OFDM水声通信中非一致多普勒补偿技术研究

With ocean development increasingly thorough, requirements of validity and reliability for underwater mobile communication are also getting higher and higher. Due to the severe underwater acoustic channel bandwidth limitation, the OFDM technology with its high bandwidth utilization characteristics, which has been successfully applied in the field of wireless communications, becomes a popular research topic in the field of underwater acoustic communication. The performance of the underwater acoustic communication is largely dependent on the underwater acoustic channel propagation conditions because the underwater channel is time-varying, space-varying, multipath fading channel whose bandwidth is severely limited. Also, in underwater acoustic OFDM system the Doppler frequency shift relative to the subcarrier spacing is a thousand times higher than that in the wireless communication field. Thus, so far there aren't any effective methods to handle the problem of compensating non uniform Doppler of the OFDM underwater acoustic communication. In this research, we propose a kind of broadband Doppler compensation method based on adaptive iteration to solve the non-uniform Doppler preliminary compensation in the underwater acoustic OFDM system. This method can inhibit interference among adjacent carriers in the iterative process, and finally achieve the purpose of the preliminary compensation.To deal with the residual Doppler frequency shift, a broadband Doppler compensation method based on compressed sensing is proposed. The method can estimate the amplitude, time delay and Doppler frequency shift of each path, which is superior to the channel estimation approach based on the training sequences. At last, carry out experiments in lakes and seas to validate and improve the performance of the algorithm.

随着海洋开发的不断深入，对水下移动通信的有效性和可靠性的要求也越来越高。由于水声信道的严重带宽限制，在无线通信领域已成功应用的OFDM技术以其带宽利用率高的特点成为水声通信领域内的热门研究课题。但是水声信道时变、空变和通信双方相对运动产生的多普勒会破坏OFDM正交性从而影响系统性能。同时由于水声OFDM中多普勒频偏相对于子载波间隔要比无线通信中大上千倍，因而目前还有行之有效的方法来补偿OFDM水声通信中的非一致多普勒问题。本课题研究并提出基于自适应迭代的宽带多普勒补偿方法，解决水声OFDM中的非一致多普勒初步补偿问题，该方法在迭代过程中抑制自身与相邻载波的干扰，达到初步补偿的目的。提出基于压缩感知的宽带多普勒补偿方法，解决残余多普勒的补偿问题，该方法能够对信道每条路径的幅度、时延和多普勒进行估计，性能优于利用训练序列估计信道的方法。开展湖上试验和海上试验，验证并改进算法性能。

本课题主要研究水声OFDM中非一致多普勒的估计、补偿算法，具体包括时变信道建模、多普勒初步补偿和精细补偿算法。.A. 基于宽带非一致多普勒的时变水声信道建模与实测数据分析。重点考虑水声信道小尺度变化的建模，首先根据给定的声速梯度、发射接收机机位置信息和水深等环境信息建立确定性信道，然后建模由于散射等引起的小尺度变化，最后考虑由于风浪等原因引起的多普勒频偏。最后通过外场实验数据对信道建模方法进行了验证。.B. 水声OFDM非一致多普勒自适应跟踪估计、补偿方法研究。在每条路径多普勒因子近似相等的假设前提下，提出一种非一致多普勒频偏自适应跟踪估计、补偿方案，可实现多普勒频偏的初步补偿。首先在帧头发送添加循环前缀的两个重复短OFDM符号实现多普勒因子的盲初始估计，作为下一步多普勒频偏跟踪的初值；然后基于相关二维搜索算法，利用每个OFDM数据符号的循环前缀实现时间细同步和多普勒因子跟踪估计；最后通过湖上、海上移动通信实验验证。.C. 基于压缩感知的水声OFDM非一致多普勒精细补偿方法研究。在完成上述多普勒频偏初步补偿后，为了消除各个路径残留多普勒带来的子载波间干扰，研究了基于压缩感知的水声OFDM非一致多普勒精细补偿方法，可同时估计每条路径的复增益、时延和多普勒因子。此外，提出了一种迭代接收判决反馈接收机结构，利用信道编码软判决提供的信息和高精度的基于压缩感知的匹配追踪信道估计算法，通过迭代的方式为接收机提供更多有用信息，从而进一步消除信道多途和多普勒带来的信道干扰。以上研究内容均通过了外场实验验证。.本课题的研究成果可明显提高水声OFDM系统在运动状态下的通信性能，基于OFDM高速通信制式实现水下设备间无线视频、无线点对点大数据量数据传输，符合军用和民用信息化的需求。