Robust congestion control in cognitive radio network using dynamic event‐triggered sliding mode

The ever‐increasing service demand from wireless users under restricted bandwidth necessitates the development of suitable congestion control scheme for throughput maximization. A robust congestion controller design has been addressed in this work to sustain necessary Quality of Service in Cognitive Radio Network. The goal is to reduce packet loss while ensuring optimum utilization of available resources. Sliding mode controller proclaimed for its disturbance rejection capabilities and robustness has been used to design the proposed controller. Using the benefits of sliding mode control, dynamic event‐triggering strategies have been combined for better utilization in resource‐constrained environments. Control execution requires minimal updates while guaranteeing the desired closed‐loop system behavior. The controller efficacy has been validated in simulations.     

Impact of secondary user mobility on spectrum handoff under generalized residual time distributions in cognitive radio networks

Cognitive Radio is an emerging technology to accommodate the growing demand for wireless technology via dynamic spectrum access to enhance spectrum efficiency. Spectrum handoff is an important component of Cognitive Radio technology for practical implementation of radio frequency access strategy and better utilization of spectrum in both primary and secondary networks. The probability of spectrum handoff and expected number of spectrum handoffs are key parameters in performance analysis and design of the cognitive radio network. This work presents an analytical model to evaluate the impact of secondary users’ mobility on intra-cell spectrum handoff considering primary users’ activity model in a cognitive radio network. A standard form of intra-cell spectrum handoff probability and expected number of intra-cell spectrum handoffs are derived for complete call duration of a non-stationary secondary user. The probability and expected number of intra-cell spectrum handoffs of a post inter-cell handoff call are also derived for generalized residual time distributions of call holding time and spectrum holes. A detailed analysis of these performance measuring metrics is presented under the impact of departure rate and cell crossing rate of secondary users. The accuracy of the derived analytical result is validated by Monte-Carlo simulation of the model.     

分层认知无线电网络中基于稳定匹配的资源分配算法

频谱资源的合理分配是认知无线电技术追求的目标之一,随着认知无线电网络中的次用户(SUs)数量不断增加,频谱资源的精确、实时分配与管控越来越难以实现。针对此问题,该文提出一种分层的认知无线电网络(CRN)架构,多个管理实体专注于为各层用户提供频谱服务;并在该架构下,提出一种基于稳定匹配的资源分配算法,用户通过自主协商形成分配结果,不仅保证了主用户(PUs)对次用户的功率限制,还充分考虑了各自的效用。仿真结果表明,所提算法的性能接近于最优方案,并降低了计算复杂度和系统时延。     

Recurrent Network Based Protocol Design for Spectrum Sensing in Cognitive Users

Wireless Personal Communications - This work focuses on cognitive users and its utilization of spectrum with channel bonding. Recurrent Channel Bonding Cognitive Users protocol (RCBCU) has been...     

A fair MAC protocol for resource sharing in ad-hoc cognitive networks

Cognitive Radio (CR) technology allows an opportunistic use of the licensed spectrum by the CR users, avoiding harmful interference to Primary Users (PUs). To perform their activity, secondary users (SUs) have particular features compared to the PUs; sensing is one of the principal. Specifically the CR users must detect the spectrum holes left by PUs by performing sensing. All the protocol stack need to be redesigned taking into account the specificity of the cognitive environment. In this paper a novel MAC protocol for cognitive radio wireless ad-hoc networks is presented and analysed. The introduced protocol is distributed, collision-free and guarantees a fair channel assignment, also taking into account the requests of Quality of Service (QoS) of the CR nodes. The performance of the protocol has been studied through statistical computations. In particular, a Markov chain has been introduced to study the global performance of the protocol. In addition a simulation tool has been developed to validate the mathematical model and to prove the fairness of the resource sharing mechanism. The results prove the protocol efficiency and the high fairness, measured with the help of the Jain’s fairness index.     

A novel approach of user existence awareness using adaptive spectrum sensing controllers in emergency‐based cognitive radio adhoc networks

Spectrum sharing can be considered as an alternative solution to overcome spectrum limitation. Cognitive radio is the most important spectrum sharing technique in wireless communication system, which aims to enhance the utilization of radio frequency spectrum. Identification of spectrum environments like location of both licensed and unlicensed users has been considered in cognitive radio technology. In this paper, cognitive controller is an emergency repairing unit, which is introduced to maximize the number of connected users in an emergency situation. The analysis shows that the sensing efficiency of fixed sensing controller to identify users is limited to its sensing region. A hybrid technique with overlay and underlay accessing to perform data offloading in emergency situations and to connect the disconnected users is proposed to enhance the location sensing efficiency of the controller. A cognitive user node located at the interference region of controller experiences hidden node problem and causes interference to other users. In order to identify such users, an adaptive and cooperative sensing‐based controller is proposed, and efficiency of which is compared with the efficiency of fixed sensing controller. Theoretical and simulation analysis explores that the sensing capacity of adaptive sensing controller provides 42% of higher efficiency than the fixed sensing method.     

Routing in Distributed Cognitive Radio Networks: A Survey

Cognitive Radio Networks (CRNs) have been receiving significant research attention recently due to their ability to solve issues associated with spectrum congestion and underutilization. In a CRN, unlicensed users (or Secondary Users, SUs) are able to exploit and use underutilized licensed channels, but they must evacuate the channels if any interference is caused to the licensed users (or Primary Users, PUs) who own the channels. Due to the dynamicity of spectrum availability in CRNs, design of protocols and schemes at different layers of the SU’s network stack has been challenging. In this article, we focus on routing and discuss the challenges and characteristics associated with it. Subsequently, we provide an extensive survey on existing routing schemes in CRNs. Generally speaking, there are three categories of challenges, namely channel-based, host-based, and network-based. The channel-based challenges are associated with the operating environment, the host-based with the SUs, and the network-based with the network-wide SUs. Furthermore, the existing routing schemes in the literature are segregated into three broad categories based on the relationship between PUs and SUs in their investigation, namely intra-system, inter-system, and hybrid-system; and within each category, they are further categorized based on their types, namely Proactive, Reactive, Hybrid, and Adaptive Per-hop. Additionally, we present performance enhancements achieved by the existing routing schemes in CRNs. Finally, we discuss various open issues related to routing in CRNs in order to establish a foundation and to spark new interests in this research area.     

认知无线网络中次用户的一种协作传输策略

在认知无线网络中同时存在着主用户和次用户,次用户的通信行为必须在不影响主用户数据传输的前提下进行。为了保证次用户的传输连续性并改善次用户Qos,研究人员提出了次用户间相互协作传输的策略,基于此该文提出了一种基于放大转发的双中继协作传输方案并对所提方案次用户的无冲突传输时间及误比特率进行了详细的理论分析。蒙特卡洛仿真结果表明,双中继协作传输策略能在单中继协作传输的基础上进一步增加次用户的无冲突传输时间并减小误比特率,双中继协作传输显著地提高了系统的传输性能。      

A distributed cooperative relaying optimization scheme for secondary transmission in Cognitive Radio networks

In Cognitive Radio (CR) networks, cooperative communication has been recently regarded as a key technology for improving the spectral utilization efficiency and ensuring the Quality of Service (QoS) for Primary Users (PUs). In this paper, we propose a distributed joint relay selection and power allocation scheme for cooperative secondary transmission, taking both Instantaneous Channel State Information (I-CSI) and residual energy into consideration, where secondary source and destination may have different available spectrum. Specifically, we formulate the cognitive relay network as a restless bandit system, where the channel and energy state transition is characterized by the finite-state Markov chain. The proposed policy has indexability property that dramatically reduces the compu-tation and implementation complexity. Analytical and simulation results demonstrate that our pro-posed scheme can efficiently enhance overall system reward, while guaranteeing a good tradeoff between achievable date rate and average network lifetime.     

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。     

感知无线电中的高效频谱侦测方案

感知无线电是一种能有效提高频谱利用率的先进技术,他能在主用户没有使用频谱的时候发现并使用"频谱空洞".近来有研究结果表明,在衰落和阴影效应影响下频谱侦测的结果会有大幅度下降.为了削弱衰落和阴影效应的影响联合侦测诞生了,传统的联合侦测方式在每个用户所受衰落不同的情况下不能有效的工作.文章提出一种加权联合侦测来提高联合侦测性能.由大量分析和仿真结果可以表明加权联合侦测能大幅度提高侦测性能.     

Spectrum handoff in cognitive radio with fuzzy logic control

The secondary usage of spectrum has been investigated in Cognitive Radio (CR) network to resolving the spectrum scarcity issue in wireless communication. When Primary Users (PU) who own the spectrum appear, spectrum handoff is needed to maintain the communications of Secondary Users. But the decision making of spectrum handoff is a challenge issue for CR network, because the input of decision making, which obtain through spectrum sensing, is heterogeneous and inexact. In this paper we will use fuzzy logic control theory to solve this issue and make use of new information for handoff operation: the probability of PU’s occupancy at a certain channel. Our new algorithm can make more intelligent decision compared to simple traditional spectrum handoff decision making and reduce the probability of spectrum handoff, also the performance of SU’s communication can be enhanced.     

实高斯信号下的能量检测技术

认知无线电被认为是目前提高频谱资源利用率的最有效手段。次用户要使用主用户的空闲频段,必须能够准确的检测到主用户是否出现。能量检测技术由于无需信号的任何先念知识,应用最为广泛。在实高斯信号下,对基于能量的独立检测和协作检测方式进行了仿真研究。仿真结果表明：信号样本数和参与协作的用户数的增加可以有效地改善系统检测性能,但当用户数达到一定数目后,错误率基本无变化,反而还会增加系统开销。     

Interference estimation and its applications in cognitive radio networks

Cognitive Radio (CR) has been proposed as a system-level means to improve the spectrum utilization efficiency. The most significant premise for CR networks is to avoid harmful interference to the licensed users. Therefore, it is very important to estimate the potential interference introduced by the deployment of CR networks so that CR networks can be coexistence with Licensed User (LU) networks by designing proper system parameters. In this paper, two statistical models of potential interference due to CR networks are developed based on transmitter and receiver oriented spectrum sensing schemes, respectively. The approximate probability distributions of aggregate interference introduced by CR networks are then derived with respect to the obtained models. With the help of these probability distributions, a method is further presented to get the critical system parameter, i.e., sensing distance and user density of the CR networks, so that the introduced interference can be controlled to predefined level. Numerical results validate the proposed interference estimation method and confirm the effectiveness of interference distribution based system parameter design.     

基于Dec-POMDP的认知无线电网络频谱接入算法

针对认知无线电网络中认知用户（CR）的机会频谱感知及接入问题,提出了一种基于分布式部分可观测马尔科夫决策过程（Dec-POMDP）的多用户频谱接入算法。在该模型框架下,相邻CR用户通过交换接入策略,以区域策略梯度方向为基准,对各个CR用户的接入策略做出调整,从而得到最优联合接入策略。仿真结果表明：该算法有效降低了授权用户的容量损失,提高了空闲频谱的利用效率,能够更有效地做出接入决策。     

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.     

Increasing Spatial Spectrum Utilization Through Opportunistic User-to-User Communications

The requirements for ubiquitous and highly reliable wireless services, combined with the low utilization of licensed spectrum, call for flexible and efficient spectrum management schemes. To this end, a lot of attention is paid in the literature on allowing secondary-external users to opportunistically access the licensed spectrum. In parallel to these efforts, the question is whether the licensed users could further improve their own spectrum utilization. In this paper, we focus on increasing the spatial spectrum utilization of an infrastructure-based wireless system by adding autonomous functionality to the primary (system) users. An opportunistic operation mode for the uplink (UL) period, totally transparent to the base station (BS) of the system, is introduced. Users operating in this mode identify spatial spectrum UL opportunities by interpreting BS broadcast messages, and exploit these opportunities by establishing direct connections. It is shown that multiple direct connections can take place in parallel with a single standard UL transmission. Moreover, significant additional throughput is achieved, and in most of the cases, the energy consumption for the direct connections is lower than that of the conventional ones (using the standard mode).     

基于认知无线电的小卫星群通信动态频谱分配

文中以认知无线电技术(cognitive Radio, CR)为基础,提出了一种基于CR的小卫星群通信动态频谱分配MAC方案.该方案允许未授权用户自适应地选取可用带宽,实现了动态频谱接入,有效地提高了频谱利用率.提出一种动态信道的跳预约多址接入(DC-HRMA)协议,在不需要公共信道的情况下,解决了信道有效接入与退让问题.仿真结果表明,该协议性能和主次用户数目的合理搭配相关.     

Outage Analysis of OFDM‐Based Cognitive AF Relay Network in the Presence of Narrowband Interference

Orthogonal frequency‐division multiplexing (OFDM) is one of the most widely used technologies in current wireless communication systems and standards. Cognitive radio (CR) provides a robust solution to the problem of spectrum congestion as it offers opportunistic usage of frequency bands that are not occupied by primary users. Due to the underlying sensing, spectrum shaping, scaling, and interoperable capabilities of OFDM, it has been adapted as a best transmission technology for CR wireless systems. However, the performance of an OFDM‐based CR wireless system is affected by the existence of narrowband interference (NBI) from other users. Further, due to carrier frequency offset in NBI sources, NBI energy may spread over all subcarriers of an OFDM signal. In this paper, a fixed Amplify‐and‐Forward (AF) relay that operates at a frequency band that is different from that of direct mode is introduced to suppress the effect of NBI. Analytical expressions are derived for outage probability in direct, AF‐relay, and incremental relaying modes. The outage performance of the proposed AF relay–based CR network is proven to be better than that of direct mode.     

基于信噪比墙的协作能量检测算法

认知无线电技术可有效地检测到授权频段的频谱空洞,从而提高频谱效率.能量检测由于不需要授权用户的先验信息而被广泛应用.然而由于接收的噪声存在不确定性,使得在信噪比低于某一闸值时,无论观测时间多长,都无法保证检测结果满足要求的检测性能,这一闸值被称作“信噪比墙”.本文通过信噪比墙这一现象进行分析,同时由于协作感知算法在确定噪声下在提高检测性能方便表现出的优势,提出一种基于信噪比墙的协作能量检测算法,通过仿真结果分析,表明本文算法在检测性能和节能上较已有的协作算法具有优势.