Real-time communication in multihop networks

Communication in real-time systems has to be predictable, because unpredictable delays in the delivery of messages can adversely affect the execution of tasks dependent on these messages. We develop a scheme for providing predictable interprocess communication in real-time systems with (partially connected) point-to-point interconnection networks, which provide guarantees on the maximum delivery time for messages. This scheme is based on the concept of a real-time channel, a unidirectional connection between source and destination. A real-time channel has parameters that describe the performance requirements of the source-destination communication, e.g., from a sensor station to a control site. Once such a channel is established, the communications subsystem guarantees that these performance requirements will be met. We concentrate on methods to compute guarantees for the delivery time of messages belonging to real-time channels. We also address problems associated with allocating buffers for these messages and develop a scheme that preserves delivery time guarantees     

新型信道自适应编码协作体制

针对传统编码协作体制在信道条件动态变化的移动场景中存在较严重的性能损失问题,提出一种码率兼容低密度奇偶校验(LDPC)码与混合自动重传请求(HARQ)协议相结合的新型自适应编码协作体制.假设信道状态信息在每次传输时发生变化,通过不等长增量冗余的自动重传,协作节点与目的节点处的等效码率随信道条件变化而获得自适应非线性调整.推导所提体制的中断概率与吞吐量等系统性能表达式,并给出理论分析及仿真结果.实验结果表明,在适当的兼容码率设计下,所提体制与传统体制和等长传输体制相比较可有效降低系统中断概率,提高系统的吞吐量,改善移动环境下协作通信系统的传输可靠性.     

紫外非视距通信的MLSE均衡器

针对无线非视距紫外通信中的大气信道模拟问题,提出将最大似然序列估计均衡器应用于无线非视距紫外通信中.推导紫外通信中接收信号的概率密度函数,以此近似研究均衡器的输出误码率.理论分析与仿真结果表明,在短距离通信时,大气衰减系数与信道带宽的变化不影响均衡器性能.在接收信噪比不变的较长距离通信时,两者的变化对均衡器性能影响明显.信道记忆长度等因素对均衡器性能影响显著,而对调制方式不敏感.     

无线传感器网络中协作误差传播感知的机会可靠传输机制

针对无线传感器网络协作通信过程中误差传播对系统性能的影响,提出了一种基于机会式误差修正的可靠传输机制。首先,在多节点协作无线传感器网络中建立三种协作传输方案,基于信道质量和误符号率建立协作误差传播模型。接着,针对协作误差中的合并、调度和干扰等类型,通过在信道、信源和协作网络物理层提出机会式误差修正算法。最后,在上述结论基础上,综合感知用户的性能要求、调度复杂度和协作传播模型,提出了机会式可靠传输机制。数学分析结果不仅验证了机会式传输机制比静态机制具有高可靠性,而且证明了所提机制在端到端通信的实时性、可靠性、吞吐率和能效等方面有优越性。     

Novel power control and collision resolution schemes for device-to-device discovery

Device-to-Device (D2D) communications allow devices to communicate directly without going through infrastructure. It is considered a promising solution to improve communication performance and network capacity of LTE-Advanced system. In addition, the direct proximity communication implies reduced delay and energy consumption. However, from the perspective of D2D networks, co-existence of multiple D2D User Equipments (UEs) is a challenging issue because of the proximity interference management, especially, without a central controller in a distributed scheme. In this article, we propose a novel distributed power control and collision resolution schemes, which can enhance discovery success of proximity devices conforming to LTE-A networks. The simulation results demonstrate that our proposed schemes can significantly improve the performance of discovery success and detectable coverage by mitigating D2D interference.     

基于通信优化的Infiniband集群MPI作业加载*

针对如何缓解Infiniband集群中因通信冲突引起的MPI程序性能下降问题进行了研究,从系统管理的角度出发,提出了通过改变进程映射来优化MPI作业加载方案从而优化应用程序通信性能的方法,设计了用于评价MPI作业加载方案的通信性能损失系数（CPLR）指标,基于模拟退火算法设计了优化加载方案的搜索算法,并对所提出的指标和算法进行了实现和测试。测试结果表明,经过优化加载后的MPI程序在通信性能上有一定程度的提高。     

An overlapping communication protocol using improved time-slot leasing for Bluetooth WPANs

In this paper, we propose an overlapping communication protocol using improved time-slot leasing in the Bluetooth WPANS. One or many slave–master–slave communications usually exist in a piconet of the Bluetooth network. A fatal communication bottleneck is incurred in the master node if many slave–master–slave communications are required at the same time. To alleviate the problem, an overlapping communication scheme is presented to allow slave node directly and simultaneously communicates with another slave node to replace with the original slave–master–slave communication works in a piconet. This overlapping communication scheme is based on the improved time-slot leasing (TSL) scheme which modified from the original TSL, while the original TSL scheme only provides the slave-to-slave communication capability. The key contribution of our improved TSL scheme is to offer the overlapping communication capability. With the overlapping communication scheme, we developed an overlapping communication protocol in a Bluetooth WPANs. Finally, simulation results demonstrate that our developed communication protocol achieves the performance improvements on bandwidth utilization, transmission delay time, network congestion, and energy consumption.     

低信噪比下星地信道监测序列长度设计

星地通信系统中,信道误码率直接影响系统的通信性能。针对星地通信特点,提出了星地信道监测序列长度设计方法,考虑了接收端对监测序列的捕获概率和捕获时间要求,避免了低捕获或长时延对信道实时监测的影响。通信系统中,信噪比不同将影响监测序列的捕获概率和捕获时间,因此,针对星地通信的特点,重点考虑了低信噪比下监测序列的长度设计,并进行了仿真验证分析。仿真结果表明,在保证监测序列捕获时间可以和传输时间相比拟的前提下,监测序列长度至少取8485bit才能保证捕获概率为1。     

Analysis of the Desynchronization Attack Impact on the E2EA Scheme

The healthcare IoT system is considered to be a significant and modern medical system. There is broad consensus that these systems will play a vital role in the achievement of economic growth in numerous growth countries. Among the major challenges preventing the fast and widespread adoption of such systems is the failure to maintain the data privacy of patients and the integrity of remote clinical diagnostics. Recently, the author proposed an end-to-end authentication scheme for healthcare IoT systems (E2EA), to provide a mutual authentication with a high data rate between the communication nodes of the healthcare IoT systems. Although the E2EA authentication scheme supports numerous attractive security services to resist various types of attack, there is an ambiguous view of the impact of the desynchronization attack on the E2EA authentication scheme. In general, the performance of the authentication scheme is considered a critical issue when evaluating the applicability of such schemes, along with the security services that can be achieved. Therefore, this paper discusses how the E2EA authentication scheme can resist the desynchronization attack through all possible attack scenarios. Additionally, the effect of the desynchronization attack on the E2EA scheme performance is analyzed in terms of its computation and communication costs, based on a comparison with the recently related authentication schemes that can prevent such attack. Moreover, this research paper finds that the E2EA authentication scheme can not only prevent the desynchronization attack, but also offers a low cost in terms of computations and communications, and can maintain consistency and synchronization between the communication nodes of the healthcare IoT systems during the next authentication sessions.     

Performance analysis of a channel assignment scheme in cellular communication systems

In cellular communication systems, channel assignment schemes are very important to improve teletraffic performance characteristics. Because of the overlapping design of the cells in cellular communication systems, a mobile user is capable of communicating with two different bases. In this paper, a new channel assignment scheme is proposed to improve the blocking probability of a cellular communication system. The blocking probability of the cellular communication systems is analyzed based on Markov chain. According to the analytical results, the proposed channel assignment scheme shows different characteristics in comparison with fixed channel assignment scheme.     

基于MIMO信道的四天线发射分集及其性能分析

发射分集是一项有效改善信道衰落和提高系统容量的技术,在第3代移动通信系统中已经开始普遍使用。本文给出了几种基于MIMO信道的四天线发射分集方案,并对他们的性能进行了分析和仿真比较。     

A scalable encryption scheme for multi-privileged group communications

In multi-privileged group communications, since users, who can subscribe to different data streams according to their interests, have multiple access privileges, security issues are more difficult to be solved than those in traditional group communications. The common drawback of traditional key management schemes is that they will result in the “one-affect-many” problem, because they use a key graph to manage all the keys in a group, which makes one key being shared by many users. Recently, a key-policy attribute-based encryption (KP-ABE) scheme is proposed to encrypt messages to multiple users efficiently, which has been applied in secure multi-privileged group communications. However, user revocation in KP-ABE is still not resolved when applied to multi-privileged group communications. So, in this paper, by uniquely combining a collusion-resistant broadcast encryption system and a KP-ABE system with a non-monotone access structure, we propose a scalable encryption scheme for multi-privileged group communications (EMGC). Based on the features of different multi-privileged group communication systems, we also propose two constructions for our EMGC scheme. With the two constructions, a system can support a user not only to join/leave a group at will, but also to change his access privilege on demand, and the expenses during rekeying operations are small. Therefore, our scheme, which can accommodate a dynamic group of users, is more applicable to multi-privileged group communications.     

基于图着色理论的全双工D2D分簇资源分配方案

全双工通信允许用户同时同频收发信号,将其应用在D2D(Device-to-Device,D2D)通信中虽然可以提高系统吞吐量,但是也带来了更加复杂的干扰关系。为了降低干扰,提升系统吞吐量,本文提出了以簇为单位的资源分配方案。该方案先引入图着色理论为全双工D2D用户进行合理的分簇,然后采用匈牙利算法进行链路资源的分配,从而优化蜂窝系统的性能。仿真结果表明,该方案在提高频谱利用率的同时提升了整个蜂窝网络的系统容量。     

基于FPGA的MC-CDMA基带系统的实现

MIMO技术、多载波技术与链路自适应技术是未来移动通信系统最值得关注的几种物理层技术。MIMO技术在提高系统频谱利用率方面性能卓越,多载波CDMA技术则能有效地对抗频率选择性衰落,将MIMO技术与MC-CDMA方案相结合,构成空域复用MC-CDMA系统,将在很大程度上提高系统的性能和容量,更有效地提高信息传输速率,完成基于FPGA的空域复用MIMOMC一CDMA系统的基带信号处理平台的设计与实现的任务[1]。本文采用硬件仿真模型模拟MIMO信道的方法,实现了对系统的联合调试与功能验证,与软件仿真结果进行比较,性能良好。     

Using Distributed Computers to Deterministically Approximate Higher Dimensional Convection Diffusion Equations

A new approach to solving D> 3 spatial dimensional convection-diffusion equation on clusters of workstations is derived by exploiting the stability and scalability of the combination of a generalized D dimensional high-order compact (HOC) implicit finite difference scheme and parallelized GMRES(m). We then consider its application to multifactor Option pricing using the Black–Scholes equation and further show that an isotropic fourth order compact difference scheme is numerically stable and determine conditions under which its coefficient matrix is positive definite. The performance of GMRES(m) on distributed computers is limited by the inter-processor communication required by the matrix-vector multiplication. It is shown that the compact scheme requires approximately half the number of communications as a non-compact difference scheme of the same order of truncation error. As the dimensionality is increased, the ratio of computation that can be overlapped with communication also increases. CPU times and parallel efficiency graphs for single time step approximation of up to a 7D HOC scheme on 16 processors confirm the numerical stability constraint and demonstrate improved parallel scalability over non-compact difference schemes.     

无线传感器网络中一种抗无线局域网干扰的信道分配机制

无线传感器网络(WSN)易受到与其共享信道的无线局域网(Wifi)干扰,造成通信可靠性及吞吐量下降.当具有不同优先级的多个WSN受到Wifi干扰时,如何按优先级分配信道,并兼顾整体通信可靠性及吞吐量是一个重要问题.针对该问题,作者提出了一种抗Wifi干扰的信道分配机制EasiCAP(Channel Allocation for wireless sensor networks with Priority).该机制利用基于干扰强度和活跃比率的干扰特征模型(External Interference Model,EIM)度量WSN中各信道的Wifi干扰;同时,采用以接收端为中心的模型(Internal Interference Model,IIM)度量各WSN之间的干扰.然后,各WSN根据EIM和IIM度量的结果,采用局部化贪婪信道分配算法独立、实时地选择信道,通过保持信道、切换信道及抢占信道操作实现按优先级分配信道,并尽可能降低所有网络所受干扰之和.实际测量和仿真结果表明,EasiCAP可为各WSN提供与其优先级相对应的通信可靠性和吞吐量;而且该机制下的平均通信可靠性及吞吐量也比现有方法高.此外,EasiCAP未带来过大的开销.     

A hybrid TDMA/Random-access scheme for multiple-access communication networks

A hybrid TDMA/Random-Access multiple-access (HTRAMA) scheme is introduced for providing an access-control coordination for a multi-access communication channel. Such a scheme is applicable to a large spectrum of computer communication network applications. Under this hybrid scheme, the system sources are divided into groups. Sources in different groups are allocated disjoint time slots for their transmissions. Sources within a group share their allocated time slots by transmitting according to a tree random-access policy. The number of groups (and their sizes) is dynamically adjusted to properly (and optimally) match the underlying channel traffic characteristics. In this fashion the hybrid scheme dynamically adapts to a random-access structure at lower traffic throughput levels and to a TDMA structure at higher throughput levels. We carry out detailed delay throughput analysis for these hybrid schemes under both limited and unlimited source buffer capacities. The hybrid scheme is demonstrated to yield very good delay-throughput performance curves under wide ranges of network traffic statistical fluctuations and spans.     

Sensor scheduling over a packet-delaying network

We consider sensor scheduling for state estimation of a scalar system over a packet-delaying network. The current measurement data can be sent over a delay-free channel if the sensor uses larger communication energy; the data will be delayed for one time step if the sensor uses less communication energy. We consider a cost function consisting of a weighted average estimation error and a weighted terminal estimation error and explicitly construct optimal power schedules to minimize this cost function subject to communication energy constraint. Simulations are provided to demonstrate the key ideas of the paper.     

Compiler Techniques for Efficient Communications in Circuit Switched Networks for Multiprocessor Systems

In this paper we explore compiler techniques for achieving efficient communications on circuit switching interconnection networks. We propose a compilation framework for identifying communication patterns and compiling these patterns as network configuration directives. This has the potential of providing significant performance benefits when connections can be established in the network prior to the actual communications. The framework includes a flexible and powerful communication pattern representation scheme that captures the property of communication patterns and allows manipulation of these patterns. In this way, communication phases can be identified within the application. Additionally, we extend the classification of static and dynamic communications to include persistent communications. Persistent communications are a subclass of dynamic communications that remain unchanged for large segments of the application execution. An experimental compiler has been developed to implement the framework. This compiler is capable of detecting both static and persistent communications within an application. We show that for the NAS Parallel Benchmarks, 100% of the point-to-point communications can be classified as either static or persistent and 100% of the collectives are either static or persistent with the exception of IS. Simulation-based performance analysis demonstrates the benefit of using our compiler techniques for achieving efficient communications in multiprocessor systems.     

Zynq-7000平台上的MIMO系统的时频同步

在目前的通信技术当中,MIMO技术优势明显.MIMO通信系统使用多个发射天线和接收天线,充分利用空间资源,在不增加频谱资源和天线发射功率的前提下改善通信质量、提升信道容量.然而在MIMO通信系统中,时频同步问题将会极大影响通信系统的性能.Zynq-7000是新一代可编程片上系统,包含了ARM处理器以及FPGA,为开发者提供了良好的软件无线电开发环境.本文将于Zynq-7000平台搭建MIMO通信系统,提出一种时频同步算法,以及实现流程.同时系统测试表明,该算法有效提升了系统性能.