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.     

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。     

基于MIMO技术的LED可见光通信系统

为了改善室外发光二极管(LED)可见光通信系统的性能, 解决湍流效应引起的光束相位变化、光束漂移、光束扩展等干扰问题, 提出了一种基于多输入多输出(MIMO)技术的LED可见光通信系统。首先构建了大气湍流信道模型, 然后利用MIMO技术相关原理搭建了LED可见光通信系统模型, 最后采用最大比合并的方法恢复出原始的信号, 并计算误比特率。结果表明, 在相同的湍流强度下, 随着系统分集程度越大, 误比特率越低; 在强湍流信道环境下, M=3, N=4的通信系统实现了10-7的误比特率, 与M=1, N=1的通信系统相比, 误比特率降低了5个数量级。该研究验证了MIMO技术抑制湍流效应的可行性与有效性。     

Exponentiated Weibull大气湍流下航空激光通信性能分析

研究了Exponentiated Weibull(EW)大气湍流信道 下航空激光通信的性能,综合考虑大气 湍流及气动光学效应的影响,利用Meijer′s G函数推导出了航空激光通信链路的性能指标 的 闭合表达式,包括平均误码率(BER)、中断概率及平均信道容量。在不同 的航空飞行条件下,根据 平均BER、中断概率和平均容量闭合表达式分别给出了数值仿真实例,分析了航空飞行高 度、传输距离、信噪比(SNR)与航空激光通信系统性能的关系,同时分析了孔径平均效应对 航空激光通信链路性能改善作用。     

无线光自适应副载波MDPSK调制系统特性分析

无线光通信中的自适应传输技术可有效抑制大气湍流引起的信道衰落.根据接收信噪比和预定目标误比特率要求,本文对通过瞬时湍流特性改变调制阶数的无线光自适应传输的通信系统进行了研究.给出采用Malaga分布湍流模型分别描述Gamma-Gamma、对数正态以及K分布湍流信道的相关参数设置;推导了Malaga湍流信道下无线光自适应多进制差分相移键控（MDPSK,M-ary Differential Phase Shift Keying）调制系统的平均误比特率、频谱效率以及中断概率表达式,以及基于MeijerG函数的渐近表达式.MDPSK自适应和非自适应两种调制系统特性分析结果表明：自适应调制系统不但在相同电信噪比下可获得更低的平均误比特率,还可以大大提高频谱效率,而不需要增加额外传输功率或牺牲误比特率.     

大气湍流综合效应下空间分集接收性能研究

分析和研究大气湍流和瞄准误差综合效应下,空间分集接收技术对差分相移键控(DPSK)光通信性能的改善。在不同湍流情况下,讨论采用多入多出(MIMO)和单入多出(SIMO)空间分集技术的系统性能;并将3种分集合并技术对系统误码率(BER)和中断概率的影响进行分析;采用广义超几何方法推导出自由空间光通信(FSO)系统误码率闭合表达式。由分析和实验结果可知:空间分集技术可以提高系统误码率并降低中断概率,有效地改善大气湍流引起的信道衰落;当分集数增大时,系统性能改变越明显。对比3种分集技术,最大比合并接收分集技术最为优越。     

大气湍流中直升机助降紫外光引导调制研究

为了研究大气湍流中不同调制方式对无线紫外光通信系统的性能影响,基于紫外光非直视通信模型,理论推导了弱湍流条件下开关键控、脉冲位置调制的误比特率。采用紫外光引导直升机助降模型,在不同调制方式下仿真分析了发射功率、通信距离、发散角、接收视场角、收发仰角对误比特率的影响。结果表明,不同调制方式的误比特率随着发射功率、发散角、接收视场角的增大而不断减小,随着通信距离、收发仰角的增大而增大; 在相同条件下,脉冲位置调制比开关键控的误比特率更低,而且随着调制阶数的增加,误比特率会越来越小。这一结果对提高紫外光通信系统在大气湍流中的抗干扰能力具有一定的应用价值。     

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。     

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.     

孔径接收下各向异性海洋湍流UWOC系统误码分析

为了研究孔径接收对各向异性海洋湍流条件下水下无线光通信(UWOC)系统误比特率的影响, 系统采用高斯光束传输, 接收端通过孔径接收, 在脉冲位置调制方式下通过各向异性海洋湍流信道。引入各向异性海洋湍流结构常数, 通过对闪烁的形成原理和各向异性海洋湍流条件下闪烁系数的分析, 数值模拟得到了在不同接收孔径和各向异性因子下, 海洋湍流参量、传输距离、雪崩光电二极管(APD)平均增益和调制阶数对系统误比特率的影响。结果表明, 相同各向异性因子和海洋湍流参量下, 大孔径接收能有效提升系统误比特率性能; 相同孔径直径和海洋湍流参量下, 各向异性因子越大, 系统通信性能越好; 均方温度耗散率、温度和盐度对海洋功率谱变化贡献的比值较小, 湍流动能耗散率、动力粘度较大以及传输距离越短, 系统误码性能越好; APD增益为100或150时, 系统通信性能最佳; 调制阶数M=8时, 系统通信性能最佳, M>64时, 系统误比特率变化程度几乎饱和。该研究为UWOC系统平台搭建和性能估计提供了参考。     

海洋湍流下波长分集无线光通信系统性能分析

由于海水的吸收、散射衰减以及海洋湍流效应会引起水下无线光通信（Underwater wireless optical communication,UWOC）系统接收端光信号的闪烁,导致UWOC系统传输性能下降。基于Gamma-gamma分布的海洋湍流信道模型,根据海洋湍流参数和各向异性因子表示的等效结构参数,推导出波长分集UWOC系统中断概率（Outage probability,OP）与平均误码率（Bit error rate,BER）封闭表达式。研究分析随着各向异性因子的增加,具有不同波长分集阶的水下无线光通信系统中断概率与平均误码率的变化,比较接收端使用最佳组合（Optimal combining,OC）与等增益组合（Equal gain combining,EGC）技术的水下无线光通信系统平均误码率,并仿真不同海洋湍流参数、传输距离对波长分集UWOC系统性能的影响。数值结果表明,随着各向异性因子的增加,海洋湍流对水下无线光通信系统产生的影响逐渐减弱,使用波长分集技术的UWOC系统比无波长分集技术的UWOC系统中断概率与平均误码率明显改善。     

Performance Analysis of Cooperative Diversity Wireless Networks over Nakagami-m Fading Channel

This letter analyzes the performance of cooperative diversity wireless networks using amplify-and-forward relaying over independent, non-identical, Nakagami-m fading channels. The error rate and the outage probability are determined using the moment generating function (MGF) of the total signal-to-noise-ratio (SNR) at the destination. Since it is hard to find a closed form for the probability density function (PDF) of the total SNR, we use an approximate value instead. We first derive the PDF and the MGF of the approximate value of the total SNR. Then, the MGF is used to determine the error rate and the outage probability. We also use simulation to verify the analytical results. Results show that the derived error rate and outage probability are tight lower bounds particularly at medium and high SNR     

Performance Analysis of System with Micro- and Macrodiversity Reception in Correlated Gamma Shadowed Rician Fading Channels

In this paper, the performance of wireless system employing microdiversity to mitigate the effects of short-term fading and macrodiversity to reduce long-term fading (shadowing) effects is studied. The system model assumes implementation of maximal-ratio combining (MRC) at the microlevel and selection combining (SC) at the macrolevel. The received signal envelope follows a Rician distribution and it also suffers gamma shadowing. Novel expressions for the probability density function (PDF), cumulative distribution function (CDF), and moment-generating function (MGF) of the output signal-to-noise ratio (SNR) are obtained. Several useful performance criteria, such as the moments of the output SNR and outage probability are analytically derived. Moreover, the average bit error probability (ABEP) for noncoherent binary differential phase-shift keying (BDPSK) is calculated using the MGF based approach while the ABEP for coherent binary phase-shift keying (BPSK) is studied by averaging the conditional bit error probability over the PDF. Numerical results are graphically presented to show the effects of various system parameters to the system performance, as well as the enhancement due to use of the combination of micro- and macrodiversity. Some of numerical results are complemented by equivalent computer simulated results which validate the accuracy of the proposed analysis. The agreement between the Rician-gamma and Rician-lognormal fading model is also established.     

Serial relaying communications over generalized‐gamma fading channels

In this paper, a study on the end‐to‐end performance of multi‐hop non‐regenerative relaying networks over independent generalized‐gamma (GG) fading channels is presented. Using an upper bound for the end‐to‐end signal‐to‐noise ratio (SNR), novel closed‐form expressions for the probability density function, the moments, and the moments‐generating function of the end‐to‐end SNR are presented. Based on these derived formulas, lower bounds for the outage and the average bit error probability (ABEP) are derived in closed form. Special attention is given to the low‐ and high‐SNR regions having practical interest as well as to the Nakagami fading scenario. Moreover, the performance of the considered system when employing adaptive square‐quadrature amplitude modulation is further analyzed in terms of the average spectral efficiency, the bit error outage, and the ABEP. Computer simulation results verify the tightness and the accuracy of the proposed bounds. Copyright © 2011 John Wiley & Sons, Ltd.     

Gamma Gamma强海洋湍流和瞄准误差下水下无线光通信系统的性能研究

采用外差式差分相移键控(Differential phase-shift keying,DPSK)调制的水下无线光通信(Underwater wireless optical communication,UWOC)系统经过Gamma Gamma强海洋湍流信道传输,当接收端与发送端之间存在瞄准误差并采用孔径接收方式时,分析了湍流效应和瞄准误差对接收光强的抖动影响,推导了UWOC系统的平均误码率(Bit error rate,BER)和中断概率(Outage probability,OP)的解析表达式。数值模拟研究了不同的瞄准误差、束宽、接收孔径和海洋湍流参数对平均BER和OP性能的影响。结果表明,在相同的束宽和信道环境下,瞄准误差越大,系统性能越差;光束束宽与孔径半径之比越大,接收孔径直径越大,系统性能越好;另外,选择较小的温度和盐度波动对海洋湍流贡献的比值ω和均方温度耗散率χT,以及较大的湍流动能耗散率ε和动力粘度u的海洋湍流环境也有利于获得较好的系统性能。     

Effects of carrier phase error on EGC receivers in correlated Nakagami-m fading

The effects of incoherently combining on dual-branch equal-gain combining (EGC) receivers in the presence of correlated, but not necessarily identical, Nakagami-m fading and additive white Gaussian noise are studied. Novel closed-form expressions for the moments of the output signal-to-noise ratio (SNR) are derived. Based on these expressions, the average output SNR and the amount of fading are obtained in closed-form. Moreover, the outage and the average bit error probability for binary and quadrature phase-shift keying are also studied using the moments-based approach. Numerical and computer simulation results clearly depict the effect of the carrier phase error, correlation coefficient, and fading severity on the EGC performance. An interesting finding is that higher values of the correlation coefficient results to lower irreducible error floors.     

Performance of cooperative diversity using Equal Gain Combining (EGC) over Nakagami-m fading channels

Cooperative diversity is a promising technology for future wireless networks. In this paper, we derive exact closed-form expressions for the average bit error rate (BER) and outage probability (Pout) for differential equal gain combining (EGC) in cooperative diversity networks. The considered network uses amplify-and-forward relaying over independent non-identical Nakagami-m fading channels. The performance metrics (BER and Pout) are derived using the moment generating function (MGF) method. Furthermore, we found (in terms of MGF) the SNR moments, the average signal-to-noise ratio (SNR) and amount of fading. Numerical results show that the differential EGC can bene?t from the path-loss reduction and outperform the traditional multiple-input single output (MISO) system. Also, numerical results show that the performance of the differential EGC is comparable to the maximum ratio combining (MRC) performance.     

Switched diversity receivers over generalized gamma fading channels

A versatile envelope distribution which generalizes several commonly used fading models is the generalized Gamma (GG) distribution. This letter deals with the performance analysis of switch and stay combining (SSC) receivers operating over not necessarily identical GG fading channels. For these receivers, novel analytical expressions for the moments of the output signal-to-noise ratio (SNR) (including average SNR and amount of fading), outage probability, average bit error probability (ABEP), and Shannon average spectral efficiency (ASE) are derived. Moreover, closed-form expressions are obtained for the optimal average SNR, ABEP, and ASE switching thresholds. Special cases of the derived expressions agree with known results.     

CDF and MGF based analysis over Rayleigh TWDP shadowed fading channel for indoor communication

Recently, the two-wave with diffuse power (TWDP) distribution has been extensively used to model the shadowing in multipath-faded/shadowed indoor environment. In this article, novel expressions for joint moments, mean, second moment, variance and cumulative distribution function for Rayleigh TWDP shadowed fading model are derived. By using the derived expression of mean and variance, the expression for amount of fading is obtained. Also, the outage probability, moment generating function and average bit error rate (ABER) for various modulation schemes namely binary phase shift keying (BPSK), binary frequency shift keying (BFSK), minimum shift keying (MSK), differentially coherent phase shift keying (DCPSK) and non-coherent frequency shift keying (NCFSK) are calculated. The derived expressions for cumulative distribution function, outage probability and ABER are presented in analytical format and have been numerically evaluated. Moreover, the numerical results of ABER using MSK and DPSK modulation schemes is compare with results of Rayleigh Gamma composite fading model. The study shows that better outage probability (0.01) is observed at 40dB average signal to noise ratio (SNR) with 5dB lowest threshold SNR, however, at higher threshold SNR (>5dB) with fixed average SNR (40dB), poor outage probability performance are obtained. Further, at higher shadowing (10dB), for fixed average SNR (15dB), minimum error probability (10^?4) is observe, while at lower shadowing (less than 10dB), higher error probability (greater than 10^?4) is observed that represents poor BER performance.