A Novel One-tap Equalizer for Zero-Padded AFDM System over Doubly Selective Channels

TL;DR

This paper introduces a low-complexity one-tap equalizer for zero-padded AFDM systems over doubly selective channels, utilizing parameter selection, zero padding, and a new domain transformation to enhance efficiency and robustness.

Contribution

It proposes a novel one-tap equalizer for ZP-AFDM systems that simplifies affine domain IOR and improves performance over doubly selective channels.

Findings

Effective equalization with high $c_1$ values

Simplified affine domain IOR via zero padding

Robust performance demonstrated numerically

Abstract

Recently, affine frequency division multiplexing (AFDM) has gained traction as a robust solution for doubly selective channels. In this paper, we present a novel low-complexity one-tap equalizer for zero-padded AFDM (ZP-AFDM) systems. We first select the AFDM parameters, $c_1$ and $c_2$, such that $c_1$ has a relatively high value, and $c_2$ depends on $c_1$, which simplifies the affine domain input-output relation (IOR). This selection also demonstrates that a phase term that varies slowly along the affine domain is experienced by all affine domain symbols and this variation is significantly slower compared to that experienced by the time domain symbols over doubly selective channels. To simplify the equalization, we then introduce zero padding to the transmitted affine domain symbols and reconstruction operation on the received affine domain symbols. By doing so, we convert the effective affine domain IOR of our ZP-AFDM system to be characterized using approximately circular convolution. Next, we transform the resulting affine domain symbols into a new domain called the frequency-of-affine (FoA) domain. We propose our one-tap equalizer in this FoA domain to efficiently recover the transmitted symbols. Numerical results demonstrate the effectiveness of our proposed one-tap equalizer, particularly when $c_1$ is high, without compromising performance robustness.