基于传输中断概率的认知无线电系统性能分析

如何设计最优的频谱感知与传输框架是认知无线电技术的重要环节。考虑频谱接入过程中数据传输中断对认知网络性能影响的问题,提出了一种新的基于传输中断概率的频谱感知与传输模型,联合优化频谱感知和数据传输两个阶段,将问题建模为对主用户的干扰量约束条件下的非凸优问题,以最大化认知网络吞吐量为目标联合优化感知时间、传输速率,并通过数值计算方法对其进行求解与仿真。数值分析表明,引入传输中断概率后,在满足上述约束条件的同时,在保护主用户和认知网络吞吐量、传输时延之间有了更好的权衡。     

基于放大重传的认知共存网络传输容量分析

采用随机几何方法对认知共存网络中认知用户对主用户造成的累加干扰进行建模,并在无衰落信道和瑞利衰落信道中分别分析了主用户采用放大重传协作通信模式下的中断概率和传输容量。仿真结果表明,放大重传模式可以有效降低共存网络中主用户的中断概率、提高主用户的传输容量,且易于实现。     

认知无线Ad Hoc网络单跳传输容量的研究

研究了认知无线电AdHoc网络的单跳传输能力,该网络与主用户网络工作在同一地理区域和共享同一频谱。主用户网络具有更高的优先级访问认知用户网络频谱,认知网络需要控制其发射机密度以限制对主用户干扰。认知、主用户节点位置假设服从泊松点分布,推导了认知、主用户网络单跳传输容量,最后进行了仿真验证其正确性。仿真结果表明:主用户网络传输容量随主用户中断概率增加而增加,随增量中断概率的增加而降低。认知用户网络传输容量仅由次用户中断概率参数决定。     

认知中继网络中认知用户基于频谱感知机会中继的中断性能分析

认知无线电中继网络中,认知用户需要成功感知到其所在簇内的主用户频谱空穴后才能成为认知中继节点,且各认知中继节点发射功率受到各自主用户干扰温度限制(ITC)。该文对认知中继节点采用分布式空时编码和解码转发协议时认知用户的中断性能进行了分析;给出了认知用户在干扰温度限制下中断概率的上下界,得出中断概率的上下界在不同干扰温度限下与认知用户归一化数据速率、中继数量和其对主用户检测概率的关系。给出了源节点和频谱感知中继节点在相同干扰温度限下的数值仿真,并对仿真结果进行了分析。     

认知频谱共享系统最大比例合并分集的性能分析

研究了一个认知频谱共享系统,该系统是由一个次用户发射机、一个次用户接收机和一对主用户发射机和接收机组成,次用户接收机利用最大比合并策略提高系统性能。首先分析了来自主用户发射机的干扰对频谱共享系统中断概率的影响。经过一些运算得到了中断概率确切的封闭表达式,为评价系统关键参数的联合作用提供了有效手段,如次用户接收机天线的数目、次用户最大的发射功率、干扰温度限制以及主用户发射功率等。另外,还对系统中断概率的渐近性能进行了研究,揭示了次用户系统中断概率具有饱和现象。最后,分析了该系统分集复用增益。仿真结果表明,该中断概率确切封闭表达式与Monte Carlo仿真结果非常吻合,干扰温度约束和主用户的干扰对中断概率具有显著的不利影响,增加次用户接收机的天线数目可提高系统性能。     

多天线频谱共享认知网络保密中断概率分析

针对单输入多输出认知无线电网络,研究了瑞利衰落信道下采用最大比合并时保密中断性能。在所研究的系统中,次用户发射机发送机密信息给另一个次用户接收机,次用户接收机配备多个天线并且采用最大比例合并多个接收信号。同时,拥有多个天线窃听者也采用最大比合并方案偷听次用户发射机和次用户接收机之间传送的信息。频谱共享下次用户发射机工作时必须保证主用户的服务质量。推导了保密中断概率的精确表达式,分析了系统保密中断概率渐近性能。仿真结果验证了分析的正确性。     

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.     

新的认知无线电功率控制博弈算法

针对认知无线电系统中各种用户通信需求,采用多载波的码分多址(MC-CDMA)认知无线电(CR)系统,研究如何克服认知用户对主用户干扰和通信中断问题,给出了一种认知用户切换策略,为实现认知频谱资源的有效分配,提出了一种新的认知无线电功率控制算法。仿真结果表明,该算法既满足不同种类用户SIR要求,又达到了系统吞吐量的提高,实现了对不同用户发射功率有效控制,系统性能明显提高。     

认知无线电非正交多址接入随机网络物理层安全性能分析

该文针对干扰源以及窃听节点均随机分布的通信场景,分析了认知无线电启发式非正交多址接入(CR-NOMA)网络中次用户通信对的安全通信性能。采用随机几何理论,将窃听节点和干扰节点建模为服从特定分布的齐次泊松点过程(PPP)。首先,在保证主用户通信对通信可靠性的前提下,得到了发端设定的功率分配系数,进一步得到了次用户通信对的连接中断概率和安全中断概率的闭式表达式。随后,得到了功率分配系数随主用户可靠性能约束的变化规律。最后,研究了次用户对的中断概率随着窃听节点密度、发端发送功率的变化情况,结果表明干扰信号的增强在降低网络可靠性能的同时,换来了安全性能的提高。仿真结果验证了理论分析的正确性。     

基于空时聚焦传输的多源单中继超宽带网络传输性能分析

超宽带空时聚焦传输降低了多用户传输时的互相干扰,可以让多个源节点和多个目的节点通过一个中继节点进行通信。研究了基于空时聚焦传输的多源单中继超宽带网络的传输性能,分别推导了多址阶段和广播阶段的中断概率,得到了网络吞吐量与用户数目、节点距离、超宽带脉冲宽度、信号帧周期、接收信干噪比等参数之间的解析关系,并通过最大化网络吞吐量以及优化结果分析得到了传输方案的设计准则。最后,仿真结果验证了不同路径损耗因子下2个阶段的中断概率。     

Opportunistic power allocation strategies and fair subcarrier allocation in OFDM-based cognitive radio networks

In this paper we have studied the subcarrier and optimal power allocation strategy for OFDM-based cognitive radio (CR) networks. Firstly, in order to protect the primary user communication from the interference of the cognitive user transmissions in fading wireless channels, we design an opportunistic power control scheme to maximize the cognitive user capacity without degrading primary user’s QoS. The mathematical optimization problem is formulated as maximizing the capacity of the secondary users under the interference constraint at the primary receiver and the Lagrange method is applied to obtain the optimal solution. Secondly, in order to limit the outage probability within primary user’s tolerable range we analyze the outage probability of the primary user with respect to the interference power of the secondary user for imperfect CSI. Finally, in order to get the better tradeoff between fairness and system capacity in cognitive radio networks, we proposed an optimal algorithm of jointing subcarrier and power allocation scheme among multiple secondary users in OFDM-based cognitive radio networks. Simulation results demonstrate that our scheme can improve the capacity performance and efficiently guarantee the fairness of secondary users.     

Secrecy outage analysis in a hybrid cognitive relay network with energy harvesting

In this paper, we investigate the physical layer security of a hybrid cognitive relay network using an energy harvesting relay in presence of an eavesdropper. In the hybrid scheme, a secondary user (SU) as well as a cognitive relay works either in underlay or in overlay mode. In underlay, the transmit power of the SU as well as the relay is limited by the maximum acceptable interference at primary user (PU) receiver as required by an outage constraint of PU, a quality of service for PU. The secondary network consists of a decode and forward relay that harvests energy from radio frequency signal of secondary transmitter as well as PU transmitter to assist the SU in forwarding the information signal to the destination. A time switching relaying protocol is used at the relay. We evaluate the secrecy outage probability of secondary relay network assuming that channel state information of the interfering links from both the SU and relay transmitter to PU receiver is imperfect. Our results reveal the impact of imperfect channel state information, energy harvesting time, tolerable interference threshold, and PU outage constraint on the secrecy outage probability of SU.     

Auction-Based Throughput Maximization in Cognitive Radio Networks Under Interference Constraint

Cognitive radio is an emerging technique to improve the utilization of radio frequency spectrum in wireless communication networks. That is, spectrum efficiency can be increased significantly by giving opportunistic access of the frequency bands to a group of cognitive users to whom the band has not been licensed. In this paper, as a cross layer application (MAC and physical layers) of graph theory, we consider the problem of throughput maximization of spectrum allocation in cognitive radio networks under interference constraint. We propose a novel auction-based channel allocation mechanism which tries to maximize both total and primary users’ utilities while satisfying signal to interference ratio constraint on primary receivers so that transmitted packets will be successfully received, without controlling secondary user powers. For comparison we discuss a greedy algorithm as well, however, one that does not handle interference issue. In order to compare results of proposed and greedy algorithms, we propose net throughput by taking into account outage probability of primary receiver. Simulation results show that exposing higher SINR (outage) threshold not only decreases total gain and primary users’ utilities but also worsens channel distribution performance. On the other hand adding auction mechanism significantly increases total gain throughput and primary user’ s utility. Particularly, up to SINR threshold values of 20 dBs, auction provides outstanding performance and proposed algorithm has total throughput results close to those of the greedy one even though no interference constraint is applied in the greedy algorithm. Another noticeable point of simulation results is crossover of net throughputs of proposed and greedy algorithms at a SINR threshold level after which results of ABSA-UNIC and NASA-UNIC are much better. This clearly shows superiority of proposed mechanism.     

Analysis of Network Path Selection Based on Outage Probability in Cognitive Relay Networks

This paper evaluates the outage performance of cognitive relay networks with mutual interference between secondary users and primary users under the underlay approach, while adhering to the interference constraint on the primary user. A network path selection criterion, suitable for cognitive relay networks, is provided, from which we derive the outage probability expression of cognitive relay networks. It is shown that the outage probability considering the interference to secondary user from primary user is higher than that without considering the interference to secondary user from primary user. In addition, the outage probability is affected by key network parameters. We analyze network path selection method based on outage probability and prove that the interference to secondary user from primary user has a significant effect on the network path selection and can not be ignored in practical wireless communication environments. Simulation investigation is also provided and used to verify the theoretical analysis.     

Impact of Quality of Service Constraints on the Performance of Spectrum Sharing Cognitive Users

This article investigates the impact of choosing a specific quality of service constraint on the performance of the cognitive users in a spectrum sharing cognitive environment. To communicate over a wireless channel reserved to a primary user, the cognitive user has to satisfy the primary user’s quality of service constraint. Cognitive systems under interference temperature and outage probability constraints are investigated in this work. The outage probability of the primary user in an interference temperature-constraint environment is analyzed, and the performance measures of the cognitive users are developed. A comparative study of the cognitive user’s performance under equivalent outage probability and interference temperature constraints is conducted as well. Numerical results are presented to verify the theoretical analysis and compare the performance measures under these constraints. Results of this work illustrate the effects of the communication environment parameters on the cognitive users and detail the performance differences between the equivalent outage probability-constraint and interference temperature-constraint cognitive systems.     

Optimal cooperative strategy based on quantum bat for cognitive radio of energy harvesting

In order to reduce energy consumption and improve spectral efficiency of the cognitive relay wireless communication system in 5G network,an optimal cooperative transmission strategy of information and energy was designed for cognitive relay radio with wireless energy harvesting.For the proposed optimal cooperative strategy,the maximal throughput formula and outage probability of secondary user were deduced.In order to resolve the derived maximum throughput equation,a quantum bat algorithm which was based on the optimization mechanism of quantum computing and bat algorithm was designed to solve the deduced equation,and the optimal cooperative transmission scheme for information and energy could be obtained.Simulation results show that the proposed optimal cooperative strategy not only can meet the information transfer demand of primary user,but also can realize the energy self-supply of the secondary user system and improve the communication quality of the secondary user.The proposed optimal cooperative strategy has a better performance than the cooperative strategy of existing cognitive relay radio for different simulation scenarios.     

Secrecy performance analysis on cooperative CR-NOMA network

In order to improve the secrecy performance of communication system and make efficient use of limited spectrum,overlay cognitive radio (OCR) technology was combined with non-orthogonal multiple access (NOMA) technology and the communication model was proposed,in which secondary network realized dynamic switching between assisting primary network communication and secondary network communication by sensing whether the primary user occupied the spectrum or not.Artificial noise (AN) aided technology was used in primary and secondary networks respectively to further improve the secrecy performance of the system.The secrecy performance of the system was studied by deducing the expressions of the primary and secondary network secrecy outage probability and secrecy throughput respectively.The simulation results show that the proposed cognitive cooperative NOMA communication scheme is beneficial in reducing secrecy outage probability and increasing secrecy throughput.Furthermore,the influence of AN power allocation factor on system performance is given.     

Wireless powered underlay cognitive radio network with multiple primary transceivers: Energy constraint,node arrangement,and performance analysis

This paper considers a cognitive radio–assisted wireless information and power transfer system consisting of multipair of transceiver in primary network and 2‐hop relaying link in secondary network. In this investigation, a decoded‐and‐forward–assisted relay node and power splitting protocol are deployed to obtain ability of wireless energy transfer. The relay node harvests energy from the radio frequency signals of the secondary transmitter and primary transmitters in data transmission to the destination by reusing the licensed spectrum resource. We propose 2 policies for wireless power transfer at the relay, namely, (1) multisource power transfer and (2) single‐source power transfer. To evaluate performance under energy harvesting regime, we derive the closed‐form outage probability expressions and achievable throughput of the secondary network in delay‐limited transmission mode. In addition, we investigate the impact of various system parameters including number of primary transceivers, primary outage threshold, and position arrangement of nodes in primary transceivers on the outage performance of the proposed scheme. Furthermore, we evaluate the system energy efficiency to show trade‐off metric of energy consumption and throughput. Performance results are presented to validate our theoretical derivation and illustrate the impacts of various system parameters. An important result is that the secondary network is more beneficial than harmful from the primary interference under power constraint and reasonable node location arrangement.