基于OFDM的水声通信技术研究

发布时间：2019-01-11 15:12

【摘要】：相比于陆地上的无线电通信,水声通信的通信速率还很低,由于声波在水中传播速率较低,水声信道多径效应严重,高速水声通信面临严重的码间干扰。以正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)为代表的多载波调制技术通过将数据调制到多路载波上并行发送,降低了码元速率,能有效对抗多径干扰。现有的水声OFDM调制系统,对于IFFT得到的两路数据,大多数通过I-Q正交调制将两路数据都发送传输,其系统的成本和复杂度都较高;少数采取频域补零取实部发送的方法进行传输,但这会占用额外的子载波频率,同时造成了发射功率的浪费。对此,本文对比研究现有的水声OFDM调制方案,提出了通过频域补零、补共轭再经IFFT处理后取实部发送的调制传输方案。同时,依据实际情况拟定了水声OFDM通信系统的参数,并完成了发射机的FPGA设计实现及片上验证。为了在接收端精准定位OFDM符号的起始位置,研究了水声OFDM通信过程中的同步技术,提出了通过混沌角调制序列相关检测,来完成帧同步的方法,并设计生成了混沌角调制同步序列。为了能正确接收、恢复出发送数据,研究了水声OFDM通信的信道估计与补偿技术,选择了适合本文的块状导频估计方案,并对LS、MMSE、LMMSE三种信道估计算法的估计效果进行仿真,最终选定用LMMSE来估计本文的信道频率响应函数,完成补偿处理。最后,搭建了完整的水声OFDM通信试验系统,进行了通信实验,实验结果表明,依据本文拟定调制传输方法及参数,实现了水声OFDM通信,传输距离为1.3m,频谱效率为0.74bps/Hz,误码率为0.074,验证了所提出的调制传输方案的有效性。
[Abstract]:Compared with the radio communication on land, the communication rate of underwater acoustic communication is still very low. Due to the low rate of acoustic wave propagation in the water, the multipath effect of underwater acoustic channel is serious, and the high-speed underwater acoustic communication faces serious inter-symbol interference. The multicarrier modulation technology, represented by orthogonal Frequency Division Multiplexing (Orthogonal Frequency Division Multiplexing,OFDM), reduces the symbol rate by modulating the data to the multi-channel carrier and can effectively resist the multipath interference. In the existing underwater acoustic OFDM modulation system, most of the two channels of data obtained by IFFT are transmitted through I-Q quadrature modulation, and the cost and complexity of the system are high. A few methods are used to transmit in frequency domain zero compensation and real part, but this will take up extra subcarrier frequency, and cause a waste of transmission power at the same time. In this paper, the existing underwater acoustic OFDM modulation schemes are compared and studied, and a modulation and transmission scheme is proposed, which is transmitted by adding zero in frequency domain, adding conjugate and then being processed by IFFT. At the same time, according to the actual situation, the parameters of underwater acoustic OFDM communication system are worked out, and the FPGA design and on-chip verification of the transmitter are completed. In order to accurately locate the starting position of OFDM symbols at the receiving end, the synchronization technology in underwater acoustic OFDM communication is studied, and a method to complete frame synchronization through correlation detection of chaotic angle modulation sequences is proposed. The chaotic angle modulation synchronization sequence is designed and generated. In order to receive and recover the transmitted data correctly, the channel estimation and compensation technology of underwater acoustic OFDM communication is studied, and the block pilot estimation scheme suitable for this paper is selected, and the estimation effect of the three channel estimation algorithms of LS,MMSE,LMMSE is simulated. Finally, LMMSE is selected to estimate the channel frequency response function to complete the compensation process. Finally, a complete underwater acoustic OFDM communication test system is built. The experimental results show that according to the modulation transmission method and parameters, the underwater acoustic OFDM communication is realized, and the transmission distance is 1.3 m. The spectral efficiency is 0.74 BP / Hz and the bit error rate is 0.074, which proves the effectiveness of the proposed modulation and transmission scheme.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN929.3

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