Investigation on outage capacity of spectrum sharing system using CSI and SSI under received power constraints

In this paper, we have investigated the outage capacity of secondary user for opportunistic spectrum sharing under the joint peak and average received power constraints for Rayleigh fading environment. Under this communication scenario, on detecting the licensed primary user inactive, the secondary unlicensed users transmit data/information in the licensed frequency band such that no or minimum interference may be experienced by the primary user. The soft sensing information (SSI) and secondary user’s channel state information is used to obtain the closed form expressions for the ergodic and outage capacity using truncated channel inversion with fixed rate technique under the joint peak and average received power constraints. Numerically simulated results are provided to demonstrate the improvement in outage capacity of secondary user under the proposed spectrum sharing scheme. Moreover, the proposed scheme is also compared with other conventional spectrum sharing schemes to illustrate the benefits of SSI and received power constraints on the outage capacity of secondary user.

     

Capacity in fading environment based on soft sensing information under spectrum sharing constraints

In this paper, the ergodic channel capacity for a secondary user is investigated using soft sensing information about primary user activity in a shared channel under joint peak transmit power and average received interference power constraints for Nakagami-m fading channel. The results of the proposed power adaptation scheme illustrate the effect of communication environment parameters and soft sensing information about primary user activity on the channel capacity of secondary user. In particular, the effect of cross link channel state information to maximize the channel capacity for the power adaptation scheme is emphasized by considering the Lagrangian optimization problem for joint peak transmit power and average interference power constraints. Moreover, the performance of the primary user is also investigated considering the interference of the secondary user to the primary in spectrum sharing environment in terms of transmission rate and average channel capacity.     

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.     

Performance of cognitive relay network with novel hybrid spectrum access schemes with imperfect CSI

Two novel spectrum access schemes, a hybrid spectrum access scheme (HSAS) and a modified HSAS combining underlay mode and overlay mode, are proposed for a relay based cognitive radio (CR) network. The CR employs the underlay mode with imperfect channel state information of the interfering link between CR transmitter and primary user receiver if primary user is sensed to be present else it employs overlay mode. In both the schemes, transmission of CR is assisted by relay working in amplify and forward scheme by maintaining interference below an interference threshold in underlay mode and a collision constraint in overlay mode. In HSAS, CR transmits either in underlay mode or in overlay mode only during the transmission slot of a detection cycle, whereas in modified HSAS, the CR transmits for the entire frame including the sensing time. The outage probability of CR user is considered as the performance metric. Novel expressions of outage probability for both the schemes have been developed. Impact of several sensing parameters such as sensing time, correlation coefficient, and tolerable interference threshold has been investigated. Copyright © 2016 John Wiley & Sons, Ltd.     

Optimal power allocation for cognitive radio under interference outage constraint

Cognitive radio is able to share the spectrum with primary licensed user, which greatly improves the spectrum efficiency. We study the optimal power allocation for cognitive radio to maximize its ergodic capacity under interference outage constraint. An optimal power allocation scheme for the secondary user with complete channel state information is proposed and its approximation is presented in closed form in Rayleigh fading channels. When the complete channel state information is not available, a more practical transmitter-side joint access ratio and transmit power constraint is proposed. The new constraint guarantees the same impact on interference outage probability at primary user receiver. Both the optimal power allocation and transmit rate under the new constraint are presented in closed form. Simulation results evaluate the performance of proposed power allocation schemes and verify our analysis.     

Impact of the secondary service transmit power constraint on the achievable capacity of spectrum sharing in rayleigh fading environment

The two main constraints on the transmit power allocation of the secondary service in a spectrum sharing scheme are the received interference threshold at the primary receiver, and the maximum transmit power of the secondary user. We obtain a critical system parameter which relates these two constraints and enables the system designer to eliminate the interference threshold constraint by adjusting the maximum transmit power of the secondary users. Eliminating the interference threshold constraint significantly reduces the system complexity by making the power allocation of the secondary service independent from the channel state information between the secondary transmitter and the primary receiver; thus removes the need for signaling between primary and secondary systems.     

Adaptive dual‐radio spectrum‐sensing scheme in cognitive radio networks

In this paper, a novel spectrum‐sensing scheme, called adaptive dual‐radio spectrum‐sensing scheme (ADRSS), is proposed for cognitive radio networks. In ADRSS, each secondary user (SU) is equipped with a dual radio. During the data transmission, with the received signal‐to‐noise ratio of primary user (PU) signal, the SU transmitter (SUT) and the SU receiver (SUR) are selected adaptively to sense one channel by one radio while communicating with each other by the other one. The sensing results of the SUR are sent to the SUT through feedback channels (e.g., ACK). After that, with the sensing results from the SUT or the SUR, the SUT can decide whether the channel switching should be carried out. The theoretical analysis and simulation results indicate that the normalized channel efficiency, defined as the expected ratio of time duration without interference to PUs in data transmission to the whole frame length, can be improved while satisfying the interference constraint to PUs. After that, an enhanced ADRSS is designed by integrating ADRSS with cooperative spectrum sensing, and the performance of ADRSS under imperfect feedback channel is also discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

基于可靠次用户信息的协作频谱感知算法研究

对认知无线电系统最基本要求之一就是次用户必须有能力以高的精确率来确定主用户是否存在。而以前对认知无线电频谱感知的研究表明:在实际认知网络中次用户之间的相互协作可以提高其频谱检测性能。然而,对于协作频谱感知而言,随着协作次用户数目的增加,势必会增大用于传输本地检测结果到融合中心的专用控制信道带宽,从而增加系统开销。该文在控制信道带宽有限的约束条件下,提出一种通过考虑可靠次用户信息的协作频谱感知算法来进一步改善频谱检测的性能。该算法的基本思想:只有具有可靠的本地检测结果的次用户才发送自己的检测结果到融合中心,否则,该次用户不发送任何信息。同时,对提出的该算法在理论上进行了推导,通过仿真结果表明:在控制信道带宽受限的约束下,相比于传统的或门协作频谱感知算法,提出的算法能够大大改善对主用户的检测性能。     

非理想信道感知下的频谱共享容量的理论分析

在现有的以理想信道感知为条件的机会频谱共享容量分析基础上,重点讨论非理想感知对机会频谱共享中次用户信道容量的影响。关注两条不同传输途径的信道,一条是从次用户发送端到次用户接收端的无线信道,另一条是次用户发送端到主用户接收端的无线信道。以主用户接收端功率受限作为约束条件,得到了关于非理想信道信号噪声比条件下机会频谱共享的次用户信道容量的关系表达式。首先分析次用户发送端到主用户接收端信道和次用户发送端到次用户接收端信道为非对称时次用户的信道容量,其次分别探讨不同衰落信道模型下两条信道上感知（包括信道估计和预测）误差为对称和非对称结果时,次用户信道容量的变化。     

Error Analysis of Grouped Multilevel Space-Time Trellis Coding with the Combined Application of Massive MIMO and Cognitive Radio

In today’s scenario, demand for error-correcting codes with minimal error constraints for wireless communications. Multilevel coding scheme with trellis codes as component codes provides flexible data transmission rates, coding gain, diversity gain with improved spectral efficiency and low decoding complexity. This paper investigates the potential improvements by using the Multilevel coding scheme with massive Multiple-Input Multiple-Output in Cognitive Radio Networks with trellis codes as component codes. This paper discussed space-time coding with beamforming and antenna grouping according to the channel state information. Multilevel Space-time coding is based on multi-level Quadrature Amplitude Modulation signaling and beamforming to mitigate the effect of primary users for the enactment of secondary users in Cognitive Radio. The primary users provide channels dynamically to the secondary user for an unknown duration. Our transmission use Quadrature Amplitude Modulation based signals, with an adaptive grouping of antenna which weight according to the optimization, which inherently depends upon the resource allocation of the secondary user. The results show that the proposed coded system achieves Bit error rate/Symbol error rate/Frame error rate and Signal to noise ratio varies according to sources sensing time.

     

On the Impacts of Channel Estimation Errors and Feedback Delay on the Ergodic Capacity for Spectrum Sharing Cognitive Radio

Spectrum sharing cognitive radio aims to improve the spectrum efficiency via sharing the spectrum band licensed to the primary user (PU) with the secondary user (SU) concurrently provided that the interference caused by the SU to the PU is limited. The channel state information (CSI) between the secondary transmitter (STx) and the primary receiver (PRx) is used by the STx to calculate the appropriate transmit power to limit the interference. We assume that this CSI is not only having channel estimation errors but also outdated due to feedback delay, which is different from existing studies. We derive closed-form expressions for the ergodic capacities of the SU with this imperfect CSI under the average interference power (AIP) constraint and the peak interference power (PIP) constraint. Illustrative results are presented to show the effects of the imperfect CSI. It is shown that the ergodic capacity of the SU is robust to the channel estimation errors and feedback delay under high feedback delay. It is also shown that decreasing the distance between STx and secondary receiver (SRx) or increasing the distance between STx and PRx can mitigate the impact of the imperfect CSI and significantly increase the ergodic capacity of the SU.     

基于无人机中继的星地认知网络波束成形算法

针对基于无人机中继的星地认知网络,提出了两种波束成形（beamforming, BF）算法,通过对各种干扰进行抑制,实现系统间的频谱共享。具体而言,在基于无人机中继的卫星网络作为次级网络、地面网络作为主网络的情况下,以无人机最大发射功率和主用户所受干扰为约束条件,建立次级用户信干噪比最大化准则的优化问题;接下来在已知次级用户统计信道状态信息的条件下,提出一种基于迭代的BF算法对优化问题进行求解;更进一步,为了降低迭代算法的实现复杂度,提出了一种基于迫零的BF算法。最后,计算机仿真验证了所提两种波束成形方案的正确性与有效性。     

基于粒子滤波的协作式空时联合频谱检测方法

认知无线电系统中,通过频谱检测所获得的主用户位置信息和信道使用状态信息分别反映空间域和时间域的频谱使用情况,其准确性关系到次用户伺机频谱接入的效率。本文研究空间和时间联合频谱检测问题,将其建模为主用户位置参数和信道使用状态的联合估计问题,提出了一种基于粒子滤波的协作式空时联合频谱检测方法,主要思想是采用离散随机测度逼近位置参数和信道状态的联合后验概率分布函数,根据该分布估计出主用户位置和信道状态。同时,该方法结合由估计得到的空间和时间信息,自适应选择靠近主用户且对称分布的次用户参与协作检测,增加各次用户提供信息的有效性,从而提高估计的准确性;最后,通过仿真验证了方法的有效性。      

A novel approach for energy‐efficient resource allocation in double threshold‐based cognitive radio network

This paper mainly focuses on solving the energy efficiency (EE) maximization problem in double threshold‐based soft decision fusion (SDF) cooperative spectrum sensing (CSS) in the cognitive radio network (CRN). The solution to this objective problem starts with the selection of suitable secondary users (SUs) both for the spectrum sensing and data transmission. Here, energy efficiency is maximized under the constraints of interference to the primary user (PU), an acceptable outage of SUs, the transmission power of the SUs and the probability of false alarm. We propose a novel algorithm called iterative Dinkelbach method (IDM) which jointly optimizes the sensing time and transmission power allocation to the SUs. Further, Lagrangian duality theorem is employed to find the exact power assigned to the SUs. Finally, simulation results are carried out to validate the effectiveness of our proposed scheme by comparing with the other existing schemes. The performance is also analyzed for different system parameters.     

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.     

Scheduling in a Spectrum-Sharing Cognitive Environment Under Outage Probability Constraint

This article investigates a multiuser cognitive environment where secondary users compete to communicate over a channel licensed to a primary user using spectrum sharing. In this environment, both the primary and secondary users transmit to the same receiver unit, and the transmission power of the scheduled secondary user should satisfy the outage probability requirement of the primary user. Secondary users are ranked according to their channel strength, and performance measures are derived as a function of a generic channel rank. Bit error rate, channel capacity, and generated interference are investigated as performance measures. In addition, the performance of the proportional fair, random selection, and round-robin scheduling algorithms are investigated. Numerical results are presented to verify the theoretical analysis and investigate the effects the parameters of the communication environment have on the performance measures and the transmission power of the cognitive users.     

An adaptive handoff strategy for cognitive radio networks

Spectrum handoff plays an important role in spectrum management as it is the process of seamlessly shifting the on-going transmission of a secondary user (SU) to a free channel without degrading the quality of service. In this paper, we develop an adaptive handoff algorithm that allows an SU to detect the arrival of a primary user (via sensing) and adapt to a reactive or a proactive handoff strategy accordingly. The adaptive handoff scheme first allows an SU to decide whether to stay and wait on current channel or to perform handoff. Then, in case of handoff, an SU intelligently shifts between proactive or reactive handoff modes based on primary use (PU) arrival rate. Further, a PU prioritized Markov approach is presented in order to model the interactions between PUs and SUs for smooth channel access. Numerical results show that the proposed handoff scheme minimizes the blocking probability, number of handoffs, handoff delay and data delivery time while maintaining channel utilization and system throughput at maximal level compared to simple reactive and proactive schemes.     

碰撞约束和非理想感知下认知多址接入信道的有效吞吐量

在碰撞约束和非理想信道信息下,研究认知多址接入信道中多个次用户接入主用户频谱的有效吞吐量问题。在机会频谱接入方式（OSA）下,定义有效吞吐量并作为次用户的性能指标。考虑信道质量信息,在信道质量分布参数未知的情况下采用有限的信道样本对参数进行估计,并对非理想感知下次用户的性能进行分析。通过仿真实验,分别讨论了信道质量门限与碰撞概率及次用户性能之间的关系,对比了理想感知和非理想感知下次用户的性能,并与其他算法进行对比,验证了本文接入策略的有效性。     

认知无线电网络中基于主系统有限反馈的频谱共享方案

摘 要：提出一种频谱共享方案,该方案适用于同时存在多个主用户和一对次用户的场景。各主用户依据接收机反馈的有限信道质量信息（CQI, channel quality information）分配发送功率及传输速率。次用户根据偷听到的主系统CQI有限反馈,以适当的功率及速率接入信道。次用户接入信道的行为对各主用户造成一定干扰,以致主系统传输速率遭受一定损失。本文在主系统速率损失约束条件下,研究得出了使次系统吞吐量最大化的次用户发送功率及传输速率最佳分配方案。数值结果表明,对于每个主用户仅需反馈3-4个量化比特,次系统的有效吞吐量就可堪比于主次发射端均拥有主系统链路完整CQI的情况。仿真结果显示,所提出的频谱共享方案能够满足主系统速率损失约束。     

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.