水声单载波系统中的块迭代频域判决反馈均衡

In order to gain a better performance and reduce the computational complexity of the filter design in the underwater acoustic single carrier system, a new Iterative Block DFE ( IBDFE) is proposed, which operates iteratively on blocks of the received signal, and fully implements its filtering operations by Discrete Fourier Transforms ( DFTs ). Two design methods are considered for IBDFE: one is HD-IBDFE, and the other is SD-IBDFE. In this paper, the first one is adopted. In this scheme, hard detected data are used as input of the feedback, and filters are designed according to the correlation between detected and transmitted data. In the simulations and experiments, the method of the HD-IBDFE is introduced, and for comparison, the performance of H-DFE is shown, as well as that of ZF, MMSE and Matched-Filter-Bound (MFB). From the results of the simulations on a Rayleigh fading channel, it is easily found that on aver-age, the HD-IBDFE outperforms H-DFE. When the number of iteration is 4, HD-IBDFE outperforms ZF, MMSE and H-DFE by about 11dB, 5dB and 0.7dB respectively at BER= 10-4 . As for MFB, the HD-IBDFE still has a degradation of 1.6 dB. In addition, the experimental results in both experiment pool and shallow water also verify the achievement. The simulation and experiment results indicate that the IBDFE outperforms other equalization schemes. What狆s more, it exhibits a reduction of the computational complexity.     

基于卡尔曼和扩展卡尔曼滤波的耦合载波跟踪方法

鉴于低信噪比高动态环境下的载波跟踪过程中,接收信号存在显著的各阶频偏变化率,故提出了一种基于卡尔曼和扩展卡尔曼滤波的耦合载波跟踪方法。载波跟踪通过基于卡尔曼滤波的锁频环辅助基于扩展卡尔曼滤波的锁相环来实现,对频率斜升信号和频率加速信号分别进行了载波跟踪环路结构的分析,得到系统方程,并进行了载波跟踪系统性能仿真。经仿真验证,在信噪比为-20 dB条件下,该方法跟踪频率斜升信号收敛时间小于60 ms,跟踪频率加速信号收敛时间小于90 ms,对两种信号的频率跟踪残差均小于5 Hz,相位跟踪残差均小于0.25rad,跟踪性能显著优于传统环路。     

RA码在水声OFDM通信系统中的应用研究

正交频分复用(Orthogonal Frequency Division Multiplexing, OFDM)技术由于具有频谱利用率高、抗多径能力强等优点,成为当前水声通信的研究重点和热点,但较高的峰均功率比(Peak-to-Average Power Ratio, PAPR)严重影响了水声OFDM通信系统的性能。采用重复累积码(Repeat Accumulate, RA)作为信道编码方案,并用线性反馈移位寄存器(Linear Feedback Shift Registers, LFSR)代替原RA码结构中的累加器,再通过选择映射(Selective Mapping, SLM)方法降低系统的峰均功率比。计算机仿真和水池实验结果表明,采用改进结构的RA码结合SLM技术能有效降低水声OFDM系统的PAPR,提高系统的性能,具有很好的应用前景。     

叠加编码技术在水声OFDM通信系统中的应用研究

<正>交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)通信技术由于具有频谱利用率高、抗多径能力强等优点,成为当前水声通信的研究重点和热点。在保证鲁棒性能的前提下,为了能够进一步提高其吞吐量,将叠加编码(Superposition Coding,SC)技术应用于水声OFDM通信系统中,在保证基本信号的同时获得额外的信息。仿真结果和水池实验结果表明:通过选择合适的功率分配因子,叠加编码在保证两路信号误比特率性能的前提下,可以提高系统的吞吐量,具有很好的应用前景。