基于最大化信干噪比的广播信道干扰消除算法

研究了广播信道分布式干扰消除算法的性能,提出了一种基于动态功率分配的多天线广播干扰信道对齐算法.该算法利用多用户多天线干扰信道相关矩阵的迹来计算分配功率,并采用最大化码流信干噪比的方法来得到预编码矩阵和接收滤波器矩阵.数值仿真表明,该动态功率分配算法与等功率分配算法相比,尽管低负荷下干扰对齐后的平均信干噪比增益不明显,但中、高负荷下其干扰对齐后的平均信干噪比大幅提高,特别是高负荷下可以解决等功率方法存在的信干噪比瓶颈效应.由于低负荷的应用需求并不强烈,因而该算法是一种实用的广播信道干扰消除方法.     

数字微波通信中自适应均衡器的应用

在移动通信及高速无线数据通信中,由于多径效应和信道带宽的有限性以及信道特性的不完善性而产生的码问干扰（ISI）成为影响通信质量的重要因素,信道的均衡技术是克服码间干扰的主要手段,而自适应均衡器能够跟踪信道变化而获得广泛应用。本文围绕自适应均衡技术进行了深入的探讨,重点研究了自适应均衡算法、信道模型等问题,并针对几种盲均衡算法应用于数字微波无线信道的均衡性能进行了仿真和比较,其结果对于开发具有更高频谱利用率的数字微波通信链路有着重要的指导意义。本文讨论的重点是计算复杂度低、易于在数字微波系统中实现的自适应均衡器。     

面向多媒体业务的无线ATM多址接入协议

基于MDR-TDMA（Multi-service Dynamic Reservation-TDMA）的无线ATM多址接入控制协议包括两个主要的过程，即请求报文的信息时隙的分配过程，对于前者，通过基于帧的自适应伪贝叶斯ALOHA算法，在保证请求报文最优吞吐率的条件下，实现了不同优先级的请求报文接入。对于后者，着重分析了以视频会议为模型的VBR业务的带宽分配，提出了一种新的带宽分配方法-Minmax算法，并将它的仿真结果与线性比例算法进行比较。     

一种基于自适应子空间跟踪与Jacobi算法的时变信道有限反馈预编码方法

提出了一种基于自适应子空间跟踪与Jacobi算法的时变信道有限反馈预编码方法.该方法针对无线信道的时变性,利用梯度算法自适应跟踪时变信道的发射预编码矩阵,同时考虑了反馈信道有限比率的反馈比特数,将Jacobi迭代算法应用于时变信道右奇异矩阵的跟踪,从而有效降低了每个反馈帧的反馈比特数.计算机仿真表明,在时变信道,该方法在降低反馈量的同时,还获得了比存在反馈延时的Grassmannian预编码方法更好的系统容量性能.     

广义多载波系统中基于双循环自适应时隙结构的空时联合检测

广义多载波并行传输方案是一种宽子带方案,每个子带带宽达到1.28MHz且子带交叠在-15dB以下.这种多载波结构能够有效地克服多载波系统的峰均比问题和对频偏的敏感度.首先给出了广义多载波并行传输方案的数字基带模型.为了便于信道估计和信号检测,设计了一种双循环的自适应时隙结构,基于该结构设计了频域均衡空时联合检测器,并证明它是最小均方误差准则下的最优检测器.最后在ITU M.1225信道下计算机仿真证明了该方案在宽带移动通信环境中的有效性.     

EPON中一种改进的DBA算法

动态带宽分配是EPON系统的关键技术之一。由于多个ONU共享同一上行信道,对上行数据流的控制显得尤为重要。EPON系统使用请求/应答机制对ONU进行带宽分配。在ETRI算法的基础上,提出了一种改进的算法,它支持队列优先级和ONU之间的公平性。通过仿真结果可以看出,改进的算法与ETRI相比,大大减少了平均队列长度。     

一种浅海水声信道分数间隔自适应均衡算法研究

水声信道是最为复杂的数据通信环境之一,而具有重要军用和商用价值的浅海水声信道,其多径与频散效应更为严重。在浅海水声数字通信中,普遍存在着码间干扰和码内干扰效应,严重影响了水下通信的速度和质量。在判决反馈结构的基础上,采用分数的方法,提出了一种适用于浅海水声信道的自适应均衡算法,并通过计算机仿真实验与整数方法进行了性能对比。传输信号采用正交相移键控调制方式,以有效利用有限通信带宽。仿真结果表明,该算法获得了较快的收敛速度和较小的稳态误差,提高了水声通信的有效性及可靠性,因而具有良好的工程应用价值。     

基于数字信道化技术的自适应门限检测算法

当卫星通信系统中同时存在强信号和弱信号时,固定门限对微弱信号出现大概率漏警问题,该文提出了一种基于数字信道化技术的自适应门限检测算法。该算法针对不同的子信道集产生适配的自适应检测门限,在强信号的检测上保持了固定门限的优势,在弱信号的检测上能够有效检测和跟踪目标频率信息,支持对强信号和弱信号进行分离和检测。通过蒙特卡洛仿真对数字信道化后的固定门限检测和自适应门限检测进行对比,自适应门限算法能够有效检测强信号和弱信号,实现强弱信号的有效分离,验证了基于数字信道化技术的自适应门限检测算法的有效性。     

基于互信息量的CMMB系统物理层抽象算法

为了准确和高效地评估在构建下一代广播电视网（NGB）中起重要作用的中国移动多媒体广播（CMMB）系统的链路传输性能,根据CMMB协议标准,利用大量高斯信道下的仿真数据拟合出了接收比特互信息率（RBIR）与误帧率(FER)之间的一一对应关系,然后给出了基于互信息量的CMMB物理层抽象算法——能在解调的输入端计算平均互信息量的RBIR算法,并利用开发的CMMB物理链路仿真平台在巴西信道模型中验证了该抽象算法的准确性：能够精确地预测当前无线信道的质量。     

瑞利衰落信道下改进的AMC/SR-ARQ跨层设计方案

针对瑞利衰落信道提出了一种改进的自适应调制编码(AMC)与选择性自动重传请求(SR-ARQ)相结合的无线网络跨层设计方案.通过在计算不同调制方式对应的信噪比区间门限值时使用信道状态信息的二阶统计特性来计算误比特率(BER),使得选取的调制方式因考虑了无线信道的时变特性而更为合理,从而保证了为用户提供有服务质量(QoS)保证的服务.同时,对系统信道状态和系统吞吐进行了建模,并提出了N-成功/N 1-失败系统吞吐模型.在系统模型的基础上,对比分析了改进的方案和现有方案的性能指标.仿真实验证明,改进的AMC/SR-ARQ方案可以真正确保网络的平均误包率约束条件并提高平均频谱效率.     

Alternate video broadcasting scheme for popular videos

A video segment broadcasting scheme can reduce server and network bandwidth by periodically broadcasting popular videos that are most likely demanded by clients, instead of responding to each client requests. When video segments broadcast on a channel, in general, alternate broadcasting schemes periodically transmit all segments on a given channel with the same transmission period, which reduces the transmission efficiency of stream channels and requires sufficient client storage space for video segments broadcast on simultaneous channels. The author proposed a novel alternate video broadcast scheme, a delayed buffering broadcast that requires lower server bandwidth and client buffer space compared with those of previous approaches. In addition, the study provides an analytical analysis of the scheme, including a lower bound on the video segment transmission rate for any alternate broadcast scheme. It also derives an upper bound on its storage requirements from the client side. Using the performance study of the proposed scheme and simulation results, the author establishes that the proposed scheme uses fewer server channels and storage resources than previously reported alternate video broadcast schemes for any given client waiting time.     

Multiplexed harmonic broadcasting scheme for efficient video-on-demand services

Periodic broadcasting schemes can improve the efficiency of video-on-demand (VOD) services by reducing the bandwidth requirement to transmit popular videos. The harmonic broadcasting scheme has the best performance in reducing service bandwidth under a given access time, but it uses too many channels. However, a multiplexed harmonic broadcasting scheme that overcomes this drawback is now proposed. This scheme divides each video into equal-sized segments and then broadcasts segments periodically in a small number of sever channels with equal bandwidth. The idea of segment-to-channel mapping in the scheme is inspired by the time division multiplexing system. Each segment is divided equally into several subsegments; subsegments of different segments are multiplexed in a slot with the guarantee of being able to keep playing out continuously for every user. The proposed scheme outperforms the pagoda broadcasting and recursive frequency splitting schemes in reducing the viewers' maximum waiting time, and the scheme requires less client storage     

Experimental evaluation of a bandwidth allocation scheme for foundation fieldbus

Operation of the data link layer of the foundation fieldbus is based on scheduling and token-passing disciplines. This paper presents a network design for the foundation fieldbus protocol using a bandwidth allocation scheme. Fieldbus traffic consists of periodic data and sporadically generated time-critical and time-available data. The bandwidth allocation scheme schedules the transmission of periodic data. Time-critical and time-available data are transmitted via a token-passing service. The validity of this bandwidth allocation scheme was determined using an experimental model of a network system. The results obtained from the model show that the proposed scheme restricted the delay of both periodic and time-critical data to a pre-specified bound. The proposed bandwidth allocation scheme also fully utilized the bandwidth resources of the network system.     

Cluster-Based Stable BSM Dissemination System for Safe Autonomous Platooning

Recently, the importance of vehicle safety supporting system has been highlighted as autonomous driving and platooning has attracted the researchers. To ensure driving safety, each vehicle must broadcast a basic safety message (BSM) every 100 ms. However, stable BSM exchange is difficult because of the changing environment and limited bandwidth of vehicular wireless communication. The increasing number of vehicles on the road increases the competition to access wireless networks for BSM exchange; this increases the packet collision rate. An increased packet collision rate impairs the transmission and reception of BSM information, which can easily cause a traffic accident. We propose a solution, the vehicular safety support system (V3S), which exchanges BSMs reliably even when many vehicles are on the road. The V3S uses a clustering scheme to decrease network traffic by reducing the amount of data exchanged between a vehicle and the roadside unit (RSU). In addition, the V3S reduces the collision rate of wireless network packets by broadcasting the vehicle's BSM in an allocated timeslot using the time division multiple access (TDMA) MAC protocol. The V3S also deals with insufficient bandwidth for dedicated short-range communications (DSRC) by changing DSRC channels according to traffic flow. In evaluating the packet error rate for stable BSM packet delivery, the V3S demonstrates an excellent packet error rate of less than 1%, compared to the 802.11p with its packet error rate of 82%.     

Implementation of a bandwidth allocation scheme in a token-passingfieldbus network

This paper presents a method for implementing a bandwidth allocation scheme on Profibus that operates on a token-passing discipline basis. In order to implement the bandwidth allocation scheme, this study incorporates the following additional functions to the fieldbus datalink layer (FDL) protocol of Profibus. First, the medium bandwidth of the network system is separated into both periodic and time-available intervals, and, second, node timers are synchronized over a local link. The validity of this bandwidth allocation scheme is determined using an experimental model of a network system. The results obtained from the experimental model show that the proposed scheme restricts the delay of both periodic and time-critical data to a pre-specified bound. The proposed bandwidth allocation scheme also fully utilized the bandwidth resource of the network system     

基于随机逼近动态带宽分配的CAC研究

ATM网络中，基于动态带宽分配的CAC，即可以提高ATM网络资源的利用率又能保证业务的QoS要求。本文运用自适应随机逼近算法研究了ON／OFF信源模型的带宽估计及接入问题，数值计算的结果表明，随机逼近能较好地逼近实际值，与社会网络方法相比，随机逼近算法的特点是不需要离线训练，也不需要已准好的样本，这能在网络实际运行中自动调整自动收敛。     

Error recovery in video transmission over CDMA2000 broadcast networks

Multimedia services over a CDMA2000 broadcast network face a challenge from the unreliable and error-prone nature of the radio channel. Reed-Solomon (RS) coding, integrated with the MAC protocol, is used to cope with this problem. However, performance analysis of RS coding under varying channel conditions shows that it is not always effective, especially for slow-moving nodes which experience relatively long error bursts. Therefore a more efficient scheme is proposed that uses a RS code with reduced parity overhead, and freeing bandwidth can be used flexibly for retransmission. The packets to be retransmitted are prioritised by a utility function derived from the map of the error control block at each mobile node and the number of mobile nodes that require the lost packet. Simulation results show that the gain of retransmission exceeds the loss incurred by reducing the parity, leading to an improvement in the playback quality of MPEG-4 video streams. As a result, service area for high-quality multimedia can be expanded.     

LFF:一种面向大数据应用的众核处理器访存公平性调度机制

研究了众核处理器的访存公平性问题。针对众核处理器距离访存资源较近的处理单元拥有较大的访存带宽而造成的访存公平性问题,提出了一种面向大数据应用的众核处理器访存公平性调度机制:最少最远(LFF)优先访存。这种机制的原理如下:依据处理单元距离访存资源的距离以及处理单元访存的次数来调度访存顺序,以保证各个处理单元的公平性。首先,访问次数较少的节点被赋予更高的访存优先权。其次,在具有相同访问次数的节点中,距离更远的节点优先访存。再次,在相同距离的节点中,已被选中优先次数少的有优先级。实验评估表明,该调度机制能够有效解决众核处理器的访存公平性问题,其公平性调度效果优于FR-FCFS,PAR-BS、ATLAS。在1024核情况下,系统异步率由FR-FCFS的15.5%降低到1.89%。     

复杂截面周期性隔振桩带隙特性构型影响因素研究

提出带隙特性丰富的蜂窝截面、正交截面和X截面三种周期性隔振桩,采用平面波展开法对三种隔振桩进行频散及带隙分布展开研究,揭示平面内和平面外首阶完全带隙的起始频率、截止频率以及带宽随构型影响因素如周期常数、填充率以及控制尺寸变化的规律,为该类型排桩应用及设计选型提供理论依据.研究表明:降低周期常数可以增加三种隔振桩平面内和...     

Optimisation of limited feedback design for heterogeneous users in multi-antenna downlinks

The authors study the problem of limited channel information feedback in multiple-input single-output (MISO) broadcast channels serving heterogeneous users. The heterogeneous users have different feedback channel capacities because of their physical constraints and limitations. Our objective is to design an optimised limited feedback strategy for multiple users by using a set of multi-resolution codebooks such that, under varying and quantised channel information feedback, the multiuser system can maximise its achievable sum rate. By exploiting the receive antenna combining technique, the authors further generalise the proposed scheme to the multiuser beamforming case with multi-antenna users. Finally, the authors verify the proposed scheme by numerical methods. Simulation results show that the sum rate performance for heterogeneous users can be effectively improved by using the proposed limited feedback scheme, which is optimised according to only statistic channel information of users.