Multiple access system capacity with M-ary orthogonal modulation

This paper proposes a multiple access scheme suitable for general M-ary orthogonal modulation, where users are distinguished by different coding patterns. The mathematical models for both synchronous and asynchronous users are presented, and the system capacities are studied. Simulation results show that the proposed system outperforms CDMA systems by as much as 25% in capacity for asynchronous users. In addition, a synchronous system has higher capacity when user number is larger, but will suffer from great capacity loss otherwise.