Sparse Delay-Doppler Channel Estimation in Rapidly Time-Varying Channels for Multiuser OTFS on the Uplink
O K. Rasheed, G. D. Surabhi, A. Chockalingam
Abstract
Orthogonal time frequency space (OTFS) modulation is a new modulation scheme that operates in the delay-Doppler (DD) domain. In this paper, we consider the problem of delay-Doppler channel estimation in OTFS multiple access (OTFS-MA) systems on the uplink. Recognizing the inherent sparse nature of the delay-Doppler (DD) representation of time-varying channels, we model the DD channel estimation problem as a sparse signal recovery problem. To solve this problem, we employ compressed sensing (CS) based estimation techniques. Specifically, we present orthogonal matching pursuit (OMP) and modified subspace pursuit (MSP) based algorithms for DD channel estimation in uplink OTFS-MA. We compare the performance of the proposed CS-based estimation schemes with that of the impulse based channel estimation scheme reported in the OTFS literature. The proposed CS-based algorithms are shown to achieve superior normalized mean squared error and bit error performance compared to those of the impulse based channel estimation scheme.