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面对行车安全监控无线数据通信的迫切需求，我国铁路传统的450MHz的模拟无线通信系统显得无能为力.而正在实施的GSM-R通信系统主要服务于行车调度业务，其容量和技术体制也难以满足这种要求.通过综合集成当今先进成熟的移动通信技术，包括正交频分复用(OFDM)技术、无线局域网技术和移动IP技术，提出了一种新的基于OFDM调制技术的铁路无线数据通信系统设计.该系统在2MHz的频率带宽内，数据通信速率最高可达4.86Mbps，可以容忍的时延扩展为2.5 us.     

LTE-R应用于铁路通信多径衰落信道下的时频同步研究

LTE-R(Long Term Evolution-Railway,长期演进)作为下一代铁路无移动通信系统,采用OFDM(正交频分复用)的调制方式来提高频谱利用率。铁路无线通信系统易受到多径衰落和突发干扰的影响,严重影响铁路的行车安全和运输效率。因此研究符号定时同步和载波频率同步对铁路无线通信系统具有很重要的意义。采用重复共轭结构训练符号的自适应符号同步算法,首先确定训练符号的符号定时同步、载波频率同步以及信道参数,再经过迭代递推把符号定时同步起始位置调到FFT窗口的理想位置和对载波频偏进行补偿。仿真结果表明,该方法在多径衰落信道下有很好的符号定时同步估计和对载波频偏的补偿,信噪比越高符号定时同步估计精度也越高。     

用特殊训练符号的MIMO-OFDM信道估计算法

提出了一种使用特殊训练符号的MIMO-OFDM系统时域LS信道估计的改进算法.采用插零的恒包络指数序列作为训练符号,可以使系统获得较理想的峰平比(PAPR),并能减少码间干扰(ISI)的影响.仿真结果表明,恒包络训练符号比随机训练符号具有很大的优势,在信噪比为20 dB时,利用恒包络训练符号的信道估计算法比利用随机训练符号的算法均方误差(MSE)降低15 dB;在采用特殊训练符号的前提下,改进算法相对传统算法也表现出较大的优越性,信噪比为25 dB时,改进算法的MSE要比传统算法低10 dB.     

基于改进BOMP算法的水声信道估计

近年来,水声信道估计主要是基于稀疏模型展开.水声介质的非均匀性等使声线以簇的形式传播,导致水声信道展现出块结构稀疏特性.本文针对信道的块结构稀疏特性,在OFDM通信系统中,提出使用改进的BOMP算法进行水声信道估计.BOMP算法一次筛选1个最大相关块,改进的算法一次挑选t个非零块,算法重构时间将降低t倍.仿真结果表明:改进的BOMP算法误码率和重构时间要优于传统的LS、基于压缩感知的OMP算法;在不降低BOMP算法重构精度的前提下,将重构时间降低t倍.     

OFDM高速水声移动通信系统方案设计(英文)

The major constraint on the performance of orthogonal frequency division multiplexing(OFDM) based underwater acoustic(UWA) communication is to keep subcarriers orthogonal.In this paper,Doppler estimation and the respective compensation technique along with various diversity techniques were deliberated for OFDM-based systems best suited for underwater wireless information exchange.In practice,for mobile communication,adjustment and tuning of transducers in order to get spatial diversity is extremely difficult.Considering the relatively low coherence bandwidth in UWA,the frequency diversity design with the Doppler compensation function was elaborated here.The outfield experiments of mobile underwater acoustic communication(UWAC) based on OFDM were carried out with 0.17 bit/(sHz) spectral efficiency.The validity and the dependability of the scheme were also analyzed.     

OFDM System Channel Estimation with Hidden Pilot

Channel estimation using pilot is common used in OFDM system.The pilot is usually time division multiplexed with the informative sequence.One of the main drawbacks is bandwidth losing.In this paper,a new method was proposed to perform channel estimation in OFDM system.The pilot is arithmetically added to the output of OFDM modulator.Receiver uses the hidden pilot to get an accurate estimation of the channel.Then pilot is removed after channel estimation.The Cramer-Rao lower bound for this method was deprived.The performance of the algorithm is then shown.Compared with traditional methods,the proposed algorithm increases the bandwidth efficiency dramatically.     

结合STBC的VBLAST MIMO—OFDM系统研究

结合分层空时（vertical bell layered space time，VBLAST）结构和空时块分组码（space time block code，STBC）的优点，提出了一种新的编码方法。在发射端对发射天线分组，每组独立进行空时编码和OFDM调制；在接收端，采用分组干扰抑制结合奇异值分解实现解码，降低了计算复杂度。相对于空时分层码而言，该方法在同样信噪比的条件下可以取得明显低的误码率；相对于空时分组码而言，该方法具有更高的频谱利用率和码速率。仿真采用SUI-3信道模型，仿真结果表明该方法的抗衰落性能明显优于VBLAST。     

OFDM仿真系统的快速创建方法

阐述OFDM的基本原理，分步骤展示了OFDM仿真番统建立过程，重点提出从仿真OFDM调制与解调技术的基本模型，到仿真全部OFDM相关技术的模型的扩展方法。     

一种改进的OFDM联合时间频率快速同步算法

对文献[9]和文献[10]的算法进行修改,提出一种改进的OFDM联合时间频率快速同步算法,通过使用1个OFDM符号长度的训练符号,可以很好地完成OFDM通信系统的同步。接收端首先通过搜索1个特殊的训练符号,计算出定时同步位置和小数频偏。然后对训练符号的样点数据进行小数频偏补偿和FFT变换,再估算出整数频偏,通过定量分析得出结论,当整数频偏大于7个子载波间隔时,改进的算法具有更快的同步速度。仿真结果表明,改进的算法具有更小的频偏估计方差。     

A Reduced Complexity Time-Delay Tracking and Channel Estimation for OFDM Systems

Introduction OFDM[1]is a special case of multicarrier trans-mission, where a single datastream is transmittedover a number of orthogonal subcarriers. Becausethe symbol duration increases for the lower rateparallel subcarriers, the relative amount of disper-sion in time caused by multipath delay spread is de-creased. Intersymbol interference is eliminated al-most completely by introducing a guard time in ev-ery OFDM symbol. Due to these advantages,OFDM is widely exploited for the communica…