MIMO Systems: Multiple Antenna Techniques

Transcription

1 ADVANCED MIMO SYSTEMS MIMO Sytem: Multiple Antenna Technique Yiqing ZOU, Zhengang PAN, Kai-Kit WONG Dr, Senior Member of IEEE, Aociate Editor, IEEE TWirele, IEEE CL, and JoC (AP), Senior Lecturer, Department of EEE, Univerity College London, London, WCE 7JE, United Kingdom Tel: +44-(0) , Fax: +44-(0)

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3 .. Abtract Thi chapter review mot known multiple antenna technique for ingle-uer point-to-point ytem, from how multiple antenna help provide diverity and multiplexing to the detection technique for thee ytem. Finally, thi chapter alo dicue the poibility of uing multiple antenna for multiuer ytem for patial multiplexing... Literature Review The concept of multiple antenna can be traced back long time ago. In 960, antenna array wa applied in military radar ytem for ignal copying, direction finding and ignal eparation [,]. Thee ignal parameter etimation need high reolution. Many algorithm have been propoed in thi field, uch a the maximum likelihood (ML) baed approach [3] and maximum entropy (ME) baed approach [4]. The main limitation of thee approache are the bia and high enitivity. Thee problem were olved by Schimidt [5,6] and Bienvenu [7] independently. Particularly, Schimidt method i known a MUSIC (Multiple Signal Claification), which can provide ubtantial performance improvement at the cot of high computational complexity and torage conumption. Then, another cheme, ESPRIT (Etimation of Signal Parameter via Rotational Invariance Technique), i propoed to achieve performance cloe to that of MUSIC but with a ignificantly reduced complexity [8]. In wirele communication ytem, due to the limited phyical ize of mobile device, the application of multiple antenna i initially propoed for bae tation (BS) only. Invetigation on thee multiple antenna ytem focu on beamforming, etimation of direction of arrival (DOA), and patial diverity. The aforementioned algorithm like MUSIC and ESPRIT can be employed to realize the beamforming and the etimation of DOA, where the received/tranmitted ignal from/for different antenna are coherently combined to point at a pecific direction. In thi way, the co-channel interference from other mobile tation (MS) can be reduced in the uplink and the tranmiion power can be focued to the deired MS in the downlink. For example, in [9,0,] and ome reference therein, multiple antenna are deployed at BS to obtain receive diverity and/or co-channel interference rejection in the uplink baed on the DOA. It i demontrated that ignificant capacity improvement can be achieved. Then, in [0,], the antenna at the BS are ued a a tranmit beamformer in downlink. By focuing the tranmit energy in the direction of the deired MS, tranmit beamforming increae the ignal-to-noie ratio (SNR) at the MS. Similar to the ingle-input ingle-output (SISO) ytem with only one antenna at both ide, the aforementioned receive diverity and tranmit diverity achieving ytem are called ingle-input multiple-output (SIMO) and multiple-input ingle-output (MISO) ytem, repectively. Nowaday, multiple-input multiple-output (MIMO) ytem have become one of the hottet reearch topic due to the magnificent enhancement brought by multiple antenna technique. The poibility to deploy multiple antenna at both ide of the communication link lay on the following fact: ) the development in hardware miniaturization and advance in antenna deign make the deployment of multiple antenna at the mall MS more feaible; ) wirele application like wirele local area network (WLAN) and fixed wirele acce (FWA) allow large phyical ized device that can afford multiple antenna, uch a laptop computer. The reearch on MIMO ytem tart from early 990. Telatar [3] found that uing MIMO ytem, there could be a dramatic improvement in the ytem throughput while no extra pectrum i needed. In 996, Fochini publihed the famou paper [4], where he propoed a Bell Lab Layered Space-Time (BLAST) architecture for MIMO ytem and it wa hown that high pectral efficiencie uch a 0 to 0 bit//z can be achieved. Then, an elegant pace time block coding (STBC) architecture wa propoed by Alamouti [5], which i imple yet effective in obtaining patial diverity. Alamouti code ha led to a reearch fervor on STBC. In ummary, MIMO can be employed to achieve both tranmit and receive diverity, or make the ytem throughput increae linearly with the minimum number of the tranmit and receive antenna..3. Space-Time Coding Tranmitter diverity wa firtly propoed in [6,7] for BS imulcating, where copie of the ame ymbol are tranmitted through multiple antenna at different time, creating an artificial multipath ditortion at the receiver. 3

4 A ML equence detection or a minimum mean quare error (MMSE) equalizer can be employed to reolve the multipath interference and obtain diverity gain. Thi delay coding cheme can be taken a a repetition channel coding in patial domain. The idea of channel coding in pace and time domain wa generalized by Tarokh et al. in [8] and the o-called pace-time coding (STC) wa introduced. There are everal kind of STC with different tructure..3.. Space-Time Block Coding Alamouti dicovered an elegant STBC cheme for MIMO ytem with two tranmit antenna. A hown in Figure., the input ymbol to the STBC encoder are divided into group of two ymbol. In the firt ymbol duration, two ymbol, and, are tranmitted imultaneouly from antenna # and #, repectively. Then, in the next ymbol duration, the ignal and are tranmitted from antenna # and #, repectively. Auming that h, and h, are the fading coefficient correponding to the firt and econd tranmit antenna to the receive antenna, repectively, and are contant over two conecutive ymbol time, the ignal received over two conecutive ymbol period are and y h, h n h h n,,,, y h, h h h n,,,, (.). (.) They can be rearranged into a matrix form a follow y h, h, n y y h, h, n eff (.3) where eff i the effective channel matrix. Since eff i orthogonal, by a imple linear operation by MISO ytem can be plit into two eparate parallel SISO ytem a follow eff y, the h,n h, n z eff y h, h, (.4) h,n h, n Figure.. Alamouti code 4

5 Figure.. A 4-tate pace time trelli code Thi orthogonal property can be extended to the cae where the receiver ha multiple antenna. It can be een that the Alamouti cheme decouple the vector ML decoding problem into calar problem. Therefore, the cheme can realize full diverity while reduce the receiver complexity dramatically. It will be hown later that the Alamouti code provide a performance gain imilar to that obtained by uing one tranmit antenna and two receive antenna with maximum ratio combiner (MRC) except for a power reduction of (3 db). The Alamouti cheme can be generalized to an arbitrary number of antenna [9] and i able to achieve the full diverity promied by the number of tranmit and receive antenna. Note that in the previou example with two tranmit antenna, two different data ymbol are tranmitted in two ymbol duration. Thu the coding rate i ymbol duration, or the full rate. owever, for arbitrary number of antenna, full rate i not alway achievable. Letting the i th row contain the data ymbol tranmitted at the i th antenna in different ymbol duration, two STBC with coding rate 3/4 and / are given by (.5) and (.6) repectively..3.. Space-Time Trelli Code (STTC) 5