基于随机旋转的准正交空时分组码

1、1基于随机旋转的准正交空时分组码基于随机旋转的准正交空时分组码PCN&SS 邓单1/28/20052I. Background1.Alamouti code (1998)2.SpaceTime Block Codes from Orthogonal Designs3.Quasi-Orthogonal SpaceTime Block Code31.Alamouti codea.Full rateb.Full diversity gainsc.Simple ML decode algorithm121, 2*21()sss sssC42.Orthogonal-STBCn rate for

2、arbitrary transmit antennas.nFor full rate, only N=2 exists complex orthogonal STBCa.Simple decode algorithm based on linear processingb.Full diversity O-STBC:53.QO-STBCnGroup orthogonal (s1,s4)(s2,s3)nFast group ML decodernChoice: low SNR QO is better; high SNR Orthogonal-STBC is good.1234*21341234

3、3412*3421( , , , )TBHssssssssA Bs s s sssBAssssssS1234*21341234*34123421( , , , )JssssssssABs s s sBAssssssssS6Performance in 4x1 systemQPSK for QO-STBCRate 16QAM forO-STBC73.QO-STBCnQO-STBC 牺牲码字正交性，达到全速率，从而引入ISIn由于发射端满足功率归一化限制，所以a=1。n由于干扰分量b的影响，使得准正交空时分组码在高信噪比环境下性能劣于正交空时分组码。00000000HTBHTBHTBHababba

4、baRSS421|iias*1 3242Rebs ss s894.Random-Rotation QO-STBCT: Random Unitary matrix C(N,N) different and independent from each other lxTs()TQOrSxHN104.RR-QO-STBCn根据最大似然准则解调出原始符号序列：argmin() TQOlssrSTsH114.RR-QO-STBCRandom-matrix generator:1.Gauss i.i.d random matrix2.QR decompose3.4.Precomputed and stor

5、ed in a lookup table in practice.N NCYYUlT12随机旋转前后星座图分布比较图 1.旋转前星座图位 置固定.2.旋转后星座图的位 置随机分布13干扰功率b的概率密度分布 1.旋转前b为点状分布，且b=1 概率较大；2.旋转后，由于星座图的随机分布使干扰的分布”白化”,并且在干扰较大的概率变小.14干扰功率b的概率累积分布 15Performance Comparison (TBH-code &J-code)16Performance Comparisonl对两种码字，随机旋转在高信噪比环境下均有一定的增益: BER=e-4,2dB增益BER=e-5

6、,4dB增益l相对ST-LCP(固定旋转) 0.5-1dB 增益17矩阵数(P)对性能影响18矩阵数(P)对性能影响n当P=256,16时，相对于理想随机情况(P不受限)下的系统性能影响完全可以忽略n当P=4时，在高信噪比下，系统约有1dB的性能损失 19Future WorknPerformance in correlation channelnPerformance in imperfect CSIn theoretical analyses20ReferencesnYan Xin, Zhengdao Wang, Georgios B. Giannakis, “Space-time diversity systems based on linear constellation precoding”, IEEE Transaction on Wireless Communications, vol.2, Mar, 2003.nErik G. Larsson, “Improving the Frame-Error-Rate of Spatial Multiplexing in Block Fading by Ran