CONVOLUTIONAL CODED DS/CDMA WITH TWO SETS OF ORTHOGONAL SPREADING SEQUENCES AND ITERATIVE DETECTION

摘要

In this letter a convolutional coded Direct-Sequence Code-Division Multiple Access(DS/CDMA) concept is introduced. The number of the users it can accommodate is greater than the spreading factor N. Each of the available orthogonal spreading sequences of length N is assigned to one of the first N users which employ a common Pseudo-Noise (PN) scrambling sequence. When the number of users K exceeds N, say K = N + M with M ＜ N, the M additional users reuse M of those orthogonal spreading sequences but in combination with another PN scrambling sequence. An iterative multistage detection technique aided by Viterbi decoding is used to cancel the interference between the two sets of users when K ＞ N. The proposed technique thus accommodates N users without any mutual interference and a number of additional users almost without signal-to-noise ratio penalty.