Orthogonality division multiple access LTI transmit filters for ISI-channels

In this paper, the problem of multiple access over digital subscriber loops is introduced and defined as FIR LTI filter design over linear dispersive channels. The 2-D FIR CAP/QAM based modulation line code is extended to the multi-dimensional system to accommodate multiple access topology. The concept of orthogonality division multiple access, ODMA, is used as the methodology to achieve that goal. The problem of increasing the number of dimensions is stated as a minimax optimization problem, then solved using sequential quadratic programming. 3, 4, and 6-dimensional systems are introduced to support multiple access applications. Computer simulations are carried out to evaluate the performance and functionality of the orthogonal signaling line code.