We consider the problem of carrier frequency offset estimation in OFDM underwater acoustic communication. In our previous work, we suggested transmitting equi-power and equi-spaced pilot tones which led to a simple carrier frequency offset estimator. Here, we extend this work in two directions: First, equi-power pilots may result in a large peak to average power at the transmitter. Thus, we propose a method to design the phases of the pilot tones so as to keep the peak to average power low, while still obtaining large enough pilot to data ratio needed to decode the pilot symbols. The design method is based on ideas adopted from phase retrieval techniques. Second, we modify the previous carrier frequency offset estimators to the case of a time-varying underwater acoustic channel. These modifications are based on modeling the carrier offset by polynomial and piece-wise models. The estimators use the correlations and intervals between the pulses, and approximate the frequency offsets by small order polynomials. Simulations results show that for constant offsets, the proposed estimators achieve similar performances as state-of-the-art techniques, while for time-varying offsets the proposed estimators are superior.

我们考虑了OFDM水声通信中的载波频偏估计问题。在我们之前的工作中，我们建议传输等功率和等间隔的导频音，这导致了一个简单的载波频率偏移估计器。在这里，我们将这项工作扩展到两个方向：首先，等功率导频可能会导致发射机的峰值平均功率较大。因此，我们提出了一种设计导频音相位的方法，以保持峰值平均功率较低，同时仍然获得解码导频符号所需的足够大的导频数据比。该设计方法基于从相位检索技术中采用的思想。其次，我们将之前的载波频率偏移估计器修改为时变水下声学信道的情况。这些修改基于通过多项式和分段模型对载波偏移进行建模。估计器使用脉冲之间的相关性和间隔，并通过小阶多项式来近似频率偏移。模拟结果表明，对于恒定偏移量，所提出的估计器实现了与最先进技术相似的性能，而对于时变偏移量，所提出的估计器则更为优越。