【正文】 （315）如果設(shè)公式（315）的左側(cè)可以寫(xiě)為特征多項(xiàng)式 ： （316）將該特征多項(xiàng)式展開(kāi)可以得到： （317）其中為的根，即矩陣H的奇異值。進(jìn)行仿真的編碼見(jiàn)附錄1[8] ，： 在=4，SNR=15dB下容量隨變化的仿真圖結(jié)果分析：由仿真結(jié)果可以很明顯地看出隨著發(fā)射天線的增加，MIMO通信系統(tǒng)的信道容量變化情況。首先我們可以清楚的看出無(wú)論SNR為多少，在發(fā)射天線數(shù)從1增加到5過(guò)程是信道容量增加最顯著的；然后我們可以發(fā)現(xiàn)當(dāng)接收天線數(shù)與發(fā)射天線數(shù)相同的情況下，SNR越大信道容量的值越大。四、相同信噪比、不同接收天線下的仿真為了研究接收天線數(shù)量對(duì)信道容量增加速度快慢以及信道容量增速飽和點(diǎn)的影響，我們將仿真條件設(shè)定為：信道為瑞利衰落信道模型，SNR是15dB,接收天線取值4與8，發(fā)射天線取值從1到30，每種天線配置都計(jì)算1000次求平均值；進(jìn)行仿真的編碼見(jiàn)附錄3，： SNR=15dB下，當(dāng)=4與8時(shí)，容量隨變化的仿真圖結(jié)果分析：紅色線與綠色線分別表示=8與4時(shí)信道容量隨變化的圖，通過(guò)仿真圖我們可以看出：相同時(shí)，發(fā)射天線數(shù)越多系統(tǒng)信道容量增加幅度越大；而且為4的系統(tǒng)的信道容量增加幅度在增加到5后就變緩，而為8的系統(tǒng)的信道容量增加幅度在增加到10后才開(kāi)始變緩。此外，由于本次研究是基于瑞利衰落信道模型，沒(méi)有考慮萊斯衰落信道下MIMO通信系統(tǒng)信道容量變換情況，所以有待后面進(jìn)一步完善。假設(shè)在雙發(fā)射天線情形下，天線1與天線2分別發(fā)出與信號(hào)，下一個(gè)碼元周期分別變?yōu)榕c。 空時(shí)分組編碼（STBC）示意圖第二節(jié) 正交空時(shí)分組編碼、譯碼與性能分析一、正交空時(shí)分組編碼如果我們用N的矩陣X表示空時(shí)分組碼矩陣，則若矩陣X中的元素是待傳輸?shù)男亲鶊D符號(hào)點(diǎn)的線性組合，我們就可以通過(guò)施加約束條件讓矩陣X的列是正交的，即 是對(duì)角矩陣。二、正交空時(shí)分組碼譯碼在經(jīng)過(guò)以上的闡述后，現(xiàn)在我們來(lái)介紹一下正交空時(shí)分組碼的譯碼。三、正交空時(shí)分組碼性能分析以下是對(duì)在瑞利衰落信道下的空時(shí)分組碼進(jìn)行的誤碼率計(jì)算。更進(jìn)一步，如果對(duì)于大信噪比來(lái)說(shuō)，對(duì)取平均可得[19] ： （411）第三節(jié) 4QAM與其他調(diào)制方式下的仿真與結(jié)果分析 首先使用Simulink仿真編寫(xiě)一個(gè)基于正交空時(shí)分組編碼的22的MIMO通信系統(tǒng)，如附錄圖1所示[10] 。將運(yùn)行時(shí)間設(shè)定為200，： 4PAM調(diào)制下運(yùn)行結(jié)束后的誤碼率 4PAM調(diào)制下誤碼率的動(dòng)態(tài)變化圖 4PAM調(diào)制下運(yùn)行結(jié)束后的接收信號(hào)的信號(hào)軌跡 4PAM調(diào)制下運(yùn)行結(jié)束后接收信號(hào)的眼圖 4PAM調(diào)制下接收信號(hào)的離散時(shí)間散點(diǎn)圖結(jié)果分析：首先來(lái)比較兩種調(diào)制方式下的誤碼率：，可以發(fā)現(xiàn)4QAM調(diào)制下通信系統(tǒng)具有更穩(wěn)定的誤碼率；，可以發(fā)現(xiàn)4QAM調(diào)制下的通信系統(tǒng)誤碼率比4PAM的一半還要少。最后我們來(lái)比較一下兩種調(diào)制下接收信號(hào)的眼圖：，可以很明顯地發(fā)現(xiàn)在4QAM調(diào)制下的通信系統(tǒng)眼睛睜得更大。通過(guò)仿真得出了結(jié)論：4QAM調(diào)制比4PAM調(diào)制更適用于MIMO通信系統(tǒng)。最后本文對(duì)基于正交空時(shí)分組編碼、譯碼以及性能進(jìn)行了理論分析并對(duì)正交空時(shí)分組編碼下的MIMO通信系統(tǒng)進(jìn)行了仿真。致 謝在我大學(xué)即將畢業(yè)之際，首先要感謝我的母?！貞c郵電大學(xué)，在這四年的學(xué)習(xí)生活中，我的母校不但為我提供了良好的學(xué)習(xí)的環(huán)境，創(chuàng)造了良好的學(xué)習(xí)氛圍，讓我能夠盡情翱翔在知識(shí)的殿堂，而且還激發(fā)了我對(duì)知識(shí)的渴望，為我以后的繼續(xù)學(xué)習(xí)研究打下了良好的基礎(chǔ)。在我完成畢業(yè)論文的過(guò)程中，她利用寶貴的時(shí)間和精力給予了我悉心的指導(dǎo)，為我解決設(shè)計(jì)中遇到的難題提供了很大的幫助，同時(shí)還幫我借閱了大量的資料供我閱讀，讓我在仿真時(shí)有許多的例題可以練習(xí)，極大地提高了我對(duì)對(duì)仿真工具的熟練程度?？傊?，如果只有我一個(gè)人不可能完成我的畢業(yè)設(shè)計(jì)，它是許多人共同的智慧結(jié)晶。rn Ottersten, researchers at ArrayComm, in 1991. Their US patent (No. 5515378 issued in 1996[3]) emphasizes an array of receiving antennas at the base station and plurality of remote users.Arogyaswami Paulraj and Thomas Kailath proposed the concept of spatial multiplexing (SM) using MIMO in 1993. Their US patent (No. 5,345,599 issued in 1994[4]) emphasized wireless broadcast munications applications and splitting a highrate signal into several lowrate signals.In 1996, Greg Raleigh, Gerard J. Foschini, and Emre Telatar refined new approaches to MIMO technology, considering a configuration where multiple transmit antennas are colocated at one transmitter to improve the link throughput effectively.[5][6][7]Bell Labs was the first to demonstrate a laboratory prototype of spatial multiplexing in 1998, where spatial multiplexing is a principal technology to improve the performance of MIMO munication systems.[8]Wireless standardsIn the mercial area, Iospan Wireless Inc. developed the first mercial system in 2001 that used MIMO with orthogonal frequencydivision multiple access technology (MIMOOFDMA). Iospan technology supported both diversity coding and spatial multiplexing. In 2005, Airgo Networks had developed an IEEE precursor implementation based on their patents on MIMO. Following that in 2006, several panies (including at least Broad, Intel, and Marvell) fielded a MIMOOFDM solution based on a prestandard for WiFi standard. Also in 2006, several panies (Beceem Communications, Samsung, Run Technologies, etc.) had developed MIMOOFDMA based solutions for IEEE WiMAX broadband mobile standard. All uping 4G systems will also employ MIMO technology. Several research groups have demonstrated over 1?Gbit/s prototypes.Functions of MIMOMIMO can be subdivided into three main categories, precoding, spatial multiplexing or SM, and diversity coding.Precoding is multistream beamforming, in the narrowest definition. In more general terms, it is considered to be all spatial processing that occurs at the transmitter. In (singlestream) beamforming, the same signal is emitted from each of the transmit antennas with appropriate phase and gain weighting such that the signal power is maximized at the receiver input. The benefits of beamforming are to increase the received signal gain, by making signals emitted from different antennas add up constructively, and to reduce the multipath fading effect. In lineofsight propagation, beamforming results in a well defined directional pattern. However, conventional beams are not a good analogy in cellular networks, which are mainly characterized by multipath propagation. When the receiver has multiple antennas, the transmit beamforming cannot simultaneously maximize the signal level at all of the receive antennas, and precoding with multiple streams is often beneficial. Note that precoding requires knowledge of channel state information (CSI) at the transmitter and the receiver.Spatial multiplexing requires MIMO antenna configuration. In spatial multiplexing, a high rate signal is split into multiple lower rate streams and each stream is transmitted from a different transmit antenna in the same frequency channel. If these signals arrive at the receiver antenna array with sufficiently different spatial signatures and the receiver has accurate CSI, it can separate these streams into (almost) parallel channels. Spatial multiplexing is a very powerful technique for increasing channel capacity at higher signaltonoise ratios (SNR). The maximum number of spatial streams is limited by the lesser of the number of antennas at the transmitter or receiver. Spatial multiplexing can be used without CSI at the transmitter, but can be bined with precoding if CSI is available. Spatial multiplexing can also be used for simultaneous transmission to multiple receivers, known as spacedivision multiple access or multiuser MIMO, in which case CSI is required at the transmitter.[9] The scheduling of receivers with different spatial signatures allows good separability.Diversity Coding techniques are used when there is no channel knowledge at the transmitter. In diversity methods, a single stream (unli