Two-Dimensional Power Allocation for OTFS-Based High-Mobility Cognitive Radio Networks

This paper addresses the problem of delay-Doppler (DD) domain power allocation for orthogonal time frequency space (OTFS)-based cognitive radio (CR) systems with the high-mobility secondary user (SU) reusing the spectrum of the low-mobility primary user (PU). A fundamental challenge for such an OTFS-CR network is to maximize the SU's achievable rate while ensuring the quality of service (QoS) of the PU. For this goal, we first derive the explicit expressions of the signal-to-interference-plus-noise ratio (SINR) of the SU of the DD domain. Two cases of the interference introduced by the PU received at the SU are considered: the cases without and with successive interference cancellation (SIC). For the first case, we have proven that the maximal SU's achievable rate can be obtained through equal power allocation. For the second case, the optimization problem is more intractable. Utilizing the Karush-Kuhn-Tucker (KKT) conditions of the optimization problem, an asymptotic-optimal DD domain power allocation scheme has been proposed. Numerical simulations show the priority of the proposed algorithms, where the performance gain is significant compared with other classical allocation algorithms.