Oversampled Low Ambiguity Zone Sequences for Channel Estimation over Doubly Selective Channels

TL;DR

This paper introduces a novel class of pilot sequences called O-LAZ sequences, optimized for channel estimation in doubly selective channels by minimizing ambiguity, and demonstrates their superior performance through numerical experiments.

Contribution

It proposes a new metric, O-AF, and a sequence design method for improved channel estimation in DSC systems, which is a novel approach in this context.

Findings

O-LAZ sequences outperform traditional sequences in channel estimation accuracy.

Optimized sidelobes of O-AF improve sequence robustness against Doppler shifts.

Numerical results confirm the effectiveness of the proposed sequences over existing methods.

Abstract

Pilot sequence design over doubly selective channels (DSC) is challenging due to the variations in both the time- and frequency-domains. Against this background, the contribution of this paper is twofold: Firstly, we investigate the optimal sequence design criteria for efficient channel estimation in orthogonal frequency division multiplexing systems under DSC. Secondly, to design pilot sequences that can satisfy the derived criteria, we propose a new metric called oversampled ambiguity function (O-AF), which considers both fractional and integer Doppler frequency shifts. Optimizing the sidelobes of O-AF through a modified iterative twisted approximation (ITROX) algorithm, we develop a new class of pilot sequences called ``oversampled low ambiguity zone (O-LAZ) sequences". Through numerical experiments, we evaluate the efficiency of the proposed O-LAZ sequences over the traditional low ambiguity zone (LAZ) sequences, Zadoff-Chu (ZC) sequences and m-sequences, by comparing their channel estimation performances over DSC.