基于差分检测的多载波无线通信系统研究

针对载波相位难以恢复的不足,在研究的基础上选择了独特的方式对多载波频域扩频码片级差分进行检测,检测时克服各种难度,同时对接收机设计进行简化。该方法可提高直接序列扩频系统抵抗信道时间选择性衰落的能力,同时针对多载波频域扩频码片级差分检测的误码率性能进行理论分析。仿真实验表明,该方法可减少载波间干扰对码片级差分检测的影响,改善了在时间选择性较强的多载波频域扩频码片级差分检测信道中的性能。     

二维扩频系统中时频码片级差分检测的性能分析

时变频率选择性衰落信道中,针对二维扩频系统提出了一种时频码片级差分检测方法,并进行了误码率分析,同时进行了仿真验证.分析和仿真结果表明,时频码片级差分检测同时具有抵抗信道频率选择性和时间选择性衰落的能力,在选择性衰落信道中的性能优于平坦衰落信道中的性能.通过性能对比发现,时频码片级差分检测相对多载波扩频码片级差分检测能够更加有效地降低了载波间干扰对系统性能的影响.     

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.     

一种混沌直扩信号相关检测的误码性能研究

本文讨论了一种新型的混沌在扩信号的相关检测方案，通过利用混沌序列良好的统计特性可以有效地检测出信号．文中推导出该方案误码率的解析表达式，发现了混沌扩频序列码片数和信道噪声与误码性能的内在联系．仿真结果表明该相关检测方案对信道噪声有很好的鲁棒性，并通过仿真得到了误码率的经验公式．     

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。     

MC-CDMA调制在散射通信信道下的性能分析

为提高对流层散射通信系统容量和抗干扰能力,对散射信道下的多载波扩频方案进行研究.基于所建立的Rayleigh 分布对流层散射信道模型,分析了频域扩频多载波技术MC-CDMA的系统性能,对典型散射信道下的系统误码率进行了分析与仿真.结果表明:MC-CDMA可有效提升散射通信系统容量,单用户时系统误码率性能较好,随着用户数和散射信道多普勒频移的增大,系统误码率随之增大,需采用多址干扰控制和子载波干扰消除技术来改善系统误码率性能.     

多径信道下解调加权分数傅里叶变换加密的混沌直扩信号

为了在多径信道下解调加权分数傅里叶变换加密的混沌直扩(WFRFT-CD3S)信号,该文提出一种广义信道差分解调算法。在WFRFT-CD3S系统的发射端先对信息码进行差分调制,接收端将差分码与信道的乘积视为广义信道,并通过本地扩频序列构建频域匹配滤波器以估计广义信道冲击响应。接收端通过解差分广义信道冲击响应的估计值来合并各径能量并恢复信息码。对所提算法的误码率进行了理论分析,数值仿真验证了理论分析结果。数值仿真结果表明提出的解调算法可以在低信噪比下解调多径WFRFT-CD3S信号,保证了WFRFT-CD3S系统抗能量检测的能力。     

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.     

Hadamard扩谱及CDMA的研究

在MATLAB平台上,对直接序列扩频系统进行仿真分析.系统采用Hadamard序列作为扩频码,对系统在平坦衰落和瑞利衰落信道环境下的误码率进行分析,讨论了扩频、解扩过程.此外,还仿真比较了不同用户数和不同扩频码的系统,为分析设计直扩系统提供依据.仿真结果表明,本实验系统可在SNR为-1.6dB的传输条件下得到10-3量级的误码率,Hadamard序列可用作扩频序列,系统可用作检验各种正交码组的正交性.     

多载波码分多址系统联合特征码与子信道动态分配

针对多载波码分多址系统中固定的子信道分配方案不能依据信道变化进行调整，而固定的扩频码分配又降低了系统的软容量等问题，本文在上行链路盲信道估计的基础上，提出下行链路联合特征码与子信道动态分配方案．根据接人的用户数多少及各个用户的信道信息，进行联合码域与频域的动态资源分配，进一步降低了多址干扰．数值仿真结果表明，本方案收敛快，信道跟踪性能好，在相同误码率条件下系统平均发射功率可以降低3～4dB．     

基于AMC和HARQ的大气激光通信跨层系统性能研究

针对大气激光通信中由大气湍流引起的系统性能下降问题,研究了基于物理层自适应调制编码(AMC)和数据链路层混合自动请求重传(HARQ)的大气激光通信跨层系统性能。在建立了大气湍流信道瞬时信噪比模型的基础上,建立了大气激光通信AMC-HARQ系统模型,并推导了系统误包率和频带利用率公式,最后在双伽马信道模型下进行了仿真分析。仿真结果表明,大气激光通信AMC-HARQ系统能够在保证一定误包性能的条件下,大大提高系统频带利用率,提高单一应用AMC时的系统误包性能。随着重传次数增加,误包率和频带利用率均提高,但频带利用率增幅随重传次数增加而减小。     

无人机抗火花电磁干扰的一种方法

无人机活塞发动机工作时将产生很强的电磁干扰,如果遥控接收机不采取干扰抑制措施将严重影响正常的通信。通过分析发动机火花塞电磁干扰产生的机理,提出了一种宽带抑制电磁干扰的接收机实现方案,通过缩短信道脉冲响应长度及自适应限幅等措施降低火花塞电磁干扰在时域上的扩展,从而将发动机火花塞产生的电磁干扰影响局限在较短的时间内,并大幅降低干扰能量。仿真和试验表明,可有效降低火花塞电磁干扰对数据解调的影响。     

Adaptive subcarrier bandwidth and power in OFDM‐based cognitive radio systems for high mobility applications

OFDM‐based cognitive radio systems are spectrally flexible and efficient, but they are vulnerable to intercarrier interference (ICI), especially in high mobility environments. High mobility of the terminal causes large Doppler frequency spread resulting in serious ICI. Such ICI severely degrades the system performance, which is ignored in the existing resource allocation of OFDM‐based cognitive radio systems. In this paper, an adaptive subcarrier bandwidth along with power allocation problem in OFDM‐based cognitive radio systems for high mobility applications is investigated. This adaptive subcarrier bandwidth method should choose the suitable subcarrier bandwidth not only to balance the tradeoff between ICI and intersymbol interference but also to be large enough to tolerate an amount of Doppler frequency spread but less than the coherence bandwidth. The power budget and interference to primary users caused by cognitive radio users are imposed for primary users' protection. With these constraints, a joint optimization algorithm of subcarrier bandwidth and power allocation is proposed to maximize the bandwidth efficiency of OFDM‐based cognitive radio systems in such conditions. Numerical simulation results show that the proposed algorithm could maximize the system bandwidth efficiency and balance this tradeoff while satisfying the constraints. Copyright © 2012 John Wiley & Sons, Ltd.     

The off‐grid frequency selective millimeter wave channel estimation

Broadband millimeter wave (mmW) systems are a promising pioneer of cellular communication for next generation which is utilizing the hybrid baseband/analog beamforming structures along with the miniature massive antenna arrays at both sides of the communication link. mmW channel with an available unlicensed spread spectrum is frequency selective because the signal bandwidth can be larger than the coherence bandwidth. Due to the sparse nature of mmW channel, extracting compressive sensing model of the system is preferable. In fact, exploiting the sparse structure will lead to the reduction of the computational complexity, because there is a reduction in the channel training length compared with the conventional methods such as least square estimation. Most of the prior works have considered on‐grid quantized departure/arrival angles in the input/output antennas to obtain a sparse virtual channel model. However, the sparse angles in the physical channel model are continuous where this continuity indicates a mismatch between the physical angles and the on‐grid angles. Such a mismatch will contribute to unwanted components in the virtual channel model. Given these extra components, the conventional compressive sensing tools are unable to recover the channel. In this paper, we propose two solutions for overcoming the problem caused by off‐grid angle selection. The first is based on the vector shaping, and the second one is based on the sparse total least square concepts. Simulation results demonstrate that the proposed methods both could obtain an adequate channel recovery and are preferable regarding computational complexity concerning the newly developed surrogate method.     

On the performance of data-dependent superimposed training without Cyclic Prefix for SISO/MIMO systems

Compared with channel estimation method based on explicit training sequences,bandwidth is saved for those methods using superimposed training sequences,while it is wasted when Cyclic Prefix(CP) is added.In previous work of McLernon,the Mean Square Error(MSE) performance of Data-Dependent Superimposed Training(DDST) without CP for Single-Input Single-Output(SISO) system was analyzed under the assumption that the data-dependent sequence matrix was a circulant matrix and not interfered by others.In fact,for th...     

一种新的部分频带噪声干扰模型下的FH/MFSK系统性能分析

部分频带噪声干扰(PBNJ)是一种主要的窄带干扰,它对通信系统性能的影响十分突出。该文针对FH/ MFSK系统中,传统的部分频带干扰模型的干扰带宽最小分辨率是一个跳频子带带宽(即MFSK信号的带宽),研究了更具有实际价值的新的部分频带干扰模型,即将干扰带宽最小分辨率精确到MFSK信号带宽的1/M。该文推导了莱斯衰落信道下的误比特率(BER)公式,给出了其闭合表达式,并通过计算机仿真验证了理论推导的正确性。理论分析与仿真结果表明,M,Nh,越小,传统与新PBNJ模型下FH/MFSK信号的BER性能差异就越大。     

Unitary matrix modulation with splitting over the coherence bandwidth for OFDM in a single antenna system

Recently, unitary matrix modulation (UMM) has been investigated in multiple antenna systems which is called unitary space‐time modulation (USTM). In an OFDM, different channel delay profiles and path strengths bring different frequency selective patterns. Therefore, OFDM system can potentially provide a diversity at the frequency selective fading due to the different channel delay profiles. When we consider only the diagonal components of UMM with splitting over the coherence bandwidth, the system can obtain a frequency diversity in a single antenna, since the channel response of the diagonal components of UMM that split over the coherence bandwidth shows to be totally different. In this paper, we propose the diagonal components of UMM/OFDM with splitting over the coherence bandwidth (UMM‐S/OFDM) in a single antenna. The proposed system can obtain the frequency diversity with splitting the diagonal components of UMM/OFDM over the coherence bandwidth. Therefore, the proposed system with a single antenna can obtain good BER performance like the USTM/OFDM with two antennas. Copyright © 2006 John Wiley & Sons, Ltd.     

Blind channel and symbol joint estimation in cooperative MIMO for wireless sensor network

In this paper,application of Sequential Quasi Monte Carlo（SQMC）to blind channel and symbol joint estimation in cooperative Multiple-Input Multiple-Output（MIMO）system is proposed,which does not need to transmit training symbol and can save the power and channel bandwidth.Additionally,an improved version of SQMC algorithm by taking advantage of current received signal is discussed.Simulation results show that the SQMC method outperforms the Sequential Monte Carlo （SMC）methods,and the incorporation of current received signal improves the performance of the SQMC obviously.     

An enhanced multi-channel bacterial foraging optimization algorithm for MIMO communication system

Channel estimation and optimisation are the main challenging tasks in Multi Input Multi Output (MIMO) wireless communication systems. In this work, a Multi-Channel Bacterial Foraging Optimization Algorithm approach is proposed for the selection of antenna in a transmission area. The main advantage of this method is, it reduces the loss of bandwidth during data transmission effectively. Here, we considered the channel estimation and optimisation for improving the transmission speed and reducing the unused bandwidth. Initially, the message is given to the input of the communication system. Then, the symbol mapping process is performed for converting the message into signals. It will be encoded based on the space–time encoding technique. Here, the single signal is divided into multiple signals and it will be given to the input of space–time precoder. Hence, the multiplexing is applied to transmission channel estimation. In this paper, the Rayleigh channel is selected based on the bandwidth range. This is the Gaussian distribution type channel. Then, the demultiplexing is applied on the obtained signal that is the reverse function of multiplexing, which splits the combined signal arriving from a medium into the original information signal. Furthermore, the long-term evolution technique is used for scheduling the time to channels during transmission. Here, the hidden Markov model technique is employed to predict the status information of the channel. Finally, the signals are decoded and the reconstructed signal is obtained after performing the scheduling process. The experimental results evaluate the performance of the proposed MIMO communication system in terms of bit error rate, mean squared error, average throughput, outage capacity and signal to interference noise ratio.