基于公共DF中继的认知无线电中继选择和功率分配

为提高认知无线电网络中主用户和次用户的通信质量,并可简单有效地利用中继节点来控制主用户和次用户之间的相互干扰,提出了一种基于公共中继的最佳中继选择和功率分配方案.首先,在认知无线电网络中建立了基于公共DF中继的无线通信模型;然后,根据无线通信理论推导出要优化的目标函数;最后,在保证主用户中断概率低于目标值的前提下,利用凸优化理论得出了模型中的最佳中继选择和功率分配方案.仿真实验结果表明,与常见的直接传输方案和功率平均分配的中继方案相比,本文提出的中继选择和功率分配方案提高了次用户的通信距离和速率,并且降低了主用户的中断概率,为更好地解决认知无线电网络中主用户和次用户的相互干扰问题提供了新的思路.     

基于能量收集的认知无线电资源分配研究

本文将能量收集及协作中继技术引入到认知无线电网络中,研究次用户作为中继节点帮助主用户转发数据的协作认知场景,提出了一种基于解码转发模式下的最优能量收集时间及功率分配策略.仿真结果表明:和直接传输相比,不仅降低了主用户的中断概率,增大了次用户的传输速率,而且节省了网络传输能量,延长了网络的寿命周期.     

基于认知无线电网络的协作中继资源分配算法

频谱资源紧张己经成为制约下一代无线通信系统发展的主要因素之一.认知无线电技术通过大力发掘授权频谱的复用潜力,可有效解决频谱紧缺问题.本文把协作中继传输技术引入到认知网络中,建立了配置双天线的次用户帮助主用户传输的协作模型,基于此提出了基于译码转发的协作功率及频谱资源分配算法,并进行了详细的理论分析.仿真结果表明,本文提出的协作传输策略能够在保障主用户正常传输情况下提高次用户的传输机会并减小中断概率.     

一种多源协作网络中轮询节点选择算法

针对放大转发(AF)的多源多中继两跳协作通信网络模型,提出了一种基于轮询分组调度算法的节点选择与用户调度策略.与之前所提出的中继选择选择算法相比,所提出的中继节点轮询分组调度算法,不需要额外的信令开销,复杂度低,并保证中继间的负载均衡.此外,为保证用户传输的公平性,提出一种结合多用户分集的轮询分组调度算法.最后在已选择的中继节点和所调度的源节点用户中引入分布式空时编码.仿真结果表明,该节点选择和用户调度算法能保证所有节点使用的公平性,并且结合分布式空时编码之后,可以提高频谱利用率,从而提高了系统性能.     

水声通信系统中分布式空时分组码的研究

协作传输可以获得无线信道内在的空间分集,有效改善通信系统的性能,增加通信系统的覆盖范围。对水声通信系统中两中继节点协作的译码转发方案进行了研究,提出了基于译码转发协议(DF)的分布式空时分组扩频编码(DSTBSC)方案,该方案可以克服多径衰落对分布式空时分组码(DSTBC)信号正交性的影响。给出了DSTBSC方案的系统模型,着重分析了在采用两中继译码转发时,中继节点的误码对水声通信系统性能的影响。在接收端不考虑信号冲突的情况进行仿真,结果表明,与直接传输方案相比,采用两中继节点、译码转发的DSTBSC方案,在两中继节点处均无误码和一个中继有误码时在相同的比特误码率(BER)条件下均可获得约4dB的分集增益,增加了传输距离。     

移动Ad hoc网络中中继伙伴的动态选择

通过将估计出的损耗时间与中继选择所用时间的比较，确定预警闽值。再通过信噪比与阈值的比较，来触发动态选择机制，在不间断信息传输的过程中进行中继伙伴选择，保证通信的连通性和可靠性。由于预警阈值的设定，使得信噪比小于中断门限的概率减小，因此通过对中断概率的仿真证明该方案在减小系统中断方面有所改善。     

基于融合自组网的能源计量数据采集系统

现有能源计量数据采集与传输系统大都基于无线传感网络(WSN),但该方案不仅存在传输效率问题,由于网络规模导致的大量中继转发需求,使得其依靠电池供电的WSN节点很难再作为通信主干。文章提出基于宽带电力线载波(BPL)作为工业物联网的通信主干,并使用LoRa无线通信技术作为网络的延伸。在满足传统工业物联网的安全性和可靠性的前提下,显著提高了通信速率尤其是网络效率,同时还具有低成本的优势。     

无线中继网络系统容量最大化中继选择机制

分析了基于用户频谱效率的中继选择算法的不足,基于最大流最小割定理,给出了系统容量最优化问题模型,分析了两跳中继网络接入链路和中继链路对系统容量的不同影响.基于链路权重因子,提出一种基于系统容量最大化的中继选择算法.对不同中继选择算法下的系统容量差异的理论与仿真分析结果表明,提出的系统容量最大化中继选择算法可以获得更优的系统容量性能,并对网络拓扑和节点个数具有良好的鲁棒性.     

传感器网络移动中继节点部署算法

针对传感器网络节点能量有限性及节点能量消耗不匀性问题,提出一种移动中继节点部署算法。首先假设网络中没有移动中继节点时,对静态节点提出一种最优路由树算法来构建数据传输路径;在此基础上再采用贪婪算法增加移动节点改善网络的拓扑结构提高路由树连通性;接着提出一种高效的分布式迭代算法,使得路由树的拓扑结构收敛于最优位置;最后进行理论分析与仿真实验,结果表明该方法具有一定理论意义与实用价值。     

非理想信道条件下树型结构的最优贝叶斯检测算法

由于本地检测器和融合中心的距离比较远，会加剧信道的非可靠性和增加信道的传输能量，基于非理想信道，研究了增加中继节点的分布式检测的最优化算法。为了使系统检测性能达到最优，需要对所有节点的判决规则进行联合最优化。最后对使用和不使用中继节点的系统进行性能比较。     

Cooperative Relay Selection Mechanism in Multi-Hop Networks

In this paper, we consider a three-hop relay system based on interference cancellation technique in Underlay cognitive radio (CR) network. Although underlay CR has been shown as a promising technique to better utilize the source of primary users (PUs), its secondary performance will be severely degraded. On one hand, by adapting the Underlay spectrum sharing pattern, secondary users (SUs) would observe the strict power constraints and be interfered by primary users. On the other hand, limited transmit power results in limited transmission range, which greatly degrade the secondary transmission capacity. To solve the problems above, we propose an interference cancellation protocol for multi-hop wireless communication networks in underlay CR, which could develop the long-distance transmission performance and improve the transmission efficiency significantly. As simulation results shows, proposed scheme significantly reduce the secondary outage probability and increase the secondary diversity than the traditional cases.     

Analysis of Underlay Cognitive Radio Networks Based on Interference Cancellation Mechanism

In this paper, we investigate the performance of secondary transmission scheme based on Markov ON-OFF state of primary users in Underlay cognitive radio networks. We propose flexible secondary cooperative transmission schemewith interference cancellation technique according to the ON-OFF status of primary transmitter. For maximal ratio combining (MRC) at destination, we have derived exact closed-form expressions of the outage probability in different situations. The numerical simulation results also reveal that the proposed scheme improve the secondary transmission performance compared with traditional mechanism in terms of secondary outage probability and energy efficiency.     

Outage Capacity Analysis for Cognitive Non-Orthogonal Multiple Access Downlink Transmissions Systems in the Presence of Channel Estimation Error

In this paper, we propose a downlink cognitive non-orthogonal multiple access (NOMA) network, where the secondary users (SUs) operate in underlay mode. In the network, secondary transmitter employs NOMA signaling for downlink transmission, and the primary user (PU) is interfered by the transmission from SU. The expressions for the outage probabilities are derived in closed-form for both primary and secondary users in the presence of channel estimation error. Numerical simulation results show that the channel estimation error and the inter-network interference cause degradation of the downlink outage performance. Also the power allocation and the location have a significant impact on the outage probability. The numerical experiments demonstrate that the analytic expressions of the outage probabilities match with the simulation results.     

Fairness and throughput enhancement based resource allocation scheme for underlay cognitive radio networks

Acquiring good throughput and diminishing interference to primary users (PU) are the main objectives for secondary users in a cognitive radio (CR) network. This paper proposes a centralized subcarrier and power allocation scheme for underlay multi-user orthogonal frequency division multiplexing considering the rate loss and the interference those the PU can tolerate. The main purpose of the proposed scheme is to efficiently distribute the available subcarriers among cognitive users to enhance both the fairness and the throughput performance of the cognitive network while maintaining the QoS of primary users. Simulation results show that the proposed scheme achieves a significantly higher CR network throughput than that of the conventional interference power constraint (IPC) based schemes and provides a significantly enhanced fairness performance. Also, contrary to the conventional IPC based schemes, the proposed scheme is able to significantly increase the achieved throughput as the number of CR users increases.     

Performance Analysis of Relay Based NOMA Cooperative Transmission under Cognitive Radio Network

This paper proposes a hybrid spectrum accessing mechanism by using NOMA-based cooperative transmission and beam-forming technology. In this mechanism, the secondary user employs spectrum-sensing technology to detect the existence of the primary user. If the primary user does not exist, the secondary source user directly transmits data to the destination user. If the primary user exists, the secondary source user finds the optimal relay according to certain selection principle before transmitting data to the destination user through the chosen relay node. For the signal receiving stage, the secondary user takes use of beam-forming technology to receive the signal from both the secondary source and the secondary relay node. Meanwhile the interference from the primary user is cancelled out in the stage. Furthermore, the outage probability for secondary user in the proposed mechanism is theoretically derived. Finally, the simulation results show that compared with the traditional mechanism, the proposed system model can not only guarantee the continuity of secondary transmission, but also significantly reduce the outage probability of secondary transmission.     

Throughput Analysis of HARQ Scheme Based on Full-Duplex Two-Way AF SWIPT Relay

The simultaneous wireless information and power transfer (SWIPT) relay system is one of the emerging technologies. Xiaomi Corporation and Motorola Inc. recently launched indoor wireless power transfer equipment is one of the most promising applications. To tap the potential of the system, hybrid automatic repeat request (HARQ) is introduced into the SWIPT relay system. Firstly, the time slot structure of HARQ scheme based on full duplex two-way amplify and forward (AF) SWIPT relay is given, and its retransmission status is analyzed. Secondly, the equivalent signal-to-noise ratio and outage probability of various states are calculated by approximate simplification. Thirdly, the energy harvesting power in each state is calculated. Finally, the energy harvested-throughput sum function is constructed to characterize the performance of energy harvesting and data transmission. Simulation results show that the proposed HARQ scheme has better energy harvested-throughput sum function than the traditional HARQ scheme. When P₂ = 22 dB, the maximum sum function is 54.86% (the proposed HARQ scheme) and 52.307% (the traditional HARQ scheme), respectively.     

Spectral efficiency of spectrum-pooling systems

The authors investigate the idea of using cognitive radio to reuse locally unused spectrum to increase the total system capacity. The authors consider a multiband/wideband system in which the primary and cognitive users wish to communicate to different receivers, subject to mutual interference and assume that each user knows only his/her channel and the unused spectrum through adequate sensing. The basic idea under the proposed scheme is based on the notion of spectrum pooling. The idea is quite simple; a cognitive radio will listen to the channel and, if sensed idle, will transmit during the voids. It turns out that, although its simplicity, the proposed scheme showed very interesting features with respect to the spectral efficiency and the maximum number of possible pairwise cognitive communications. We impose the constraint that users successively transmit over available bands through selfish water filling. For the first time, our study has quantified the asymptotic (with respect to the band) achievable gain of using spectrum pooling in terms of spectral efficiency compared with classical radio systems. The authors then derive the total spectral efficiency as well as the maximum number of possible pairwise communications of such a spectrum-pooling system.     

Secrecy Outage Probability Analysis Based on Cognitive Decodeand-Forward Relaying

Wireless communications have to face to several different security issues in practice due to the nature of broadcast. The information theory is well known to provide efficient approaches to address security issues in wireless communications, which attracts much attention in both industry and academia in recent years. In this paper, inspired by information theory, we study the outage probability of the opportunistic relay selection based on cognitive decode-and-forward relaying with the secrecy consideration. Specifically, the closed-form expression of the outage probability is proposed. Moreover, the asymptotic performance evaluation on the basis of the analytical results is investigated. The simulation results show that the relay selection can reduce the outage probability in accordance with our theoretical analysis.     

Cooperative transmission in wireless networks using incremental opportunistic relaying strategy

In this study, the authors develop a novel cooperative transmission scheme ? distributed opportunistic incremental decode and forward (DOIDF) that employs the incremental relaying (IR) strategy in opportunistic relaying (OR) protocols. By exploiting limited feedback from the destination, the proposed scheme starts the OR plan only when outage event happens in direct transmission (DT). The outage probability of DOIDF is derived in detail, and the results show that DOIDF can achieve the same space diversity order as multiple input single output (MISO) and single input multiple output (SIMO) systems, which is the upper limit of cooperative diversity. By analysing and comparing the approximate expression of outage probability of various protocols in high-signal-to-noise ratio (SNR) regime, the concept of system overhead factor (SOF), which reveals the effects of channel allocation in cooperative protocols on system performance, is proposed. Subsequent analysis and simulation results show that DOIDF outperforms corresponding OR schemes in outage probability, spectral efficiency and SNR gain over DT.