单位抗衰落复正交空时分组码级联的Turbo码毕业论文外文翻译.doc

Unit-Rate Complex Orthogonal Space-Time Block Code Concatenated With Turbo CodingSpace-Time Block (STB)code has been an effective transmit diversity technique for combating fading due to its orthogonal design，simple decoding and high diversity gins. In this paper, a unit-rate complex orthogonal STB code for multiple antennas in Time Division Duplex (TDD) mode is proposed. Meanwhile, Turbo Coding (TC) is employed to improve the performance of proposed STB code further by utilizing its good ability to combat the burst error of fading channel. Compared with full-diversity multiple antennas STB codes, the proposed code can implement unit rate and partial diversity; and it hay much smaller computational complexity under the same system throughput. Moreover, the application of TC can effectively make up for the performance loss due to partial diversity. Simulation results show that on the condition of same system throughput and concatenation of TC, the proposed code has lower Bit Error Rate (BER) than those full-diversity codes. IntroductionRecently, transmit diversity has been studied extensively as a method of combating detrimental effects in wireless fading channels due to its relative simplicity of implement and feasibility of having multiple antennas at the Base Station (BS).A simple transmitter diversity scheme using tw0 transmit antennas is proposed by Alamouti .An extension to more than two transmit antennas is presented ,where it is shown that the Alamouti scheme is a special case of Space-Time Block(STB) code. The STB code scheme can achieve full transmit diversity and has a simple Maximum Likelihood (ML) decoding algorithm while used at the decoder. For this, STB code is an attractive approach for practical purposes. But ,it is proved that for STB code, a complex orthogonal design which provide full diversity and unit rate is not possible for more than two antennas, and the 1/2-rate or 3/4-rate STB code for three and four transmit antennas (4Tx) are also given with the code-rate<1.And 2/3-rate STB code for five transmit antennas is proposed recently. Considering the full rate is the important means to implement high data rate service and very important for low Signal to Noise Ratios (SNRs). Unit-rate Complex Orthogonal STB Code1.Full diversity STB codes review In this subsection, we review the basic principle of STB code that provides maximum possible diversity for multiple transmit antennas in wireless communications. Let L,M and T be positive integers, a complex orthogonal STB code is defined by a T×M dimensional transmission matrix G, every entry of which is complex linear combination of the ; input symbols ,and their conjugates ,and it satisfies the following complex orthogonal condition where superscript "H" denotes the Hermitian conjugation and I is the M×M identity matrix. M and T are the numbers of transmitting antenna and time slots used to transmit L input symbols, respectively.2.Unit-rate STB codeIn this subsection, we consider a communication system comprising 3 transmit antenna and 1 receive antenna that operates in a Rayleigh of analysis. The transmitter and receiver structures of the communication system with TC are shown in Fig.1 and Fig.2, respectively. The data source bits are firstly encoded by the turbo encoder, then are mapped into corresponding constellation symbols; the symbols are STB encoded, the resulting encoded symbols are modulated onto a pulse waveform and then transmitted from three transmit antennas respectively. Fig.1Fig.2In TDD model, the channel gain estimated by the uplink can be used to downlink transmission, so we can choose two maximum channel gain amplitudes from estimated three antenna channel gains, and use corresponding two transmit antennas to transmit the coded symbols, respectively. Namely, if |h1|h3| and |h2|h3|, we choose Txl and Tx2 to transmit symbols. Similarly, the other two cases are also easy to analysis. Here, let and denote the two chosen maximum channel gains, respectively. Then at the receiver, the received signal matrix at time slot 1 and slot 2 can be expressed byIt can be changed asThe normalized constant is used to keep the total transmitted energy be E ,here =, E is the transmitted energy at each transmission interval. n is the 2×1 white noise matrix ，The SNR is defined as E/No. The elements of H can be obtained from the estimated channel gain coefficients in the uplink by the use of TDD mode. Considering Then,Thus the decoding can be performed via linear combining and maximum likelihood decision as follows: References 1 Siavash M Alamouti. A simple transmit diversity technique for wireless communications.1998(08).2 V Tarokh.H Jafarkhani.A R Calderbank. Spacetime block codes from orthogonal designs.1999(07).3 Xue-Bin Liang. A high-rate orthogonal space-time block code. 2003(05).4 T H Liew.L Hanzo. Space-time codes and concatenated channel codes for wireless communications 2002(02).5 C Berrou.A Glavieux. Near optimum error correcting coding and decoding:Turbo-codes1996. 译文单位抗衰落复正交空时分组码级联的Turbo码 空时编码因其正交性简单解码和高分集增益是一种防止衰落的有效的发射变化技术。在本文中，假设对于多个天线的时分双工模型有一个单位速率的复正交空时编码。同时，使用Turbo码通过利用其良好的性能来改进所假设的空时分组码的抵抗衰落信道的突发的错误的能力。与全样性的多天线空时分组码相比，所假设的码能够有单位速率以及部分的多样性，并且它在相同的系统吞吐量时计算复杂性要小的多。更好的是，因其部分多样性，Turbo码的应用能有效的弥补性能损失。仿真结果表明在相同的系统的吞吐量以及Turbo码串连情况下，所假设的码相对于那些全样性的码有更加低的误码率。介绍 近年来，因在基站使用的简单性和多天线的灵活性，传送多样性作为在衰落信道中抵抗严重衰落的方法而被广泛研究。Alamouti建议一种用两个天线的简易传送多样性计划。一种对超过两个传送天线的引申也产生了，它显示出Alamouti是空时分组编码的一种特殊例子。这个空时分组编码能够达到传送全样性并且在译码时有最大的解码可能性。因此，空时分组码是一种有实用性的很有吸引力的编码方式。然而，对于正交分组码。对于超过两个天线的复正交设计，提供全传送和单位速率是不大可能的，对于三根或四根天线1/2速率或者3/4速率的空时分组码也给出。对于5根传送天线的2/3速率的空时分组码也被提出了。近来，考虑到全速率是一种非常重要的方法来运行高数据速率服务，同时对低信号比率也非常重要。另外，由于接收大小和能力的限制，空时分组码的低复杂解码算法也是必需的。单位速率正交空时分组码1.回顾全部分集的空时分组码在这部分，我们回顾在无线通信中对于传送天线的提供最大多样性的空时分组码的基本原则。假设L,M,T都是正整数，一个复正交空时编码被定义为一个的传输矩阵G,对于这个矩阵中的每一个词条都是输入为的L的复杂线性组合,并且它们的共轭,而且它满足下面的复正交条件在此,上标H代表的是厄米的结合,而I则是的单位矩阵。M和T是传送天线的数量和传送L输入信号的时间标志。2 单位速率空时分组码在这一部分，我们考虑一个由三根天线所组成的通信系统，1接收到在平稳衰落环境和时分双工模型的天线信号。包含Turbo码的这个通信系统的传送和接收结构分别在图1和图2中给出。图1 图2数据来源位首先是由Turbo码的输入，然后被映射入对应的标志。这个表示就是空时分组码所编码的，由此产生的编码符号调制到一个脉冲波形，然后分别从三个传输天线转交。在时分双工模型中在时分双工模式，信道增益估计上行可用于下行传输，所以我们能够从估计三个天线通道增益来选择两个最大振幅增益的通道，并使用两个相应的发射天线。我们定义，如果|h1|h3|并且|h2|h3|，我们选择Tx1和Tx2来传递标志。相似的，另外两个情况也很容易分析。假设和分别指代两个被选择的最大的通道增益。然后在这接收端，时隙1和时隙2接收信号矩阵可以表示为也可以表示为归一常数用来保持总的传送能量E，这里，E是每一个传送间隔传送能量。N是元素独立的2×1的白噪声矩阵。在时分双工模型对空通讯中H的元素能够从估计的通道增益系数得到。考虑到，然后因此解码可以通过如下的线性组合和最大的可能结论表示出来。 参考文献1 Siavash M Alamouti. A simple transmit diversity technique for wireless communications.1998(08).2 V Tarokh.H Jafarkhani.A R Calderbank. Spacetime block codes from orthogonal designs.1999(07).3 Xue-Bin Liang. A high-rate orthogonal space-time block code. 2003(05).4 T H Liew.L Hanzo. Space-time codes and concatenated channel codes for wireless communications 2002(02).5 C Berrou.A Glavieux. Near optimum error correcting coding and decoding:Turbo-codes1996.