Some limits on time orthogonal multiple access codes

In this paper, the design of time orthogonal multiple access line coding (TOC) is presented. It utilizes multi time slots for transmission, with aggregate transmitted bits per time slot (baud) is greater than 1. It is different from QAM in three aspects: TOC allows multiple users, employs simple addition of the same signal type in each time slot, and it utilizes time orthogonal rather than phase orthogonal signals used in QAM, and hence have less stringent synchronization requirements. We investigate the limits on the performance of TOC, where it was found to be 22 users and 4.4 bits / time slot using 5 time slots with 2 symbols /user and 22 users.