Near-orthogonal coding for spread spectrum and error correction

摘要

Since the spreading operation and error correction must share thebandwidth available in a CDMA system, it is appropriate to approachthese problems jointly. Several papers have addressed this problem withpromising results. Hui (1984) has shown that under certain assumptions,the system performs better when more bandwidth is devoted to errorcorrection. Giallorenzi (see PhD thesis, Univ. of Virginia,Charlottesville, VA, 1994) shows that combining error correctiondecoding and multiuser detection significantly improves systemperformance. We extend this research by considering not onlysimultaneous despreading and decoding, but also the simultaneousencoding and spreading. We consider a coded asynchronous CDMA systemover an AWGN channel with constant information rate, R_I. Eachuser's transmission rate isR_tx=R_I·Q·N where 1/Q is theconvolutional code rate and N is the spreading factor. The receivermatches to each signature sequence and performs maximum likelihoodsequence detection