基于隨機(jī)旋轉(zhuǎn)的準(zhǔn)正交空時分組碼

1、1基于隨機(jī)旋轉(zhuǎn)的準(zhǔn)正交空時分組碼基于隨機(jī)旋轉(zhuǎn)的準(zhǔn)正交空時分組碼PCN&SS 鄧單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 犧牲碼字正交性，達(dá)到全速率，從而引入ISIn由于發(fā)射端滿足功率歸一化限制，所以a=1。n由于干擾分量b的影響，使得準(zhǔn)正交空時分組碼在高信噪比環(huán)境下性能劣于正交空時分組碼。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根據(jù)最大似然準(zhǔn)則解調(diào)出原始符號序列：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隨機(jī)旋轉(zhuǎn)前后星座圖分布比較圖 1.旋轉(zhuǎn)前星座圖位 置固定.2.旋轉(zhuǎn)后星座圖的位 置隨機(jī)分布13干擾功率b的概率密度分布 1.旋轉(zhuǎn)前b為點(diǎn)狀分布，且b=1 概率較大；2.旋轉(zhuǎn)后，由于星座圖的隨機(jī)分布使干擾的分布”白化”,并且在干擾較大的概率變小.14干擾功率b的概率累積分布 15Performance Comparison (TBH-code &J-code)16Performance Comparisonl對兩種碼字，隨機(jī)旋轉(zhuǎn)在高信噪比環(huán)境下均有一定的增益: BER=e-4,2dB增益BER=e-5

6、,4dB增益l相對ST-LCP(固定旋轉(zhuǎn)) 0.5-1dB 增益17矩陣數(shù)(P)對性能影響18矩陣數(shù)(P)對性能影響n當(dāng)P=256,16時，相對于理想隨機(jī)情況(P不受限)下的系統(tǒng)性能影響完全可以忽略n當(dāng)P=4時，在高信噪比下，系統(tǒng)約有1dB的性能損失 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