The discussion on using zero padding (ZP) instead of a cyclic prefix (CP) for enhancing channel estimation and equalization performance is a recurring topic in waveform design for future wireless systems that high spectral efficiency and location awareness are the key factors. This is particularly true for orthogonal signals, such as orthogonal frequency-division multiplexing (OFDM). ZP-OFDM is appealing for joint communications and sensing (JCS) in 6G networks because it takes the advantage of both OFDM and pulse radar. In term of communication, ZP-OFDM compared to CP-OFDM, has higher power efficiency and lower bit error rate (BER). However, time synchronization is challenging in ZP-OFDM systems due to the lack of CP. In terms of sensing, ZP facilitates ranging methods, such as time-sum-of-arrival (TSOA). In this paper, we propose a moment-based timing offset (TO) estimator for multiple-input multiple-output (MIMO) ZP-OFDM system without the need for pilots. We then introduce the which significantly improves the estimation accuracy of the previous estimator. We show that the proposed method asymptotically reaches the maximum likelihood (ML) estimator. Simulation results show very high probability of lock-in for the proposed estimators under various practical scenarios.

翻译：关于在波形设计中用零填充代替循环前缀以增强信道估计和均衡性能的讨论，是面向未来无线系统（高频谱效率和位置感知是关键因素）的持续议题。这对于正交信号尤为显著，例如正交频分复用。零填充正交频分复用因兼具OFDM和脉冲雷达的优势，在第六代网络的联合通信与感知中具有吸引力。在通信方面，与CP-OFDM相比，ZP-OFDM具有更高的功率效率和更低的误码率。然而，由于缺乏CP，ZP-OFDM系统中的时间同步具有挑战性。在感知方面，ZP有利于测距方法，例如到达时间之和。本文针对多输入多输出ZP-OFDM系统，提出一种无需导频的基于矩的定时偏差估计器。随后引入了一种显著提升前一种估计器精度的改进方法。我们证明所提方法渐近达到最大似然估计器性能。仿真结果表明，在多种实际场景下，所提估计器具有极高的锁定概率。