认知 mesh 网络服务区分的动态频谱接入策略

动态频谱接入策略是实现认知无线电网络高效利用频谱的关键。与传统认知无线电网络不同,认知mesh网络中不同QoS需求的多类型业务共同接入,为适应这一特点,提出服务区分的动态频谱接入策略。策略依据业务的QoS需求确立优先级,针对不同优先级业务采取不同的信道接入方案,实时业务依据最优传输延迟期望选择接入信道集合,在减小传输延迟的同时降低数据传输过程授权用户出现的概率,普通业务选择最优理想传输成功概率的信道,降低信道切换概率。理论与实验结果表明,与传统的认知网络频谱接入策略相比,提出的策略能提供不同业务的服务区分,满足实时业务的低延迟需求,降低数据传输的中断率,同时在授权信道空闲率与网络负载较大时吞吐量性能较优。     

基于QoS保证的广播/组播OFDM系统资源分配策略

该文提出了一种基于服务质量(QoS)保证的次优广播/组播OFDM系统资源分配算法。算法在最优分配原则的基础上采用不同广播/组播业务目标速率作为约束条件,并以业务组中最差接收用户传输速率作为搜索目标,使得业务组中全部用户达到QoS要求,算法的公平性及有效性得到提高;同时采用时频格作为分配算法中的基本资源单位,以降低分配算法的复杂度。仿真结果表明,改进分配策略的系统吞吐量性能接近最优广播/组播分配算法,提高了广播/组播系统资源分配的公平性。     

认知无线网络中基于业务区分的自适应MAC协议

为了提高认知用户的接入效率,同时兼顾其QoS需求,提出了一种应用于认知无线网络的基于业务区分的自适应MAC协议。对不同业务采取不同的最优频谱检测时间,实时业务(RT)以最小化接入时延为目的确定最优的频谱检测时间,而非实时用户(NRT)则以最大化吞吐率为目标确定最佳的频谱检测时间。根据所确定出的最佳频谱检测时间,结合当前的业务到达速率和调度策略,不同业务以时隙Aloha的方式接入空闲频谱。理论分析和仿真表明,所提出的自适应MAC协议能够自适应地为认知用户的不同业务确定最优频谱检测时间,从而有效地提高频谱使用效率,保证不同业务的QoS需求。     

保证QoS的路径级网络资源分配算法研究

随着越来越多的实时业务接入因特网,如何在满足业务端到端QoS要求的前提下,使网络接纳更多用户成为一个严峻的挑战.本文首先对路径级的网络资源最优分配问题建立数学模型.理论推导证明:该问题可以通过一个简单的最优规划问题求解.随后,根据求得的最优解的特点,本文提出了一种结合网络资源状态和用户业务QoS要求的资源分配算法—ERA算法.ERA算法不仅运算简单,而且仿真结果也表明,在相同网络资源总量的前提下,其接纳的用户数目可以达到理论的上界.     

用于准二维移动容迟容断网络的实时资源分配策略

资源分配是移动容迟容断网络的核心问题之一,影响着容迟容断网络路由甚至整个系统的效率.然而目前移动容迟容断网络的资源分配策略大多基于神经网络和遗传算法的混合算法,计算量大,不利于实时应用.为此根据移动网络可预测环境,提出了接入路由器消息矩阵及准二维接入带宽的约束条件,在此基础上建立了基于效用函数的资源分配策略,以满足实时要求.算法具有O(n)的算法复杂度,仿真结果显示切换掉话率和新呼叫阻塞率仅比最优化算法升高约1/4,计算用时则只有其36.99％.说明其在保证实时性的前提下仍能提供较好的QoS.算法可以进一步推广到二维移动场景中.     

基于QoS保证的蜂窝系统接入算法研究

无线通信系统中的关键技术之一就是无线接入控制,它将影响用户终端传输语音和数据业务时得到服务质量的好坏.本文针对3G系统各种业务的特点论述了能有效保障QoS的上行接入控制方案,并据此提出了一种新的接入算法-PCD(Priority Code based Diffserv)算法.它的特点是依据具体业务的分类和QoS指标来分配网络资源,支持大量的用户拥有合理的服务质量水平,有效的解决了上行接入控制.文中设计了实时和非实时业务呼叫的信令流程,并对提出的算法和现有的接入算法进行了仿真评估.     

非实时业务下认知网络的频谱共享

根据某种特定业务的QoS要求制定相应的频谱共享策略,可以在这种情况下提高系统的频谱利用率,增加用户平均收益。对非实时业务下的认知网络的频谱共享策略进行了研究,考虑各非授权用户业务量和信道质量对系统频谱效率的影响,提出了一种非实时业务专用的NRT-dedicate频谱共享算法。仿真结果表明,在非实时业务情况下,该算法可以获得比通用业务的频谱共享算法的频谱利用率。     

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。     

基于认知无线电的WiMAX系统多用户资源分配算法

基于认知无线电(CR)和OFDM的传输特性,提出了一种WiMAX系统多用户资源分配算法.感知用户根据认知到的频谱资源信息,在不对授权用户造成干扰的前提下使用空闲频谱资源.利用注水算法对多个用户请求使用同一子载波进行裁决,在满足传输速率以及QoS要求下,完成子载波、比特和功率分配,使整个系统传输功率最小.仿真结果表明,基于认知无线电的WiMAX系统多用户资源分配算法的传输功率和性能明显优于使用静态算法方案的系统.     

基于多主用户活跃性的多功率认知接入策略

针对大多数认知无线电场景中存在多个主用户,且具有较强活跃性的问题,提出了一种基于授权用户活跃性的多主用户多状态认知接入机制以及对应的多功率接入策略。该方法能够使认知用户选择最优的授权信道接入,并采用合适的功率进行传输,实现了认知系统吞吐量的最大化。数值仿真结果表明,该接入机制能够使认知用户充分利用多主用户信息和资源。与传统的功率接入方式相比,既能减小对主用户的干扰,又能提升认知系统的容量。     

Joint spectrum load balancing and handoff management in cognitive radio networks: a non-cooperative game approach

We propose a non-cooperative game theory based algorithm for spectrum management problem in cognitive radio networks taking into account the spectrum handoff effects. The objective is to minimize the spectrum access time of Secondary Users (SUs) which are competing for spectrum opportunities in heterogeneous environment. In this paper, the preemptive resume priority (PRP) M/G/1 queuing model is used to characterize the multiple handoff and data delivery time of SUs. Also an explicit solution for channels selection probabilities of each SU is extracted for PRP M/M/1 model specifically. The effect of handoffs is considered as the interrupted packets which return to the SUs’ low priority queue when the high priority Primary User’s packets are arrived to take service. The queuing delay of SUs’ and the effect of these returned packets are considered in order to balance the load of SUs on channels so that the minimum spectrum access time is sensed by each SU. The non-cooperative spectrum load balancing with handoff management game is proposed to find a distributed solution for each SU. It is shown that this game has a unique Nash equilibrium point which can be achieved by SUs as decision makers. At this equilibrium, each SU incurs the minimum delay on all channels while the free spectrum holes of channels are utilized efficiently. Simulation results are provided to evaluate the performance of the proposed scheme in terms of spectrum access delay, fairness, and channels spectrum holes utilization.     

Delay QoS Guaranteed Cooperative Double-Threshold Sensing Scheme in Cognitive Radio Networks

In cognitive radio networks, cooperation can greatly improve the performance of spectrum sensing. This paper proposes a delay (QoS) quality-of-service guaranteed cooperative spectrum sensing frame structure in which secondary users (SUs) conduct spectrum sensing and data transmission concurrently over two different parts of the primary user spectrum band. A double-threshold sensing scheme is employed in the local sensing step, only the SUs with reliable sensing information are allowed to transmit their “one bit” local decisions to the fusion center. The sensing performance and the SU transmission delay are analyzed in detail in this paper. Computer simulations show that the delay QoS guaranteed cooperative double-threshold sensing scheme could not only decrease the SU transmission delay but also save the reporting overhead of the SUs compared with the conventional detection method with one threshold.     

基于M/G/1/K排队模型的IEEE802.11e EDCA性能研究

该文利用二维Markov链分析方法,提出了一种新的IEEE802.11e EDCA网络分析模型,该模型引入了空闲状态和不同接入等级的仲裁帧间隔(AIFS)的使用;利用Markov链状态转移图的Z域信号传递函数推导了MAC层平均服务时间的概率分布;结合M/G/1/K排队模型分析了增强分布式信道接入(EDCA)在非饱和和饱和负载下的性能。经过访真实验结果与数值分析结果的对比,验证了分析模型的准确性。分析结果表明:EDCA接入机制只为不同优先级业务提供QoS区分;不同优先级业务信道接入的不公平性是EDCA接入机制的特点。     

Quality of service‐aware coordinated dynamic spectrum access: prioritized Markov model and call admission control

In this paper, we propose a heterogeneous‐prioritized spectrum sharing policy for coordinated dynamic spectrum access networks, where a centralized spectrum manager coordinates the access of primary users (PUs) and secondary users (SUs) to the spectrum. Through modeling the access of PUs and multiple classes of SUs as continuous‐time Markov chains, we analyze the overall system performance with consideration of a grade‐of‐service guarantee for both the PUs and the SUs. In addition, two new call admission control (CAC) strategies are devised in our models to enhance the maximum admitted traffic of SUs for the system. Numerical results show that the proposed heterogeneous‐prioritized policy achieves higher maximum admitted traffic for SUs. The trade‐off between the system's serving capability and the fairness among multiple classes of SUs is also studied. Moreover, the proposed CAC strategies can achieve better performance under max‐sum, proportional, and max‐min fairness criteria than the conventional CAC strategies. Copyright © 2011 John Wiley & Sons, Ltd.     

Initial spectrum access control with QoS protection for active users in cognitive wireless networks

In this paper, an initial spectrum access control algorithm for cognitive wireless networks was studied. The objective was to maximize the number of admitted secondary users (SUs) under the constraints of interference temperature at multiple measurement points (MPs), while providing active SUs' QoS protection (AQP). Here, AQP means that the signal‐to‐interference‐plus‐noise ratios (SINRs) of all active SUs will not fluctuate below some predefined thresholds during a new SU's initial spectrum access process. To this end, we proposed a new distributive power control algorithm in conjunction with a simple alarm mechanism that ensures the interference temperatures at multiple MPs to be always below their thresholds during the initial spectrum access process. Then, two realizations of the spectrum access algorithms, namely, D‐AQP and C‐AQP, according to whether the MPs can act as local controllers or not, were presented. In the D‐AQP algorithm, each SU updates its transmit power distributively based on the local information including the current SINR, the QoS requirement, and the indicator from the MPs so that the resultant SINRs of the active SUs are able to stay above the predefined thresholds. Whereas in the C‐AQP algorithm, apart from the same procedure as mentioned, each MP is supposed to be able to decide which new SU should quit the initial spectrum access process so as to protect the communication quality of the primary system. Finally, the performances of the proposed algorithms were validated by extensive simulations. Copyright © 2011 John Wiley & Sons, Ltd.     

CATECAS: a content-aware transmission efficiency based channel allocation scheme for cognitive radio users with improved QoE

Cognitive radio (CR) is a promising technology for the upcoming 5G communication which addresses opportunistic channel usage for enhanced spectrum utilization. However, Quality of Service (QoS) provisioning is a major challenge for CR Network due to the service interruption and packet error caused by random primary activities. In addition to this, periodic spectrum sensing for primary user protection reduces the effective throughput of the secondary users (SUs). However, to ensure QoS of SUs especially for video application, throughput enhancement is necessary which can be achieved by efficient spectrum sensing and channel allocation policy. As the QoS requirements are different for different secondary applications, we propose a novel content aware channel allocation scheme that enhances the Quality of Experience (QoE) of SUs. At first, the proposed scheme analyzes the QoS requirements of different SUs and prioritizes them. Consequently, the optimum sensing duration is determined to maximize the transmission efficiency and throughput of SUs. Finally, a novel content aware transmission efficiency-based channel assignment scheme (CATECAS) is proposed for SUs, considering the estimated channel quality and QoS requirements concurrently. Extensive performance analysis of CATESCAS on real-time video and file download applications confirms significant QoE improvement for SUs especially for rapid movement type of video application, which is considered as the most critical among different secondary applications.

     

Analysis of secondary user performance in cognitive radio networks with reactive spectrum handoff

Cognitive radio networks use dynamic spectrum access of secondary users (SUs) to deal with the problem of radio spectrum scarcity . In this paper, we investigate the SU performance in cognitive radio networks with reactive-decision spectrum handoff. During transmission, a SU may get interrupted several times due to the arrival of primary (licensed) users. After each interruption in the reactive spectrum handoff, the SU performs spectrum sensing to determine an idle channel for retransmission. We develop two continuous-time Markov chain models with and without an absorbing state to study the impact of system parameters such as sensing time and sensing room size on several SU performance measures. These measures include the mean delay of a SU, the variance of the SU delay, the SU interruption probability, the average number of interruptions that a SU experiences, the probability of a SU getting discarded from the system after an interruption and the SU blocking probability upon arrival.     

Adaptive and Distributed Access to Spectrum Holes in Cognitive Radio System

Cognitive radio technology enables Secondary Users (SUs) to access the frequency channels licensed to Primary Users. In this paper, we propose a novel dynamic multichannel access scheme for cognitive radio systems, which are based on a multichannel variation of a p-persistent Carrier Sensing Multiple Access scheme. To optimize the system-wide performance, the proposed scheme exploits different gains of frequency channels due to frequency-selective fading. With the proposed scheme, SUs share frequency channels in a fully distributed way, without any explicit control information exchange. To design the proposed scheme, we formulate the whole system as a “channel access game,” according to game-theoretic framework. In the channel access game, the utility function should reflect the system-wide performance. We derive closed-form performance measures by modelling the system as a continuous time Markov chain, and use them to construct a proper utility function. Then, each SU independently decides its own channel access strategy (i.e., the distribution of the random backoff time) which optimizes the utility function. The simulation results show that the proposed scheme promotes SUs to compete and cooperate with each other to a suitable level and, as a result, performs well in all range of SU population.     

Efficient Spectrum Sensing with Minimum Transmission Delay in Cognitive Radio Networks

In cognitive radio (CR) networks, the secondary users (SUs) need to find idle channels via spectrum sensing for their transmission. In this paper, we study the problem of designing the sensing time to minimize the SU transmission delay under the condition of sufficient protection to primary users (PUs). Energy detection sensing scheme is used to prove that the formulated problem indeed has one optimal sensing time which yields the minimum SU transmission delay. Then, we propose a novel cooperative spectrum sensing (CSS) framework, in which one SU’s reporting time can be used for other SUs’ sensing. The analysis focuses on two fusion strategies: soft information fusion and hard information fusion. Under soft information fusion, it is proved that there exists one optimal sensing time that minimizes the SU transmission delay. Under hard information fusion, for time varying channels, the novel multi-slot CSS is derived. The performance of SU transmission delay is studied in both perfect and imperfect reporting channels. Some simple algorithms are derived to calculate the optimal sensing settings that minimize the SU transmission delay. Computer simulations show that fundamental improvement of delay performance can be obtained by the optimal sensing settings. In addition, the novel multi-slot CSS scheme shows a much lower transmission delay than CSS based on general frame structure.     

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.