Adaptive Modulation over Nakagami Fading Channels

We first study the capacity of Nakagami multipath fading (NMF) channels with an average power constraint for three power and rate adaptation policies. We obtain closed-form solutions for NMF channel capacity for each power and rate adaptation strategy. Results show that rate adaptation is the key to increasing link spectral efficiency. We then analyze the performance of practical constant-power variable-rate M-QAM schemes over NMF channels. We obtain closed-form expressions for the outage probability, spectral efficiency and average bit-error-rate (BER) assuming perfect channel estimation and negligible time delay between channel estimation and signal set adaptation. We also analyze the impact of time delay on the BER of adaptive M-QAM.     

不同数字电视地面广播传输系统 在多径衰落信道下的性能比较

本文分析了数字电视地面广播通信信道具有长脉冲响应的多径衰落的特点,从频域上表达了其多径衰落信道模型;基于单载波和多载波两种不同的传输模式,推导了数字电视地面广播传输系统在该多径衰落信道下的系统截止率和中断概率的表达式;比较了基于不同数字电视地面广播传输标准和解决方案的传输系统在数字电视地面广播多径衰落信道下的系统输出的截止率和中断概率的性能.     

相关衰落信道上广义矩形MQAM的性能

研究相关多输入多输出Nakagami衰落信道上的正交空时分组编码广义矩形M进制正交幅度调制（MQAM）方案,使用矩生成函数方法推导其平均误符号率（SEP）的精确闭合表达式。比较了独立同分布Nakagami衰落信道上和相关Nakagami衰落信道上广义矩形MQAM的平均SEP性能。数值计算结果阐明Nakagami衰落系数和天线间的相关性对正交空时分组编码广义矩形MQAM平均SEP性能的影响。     

Performance of two-way amplify-and-forward relaying with adaptive modulation over Nakagami-m fading channels

This paper investigates the performance of a two-way amplify-and-forward(AF)relay system with adaptive modulation over independent and non-identical Nakagami-m fading channels.The tight closed-form cumulative distribution function(CDF)expression of the instantaneous end-to-end signal-to-noise ratio(SNR)is provided.Further,approximate closed-form expression for the average spectral efficiency of the two-way AF system with adaptive modulation is obtained.Then,a tight lower bound of outage probability is deriv...     

Implementation of the Decorrelating Receiver for Asynchronous DS-CDMA Systems over Multipath Fading Channels

This paper presents a decorrelating detector for DS-CDMAasynchronous systems over multipath fading channels. The decorrelatingreceiver applies the inverse correlation matrix of signature waveformsto detect the received signal. A procedure for finding such an inversematrix is developed. This procedure employs the reciprocal basis,derived from the basis of normalized user signatures, to cancelsimultaneously both the multiuser and the intersymbolinterference. The proposed multiuser detector operates over a finitedetection window, and the only restriction imposed on the set of signaturesis that the signatures must be independent at the receiver end. If the channelis slowly variant, the detectorcan be very efficient for high bit rate transmissions. Theoreticalbounds for the multiuser interference are obtained. Simulationresults, in which both binary and non-binary sequences are used,reveal that the behaviour of the detector approaches the single userbound when an adequate set of signatures is employed. The reducedcomplexity of this detector indicates that it could be a good candidatefor practical implementation.     

非频率选择性衰落信道下捕获性能的分析

对基于数字匹配滤波器(DMF)捕获系统在非频率选择性衰落信道下的捕获性能进行了深入讨论,利用状态转移图推导出单次驻留判决方式时平均捕获时间的表达式。对平坦慢衰落信道和快衰落信道下的平均捕获时间进行了数字分析,得出的主要结论是：无论信道是否存在衰落,基于DMF的捕获系统都具有很快的捕获速度;基于DMF的捕获系统在衰落信道下的捕获性能明显要比非衰落信道差;衰落速度越快,平均捕获时间就越长,系统的捕获性能就越差。因此当信道存在非频率选择性衰落时,可以在接收端采用分集接收(比如空间分集)来改善系统的捕获性能。     

在多径衰落信道下FD/SSMA系统的性能分析

多载波频率分集扩展频谱码分多址系统（ＦＤ／ＳＳＭＡ）是一种基于多载波传输,与直接序列扩展频谱码分多址系统（ＤＳ／ＳＳＭＡ）存在时间－频率对偶关系的扩频多址通信方案。在多径传输信道下,基于ＦＤ／ＳＳＭＡ信号的锐自相关和低互相关特性,本文提出ＦＤ／ＳＳＭＡ系统可以采用路径分集接收的方案。分析和模拟计算表明,在多径衰落信道下,采用路径分集方案时ＦＤ／ＳＳＭＡ系统的性能将得到明显的改善。     

基于多径信道能量随机动态打散的隐蔽无线通信方案

为应对无线通信中的未知非法检测威胁,该文提出一种随机跳径隐蔽通信方案,实现了信号能量在多径上随机动态打散。首先,基于我方多径信道信息设计了隐蔽传输策略,并构建了敌方检测模型。接着,通过引入相关性纠偏因子,分别推导了所提方案、选最强径方案和经典最大比发送方案的敌方平均接收信噪比(SNR)闭式表达式,并基于曲线拟合的方法计算了我方最小平均隐蔽概率,完成了隐蔽性能定性和定量评估。然后,推导了我方平均接收信噪比闭式解,分析了系统速率性能。仿真实验表明,所提方案不仅在未知敌方任何信息的一般情形下具有隐蔽性能优势,而且在敌方抵近我方的极端情形下可以最大程度地解决隐蔽通信失效问题。     

非衰落信道下基于DMF的伪码捕获性能分析

基于数字匹配滤波器（DMF）的PN码捕获电路具有较快的捕获速度,因此在扩频系统中已得到广泛应用,为了在高斯白噪声环境的非衰落信道下改善DMF捕获性能,对影响捕获性能的虚警概率和检测概率进行了推导和分析,进而计算出了平均捕获时间,最后做出了仿真和分析。     

利用样本协方差矩阵特征值分解实现双通道SAR动目标检测

该文针对机载双通道SAR-GMTI系统及实测数据,提出一种新的地面慢动目标检测方法。该方法基于双通道样本协方差矩阵特征值分解,将杂波第2特征值和干涉相位联合统计特性的研究结果用于慢动目标检测,即根据给定的恒虚警概率确定一条联合分布的第2特征值干涉相位等高线作为门限检测曲线,同时结合第2特征值、干涉相位门限预处理,实现地面慢动目标的精确检测。实测数据实验结果表明：该方法不但扩大了慢动目标的可检测速度范围,同时还降低了系统的虚警概率。     

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。     

瑞利衰落信道下基于DMF的伪码捕获性能分析

基于数字匹配滤波器(DMF)的PN码捕获电路具有较快的捕获速度,因此在扩频系统中得到广泛的应用,为了在瑞利衰落信道下进一步提高捕获性能,对影响捕获性能的虚警概率和检测概率进行了推导和分析,进而计算出了平均捕获时间,并且作出了仿真和分析,为改善瑞利衰落信道下捕获性能提供了解决思路和理论依据。     

衰落信道下基于簇的协作频谱感知分析

在分布式协作频谱感知网络中,认知用户向融合中心上报本地检测的信道是带宽受限的,并且受各种衰落的影响。分析了衰落信道下认知用户通过"与"规则进行融合的协作感知策略,提出了认知用户间为Nakagami信道时基于簇理论的协作感知方案,推导得出了2种方法的检测概率和归一化平均感知比特数。仿真结果表明,基于簇理论的协作感知通过牺牲一定的信令开销得到较好的感知性能。     

基于OFDM的PLC系统模型和性能分析

给出OFDM系统在PLC信道中的一种通用系统模型。在此基础上对该系统模型进行分析，并基于QAM推导出信道衰落和噪声对系统性能影响的具体数学公式，给出分析结论。     

基于多点协作联合传输的超密集组网性能分析

超密集组网的基站高密度特性会带来严重的小区间干扰,多点协作联合传输应用于超密集组网进行干扰管理是目前的研究热点,该文对多点协作联合传输时基站密度对网络性能的影响进行了分析。首先采用随机几何方法推导了3维空间基站与用户距离的概率密度函数,为选取距离用户最近的多个基站联合传输的协作机制提供了基础;然后结合有界双斜率路径损耗模型,进行用户下行链路的干扰建模,进一步推导出用户下行链路覆盖率和网络区域频谱效率的表达式,并分析了协作基站数、基站密度等参数对网络性能的影响。数值仿真表明：协作基站数为2时就可使下行链路覆盖率增加10%,且实现2到3倍的频谱效率的增益,当协作基站数为3时,费效比更优,同时可得到多点协作下的基站密度极限使区域频谱效率最高。该文工作可为下一代移动通信网络的基站部署提供理论支持。

     

Performance evolution of ED-based spectrum sensing in CR over Nakagami-m/shadowed fading channel with MRC reception

Internet of things contains the hefty number of devices with diverse types of communication interfaces. Therefore, these devices act as a source of interference to the primary users in the absence of appropriate collision detection technique. Spectrum sensing is the important function of cognitive radio and energy detector is the most popular technique used for spectrum sensing. Detection of the availability of unused spectrum for the secondary user becomes difficult when the channel is affected by composite multipath/shadowed fading. In this paper, analytical expressions of average probability of detection and average area under the receiver operating characteristic over Nakagami-m/log-normal with maximum ratio combining diversity are derived using Gaussian-Hermite integration approximation. In addition, an optimized threshold has been incorporated to overcome the problem of spectrum sensing even at low signal-to-noise ratio. To verify the correctness of exact results and derived analytical expressions, Monte Carlo simulations are incorporated.     

New analytical expressions for the performance metrics of wireless communication system over Weibull/Lognormal composite fading

A realistic propagation scenario is more frequently characterized by a composite multipath/shadowed fading. In this work, a class of Weibull/Lognormal (W-LN) composite fading channel has been analysed and investigated. New analytical approximations to various important performance metrics of wireless communication systems such as the average symbol error probability (SEP), the outage probability, the amount of fading (AF), and the channel capacity are derived. Further, an asymptotic analysis of the composite fading channel is carried out and closed form expressions of the average SEP with and without maximal ratio combining (MRC) diversity along with the coding and diversity gain are presented. The solutions are presented in terms of Fox H-function and are valid for both the integer and non-integer values of the multipath and shadowing parameters. The results are validated via Monte-Carlo simulations and exact numerical results.     

Dual-Space Diversity over Land Mobile Satellite Channels Operating in the L and K Frequency Bands

Land mobile satellite communication systems at Ka/K band (30/20 GHz) are attracting more and more attention to researchers because of its frequency band availability and the possibility of using small earth stations and satellite antennas for the systems. However, the Ka/K-band communications also give significant challenges in the system design due to severe channel impairments expected from the satellite links. In this paper, K-band channel characteristics are studied and compared with those at L band. The channel is modeled as Rayleigh multipath fading with the line-of-sight (LOS) component following a lognormal distribution. The first and second-order statistics of the fading channel are studied. Dual-space diversity reception is investigated to combat the flat channel fading. The bit error rate performance of coherent binary phase shift keying (BPSK) with ideal bit and carrier phase synchronization over the fading channel at K band is evaluated theoretically and verified by computer simulations in the case with and without diversity reception.     

提高广播电视微波传输通道效率的方法探析

随着人们文化水平的不断提升,对广播电视节目的要求也越来越高,微波传输技术是目前广播电视得以顺利运行的基础,以其独特的优势广泛应用于广播电视的运作中.针对这一问题,笔者进行了相关研究.     

A new closed-form of ASEP and channel capacity with MRC and selection combining over Inverse Gaussian shadowing

This paper analyse and investigate the performance of communication system with maximal ratio combining (MRC) and selection combining (SC) over Inverse Gaussian (IG) fading distribution. All formats of coherent and non-coherent modulation schemes are considered and novel analytical expressions of average symbol error probability (ASEP) with diversity are derived. Gamma and IG fading distributions are popularly used as a mathematically less complex solution to lognormal in the open literature. Hence, we provide a comparative analysis between IG and gamma fading with the aim to provide a quantitative measure of the difference between the two distributions in the context of ASEP. Moreover, the novel closed-form expressions of channel capacity under transmission schemes such as optimal rate adaptation (ORA) and channel inversion fixed rate (CIFR) are derived and analysed with MRC and SC diversity over IG fading. The analytical results have been validated with the Monte Carlo simulations and the exact numerical results.