基于非理想感知的认知无线电系统感知时间与频谱分配联合优化算法

针对非理想感知情况下感知时间与频谱分配联合优化问题,同时考虑漏检与主用户重新占用频谱两种场景所造成的主次用户碰撞,并通过量化主用户对认知用户的干扰,给出有无主用户存在时认知系统可获得的吞吐量。在总传输功率约束以及对主用户的最大干扰功率约束两个限制条件下,以最大化系统平均吞吐量为优化目标,给出感知时间与频谱分配联合优化算法。算法首先通过折半法搜索最优感知时间,在既定的感知时间下,将子信道分配给能获得最大平均吞吐量的认知用户,在此基础上,利用凸优化相关理论求得最优功率分配。仿真结果表明,本文所提算法相比于传统频谱分配算法系统平均吞吐量性能提升了10%左右。     

MME频谱感知算法能量效率优化分析

绿色通信是未来无线通信发展的必然趋势,为了提高认知无线网络频谱感知算法的能量效率以及算法稳定性,实现低功耗绿色通信,该文在噪声不确定的实际环境下分析了基于特征值的最大最小特征值（MME, Maximum-Minimum Eigenvalue）频谱感知算法的能量效率,并利用黄金分割优化算法获得了使能量效率最大化的最优感知时间。理论分析和仿真结果表明,在噪声不确定的情况下,基于特征值的MME感知算法的能量效率要明显优于传统的能量检测算法,且MME感知算法不受噪声不确定性的影响,在低信噪比下具有更稳定的感知性能。      

基于能量收集驱动和信道感知的CRN

针对能量采集器供电的认知无线电网络进行了研究。首先,在采用离散时间马尔可夫链的建模基础上,通过分析认知用户在收集到的能量包和电池容量的限制下有效地利用能量,以最大化当前时隙的吞吐量。然后,找到多个信道的最优感知顺序和对应于该感知顺序下信道的最优传输能量集,得到使认知无线电网络在多个时隙的预期吞吐量最大化的递归表达式。最后提出了一种基于该递归表达式实现最大化预期吞吐量的算法。仿真实验结果表明,所提出的方案相比于其他方案,不仅提高了认知无线电网络的吞吐量,而且降低了主信道上的平均碰撞比。     

考虑恶意节点的CRN合作频谱感知方法

基于带有恶意节点的更为实际的频谱感知环境,研究了基于合作感知的频谱共享网络模型,次级用户将会根据合作感知结果动态地调整其发射功率。为了防止恶意节点对感知系统的感知性能造成严重影响,研究了如何进行合作感知以提高感知性能。在一定的检测概率和相关功率约束下,建立了一个以最大化次级网络的吞吐量为目标函数的优化问题。仿真实验首先突出说明了恶意节点数目对频谱感知影响重大,同时还表明无论是否存在恶意节点,提出的算法均可有效地计算出最优的感知时间和发射功率,且在降低最大干扰功率限制和最大发射功率限制时,网络的吞吐量是增大的。     

认知网中感知时间和功率控制的联合优化机制

针对认知无线网中为了最大化认知用户的吞吐量问题,提出了一种感知时间和功率控制的联合优化机制。该机制保证认知系统在低于一定干扰限制下,将认知用户吞吐量描述成为一个多约束优化问题,从理论上分析了最优功率分配方案与最优感知时间分配方案。根据理论分析结果,设计了联合迭代机制通过确定合适的感知参数从而达到最大化认知用户吞吐量的目的。仿真结果表明：提出的联合优化机制复杂度较低,并且该方案的认知吞吐量性能最接近理论最优方案的性能。     

基于认知无线电的双向中继网络的资源分配

针对认知无线电中的双向中继网络,研究了基于非完美感知的频谱机会式接入和频谱共享接入下的资源分配问题.与传统基于认知的双向中继的资源分配方法不同,提出的算法联合考虑了感知时间和次级系统的发射功率.在感知时间和发射功率满足条件的情况下,使次级系统的吞吐量最大.为了有效地保护主用户不受干扰,在每一跳都考虑了平均干扰功率约束,同时考虑次级系统总的功率约束.在非完美感知的频谱机会式接入和频谱共享接入机制下,新算法能够获得最优的感知时间和功率分配.最后,仿真比较了两种方案的性能,验证了新算法的有效性.     

一种新型的基于最大特征值的合作频谱感知算法

针对认知无线电中经典频谱感知方法的缺点,该文利用随机矩阵理论的相关研究成果,提出了一种基于采样协方差矩阵最大特征值与平均能量的合作频谱感知新算法。该算法将次用户接收信号协方差矩阵的最大特征值与接收信号平均能量的比值(Maximum Eigenvalue-Energy Detection, ME-ED)作为统计判决量,以此判决出主用户是否存在,从而实现频谱感知功能。理论分析表明,与经典频谱感知方法相比,ME-ED算法无需知晓主用户信号的任何先验知识及噪声功率。仿真结果显示,与MED算法和ED方法相比,该算法不仅对噪声的不确定性不敏感,而且在噪声存在波动的情况下,其感知性能最优,鲁棒性最强。     

碰撞冲突下认知无线网络能量效率分析

在认知无线网络的实际应用中,对于一些能量受限的认知用户来说,提高认知无线网络的能量效率尤其重要。该文从最大化认知无线网络能量效率的角度出发,考虑当认知用户在发送数据时突然出现的主用户信号引起碰撞冲突的情况,提出了对感知时间和帧周期进行分别优化和联合优化的单目标最优化问题,并进行理论推导分析。同时,实验仿真验证了理论分析的正确性。结果表明,能量效率分别随感知时间和帧周期的增大而先增大后减小,存在一组最优感知时间和帧周期使能量效率最大化。      

一种用于频谱感知的增强型能理检测算法

基于传统能量检测算法,提出了一种用于频谱感知的增强型能量检测算法,即利用对接收信号绝对幅度值的任意正数次方代替平方操作。在给定虚警概率时,理论推导出该算法在加性高斯白噪声信道中对随机信号的检测概率的闭合表达式。仿真表明,在不同信噪比条件下,与传统能量检测器相比,最优的增强型能量检测器能够体现出更佳的性能,尤其是在低信噪比情况下。     

一种用于频谱感知的增强型能量检测算法

基于传统能量检测算法,提出了一种用于频谱感知的增强型能量检测算法,即利用对接收信号绝对幅度值的任意正数次方代替平方操作。在给定虚警概率时,理论推导出该算法在加性高斯白噪声信道中对随机信号的检测概率的闭合表达式。仿真表明,在不同信噪比条件下,与传统能量检测器相比,最优的增强型能量检测器能够体现出更佳的性能,尤其是在低信噪比情况下。     

基于状态转移概率的频谱利用率和检测持续时间权衡

本文考虑了主用户的状态转移概率,并引入最大漏检概率限制条件,将频谱利用率与检测持续时间的权衡问题转化为优化问题,进而求出了满足无冲突时间最短且频谱利用率最大的最优检测持续时间的闭式表达式。通过仿真可以得到,存在一个最优的检测持续时间,使得频谱利用率达到最大。     

Joint impact of sensing time and IED parameter on the performance of an energy efficient cognitive radio system

Joint impact of sensing time and improved energy detector (IED) parameter is evaluated for an energy efficient cooperative cognitive radio (CR) system where the CR users use IED. The aim of this work is to design the CR system in such a way that it can achieve two objectives for a given level of protection on primary user: (i) optimization of sensing time to make balance between detection performance and throughput and (ii) appropriate allocation of energy between sensing time and transmission time so as to enhance the energy efficiency of the CR system. The key parameters such as sensing time and IED parameter are set appropriately to meet the objectives. The performance is assessed in terms of throughput and energy efficiency of the system. The effect of the sensing time and the IED parameter on the performance is evaluated under a collision constraint. Furthermore, the optimal sensing time and IED parameter are investigated jointly for which the higher throughput as well as maximum energy efficiency can be obtained, and at the same time, a desired detection probability can also be maintained by the CR system. Copyright © 2016 John Wiley & Sons, Ltd.     

Performance of positron imaging systems as a function of energy threshold and shielding depth

The effect of energy discrimination and shielding on positron imaging data quality was investigated using a detector pair to simulate a ring positron emission tomograph. Formulas are presented relating the sensitivity, random fraction, and scatter fraction for a detector pair to the same parameters for a ring system. Data were fitted to detector pair expressions for the variation of the above parameters with shielding depth in order to obtain information on the effect of energy threshold level. These fitted curves were used to determine the sensitivity, random fraction, and scatter fraction, as well as an overall data quality factor as a function of energy threshold level and shielding depth. Data were obtained for both NaI(T1) and BGO detector types using activity levels in the range of 1.5 muCi/cm3. Results show that for NaI(T1) detectors, the lowest possible energy threshold level is optimal, with the corresponding optimal shielding depth determined by the level of activity to be imaged. For BGO detectors, a tradeoff exists between energy thresholds of 100-400 keV and shielding depths of 15-30 cm with smaller shielding depths requiring higher energy thresholds.     

Spectrum-energy-efficient sensing with novel frame structure in cognitive radio networks

Cooperative spectrum sensing (CSS) is a promising technology in spectrum sensing with an admirable performance. In this paper, we define a utility function which jointly considers the spectrum-efficiency and the energy-efficiency. In a single-user sensing scenario, by maximizing the utility function, a rigorous analytical expression for the optimal threshold of the energy detector is derived. In CSS, the general frame structure is inefficient since the time consumed by reporting contributes little to the sensing performance. In this paper, we propose a novel CSS frame structure, in which one secondary user's (SU's) reporting time is also used for other SUs’ sensing. For time varying channels, collecting the sensing results at different time points is expected to achieve a time diversity gain for a SU, then the novel multi-minislot CSS scheme is proposed. In CSS, the optimal randomized rule and the optimal final decision threshold are derived. Simulation results show a significant improvement of the utility by using the proposed multi-minislot CSS scheme. It is also shown that there exists an optimal number of cooperating SUs that maximizes the utility, and the optimal number decreases as the price of the sensing energy increases.     

Performance evolution of ED-based spectrum sensing in CR over Nakagami-m/shadowed fading channel with MRC reception

Internet of things contains the hefty number of devices with diverse types of communication interfaces. Therefore, these devices act as a source of interference to the primary users in the absence of appropriate collision detection technique. Spectrum sensing is the important function of cognitive radio and energy detector is the most popular technique used for spectrum sensing. Detection of the availability of unused spectrum for the secondary user becomes difficult when the channel is affected by composite multipath/shadowed fading. In this paper, analytical expressions of average probability of detection and average area under the receiver operating characteristic over Nakagami-m/log-normal with maximum ratio combining diversity are derived using Gaussian-Hermite integration approximation. In addition, an optimized threshold has been incorporated to overcome the problem of spectrum sensing even at low signal-to-noise ratio. To verify the correctness of exact results and derived analytical expressions, Monte Carlo simulations are incorporated.     

Joint impact of sensing time and SPRF parameter on the performance of a continuous energy harvesting cooperative cognitive radio network

Joint impact of sensing time and signal power raise factor is studied for an improved energy detector–based energy harvesting cooperative cognitive radio network. All the cognitive radio nodes harvest energy either from radio frequency resources or from non–radio frequency resources. The probability density function of harvested energy from both the sources is exponentially distributed. Novel theoretical expressions for harvested energy and throughput are derived. Impact of several sensing parameters and a device constraint on the outage is studied. Optimal values of sensing time and signal power raise factor parameter pair are estimated for maximum harvested energy and maximum throughput. Energy efficiency of the network is also evaluated, and impact of sensing time on it is indicated.     

Optimal energy-efficiency capacity and sensing tradeoff for hybrid spectrum sharing in CRN

This paper investigates the tradeoff between energy-efficiency capacity and spectrum sensing under hybrid spectrum sharing model,where the spectrum sharing method is based on sensing results of seconda...     

Degree of polarization detection: a dual‐polarized antenna based spectrum sensing algorithm for cognitive radio

A new spectrum sensing algorithm‐degree of polarization (DoP) sensing algorithm is proposed in this paper. By exploiting a pair of dual‐polarized antenna at the receiver, DoP of the received vector signal is estimated and utilized to detect the presence of primary users based on the polarization characteristics of electromagnetic waves. The dual‐polarized narrowband and broadband systems are both considered for DoP detection. In theoretical analysis, we derive the probability of detection, the probability of false and detection threshold of the proposed algorithm. It is shown that our algorithm overcomes the noise uncertainty problem. Considering the polarization‐sensitive channel impairments, the impact of polarization mode dispersion on DoP detector is discussed. This method can be utilized for various signal detection applications without requiring the knowledge of signal, transmission channel, and noise power. In simulations based on wireless microphone signals, by applying polarization information signal carries, DoP achieves a better detection performance than arithmetic‐to‐geometric mean detector, the maximum‐to‐minimum ratio eigenvalue detector, and energy detector with noise uncertainty. The simulations based on digital video broadcasting‐terrestrial signals are also presented, which may show the detection performance of the proposed method may be affected by polarization mode dispersion. Copyright © 2013 John Wiley & Sons, Ltd.     

Cooperative Spectrum Sensing with Adaptive Double-Threshold Based Energy Detector in Cognitive Radio Networks

Spectrum sensing is one of the key functionalities in the implementation of cognitive radio. It is used to sense the unused spectrum in an opportunistic manner. In this paper, we propose an energy detector with adaptive double-threshold for spectrum sensing, to optimize the detection performance at a fixed probability of false alarm $(\text{ P }_\mathrm{f})$ i.e. 0.1, which also overcomes sensing failure problem. In the present work, the detection threshold is made adaptive to the fluctuation of the received signal power in each local detector of cognitive radio (CR) user. Simulation results show that proposed scheme optimizes better detection performance and outperforms both conventional energy detector and cooperative spectrum sensing (CSS) method by 12.8 and 3.3 % at $-$ 8 dB signal to noise ratio (SNR), respectively. While utilizing CSS with proposed adaptive double-threshold scheme, where each CR user use a double threshold detectors for local detection and send detection decisions to fusion center (FC) to give the final decision based on hard decision rule. It is further found that CSS with adaptive double-threshold improves detection performance around 26.8 and 7.6 % as compare to CSS with single threshold and Hierarchical with quantization method at $-$ 10 dB SNR, respectively, under the case when a small number of sensing nodes are used in spectrum sensing.     

Detection of signals of unknown duration by multiple energy detectors

An extension of the classical energy detector is proposed to deal with the case of unknown signal duration. Multiple energy detectors are applied to partitions of the original observation interval; presence of signal is decided if at least one of the detectors is in favor of it. We have derived the corresponding probabilities of false alarm and detection for a particular strategy of successive segmentations of the original interval, thus obtaining a layered structure of energy detectors. One key problem is that individual decisions obtained from the multiple energy detectors are statistically dependent, thus complicating the derivation of the overall probabilities of detection and false alarm. ROC curves have been computed, showing significant improvements in detectability when there is a large mismatch between the duration of the observation interval and the actual duration of the signal. This can be especially interesting in the framework of novelty detection where specific parameters of the signal, like duration, are totally unknown.