基于隐马尔可夫模型的认知无线频谱切换方法

认知无线网络(cognitive radio network,CRN)中,为降低认知用户对授权用户干扰,需尽可能的减少频谱切换次数。提出了一种基于预测信道空时间(prediction of the channel idle time,PCIT)的认知无线动态频谱切换方法。该方法基于已知状态序列的隐马尔可夫模型(known-state sequence hidden Markov model,KSS-HMM),利用信道状态的历史信息预测信道未来空闲时间期望及传输数据包的数量,并给出了备选信道的选择方法,通过比较每个备选信道的传输数据量来选择最佳信道进行数据传输。仿真结果表明,与随机信道选择和传统选择方法相比,该方法能明显减少信道切换次数,同时提高了认知用户的吞吐量。     

基于纠删码的海洋无线传感器网络丢包恢复方法

针对无线传感器网络在恶劣海洋环境下存在的严重丢包问题,设计并实现了一种低复杂度的基于里德-所罗门(RS)码 的丢包恢复方法。 具体而言,发送节点对信息数据包进行分析,进一步利用 RS 码编码生成并插入少量的冗余数据包,可以保 证数据包的顺序发送,同时利用较少的资源编码生成了冗余校验数据包。 接收节点基于接收的信息数据包与校验数据包,通过 RS 码对丢失的数据包进行纠删恢复。 在陆地和海洋两种复杂信道中测试提出的方法,以丢包率(packet loss rate, PLR)作为 RS 码丢包恢复方法性能的度量指标。 测试结果表明,采用低复杂度的 RS 码丢包恢复方法能降低信道衰落影响的丢包率,保证了 数据在严重丢包情况下的完整性,提高系统的可靠性。     

用电信息采集系统远程应急通道平台设计

目前除有线方式（光纤、PLC）外,多种新型无线通信技术（LTE、WiMax等）也在用电信息采集系统中大量应用。这类通信系统采用基站对区域内大量采集终端进行信息采集和管理,一旦出现故障,会引起大范围电力用户信息无法获取,影响整个电力输配系统的正常运行。设计了一种利用无人机搭建低空无线通信平台的应急方案,并对该场景下的空中无线信道进行了分析和建模,以此为根据,设计了基于宽带正交频分复用技术（OFDM）的远距离上行信道传输方案,并分析了该方案的通信性能和系统容量。仿真结果表明该方案可以满足10 km范围内的远程应急补站。     

An efficient cooperative sensing scheme with bandwidth-limited control channel

The conflict between scarcity of spectrum resources and low spectrum utilization motivates the concept of cognitive radio, which allows secondary unlicensed users to borrow temporally unused spectrum bands from primary licensed users. Spectrum sensing is one of the key functionalities that enable spectrum hole discovery and interference avoidance. As single user spectrum sensing may experience performance degradation in harsh wireless environment due to fading and shadowing, user cooperation is introduced to exploit spatial diversity for better sensing performance. However, local sensing results must be transmitted via a control channel. The advantage of cooperative sensing can be compromised by bandwidth limitation of the control channel. To overcome this, a benching cooperative sensing scheme is proposed in this paper. This scheme can reduce time overhead of sensing information exchange under a communication constraint. Analytical results of periodic sensing efficiency are then deduced while sensing parameters are optimized. Based on these, a recursive sensing algorithm exploiting prior channel state information is developed. Numerical results are presented to demonstrate the potential of our scheme.     

多跳中继宽带电力线通信网络中的OFDM跨层资源分配

为保障宽带电力线通信网络的有效性和可靠性,提出一种综合多跳中继宽带电力线通信网络的业务层、网络层、介质访问控制(Media Access Control,MAC)层和物理层信息的正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)跨层资源分配方法。首先建立综合跨层信息的MAC层数据包调度效用值模型和基于公平性阈值控制的物理层子载波分配模型。提出为满足各用户服务质量需求的MAC层高效用值数据包优先调度准则。再将该模型和准则应用于宽带电力线通信网络各交叉节点的资源分配过程中。最后在典型电力线信道环境下对所提算法及对比算法进行仿真。仿真结果表明所提算法能够保证实时用户与非实时用户的通信速率和时延的服务质量需求,且具有较大的系统吞吐量和较好的时延特性,有效解决了多跳中继宽带电力线通信网络的OFDM资源分配问题。     

合作分集无线网络合作伙伴选择

在未来无线网络中提出了合作分集的概念。基于合作分集技术的无线网络的关键问题之一在多终端网络中如何分配和管理合作伙伴，即对于一次特定的通信过程如何确定由网络中哪些空闲终端协作完成，以及重新分配合作伙伴的频度，以达到网络某些性能指标最优化。提出一种离散随机优化算法自适应选择最好的合作伙伴集合达到误码率性能或系统容量性能最优。通过蒙特卡罗仿真验证了分析结果以及该算法的性能，并举例说明该算法的收敛性。     

基于DSS的直播系统研究与实现

本文设计并实现了一个基于达尔文流媒体服务器(darwin streaming server,DSS)的直播系统,首先对DSS服务器的软件核心架构进行了研究分析,针对直播系统中UDP传输导致的网络拥塞现象和丢包问题,采用了基于RTCP反馈的拥塞控制方案,经过系统测试表明直播时的平均延时约为100 ms,画面质量总体清晰流畅,有效减轻了网络拥塞、降低了丢包;且通过CPU占用率测试表明随着用户的增多CPU占用率并未呈现明显增加,单用户情况下CPU占用率稳定在1％～3％,20个用户情况下CPU占用率稳定在6％～9％,说明系统并发处理性能较好.系统总体具有较好的性能,能够满足实际应用需求.     

Comparison of CDMA and OFDM Systems for Broadband Power Line Communications

Direct sequence code division multiple access (DS-CDMA) and orthogonal frequency division multiplexing (OFDM) systems are two options for broadband power line communications. In this paper, a comparison is made between the CDMA and OFDM systems. The bit error rate (BER) performance and the optimum overall data rate of the CDMA and OFDM systems are analyzed and compared, using the criteria of the same bandwidth occupation, the same transmission power for each user, the same total number of users in the system and the same power line channel. The comparison is based on the analytical models that are developed and verified by simulations.     

多用户MIMO下行链路物理层安全研究

随着无线通信的迅猛发展,如何实现信息的安全传输,越来越受到研究人员的广泛关注。考虑实际的通信场景,即发送端已知不完备的信道状态信息(channel state information,CSI),研究了多用户多输入多输出下行链路的物理层安全性能。具体而言,以最大化系统安全容量为多用户调度准则,采用最大比传输波束成形方案,获得了系统安全中断概率(secrecy outage probability,SOP)的闭合表达式及在高SNR下的渐近结果。除此之外,也获得了在已知完备CSI情形下,系统SOP的准确的理论结果及渐近结果。研究表明:已知不完备CSI情形下,网络可获得的分集增益为K;已知完备CSI情形下,分集增益为K×N_B×N_S,其中K、N_B、N_S分别代表用户数目,基站的天线数目和用户的天线数目。最终,通过蒙特卡洛仿真,验证了理论分析的正确性。     

基于QoS的变电站设备无线监测网络拓扑研究

随着无线传感器网络在智能变电站不同业务应用中的深化,网络的高数据率传输和网络的服务质量（qual-ity of service,QoS）问题成为无线传感器网络（wireless sensor network,WSN）的新热点。针对智能变电站的设备状态监测应用,利用无线传感器网络技术,建立分簇的三层智能变电站设备无线监测网络结构;参考 Zigbee协议和 IEC 61850报文规定,对监测网络数据流进行建模;从用户感知 QoS、网络 QoS 和节点 QoS 三个方面,结合Opnet仿真功能,提出包括端到端时延、MAC层时延、MAC层吞吐率、MAC层丢包率、数据碰撞、丢包率、比特误码率、信噪比和接收功率的QoS指标。根据实际变电站设备监测配置,建立起仿真网络模型,仿真研究表明相比于树状拓扑、Mesh拓扑网络,设计的簇状拓扑网络具有更好的QoS综合性能。     

基于最优功率分配原则的无线网络D2D用户通信质量分析

构建了一种基于最优功率分配原则的D2D用户通信质量分析算法,能够促进通信网络吞吐量获得明显提高,从而为D2D用户提供最佳资源分配方案。研究结果表明:研究构建得到的资源分配算法实现了吞吐量的显著提高,表现出比其它两种算法更优的计算性能。当D2D用户不断变多后,所有算法都获得了更高的吞吐量。在同样的D2D用户数情况下,采用资源分配算法可以获得比其它算法更优的运算性能。当最大发射功率提高后,吞吐量也明显上升,显著改善了算法性能。当蜂窝用户在系统中的最小速率需求持续提高后,将会引起整个系统出现吞吐量持续减小的情况。     

多媒体应用的分布式动态信道选择算法

在异构无线网络上支持多媒体应用是一个普遍和具有挑战的问题.对异构网络下不同用户传输不同的多媒体应用提出了一种分布式动态信道选择算法.不同于以前的研究很少考虑多媒体用户的应用层需求,算法考虑了不同多媒体用户有不同的传输速率需求、不同的效用函数和不同的时延阀值等.为了有效地分布式管理可用信道资源,通过对优先级虚拟队列进行优...     

几种典型Ad hoc路由协议的仿真分析

路由算法是无线自组网的重要组成部分,路由的好坏直接影响网络的性能.文章以无线自组网在电力系统通信中的应用为出发点,研究了DSDV,DSR,AODV和OLSR四种典型的路由协议,采用定性比较和仿真实验的方法,分析了静止节点在不同规模和负载流量场景下,路由协议的分组投递率、时延、吞吐率以及路由控制开销的变化情况,并在此基础上,对4种协议的性能进行了比较和评估,为基于无线自组网的电力系统通信提供了路由选择参考.     

应用VDE的QPSK-CPM扩频系统多用户检测算法

连续相位调制扩频信号因为扩频序列随机变化,可以适应多用户通信,逐渐被应用到卫星通信中。甚高频数据交换系统随机接入信道采用了QPSK-CPM扩频调制方案,针对QPSK-CPM扩频系统的多用户检测问题,提出一种基于干扰消除检测的新型多用户检测算法,该算法通过对接收用户信息进行串行干扰消除级联一次迭代消除的方法来对多用户信息进行检测,且该算法能够有效消除用户的多普勒频偏及减小用户功率差带来的性能损失。通过对新算法仿真验证,结果表明,新算法比传统干扰消除检测算法具有更好的检测性能,在实时通信船舶数量达到800艘时,8个用户以内的混叠信息解帧率可达90%。     

Fixed-Data-Rate Power Minimization Algorithm for OFDM-Based Power-Line Communication Networks

In this paper, we present a suboptimal integer bit allocation algorithm that minimizes power output for given user demands in multiuser orthogonal frequency-division multiplexing (OFDM) systems implemented in downlink transmission of power-line communication (PLC) networks. Assuming complete knowledge of a channel and the predetermined data rates for every user, the presented algorithm solves the power minimization problem analytically. The simulation results have shown significant advantages of this approach, especially in comparison with algorithms that deal with the problem of user data rate demands in an iterative manner. Compared to iterative algorithms, the proposed algorithm proves to be a much more effective solution regarding processing time and computational complexity. In addition, the losses in its power allocation efficiency due to its suboptimal approach remain very small in cases where the number of users does not exceed half the number of available subchannels.     

Cellular digital packet data

Cellular digital packet data (CDPD) offers on-the-go users access to a low-cost, widespread, wireless data network. CDPD can be overlaid on existing analog cellular systems, and share their infrastructure equipment on a non-interfering basis. Basically, CDPD transmits packet data over idle cellular channels. It autonomously switches to another channel when the current channel is about to be assigned for voice usage. CDPD does not communicate with the underlining cellular network. However, CDPD does use its knowledge about the channel assignment algorithm of the cellular cell to predict the channels available for CDPD use. CDPD may serve as the wireless extension to other data networks (e.g., Internet) or public switched telephone networks. It supports connectionless network services which have packets called network protocol data units (NPDU). Every packet is routed individually based on the destination address of the packet and knowledge of the current network topology. Initially, CDPD provides two connectionless network services: the standard open systems interconnection connectionless network protocol and the Internet protocol     

应用电力负荷管理系统开发技术防窃电功能

通过动态比较电力用户在正常与异常计量情况下模拟量回路与电能计量回路的功率、电流和脉冲,并调用电能表本身防窃电信息,通过借助无线信道传输,对电力负荷管理中心主站集中监视和发现用户窃电和计量回路异常的问题提出了解决方案。     

Operational Fault Detection in cellular wireless base-stations

The goal of this work is to improve availability of operational base-stations in a wireless mobile network through non-intrusive fault detection methods. Since revenue is generated only when actual customer calls are processed, we develop a scheme to minimize revenue loss by monitoring real-time mobile user call processing activity. The mobile user call load profile experienced by a base-station displays a highly non-stationary temporal behavior with time-of-day, day-of-the-week and time-of-year variations. In addition, the geographic location also impacts the traffic profile, making each base-station have its own unique traffic patterns. A hierarchical base-station fault monitoring and detection scheme has been implemented in an IS-95 CDMA Cellular network that can detect faults at - base station level, sector level, carrier level, and channel level. A statistical hypothesis test framework, based on a combination of parametric, semi-parametric and non-parametric test statistics are defined for determining faults. The fault or alarm thresholds are determined by learning expected deviations during a training phase. Additionally, fault thresholds have to adapt to spatial and temporal mobile traffic patterns that slowly changes with seasonal traffic drifts over time and increasing penetration of mobile user density. Feedback mechanisms are provided for threshold adaptation and self-management, which includes automatic recovery actions and software reconfiguration. We call this method, Operational Fault Detection (OFD). We describe the operation of a few select features from a large family of OFD features in Base Stations; summarize the algorithms, their performance and comment on future work.     

5G TM 信号无线信道测量平台研究与实现

为了研究第五代移动通信（5G）系统无线信道，获得准确的5G无线信道特性和信道模型，提出了一种基于5G新空口（NR）测试模式（TM）信号的无线信道测量平台。开展了TM无线信道测量平台的总体架构及测量信号接收处理算法设计，并基于软件无线电设备和高性能计算设备搭建测量平台。针对功率谱平坦度、峰均功率比和相关性等指标，对多种TM信号的测量性能进行评估。根据性能评估结果，选择适合作为测量波形的TM信号。采用射频馈线直连、多径信道模拟和静态空口实测3种方法对TM无线信道测量平台进行验证，该平台不仅可以实现准确的信道测量，同时能够对矢量幅度误差和误比特率等传输性能进行测试。     

AX.25 [data link layer protocol for packet radio networks]

For packet radio networks, the AX.25 data link layer protocol is most often used. However, TCP/IP (Transport Control Protocol/Internet Protocol) is also popular. The AX.25 protocol is a variant of the international X.25 protocol applied to wireless communication and packet radio. Most networks are composed of copper or fiber optic cable and provide reliable communication between hosts. The wireless medium is vastly different. It is less reliable and suffers from phenomena that are not present in conventional wired networks. For example, in a cable network all hosts on a network can hear each other. This makes "carrier sense" protocols such as Ethernet easy to implement. Before any host seizes the network, it first listens to help avoid collisions. Wireless networks also support carrier sense. However, hosts on the network cannot always hear each other for numerous reasons. Buildings and the local terrain are two important factors that determine the ability to receive information. We concentrate on the analysis of AX.25 packet radio networks operating in the 144-148 MHz band. Understanding and studying a network is a com analyzers, sometimes called "sniffers," are available to aid the packet user in understanding how a network operates. XNET, a network analyzer developed specifically to examine AX.25 networks, is described.