Adaptive power control and beam-forming joint optimization in cognitive radio networks

A novel adaptive power control and beam-forming joint optimization algorithm is proposed in cognitive radio(CR) underlay networks,where cognitive network share spectrum with primary network which spectrum is licensed.In this paper,both primary base station(PBS) and cognitive base station(CBS) are all equipped with multi antennas,while each primary user(PU) and cognitive user(CU) has only one antenna.Different from traditional algorithms,an adaptive weight factor generating solution is supplied to different access users(both PUs and CUs) in this paper,and the different priority of users is also considered,because PUs have higher priority,the weight factor of PUs is fixed as constant and signal-to-interference and noise ratio(SINR) threshold is unchanged,while for CUs,it is set adaptively and SINR threshold is also changed accordingly.Using this algorithm,the transmit power is decreased,which relax the strict requirements for power amplifier in communication systems.And moreover,owing to PUS has fixed SINR threshold,the calculated SINR at receiver is nearly unchanged,but for CUs,the SINR is changing with the adaptive weight factor.Under the assurance of quality of service(QoS) of PUs,the solution in this paper can enable CRs access to the CR network according to adaptive SINR threshold,therefore which supplies higher spectrum utilization efficiency.     

Efficient Power Allocation for Multiuser Cognitive Radio Networks

Cognitive radio has been recently considered as a flexible spectrum usage model to improve the spectrum efficiency. In this paper, we develop a new power allocation approach by geometric programming (GP) to realize the coexistence of a primary user (PU) and multiple cognitive users (CUs) in the same frequency band. The objective is to minimize the total power consumption of CUs while guaranteeing the not only protection of PU but also the quality of service (QoS) of multiple CUs, which is different from previous works. In order to facilitate the centralized computation, a distributed algorithm is developed to adaptively adjust the transmit power of each CU. Numerical results are provided to show the effectiveness of the proposed algorithm in power saving.     

QoS保证的多信道混合接入CRN频谱共享策略设计

根据既不对主用户(Primary Radio user,PR)产生干扰,又对认知无线电用户(Cognitive Radio user,CR)提供QoS保证的原则,将认知无线电网络(Cognitive Radio Network,CRN)中多信道接入频谱共享问题建模为混合整数非线性规划。采用多级功率限制保证PR不被干扰,以CR物理层能够提供的速率作为信道和功率分配的依据,提出将能够为CR提供最大传输速率的信道分配给该CR的分配策略,将混合整数非线性规划转化为整数线性规划,并给出集中式启发算法和基于功率速率比(Power Rate Ratio,PRR)最小的分布式启发算法求解该整数线性规划。仿真结果表明,文中给出的算法能够提供较高的CRN吞吐量和较好的CR用户QoS保证。     

Primary user supported routing protocol for cognitive radio ad hoc networks in search of higher throughput

A routing protocol for cognitive radio ad hoc networks (CRAHNs), namely, primary user supported routing (PSR) is demonstrated in this research. Unlike existing routing protocols for CRAHN, where routing of cognitive users (CUs) is accomplished within CUs, in this proposed protocol, some of the primary users (PUs) support CUs to communicate, by forwarding CU packets. This service provided by PU is of voluntary nature. However, such assistance shall be provided by the PUs, only when they are idle, thereby, preserving the principles of cognitive radio networks (CRNs), which indicates that the operation of PU should not be disturbed by the CU activities. The proposed work is compared with cognitive ad hoc on-demand distance vector (CAODV) protocol. The performance parameters considered are routing overhead, rate of loss of packets, and e2e packet delay. PSR outperforms CAODV in all these performance parameters. There has been on average 26.25% improvement in routing overhead, 34.12% decrease in loss, and 27.01% improvement in e2e delivery in the proposed PSR.     

Multiple Relay Selection Based on Game Theory in Cooperative Cognitive Radio Networks

Due to the inefficiency of traditional fixed spectrum allocation policies, the paradox of apparent spec-trum scarcity occurs while most of the bands are under-utilized. This has prompted proposals for Dynamic spec-trum sharing (DSS), which explains why Cognitive radio network (CRN) has been widely accepted as a promising approach to settle inefficient usage of scarce available radio spectrum. As a subset of DSS, Dynamic spectrum leasing (DSL) strategy has been proposed based on game idea, where Primary user (PU) has an incentive to allow Cog-nitive users (CUs) to access its licensed spectrum for a fraction of time in exchange for revenue. This paper pro-poses an approach, named multiple relay selection based on Game theory (GTMRS), to optimize the utilities of PU and CUs as a whole, where a pricing-based spectrum leas-ing mechanism is applied. While the parameter price c is jointly determined by PU and CUs, all selected cognitive user's optimal cooperative powers can be satisfied through a non-cooperative game among themselves. Numerical re-sults show that more CUs are involved in the cooperation and both utilities of PU and CUs as a whole are improved, which means the whole system throughput is increased.     

Prediction based channel allocation performance for cognitive radio

The interdependency, in a cognitive radio (CR) network, of spectrum sensing, occupancy modelling, channel switching and secondary user (SU) performance, is investigated. Achievable SU data throughput and primary user (PU) disruption rate have been examined for both theoretical test data as well as data obtained from real-world spectrum measurements done in Pretoria, South Africa. A channel switching simulator was developed to investigate SU performance, where a hidden Markov model (HMM) was employed to model and predict PU behaviour, from which proactive channel allocations could be made. Results show that CR performance may be improved if PU behaviour is accurately modelled, since accurate prediction allows the SU to make proactive channel switching decisions. It is further shown that a trade-off may exist between achievable SU throughput and average PU disruption rate. When using the prediction model, significant performance improvements, particularly under heavy traffic density conditions, of up to double the SU throughput and half the PU disruption rate were observed. Results obtained from a measurement campaign were comparable with those obtained from theoretical occupancy data, with an average similarity score of 95% for prediction accuracy, 90% for SU throughput and 70% for PU disruption rate.     

Improving TDMA Channel Utilization in Random Access Cognitive Radio Networks by Exploiting Slotted CSMA

This paper aims to improve the spectrum efficiency of the licensed time division multiple access (TDMA) channel by exploiting the unused periods of primary users (PUs) in cognitive radio networks. A wireless network that consists of two classes of users, PUs and CR users, accessing a time slotted based common communication channel is considered. PUs employ TDMA and have always high priority over the CR users to access the channel. CR users utilize slotted Carrier Sense Multiple Access and can access the channel when it is not occupied by the PUs. New expressions for the throughput of both CR network and overall network have been derived in order to evaluate the channel utilization. Besides, an example network have been developed, modeled and simulated by using the OPNET Modeler simulation software with the purpose of verifying the analytical throughput results. The simulation results obtained under various network load conditions are consistent with the analytical results. This study has also proposed that the overall channel utilization can be improved by well exploiting the spectrum holes without interfering with the PU transmissions.     

Characterization and exploitation of heterogeneous OFDM primary users in cognitive radio networks

The fundamental features of cognitive radio (CR) systems are their ability to adapt to the wireless environment where they operate and their opportunistic occupation of the licensed spectrum bands assigned to the primary network. CR users in CR systems should not cause any interference to primary users (PUs) of the primary network. For this purpose, CR users need to accurately estimate the features and activities of the primary users. In this paper, a novel characterization of heterogeneous PUs and a novel reconfigurability solution in CR networks are introduced. The characterization of PUs consists of a detector and classifier that distinguishes between heterogenous PUs. The PU characteristics stored in radio environmental maps are utilized by an interference/throughput adapter for the optimization of CR parameters. The performance of the proposed solutions is evaluated by showing false alarm and missed detection probabilities of the detector/classifier in a multipath fading channel with additive white Gaussian noise. Moreover, the impact of the PU characteristics on the CR throughput is analyzed.     

Throughput analysis in censoring-based cooperative cognitive radio network with energy harvesting

An energy harvesting (EH) and cooperative cognitive radio (CR) network (CRN) is studied in this paper where CR users transmit data through a primary user (PU) channel if the channel remains idle, else an optimal number CRs helps in transmission of PU. To achieve the optimum number of CRs (ONCR) involved in cooperation, a novel scheme based on a combination of channel censoring and total error is proposed. The performance of the proposed scheme is investigated under RF harvesting scenario. The EH is dependent on sensing decision and a CR source harvests energy from PU's RF signal. The harvested energy (HE) is split into two parts: One part is used by the CR network (CRN) for its own transmission, and the other part is used for supporting PU. The effect of the energy allocation factor on total throughput is also investigated. New expressions for optimal number of CRs and throughput are developed. The effect of network parameters such as sensing time, censoring threshold, and energy allocation parameter (EAP) on throughput is investigated. Impact of distance between nodes is also studied.     

移动用户目标系统中基于拍卖模型的信道资源分配

为了提高卫星通信信道的频谱利用率,从卫星通信中的认知无线电技术出发,简述了当前认知卫星研究现状。针对移动用户目标系统( Mobile User Objective System,MUOS)的特殊通信环境,提出了插空式( overlay)频谱共享方式下基于拍卖模型的认知卫星信道分配方式,并建立了收益公式。同时,引入星上频谱共享干扰公式来计算认知用户对系统造成的影响,并代入收益公式以计算认知技术给系统带来的收益大小;之后给出模拟通信环境参数,利用Matlab进行仿真计算。仿真结果表明,认知用户的加入虽会使主用户通信质量略有下降,但使系统总体收益呈上升趋势。     

Interference Mitigation Based on Radio Aware Channel Assignment for Wireless Mesh Networks

An intricate network deployment for high demand users leads to simultaneous transmission in wireless mesh networks. Multiple radios are adapted to individual nodes for improving network performance and Quality of Service (QoS). However, whenever multiple radios are assigned to the same channel, co-located radio interference occurs, which poses a major drawback. This paper proposes a Radio aware Channel Assignment (Ra-CA) mechanism based on a direct graphical model for mitigation of interference in multi-radio multi-channel networks. Initially, the co-located radio interference is identified by classifying non-interfering links for simultaneous transmission in the network. Proposed channel assignment mechanism helps in allocating the minimal number of channels to the network that mitigate co-located radio interference. Performance analysis of the proposed Ra-CA strategy is carried out compared with other existing techniques, like Breadth First Search-Channel Assignment (BFS-CA) and Maximal Independent Set Channel Assignment (MaIS-CA), in multi-radio networks. Simulation results demonstrate that the proposed channel assignment scheme is more efficient compared to the existing ones, in terms of QoS parameters like, packet drop rate, packet delivery ratio, transmission delay and throughput.     

基于干扰对齐的认知无线电网络中用户性能的优化设计

干扰对齐（IA）是一种新兴的干扰管理技术,被广泛的应用于认知无线电（CR）网络之中,以期消除认知用户（CU）对授权用户（AU）的干扰。然而干扰对齐技术带来了授权用户接收信干噪比（SINR）的下降,使得授权用户的传输速率受到影响。在低信噪比下,授权用户性能无法保证。本文创新性地提出了两种算法设计授权用户预编码滤波器,优化其传输速率,极大地提高了授权用户的性能。同时,为了提高认知用户的性能,本文给出了认知用户的干扰抑制滤波器的优化方案,最大化认知用户的和速率。仿真结果表明,这两种算法都能在一定程度上提高授权用户的传输速率,同时认知用户的传输速率也得以保证。      

Multi slot-throughput tradeoff in an improved energy detector based faded cognitive radio network

In this paper, the impact of a multi slot based cooperative spectrum sensing (CSS) on the performance of a cognitive radio (CR) network has been investigated. Each CR user, equipped with an improved energy detector (IED), uses a number of mini slots of the sensing time to perform the spectrum sensing. Each CR uses OR logic to combine the sub local decisions generated in each mini slot to obtain a local decision at CR level. Local decisions are sent to fusion centre (FC) over reporting channel. The FC obtains a final decision about the presence of primary user (PU) by combining the local decisions using a fusion rule: Majority or Maximal Ratio Combining. The performance of the CSS is assessed in terms of detection probability and false alarm probability considering both the sensing and reporting channels are Rayleigh faded. Furthermore, the impact of a number of sensing slots and IED parameter on throughput of CR network is also evaluated under the proposed spectrum sensing scenario. Impacts of several sensing parameters such as sensing channel SNR and reporting channel SNR on the performance of CR network are also evaluated. Performances of two fusion rules under study are compared. Effect of sensing error and synchronisation error is indicated. Further the study is extended for independent but non identically distributed (i.n.i.d.) Rayleigh faded channels as well as for a multiple PU scenario also.     

Optimization algorithm of periodical cooperative spectrum sensing in cognitive radio

To decrease the interference to the primary user (PU) and improve the detected performance of cognitive radio (CR), a single‐band sensing scheme wherein the CR periodically senses the PU by cooperative spectrum sensing is proposed in this paper. In this scheme, CR first senses and then transmits during each period, and after the presence of the PU is detected, CR has to vacate to search another idle channel. The joint optimization algorithm based on the double optimization is proposed to optimize the periodical cooperative spectrum sensing scheme. The maximal throughput and minimal search time can be respectively obtained through the joint optimization of the local sensing time and the number of the cooperative CRs. We also extend this scheme to the periodical wideband cooperative spectrum sensing, and the joint optimization algorithm of the numbers of the sensing time slots and cooperative CRs is also proposed to obtain the maximal throughput of CR. The simulation shows that the proposed algorithm has lower computational quantity, and compared with the previous algorithms, when SNR = 5 dB, the throughput and search time of the proposed algorithm can respectively improve 0.3 kB and decrease 0.4 s. The simulation also indicates that the wideband cooperative spectrum sensing can achieve higher throughput than the single‐band cooperative spectrum sensing. Copyright © 2012 John Wiley & Sons, Ltd.     

基于网络编码的衰落信道频谱感知算法

针对传统认知无线电网络中频谱状态转换频繁和频谱检测时延长的问题,提出基于随机线性网络编码的累积和能量检测频谱感知算法。该算法在主用户信道中引入随机线性网络编码,利用网络编码对频谱的整形作用,使频谱状态转换稀疏,频谱结构更规律化,减小频谱检测时延,提高系统吞吐率。此外,针对传统累积和能量检测算法抗衰落性能差的问题,通过比较该算法在五种衰落信道下的检测时延和吞吐率,研究该算法的抗衰落性能。实验结果表明,在一定的虚警概率下,该算法有效降低了检测时延,提高了吞吐率及抗衰落能力,能够更好地适应复杂的衰落信道环境。     

MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).     

Routing for cognitive radio networks consisting of opportunistic links

Cognitive radio (CR) has been considered a key technology to enhance overall spectrum utilization by opportunistic transmissions in CR transmitter–receiver link(s). However, CRs must form a cognitive radio network (CRN) so that the messages can be forwarded from source to destination, on top of a number of opportunistic links from co‐existing multi‐radio systems. Unfortunately, appropriate routing in CRN of coexisting multi‐radio systems remains an open problem. We explore the fundamental behaviors of CR links to conclude three major challenges, and thus decompose general CRN into cognitive radio relay network (CRRN), CR uplink relay network, CR downlink relay network, and tunneling (or core) network. Due to extremely dynamic nature of CR links, traditional routing to maintain end‐to‐end routing table for ad hoc networks is not feasible. We locally build up one‐step forward table at each CR to proceed based on spectrum sensing to determine trend of paths from source to destination, while primary systems (PSs) follow original ways to forward packets like tunneling. From simulations over ad hoc with infrastructure network topology and random network topology, we demonstrate such simple routing concept known as CRN local on‐demand (CLOD) routing to be realistic at reasonable routing delay to route packets through. Copyright © 2009 John Wiley & Sons, Ltd.     

A reliable cooperative spectrum detection scheme in cognitive radio networks

Reliable spectrum detection of the primary user (PU) performs an important role in the cognitive radio network since it’s the foundation of other operations. Spectrum sensing and cognitive signal recognition are two key tasks in the development of cognitive radio (CR) technology in both commercial and military applications. However, when the CR terminals receiving signals have little knowledge about the channel or signal types, these two tasks will become much more difficult. In this paper, we propose a reliable cooperative spectrum detection scheme, which combines the cooperative spectrum sensing with distributed cognitive signal recognition. A novel improved cooperative sensing algorithm is achieved by using a credibility weight factor and the “tug-of-war” rule, which is based on the double threshold detection and Dempster–Shafer theory, to determine whether the PU signals exist. In this scheme, cognitive signal recognition can be used to identify the signal type when the PU signal is present. During the cognitive signal recognition processing, the CR terminals make local classification of the received signals by using Daubechies5 wavelet transform and Fractional Fourier Transform, and send their recognition results to the globe decision making center. A distributed processing uses these cognitive terminals’ local results to make final decisions under the Maximum Likelihood estimation algorithm. Simulation results show that the proposed method can achieve good sensing probability and recognition accuracy under the Additive White Gaussian Noise channel.     

Optimal channel access for TCP performance improvement in cognitive radio networks

Cognitive radio (CR) is a promising technology to improve spectrum utilization. Most of previous work on CR networks concentrates on maximizing transmission rate in the physical layer. However, the end-to-end transmission control protocol (TCP) performance perceived by secondary users is also a very important factor in CR networks. In this paper, we propose a novel multi-channel access scheme in CR networks, where the channel access is based on the TCP throughput in the transport layer. Specifically, we formulate the channel access process in CR network as a restless bandit system. With this stochastic optimization formulation, the optimal channel access policy is indexable, meaning that the channels with highest indices should be selected to transmit TCP traffic. In addition, we exploit cross-layer design methodology to improve TCP throughput, where modulation and coding at the physical layer and frame size at the data-link layer are considered together with TCP throughput in the transport layer to improve TCP performance. Simulation results show the effectiveness of the proposed scheme.     

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.