A Channel Hopping Algorithm for Guaranteed Rendezvous in Cognitive Radio Ad Hoc Networks Using Swarm Intelligence

Wireless Personal Communications - Achieving fast Time to Rendezvous (TTR) on a common coordination channel in an Ad hoc network remains a contemporary issue in Cognitive Radio research. In this...     

Channel Allocation with MIMO in Cognitive Radio Network

Wireless Personal Communications - The bulk volume and diverse data generated by Smart grid applications require use of Cognitive Radio (CR) technology for efficient handling. The CR technology...     

Channel Selection Algorithm Optimized for Improved Performance in Cognitive Radio Networks

Wireless Personal Communications - A major concern in the recent past was the traditional static spectrum allocation which gave rise to spectrum underutilization and scarcity in wireless networks....     

认知无线网状网中基于差分演化的功率控制与信道分配

信道分配对于提高认知无线网状网性能具有重要作用.考虑到节点功率对网络干扰的影响,定义了网络干扰边及潜在干扰边,通过量化通信功率控制等级,给出了联合功率控制与信道分配的网络模型.提出一种基于差分演化的功率控制与信道分配算法,设计了实数编码规则及相应的约束控制机制以保证个体的有效性,确保算法的快速收敛.一系列仿真实验表明本文算法的有效性.     

认知无线电网络中基于强化学习的智能信道选择算法

认知无线电系统不仅要具有自适应性,更应具备一定的智能性。该文将强化学习理论引入到认知无线电系统中,用于解决次用户在频谱感知过程中的信道选择问题,提出了一种基于强化学习的信道选择算法。该算法在未知主用户占用规律和动态特性的前提下,仅通过不断与环境进行交互学习,便能够引导次用户选择“较好”信道优先进行感知,使次用户吞吐量得到提高。仿真结果表明,相对于现有信道选择算法,所提算法可有效提高次用户的吞吐量,并且在主用户使用规律发生变化时,能够自动实现二次收敛,可作为认知无线电系统迈向智能化的一种尝试。      

认知无线网络中基于信道感知排序的频谱切换

在认知无线网络中,一旦主用户出现,正在使用该频段的认知用户需退出该频段,寻找另外一个空闲的频段继续未完成的传输,这就是认知无线网络中的频谱切换。评价认知用户频谱切换性能有两个重要的参数:切换时延和切换次数。本文提出了一种基于信道感知排序的频谱切换方法,以同时减少切换时延和切换次数。在进行信道感知排序时,本文使用的方法同时考虑了切换发生时信道空闲概率以及使用该信道时不再发生切换的概率。仿真结果表明,与传统信道排序方法相比,本方法的切换时延可以达到与传统方法一样的性能,然而切换次数却大大地减少了。     

一种短波跳频通信网的信道混合分配算法

基于最大包(MP)和顺序包(SP)的分配策略,在信道的分配问题上,以平均需求向量作为固定分配(FCA)的基点,以需求向量的增量作为动态分配(DCA)的出发点,将二种策略相结合形成的混合信道分配算法(SP-MP算法)。对该分配算法的单个小区分配阻塞概率进行了推导,并对短波跳频通信网进行了数值计算与分析,结果表明:在特定信道条件下,利用该算法易于解决混合分配时对固定信道数目的确定。     

基于认知的拓扑生成与信道分配算法

认知无线电技术通过感知周围环境,自适应地调整拓扑结构和通信参数,可以有效地提高通信性能。由于环境的变化,尤其授权用户工作状态的变化,认知无线电网络的拓扑结构和信道分配结果也动态变化。主要基于图论模型研究最大化瓶颈链路吞吐率目标下的拓扑生成与信道分配问题。基于KM算法提出了干线节点和剩余节点的信道分配方法,仿真分析表明,可用信道比例较低时,EC、PCA、MDS、LTSA和DM方法可以在一定程度上提高组网的成功率。     

用于认知无线电的自适应双模跳频OFDM系统

认知无线电感知的空闲频谱具有非连续、非均匀特性,对认知无线电物理层实现提出挑战。跳频正交频分复用技术(Orthogonal Frequency Division Multiplexing,OFDM)兼具跳频与OFDM二者优势,适用于宽带无线传输。提出一种自适应双模跳频OFDM系统,即把射频跳频OFDM与基带跳频OFDM相结合,根据频谱感知信息和基带处理能力自适应地在2种模式间切换,给出系统的设计规则和实现流程。分析表明该系统可提高非连续、非均匀空闲频谱的利用率,是一种可行的认知无线电物理层实现机制。     

认知网络中基于簇结构的拓扑形成算法

在多跳的认知无线网络中,网络的拓扑发现算法都必须极其灵活以适应于环境内频谱空洞的改变。研究了认知无线电网络的基本特点,结合Ad-hoc网络簇的概念,在得到认知设备的感知结果的基础上,提出了一种适合于认知无线电网络的有效的拓扑形成算法。在提出的算法中,将可用的频谱空洞信息和节点的能量信息综合考虑,是一个组合的优化算法。     

一种适用于认知无线电系统的盲感知算法

频谱感知是认知无线电中最具挑战的问题之一。提出一种基于信号协方差矩阵特征值的盲感知算法,仿真显示这种方法有较好的检测性能,适用于认知无线电系统中授权用户的检测。     

Robust Probabilistic Distributed Power Control Algorithm for Underlay Cognitive Radio Networks under Channel Uncertainties

Due to limited cooperation among users and erratic nature of wireless channel, it is difficult for secondary users (SUs) to obtain exact values of system parameters, which may lead to severe interference to primary users (PUs) and cause communication interruption for SUs. In this paper, we study robust power control problem for spectrum underlay cognitive radio networks with multiple SUs and PUs under channel uncertainties. Precisely, our objective is to minimize total transmit power of SUs under the constraints that the satisfaction probabilities of both interference temperature of PUs and signal-to-interference-plus-noise ratio of SUs exceed some thresholds. With knowledge of statistical distribution of fading channel, probabilistic constraints are transformed into closed forms. Under a weighted interference temperature constraint, a globally distributed power control iterative algorithm with forgetting factor to increase convergence speed is obtained by dual decomposition methods. Numerical results show that our proposed algorithm outperforms worst case method and non-robust method.     

Optimal Pilot-Based Channel Estimation in Cognitive Radio

Cognitive radio (CR) technology is to assure the better utilization of the spectrum, permitting the non-licensed users to utilize the unused bands provided to the Licensed or primary users, which is made effective through the application of the Orthogonal Frequency Division Multiplexing (OFDM). The effective utilization of the OFDM channels through temporarily allocating the bands to the unlicensed users avoids interference. In order to ensure the reliable spectrum sensing in CR with effective spectral efficiency, the channel estimation (CE) is enabled in the OFDM-based multi-input and multi-output systems. The channel estimation is facilitated through the pilot-based sequential approach for the least square CE in OFDM-based CR. The optimal insertion of the pilots in the input data symbols before transmitting the signal through the fading OFDM channels in CR is made through the proposed rider grey wolf optimization, which is the integration of the grey wolf optimization and rider optimization algorithm. The estimation is done through the least square of the original channel state and the estimated symbols. The experimental analysis is progressed both in Rician and Rayleigh environments with minimal mean square error of 1.28E?06 and bit error rate of 0.000626.

     

Soft-Decision Algorithm in Radio Communication Systems with Frequency Hopping

Journal of Communications Technology and Electronics - An expression for soft decisions is obtained for incoherent demodulation of signals with m-digit frequency-shift keying in radio communication...     

New-User Detection in Time Hopping Multi-User Environment for UWB Impulse Radio Systems

This paper addresses the problem of detecting a new user in time-hopping multiple access communication environment targeted for ultra wideband impulse radio (IR) systems. The proposed detector is based on exploiting the orthogonality between the new user and the other active user(s) in frequency domain. This is because the time-domain orthogonality is destroyed due to the long delay spread of a dense multipath channel experienced by IR transmission. This results in the presence of inter-frame, inter-path as well as inter-symbol interferences. To ensure the frequency-domain orthogonality, we propose a TH code design as a means of encoding a unique spectrum that is orthogonal to each user. Simulation results highlight the note-worthy improvement in frequency-domain detection performance that utilizes our proposed design algorithm. This gain is obtained without any significant increase in computational complexity or hardware costs. Unlike the rake detector, the frequency-domain detector does not require the time-of-arrival information of the multipath components.     

An Energy-Efficient Model of Random Cognitive Radio Network: Rayleigh-Lognormal Environment

Wireless Personal Communications - Motivated by the current demand for improvements in transmission rate and energy efficiency of random wireless cellular networks, we investigate the theoretical...     

认知无线电频谱切换目标信道访问机制

针对认知无线电先应式决策频谱切换,该文提出按照信道平均空闲时间递减的顺序对目标信道进行访问的机制,证明了该机制在主用户信道空闲时间服从均匀分布、Rayleigh分布以及Weibull分布下均能够保证频谱切换失败概率最小。仿真结果表明所提机制得到的频谱切换失败概率要远远小于随机访问机制的切换失败概率。另外,当能够获得数十次信道空闲时间观测样本情况下,虽然存在估计误差,但所得频谱切换失败概率与理想最优频谱切换失败概率非常接近。