Joint optimisation of transmission and waiting times in cognitive radio

Transmission time optimisation is one of the key considerations of cognitive network design. There are many studies in cognitive radio networks (CRNs) focusing on finding the best transmission time for secondary users (SUs) to maximise transmission or energy efficiency. While longer sensing duration leads to a higher sensing accuracy and causes less interference, the SU spends less time for transmission and more energy on sensing spectrum. On the other hand, when the transmission duration becomes longer, although the SU has more opportunities to access the channel, it may encounter higher interference due to primary user (PU) returns and the probability of collision becomes higher. In this article, in a decentralised slotted protocol for CRN, the SU spectrum access is proved as a renewal process, then the interference due to PU return during SU transmission, the missed opportunities due to waiting for the channel to become idle and the energy consumed by the SU in the whole spectrum access process including idling energy, transmission energy and sensing energy consumption are formulated and integrated into newly defined efficiency to obtain the optimum transmission time and waiting time.     

Simultaneous Information and Power Transfer for Multi‐antenna Primary‐Secondary Cooperation in Cognitive Radio Networks

In this paper, cognitive radio and simultaneous wireless information and power transfer (SWIPT) are effectively combined to design a spectrum‐efficient and energy‐efficient transmission paradigm. Specifically, a novel SWIPT‐based primary‐secondary cooperation model is proposed to increase the transmission rate of energy/spectrum constrained users. In the proposed model, a multi‐antenna secondary user conducts simultaneous energy harvesting and information forwarding by means of power splitting (PS), and tries to maximize its own transmission rate under the premise of successfully assisting the data delivery of the primary user. After the problem formulation, joint power splitting and beamforming optimization algorithms for decode‐and‐forward and amplify‐and‐forward modes are presented, in which we obtain the optimal PS factor and beamforming vectors using a golden search method and dual methods. Simulation results show that the proposed SWIPTbased primary‐secondary cooperation schemes can obtain a much higher level of performance than that of non‐SWIPT cooperation and non‐cooperation schemes.     

Resource allocation based on dynamic hybrid overlay/underlay for heterogeneous services of cognitive radio networks

In cognitive radio networks (CRNs), hybrid overlay and underlay sharing transmission mode is an effective technique to improve the efficiency of radio spectrum. Unlike existing works in literatures where only one secondary user (SU) uses both overlay and underlay mode, the different transmission modes should dynamically be allocated to different SUs according to their different quality of services (QoS) to achieve the maximal efficiency of radio spectrum. However, dynamic sharing mode allocation for heterogeneous services is still a great challenge in CNRs. In this paper, we propose a new resource allocation method based on dynamic allocation hybrid sharing transmission mode of overlay and underlay (Dy-HySOU) to obtain extra spectrum resource for SUs without interfering with the primary users. We formulate the Dy-HySOU resource allocation problem as a mixed-integer programming to optimize the total system throughput with simultaneous heterogeneous QoS guarantee. To decrease the algorithm complexity, we divide the problem into two sub-problems: subchannel allocation and power allocation. Cutset is used to achieve the optimal subchannel allocation, and the optimal power allocation is obtained by Lagrangian dual function decomposition and subgradient algorithm. Simulation results show that the proposed algorithm further improves spectrum utilization with simultaneous fairness guarantee, and the achieved Dy-HySOU diversity gain is satisfying.     

基于射频能量采集的Underlay CRN的能效优化

提出一种基于射频(RF)能量采集的认知无线电网络(CRN)架构。次用户(SU)消耗的总能量必须等于或小于采集的总能量,以保护主用户(PU)不受干扰。在满足次用户的服务质量前提下,确定在射频能量采集认知无线网络中最大化能效的最优传输时间和功率分配。在能效最大化过程中,引入吞吐量约束,找到服务质量和能源消耗之间的平衡。能效优化是一个非线性分式规划问题,使用坐标上升将其分成2个子问题,即给定传输时间下的功率分配与给定功率分配下的传输时间选择,然后使用Charnes-Cooper变形方法将非凸问题转化为一个等价凹问题。仿真结果表明,该方案能够实现有效的能效优化。     

A prediction and scheduling framework in centralized cognitive radio network for energy efficient non‐real time communication

Advent of Internet of Things led to an exponential rise in battery‐operated sensors transmitting small non‐real time (NRT) data regularly. To this end, this work proposes a framework for centralized cognitive radio network (CRN) that facilitates better spectrum utilization and low‐cost opportunistic NRT data transfer with high energy efficiency. The novelty of this framework is to incorporate Hidden Markov Model–based prediction within the traditional cognitive radio sensing‐transmission cycle. To minimize the prediction time, we design a Hardware‐based Hidden Markov Model engine (H2M2) to be used by the cognitive base station (CBS). CBS exploits the H2M2 engine over high primary user (PU) activity channels to minimize the collisions between PUs and NRT secondary users, thereby reducing the SU energy consumption. However, this is at the cost of reduced throughput. Taking this into account, we propose an Intersensing‐Prediction Time Optimization algorithm that identifies the predictable PU activity channels and maximizes the throughput within a PU interference threshold. Furthermore, to minimize the total battery consumption of all the SUs within CRN, a Battery Consumption Minimizing Scheduler is designed at the CBS that efficiently allocates the predictable PU channels to the NRT SUs. By exploiting the unutilized high PU activity channels, the proposed Centralized Scheduling, Sensing and Prediction (CSSP) framework improves the spectral efficiency of the CRN. Exhaustive performance studies show that CSSP outperforms traditional nonpredictive sensing techniques in terms of energy efficiency and interference management. Finally, through a proof of concept, we validate the ability of CSSP framework in enabling NRT communication.     

Optimization of spectrum utilization in cognitive radio system

In Cognitive Radio (CR) networks, CR user has to detect the spectrum channel periodically to make sure that the channel is idle during data transmission frame in order to avoid the collisions to the primary users. Hence recent research has been focused on the interference avoidance problem. Quality of Service (QoS) requirement of CR user will affect the time of data transmission in each frame. In this paper, in order to solve the interference avoidance and spectrum utilization problems without cooperation among CR users, a new scheme to obtain the optimal duration of data transmission frame is proposed to maximize the spectrum utilization and guarantee the protection to the primary users. The main advantages of our proposed scheme include the followings: (1) QoS requirement of CR user is concerned; (2) p-persistent Media Access Control (MAC) random access is used to avoid the collisions among CR users; (3) CR network system capacity is considered. We develop a Markov chain of the primary spectrum channel states and an exponential distribution of the CR user??s traffic model to analyze the performance of our proposed scheme. Computer simulation shows that there is an optimal data transmission time to maximize the spectrum utilization. However, the regulatory constraint of the collision rate to the primary users has to be satisfied at the expense of spectrum utilization. And also the tradeoff between the spectrum utilization and the capacity of the CR system is taken into account.     

认知无线Ad hoc网络的功率控制

当FCC提出传统电视系统和认知无线电网络频谱共享,以增加频谱的利用率时,主要涉及到的问题之_是来自认知无线电网络的干扰不得影响主用户的QoS。在本文中,考虑由低功耗个人／便携设备组成的认知无线电网络与传统电视系统同时运作的情况。本文在保证主用户和认知用户的QoS的情况下,推导出问题的可行性条件,并提出集中式和分布式两种解决方案,最大限度地提高认知用户的能源效率。并且通过仿真表明该方案的有效性。     

Performance analysis of two-way relay cooperation underlay cognitive radio networks based on WIPT

The two-way relay cooperation for underlay cognitive radio networks based on WIPT was presented,where secondary system adopted the two-way relay cooperative transmission.First,the relay adopted a power splitting protocol to harvest energy and to decode information transmitted by secondary users,then the relay forwarded information to two secondary users by using the harvested energy.Subsequently the exact expression of the outage probability,the ergodic capacity and energy efficiency of the secondary user system were derived.Finally,numerical simulation discusses the impact on the system performance with regard to secondary transmission power.The results reveal that the two-way relay cooperation effectively reduces the outage probability of data transmission.The capacity and energy efficiency of the system reaches optimal level when the power allocation coefficient is 0.5.     

Transceiver Designs for Interference Alignment Based Cognitive Radio Networks with Energy Harvesting

Cognitive radio (CR) can improve the usage of spectrum resources, although the secondary users (SUs) will cause interference. Interference alignment (IA) is a prospective technique that can manage the interference effectively and has been applied to CR networks. However, interference can be used as an energy source by wireless energy harvesting techniques. In this paper, we consider an underlay CR network consisting of a primary user (PU) and SUs that are either energy harvesting users or information transmission users. The normal IA scheme neglects the priority of the PU, which leads to poor performance, particularly at low signal noise ratio (SNR) values. Three transceiver designs are proposed to improve the information rate of the PU and these benefit from the existence of energy harvesting users, by aligning the interference created by those energy harvesting users at information transmission users. Simulation results are presented to show the proposed designs can significantly improve the performance especially in low SNR situations.     

Throughput analysis in censoring-based cooperative cognitive radio network with energy harvesting

An energy harvesting (EH) and cooperative cognitive radio (CR) network (CRN) is studied in this paper where CR users transmit data through a primary user (PU) channel if the channel remains idle, else an optimal number CRs helps in transmission of PU. To achieve the optimum number of CRs (ONCR) involved in cooperation, a novel scheme based on a combination of channel censoring and total error is proposed. The performance of the proposed scheme is investigated under RF harvesting scenario. The EH is dependent on sensing decision and a CR source harvests energy from PU's RF signal. The harvested energy (HE) is split into two parts: One part is used by the CR network (CRN) for its own transmission, and the other part is used for supporting PU. The effect of the energy allocation factor on total throughput is also investigated. New expressions for optimal number of CRs and throughput are developed. The effect of network parameters such as sensing time, censoring threshold, and energy allocation parameter (EAP) on throughput is investigated. Impact of distance between nodes is also studied.     

A novel approach for energy‐efficient resource allocation in double threshold‐based cognitive radio network

This paper mainly focuses on solving the energy efficiency (EE) maximization problem in double threshold‐based soft decision fusion (SDF) cooperative spectrum sensing (CSS) in the cognitive radio network (CRN). The solution to this objective problem starts with the selection of suitable secondary users (SUs) both for the spectrum sensing and data transmission. Here, energy efficiency is maximized under the constraints of interference to the primary user (PU), an acceptable outage of SUs, the transmission power of the SUs and the probability of false alarm. We propose a novel algorithm called iterative Dinkelbach method (IDM) which jointly optimizes the sensing time and transmission power allocation to the SUs. Further, Lagrangian duality theorem is employed to find the exact power assigned to the SUs. Finally, simulation results are carried out to validate the effectiveness of our proposed scheme by comparing with the other existing schemes. The performance is also analyzed for different system parameters.     

Resource allocation in heterogeneous cooperative cognitive radio networks

In cognitive radio networks (CRNs), resources available for use are usually very limited. This is generally because of the tight constraints by which the CRN operate. Of all the constraints, the most critical one is the level of permissible interference to the primary users. Attempts to mitigate the limiting effects of this constraint, thus achieving higher productivity, are a current research focus, and in this work cooperative diversity is investigated as a promising solution. Cooperative diversity has the capability to achieve diversity gain for wireless networks. In the work, therefore, the possibility of and mechanism for achieving greater utility for the CRN when cooperative diversity is incorporated are studied. To accomplish this, a resource allocation model is developed and analyzed for the heterogeneous, cooperative CRN. In the model, during cooperation, a best relay is selected to assist the secondary users that have poor channel conditions. Overall, the cooperation makes it feasible for virtually all the secondary users to improve their transmission rates while still causing minimal harm to the primary users. The results show a marked improvement in the resource allocation performance of the CRN when cooperation is used in contrast to when the CRN operates only by direct communication.     

一种多用户协同频谱感知功率控制方案

分析和研究了多用户协同频谱感知原理,通过时分方式,实现了多用户之间的频谱共享。同时为避免对主用户产生有害的干扰,从用户通过一种算法控制它的发射功率,保证主用户的通信服务质量。最后对多用户协同频谱感知和单用户频谱感知的性能进行了仿真研究,结果表明多用户协同频谱感知可以明显提高频谱感知的性能,克服阴影/衰落作用的不利影响,提高频谱利用率。     

基于合约制的认知网络协作频谱共享模型

为了提高认知无线电网络中主用户的能效和谱效,提出了一种基于合约制的协作频谱共享新模型。在该模型中,当主用户信道质量差时,次用户为其提供中继服务;作为回报,在主用户信道质量好时,次用户可以在一定的干扰约束下以underlay的模式和主用户共享频谱。在此框架下引入经济学中的合约理论,将主次用户间的协作问题建模为合约设计问题,并建立了主次用户评价合约收益的效用函数,将提高主用户的能效和谱效问题转变为设计合约使主用户获得最大效用的优化问题,并利用差分进化算法对该问题求解。最后,在不同的环境下,将主用户协作与不协作获得的效用进行对比,结果表明,主用户在没有额外投入频谱资源的条件下,不仅节省了发送功率,而且有效地提高了数据传输速率,进而提高了能效和谱效。     

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.     

On Time-Frequency Resource Leasing in Cognitive Radio Networks

In this work, we introduce a new spectrum leasing based cognitive radio for OFDM-based primary/secondary networks. More precisely, we propose a new leasing scheme both in time and frequency domains in a network composed of a primary transmission and some secondary (cognitive) users forming a cooperative relay network. In the proposed scheme, the primary user decides to lease a part of its available resources (time and frequency) to a selected set of relays, with the aim of increasing its link reliability. The selected relays use a part of the leased resources for relaying the primary signal, and in counterpart, they are allowed to exploit the rest of the frame for their own data transmission. By defining appropriate cost functions, the proposed algorithm decides whether it is of advantage for the primary user to cooperate with the relay network or not. Moreover, if cooperation is advantageous for the primary network, the algorithm selects the optimal amount of the time-frequency resources (number of OFDM symbols and subcarriers) that are involved in the cooperation process. Simulation results show that by using the proposed relaying scheme, both primary and secondary (relay) networks can take advantage in terms of achievable data rates compared to classical leasing systems.     

Elastic bandwidth allocation scheme with softened peak interference power constraint for the dynamic cognitive radio systems

The popularity of diverse wireless communication systems has led to increased strains on the unlicensed spectrum. However, investigations have shown that vast portions of the licensed spectrum remain underutilized across frequency, space and time. To improve the utilization of the existing radio spectrum, cognitive radio (CR) allows a secondary system to access the licensed spectrum as long as the primary system’s operation is not compromised. Two main CR transmission modes, spectrum overlay and underlay have been proposed. In the spectrum overlay mode, challenges in quality-of-service (QoS) provisioning arise due to the necessity for secondary users to vacate the channels when a primary user appears. In the underlay model, interference caused to the primary system has to be carefully managed resulting in a constraint of the secondary system’s transmit power, which causes difficulty in QoS provisioning. In this paper, we propose an elastic bandwidth allocation scheme to make concurrent use of both spectrum overlay and underlay transmission modes. Different from existing hybrid transmission strategy, our scheme employ a novel softened peak interference power constraint to improve the performance of the secondary system while still granting the superior protection to the primary system transmissions. This allows the proposed scheme to achieve a superior transmission capacity in the CR network while avoiding the weaknesses of the both spectrum overlay and spectrum underlay transmission modes.     

Comprehensive Survey on Quality of Service Provisioning Approaches in Cognitive Radio Networks: Part One

Much interest in Cognitive Radio Networks (CRNs) has been raised recently by enabling unlicensed (secondary) users to utilize the unused portions of the licensed spectrum. CRN utilization of residual spectrum bands of Primary (licensed) Networks (PNs) must avoid harmful interference to the users of PNs and other overlapping CRNs. The coexisting of CRNs depends on four components: Spectrum Sensing, Spectrum Decision, Spectrum Sharing, and Spectrum Mobility. Various approaches have been proposed to improve Quality of Service (QoS) provisioning in CRNs within fluctuating spectrum availability. However, CRN implementation poses many technical challenges due to a sporadic usage of licensed spectrum bands, which will be increased after deploying CRNs. Unlike traditional surveys of CRNs, this paper addresses QoS provisioning approaches of CRN components and provides an up-to-date comprehensive survey of the recent improvement in these approaches. Major features of the open research challenges of each approach are investigated. Due to the extensive nature of the topic, this paper is the first part of the survey which investigates QoS approaches on spectrum sensing and decision components respectively. The remaining approaches of spectrum sharing and mobility components will be investigated in the next part.     

Routing for cognitive radio networks consisting of opportunistic links

Cognitive radio (CR) has been considered a key technology to enhance overall spectrum utilization by opportunistic transmissions in CR transmitter–receiver link(s). However, CRs must form a cognitive radio network (CRN) so that the messages can be forwarded from source to destination, on top of a number of opportunistic links from co‐existing multi‐radio systems. Unfortunately, appropriate routing in CRN of coexisting multi‐radio systems remains an open problem. We explore the fundamental behaviors of CR links to conclude three major challenges, and thus decompose general CRN into cognitive radio relay network (CRRN), CR uplink relay network, CR downlink relay network, and tunneling (or core) network. Due to extremely dynamic nature of CR links, traditional routing to maintain end‐to‐end routing table for ad hoc networks is not feasible. We locally build up one‐step forward table at each CR to proceed based on spectrum sensing to determine trend of paths from source to destination, while primary systems (PSs) follow original ways to forward packets like tunneling. From simulations over ad hoc with infrastructure network topology and random network topology, we demonstrate such simple routing concept known as CRN local on‐demand (CLOD) routing to be realistic at reasonable routing delay to route packets through. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimal Mode Selection Policies in Cognitive Radio Networks with RF Energy Harvesting

Applying energy harvesting technology in cognitive radio networks (CRNs) leads to a tradeoff between the time allocated for spectrum sensing followed by spectrum accessing and that for energy harvesting. This tradeoff can be formulated as a mode selection problem for the secondary users. In this paper, we consider a CRN working in the time-slotted manner. The secondary users powered by radio frequency energy harvesting can perform overlay transmission or cooperate with the primary users. To maximize the long-term throughput of the secondary network, we propose two optimal mode selection policies by formulating this problem under a partially observable Markov decision process framework. Numerical simulations show that both of our proposed policies achieve more throughput than the overlay-only policy. Finally, we also evaluate the effect of the cooperative threshold and the energy harvesting process on the optimal policies.