Time-Frequency Orthogonal Multiple Access Using Cyclic-Prefix OTFS Modulation

Cyclic-prefix orthogonal time frequency space (CP-OTFS) modulation is an effective multicarrier modulation technique that can provide better error performance than traditional cyclic-prefix orthogonal frequency-division multiplexing modulation for signal transmission over linear time-varying multipath (LTV) channels exhibiting sparse delay and Doppler spread characteristics. To enable multi-user communication over the same spectrum resource, it is also crucial to investigate the performance characteristics of multiple-access (MA) systems based on CP-OTFS signal transmission over LTV channels. In this paper, two CP-OTFS MA systems based on localized and interleaved time-frequency orthogonal MA strategies are developed for downlink cellular communication to operate without causing multi-user interference at the receiver end. Both CP-OTFS MA systems are studied and compared in terms of uncoded and coded bit error rate characteristics over random LTV channels.