外文翻译--基于MIMO-OFDM系统的正交空时分组码【适用于毕业论文外文翻译】.doc

外文资料（一） On Orthogonal Space-Time Block Codes for MIMO-OFDM Systems Space-time code in mobile communication system, and orthogonal desing in multiple- antennas scneme are dicsussed. By the methods, data is encoded using a space- time block code and is split into several streams which are simultaneously transmitted by antennas. So a maximum- likelihood decoding algorithm can be used at the receiver to achieve the maximum diversity orderIntroduction Most work on wireless communications had focused on having an antenna array at only one end of the wireless link usually at the receiver. Seminal papers by Gerard J. Foschini and Michael J. Gans1, Foschini2 and Emre Telatar3 enlarged the scope of wireless communication possibilities by showing that for the highly-scattering environment substantial capacity gains are enabled when antenna arrays are used at both ends of a link. An alternative approach to utilizing multiple antennas relies on having multiple transmit antennas and only optionally multiple receive antennas. Proposed by Vahid Tarokh, Nambi Seshadri and Robert Calderbank, these spacetime codes (STCs) achieve significant error rate improvements over single-antenna systems. Their original scheme was based on trellis codes but the simpler block codes were utilized by Siavash Alamouti,and later Vahid Tarokh, Hamid Jafarkhani and Robert Calderbank to develop spacetime block-codes (STBCs) 4. STC involves the transmission of multiple redundant copies of data to compensate for fading and thermal noise in the hope that some of them may arrive at the receiver in a better state than others. In the case of STBC in particular, the data stream to be transmitted is encoded in blocks, which are distributed among spaced antennas and across time. While it is necessary to have multiple transmit antennas, it is not necessary to have multiple receive antennas, although to do so improves performance. This process of receiving diverse copies of the data is known as diversity reception and is what was largely studied until Foschinis 1998 paper. An STBC is usually represented by a matrix. Each row represents a time slot and each column represents one antennas transmissions over time. Here, sij is the modulated symbol to be transmitted in time slot i from antenna j. There are to be T time slots and nT transmit antennas as well as nR receive antennas. This block is usually considered to be of length TThe code rate of an STBC measures how many symbols per time slot it transmits on average over the course of one block. If a block encodes k symbols, the code-rate is Only one standard STBC can achieve full-rate (rate 1) Alamoutis codeOrthogonality STBCs as originally introduced, and as usually studied, are orthogonal. This means that the STBC is designed such that the vectors representing any pair of columns taken from the coding matrix is orthogonal. The result of this is simple, linear, optimal decoding at the receiver. Its most serious disadvantage is that all but one of the codes that satisfy this criterion must sacrifice some proportion of their data rate (see Alamoutis code).Moreover, there exist quasi-orthogonal STBCs that achieve higher data rates at the cost of inter-symbol interference (ISI). Thus, their error-rate performance is lower bounded by the one of orthogonal rate 1 STBCs, that provide ISI free transmissions due to orthogonality.Higher order STBCs Tarokhet al. discovered a set of STBCs that are particularly straightforward, and coined the schemes name. They also proved that no code for more than 2 transmit antennas could achieve full-rate. Their codes have since been improved upon (both by the original authors and by many others). Nevertheless, they serve as clear examples of why the rate cannot reach 1, and what other problems must be solved to produce good STBCs. They also demonstrated the simple, linear decoding scheme that goes with their codes under perfect channel state information assumption.4 transmit antennas Two straightforward codes for 4 transmit antennas are:and These codes achieve rate-1/2 and rate-3/4 respectively, as for their 3-antenna counterparts.C4,3 / 4 exhibits the same uneven power problems as C3,3 / 4. An improved version of C4,3 / 4 iswhich has equal power from all antennas in all time-slots.Decoding One particularly attractive feature of orthogonal STBCs is that maximum likelihood decoding can be achieved at the receiver with only linear processing. In order to consider a decoding method, a model of the wireless communications system is needed. At time t, the signal received at antenna j is:,where ij is the path gain from transmit antenna i to receive antenna j, is the signal transmitted by transmit antenna i and is a sample of additive white Gaussian noise (AWGN). The maximum-likelihood detection rule is to form the decision variables where k(i) is the sign of si in the kth row of the coding matrix, k(p) = q denotes that sp is (up to a sign difference), the (k,q) element of the coding matrix, for i = 1,2.nT and then decide on constellation symbol si that satisfies , withthe constellation alphabet. Despite its appearance, this is a simple, linear decoding scheme that provides maximal diversity.References 1 Gerard J. Foschini and Michael. J. Gans (January 1998). “On limits of wireless communications in a fading environment when using multiple antennas”. Wireless Personal Communications 6 (3): 311335.2 Gerard J. Foschini (autumn 1996). “Layered space-time architecture for wireless communications in a fading environment when using multi-element antennas”. Bell Labs Technical Journal 1 (2): 4159.3 I. Emre Telatar (November 1999). “Capacity of multi-antenna European Transactions on Telecommunications , 10 (6): 585595.4 Vahid Tarokh, Nambi Seshadri, and A. R. Calderbank (March 1998). Spacetime codes for high data rate wireless communication: Performance analysis and code construction. IEEE Transactions on Information Theory 44 (2): 744765. 译文 基于MIMO-OFDM系统的正交空时分组码 本文介绍了移动通信中的空时码, 针对多天线系统提出了空时分组码的正交设计理论, 可以采用高效的调制技术(QAM,PSK) ,由多天线同时发射。接收端采用最大似然译码可以获得最大的分集增益。并因空时码有很高的频谱利用率, 从而使空时码在未来移动通信及无线局域岗中得到广泛的应用。介绍Alamouti于1998年提出了一种发射端采用两根天线的空时分组码方案, 该方案能够实现最大分集增益和全发射速率, 在接收端使用了简单的最大似然译码。为了将空时分组码推广到多个天线, Vahid Tarokh等基于满分集提出了正交空时分组码。由于正交空时分组编码发射矩阵各行之间的正交性, 可以获得满分集增益, 但是当发射天线数大于2时, 利用复正交设计得到的正交空时分组编码不能达到最大传输速率。为此,H. Jafarkhan等和Tirkkonen等分别提出了两种基于全速率的准正交空时分组编码, 即Jafarkhani 码和TBH 码。JiaHou等在Jafarkhani 码和TBH码的基础上, 讨论了变形Jafarkhani 码和变形TBH 码, 并提出了2种新的准正交编码。在既定的情况下,在特定的数据流传输编码在blocks块, 间隔,将分布在天线和跨越时空。虽然是必要的,它有多个发射天线,这是没有必要有多个接收天线,虽然这样做改进效能。这个过程接收不同的数据备份,是众所周知的最大似然译码,直到1998年Foschini研究论文。空时编码通常用矩阵来表示。在矩阵中，每一行代表一个时间段,而每一列代表每一根天线的传输。正交由于最初的对空时编码做出的研究,并介绍了这样的正交。这意味着,例如既定设计向量任何两个柱代表掠正交编码矩阵。这是简单的结果,线性,最佳解码的接收机。最严重的不利因素是所有之一,同时满足这一标准法典,必须牺牲一些比例的数据传输速率。此外,存在着在利率,以达到更高的数据传输干扰的成本(ISI)。因此,他们的误码率是空时编码的界定标准之一,正交率提供免费传授由于正交码。高阶空时编码方法Tarokhetal等在1998年10月发现了一组空时编码。这是特意直截了当的以创造了这个方案的创始人名字为名。他们也证明了不能超过2个发射天线可以达到的目标。他们的代码。一直以来的改进。然而,作为明确的例子,为什么不能到达率1,其他什么必须解决的问题有如何用空时码接收更好的信号。他们也体现了简单的，直线解码是伴随着他们的编码方案,在完美的信道状态信息。4个发射天线 两个直截了当的代码为4发射天线是:以及.这些编码实现-1/2比特和-3/4比特的空时编码,从所有具有相同能力的天线可知。译码一个特别吸引人的特征的正交STBC就是这个了最大似然解码,可以较好地实现在接收者对而已线性加工。为了考虑解码方法,无线通信系统的模型是必需的。 在时间t上的信号,天线接收到的是:,是路径获得传送天线吗接收天线是信号通过传送天线i和有一份添加剂白色高斯噪声检测规则的就是要形成的决策变量。满足对于准正交空时分组编码而言, 由于发射矩阵的各行不是完全正交的, 因此在接收端进行最大似然译码时需对信号进行联合检测, 这就使得其译码算法较之正交空时分组编码要复杂一些。由最大似然准则, 其解码过程即求其中, 是映射后的符号。虽然从表面上看,这是一个简单的直线解码方案,提供最大的似然性。参考文献1 Gerard J. Foschini and Michael. J. Gans (January 1998). On limits of wireless communications in a fading environment when using multiple antennas. Wireless Personal Communications 6 (3): 311335.2 Gerard J. Foschini (autumn 1996). Layered space-time architecture for wireless communications in a fading environment when using multi-element antennas. Bell Labs Technical Journal 1 (2): 4159.3 I. Emre Telatar (November 1999). Capacity of multi-antenna gaussian channels. European Transactions on Telecommunications , 10 (6): 585595.4 Vahid Tarokh, Nambi Seshadri, and A. R. Calderbank (March 1998). Spacetime codes for high data rate wireless communication: Performance analysis and code construction. IEEE Transactions on Information Theory 44 (2): 744765.外文资料（二）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-rate1.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 TM 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 MM 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 21 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