【正文】 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 (unlike multiple streams in spatial multiplexing) is transmitted, but the signal is coded using techniques called spacetime coding. The signal is emitted from each of the transmit antennas with full or near orthogonal coding. Diversity coding exploits the independent fading in the multiple antenna links to enhance signal diversity. Because there is no channel knowledge, there is no beamforming or array gain fr。參考文獻(xiàn) [1] 王怡瑩, 王云生. MIMO無線技術(shù)的研究現(xiàn)狀[J]. 新技術(shù)與新業(yè)務(wù). 2006, 23(5): 5558. [2] 周平. 基于空時(shí)分組碼的MIMO的研究[D]. 南京: 南京師范大學(xué), 2007. [3] 敖珺. MIMO無線通信系統(tǒng)中的空時(shí)編碼方法研究[D]. 西安: 西安電子科技大學(xué), 2009. [4] 趙維娜. LTE系統(tǒng)的MIMO信道建模與仿真[D]. 西安: 西安電子科技大學(xué), 2013. [5] XuHao, Chizhik D, Huang H. A generalized spacetime multipleinput multipleoutput(MIMO)channel model[J]. IEEE Transactions on Wireless Communications. 2004, 3(3): 966975. [6] Liu F, Yang D, Chen Z. ClosedForm Performance Analysis of Variable Gain Relaying over NonIdentical Nakagamim FadingChannel[J]. International Conference on Information Technology and Computer Science. 2009, 4(24): 156168. 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