Superimposed Pilot-Based OTFS: Will It Work?

TL;DR

This paper introduces a novel multiple superimposed pilot scheme and an iterative interference cancellation algorithm for OTFS, significantly improving channel estimation accuracy and throughput in doubly-selective fading scenarios.

Contribution

It proposes a new pilot assignment and iterative algorithm for OTFS that enhances channel estimation and throughput, addressing limitations of existing schemes.

Findings

Multiple SP-based scheme achieves highest throughput.

Proposed interference cancellation improves channel estimation.

Trade-off between throughput and computational complexity.

Abstract

Orthogonal time frequency space (OTFS) modulation is a promising solution to handle doubly-selective fading, but its channel estimation is a nontrivial task in terms of maximizing spectral efficiency. Conventional pilot assignment approaches face challenges: the standard embedded pilot-based scheme suffers from low transmission rates, and the single superimposed pilot (SP)-based scheme experiences inevitable data-pilot interference, leading to coarse channel estimation. To cope with this issue, focusing on the SP-based OTFS system in channel coded scenarios, we propose a novel pilot assignment scheme and an iterative algorithm. The proposed scheme allocates multiple SPs per frame to estimate channel coefficients accurately. Furthermore, the proposed algorithm performs refined interference cancellation, utilizing a replica of data symbols generated from soft-decision outputs provided by a decoder. Assuming fair and unified conditions, we evaluate each pilot assignment scheme in terms of reliability, channel estimation accuracy, effective throughput, and computational complexity. Our numerical simulations demonstrate that the multiple SP-based scheme, which balances the transmission rate and the interference cancellation performance, has the best throughput at the expense of slightly increased complexity. In addition, we confirm that the multiple SP-based scheme achieves further improved throughput due to the proposed interference cancellation algorithm.