基于频谱预测的认知无线接入研究

本文提出基于认知无线电的语音类业务,来扩大认知无线电的应用范围。并且针对认知无线电中,频谱变化时,会强制中断语音类业务,降低认知无线电服务质量,引入一种基于测量的不断修正的频谱资源预测模型。通过频谱资源预测模型,在发生强制中断时或者前,提前切换到其他在下一时刻发生强制中断率低的信道。     

基于频谱预留的认知无线接入研究

动态频谱接入是认知无线电技术的一个重要应用,它利用通信过程中出现的频谱空洞机会式地接入频谱,能极大地提高频谱的利用率。文章基于马尔可夫理论提出了一种改进的频谱预留接入方案,即按照业务需求对用户进行用户模型改进,并根据优先级不同进行接入策略改进。仿真结果显示该方案能有效保障高优先级用户的服务质量。     

典型部署策略下认知无线传感网的机会频谱接入方法

在典型规则拓扑模式及覆盖部署方式的传感网中探讨无冲突的认知频谱接入方法（包括频谱和时隙分配、协作频谱感知和感知结果汇报方案）,为数据采集提供高效的传输手段。提出对应网络环境下的次级用户的阻塞率和掉话率、各拓扑模式下的网络有效接收带宽和最大传输时延的分析模型。通过对几种拓扑模式的比较,表明Triangle的协作频谱感知效果最佳,而Square的有效接收带宽最佳;在完全覆盖部署方式下,Square和Triangle的传输时延较小,而多重覆盖部署方式下Square的时延最小。指出单个节点上的虚警概率对传输时延的影响不大,授权用户出现概率则对时延有明显影响,而选择较大的传输时隙/感知时隙比能显著降低时延。     

应急通信网络的动态频谱接入方案研究

利用认知无线电的动态频谱接入技术,提高应急通信网络在突发事件中的反应效率已成为无线通信领域的研究热点。对认知无线电的几种动态频谱接入方案进行了探索及研究。由分析可知,选择合适的接入方案,将会形成认知用户间的良性竞争,降低CR业务的通信中断率,从而增大系统的吞吐量,提升整个系统的性能。     

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。     

支持无线接入的新一代商用通信网络系统的设计与实现

一些大型企业在中国的许多城市都有高端客户群体,在这些城市已经拥有先进的IT基础网络和应用,随着企业的战略扩张,企业的IT网络将覆盖全中国。为充分利用企业现有的网络,同时为将来的网络建设制定好规范,需要在企业中部署一些新的服务,以领先的IT技术推动企业的商业模式创新和成长。文章从工程实际出发,介绍一种支持无线接入的新一代商用通信网络系统的设计与实现。     

认知Ad Hoc网络能量有效频谱接入策略

针对认知无线Ad Hoc网络中次用户能量受限问题,提出一种基于能量有效性的机会频谱接入策略。联合考虑信道状态的时变性和次用户的频谱感知准确性,基于部分可观测马尔科夫决策过程（POMDP）建立了一种最大化能量有效性的分析架构,指导次用户选择能效最佳信道,并根据信念状态、信道增益和检测概率,自适应控制传输功率。仿真结果表明,该策略能够有效提高次用户传输的能量有效性,通过对传输功率的有效控制,实现了传输性能和能量开销的有效折中。      

认知无线电网络频谱感知与接入算法研究

在对认知无线电网络频谱感知和接入研究成果进行分析的基础上,文章首先讨论了认知无线电网络频谱感知的基本方法以及协作频谱感知、单智能体和多智能体强化学习算法,比较了各种算法的优缺点,并展望了这一领域未来研究的方向。     

支持未来全频谱接入通信的基站天线研究综述

随着移动通信系统的快速更新迭代,使用的频段也越来越丰富,支持全频谱接入通信成为未来基站天线的发展趋势.而日趋紧张的站址资源对未来基站天线的小型化水平提出了更高的要求.文章首先介绍了当前多频段基站天线的研究进展和成果,概括了并排式、交错式、堆叠式和嵌套式四种多频段结构类型,着重分析了异频耦合的产生原理和抑制方法;然后总结出共口径技术和异频解耦技术是未来全频谱基站天线的关键技术;最后阐述了当前共口径技术和异频解耦技术存在的局限性,展望了未来全频谱基站天线的研究方向,包括多种共口径方式组合技术、宽带异频解耦技术和大规模共口径天线阵列解耦技术.     

无线认知传感器网络协同频谱感知研究

作为无线认知传感器网络的基本功能,协同频谱感知能够有效降低单用户频谱感知不可靠性,提升对完整频谱使用状态的检测能力。文章分析协同频谱感知在无线认知传感器网络中的地位和作用,探讨高维协方差矩阵的估计问题,给出协同频谱感知的假设检验,研究样本协方差矩阵中的均值向量和协方差矩阵、多元散射测量以及线性组合等问题。     

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。     

认知无线电中的频谱接入技术

认知无线电是一种基于软件无线电的智能通信系统,它能够认知周围环境,并能通过一定的方法相应地改变某些工作参数来实时地适应环境,从而达到提高频谱利用率、缓解频谱资源紧张的目的.授权频段的频谱利用问题是认知无线电实现的关键技术之一.研究了授权频段的两种频谱利用方法:动态频谱接入和基于动态频谱接入模型之一的机会频谱接入.     

Exploiting temporal and spatial diversities for spectrum sensing and access in cognitive vehicular networks

In cognitive vehicular networks (CVNs), spectrum sensing and access are introduced as the promising technologies to fully exploit the underutilized licensed spectrum. Because the sensing ability of a single secondary vehicular user (SVU) is affected by high mobility, dynamic topology, and unreliable wireless environment, collaborative sensing is developed to increase the sensing accuracy and efficiency. Generally, the synchronization is required in the collaborative sensing in CVN. However, it is difficult to keep all SVUs synchronized with others for sensing under the high dynamic network topology, and the sensing overhead of the synchronous cooperative action may be significant. In this paper, we first propose an asynchronous cooperative sensing scheme in which each SVU provides an energy information (EI) that is tagged with location and time information. The sensing decision will be made on account of the EI. Considering the temporal and spatial diversities of each SVU, we assign different weights to each EI and formulate the probabilities of detection and false alarm as the optimization problems to find the optimal weight of each EI. Then, based on the asynchronous sensing, the specifications of the opportunistic spectrum access mechanism are elaborated in both centralized and decentralized CVNs for the sake of practical implementation. We analyze the system performance in terms of achievable throughput and transmission delay. Numerical results show that the proposed scheme is able to achieve substantially higher throughput and lower delay, as compared with existing schemes. Copyright © 2014 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.     

动态频谱接入MAC协议研究

机会频谱接入（OSA,opportunistic spectrum access）允许未授权用户在空间域和时域上共享授权频谱,但仅当授权用户没有占用这些频谱时认知用户才能接入。另外频谱环境的动态性使MAC协议设计面临着几个重要的问题,即认知用户需要确定何时以什么方式接入哪一个信道发送/接收数据而不影响主用户的通信。从OSA-MAC设计面临的技术挑战出发,对近年来国内外在该方向的研究成果做了总结和分析,并阐述了OSA-MAC设计亟待解决的问题和今后的研究方向。     

A Path-Centric Channel Assignment Framework for Cognitive Radio Wireless Networks

Today’s static spectrum allocation policy results in a situation where the available spectrum is being exhausted while many licensed spectrum bands are under-utilized. To resolve the spectrum exhaustion problem, the cognitive radio wireless network, termed CogNet in this paper, has recently been proposed to enable unlicensed users to dynamically access the licensed spectrum bands that are unused in either temporal or spatial domain, through spectrum-agile cognitive radios. The CogNet plays the role of secondary user in this shared spectrum access framework, and the spectrum bands accessible by CogNets are inherently heterogeneous and dynamic. To establish the communication infrastructure for a CogNet, the cognitive radio of each CogNet node detects the accessible spectrum bands and chooses one as its operating frequency, a process termed channel assignment. In this paper we propose a graph-based path-centric channel assignment framework to model multi-hop ad hoc CogNets and perform channel assignment from a network perspective. Simulation results show that the path-centric channel assignment framework outperforms traditional link-centric approach.

基于部分可观察马氏决策过程的频谱接入方法

为了提高分等级网络中次用户通过机会频谱接入获得的有效吞吐率, 提出了一种基于信道质量的鲁棒机会频谱接入策略.该策略利用信道质量信息和信道占用信息做出传输决策, 使得次用户在信道感知结果为空闲和占用时分别以不同的信道质量门限选择传输机会发起传输, 充分利用了信道质量好的传输机会.结合该策略, 建立了以对主用户的干扰为约束条件, 最大化次用户有效吞吐率的优化问题, 并考虑到了信道传播特性统计参数存在不准确估计的情况, 对该接入策略的门限进行了鲁棒性设计.仿真结果表明:所提出的鲁棒机会频谱接入策略能够显著提高次用户的有效吞吐率.     

一种针对超短波电台接入网的混合信道接入方案

为超短波电台接入网提供了一种混合信道接入方案,方案借鉴了民用接入技术的一些先进理念,并结合军用跳频电台网络的特殊业务应用需求,采用了一种静态TDMA、动态TDMA和频分多址FDMA的混合信道接入策略,实现了多用户多业务传输的QOS保障,满足了军用业务的特殊传输需求。     

基于最优停止的认知无线网络下行频谱接入算法

为有效平衡认知无线网络中次用户系统中接入信道的感知时间和信道总的吞吐量之间的矛盾,提出了一种只对部分信道进行感知的频谱接入策略,联合总的感知信道数和各条信道的感知时间进行优化,并通过最优停止算法求解,在最大化节省感知时间的同时,取得较大的平均吞吐量。与HC-MAC(Hardware Constrained- Media Access Control)算法的仿真分析对比表明,该算法在相同给定条件下感知时间更短,吞吐量更大,具有明显的优势。     

Hierarchical game based spectrum access optimization for anti-jamming in UAV network

For the anti-jamming spectrum access optimization problem in unmanned aerial vehicle (UAV) communication networks,considering the complex and diverse malicious jamming from jammers,a Bayesian Stackelberg game was proposed to formulate the competitive relations between UAV users and jammers.Specifically,jammers acted as the leader,whereas users acted as followers of the proposed game.Based on their different utility functions,the jammer and users independently and selfishly selected their optimal strategies and obtained the optimal channels selection.Due to the NP-hard nature,it was challenging to obtain the Stackelberg Equilibrium of the proposed game.To this end,a hierarchical learning framework was formulated,and a hierarchical channel selection-learning algorithm was proposed.Simulations demonstrate that with the proposed hierarchical learning algorithm,UAV nodes can adjust their channel selection and obtain superior performance.