Existing Orthogonal Frequency-Division Multiplexing (OFDM) variants based on cyclic prefix (CP) allow for efficient time synchronization, but suffer from lower power efficiency compared to zero-padded (ZP)-OFDM. Because of its power efficiency, ZP-OFDM is considered as an appealing solution for the emerging low-power wireless systems. However, in the absence of CP, time synchronization in ZP-OFDM is a very challenging task. In this paper, the non-data-aided (NDA) maximum-likelihood (ML) time synchronization for ZP-OFDM is analytically derived. We show that the optimal NDA-ML synchronization algorithm offers a high lock-in probability and can be efficiently implemented using Monte Carlo sampling (MCS) technique in combination with golden-section search. To obtain the optimal NDA-ML time synchronization algorithm, we first derive a closed-form expression for the joint probability density function (PDF) of the received ZP-OFDM samples in frequency-selective fading channels. The derived expression is valid for doubly-selective fading channels with mobile users as well. The performance of the proposed synchronization algorithm is evaluated under various practical settings through simulation experiments. It is shown that the proposed optimal NDA-ML synchronization algorithm and its MCS implementation substantially outperforms existing algorithms in terms of lock-in probability.

翻译：以环形前缀(CP)为基础的现有奥氏频率-多功能变体(OFDM)变体(OFDM)允许高效的时间同步,但与零加(ZP)-OFDM(OFDM)相比,动力效率较低。ZP-OFDM(OFDM)被认为是新兴低功率无线系统的一个诱人的解决办法。然而,在没有CP的情况下,ZP-OFDM(OFDM)的时间同步是一个非常具有挑战性的任务。在本文件中,ZP-OFDM(NDA)的无数据辅助(NDA)最大类似时间同步(ML)是分析性的。我们表明,最佳NDA-ML同步算算算法(ZP-OFDM)比对ZP-OFDM(M)最大类似时间同步(MML)的同步(MMLM(MDM)比对时间同步(MML)比(MDA)比对当前最佳定式的模拟操作率和MLML(ML)的模拟运行模式进行模拟的模拟的模拟分析。