一种基于马尔可夫决策过程的认知无线电网络传输调度方案

该文提出了一种适用于认知无线电网络的跨层传输调度方案,即满足掉包率约束的前提下最小化平均功率消耗。此方案被建模为约束马尔可夫决策过程(MDP)。采用拉格朗日乘子法求解此MDP,并且提出了一种黄金分割乘子搜索法。提出两种简化方法,即状态聚合以及行动集缩减来解决维灾问题。仿真结果显示简化方法对该方案的性能影响很小,且该方案的平均功耗最低。     

一种基于认知无线电的动态频谱接入MAC方案

在传统的无线通信系统中,频谱的分配是固定的。但是由于通信过程的突发性,这些频谱的使用率很低。另一方面,随着无线通信和多媒体的高速发展和广泛应用,无线频谱资源日趋紧张。如何提高频谱利用率已经成为迫切需要解决的问题。一种可行的思路是把这些授权频谱向未授权用户开放,未授权用户采用动态频谱接入技术,在不对授权用户造成干扰的前提下使用频谱。本文以认知无线电技术(Cognitive Radio,CR)为基础,提出了一种基于CR的动态频谱接入MAC方案(CR-Ad Hoc-MAC)。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。     

基于收益的认知无线电多信道阶梯排队接入机制分析

为了简化分析认知无线电系统中授权用户享有更高优先级对认知用户造成的影响,该文将2维生灭排队过程等效为1维非占先排队模型进行分析;并在多信道情景下,提出了一种基于信道收益的阶梯式排队接入方案,给出了由队列结构系数决定的系统性能参数阻塞概率及强制中断率的解析结果。仿真与数值计算验证了等效1维非占先排队模型的有效性;同时比较几种排队机制的性能参数,该文接入方案有较低的阻塞率,并且可根据系统环境自适应调整队列结构将强制中断率控制在较低范围内,不会随系统负荷率增高而增高。     

非理想信道检测的认知无线电网络中能量感知频谱接入

Due to the problem of spectrum underutilization and energy inefficiency in wireless communications, the research on energy efficient Cognitive Radio Networks (CRNs) has received significant attention in both industry and academia. In this paper, we consider the problem of optimal spectrum selection and transmission parameters design with the objective of minimizing energy consumption in CRNs. Since the system state cannot be directly observed due to miss detections and estimation errors, we formulate the optimal spectrum access problem as a Partially Observable Markov Decision Process (POMDP). In particular, the proposed scheme selects the optimal spectrum, modulation and coding scheme, transmission power, and link layer frame size in each time slot according to the belief state, which captures all the history information of past actions and observations. The optimal policy can be acquired by solving POMDP problem with linear programming based algorithm. Simulation results show that significant energy savings can be achieved by the proposed scheme.     

认知无线电系统中的自适应动态频谱分配方法

该文提出了一种认知无线电系统中多小区间的动态频谱分配方法。该方法提出了对检测到的空闲频谱的空闲时长的预测机制,在此基础上,提出了基于频谱可靠性的自适应频谱分配算法。该算法在提高系统稳定性的基础上,最大化频谱资源的连续性;不仅实现了认知系统中频谱切换率的降低,同时保证了各小区所分配频谱的连续性,避免系统开销的增加及频谱管理的复杂化。此外,该方法采用图论着色理论模型实现了各小区之间干扰的抑制。仿真结果验证了该文方法的正确性。     

Optimal Transmission Strategies for Dynamic Spectrum Access in Cognitive Radio Networks

Cognitive radio offers a promising technology to mitigate spectrum shortage in wireless communications. It enables secondary users (SUs) to opportunistically access low-occupancy primary spectral bands as long as their negative effect on the primary user (PU) access is constrained. This PU protection requirement is particularly challenging for multiple SUs over a wide geographical area. In this paper, we study the fundamental performance limit on the throughput of cognitive radio networks under the PU packet collision constraint. With perfect sensing, we develop an optimum spectrum access strategy under generic PU traffic patterns. Without perfect sensing, we quantify the impact of missed detection and false alarm, and propose a modified threshold-based spectrum access strategy that achieves close-to-optimal performance. Moreover, we develop and evaluate a distributed access scheme that enables multiple SUs to collectively protect the PU while adapting to behavioral changes in PU usage patterns. Our results provide useful insight on the trade-off between the protection of the primary user and the throughput performance of cognitive radios.     

认知无线电中基于SA-MIMO-OFDM的动态频谱共享方案

该文提出一种结合频谱自适应(Spectrum Adaptation,SA)与MIMO-OFDM技术的动态频谱共享方案。该方案基于功率门限模型实现非授权信号的自适应频谱成型,并给出了一种简单的动态功率分配算法以最大化比特率。仿真结果表明,该方案能够克服干扰温度模型的局部干扰问题,使用MIMO技术可进一步提高系统性能,通过动态功率分配算法可降低计算复杂性并提高频谱利用率。     

Modified 802.11‐Based Opportunistic Spectrum Access in Cognitive Radio Networks

In this letter, a modified 802.11‐based opportunistic spectrum access is proposed for single‐channel cognitive radio networks where primary users operate on a slot‐by‐slot basis. In our opportunistic spectrum access, control frames are used to reduce the slot‐boundary impact and achieve channel reservation to improve throughput of secondary users. An absorbing Markov chain model is used to analyze the throughput of secondary users. Simulation results show that the analysis accurately predicts the saturation throughput.     

基于预留最优信道机制的CR动态频谱接入研究

在认知无线电网络中,如何提高次用户的性能是当前研究的热点。针对等级覆盖式频谱接入模型进行研究分析,考虑了动态频谱切换过程,建立三维的持续时间马尔可夫链模型,计算出切换概率、阻塞概率、掉线概率,并综合分析各个参数对这些概率的影响。同时提出为主用户预留最优信道数的方案,数值结果表明此方案能有效降低次用户的切换概率和掉线概率,使次系统的切换概率、阻塞概率、掉线概率更加均衡,且提高了次用户系统的接入容量。     

基于认知无线电技术的动态频谱管理构想

本文介绍了认知无线电的感知、分配及共享等相关技术,并针对其技术特点提出了一种以无线电管理机构为感知主体,基于认知无线电技术进行统筹分配的动态频谱管理构想。     

基于业务区分的频谱接入策略分析

在认知无线网络中,如何保证认知用户的传输质量,满足其QoS要求是值得关注的问题。本文首先根据认知用户的QoS要求,将其分成两种等级,实时用户和非实时用户,并分别被建模成M/G/1排队模型,降低了对应的系统时延均值。然后根据系统传输时间均值,讨论了多信道接入策略,通过经典的遗传算法可得最优接入策略,考虑到遗传算法的高复杂度,实际应用中采用反比例接入算法求得次优解,实验数据表明反比例接入算法可以取得与最优接入策略相近的结果且能极大地降低计算时间。     

Secondary Spectrum Access in Cognitive Radio Networks Using Rateless Codes over Rayleigh Fading Channels

In this paper, we propose secondary relaying schemes in cognitive spectrum leasing. In the proposed protocols, a primary transmitter uses rateless code to transmit its data to a primary receiver. In the secondary network, \(M\) secondary transmitters are ready to help the primary transmitter forward the data to a primary receiver so that they can find opportunities to transmit their data. For performance evaluation, we derive the average outage probability, the average number of encoded packets transmitted by the primary transmitter, the average number of remaining time slots for secondary network and the average capacity of the secondary network over Rayleigh fading channels. Various Monte-Carlo simulations are presented to verify the derivations.     

基于主动频谱感知接入的认知无线电台研究

讨论了所研制的工作于30-512 MHz的基于主动频谱感知接入的认知无线电台。该电台实现了认知无线电动态频谱接入最为关键的几大功能：频谱感知、频谱会合、频谱监视,以及频谱切换。试验结果表明,该电台具备在不依赖于公共控制信道的情况下自动寻找空闲信道建立链路的能力,也具备在当前通信信道上出现主用户信号或其他干扰信号时自动切换到其他空闲信道上继续通信的能力,为认知无线电技术的实用化提供了很好的借鉴。     

Fast Spectrum Sensing with Coordinate System in Cognitive Radio Networks

Spectrum sensing is an elementary function in cognitive radio designed to monitor the existence of a primary user (PU). To achieve a high rate of detection, most techniques rely on knowledge of prior spectrum patterns, with a trade‐off between high computational complexity and long sensing time. On the other hand, blind techniques ignore pattern matching processes to reduce processing time, but their accuracy degrades greatly at low signal‐to‐noise ratios. To achieve both a high rate of detection and short sensing time, we propose fast spectrum sensing with coordinate system (FSC) — a novel technique that decomposes a spectrum with high complexity into a new coordinate system of salient features and that uses these features in its PU detection process. Not only is the space of a buffer that is used to store information about a PU reduced, but also the sensing process is fast. The performance of FSC is evaluated according to its accuracy and sensing time against six other well‐known conventional techniques through a wireless microphone signal based on the IEEE 802.22 standard. FSC gives the best performance overall.     

动态频谱接入网络的路由技术研究

新一代宽带无线通信网络迫切需要引入认知无线电技术以提升系统性能。针对动态频谱接入(DSA)的无线网络环境,首先探讨了其路由技术研究所面临的新挑战,然后以体现动态频谱管理特征的独特分类方式,分析了其路由技术研究的最新进展,最后展望了路由技术研究的未来发展方向。     

具有约束条件的认知无线电网络最优频谱价格函数

保证主用户的QoS是认知无线电网络中必须遵循的原则之一.本文利用伺机频谱共享方式中的实际约束条件,求解出既能保证主用户的QoS,又能使主业务运营商获得较大利润的最优频谱价格函数.该价格函数能反映实际的通信环境(如信道质量、业务动态性)对频谱价格的影响,同时在动态环境下,通过迭代可以使频谱价格收敛到最优价格.仿真结果表明...     

认知无线网络基于信号博弈的分布式功率控制算法

针对认知无线网络分布式环境下信道信息不对称导致资源分配冲突的问题,该文提出一种基于信号博弈的分布式功率分配算法.考虑具有竞争关系的次用户在不使用控制信道的情况下,通过信号博弈策略依次选择功率分配策略,达到信道信息共享的目的,能有效避免对主用户正常传输的干扰以及竞争次用户之间功率分配冲突.该文对均衡结果进行分析,仿真结果表明该算法可以有效估计信道增益,次用户的吞吐量相对于已有研究得到明显提升.     

Energy-Based Collaborative Spectrum Sensing for Cognitive UWB Impulse Radio

This paper focuses on the issue of collaborative spectrum sensing in cognitive ultra wideband (CUWB) impulse radio. We employ energy-based signal detection method and apply the Neyman-Pearson (NP) deci...     

Variable Persistence Sensing Schemes for Opportunistic Spectrum Access

Cognition technologies can significantly enhance spectrum utilization through secondary usage. Secondary users （SUs） search for spectrum holes which are not used by Primary users （PUs） and communicate through them. The design and analysis of simple opportunistic spectrum access schemes for maximizing utilization efficiency and minimizing delay of SUs under limited sensing bandwidth and energy is still at infancy. In this work, we consider PU＇s frequency occupancy patterns and propose three simple variable persistence sensing schemes for maximum exploitation of idle spectrum chunks by SUs, and perform their theoretical analysis. Numerical case studies are presented to verify the theoretical analysis and illustrate the performance of the schemes proposed.     

Q-Learning Based Interference-Aware Channel Handoff for Partially Observable Cognitive Radio Ad Hoc Networks

Channel handoff is a crucial function for Cognitive radio ad hoc networks (CRAHNs). The ab-sence of centralized infrastructures and the limited power make the handoff design more challenging. A learning-based interference-aware handoff scheme is proposed for distributed CRAHNs. We model the channel handoff pro-cess as a Partially observable Markov decision process (POMDP) and adopt a Q-learning algorithm to find an optimal handoff strategy in a long term. The proposed algorithm obtains an efficient transmission performance by considering the interferences among SUs and PUs. To achieve PU awareness, the handoff scheme predicts the PU activities by using the historical channel usage statistics. In addition, we also propose a refined channel selection rule to compromise between learning speed and cumulative trans-mission reward. The simulation results show that the pro-posed handoff scheme can adapt to the PU activities and achieves a better performance in terms of high throughput and low collisions. And the learning process keeps a consid-erable balance between convergence time and cumulative reward.