A dynamic and weighted spectrum decision mechanism based on SNR Tracking in CRAHNs

The spectrum decision concept in Cognitive Radio Ad-Hoc Networks (CRAHNs) introduces important challenges. These include the time-dependent SNR observations of individual CRAHN users due to the fading and shadowing effects in the licensed channels, the necessity of fusion mechanisms for accurate decisions, and the difficulties depending on multi-hop deployment. Considering these challenges, in this paper, we propose a dynamic, cooperative and distributed spectrum decision mechanism in order to decide the channel usage in CRAHNs accurately. The proposed mechanism introduces the SNR Tracking System which considers the time-varying local SNR observations and decisions of the CRAHN users. The proposed mechanism employs a distributed Weighted Fusion Scheme (WFS), to combine the individual decisions and hence, to obtain the cooperative decision. The proposed spectrum decision mechanism adapts itself dynamically to the multi-hop architecture of the network. The performance of the proposed mechanism is compared to some conventional fusion mechanisms based on the AND, OR and MAJORITY rules, and it is shown that the proposed weighted mechanism gives lower false alarm and higher detection probabilities compared to the conventional fusion mechanisms.     

基于POMDP的次用户多时隙信道选择算法

为了最大化次用户系统吞吐量,同时减少信道选择过程中的计算量,在多条主用户信道的次用户多时隙系统中,用半马尔科夫链(Partially Observable Markov Decision Process,POMDP)理论刻画次用户信道选择过程,并提出了对应的信道选择算法。在每一个时隙开始时,次用户选择部分信道进行感知,之后根据感知结果选择不同的传输功率接入信道,对于没有被感知的信道,次用户可以直接接入。对POMDP问题求解采用了最优策略、次优策略以及任意策略,并通过在不同仿真环境下的数值分析比较,论证了所提算法的实用有效。     

A MULTI-RESOLUTION SPECTRUM SENSING （MRSS） SCHEME UNDER MEASUREMENT-BASED CHANNEL MODELS IN COGNITIVE RADIO

Spectrum sensing is one of the key technologies in Cognitive Radios (CRs). Previous works are accomplished under simple channel models, which may lead to unreliable results when it applied to the over-the-air systems. In this paper, we investigate the performance of a Multi-Resolution Spectrum Sensing (MRSS) algorithm under measurement-based channel models in China. MRSS is a wavelet based algorithm which is suitable for non-stationary, wideband signal analysis. Using statistical modeling, measurement-based channel models are presented under typical urban and suburban scenarios in Shanghai, China. Then, the performance of the MRSS algorithm is evaluated under the measurement-based channel models. Simulation results show that, using MRSS, the performance is always better in the scenarios where Line-Of-Sight (LOS) path exist; also, in LOS scenarios, rich scattering effect helps to increase the performance.     

A decision aided channel estimation scheme

In this letter, we address the problem of mobile radio channel estimation at high channel efficiency using a small number of training symbols. A decision aided channel estimation scheme is proposed for slow fading multipath DS-CDMA channels. The approach is an extension of single-user least-square channel estimation. It is demonstrated that, due to the suggested channel estimate updating algorithm, the proposed scheme improves the channel estimation accuracy significantly.     

天线选择对MIMO信道容量的影响

该文首先分析了多天线系统的信道容量,然后研究了当信道矩阵非满秩时,选择发射和接收天线对信道容量的影响。仿真试验结果表明,发射天线选择能提高系统容量,同时选择发射和接收天线虽然减小了复杂度和硬件成本,但对系统容量的增加低于单独进行发射天线选择时的情况。     

Channel Selection for Spectrum Sharing in Wireless Networks

In this paper, we study a spectrum sharing network (SSN) where a spectrum sharing device (SSD) coexists with multiple wireless communication systems (WCSs) in the same channel. The SSD can operate with either a duty cycle (DC) channel access mechanism or a listen‐before‐talk (LBT) channel access mechanism, whereas WCSs operate with an LBT mechanism. An opportunistic channel selection scheme for the SSD in the SSN is first proposed to minimize the outage probability. The optimal data transmission time for the DC‐based SSD is derived to further improve the outage probability. We also derive the exact and closed‐form outage probability of the proposed channel selection in the SSN by assuming that the number of WCSs operating in each channel is uniformly distributed. The simulation results show that the proposed channel selection scheme outperforms other channel selection schemes. It was also observed that a DC‐based SSD with an optimal data transmission time provides a better outage performance than an LBT‐based SSD. As the number of available channels increases, the channel selection scheme plays an important role in minimizing the outage probability of the SSNs.     

基于改进人工鱼群算法的协作频谱感知用户选择策略

选择次用户是协作频谱感知的一个关键环节。针对次用户选择问题的特点,在基本人工鱼群算法AFSA基础上,通过取消鱼群密度、取消人工鱼的随机游动、改变公告板记录规则、保留每次迭代最优位置、增加最优人工鱼的觅食次数并缩小视野提出改进的人工鱼群算法次用户选择策略。仿真结果表明,对于最优次用户组选择问题,本文提出的修正AFSA在寻优成功率和运行时间等方面优于传统的AFSA。     

宽带CDMA系统中的一种新的自适应信道估计方法

该文提出了采用实测的信道自相关系数作为权重的信道估计处理方法,并给出其误差性能的数学表达式,同时给出了经典的滑动平均信道估计方法的误差性能的数学表达式。理论分析及仿真结果表明所提的方法能自动适应移动信道的时变模型及衰落速率,具有有效地抑制噪声的优点;同时克服了滑动平均估计方法的估计长度对估计准确性影响较大的缺点,在移动速度固定及移动速度变化很大的环境下都具有稳定的误差性能;尤其在移动速度变化很大的环境下具有比滑动平均估计方法更低的估计方差,大大提高了RAKE接收机的性能。     

A novel spectrum sharing scheme for cognitive radios

A novel approach, which combines spectrum adaptation and orthogonal frequency division multiplexing (OFDM), is proposed to share the licensed spectrum dynamically for cognitive radio systems. Given spectrum sensing and channel estimation information by the receiver, an improved model due to signal power thresholds is adopted to achieve spectrum adaptation for unlicensed users. In order to efficiently allocate the unlicensed signal power, a dynamic power allocation algorithm is also proposed. Simulation results indicate that the propositional scheme solves the partial interference problem of interference temperature model (ITM) and improves the spectrum utilization.     

分布式双向中继选择算法及用户功率分配

针对放大转发的瑞利双向中继信道的节点选择问题,提出了基于部分信道信息的分布式双向中继选择算法。算法通过计算双向链路的接收信噪比,推导出满足目标接收信噪比的转发阈值,各中继节点根据该阈值决定是否参与转发,从而实现分布式选择。此外,考虑用户总功率受限的情况,在分布式中继选择基础上提出了优化功率分配策略,使双向信道的接收信噪比更加接近。仿真结果表明,分布式中继选择算法与最优多中继算法的系统传输速率相似,计算复杂度大大降低,尤其是在中继数目增大的情况下更加明显。优化功率分配策略能进一步提高系统能量效率,在相同性能下可节省7%左右的功率。     

一种基于非正交信道的分布式中继选择及功率分配方法

针对非正交两跳多中继协作通信系统中的分布式中继选择问题,提出了一种基于非正交信道的中继选择准则,简化了系统的设计。分析了其误码率性能,给出了其解析表达式和以总功率为约束条件下的最优功率分配方案。仿真结果表明,最佳中继选择准则明显优于传统的中继选择准则,且在最优功率分配方案下,可以获得明显的分集增益,系统的误码率显著下降。     

卫星稀疏信道中频谱空穴的新型检测算法

面对宽带移动卫星通信中信道占用呈现的稀疏状态和时而存在的稀疏干扰,以低速率 采样和运算是简化设备的必要途径。针对宽带频谱范围内稀疏信道信号和干扰信号的检测, 提出了一种用于直接估计频谱空穴的压缩采样算法,以低速率对信号进行采样,通过相 关向量机进行迭代优化,给出检测估计值。该算法基于最大似然贝叶斯估计,具有良好的抗 噪性能,同时能够降低设备复杂度。仿真结果表明,其抗噪性能明显好于CVX方法而略逊于理 想情况,而前端随机序列的相关性是影响检测性能的重要因素。     

A network selection scheme for multicast applications in wireless network convergence

In wireless network convergence, each mobile host is expected to have multiple kinds of wireless interfaces. Multicast‐based applications are expected to be widely deployed. In this paper, a new network selection scheme is proposed for a mobile host to select the most appropriate wireless access network to maximize user satisfaction and ISP's profit, simultaneously. We have devised a metric to measure a user's satisfaction and we also developed a ‘normalized network resource’ metric for system profit measure. We have compared our scheme with three other reference schemes, through simulations. Depending on the network deployment situations, our scheme exhibits one‐fifth service disruption time of other reference schemes, while the resource consumption of our scheme is comparable to that of the minimum resource scheme. Overall, the gain of our scheme becomes higher as users move faster and/or the population density increases. Copyright © 2010 John Wiley & Sons, Ltd.     

一种ATM/MPLS网络的负荷分担方案

在某一ATM/MPLS体制的保证信息安全的通信试验网络中,网络流量呈星形分布,各个单元传送到中心节点应用网络的业务量通过单个100Mb/s以太网接口不能满足要求,需要通过多个端口接入MPLS网络。针对如何在接入的多个端口之间进行负荷分担的问题,提出了一种基于路由模式工作的防火墙网络地址转换NAT功能及MPLSTE实现的负荷分担方案,简单实用,该方案已经成功应用于实际的组网环境,并通过试验验证能够满足系统的应用需求。     

Inter-operator spectrum sharing scheme for reconfigurable system

Bargaining based mechanism for sharing spectrum between radio access networks (RANs) belonging to multioperators is studied, to improve spectrum utilization efficiency and maximize network revenue.By introducing an intelligent agent, each RAN has the ability, which includes trading information exchanging, final decision making, and so on, to trade the spectrum with other RANs.The proposed inter-operator spectrum sharing mechanism is modeled as an infinite-horizon bargaining game with incomplete information, and the resulting bargaining game has unique sequential equilibrium.Consequently, the implementation is refined based on the analysis.Simulation results show that the proposed mechanism outperforms the conventional fixed spectrum management (FSM) method in network revenue, spectrum efficiency, and call blocking rate.     

云存储环境下的密文安全共享机制

With the convenient of storing and sharing data in cloud storage environment,the concerns about data security arised as well.To achieve data security on untrusted servers,user usually stored the encrypted data on the cloud storage environment.How to build a cipertext-based access control scheme became a pot issue.For the access control problems of ciphertext in cloud storage environment,a CP-ABE based data sharing scheme was proposed.Novel key generation and distribution strategies were proposed to reduce the reliance on a trusted third party.Personal information was added in decryption key to resistant conclusion attacks at the same time.Moreover,key revocation scheme was proposed to provide the data backward secrecy.The security and implement analysis proves that proposed scheme is suit for the real application environment.     

A pilot-based dynamic channel assignment scheme for wireless access TDMA/FDMA systems

We propose a control architecture for implementing a dynamic channel assignment (DCA) algorithm which optimizes two-way channel quality in a TDMA portable radio system. Computer simulations are used to evaluate the performance of this DCA method. A common control frequency, which is frame-synchronized among base stations, provides (1) beacons for portables to locate base stations and obtain DCA information, (2) broadcast channels for system and alerting information, and (3) pilot signals to permit portables to evaluate downlink interference. This allows low-complexity radio ports and portables to mutually select channels to avoid interference and avoid creating excessive interference. Results from computer simulations demonstrate the good spectrum efficiency of this method and its potential for handling nonuniform traffic demand. This work is targeted toward understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks.A preliminary work with the same title was presented at the Second International Conference on Universal Personal Communications, October 12–15, 1993, Ottawa, Canada.     

Cooperative spectrum sharing of multiple primary users and multiple secondary users

This paper proposes a multiple-input multiple-output (MIMO) based cooperative dynamic spectrum access (DSA) framework that enables multiple primary users (PUs) and multiple secondary users (SUs) to cooperate in spectrum sharing. By exploiting MIMO in cooperative DSA, SUs can relay the primary traffic and send their own data at the same time, which greatly improves the performance of both PUs and SUs when compared to the non-MIMO time-division spectrum sharing schemes. Especially, we focus on the relay selection optimization problem among multiple PUs and multiple SUs. The network-wide cooperation and competition are formulated as a bargaining game, and an algorithm is developed to derive the optimal PU-SU relay assignment and resource allocation. Evaluation results show that both primary and secondary users achieve significant utility gains with the proposed framework, which gives all of them incentive for cooperation.     

MaxDiv: an optimal randomized spectrum access with maximum diversity scheme for cognitive radio networks

Cognitive radio network (CRN) is an emerging technology that can increase the utilization of spectrum underutilized by primary users (PUs). In the literature, most exiting investigations on CRNs have focused on how secondary users (SUs) can coexist harmlessly with the PUs. Despite the importance of such a coexistence issue, it is also crucial to investigate the coexistence of SUs because (i) the PUs usually rarely use the licensed spectrum and (ii) the advantages of CRN will significantly increase the number of SUs in the future. To address this challenging issue, we propose, in this paper, an optimal randomized spectrum access scheme, whose main ideas include the following: (i) an SU shares its sensing results with neighboring SUs and (ii) with the regional sensing results, an SU will access available channels with a non‐uniform probability distribution. We first formulate a multichannel optimal randomized multiple access (MC‐ORMA) problem that aims to maximize the throughput of the CRN; we then develop efficient distributed algorithms to solve the MC‐ORMA problem; we derive the closed‐form value of collision probability for each SU; and finally, we conduct extensive numerical experiments and compare our theoretical analysis with simulation results to demonstrate the advantages of our scheme. Copyright © 2011 John Wiley & Sons, Ltd.     

Protocols and architectures for channel assignment in wireless mesh networks

The use of multiple channels can substantially improve the performance of wireless mesh networks. Considering that the IEEE PHY specification permits the simultaneous operation of three non-overlapping channels in the 2.4 GHz band and 12 non-overlapping channels in the 5 GHz band, a major challenge in wireless mesh networks is how to efficiently assign these available channels in order to optimize the network performance. We survey and classify the current techniques proposed to solve this problem in both single-radio and multi-radio wireless mesh networks. This paper also discusses the issues in the design of multi-channel protocols and architectures.