衰落信道下基于簇的协作频谱感知分析

在分布式协作频谱感知网络中,认知用户向融合中心上报本地检测的信道是带宽受限的,并且受各种衰落的影响。分析了衰落信道下认知用户通过"与"规则进行融合的协作感知策略,提出了认知用户间为Nakagami信道时基于簇理论的协作感知方案,推导得出了2种方法的检测概率和归一化平均感知比特数。仿真结果表明,基于簇理论的协作感知通过牺牲一定的信令开销得到较好的感知性能。     

衰落信道下的协作频谱检测及其性能分析

在低信噪比和复杂性环境下,协作频谱检测是准确实现频谱感知的有效手段。文中分析了基于能量检测的单用户频谱检测算法以及基于硬判决和等权重的多用户协作频谱检测技术,导出了在高斯信道、Rayleigh衰落信道和Nakagami-m衰落信道情况下协作频谱检测虚警概率和漏检概率的闭合解析式,并对此进行了仿真验证和比较。结果表明,等权重协作频谱检测算法能够有效克服衰落信道对频谱检测的影响。     

Spatial-Temporal Cooperative Spectrum Sensing in Flat Fading Channels for Cognitive Radio Using Extend Kalman Filter

This paper investigates a new channel gain map tracking by Space-Time Extended Kalman Filtering (STEKF) for a flat channel, and a novel spectrum sensing via Time Spatial Weighted Non-negative Lasso (TSWNL) algorithm. STEKF enables CRs to estimate and interpolate channel gain map for the entire geographical area of interest with a limited number of CRs measurements. In order to sense primary users (PU) activities, include the transmission power by each PU, location and number of active PUs, TSWNL algorithm is proposed. Numerical results illustrate that the proposed STEKF channel estimation and TSWNL sensing algorithms outperforms linear methods.     

Performance of Cooperative Spectrum Sensing Under Rician and Nakagami Fading

In a dynamic spectrum access (DSA) network, a secondary user (SU) that deploys a simple energy detector could access the unoccupied spectrum upon sensing the absence of primary signal. However, sensing accuracy could be compromised due to signal fading. For improved accuracy, cooperative spectrum sensing (CSS) has been proposed, where spectrum occupancy is decided based on the combined results from multiple SUs. Two combining techniques that are commonly used are equal gain combining (EGC) and selection combining (SC). In this paper, we investigate the performance of CSS that implements (i) EGC, and (ii) SC technique, over independent and identically distributed (i) Rician, and (ii) Nakagami fading channels, which can model fading conditions that are less or more severe than the commonly used Rayleigh distribution. Novel expressions for the probability of detecting primary signal, P _d , have been derived and numerically evaluated.     

Cooperative Spectrum Sensing Optimization Using Meta-heuristic Algorithms

Wireless Personal Communications - Spectrum sensing helps to sense the unutilized spectrum in an opportunistic manner for cognitive radios. The various cognitive radios work in a cooperative manner...     

Optimization of Linear Cooperation in Spectrum Sensing Over Correlated Log-normal Shadow Fading Channels

The objective of cooperative spectrum sensing is to collaboratively detect the presence of the primary user by the aid of multiple secondary users. It is known that the performance of such a framework substantially depends on the fading assumption. In this paper, we propose an advanced framework for linear cooperative spectrum sensing in cognitive radio networks over correlated log-normal shadow fading channels. Considering the realistic sensing and reporting channels which are not addressed in similar works, motivates us to propose a novel approximation for correlated log-normal sum based on moment generating function calculation and moment matching method. Furthermore, the linear cooperative spectrum sensing coefficients are computed based on the optimization of the deflection criterion. This results in a framework with reasonable complexity which is suitable for practical applications. Simulation results show the excellent agreement between the exact and approximated statistics and the superior performance compared with conventional equally gain combiner.     

Performance Analysis of Relay-Assisted Cooperative Systems in Correlated Fading Channels

In this paper, the effect of fading correlation at the receiving elements of a linear antenna array in a relay-assisted cooperative single-input multiple-output (SIMO) system has been investigated over flat Rayleigh fading channels. Considering a model of local scatterer around the source and relay nodes and uniform angle of arrival (AOA) distribution, the spatial cross-correlation analysis is presented and extensive simulation studies are performed to determine the envelope correlation as a function of antenna spacing, mean AOA and angular spread. Error performance analysis for coherent binary and quaternary modulations are presented for fixed-gain amplify-and-forward (AF) and fixed decode-and-forward (DF) relaying with dual diversity maximal-ratio combiner (MRC) receiver array. Error probability in terms of bit error probability (BEP) and symbol error probability (SEP) is evaluated to study the effect of relevant parameters on the correlation performance. The presented results establish the fact that fixed DF relay network performs relatively well than fixed-gain AF relaying. Superior performance of dual-hop cooperative SIMO system over conventional single-hop SIMO system has also been observed.     

选择性放大传送协同通信在Nakagami信道中的性能分析

该文根据两个统计独立非负随机变量的调和平均值的概率密度函数在零点的变化特性,分析了选择性放大传送协同协议在Nakagami衰落信道中的性能,得出了高信噪比时系统误符号率的闭合表达式。理论分析和数值仿真结果表明,在Nakagami信道中选择性放大传送协同协议可获得和传统放大传送协同协议一样的分集阶数,并且具有更优的误符号率性能。     

一种认知无线网络中的协作感知优化方法

认知无线电技术能够显著提高频谱资源的利用率,因此越来越受到学术界的关注。频谱感知是认知无线电的基础,一方面它要求能够快速找到可用频谱,另一方面当授权用户返回时又要求能够快速释放信道避免干扰。提出了一种认知无线网络中多用户协作感知分级方法,并通过数学推导给出最优的分级策略。仿真结果表明,采用所提出的协作频谱感知方法,能够提高认知无线网络的吞吐量。     

基于删除的协作频谱感知分析与优化

能量消耗是协作频谱感知中一个需要重点考虑的问题。为了降低信息上传能耗以延长认知无线网络中能量受限次用户的寿命,该文提出一种新的基于删除的协作频谱感知方案,其核心思想是各次用户仅当感知结果与其前一次不同时才向融合中心发送一个指示信号,否则不发送。对比分析了该方案中的上传能耗问题,并以保证主用户利益为约束条件,给出了频谱感知周期和能量检测门限的优化过程。理论分析和仿真结果表明,相比现有研究,提出的方案可以有效降低次用户的上传能耗而不带来任何感知性能的损失。     

Energy Efficiency in Cognitive Radio Network Using Cooperative Spectrum Sensing

Wireless Personal Communications - In this paper, we consider an optimization of number of secondary users (SUs) in a cooperative spectrum sensing by maximizing the energy efficiency of the...     

Performance Analysis of Generic Amplify-and-Forward Cooperative Networks over Asymmetric Fading Channels

In this paper, we analyze the performance of multi-hop multi-branch amplify-and-forward (AF) networks over generalized fading channels. Using the moment generating function (MGF)-based approach, we develop general expressions for the outage probability and symbol-error rate (SER) performance of the system with maximal ratio combining (MRC) receiver. The MGF-based approach relies on numerical integration. To gain insights into system performance, we therefore investigate the asymptotic outage and SER performance of the system with MRC and selection combining (SC) receiver at the destination. In particular, we develop the asymptotic statistics of the end-to-end signal-to-noise ratio (SNR) of an AF multi-hop link. We further derive the cumulative density function of the sum of the individual end-to-end SNRs, received from different diversity paths for MRC receiver. We also study the power allocation problem in a multi-hop multi-branch system with MRC receiver. In generalized Gamma fading environments, we seek to find the power allocation strategy that maximizes the SNR at the destination subject to a total power constraint. By means of simulations, we validate our theoretical developments and verify the efficiency of our proposed power allocation in improving the received SNR compared to a generic cooperative system with no power allocation. We also conclude that our asymptotic expressions for the outage probability and SER match the simulations very well in medium-to-high-SNR regime.     

一种基于中继的认知无线电网络合作频谱感知方法

文章提出一种新的合作感知方法,实现网络中一个认知用户与多个中继用户的合作。认知用户通过能量检测选择中继用户,根据可信度对中继用户进行筛选,采用＂大多数＂准则对感知结果进行融合。仿真结果表明,与独立检测和传统的合作检测相比较,该方法具有更高的检测性能与频谱利用率。     

衰落环境下一种高能效协作频谱感知算法

在认知无线网络中,对于电池供电的认知设备,如何高效地利用其能量资源极为重要。在将能量效率(能效)定义为认知网络频谱利用效率和平均功率消耗之比的基础上,提出了一种高能效优化算法,在加性高斯白噪声(AWGN)信道、Rayleigh衰落信道和Nakagami衰落信道条件下使融合中心门限达到最优,并求得了最佳的参与协作的用户数。通过蒙特卡洛仿真对认知网络的能效进行了性能评估,结果表明所提算法能有效提升认知网络的能量效率。     

Performance Analysis of Cooperative ARQ with Code Combining over Nakagami-m Fading Channels

This paper presents the performance of cooperative ARQ schemes in Nakagami-m fading networks, where coherent equal gain code combining is adopted to combine the retransmitted signals at the destination. Two different retransmission protocols are adopted upon the reception failure of the destination. Once the relay node can decode correctly, the retransmission will be performed by relay in protocol I or the better node between source and relay in protocol II, where the better means having a better channel to the destination. By approximating the product of two independent Nakagami-m random variables to the sum of two independent gamma random variables, the performance of protocol I is derived at high signal-to-noise ratio (SNR). We further develop the approximation for the product of two maximum Nakagami-m random variables, which is employed to obtain the performance of protocol II at high SNR. The reliability of theoretical analysis is validated by simulation results, where the advantages of these two protocols upon the conventional protocols are presented.     

认知无线网络中动态双门限协作频谱感知性能的优化方案

频谱感知作为认知无线电的关键技术,得到广泛深入的研究。其中衡量协作频谱感知性能的主要参数为全局虚警概率和全局漏检概率,它们之和被定义为全局错误概率。本文研究基于双门限能量检测的协作频谱感知性能的优化方案,首先,固定双门限能量检测的检测门限值,对表决融合准则的投票门限进行优化,使得在该能量检测门限值条件下,协作频谱感知的全局错误概率最小;然后在表决融合准则的投票门限取最优值的前提下,对双门限能量检测的检测门限值进行了优化,在不同接收信噪比条件下,最优的检测门限值是动态的,所以要根据信噪比确定最优的检测门限值,使得协作频谱感知的全局错误概率在各信噪比条件下都达到最小值,从而提高了协作频谱感知的性能。仿真结果表明,表决融合准则的投票门限和双门限能量检测的检测门限值取得各自的最优值时,全局错误概率最低,检测性能最好。      

Performance Evaluation of Cooperative Spectrum Sensing Scheme with Censoring of Cognitive Radios in Rayleigh Fading Channel

In this paper, the performance of cooperative spectrum sensing (CSS) with censoring of cognitive radio (CR) users in Rayleigh fading channel is analyzed. More precisely, CR users which employ energy detectors are censored depending on the quality of radio channels between them and a fusion center (FC). Each CR makes a hard decision about primary user (PU) using energy detection and transmits the information to FC using BPSK signaling if that CR user is selected to transmit. A training based channel estimator is used at the FC to estimate the complex Gaussian fading coefficients characterizing the channels between the CR users and the FC. This channel state information on fading coefficients is used for censoring the CR users. Two fusion rules such as majority logic fusion and maximal ratio combining (MRC) fusion rules are applied at the FC for estimating the performance in terms of probability of missed detection (P_m). We develop a simulation test bed for evaluating the performance of CSS scheme. Probability of missed detection has been evaluated for both perfect and imperfect channel estimation for various probabilities of false alarm (P_f), reporting and sensing channel SNR values.     

协作频谱感知在认知网络中的应用

认知无线电能够灵敏感知周围环境的变化,通过频谱感知功能发现频谱空洞,使得认知无线电能够与周围通信环境相适应。在认知无线电网络中,认知用户（次用户）必须连续地监控频谱,检测主用户是否存在。如果主用户存在,次用户必须尽快地退出该频段,从而不影响主用户。在文中采用一种协作机制,即两用户进行协作频谱感知,从而提高主用户的检测率,减少了检测时间,并且得到捷变增益。我们用Matlab给出仿真结果。     

基于瑞利多径衰落信道的信号包络频谱感知

为提高信号采样值之间的相关性和降低噪声对感知性能的影响,该文提出基于信号包络自相关矩阵的频谱感知算法。首先对采样信号等间隔时长截取,以相邻间隔的采样值计算信号自相关性,并构造出近似自相关矩阵。其次依据矩阵次对角线元素性质构造了统计量。分别计算了该统计量的检测概率分布函数与虚警概率分布函数,分析了频谱感知算法的检测性能,算法优化了信号相关性的计算,降低了噪声对感知性能的影响。最后通过仿真验证了不同参数对检测概率和虚警概率的影响,并提出了进一步提高检测性能的措施。

     

周期性协作频谱感知机制的优化

为了提高检测性能和频谱资源利用率,对认知无线电网络中的周期性协作频谱感知机制进行了研究.针对不同的衰落信道环境,通过引入有效传输时长比例和干扰时长比例作为次用户服务质量的衡量标准,给出了集中式协作感知下的检测时长、数据传输时长以及协作用户数量等参数的最优选取方法,从而获得最高的信道效率.仿真结果表明,通过选取最佳的协作...