κ-信道模型的构作及其在多路存取信道中的应用

一个κ-信道是多路存取信道的推广,利用一个BIB设计的性质构作了κ-信道(Channel)模型并介绍了这一模型在多路存取信道中用户数据传输、冲突消解方面的应用.     

群测模型在多路存取信道中竞争消解方面的应用

非适应性组合群测(group testing)是组合数学的一个分支,它有着广泛的应用.在一个有限集[n]上构作了一个群测模型,并利用这个群测模型介绍了它在多路存取信道中竞争消解方面的应用.     

有限集上可用于多路存取信道的一般叠加码

一般二元叠加码(p,r,d)-superimposed codes(SC)是Kautz和Singleton码的推广,在有限集[n]上构作了(P,r,d)-SC码,并介绍了它在多路存取信道竞争消解方面的应用.     

一般多路通讯网络系统信息传输的基本定理

1.引言 多路通讯问题是Shannon信息论在近几年内获得迅速发展的一个重要分支,它以快速通讯系统网络化,卫星通讯网与广播电视卫星网为背景而建立的信息传输模型,[1]文综合介绍了1962—1977年内有关工作的进展情况,从这些结果可以看出对各种多路通讯的典型系统已在无记忆条件下得到很大程度上的解决,近两年内许多工作(如[5—10]文)针对上述多路通讯中更复杂的模型进行研究,并且得到了许多有意义的结果,本文试图用一般网络系统的观点综述各种多路系统的特点,获得了具有普遍意义的信息传输定理,这     

反馈重传差错控制系统中检错码性能的分析

在数字通信差错控制系统的设计和使用中,要求对检错码的性能作一定的、明确的分析比较。我们对常用的三个主要检错码的性能作了初步分析比较。 我们假定通信方式是连续半双工的,信道分为主信道和反馈信道,图一是简单的方框图。信源发出的信息经过编码后送入主信道传输,主信道输出的码组首先进入检错器,若检测不出错误就送入译码器,译出的信息送信宿。但若检错器检测出码组有错,就不把此码组送译码器,而且由反馈信道要求重发。发送器接收到要求重发信号时,在发完正在发     

第二类窃密信道中的组合数学方法

当信息在第二类窃密信道中传输时,线性码的广义汉明重量谱完全描述的它在该信道中的密码学特征.计算一个线性码的广义汉明重量谱是一个基本问题,首先提出了线性码的“最简基”的概念.在此基础上给出了一般线性码子码的几种计数公式,并给出了它们之间等价性的证明.     

低压电力线信道衰减特性分析及建模仿真

对低压电力线信道的衰减特性进行了研究,采用多径传输模型分析多径延时与多径传播造成的衰减的原因,依据均匀传输线理论分析了线路损耗造成的衰减的原因,并推导出电力线衰减的传输函数.根据传输函数建立电力线网络多径传输模型,并进行MATLAB仿真,得到的仿真曲线与实测曲线大体一致.     

ATIS和道路收费下的混合随机用户均衡的效率损失

在ATIS作用下的交通网络中,用户在交通信息的接受程度上是异质的;考虑到装有ATIS的用户并不总是遵循ATIS的建议,因此,引入信息遵从率这一参数,将所有用户分为三类:安装并遵从信息、安装但不遵从信息和不安装的用户;均按照随机用户均衡的方式进行择路,但对出行时间有不同的感知。同时考虑存在道路收费的情形下,用户在时间价值上是异质的。综合考虑交通信息与道路收费的影响,基于用户两方面的异质性,对其进行合理分类,构建了多用户多准则的混合随机均衡模型及其等价的变分不等式;当收费不作为系统总成本的一部分时,建立了时间准则与费用准则下的系统最优模型;在此基础之上,分别研究了两种准则下混合均衡相对于系统最优的效率损失,给出了效率损失上界,并进一步分析了效率损失上界与各参数间的关系;交通管理者可以从道路收费策略的实施、信息诱导系统的完善等角度进行路网的改造和优化设计。     

衰减信道下的决策融合问题

本文针对国际上近几年兴起的研究热点——无线传感器网络在信道衰减下的决策融合问题进行探讨。分析了已有传感器决策融合问题算法的结构,在已知信道传输错误概率的条件下,将信道无传输错误的分析方法推广到信道衰减的情况,对传输错误和融合律的关系进行了深入分析。对给定融合律的网络决策融合问题,获得了最优容错传感器观测量化器的必要条件并设计了迭代算法。在没有增加问题的计算复杂度的情况下,得到了最优观测量化器。与国际上现有结果不同,新结果不要求传感器决策条件独立,也不要求各传感器与融合中心之间的信道相互独立,具有更加广泛的使用范围。     

关于一般多路通讯网络系统信道容量区域的正、反编码定理

在[1]中我们得到了一般多路通讯网络系统的编码基本定理与若干信道容量的正、反编码定理,从而对多路通讯网络系统编码的主要特征有所了解。但在[1]中对信道容量的正、反编码定理还没有得到完全统一,因此本文在[1]文的基础上,参考了[3]的若干思想,解决了无记忆信道对一般型网络信道容量的正、反编码定理,从而使这个问     

A Stochastic Game Analysis of the Binary Exponential Backoff Algorithm with Multi-Power Diversity and Transmission Cost

In this paper, we present a game analysis of the Binary Exponential Backoff (BEB), a popular bandwidth allocation mechanism used by a large number of distributed wireless technologies. A Markov chain analysis is used to obtain equilibrium retransmission probabilities and throughput. Numerical results show that when the arrival probability increases, the behavior of mobile stations MSs become more and more aggressive resulting in a global deterioration of the system throughput. We then consider a non-cooperative game framework to study the operation and evaluate the performance of the BEB algorithm when a group of MSs competing with each other to gain access to the wireless channel. We focus our attention to the case when an MS acts selfishly by attempting to gain access to the channel using a higher retransmission probability as a means to increase its own throughput. As a means to improve the system performance, we further explore the use of two transmission mechanisms and policies. First, we introduce the use of multiple power levels (MPLs) for the data transmission. The use of multiple power levels results on a capture effect allowing the receiver to properly decode the message even in the presence of a collision. Under the proposed scheme, named MPL-BEB, the effect of the aggressive behavior, higher transmission probabilities, is diminished since the power level is chosen randomly and independently by each and every station. Second, we introduce a disutility policy for power consumption. The resulting mechanism, named MPL-BEB with costs, is of prime interest in wireless networks composed of battery-powered nodes. Under this scheme aggressive behavior is discouraged since each retransmission translates into the depletion of the energy stored in the battery. Via price of anarchy, our results identify a behavior similar to the well-know prisoner’s dilemma. A non-efficiency of Nash equilibrium is observed for all schemes (BEB, MPL-BEB, MPL-BEB with costs) under heavy traffic with a notable outperformance of MPL-BEB with costs over both MPL-BEB and BEB.     

Throughput-oriented channel assignment for opportunistic spectrum access networks

Cognitive radio (CR) is a revolutionary technology in wireless communications that enhances spectrum utilization by allowing opportunistic and dynamic spectrum access. One of the key challenges in this domain is how CR users cooperate to dynamically access the available spectrum opportunities in order to maximize the overall perceived throughput. In this paper, we consider the coordinated spectrum access problem in a multi-user single-transceiver CR network (CRN), where each CR user is equipped with only one half-duplex transceiver. We first formulate the dynamic spectrum access as a rate/power control and channel assignment optimization problem. Our objective is to maximize the sum-rate achieved by all contending CR users over all available spectrum opportunities under interference and hardware constraints. We first show that this problem can be formulated as a mixed integer nonlinear programming (MINLP) problem that is NP-hard, in general. By exploiting the fact that actual communication systems have a finite number of available channels, each with a given maximum transmission power, we transfer this MINLP into a binary linear programming problem (BLP). Due to its integrality nature, this BLP is expected to be NP-hard. However, we show that its constraint matrix satisfies the total unimodularity property, and hence our problem can be optimally solved in polynomial time using linear programming (LP). To execute the optimal assignment in a distributed manner, we then present a distributed CSMA/CA-based random access mechanism for CRNs. We compare the performance of our proposed mechanism with reference CSMA/CA channel access mechanisms designed for CRNs. Simulation results show that our proposed mechanism significantly improves the overall network throughput and preserves fairness.     

Optimal receiver scheduling algorithms for a multicast problem

This paper studies a multicast problem arising in wavelength division multiplexing single-hop lightwave networks, as well as in Video-on-Demand systems. In this problem, the same message of duration Δ has to be transmitted to a set of n receivers which are not all available simultaneously. The receivers can be partitioned into subsets, each served by a different transmission, with the objective of minimizing their overall waiting cost. When there is a single data channel available for transmission, a dynamic programming algorithm is devised which finds an optimal solution in O(nlogn+min{n²,nΔ²}) time, improving over a previously known O(n³) time algorithm. When multiple data channels are available for transmission, an optimal O(n) time algorithm is proposed which finds an optimal solution if the message has constant transmission duration, whereas an NP-completeness proof is given if the message has arbitrary transmission duration.     

A statistical study of time-sharing systems

Time-sharing systems are discussed in which competing users can achieve access only on a chance basis, depending on the availability of a system channel at the time of attempted access. A simple statistical method is presented for evaluating the relative merits of different time-sharing configurations. Calculated results for a variety of user demand levels in a representative system are shown in graphic and tabular form.     

Dynamic power control in a fading downlink channel subject to an energy constraint

A central controller chooses a state-dependent transmission rate for each user in a fading, downlink channel by varying transmission power over time. For each user, the state of the channel evolves over time according to an exogenous continuous-time Markov chain (CTMC), which affects the quality of transmission. The traffic for each user, arriving at the central controller, is modeled as a finite-buffer Markovian queue with adjustable service rates. That is, for each user data packets arrive to the central controller according to a Poisson process and packet size is exponentially distributed; an arriving packet is dropped if the associated buffer is full, which results in degradation of quality of service. The controller forwards (downlink) the arriving packets to the corresponding user according to an optimally chosen transmission rate from a fixed set A _i of available values for each user i, depending on the backlog in the system and the channel state of all users. The objective is to maximize quality of service subject to an upper bound on the long-run average power consumption. We show that the optimal transmission rate for each user is solely a function of his own packet queue length and channel state; the dependence among users is captured through a penalty rate. Further, we explicitly characterize the optimal transmission rate for each user. This project is partially supported by Motorola grant # 0970-350-AF24. The authors thank Phil Fleming,Randy Berry and Achal Bassamboo for helpful comments.     

Design of Self-Healing Key Distribution Schemes

A self-healing key distribution scheme enables dynamic groups of users of an unreliable network to establish group keys for secure communication. In such a scheme, a group manager, at the beginning of each session, in order to provide a key to each member of the group, sends packets over a broadcast channel. Every user, belonging to the group, computes the group key by using the packets and some private information. The group manager can start multiple sessions during a certain time-interval, by adding/removing users to/from the initial group. The main property of the scheme is that, if during a certain session some broadcasted packet gets lost, then users are still capable of recovering the group key for that session simply by using the packets they have received during a previous session and the packets they will receive at the beginning of a subsequent one, without requesting additional transmission from the group manager. Indeed, the only requirement that must be satisfied, in order for the user to recover the lost keys, is membership in the group both before and after the sessions in which the broadcast messages containing the keys are sent. This novel and appealing approach to key distribution is quite suitable in certain military applications and in several Internet-related settings, where high security requirements need to be satisfied. In this paper we continue the study of self-healing key distribution schemes, introduced by Staddon et al. [37]. We analyze some existing constructions: we show an attack that can be applied to one of these constructions, in order to recover session keys, and two problems in another construction. Then, we present a new mechanism for implementing the self-healing approach, and we present an efficient construction which is optimal in terms of user memory storage. Finally, we extend the self-healing approach to key distribution, and we present a scheme which enables a user to recover from a single broadcast message all keys associated with sessions in which he is member of the communication group.     

Mean delay analysis for a message priority-based polling scheme

We consider a multi-access communication channel such as a centrally-controlled polling system, a distributed token-based ring, or a bus network. A message priority-based polling procedure is used to control the access to the channel. This procedure requires the server to have no advance information concerning the number of messages resident at a station prior to its visit to the station. Messages arriving at each station belong to one of two priority classes: class-1 (high priority) and class-2 (low priority). Class-1 messages are served under an exhaustive service discipline, while class-2 messages are served under a limited service discipline. Class-1 messages have non-preemptive priority over class-2 messages resident at the same station. Using a fully symmetric system model, an exact expression for the sum of the mean waiting times of class-1 and class-2 messages is first derived. Upper and lower bounds for the mean message waiting times for each individual message class are then obtained.This work was supported by NFS Grant No. NCR-8914690, Pacific-Bell and MICRO Grant No. 90-135 and US West Contract No. D890701.     

Radio resource management for the UMTS enhanced uplink in presence of QoS radio bearers

The next step in the evolution of UMTS is the Enhanced Uplink or high speed uplink packet access (HSUPA), which is designed for the efficient transport of packet switched data. We propose an analytic modeling approach for the performance evaluation of the UMTS uplink with best-effort users over the enhanced uplink and QoS-users over dedicated channels. The model considers two different scheduling disciplines for the enhanced uplink: parallel scheduling and one-by-one scheduling. Resource Management in such a system has to consider the requirements of the dedicated channel users and the enhanced uplink users on the shared resource, i.e. the cell load. We evaluate the impact of two resource management strategies, one with preemption for dedicated channels and one without, on key QoS-indicators like blocking and dropping probabilities as well as user and cell throughput.     

On the flow-level stability of data networks without congestion control: the case of linear networks and upstream trees

In this paper, flow models of networks without congestion control are considered. Users generate data transfers according to some Poisson processes and transmit corresponding packet at a fixed rate equal to their access rate until the entire document is received at the destination; some erasure codes are used to make the transmission robust to packet losses. We study the stability of the stochastic process representing the number of active flows in two particular cases: linear networks and upstream trees. For the case of linear networks, we notably use fluid limits and an interesting phenomenon of “time scale separation” occurs. Bounds on the stability region of linear networks are given. For the case of upstream trees, underlying monotonic properties are used. Finally, the asymptotic stability of those processes is analyzed when the access rate of the users decreases to 0. An appropriate scaling is introduced and used to prove that the stability region of those networks is asymptotically maximized.