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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 fulldiversity codes. Ⅰ . Introduction Recently, transmit diversity has been studied extensively as a method of bating 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 SpaceTime 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 plex orthogonal design which provide full diversity and unit rate is not possible for more than two antennas, and the 1/2rate or 3/4rate STB code for three and four transmit antennas (4Tx) are also given with the coderate 2/3rate 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). Ⅱ . Unitrate Complex Orthogonal STB Code 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 munications. Let L,M and T be positive integers, a plex orthogonal STB code is defined by a TM dimensional transmission matrix G, every entry of which is plex linear bination of the 。 4 個(gè)發(fā)射天線 兩個(gè)直截了當(dāng)?shù)拇a為 4 發(fā)射天線是 : ???????????????????????????????????????*1*2*3*4*2*1*4*3*3*4*1*2*4*3*2*112342143341243212/14ccccccccccccccccccccccccccccccccC ， 以及 ? ? ? ?? ? ? ??????????????????????????????????????????222222222222*22*11*11*22*3*3*11*22*22*11*3*333*1*233214/3,4ccccccccccccccccccccccccccccC. 這些編碼實(shí)現(xiàn) 1/2 比特和 3/4 比特的空時(shí)編碼 , ?????????????????1*2*32*1*33*1*23214/3,40000ccccccccccccC , 從所有具有 相同能力 的 天線 可知 。因此 ,他們的誤碼率是空時(shí)編碼的界定標(biāo)準(zhǔn)之一 ,正交率提供免費(fèi)傳授由于正交碼。這個(gè)過(guò)程接收不同的數(shù)據(jù)備份 ,是眾所周知的最大似然譯碼 ,直到 1998年 Foschini 研究論文。并因空時(shí)碼有很高的頻譜利用率 , 從而使空時(shí)碼在未來(lái)移動(dòng)通信及無(wú)線局域崗中得到廣泛 的應(yīng)用。length39。 T The 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 coderate is Tkr? Only one standard STBC can achieve fullrate (rate 1) — Alamouti39。 介紹 Alamouti 于 1998年提出了一種發(fā)射端采用兩根天線的空時(shí)分組碼方案 , 該方案能夠?qū)崿F(xiàn)最大分集增益和全發(fā)射速率 , 在接收端使用了簡(jiǎn)單的最大似然譯碼。 空時(shí)編碼通常用矩陣來(lái)表示。 高階空時(shí)編碼方法 Tarokhetal 等在 1998 年 10 月發(fā)現(xiàn)了一組空時(shí)編碼。 譯碼 一個(gè)特別吸引人的特征的正交 STBC 就是這個(gè)了 最大似然 解碼 ,可以較好地實(shí)現(xiàn)在接收者對(duì)而已 線性 加工。 input symbols lssss ,..., 321 ,and their conjugates **3*2*1 ,..., lssss ,and it satisfies the following plex orthogonal condition MMLL LH ISGG ???? )||(21 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. STB code In this subsection, we consider a munication system prising 3 transmit antenna and 1 receive antenna that operates in a Rayleigh of analysis. The transmitter and receiver structures of the munication system with TC are shown in and , respectively. The data source bits are firstly encoded by the turbo encoder, then are mapped into corresponding constellation symbols。 Alamouti 建議一種用兩個(gè)天線的簡(jiǎn)易傳送多