FRFT在正交多载波水声通信系统中的应用研究

发布时间：2018-07-01 19:49

本文选题：水声通信 + 正交频分复用　；参考：《集美大学》2015年硕士论文

【摘要】：实现水下信息传输与探测的主要手段是水声通信。水下唯一可以进行远距离信息传输的物理媒质是水声信道,不同于无线电信道,水声信道是一个十分复杂的时空频变信道,它的主要特征是多变、带宽有限以及多途效应,因此,水声通信技术发展缓慢。正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)由于传输速率高、抗多径能力强、频谱利用率高等优点而在高速无线电通信中得到广泛应用。但将其应用于水声通信系统中,OFDM会受到水声信道的窄频带宽和梳状的幅频响应特性的影响,不仅没发挥其优势,反而对频偏和相位噪声非常敏感,使得OFDM的同步问题异常突出。针对这些问题,本文提出了采用对称三角线性调频(Symmetrical Triangular Linear Frequency Modulation,STLFM)信号作为同步码,基于分数阶Fourier变换(Fractional Fourier Transform,FRFT)的正交多载波水声通信系统的同步检测整体方案。通过对STLFM信号在分数阶傅里叶域能量汇聚性的分析发现,一个周期的STLFM信号分别在1p阶、2p阶处作FRFT,各能产生一次能量尖峰,这大大提高了目标分辨率,为实现同步提供了良好的条件。然后对STLFM信号作为同步码的系统模型进行了研究,推导了以STLFM信号作为同步码的联合同步算法,以及估计1p阶和2p阶处的采样频差s?f、载波频差c?f和符号定时0k算法。为了验证算法的正确性,对基于FRFT-OFDM水声通信系统进行了仿真实验和性能分析,以同步误码率(Bit Error Rate,BER)作为评价指标,在有噪声、多径传输和多普勒效应三种环境组合场景下与传统OFDM系统采用线性调频(Linear Frequency Modulation,LFM)信号作为同步码进行分析比较;并通过水池实验验证了基于FRFT-OFDM水声通信方案的有效性和可行性,具有一定的应用价值。
[Abstract]:Underwater acoustic communication is the main means of underwater information transmission and detection. The only physical medium that can transmit long-distance information under water is the underwater acoustic channel, which is different from the radio channel. The underwater acoustic channel is a very complex spatio-temporal and frequency-varying channel, which is characterized by variability, limited bandwidth and multipath effect. Therefore, the development of underwater acoustic communication technology is slow. Orthogonal Frequency Division Multiplexing OFDM (OFDM) is widely used in high-speed radio communication due to its high transmission rate, strong anti-multipath ability and high spectral efficiency. However, the application of OFDM in underwater acoustic communication system will be influenced by the narrow bandwidth of underwater acoustic channel and the characteristic of comb-like amplitude-frequency response. It not only does not give full play to its advantages, but also is very sensitive to frequency offset and phase noise, which makes the synchronization problem of OFDM extremely prominent. In order to solve these problems, this paper presents an overall scheme of synchronization detection for orthogonal multi-carrier underwater acoustic communication systems based on Fractional Fourier transform (Fractional Fourier transform) using symmetric triangular Linear Frequency Modulation (STLFM) signals as synchronization codes. By analyzing the energy convergence of STLFM signal in fractional Fourier domain, it is found that a periodic STLFM signal with FRFT at order 1p / 2p can produce a peak of energy, which greatly improves the resolution of the target. It provides a good condition for realizing synchronization. Then, the system model of STLFM signal as synchronization code is studied, and the joint synchronization algorithm using STLFM signal as synchronization code is derived, and the algorithm of estimating sampling frequency difference sf, carrier frequency difference cf and symbol timing 0k at order 1p and 2p are derived. In order to verify the correctness of the algorithm, the simulation experiment and performance analysis of the underwater acoustic communication system based on FRFT-OFDM are carried out. The bit error rate (bit error rate) is used as the evaluation index. Compared with the traditional OFDM system using linear frequency modulation (LFM) signal as synchronization code in the environment of multipath transmission and Doppler effect, the effectiveness and feasibility of the scheme based on FRFT-OFDM underwater acoustic communication are verified by pool experiment. It has certain application value.
【学位授予单位】：集美大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN929.3

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