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。     

Exponentiated Weibull大气湍流下混合RF/FSO系统容量分析

RF/FSO混合通信系统弥补了自由空间光通信受天气影响严重的问题,提高了系统的可用性。本文研究了Exponentiated Weibull大气湍流下双门限混合RF/FSO系统平均信道容量,考虑大气湍流和指向误差对平均信道容量的联合影响,利用MeijierG函数推导出平均信道容量的闭合表达式。根据平均信道容量闭合表达式进行了仿真,分析了在不同距离、大气湍流强度、抖动标准差和波束宽度条件下,平均信道容量随信噪比变化的关系。     

基于2×2放大转发中继的混合RF/FSO系统性能分析

基于放大转发中继方式,研究了2×2中继条件下混合RF/FSO航空通信系统性能。FSO链路服从适于孔径平均条件下的Exponentiated Weibull大气湍流分布模型,RF通信链路为Nakagami-m衰落信道。建立2×2中继混合RF/FSO通信系统模型,利用Meijers’G函数推导求出航空激光通信系统信噪比的概率分布函数及累积分布函数,进一步推导混合通信系统平均误码率和中断概率的闭合表达式。通过仿真分析了不同大气湍流强度、孔径尺寸和调制方式对平均误码率和误码率的影响。仿真结果表明,混合系统中断概率及误码率受湍流强度影响较大,孔径平均效应可有效改善混合RF/FSO传输系统的性能;固定增益中继方式下,混合RF/FSO系统性能主要由RF链路决定;在固定增益中继混合RF/FSO系统中起主要作用;可变增益中继混合RF/FSO系统中,具有较小信噪比的链路在对系统性能的影响起主要作用。     

基于网络丢包率的混合FSO/RF系统切换技术研究

利用C++ Builder编程软件提供的相关网络组件,提出了基于网络丢包率的混合FSO/RF系统切换判决机制,在网络中实现了对链路的监控功能,并采用无线路由器、光纤收发器等器件搭建了混合FSO/RF测试系统,对基于网络丢包率的混合系统切换机制进行了测试,结果表明采用网络切换判决方案,能够自动选择链路通信,保证数据不间断...     

Two-way中继系统的中继选择算法分析

为了提升双向AF中继系统总速率和降低系统中断概率,提出了一种最小中断概率的中继算法MOP,介绍了现有的两种中继选择算法,利用通信系统的性能指标(信噪比、中断概率、信道容量)展开分析。仿真结果表明,所提出最小中断概率中继选择算法可明显降低系统中断概率,在提升系统总速率的性能与最大化容量中继算法接近,有效地改善了系统性能。     

基于能量收集的多对双向MIMO AF中继系统的和速率分析

采用基于中继功率分配的能量收集方法,中继将接收到的部分射频信号转化为能量并利用收集到的能量放大和转发剩下的信号,通过在中继使用最大比合并/最大比传送的接收和预编码技术,推导出每个用户的遍历速率的下界表达式,然后研究了使所有用户和速率最大的最佳中继功率分配比.仿真结果说明了在最佳中继功率分配比的条件下可以得到最大的和速率,同时给出了和速率与中继天线数和用户对数的关系,并表明了在用户总功率一定的条件下,能量收集中继系统的性能优于传统的没有能量收集的中继系统.     

同频干扰下混合MUD-RF/FSO航空中继通信系统性能分析

为了建立同频干扰条件下的混合射频/自由空间光(Radio Frequency/Free Space optical,RF/FSO)航空中继通信系统链路精确模型,提出多用户分集(Multi-User Diversity,MUD)的航空平台RF/FSO混合链路性能分析方法.以独立且同分布的Nakagami-m衰落信道表征射频(Radio Frequency,RF)用户信号和同频干扰(Co-Channel Interfer-ence,CCI)信号信道;构建了指数Weibull分布大气湍流与Rayleigh分布指向误差的FSO信道传输模型;在电光转换中继节点采用解码转发协议降低噪声累积.基于系统端到端等价信噪比累积分布函数,获得了RF/FSO混合链路中断概率及平均误码率表达式.研究结果表明,采用相干二进制相移键控调制时,系统误码性能最优;可通过增加用户数的方式来减弱干扰信号的影响.     

Performance analysis of decode-and-forward partial relay selection in NOMA systems with RF energy harvesting

Wireless Networks - In this paper, we investigate a dual hop communication decode-and-forward scheme relay system where a source node wants to transmit simultaneously two symbols to two desired...     

Performance analysis of energy harvesting cognitive relay networks with primary interference

This paper investigates the outage performance of multihop energy harvesting cognitive relay network (EH-CRN), in which the secondary nodes are powered by dedicated power beacons based on the time splitting strategy. Assuming a multihop secondary network, we derive an analytical expression for the outage probability experienced by a secondary user by taking into account the effect of interference power from primary source. The developed outage probability model can be used to assess the impact of some key parameters on the reliability of the secondary user’s link in an EH-CRN. We then investigate the optimal location of the relay node in a one dimensional two-hop secondary network that minimizes the outage probability. Next, we study how the various system parameters such as energy harvesting efficiency, path loss exponent, harvest-to-transmit time duration ratio and transmit power from primary source affect the optimal relay location. The outage improvement achieved when the relay is placed at the optimum location is also investigated. Furthermore, the sensitivity of optimal relay location to the variations in position of the primary receiver is examined. Extensive simulation results are used to corroborate the analytical findings.     

Performance of cognitive relay network with energy harvesting relay under imperfect CSI

This paper evaluates the performance of an underlay cognitive relay network under imperfect channel state information (CSI) where a secondary user (SU) transmits using a secondary relay (SR) based on decode and forward scheme. The outage probability (OP) of SU is investigated in a scenario where the decode and forward relay harvests energy from radio frequency signal of SU. The relay uses a fraction of time for harvesting in time switching–based relaying (TSR) while a fraction of received power is used for harvesting in power splitting–based relaying (PSR) scheme. The SU and relay control their transmit power using a scaling factor, based on CSI of the interfering links (ie, links from SU transmitter and SR to the primary user [PU] receiver) to protect the quality of service of PU. The available CSI at the SU and SR are imperfect due to practical limitation. Analytical expressions of the OP are derived for TSR‐ and PSR‐based schemes. The impact of harvesting time, power splitting ratio, imperfect CSI, PU outage constraint and interference threshold on the OP of the SU network, and average transmit power of SR is indicated. Further, the impact of multiple SRs is also shown.     

Outage performance of relay selection with spatially random relays using RF energy harvesting

To enable green wireless networks, one appealing approach is to deploy energy harvesting (EH) relays to assist the source transmission. Unlike conventional relays relying on fixed power supplies, EH relays make use of the energy collected from the RF radiation of the source node, and thus, they do not introduce extra energy cost to the network. This paper presents an analytical study to assess the efficacy of EH relays when the one with the maximal end‐to‐end signal‐to‐noise ratio is selected to perform data relaying while others perform EH. Because the action (either harvesting energy or forwarding data) of one EH relay affects those of others, exact performance analysis is not tractable. Additionally, relay density and positions may be random, which further complicates the analysis. Our analysis is conducted based on the hypothesis that each EH relay has an equal chance to be selected. This hypothesis allows for analytical tractability and is of importance to EH relays because otherwise some may drain their batteries fast. We identify the conditions under which the aforementioned hypothesis is valid. Our analysis also considers two variants of amplify‐and‐forward relays with and without using channel state information. Numerical results are presented to validate the analysis accuracy along with extensive discussions on the impact of numerous system parameters. Copyright © 2015 John Wiley & Sons, Ltd.     

On outage minimization in RF energy harvesting relay assisted bidirectional communication

This paper explores an end-to-end outage probability experienced in a bidirectional relay assisted communication where the relay is assumed to be equipped with an RF energy harvesting circuit. First, the closed-form expression for the outage of the system is derived. This is followed by the formulation of an unconstrained optimization problem to achieve minimum outage probability with respect to the relay placement and consequent time allocation for energy harvesting. The system model is further extended in an underlay cognitive radio framework to study the impact of a primary user outage constraint on the end-to-end outage performance of the two-way communications. The accuracy of analytical results is validated through simulation results. The impact of various system parameters like relay position, time allocation factor, target rate of transmission on the outage probability is also observed. In addition, it is also shown that spectral efficiency of the communication system using hybrid power-time switching relaying protocol is much superior to similar one-way and two-way relay assisted communication system with power splitting relaying protocol.

     

Impact of residual transmit RF impairments on energy harvesting relay selection systems

In this paper, we study the impact of residual transmit radio-frequency impairments (RTRIs) on a dual-hop energy-harvesting system in which a source and a destination both having multiple antennas communicate to each other with the help of single-antenna amplify-and-forward (AF) relays. The source and destination employ maximum ratio transmission (MRT) and maximal ratio combining (MRC), respectively, to exploit the benefits of using multiple antennas. To simplify the system complexity, we propose two partial relay selection (PRS) schemes (RSSs) that maximise the combined channel gains of the first hop (PRS-1 scheme) and the second hop (PRS-2 scheme), respectively. Both time-switching relaying (TSR) and power-splitting relaying (PSR) protocols are examined. In order to evaluate the system performance, the analytical expressions for outage probability and ergodic capacity are derived, and then the throughput expressions for delay-limited and delay-tolerant transmission modes are formulated. The analytical results are validated by Monte Carlo simulations. Our results show that: (1) The impact of RTRI can be significantly reduced by increasing the number of antennas and relays. (2) The PRS-1 scheme outperforms the PRS-2 scheme. (3) In the delay-limited mode, the TSR protocol performs better than the PSR protocol at high impairment levels, whereas in the delay-tolerant mode, the throughput of the PSR protocol is superior to that of the TSR protocol.     

Performance and optimization of hybrid FSO/RF communication system in varying weather

Photonic Network Communications - Radio frequency (RF) spectrum is already dense enough and hard to add more broadband channels to meet the current user demands. Optical free-space communications...     

基于大气信道链路的混合FSO/RF系统性能分析

提出了新的混合FSO/RF系统信道模型,此模型不仅克服了雾和雨对链路的严重影响,而且降低了系统的能量衰减,提高了系统的可用性.该系统在接收端探测器采用比较光电流大小来选择适合信道传输的链路,克服了各种天气状况的影响,最大限度地满足用户对通信性能的要求.     

Performance optimisation of RF energy harvesting relay-based interweave/underlay cognitive radio network

This paper investigates the performance of energy harvesting (EH) relay-based interweave/underlay cognitive radio network. The relay employs amplify and forward (AF) technique along with time-switching relaying protocol (TSR) for EH. Based on sensing accuracy, we derive an expression for optimisation of charging duration TSR parameter and sensing duration for maximising throughput of interweave cognitive radio (CR). Based on sensing efficiency, throughput and outage probability for underlay CR is analysed considering the interference temperature constraints and optimal power distribution parameter at secondary user (SU) terminals. Variations in the sum-rate and detection probability are considered in terms of cumulative distribution functions (CDF) of the terminal Signal to Noise Ratios (SNRs). We prove that erogodic sum-rate is maximised in underlay CR case, when interference power distribution parameter is half across the SU terminals. The optimised values of switching-time ratios have been derived analytically for both interweave and underlay CR. The results thus obtained are compared by taking symmetrical and asymmetric channels between SU terminals. Analytical results are validated through Monte-Carlo simulations to confirm the accuracy of the derived expressions.