On the optimum spreading sequence and mismatched filter design for cellular CTDMA

The optimum design of spreading sequences and their mismatched despreading filters is investigated for cellular code time division multiple access (CTDMA) systems. The users in the same cell are separated by the classical CTDMA scheme (which assigns one single spreading sequence to all users of the same cell), while the users in adjacent cells are separated by the use of different cell-specific spreading sequences. The construction of these sequence sets is the main topic of this paper. Requirements on these sets can be derived from intra-and intercell interference parameters that determine the signal-to-interference ratio. It is shown that EACF sequence sets, i.e., sequence sets that yield equal aperiodic autocorrelation functions, provide an optimum intra- and intercell performance in a least square sense, They are compared with the code frequency division multiple access (CFDMA) cell separation technique, which offers more sequences on the price of a diminished intercell performance. Since the overall performance depends on the ratio of the intra-and intercell interference, we describe the optimization of the intercell interference behavior for general sequence sets