考虑混合SC/MRC分集的层叠分布式天线系统SER性能分析

针对Nakagami/lognormal复合衰落信道,研究了层叠分布式天线系统(Cascade Distributed Antenna System-CDAS)在CDMA网络中的平均误符号率性能.推导出了采用混合SC/MRC分集接收机的层叠分布式天线系统平均误符号率性能公式.利用推导出的平均误符号率表达式,分析了多径密度函数(Multipath Intensity Profile-MIP)衰减因子、空时分集维数、活动用户数以及阴影衰落因子对平均误符号率性能的影响.仿真表明层叠分布式天线系统可以有效对抗衰落,提高系统容量以及削弱对数正态阴影衰落的影响.     

基于SC分集的混合FSO/RF航空通信系统性能分析

研究了基于选择合并(SC)分集的混合激光/射频(FSO/RF)航空通信系统性能,该系统设计简单且在发射端无需信道状态信息(CSI)。激光链路服从平均孔径效应下的Exponentiated Weibull大气湍流分布模型,射频采用Nakagami-m衰落信道模型,推导求出混合FSO/RF航空通信系统接收端信噪比的累积分布函数,进一步利用Meijer′s G函数推导了混合FSO/RF通信系统中断概率以及平均误码率的闭合表达式,通过仿真对比分析了不同湍流强度、调制方式及分集通信方案对系统中断、误码性能的影响。仿真结果表明,混合FSO/RF航空通信系统有效地利用了FSO及RF链路在不同大气信道条件下的互补性质,具有更优的中断和误码性能;采用BPSK调制能有效降低大气湍流对混合FSO/RF航空通信系统的影响;信噪比高时,并行传输、分集接收的通信方案对系统误码性能的改善要优于低阶调制对误码性能的改善。     

大气湍流和瞄准误差下差分相移键控光通信系统的性能分析

详细研究了Gamma-Gamma湍流信道大气闪烁、信道衰落及瞄准误差对差分相移键控(DPSK)相干光通信系统误码性能、信道容量和中断概率等指标的影响。自由空间光通信(FSO)系统采用基于马赫-曾德尔调制器(MZM)和马赫-曾德尔干涉仪(MZI)的DPSK调制/解调结构,通过广义超几何方法分析推导出有关平均误码率、平均信道容量和中断概率的闭合表达式并简化分析。在Matlab平台下进行模拟仿真,实验结果表明,系统的平均误码率和平均信道容量随湍流程度的增强而减弱;信道容量的提升可以通过增加带宽或减小抖动方差实现;当瞄准误差过大时导致中断概率增大,严重影响系统的通信性能。     

协作认知无线电网络频谱检测性能分析

阴影热点区域环境复杂,信号传输损耗更大,协作中继转播功能能够提高通信性能.文章对阴影衰落信道上多中继认知无线电系统的联合频谱检测概率进行了分析,计算基于解码转发机制的中继器的成功解码概率;分析中继器对于一级和二级用户的中断概率的影响.误警率为0.1和0.05条件下的检测概率、一级系统和二级系统的中断概率等性能的仿真结果表明:中继器协作检测可以提高检测性能;协作中继转播可以在保证授权用户所需中断概率条件下降低认知用户的中断概率;结合联合频谱检测和协作中继转播,能提高系统通信性能,提高频谱使用效率.     

Nakagami-m衰落信道下固定增益中继系统性能分析

 在Nakagami-m衰落信道下,分析了两跳固定增益放大转发中继通信系统的性能.首先采用基于概率密度函数(PDF)的性能分析法推导了无协作分集时系统的中断概率和平均误符号率(ASER)的闭合表达式,然后采用基于矩生成函数(MGF)的方法推导了有协作分集时系统的中断概率和ASER表达式以及接收信噪比的n阶矩的闭合表达式.仿真结果显示,所推导的闭合表达式与数值仿真结果吻合良好,协作分集和较大的m值可提升系统性能,中继前后两跳的信道质量对系统性能的影响并不相同.     

Nakagami-m信道下放大转发增量中继性能分析

针对放大转发(AF)协同分集网络在独立同分布(i.i.d.)平坦Nakagami-m衰落信道上的增量中继进行了端到端性能分析,给出了误码率(BER)的最小下界解析解以及信噪比(SNR)的中断概率。数值模拟显示分析结果与仿真结果完全匹配,同时,还针对不同信噪比检测门限条件下的系统误码率和中断概率的性能进行了评估和比较。     

混合衰落信道下存在反馈时延的多天线中继性能分析

研究了混合Rayleigh-Rician衰落信道下,存在反馈时延的多天线双跳放大转发(AF)中继系统的性能.首先,基于反馈时延波束成形(BF)模型得到混合衰落信道下中继系统的输出等效信噪比(SNR).然后,利用无穷级数展开推导出输出信噪比中断概率(OP)和概率密度函数(PDF)的解析表达式,并进一步得到中继系统遍历容量和平均误符号率(ASER)的理论计算公式.最后,计算机仿真验证了所提出的性能分析方法的正确性,并定量分析了天线数量、反馈时延和信道参数对系统性能的影响.     

大气湍流和指向误差下混合RF/FSO航空通信系统性能分析

基于解码-转发中继方式,研究了混合射频/自由空间光(RF/FSO)航空通信系统性能。采用副载波多进制相移键控调制方式,建立了孔径平均作用下混合RF/激光通信系统模型,其中FSO通信链路采用指数型Weibull大气湍流信道的同时考虑指向误差影响,射频通信链路为Nakagami-m衰落信道。利用Meijer′s G函数推导得到航空激光通信系统平均误码率和中断概率的闭合表达式。在不同湍流强度和接收孔径大小条件下,对比分析了中断概率及误码率性能。仿真结果表明,与弱湍流条件相比,中等湍流强度条件下指向误差对系统中断性能影响较小;孔径平均效应可有效改善混合RF/FSO传输系统的性能;FSO信道对混合系统性能起主要作用。     

认知选择协同分集任意信噪比中断概率的分析

选择中继已被证明是一种有效和实用的协作分集方法.但是,现有的分析主要集中在渐进高信噪比(SNR)区域,因此,研究认知选择协同分集系统任意信噪比的中断概率具有现实意义.推导了瑞利衰落信道选择中继协议的中断概率解析式,并进行了仿真.仿真结果表明,选择中继协议在任意信噪比情况下,增加中继节点可降低中断概率,而解码中继协议(DF)在低、中信噪比情况下不一定降低中断概率;同时,选择中继协议的中断性能和分集增益随频谱空穴检测能力的提高而增强.     

AF中继辅助TWR-FSO通信系统的性能分析

针对大气湍流和指向误差对自由空间光通信性能的影响会随着通信距离的增大而愈发严重,基于放大转发中继(AF),提出了一种双向中继-自由空间光通信(TWR-FSO)系统方案。该系统采用差分二进制相移键控调制,建立了一个包含大气湍流和指向误差的复合衰落信道模型,其信道衰落满足Gamma-Gamma分布。利用Meijer’s G函数推导得到TWR-FSO系统中断概率和平均误码率的闭合表达式。在不同湍流强度和阈值门限条件下,对比分析了中断概率和平均误码率性能。仿真结果表明,在受到相同指向误差的条件下,当SNR=25 dB时,AF中继相较于DF中继系统的中断概率从10^-1量级下降到10^-4量级左右。当折射率结构常数为4.0×10^-15m^-2/3,SNR=40 dB时,系统的误码率可以达到10^-8量级以下。说明AF中继下TWR-FSO系统能有效降低大气湍流和指向误差对通信系统的影响。     

Outage probability for lognormal-shadowed Rician channels

A new general outage probability expression for a Rician signal received among L Rician interferers is derived. This result is shown to cover previous published expressions involving Rayleigh signal/interferers as special cases. A new method is then applied to further extend the result to include the effect of lognormal shadowing on the outage probability (for microcellular mobile radio systems in Rician/Rician fading environments). New Rician/Rician outage probability curves against the normalized reuse distance and cluster size with and without lognormal shadowing effect are presented and discussed     

Power control and diversity in mobile radio cellular systems in thepresence of Ricean fading and log-normal shadowing

The performance of a cellular mobile radio system with frequency reuse is evaluated in terms of outage probability. Deterministic path loss, log-normal shadowing, and Ricean fading are accounted for, and the use of diversity and power control is considered in order to enhance system performance. Both hexagonal and lineal cells are considered. Particular attention is given to the sensitivity of the outage probability to the system parameters, especially those related to the propagation model (fading, shadowing, and path loss). It is seen that diversity and power control can improve the system behavior. The performance is sensitive to the fading parameter (i.e., the Rice factor) of the intended user, but is relatively independent of that of the interferers. Also, a significant dependence is observed on the shadowing parameter, whereas a limited dependence is seen on the outage threshold and the channel utilization. Finally, the presence of a dual path loss law degrades the performance, and the outage probability increases as the breakpoint distance gets larger     

Micro- and macrodiversity MDPSK on shadowed frequency-selectivechannels

The performance of M-ary differential phase shift keying (MDPSK) on frequency-selective slow Rayleigh fading, lognormal shadowed channels with diversity combining is analyzed for mobile and portable applications. The use of L-branch equal gain postdetection microdiversity combining to mitigate the effects of fading and P-port macrodiversity to alleviate the effects of shadowing are investigated. Four performance criteria are considered for a frequency-selective multipath fading, intersymbol interference channel. These are, the short term bit error rate (BER), the irreducible BER, the complementary distribution over the lognormal shadowing of the average BER, and the probability that the instantaneous BER exceeds a threshold value, averaged over a spatial environment. Closed-form expressions for the four performance criteria are obtained. The BER and outage performance results show that diversity combining is an effective method for improving the system performance (and hence system reliability), when the normalized delay spread is not large. It is also seen that, in most cases, 4DPSK gives the best performance followed by 8DPSK and 2DPSK, respectively, for a given information throughput     

分布式天线系统中的系统下行中断概率分析

本文针对分布式天线系统的系统下行中断概率问题展开研究.文章首先建立了包含路径损耗、阴影衰落和瑞利衰落的复合信道模型.接着,在接收端采用最大比合并的方式接收信号,并运用矩生成函数推导出输出信噪比的概率密度函数.然后,对分布式天线采用选择传输策略,并分析出给定移动台位置时的中断概率的表达式.最后,考虑小区内移动台任意分布特...     

分布式天线系统中的系统上行中断概率分析

中断概率是无线通信系统的一个重要指标。该文针对分布式天线系统中的系统中断概率问题进行了研究。首先,建立了包含路径损耗、阴影衰落和瑞利衰落的复合信道模型;然后,在该信道模型下推导出给定移动台位置时的信噪比;接着,基于选择合并策略,分析出给定移动台位置时系统上行传输的中断概率表达式;最后,考虑到小区内移动台任意分布特点,文章给出系统上行中断概率闭合理论表达式。仿真结果表明,所提的系统上行中断概率理论表达式与仿真结果十分吻合。     

Outage Probability in Mobile Telephony Due to Multiple Log-Normal Interferers

The mobile radio channel is characterized by three important factors: path losses larger than free space, fading typically taken as Rayleigh, and shadowing generally characterized as lognormal. For cellular systems, in order to determine acceptable reuse distances between base stations and to compare modulation methods, the probability of unacceptable cochannel interference (outage probability) has to be determined in the realistic situation where both fading and shadowing occur. In this paper, the average outage probability is computed for centrally located base stations when multiple log-normal interferers are present. This is done for both the mobile-to-base and base-to-mobile communication links. An unexpected result of this study is that the outage probabilities for the two cases do not differ in a significant way. Cumulative probability curves of the short-term average-signal-toaverage-interference ratio (SIR) are presented for a variety of system parameters: channel set number, propagation law exponent (γ), and dB spread (σ) of the log-normal distribution for the signal and interferers. An important observation is the large sensitivity of the performance curves to the propagation parameters: for a system with seven channel sets with a 10 dB SIR threshold, the average outage probability varies from 10 percent forgamma = 3.7, sigma = 6dB, to 70 percent forgamma = 3, sigma = 14dB. Alternatively, for a fixed outage objective of 10 percent, the required SIR threshold value ranges from -17 dB to 11 dB, depending on the propagation parameters. These variations make it imperative that accurate measurements of these parameters be obtained for the different service areas. Outage probabilities are also easily related to specific modulation methods and diversity approaches; detailed results are given for several representative cases.     

Closed‐Form Expressions for Selection Combining System Statistics over Correlated Generalized‐K Fading Channels in the Presence of Interference

This paper considers the effects of simultaneous correlated multipath fading and shadowing on the performances of a signal‐to‐interference ratio (SIR)‐based dual‐branch selection combining (SC) diversity receiver. This analysis includes the presence of cochannel interference. A generalized fading/shadowing channel model in an interference‐limited correlated fading environment is modeled by generalized‐K distribution. Closed‐form expressions are obtained for probability density function and cumulative distribution function of the SC output SIR, as well as for the outage probability. Based on this, the influence of various fading and shadowing parameter values and the correlation level on the outage probability is examined.     

Outage analysis in wireless channels with multiple interferers subject to shadowing and fading using a compound pdf model

Wireless communication systems are subject to short- and long-term fading of the channel. Instead of the commonly used Nakagami–lognormal model to account for the conditions existing in these shadowed fading channels, a compound probability density function (pdf) model is used to evaluate the performance of wireless systems. While the Nakagami–lognormal lacks a closed-form solution to the pdf of the received power in shadowed fading channels, the compound pdf has an analytical expression for the pdf of the received signal power. The synergy between these two models for the analysis of wireless systems is explored by calculating the bit error rate in a DPSK modem as well as the outage probability in a wireless system in a shadowed fading channel. This is followed by the computation of the outage probability in the general case where both the desired and cochannels are subject to shadowing and fading. The analyses were carried out for both fixed number of cochannels and random number of cochannels. Results demonstrate the usefulness of the compound pdf model for the performance analyses of wireless systems in shadowed fading channels.     

Performance analysis of microcellular mobile radio systems with shadowed cochannel interferers

A study is presented of microcellular mobile radio systems where the desired signal has Rician statistics and cochannel interferers experience lognormal shadowing as well as Rayleigh fading. This implies a Rician/Rayleigh-plus-lognormal microcell interference model. The probability density function of the signal-to-interference ratio is derived and used to evaluate the performance of microcellular systems in terms of the outage probability.<>