A novel QO-STBC scheme with linear decoding for three and four transmit antennas

In this letter, we propose a quasi-orthogonal spacetime block coding (QO-STBC) scheme with maximum likelihood (ML) decoding via simple linear detection. A conventional QOSTBC scheme can achieve the full rate, but at the cost of decoding complexity and diversity gain. These disadvantages of the conventional QO-STBC scheme are mainly a result of interference terms in the detection matrix. In this letter, we propose a new QO-STBC scheme which eliminates interference terms. The proposed method achieves improved diversity gain with respect to the conventional QO-STBC scheme, as well as a great reduction in decoding complexity.     

一种新的3发1收准正交空时编码方案

提出了一种新的码率为1的3发1收准正交空时编码方案,通过利用Givens旋转消除检测矩阵中的干扰项.在瑞利衰落信道下仿真分析了所提算法与传统算法的误码率性能.仿真结果表明,所提算法在性能上要优于传统的4发1收QO-ST-BC方案,并且在低信噪比时,性能要优于传统的码率不为1的3发1收O-STBC算法.     

Full-rate full-diversity STBCs for three and four transmit antennas

A novel technique is presented for the construction of full-rate, fulldiversity space?time block codes (STBCs) from orthogonal STBCs (OSTBCs), having empty slots left in their codeword matrices for orthogonality. Two new STBCs are obtained, which are both fullrate and full-diversity, for three and four transmit antennas. The higher decoding complexity of these structures is reduced owing to non-orthogonality by using a conditional maximum-likelihood decoder. The new optimised codes provide better error performance than their full-rate full-diversity counterparts given in the literature.     

Space-time turbo trellis codes for two, three, and four transmit antennas

New space-time turbo trellis codes (ST turbo TCs) with 4-phase-shift keying (PSK) and 8-PSK for two, three, and four transmit antennas in slow and fast fading channels are proposed in this paper. The component codes of the space-time turbo schemes are constructed by choosing the feedforward coefficients to maximize the minimum squared Euclidean distance and the feedback coefficients to minimize the iterative decoding threshold. The performance of the proposed ST turbo TCs with various memory orders, transmit antennas, and interleaver structures is evaluated by simulation. It is shown that the new codes achieve better performance than previously designed codes. The impact of antenna correlation and imperfect channel estimation on the code performance is also discussed.     

多发射天线选择的无线信道序统计特性研究

在独立平坦的瑞利衰落信道中,提出一种确定排序信道衰落因子大小的联合概率密度函数(PDF)序系数的方法.根据输出信噪比最大的天线选择原则,就信道状态信息(CSI)正确和差错两种不同情况,分别给出n个最大排序的信道衰落因子的边缘PDF理论式.最后, 对采用正交空时分组码的多发射天线选择系统进行数值仿真,结果表明:多天线选择能极大地提高系统的传输质量, 而且能有效地抵抗CSI差错引起的性能下降.     

Super-quasi-orthogonal space-time trellis codes for four transmit antennas

We introduce a new family of space-time trellis codes that extends the powerful characteristics of super-orthogonal space-time trellis codes to four transmit antennas. We consider a family of quasi-orthogonal space-time block codes as building blocks in our new trellis codes. These codes combine set partitioning and a super set of quasi-orthogonal space-time block codes in a systematic way to provide full diversity and improved coding gain. The result is a powerful code that provides full rate, full diversity, and high coding gain. It is also possible to maintain a tradeoff between coding gain and rate. Simulation results demonstrate the good performance of our new super-quasi-orthogonal space-time trellis codes.     

Improved formulae for the resonant frequencies of triangular microstrip patch antennas

In this article, an improved formula for the effective side length (a _eff) of the equilateral triangular patch antenna is presented. The computed resonant frequencies for the first five modes, using this formula, are compared with the available experimental and theoretical results in the literature. It is shown that the proposed formula has better accuracy than other available expressions. Moreover, the 30°–60°–90° and 30°–30°–120° triangular patch antennas are studied. Specifically, improved formulae for the effective dielectric constant of these patches are derived.     

High-rate orthogonal space-time block code for four transmit antennas

A high-rate (rate 1.5) nonlinear orthogonal space-time block code for four transmit antennas is presented. It outperforms previous space- time block codes where there are more than two receive antennas. This high-rate code improves on the performance of a recently proposed nonlinear orthogonal space-time block code of the same rate and without any extra constellation expansion.     

Robust full-diversity full-rate quasi-orthogonal STBC for four transmit antennas

A novel quasi-orthogonal space-time block code (QSTBC) with full-diversity full-rate transmission and double-symbol decoding is proposed for a system with four transmit antennas, which is constructed by linearly combining two optimally power-scaled component Alamouti codes. Compared with the existing QSTBC with optimal constellation rotation, the proposed code provides excellent robustness, in terms of bit error rate performance, against spatially correlated and/or time-selective fading channels.     

信道差错对多发射天线选择性能的影响

对于多发单收天线(MISO)通信系统,考虑发射端信道状态信息的差错(ECSI).研究正交空时分组码的MISO系统的多天线选择,提出了一种CSI差错的选择性信道序统计特性求解方法.在独立的平坦瑞利衰落信道和多进制相移键控(MPSK)调制下,推导了一种较准确的系统比特误码率(BER)切诺夫上界解析式.最后系统BER性能上界的数值结果和仿真结果研究表明:多发射天线选择技术能极大地提高系统的传输质量,能有效地抵抗ECSI的影响.     

Space diversity schemes with feedback for three transmit antennas

In this paper, we propose two-space diversity schemes with feedback for three transmit antennas which perform independently for each signaling interval. The first one is a pure code selection technique which provides, with two feedback bits, an E_b/N₀ advantage of nearly compared to the pure antenna selection technique where the best one of the three antennas is used. The second one is a hybrid selection scheme which consists of a combination of antenna and code selection techniques. The selection is performed out of 13 possible precoding vectors requiring four feedback bits, to maximize the diversity for all possible channel situations. It was shown by computer simulations that E_b/N₀ gains of approximately 1.25 and are possible, compared to the pure antenna selection and code selection schemes, respectively. Mapping rules between feedback codewords and precoding vectors, which results in improvement over random mapping, are obtained to minimize the error probability in the case of feedback errors.     

基于最优延时和多天线的并行检测算法

循环平稳特征检测是一种在低信噪比时也能准确发现信号的盲检测技术,但其算法计算周期较长.针对此问题提出了一种改进的并行渐进最优卡方检测算法,通过识别循环谱特性和遍历循环自相关确定最优的循环频率和延时,用循环自相关以及渐进协方差矩阵构建检验统计量,并对二维向量和谱分量实部和虚部进行合并及迭代过程并行处理,仿真得到了检测概率和检测时间.同时,根据最大似然比统计量的有偏估计和渐进分布特性导出了检测概率的表达式,结果表明：最优延时的理论与仿真吻合得很好,多天线技术充分利用了空间分集,在干扰较强时仍然[JP2]具有较高的检测概率,且并行处理过程能有效减少检测时间.     

Super-quasiorthogonal space-time trellis codes for four transmit antennas with rectangular signal constellations

In this paper, we present the first super-quasiorthogonal space-time trellis codes (SQOSTTCs) for systems with four transmit antennas using various types of rectangular signal constellations to increase the spectral efficiency up to 5 bits/s/Hz. In our wireless communications system, we define an eight-dimensional (8D) signal constellation as Cartesian product of four two-dimensional (2D) rectangular signal sets. The transmission of an 8D point from the first antenna is achieved by transmitting four concatenated 2D points in four consecutive channel uses. The 2D symbols transmitted from the other three antennas are not independent but so chosen as to form, together with the symbols transmitted from the first antenna, the entries of a 4×4 quasiorthogonal transmission matrix. The union of two sets of quasiorthogonal transmission matrices forms a so-called super-quasiorthogonal signal set. With the 4×4 quasiorthogonal transmission matrices, we then label the state transitions of a trellis diagram describing the operation of the encoder. The simulation results of the frame error rate and the bit error rate demonstrate the excellent performance of our proposed SQOSTTCs.     

Joint carrier frequency offset and channel estimation for OFDM systems with two receive antennas

Carrier frequency offset (CFO) in OFDM systems results in loss of channel orthogonality and hence degrades the system's performance. In this paper, we propose a new method for joint CFO/channel estimation for OFDM systems with two receive antennas. Our method avoids the complexity of full search methods in one or two dimensions. Using one training OFDM symbol and utilizing the knowledge of the structure of the inter‐channel interference that results from CFO, we develop a two‐stage estimation procedure. The first stage derives an initial CFO/channel estimate based on a one shot minimization step. The second stage refines this joint estimate by conducting a small CFO search in the vicinity of the initial estimate. This procedure provides CFO estimates over a full range of −N /2–N /2, (N : number of subcarriers), as well as the channel estimates. Computer simulations show an excellent performance that is very close to the Cramer–Rao lower bound and superior to some existing methods. The effect of antenna correlation on performance is also investigated through computer simulations, showing small performance degradation even at medium correlation coefficients (0.3–0.6). Copyright © 2015 John Wiley & Sons, Ltd.     

空间光通信中分布式天线的信号检测研究

针对空间光通信中随机信道传播时延导致接收信号符号间干扰的特殊性使分布式发射天线多入多出(MIMO)信号的线性检测算法更加复杂这一问题,提出了一种基于Neyman-Pearson(NP)融合准则的分布式天线信号检测算法。仿真结果表明,当接收信号同步时,NP算法具有较好的健壮性,其性能优于等增益合并(EGC)算法,与最佳合并(OC)算法相当;当接收信号异步时,NP算法要明显优于EGC和OC算法,抑制接收符号间干扰,能体现出分布式天线系统的空间分集性能。     

基于神经网络的多波束天线自适应调零

具有一定的干扰自适应调零能力是对了卫星通信系统的基本要求。本文结合多波束天线特性，提出了一种基于RBF神经网络的MVDR波束合成器干扰抑制方案。该方法可有效避免采样矩阵求逆带来的影响，收敛速度更快，对所需信号参数具有一定的顽健性。计算机仿真验证了该方法的可行性。     

Generalized co-phasing for multiple transmit and receive antennas

We propose and study a class of transmit beamforming techniques for systems with multiple transmit and multiple receive antennas with a per-antenna transmit power constraint. The per-antenna transmit power constraint is more realistic than the widely used total (across all transmit antennas) power constraint, since in practice each transmit antenna is driven by a separate power amplifier with a maximum power rating. Under the per-antenna power constraint, from an implementation perspective, it becomes desirable to vary only the phases (as opposed to both power and phase variation) of the signals departing from the transmit antennas. We name this class of techniques generalized co-phasing and formulate an optimization problem to calculate the transmit antenna phases. Furthermore, we propose five heuristic algorithms to solve the optimization problem. All the proposed algorithms except one are optimal for the case of two transmit antennas and an arbitrary number of receive antennas. For an arbitrary number of transmit and receive antennas, simulations indicate that the proposed algorithms perform very close to the optimal solution calculated through an exhaustive search of all possible transmit phases.     

Improved signal constellations for differential unitary space-time modulations with more than two transmit antennas

In this paper, we propose new and improved unitary signal constellations for differential unitary space-time modulations utilizing more than two transmit antennas. The proposed unitary designs are constructed from fundamental building blocks which comprise the generator matrices of diagonal cyclic codes, and the 2/spl times/2 and 3/spl times/3 rotational matrices. The performances of the proposed codes are superior to those of previously proposed codes.     

Fast Differential Unitary Space-Time Modulation Decoding for a MIMO Radio Channel

Improved decoding efficiency is achieved for differential unitaryspace-time modulation across a multiple-input multiple-output(MIMO) channel. The group nature of constellations used for signaltransmission, and hence a minimised search space for maximumlikelihood (ML) decoding are utilised to give this improvement. Aprocedure using lattice reduction for fast decoding across amultiple-input single-output (MISO) channel is generalised to aMIMO channel effectively, as a modification to a previousproposal, and used to generate the ML decoder search space.Further insight into the application of this algorithm is given.The decoding technique developed is shown to have very good errorperformance for reasonably sized MIMO channels.     

Wideband patch antennas for mobile communications

This paper describes a new technique for bandwidth enhancement of microstrip patch antennas. An electromagnetically coupled (EMC) feeding structure was employed to increase the bandwidth. L-strip feeding rectangular and triangular patches were simulated and tested. The obtained bandwidth (SWR2) is about 1200 MHz (52%) for the rectangular patch, while that of the triangular one is around 1300 MHz (56%). These results provide evidence that the proposed designs can be used in the DCS, PCS, UMTS, WLAN and IMT-2000 service frequency bands.