多用户OFDM水声通信技术研究

发布时间：2018-07-07 18:53

本文选题：水声通信 + 正交频分复用　；参考：《哈尔滨工程大学》2016年博士论文

【摘要】：水声信道具有传输衰减大、传播时延大、通信带宽严重受限、多普勒频偏严重、多径时延扩展严重等特点,给水声通信网络,特别是物理层的多用户水声通信带来极大挑战。本文以频谱利用率高、抗多径能力强的正交频分复用(OFDM)技术为基础,针对上行OFDM系统多用户信道估计和异步多用户接入,以及下行OFDM系统非一致多普勒频偏估计和提高频谱利用率的非正交多址接入四个水声多用户通信中的关键问题展开研究。为建立和完善水声无线通信网络提供稳健的物理层保障。首先,针对水声上行通信多用户信道估计导频不足问题,在正交频分多址(OFDMA)系统中提出一种稀疏信道估计与导频优化方法。基于压缩感知理论估计稀疏信道冲激响应,并依据压缩感知理论中测量矩阵互相关最小化原理,提出基于随机搜索的导频图案和导频功率联合优化算法。仿真和水池实验结果表明,所提方法的性能优于基于线性内插的最小二乘估计、未经导频优化的压缩感知信道估计以及单纯基于导频图案优化的压缩感知信道估计。其次,针对水声上行通信异步多用户接入问题,在水声MIMO-OFDM系统下提出一种基于滑动迭代的异步多用户接收算法。首先研究了时间同步的多用户MIMO信号检测方法,包括基于迫零和最小均方误差的线性信号检测,以及排序的连续干扰消除信号检测。然后设计了一套适合水声信道的OFDM异步多用户接入算法,包括重叠截断、干扰消除、频域过采样、多用户信道估计与解码、以及干扰重构五个处理模块,并通过滑动迭代结构同时消除前向干扰和后向干扰影响。仿真和水池实验结果验证了滑动迭代异步多用户接收算法的有效性。再次,针对点对点或多用户下行通信中的多普勒频偏问题,提出一种非一致多普勒频偏综合估计方法。首先对帧头发送的两个重复短OFDM符号进行多普勒因子的盲初始估计,然后利用每个OFDM数据符号的循环前缀进行时间细同步和多普勒因子跟踪估计。数值仿真和湖上、海上实验结果表明,该算法能够很好的跟踪每个OFDM符号的多普勒因子变化,且经过时域重采样补偿多普勒后的系统误比特率得到明显降低。最后,提出一种高频谱利用率的水声OFDM叠加编码下行非正交多址接入方法,其中发送端利用用户的信道统计特征进行功率分配。推导了所提方法的可达速率区域边界表达式和中断概率,然后结合实际的信道编码和星座图映射设计了水声OFDM叠加编码系统。仿真结果表明,当两用户具有信噪比差异且均获得非零数据率时,功率域非正交接入的OFDM叠加编码的误块率和频谱利用率性能均优于正交接入的OFDMA系统。中距离和短距离海上实验结果表明,信道的统计特征在长时间内较为稳定,可以辅助发送端功率分配;当两用户具有信噪比差异且均获得非零数据率时,叠加编码的频谱利用率比OFDMA系统有显著提高。
[Abstract]:The underwater acoustic channel has the characteristics of large transmission attenuation, large propagation delay, limited communication bandwidth, serious Doppler frequency deviation and serious multipath delay spread, which brings great challenges to underwater acoustic communication network, especially to the multi-user underwater acoustic communication in the physical layer. Based on the orthogonal Frequency Division Multiplexing (OFDM) technology with high spectral efficiency and strong anti-multipath capability, this paper aims at multi-user channel estimation and asynchronous multi-user access for uplink OFDM systems. The key problems of non-uniform Doppler offset estimation and non-orthogonal multiple access to four underwater acoustic multiuser communications in downlink OFDM systems are studied. It provides robust physical layer guarantee for the establishment and improvement of underwater acoustic wireless communication network. Firstly, a sparse channel estimation and pilot optimization method in orthogonal frequency division multiple access (OFDMA) systems is proposed to solve the problem of inadequate pilot estimation for underwater acoustic uplink communication. Based on the theory of compressed sensing, the impulse response of sparse channel is estimated. Based on the principle of cross-correlation minimization of measurement matrix in compressed sensing theory, a joint optimization algorithm of pilot pattern and pilot power based on random search is proposed. Simulation and tank experiments show that the performance of the proposed method is superior to that of linear interpolation based least square estimation, unpilot-optimized compressed perceptual channel estimation and compressed perceptual channel estimation based solely on pilot pattern optimization. Secondly, aiming at the problem of asynchronous multi-user access in underwater acoustic uplink communication, an asynchronous multi-user receiving algorithm based on sliding iteration is proposed in underwater acoustic MIMO-OFDM system. Firstly, the detection method of multi-user MIMO signal based on time synchronization is studied, including linear signal detection based on zero forcing and minimum mean square error, and sequential interference cancellation signal detection. Then a set of OFDM asynchronous multiuser access algorithms suitable for underwater acoustic channel is designed, including five processing modules: overlapping truncation, interference cancellation, frequency domain oversampling, multi-user channel estimation and decoding, and interference reconstruction. The influence of forward interference and backward interference is eliminated simultaneously by sliding iterative structure. Simulation results and pool experiments demonstrate the effectiveness of the sliding iterative asynchronous multiuser reception algorithm. Thirdly, a non-uniform Doppler frequency offset estimation method is proposed to solve the Doppler frequency offset problem in point or multi-user downlink communication. First, the blind initial Doppler factor estimation is performed for two repetitive short OFDM symbols transmitted by the frame head, and then the time fine synchronization and Doppler factor tracking estimation are performed using the cyclic prefix of each OFDM data symbol. Numerical simulations and offshore experiments on the lake show that the proposed algorithm can track the Doppler factor change of each OFDM symbol well, and the bit error rate of the system can be significantly reduced after the time domain resampling compensates the Doppler. In the end, a high spectral efficiency non-orthogonal multiple access (NOAA) method for underwater OFDM superposition coding is proposed, in which the transmitter uses the user's channel statistics to allocate power. The boundary expression of the reachable rate region and the outage probability of the proposed method are derived, and then the superposition coding system of underwater acoustic OFDM is designed based on the actual channel coding and constellation map mapping. Simulation results show that when two users have different signal-to-noise ratio (SNR) and both obtain non-zero data rate, the block error rate and spectrum efficiency of OFDM superposition coding in power domain are better than that of OFDMA system with orthogonal access. The results of mid-distance and short-distance sea experiments show that the statistical characteristics of the channel are stable for a long time and can assist the power allocation of the transmitter. When the two users have different signal-to-noise ratio (SNR) and obtain non-zero data rate, The spectral efficiency of superposition coding is significantly higher than that of OFDMA system.
【学位授予单位】：哈尔滨工程大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN929.3

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