Sphere‐decoding based equalization for reduced‐zero‐padding orthogonal time frequency space modulation

Abstract This work studies the equalization methods for the reduced zero‐padding version of the orthogonal time frequency space modulation. Here, the focus is on applications in low data rate scenarios such as the Internet of Things, and the case where the number of subcarriers and time slots are small will be considered. First, the system equation is established to model the inter‐subcarrier and inter‐slot interference phenomena. Based on the system model, three sphere‐decoding based equalization methods are proposed. The first method is to directly apply the sphere‐decoding algorithm on the full‐scale system model; for the second method, the transmitter needs to perform the triangular precoding; and for the third method, the transmitter needs to perform the diagonal precoding. Simulation results show that the proposed sphere‐decoding based methods achieve better bit error rate performance than the state‐of‐the‐art methods like message passing, unitary approximate message passing, and variational approximate message passing, especially when the channel has severe inter‐slot interference.