频谱异构认知无线电中基于吞吐量降的空时频谱机会感知

在认知无线电(CR)中,频谱感知是实现动态频谱接入的关键技术之一。为适当保护主用户并最大化次级用户的性能,目前大部分相关工作均是用虚报概率和漏检概率作为感知度量来确定最佳感知参数的。但这种度量是用主次用户的碰撞概率来衡量次级用户对主用户的影响的,没有考虑干扰强度的影响,仅适合同构频谱环境;在不同位置次级用户有不同接入机会的异构频谱环境中,并不能最大化频谱利用率。为此,该文首先定义了吞吐量降,并提出在异构频谱环境下采用吞吐量降作为一种新的感知度量。吞吐量降是指由于次级用户占用授权频谱而导致主用户吞吐量下降的百分比。在衡量次级用户对主用户的影响时,它综合了主次用户的碰撞概率和干扰强度两个因素;其次,研究了以吞吐量降为约束的次级用户吞吐量优化问题。最后,数值仿真证实了该方案比目前几种传统方案的频谱利用率显著提高。     

非理想信道状态信息对频谱共享认知中继网络性能的影响

在频谱共享认知中继网络中,非理想信道状态信息可能导致次级用户的干扰超过主用户所能容忍的最大干扰值,从而影响到主用户的正常通信。为了衡量次级用户的传输对主用户性能的影响,该文提出了干扰概率这一性能指标。在非理想的信道状态信息条件下,推导了次级用户采用机会中继与选择协作协议时的干扰概率闭式解析式。理论分析表明,从干扰概率角度看,选择协作协议优于机会中继协议,但二者的极限干扰概率相同。此外,在非理想信道状态信息条件下,无论是采用机会中继还是选择协作协议,增加中继数量都会对主用户造成更大的干扰。最后,仿真结果验证了理论分析的正确性。     

基于业务请求数据包长度的机会频谱接入算法

针对非时隙主用户网络,研究了单个次用户在周期性感知框架下的机会频谱接入问题。通过建立次用户信道感知和接入模型,提出了一种基于次用户请求业务数据包长度的机会频谱接入算法。该算法根据每个时隙分配给次用户业务数据包长度,自适应调整机会频谱接入策略。仿真结果表明,所提算法能够在干扰水平要求较高情况下,提高次用户平均有效传输吞吐量的同时,实现有效吞吐量与碰撞概率的折中;同时当外部环境发生变化时算法具有较强的鲁棒性。     

Performance analysis of an opportunistic multi‐user cognitive network with multiple primary users

Consider a multi‐user underlay cognitive network where multiple cognitive users concurrently share the spectrum with a primary network with multiple users. The channel between the secondary network is assumed to have independent but not identical Nakagami‐m fading. The interference channel between the secondary users (SUs) and the primary users is assumed to have Rayleigh fading. A power allocation based on the instantaneous channel state information is derived when a peak interference power constraint is imposed on the secondary network in addition to the limited peak transmit power of each SU. The uplink scenario is considered where a single SU is selected for transmission. This opportunistic selection depends on the transmission channel power gain and the interference channel power gain as well as the power allocation policy adopted at the users. Exact closed form expressions for the moment‐generating function, outage performance, symbol error rate performance, and the ergodic capacity are derived. Numerical results corroborate the derived analytical results. The performance is also studied in the asymptotic regimes, and the generalized diversity gain of this scheduling scheme is derived. It is shown that when the interference channel is deeply faded and the peak transmit power constraint is relaxed, the scheduling scheme achieves full diversity and that increasing the number of primary users does not impact the diversity order. Copyright © 2014 John Wiley & Sons, Ltd.     

Performance analysis of nonorthogonal multiple access‐based underlay cognitive relay network

This paper considers cooperative non‐orthogonal multiple access (NOMA) scheme in an underlay cognitive radio (CR) network. A single‐cell downlink cooperative NOMA system has been considered for the secondary network, consisting of a base station (BS) and two secondary users, ie, a far user and a near user. The BS employs NOMA signaling to send messages for the two secondary users where the near user is enabled to act as a half‐duplex decode‐and‐forward (DF) relay for the far user. We derive exact expressions for the outage probability experienced by both the users and the outage probability of the secondary system assuming the links to experience independent, nonidentically distributed Rayleigh fading. Further, we analyze the ergodic rates of both the users and the ergodic sum rate of the secondary network. The maximum transmit power constraint of the secondary nodes and the tolerable interference power constraint at the primary receiver are considered for the analysis. Further, the interference caused by the primary transmitter (PT) on the secondary network is also considered for the analysis. The performance of the proposed CR NOMA network has been observed to be significantly better than a CR network that uses conventional orthogonal multiple access (OMA) scheme. The analytical results are validated by extensive simulation studies.     

Enhancing multicast security of cognitive radio networks with antenna correlations over Nakagami-m fading channels

In this paper, we investigate the impact of diversity and antenna correlations on the secrecy capacity and outage performance of a cognitive radio multicast network over Nakagami-m fading channels analytically. The proposed network consists of single primary and secondary user, multiple primary and secondary receivers, and multiple eavesdroppers. It is assumed that each user is equipped with single antenna while all the primary and secondary receivers, and eavesdroppers are equipped with multiple antennas. The primary and secondary users transmit their common messages to the respective receivers in the presence of multiple eavesdroppers. A mathematical model is developed to ensure successful reception of confidential information to the primary receivers protecting the activities of eavesdroppers neglecting the effect of interference due to secondary user. In order to analyze the security of the proposed model, closed-form analytical expressions have been derived for the secrecy multicast capacity, the secure outage probability for multicasting and the probability of non-zero secrecy multicast capacity. Analytical results are justified via Monte-Carlo simulations.

     

Performance analysis of cognitive relay systems with spectrum-sharing interference under a primary outage probability constraint简

This paper investigates the performance of an underlay cognitive relay system where secondary users（SUs） suffer from a primary outage probability constraint and spectrum-sharing interference imposed by a primary user（PU）. In particular, we consider a secondary multi-relay network operating in the selection decode-and-forward（SDF） mode and propose a best-relay selection criterion which takes into account the spectrum-sharing constraint and interference. Based on these assumptions, the closed-form expression of the outage probability of secondary transmissions is derived. We find that a floor of the outage probability occurs in high signal-to-noise ratio（SNR） regions due to the joint effect of the constraint and the interference from the PU. In addition, we propose a generalized definition of the diversity gain for such systems and show that a full diversity order is achieved. Simulation results verify our theoretical solutions.     

Transmit antenna selection of correlated MIMO multiuser cognitive radio networks in Nakagami‐m fading channels

In this paper, we examine the impact of antenna correlation on transmit antenna selection with receive maximal ratio combining (TAS/MRC) in multiple‐input multiple‐output multiuser underlay cognitive radio network (MIMO‐MCN) over a Nakagami‐m fading environment. The secondary network under consideration consists of a single source and M destinations equipped with multiple correlated antennas at each node. The primary network composed of L primary users, each of which is equipped with multiple correlated antennas. For the considered underlay spectrum sharing paradigm, the transmission power of the proposed secondary system is limited by the peak interference limit on the primary network and the maximum transmission power at the secondary network. In particular, we derive exact closed‐form expressions for the outage probability and average symbol error rate of the proposed secondary system. To gain further insights, simple asymptotic closed‐form expressions for the outage probability and symbol error rate are provided to obtain the achievable diversity order and coding gain of the system. In addition, the impact of antenna correlation on the secondary user ergodic capacity has been investigated by deriving closed‐form expressions for the secondary user capacity. The derived analytical formulas herein are supported by numerical and simulation results to clarify the main contributions. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of Network Path Selection Based on Outage Probability in Cognitive Relay Networks

This paper evaluates the outage performance of cognitive relay networks with mutual interference between secondary users and primary users under the underlay approach, while adhering to the interference constraint on the primary user. A network path selection criterion, suitable for cognitive relay networks, is provided, from which we derive the outage probability expression of cognitive relay networks. It is shown that the outage probability considering the interference to secondary user from primary user is higher than that without considering the interference to secondary user from primary user. In addition, the outage probability is affected by key network parameters. We analyze network path selection method based on outage probability and prove that the interference to secondary user from primary user has a significant effect on the network path selection and can not be ignored in practical wireless communication environments. Simulation investigation is also provided and used to verify the theoretical analysis.     

On the Capacity of Secondary Networks Over Opportunistic Spectrum Access in Rayleigh Fading Channels

In this paper the effect of the opportunistic spectrum access on the spectrum utilization is studied in terms of the secondary network capacity measured at the secondary receiver. A mathematical model is developed to represent the secondary network capacity in Rayleigh fading channel. An exact analytical solution for the capacity is derived for both sensing and accessing fading channels. A numerical evaluation of the channel capacity is presented for different channel sensing and accessing schemes. The effects of detection and accessing channel parameters on the capacity are investigated. The analytical results that are validated by substantial simulations showed how the utilization of the network can be increased significantly by the suggested opportunistic spectrum accessing technique. It was found that when having a good sensing system with a high secondary user signal to noise ratio, accessing the licensed band increases and drives the spectrum utilization to its maximum. In addition, this work shows how the capacity can be positively affected by three factors: the secondary accessing channel, the primary user interference and the desired quality of service (QoS) of primary user. The awareness of a proper sensing scheme can maximize the spectrum utilization without degrading the QoS of primary users.     

QoS-Driven Power Allocation Under Peak and Average Interference Constraints in Cognitive Radio Networks

Efficient radio spectrum utilization can be improved using cognitive radio technology. In this work, we consider a spectrum underlay cognitive radio system operating in a fading environment. We propose an efficient power control scheme that maximizes the effective capacity of the secondary user, provisioning quality of service while on the same time the communication of the primary user is guaranteed through interference constraints. The specific power allocation scheme uses a policy in which the outage events of the primary user are exploited leading to a significant increase of the secondary user’s effective capacity. Moreover, the interference of the primary link to the secondary is taken into account so as to study a more realistic scenario. In order to safeguard primary user’s communication, two types of restrictions are considered: the traditional interference power constraint and the proposed inverse signal to interference plus noise ratio constraint. Different scenarios depending on the nature of the constraints (peak/average) are studied and their impact on the performance of the primary and secondary users is investigated. The superiority of the proposed schemes is demonstrated through their comparison with two reference power control schemes. Finally, numerical calculations, validated with simulation results, confirm the theoretical analysis and evaluate the performance of the proposed scheme for all the different scenarios.     

Reliable Multimedia Transmission Over Cognitive Radio Networks Using Fountain Codes

With the explosive growth of wireless multimedia applications over the wireless Internet in recent years, the demand for radio spectral resources has increased significantly. In order to meet the quality of service, delay, and large bandwidth requirements, various techniques such as source and channel coding, distributed streaming, multicast etc. have been considered. In this paper, we propose a technique for distributed multimedia transmission over the secondary user network, which makes use of opportunistic spectrum access with the help of cognitive radios. We use digital fountain codes to distribute the multimedia content over unused spectrum and also to compensate for the loss incurred due to primary user interference. Primary user traffic is modelled as a Poisson process. We develop the techniques to select appropriate channels and study the trade-offs between link reliability, spectral efficiency and coding overhead. Simulation results are presented for the secondary spectrum access model.     

基于无线Mesh网络的干扰感知型路由判据

在无线Mesh网络路由判据的研究中,最小跳数、ETX、ETT等路由判据没有考虑到无线网络中的干扰问题,据此选出的一般不是最佳路由。因此,基于它们的路由协议会对整个无线Mesh网络的延时、丢包率、吞吐量等性能产生较大影响。干扰感知型路由判据的提出对无线Mesh网络性能的提升起到了一定的作用。     

Throughput optimization using simultaneous sensing and transmission in energy harvesting cognitive radio networks

A three‐dimensional continuous‐time Markov model is proposed for an energy harvesting cognitive radio system, where each secondary user (SU) harvests energy from the ambient environment and attempts to transmit data packets on spectrum holes in an infinite queuing buffer. Unlike most previous works, the SU can perform spectrum sensing, data transmission, and energy harvesting simultaneously. We determine active probability of the SU transmitter, where the average energy consumption for both spectrum sensing and data transmission should not exceed the amount of harvested energy. Then, we formulate achievable throughput of secondary network as a convex optimization problem under average transmit and interference energy constraints. The optimal pair of controlled energy harvesting rate and data packet rate is derived for proposed model. Results indicate that no trade‐off is available among harvesting, sensing/receiving, and transmitting. The SU capability for self‐interference cancelation affects the maximum throughput. We develop this work under hybrid channels including overlay and underlay cases and propose a hybrid solution to achieve the maximum throughput. Simulation results verify that our proposed strategy outperforms the efficiency of the secondary network compared to the previous works.     

Adaptive Decode-and-Forward Protocol Based Cooperative Spectrum Sensing in Cognitive Radio with Interference at the Secondary Users

In this paper a novel multiple-user cooperative spectrum sensing scheme (MCSS) based on hybrid relay is proposed to achieve the spatial diversity gain in detection of the primary user (PU) in a cognitive radio (CR) network. A practically important case where co-channel interference signals are present at the network is considered for the analysis. Closed-form expressions of detection probability \((\hbox {P}_{\mathrm{d}})\) and false alarm probability \((\alpha )\) for the proposed adaptive decode-and-forward based multiple-user cooperative spectrum sensing scheme (ADF-MCSS) using energy detector over Rayleigh fading sensing channels is derived in presence of co-channel interference at the secondary user which is far away from the PU. Further we extend the concept of two user amplify-and-forward (AF) and decode-and-forward (DF) cooperative spectrum sensing schemes in multiple-user scenario (i.e. AF-MCSS and DF-MCSS) over Rayleigh fading channels when the secondary user (which is far away from PU) is affected by interference. Closed-form expressions of AF-MCSS and DF-MCSS schemes over a Rayleigh fading channels are also evaluated and compared with that of proposed ADF-MCSS in presence of interference signals at the secondary user. Further the performance analysis of AF-MCSS, DF-MCSS and ADF-MCSS schemes are compared with the existing non-cooperative spectrum sensing schemes in presence of interference at the secondary user. Our analysis is validated by numerical and simulation results for multiple-user CR network. The impact of number of cooperative relays, SNR in sensing channel, energy of interference signal, false alarm on detection probability in proposed ADF, AF and DF schemes is shown.     

QoS Analysis in Overlay Bluetooth-WiFi Networks with Profile-Based Vertical Handover

The performance of an overlay Bluetooth and IEEE 802.11b (WiFi) network is considered in terms of quality of service parameters such as the packet latency, the packet error rate, and the throughput, in the presence of a vertical handover procedure, taking into account the mutual Bluetooth-WiFi interference and showing the influence of the main system parameters. The objective is to maximize the user QoS allowing the mobile to switch from a network to the other, with the so-called vertical handover. The basic idea is to activate the vertical handover, not on the basis of the received power level, but by the crossing of thresholds defined by the user profile, which comprises objective values for parameters such as the packet error rate and the packet delay. The results show that the use of the vertical handover procedure can lead to an improvement in the QoS parameters     

感知频谱共享下的多天线功率优化分配算法研究

本文构建了一种在感知结果下具有多天线次用户的频谱共享模型,该模型由单入单出主用户对和多入单出认知用户对构成。当认知用户感知到主用户占用信道时,主用户向认知用户发送Message信息,使得认知用户发射端能够得知主用户对干扰总功率的限制要求,通过自适应地调整认知用户发射机的发射功率,以保证其对主用户不造成有害干扰;如果主用户未占用信道,认知用户立刻以最大发射功率占用信道。并分别在主用户存在和不存在两种情况下,优化认知用户发射机各天线的发射功率来最大化系统总的数据传输率。最后,通过数值仿真来验证推导出的功率分配策略,并对其进行分析和讨论。仿真结果表明:相比于机会频谱接入（Opportunistic Spectrum Access, OSA）和基于感知的频谱共享（Sensing-based spectrum sensing）模式,推导的功率分配策略在提出的模型中可以获得更高的信息传输率。      

Capacity and Energy Efficiency of Multi-User Spectrum Sharing Systems with Opportunistic Scheduling

This paper investigates the capacity and energy efficiency of spectrum sharing systems with opportunistic user selection where a secondary network utilizes spectrum bands licensed to a primary network under interference regulation. In spectrum sharing systems, secondary users consume a fraction of their resources in sensing the channels to the primary users to comply with the interference constraints. Although more resources for sensing improve reliability and performance, the throughput loss due to time overhead and energy loss due to power overhead should be properly incorporated in performance evaluation. In this context, we define and derive a new metric ? average capacity normalized by the total energy consumption ? reflecting time and power overhead for spectrum sensing. Based on the developed framework, the optimal normalizedcapacity is investigated. We also propose a simple and practical suboptimal best-n scheme motivated by the infeasibility and high computational complexity of the optimal strategy, where n denotes the number of sensing secondary users. Our analytical and simulation results show that the proposed best-1 scheme is an energy-efficient technique with near optimality in terms of the capacity normalized by the energy consumption.     

On the Performance of Downlink Multiuser Cognitive Radio Inspired Cooperative NOMA

This paper is considered as an application of a centralized control non orthogonal multiple access (NOMA) based cognitive radio network. Here, a base station (BS) sends simultaneously two information signals by employing the superposition coding scheme to two different types of users, i.e., group of near users and one far user. The near users, namely, the secondary users, exchange cooperatively their own received information among themselves ensuring the realization of maximal diversity gain. Besides, they are responsible for relaying information to the far user, namely, the primary user. One potential secondary user is selected to decode and forward the BS information signal to the primary user and the rest of the secondary users to reinforce the reliability, as well as, mitigate the non-decodable messages. Two equivalent cases of a relay (secondary user) selection scheme are proposed. In the first case, the selection aims at maximizing the minimum of the joint secondary to secondary (S to S) and secondary to primary (S to P) channels’ coefficients under a certain limit of interference condition. In the second case, the selection aims at maximizing the minimum of the BS to S and S to S paths while a certain quality of service of the primary user is strictly guaranteed. Assuming Rayleigh fading channels, new closed form expressions are derived for the achievable capacity associated with the two information signals. Simulation results reveal the advantage of our proposed schemes over the conventional orthogonal max–min approach and confirm the validity of our analysis.     

Performance Analysis of the Primary User in the Secondary User Relay Assisted Spectrum Sharing Networks

In this paper, inaccurate spectrum detecting by the secondary user (SU) is taken into account. The impact of the interference caused by the SUs due to miss detection on the primary user (PU) in a spectrum sharing network is analyzed, and those SU nodes of correct detection are assumed to act as potential relays to assist the PU transmission process based on two proposed cooperative transmission schemes, referred to as, the distance based and the signal-to-noise-ratio (SNR) based schemes. We utilize stochastic geometry to analyze the impact of the secondary network parameters and cooperative transmission schemes on a typical primary source–destination (S–D) pair for the SU relay assisted spectrum sharing networks in Rayleigh fading environment. Using this approach, closed-form expressions for the primary system success probabilities with those cooperative transmission schemes as well as the PU direct re-transmission scheme are derived respectively. Simulations confirm our analytical derivations and results demonstrate that significant improvement on the PU success probability by using SU cooperative transmission schemes, and the SNR based scheme is superior to the distance based scheme.