小尺度时变多径衰落信道的仿真研究

从理论上分析了多径效应和多普勒效应对无线信道的影响,并分别从时域和频域给出了信号经历信道后的仿真图形,分析了典型时变多径衰落信道理论模型,并在此基础上建立了抽头延迟线（TDL）的确定性仿真模型;仿真分析表明,通过改变时延功率谱和确定性模型的参数计算方法,此模型可以进一步扩展并用于多种传播环境下的小尺度衰落仿真。     

多径衰落信道下频域差分检测OFDM系统的误码率分析

在多径衰落信道条件下，分析了正交频分复用系统中频域差分检测的误码率性能，并进行了仿真验证。分析与仿真结果表明，信道相干时间和相干带宽均影响频域差分检测的误码率性能，信道相干带宽对频域差分检测的影响比信道相干时间的影响更大，频域差分检测适合于多径延迟扩展比较小的信道。     

频域差分和时域差分检测OFDM的误码率性能对比

在多径衰落信道条件下,分析了正交频分复用系统的频域差分检测和时域差分检测的误码率性能,得到了两种系统的误码率解析表达式,并进行了仿真验证.分析和仿真的结果表明:在保护时隙长度不小于最大多径时延长度的条件下,时域差分检测的误码率性能不受信道相干带宽变化的影响,时域差分检测的误码率性能主要受到信道相干时间变化的影响;频域差分检测的误码率性能同时受到信道相干时间和相干带宽变化的影响,并且相干带宽对频域差分检测的影响更大.     

短波环境中频域差分解调器误码率性能分析

在短波信道条件下,分析了正交频分复用系统中标准的频域差分解调和相位纠正的频域差分解调的误码率性能,并给出了频域差分解调的OFDM系统子载波数N的优化值.理论分析与仿真结果表明:对于典型短波信道,多径延迟扩展对系统优化的频域差分系统的误码率性能影响不大;对于快速衰落的短波信道,系统优化的频域差分系统仍然遭受多径延迟扩展和时变干扰的影响且有较大的误码平台.此外,在快速衰落短波信道环境下相位纠正的频域差分解调器性能优于常规的差分解调器性能.     

衰落色散无线信道的电波传播预测与模拟

由多径色散及多普勒频移造成的频率－时间选择性衰落是城市移动无线信道的一个重要特性。在研究分析的基础上建立起了城市无线衰落信道的传播预测模型,并对上述无线信道传播模型的时域衰落特性进行了模拟仿真。     

基于STBC-SCFDE系统的信道估计算法研究

针对频率选择性衰落信道下2发射天线的空时分组编码-单载波频域均衡(STBC-SCFDE)系统,分别设计了2种新颖的时域多天线导频序列和频域多天线导频序列,相应地提出了一种时域导频信道估计算法和一种频域导频信道估计算法,并分别进行了信道估计的MSE性能分析以及计算复杂度对比.仿真验证表明,相比传统经典多天线信道估计算法,所提2种信道算法在中低信噪比下均能实现良好的信道估计性能,为未来无线通信系统的信道估计开辟了新的解决途径.     

一种基于频域加窗的OFDM信道估计算法

该文分析了实际OFDM系统时域信道估计中的信道冲激响应(CIR)泄漏问题。提出了一种新的OFDM时域信道估计算法,利用频域加窗降低CIR泄漏,对CIR进行过门限判决,最大限度删除CIR中的噪声。在非整数采样多径衰落信道下与已有的OFDM时域信道估计算法进行了仿真对比,证明该算法有效降低了信道估计MSE值,改善了系统BER性能。     

频域扩频码片级差分检测的误码率性能分析

该文提出了一种频域扩频系统中的差分检测方法:频域扩频码片级差分检测.通过利用判决变量的矩生成函数,并采用鞍点近似的分析方法,得到了频域扩频码片级差分检测的误码率性能的解析表达式,同时进行了仿真验证.分析和仿真结果表明,频域扩频码片级差分检测具有抵抗频率选择性衰落的能力,在信道的相干带宽不小于两个码片对应的频带宽度的前提下,随着信道多径时延扩展的增加,其误码率性能有进一步的提高.     

移动平台对无线信道特性的影响分析

针对移动平台对无线信道特性的影响,在分析移动多径信道特性的基础上,建立了不同信道模型下多普勒效应的计算机仿真模型。不仅针对不同信道衰落条件下平台移动引起的多普勒效应进行仿真,而且为进一步阐述多普勒效应的影响,还对平台移动引起的数字通信误码率进行了仿真。信真结果表明,平台移动不但会扩展多普勒频谱,而且会加快信道衰落,造成误码率上升。     

时变衰落信道中同步时间扩展信号的分集接收技术

扩频通信可以区分多径信号进行RAKE分集接收,是一种有效处理多径效应的手段。与此对应,时间扩展通信也可以在频域上进行类似RAKE的分集接收,有效处理时变衰落带来的影响。时间扩展会带来严重的符号间干扰,同步时间扩展可以有效控制和处理符号间干扰。基于信道分解的分集接收技术保证了同步时间扩展在时变衰落信道下的性能。获得10-4误码率,本文分集算法(扩展长度1024)在时变衰落信道中所需的信噪比与AWGN信道不分集处理所需的信噪比只相差1.4dB。     

Performance of a coded multi-carrier DS-CDMA system in multi-path fading channels

Multi-carrier DS-CDMA has been considered as an effective scheme for reducing multiple access interference in quasi-synchronous transmission. The scheme allows the reduction of multiple access interference by transferring the orthogonality property of the signals into the frequency domain where the orthogonality property is robust to relative chip offsets between the spreading codes of the various users. However in multi-path channels, the multi-carrier technique results in frequency non-selective fading in the sub-channels, due to the narrower bandwidth, hence a reduction of the capability of the spread spectrum signal to mitigate the effect of multi-path propagation. In this paper, we consider the use of a Reed-Muller code with soft decision decoding to regain the corresponding loss in performance, and compare the resulting system with a single carrier DS-CDMA system. The effect of system parameters such as the number of sub-channels is investigated through numerical calculation and simulation, from which a number of system design criteria are arrived at.     

多媒体传感网中的频率同步研究

文中针对基于OFDM传输体制的多媒体传感网节点，提出了一种新的频偏估计算法。在频域，可以方便去除虚拟子载波上噪声的影响，提高性能，同时根据每个子载波的解调信噪比对各个子载波的估计结果，进行最大比加权平均，可以有效的克服频率选择性衰落的影响．采用信道的统计信息，本文提出了一种低复杂度，可实现的方法。算法的仿真结果表明本文提出的算法能有效的克服多径的影响，并且在性能上比时域估计和等增益平均的方法有较大的改进。     

An interleaved TCM scheme for single carrier multiple transmit antenna systems

Single carrier (SC) block transmission with frequency domain equalization (FDE) in multi-path fading channels is considered. It is shown that uncoded SC-FDE is resistant to fading even though the multi-path diversity cannot be harnessed. We propose simple schemes based on concatenations of trellis coded modulation (TCM) and interleaving for single and multiple transmit antennas to improve the coding gain, which also exploit spatial diversity in the multi antenna case.     

On the design of space-time and space-frequency codes for MIMO frequency-selective fading channels

The authors introduced an algebraic design framework for space-time coding in flat-fading channels . We extend this framework to design algebraic codes for multiple-input multiple-output (MIMO) frequency-selective fading channels. The proposed codes strive to optimally exploit both the spatial and frequency diversity available in the channel. We consider two design approaches: The first uses space-time coding and maximum likelihood decoding to exploit the multi-path nature of the channel at the expense of increased receiver complexity. Within this time domain framework, we also propose a serially concatenated coding construction which is shown to offer a performance gain with a reasonable complexity iterative receiver in some scenarios. The second approach utilizes the orthogonal frequency division multiplexing technique to transform the MIMO multipath channel into a MIMO flat block fading channel. The algebraic framework is then used to construct space-frequency codes (SFC) that optimally exploit the diversity available in the resulting flat block fading channel. Finally, the two approaches are compared in terms of decoder complexity, maximum achievable diversity advantage, and simulated frame error rate performance in certain representative scenarios.     

Analysis of the effects of time delay spread on TCM performance

We investigate the effect of time delay spread on trellis coded modulation (TCM) in a wireless radio environment where equalization is not employed to mitigate the effects of frequency selective fading when the time delay spread is small. Using a random variable decomposition technique and a Gaussian approximation of the intersymbol interference terms, we obtain explicit bounds for the pairwise error probability of TCM over multipath Rayleigh fading channels characterized by various power delay profiles. A method to calculate an upper bound of the bit error rate (BER) based on Jamali and LeNgoc (1995) bound is also presented. These bounds are used to evaluate TCM performance as well as investigate the delay spread tolerance limit of TCM, including I-Q TCM, over frequency selective fading channels     

Performance analysis of adaptive DFE using set-membership binormalized data-reusing LMS algorithm for frequency selective MIMO channels

This paper addresses the concern of complexity involved with adaptive equalization in wireless systems operating over time-varying and frequency selective multiple-input multiple-output (MIMO) channels. Here, we propose a decision feedback equalizer using binormalized data-reusing least mean square (BNLMS) algorithm with set-membership filtering for MIMO channels. The performance of the equalizer is investigated for a MIMO receiver in a multi-path fading environment as experienced in the indoor and pedestrian environment. The equalizer performance is also studied for channels having higher delay and Doppler spread. The convergence issues, BER performance and tracking capabilities are examined through computer simulations. Moreover, the computational complexity issue for this MIMO equalizer is compared with other existing data-selective algorithm based techniques.     

多径衰落信道中导引符号辅助的二维扩频相干解调的性能分析

在多径衰落信道中,本文分析了导引辅助的二维扩频相干解调的误码率性能.提出了信道的时频二维相关区域的概念,给出了信道时频二维信道相关特性的计算方法.结果表明,分析与仿真的误码率相近;当二维扩频的扩频增益对应的时频二维区域大于信道的时频二维相关区域时,再增大扩频增益会导致误码率性能变差.