Interleaved Time-Frequency Multiple Access Using OTFS Modulation

In this paper, we consider a multiuser uplink scenario using orthogonal time frequency space (OTFS) modulation and propose a scheme for multiplexing users on an $N \times M$ time-frequency grid in which allocated time-frequency resource blocks for different users are non-contiguous and interleaved. The proposed scheme, termed as {\em interleaved time-frequency multiple access} (ITFMA), allows multiuser interference-free signal reception in the time-frequency domain thereby reduces the detection complexity. The proposed scheme is shown to achieve improved bit error performance compared to another recently proposed OTFS based multiple access scheme. We also consider the peak-to-average power ratio (PAPR) of the proposed scheme and analytically characterize its complementary cumulative distribution function for large values of $N/q$, where $q$ denotes the interleaving period in time. The use of DFT precoding is shown to improve the PAPR of the proposed scheme.