant phase sector.

By performing the same operations, one for every normalized phase rotation phase is limited to the same quadrant phase sector, to ensure the non-negative of each sum element of diversity gain g _b it can.

  This method achieves the non-negative nature of feedback diversity obtained by constraining all rotated phases of the CIR of one transmit antenna group to a π / 2 quadrant phase sector. Therefore, this is called a quadrant phase constraint method.

Since the feedback value of q _m is determined separately for each transmit antenna, in contrast to the exponentially increasing complexity of the prior art optimal quantization method, the computational complexity of the method of the present invention is It increases linearly with the number of transmitting antennas.

The feedback information calculated from the quadrant phase constraint method ensures that all elements described in equation (19) are positive if any m ≠ n, and maximized feedback to which this feedback information contributes. diversity gain _{g b} can be written as: (22).

  Combining equations (16), (17) and (22), the output SNRγ at the receiver of the detector is obtained as in the following equations (23) and (24).

Here, γ ₀ = E _S / N ₀ is SNR without diversity, and diversity gains g _c and g _b are given by equations (17) and (22), respectively.

Complexity Analysis As described above, the method according to the present invention determines feedback information for each transmit antenna separately. Thus, the computational complexity only increases linearly with the number of transmit antennas. However, for the optimal quantization feedback TxAA method, the computational complexity increases exponentially with the number of transmit antennas. Have M = 4 transmit antennas, for a system using a representation of two bits to each element of the space encoding vector _{p k,} the _{p k,} total ² 2 ^{× (4-1)} = 64 pieces of possible There is a value. This receiver using the optimum quantization feedback for all 64 possible vectors of p _k unless after calculating the ^{_{p k h k h k H p}} k H, may send feedback information means that it is not possible, the calculation of the cost function ^{_{p k h k h k H p}} k H is accompanied by a "complex" multiplier of about ⁴ 2 = 16 times. However, the sub-optimal method of the present invention requires only M-1 = 3 calculations for all antennas, and each operation involves about 2 “real” multiplications. Thus, the computational complexity of the method of the present invention is only (2 × 3) / (64 × 16 × 2) of the prior art optimum quantization feedback TxAA for a system with M = 4 transmit antennas. = 0.3%. For systems with more transmit antennas, the method of the present invention can achieve further savings in computational complexity.

Combination of Orthogonal STBC and Group Spatial Coding The method described above involves only the coding process in the spatial domain. To further reduce the amount of feedback and computation, the quadrant phase constrained feedback scheme is combined with orthogonal space-time block coding (STBC). This method also uses the time domain in the encoding process.

The structure of the system is shown in FIG. An input symbol 401 is generated and modulated by conventional means. The symbols are supplied to the orthogonal STBC encoder 410. Without loss of generality, the input to the STBC encoder is assumed to be s ₁ and s ₂ respectively in two consecutive symbol periods t ₁ and t ₂ , where j = 1, 2 s _j εS, where S is a modulation symbol set.

Energy modulation _symbols, E is a ^{(| 2 | s j) =} E S. In the STBC encoder, the input data symbols s ₁ and s ₂ are demodulated into multiple data streams (one for each transmit antenna group). The data stream 411 of the STBC encoder 410 is expressed by the following equation (25).

Here, d _k corresponds to the k-th output stream of the STBC encoder, d _kj is transmitted at time t _j , and (·) ^T indicates matrix transposition.

The M transmission antennas are divided into a plurality of transmission antenna groups 421 to 422. Each group corresponds to one of the data streams d ₁ , d ₂ generated by the STBC encoder 410. The number of antennas included in the k-th group is assumed to be M _k when k = 1 and 2, and M ₁ + M ₂ = M.

  For each transmit antenna group, adaptive linear spatial encoders 431 and 432 are applied to each data stream 411. Spatial encoders 431 and 432 map multiple data streams 411 to transmit antenna groups according to each group's channel feedback information 440.

The spatial encoding vector of the k-th group is defined as in the following equation (26) with respect to k = 1, 2, with the constraints being p ₁ p ₁ ^H + p ₂ p ₂ ^H = 1.

  Then, the encoded signal 433 transmitted by the k-th antenna group can be expressed in a matrix form as in the following equation (27) for k = 1 and 2.

The symbols in the first column of X _i are transmitted in the symbol period t ₁ , and the symbols in the second column are transmitted in t ₂ .

  In the channel, the received signal 461 is contaminated by both time-varying multipath fading and AWGN462.

  Receiver 450 includes a space-time decoder 451, a channel estimation module 452, and a feedback calculation unit 453 that generates feedback information 440 for each transmit antenna group. The signal Rx 461 received by the receiver 450 is the sum of the propagation signals from all the transmission antennas plus the noise 462. The received signal can be expressed by the following equation (28).

Here, r = [r ₁ , r ₂ ] ^T , z = [z ₁ , z ₂ ] ^T are a reception vector and an AWGN noise vector, respectively, and r _k and z _k correspond to time t _k , h _k εC ^{Mk × 1} is a channel impulse response (CIR) defined as in the following equation (29) for k = 1,2.

Elements h _{k, m} are CIRs between the m th transmit antenna and receive antenna of group k when m = 1, 2,..., M _k .

  By combining equations (1) and (5), the input-output relationship of the diversity system can be rewritten as the following equation (30).

Here, (·) ^* indicates a complex conjugate, s = [s ₁ s ₂ ] ^T is a signal vector, and the channel matrix H is defined as in the following equation (31).

The matrix H is a 2 × 2 orthogonal matrix, that is, H ^H H = (| h ₁ w ₁ | ² + | h ₂ w ₂ | ² ) · I ₂ , I ₂ is a 2 × 2 unit matrix is there. From equations (11) and (13), a decision vector y = [y ₁ , y ₂ ] ^T can be obtained as in the following equation (32).

Here, v = H ^H z is a noise component having the following covariance matrix.

  Using the decision variable given in equation (14), the signal-to-noise ratio at the receiver can be calculated as in equation (33).

Here, γ ₀ = E _s / N ₀ is the SNR without diversity. From equation (15), it can be seen that SNRγ is a function of the spatially encoded vectors p ₁ and p ₂ and the CIR vectors h ₁ and h ₂ .

By selecting p _k suitable form based on the characteristics of the fading channel, it is possible to improve the SNR of the receiver using only a small amount of feedback information 440.

In the method of the present invention, by applying the quadrant phase constraint feedback method to the design of the space encoding vector p _k of the group, to save both complexity and the amount of feedback calculations. These details are described below.

Design of Spatial Coding Vector: General Case In order to achieve the maximum SNR at the receiver, the optimal design criteria for spatial coding vectors w ₁ and w ₂ are as follows:

Where W is the set of all possible coding vector pairs with constraints p ₁ p ₁ ^H + p ₂ p ₂ ^H = 1. Optimal values for p ₁ and p ₂ can be obtained by exhaustive search of all elements of W. Since the size of the set W increases exponentially with the number of transmission antennas, this optimal spatial coding vector design method is not suitable for a system having a large number of transmission antennas.

  In order to reduce the computational complexity and to reduce the amount of feedback information, the quadrant phase constraint method is applied to the calculation of feedback information and the formulation of adaptive spatial coding vectors.

For a typical system with M transmit antennas, M ₁ = M ₂ = M / 2 when M is an even number, M ₁ = (M + 1) / 2 when M is an odd number, M ₂ = ( M-1) / 2. The space encoding vector _{p k,} with respect to k = 1, 2, defined by the following equation (35).

Here, i ² = −1 is an imaginary part symbol, q _{k, m} ∈ {0, 1, 2, 3} is m = 2, 3,..., M _k , and k = 1. 2 is feedback information, and each q _{k, m} includes 2-bit information. For a system with M transmit antennas, the total number of feedback bits required for the method of the present invention is 2M-4. In order to simplify the expression, _q1,1 = _q2,1 = 0.

When the quadrant phase constraint method is applied, the feedback information q _{k, m} can be calculated as in the following equation (36).

Here, the symbol in the above equation returns the closest smaller integer, and θ (tilde) _{k, m} is the following equation (37).

The integer l is selected such that θ (tilde) _{k, m} is in the range [0, 2π).

  The adaptive diversity algorithm described herein requires 2M-4 bits of feedback information to form a spatially encoded vector for a system with M transmit antennas. Next, it is shown that the amount of feedback information can be further reduced in the case of a system having M = 4 or M = 3 transmission antennas. This brings practical benefits to next generation communication systems.

Design of Spatial Coding Vector: Special Case In the case of a system having M ≦ 4 transmission antennas, each group has at most two transmission antennas. For a group with two transmit antennas, the sub-optimal design criteria of the present invention can be met with only 1-bit feedback information.

In the case of a system having M = 4 transmission antennas, the number of antennas in each antenna group is M ₁ = M ₂ = 2. The spatially encoded vector is defined as in the following equation (38) for k = 1 and 2.

Here, b _k ε {0, 1} is feedback information of the kth antenna group. The feedback information can be defined by the following equation (39).

  The SNR at the receiver is expressed by the following equation (40).

The conventional diversity gain g4 _{, c} and the feedback diversity gain g4 _{, b} are defined as in the following equations (41) and (42).

Similarly, for a system with M = 3 antennas, groups M ₁ = 2 and M ₂ = 1 are obtained. Since the second group has only one antenna, p ₂ = 1 / √3 is obtained.

For the first group with two transmit antennas, the spatial encoding vector p ₁ is applied. In this encoding method, the SNR of the receiver can be calculated from the equation (15) as the following equation (43).

The conventional diversity gain g3 _{, c} and the feedback diversity gain g3 _{, b} are given by the following equations (44) and (45).

If the system has only two transmit antennas, w ₁ = w ₂ = 1 / √2 is obtained, and this scheme is reduced to the orthogonal space-time block coding described above.

  Using the method of the present invention, the feedback information required for a system having M = 3 and M = 4 transmit antennas is only 1 bit and 2 bits, respectively.

Performance Limit Based on the statistical characteristics of the output signal 105 in the receiver 20, the theoretical performance limit of the diversity system of the present invention can be expressed as the following equations (46) and (47).

Here, the deviation of P ^U (E) and P ^L (E) is omitted for the sake of clarity. Using the theoretical performance limits given by equations (46) and (47), the actual error probability P (E) of the diversity scheme of the present invention satisfies the following equation (48).

  Equations (46)-(48) theoretically evaluate the method according to the present invention, and these equations can be used as guidelines for designing a wireless communication system.

  It should be noted that closed loop techniques based on conventional full rate STBC as well as orthogonal STBC can only be implemented in systems with exactly two transmit antennas.

  In contrast, the transmit diversity method according to the present invention can be used for systems with any number of transmit antennas. This is very useful for high-speed downlink data transmission in next-generation wireless communication systems that require higher diversity orders to guarantee high data throughput in the downlink using multiple transmit antennas and one receive antenna. Useful for.

EFFECT OF THE INVENTION The method according to the present invention is superior in performance up to 2 dB over conventional orthogonal STBC. The performance of the version using 2-bit feedback information is about 0.4 dB better than the version using 1-bit feedback information.

  Prior art full rate STTD and ASTTD systems can be implemented in systems having at most two transmit antennas. In contrast, the transmit diversity method of the present invention can be used for systems with any number of transmit antennas. Furthermore, the performance of the method improves substantially linearly with increasing number of transmit antennas.

  The method of the present invention is very computationally efficient compared to prior art optimal quantization methods. The method of the present invention requires only 0.3% computational effort of a prior art optimal quantization feedback TxAA for a system with four transmit antennas. This computational saving is noticeable in receivers, which are typically battery powered mobile phones.

  Although the invention has been described by way of examples of preferred embodiments, it is to be understood that various other adaptations and modifications can be made within the spirit and scope of the invention. Accordingly, the purpose of the appended claims is to cover all variations and modifications that fall within the true spirit and scope of the invention.

1 is a block diagram of a system with diversity gain according to the present invention. FIG. 4 is a quadrant diagram of a coordinate system showing quadrant phase constraints according to the present invention. FIG. FIG. 4 is a diagram of a normalized coordinate system in which the phase of the reference signal is on the x-axis of the coordinate system according to the present invention. FIG. 3 is a block diagram of a system combining orthogonal space-time block codes and quadrant phase constraints in accordance with the present invention.

Claims (7)

A method for increasing transmit diversity gain in a wireless communication system including a transmitter having a plurality of transmit antennas and a receiver having a single receive antenna,
Dividing the plurality of transmit antennas into a plurality of transmit antenna groups;
Measuring the phase of the channel impulse response of each transmit antenna at the receiver;
Separately obtaining feedback information for each transmit antenna group from the channel impulse response;
Sending the feedback information of each transmit antenna group to the transmitter;
Orthogonal space-time block coding of input symbols at the transmitter to generate a data stream for each transmit antenna group;
Increasing a transmit diversity gain in a wireless communication system comprising: adaptively linearly spatially encoding each data stream according to the feedback information of the group to generate a coded signal for each transmit antenna of each group Method. Said seeking is
Selecting one of the channel impulse responses as a reference channel impulse response;
The method of claim 1, further comprising: normalizing the measured phase according to the phase of the reference channel impulse response such that the normalized phase is in a quadrant phase sector of the reference phase.   The method of claim 2, wherein the reference channel impulse response has a highest power.   The method of claim 2, wherein the quadrant phase sector spans a range of 90 degrees.   The method according to claim 2, wherein the normalization rotates the phase, and the feedback information encodes a rotation amount.   The method of claim 1, wherein there are four transmit antennas, each group has two transmit antennas, and the feedback information is one bit for each group. Multiple transmit antenna groups;
Means for generating input symbols;
An orthogonal space-time block encoder configured to generate a data stream for each transmit antenna group;
A transmitter having an adaptive linear spatial encoder configured to generate a coded signal for each transmit antenna of the group from the data stream of the group according to feedback information of the group;
One receiving antenna,
Means for measuring the phase of the channel impulse response of each transmit antenna;
Means for separately obtaining the feedback information of each transmit antenna group from the channel impulse response;
A wireless communication system comprising: a receiver having means for sending the feedback information of each transmitting antenna group to the transmitter.

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