Applied research on RA codes in underwater acoustic ofDM communication system

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。Orthogonal frequency division multiplexing(ofDM) technology has become the research focus and hotspot of underwater acoustic communications owing to its advantages such as high spectrum efficiency and robustness to multipath fading,but it possesses high peak-to-average power ratio(PAPR) which severely degrades the performance of Underwater Acoustic ofDM Communication System.In this paper,repeat accumulate(RA) code is adopted as the channel coding scheme,and linear feedback shift registers(LFSR) is used to replace the accumulator of original RA code structure,then selective mapping(SLM) method is also adopted to reduce the PAPR of system.Computer simulation and experimental results show that modified RA code and SLM can effectively reduce the PAPR and improve the per-formance of underwater acoustic ofDM communication system,which have a very good application prospect.研究基金访问学者项目(2011631504); 中央高校基础研究基金项目(201112G020和201212G012); 国家自然科学基金项目(41176032

Carrier frequency offset and impulse noise estimation for underwater acoustic orthogonal frequency division multiplexing

载波频率偏移和脉冲干扰是水声通信系统中常见的干扰形式。为了提高系统的鲁棒性,消除这两种类型干扰的影响,提出利用空载波对载波频率偏移和脉冲干扰进行估计。空载波估计技术采用了分步优化和联合优化估计两种方法。分步优化估计首先利用重采样和空载波进行载波频率偏移估计,补偿后利用空载波对脉冲噪声进行消除。考虑到载波频率偏移和脉冲噪声估计时的相互影响特性,利用二者的联合估计得到优化解。仿真和水池实验结果表明,两种优化算法都取得了良好的效果;同时联合优化估计比分步优化估计得到更大的系统性能增益,在系统误比特率为10~(-2)时,联合优化解得到了3db左右的系统性能增益。通过对载波频率偏移和脉冲干扰的估计消除,大大提高了水声通信系统的鲁棒性。The carrier frequency offset(CFO) and impulse noise are the most common interference in the underwater acoustic system.The CFO and impulse noise could be estimated by using the null subcarriers.The null subcarriers estimation included optimal separate estimation and joint estimation.The separate estimation firstly estimated the CFO value and then estimated the impulse noise value.However,the CFO and impulse noise are always affected each other when one of them was estimated.Then a joint optimal estimation was proposed to estimate the both of them.Experimental results performed with numerical simulation and pool-trial data axe provided.The results show the improvement of the proposed algorithm under time-varying channels and the joint estimation can get more performance gain margin than the separate estimation about 3 dB at the BER of 10~(-2).Through the estimation of them,the robustness is improved.研究基金访问学者项目(中国国家留学基金管理委员会:2011631504); 美国国家科学基金(CNS-1205665); 中央高校基础研究基金(201112G020;201212G012); 国家自然科学基金(41176032)资