Network coding (NC) and multipacket reception with successive interference cancellation (SIC) have been shown to improve the performance of multihop wireless networks (MWNs). However, previous work emphasized maximization of network throughput without considering quality of service (QoS) requirements, which may lead to high packet delays in the network. The objective of this work is minimization of packet delay in a TDMA-based MWN that is jointly utilizing NC and SIC techniques for a given traffic demand matrix. We assume conflict-free scheduling and allow multipath routing. We formulate a cross-layer optimization that assigns time slots to links in a way that the average packet delay is minimized. The problem formulation results in a difficult mixed integer nonlinear programming (MINLP) that the state-of-art software can only solve for very small-sized networks. For large networks, we develop a heuristic approach that iteratively determines the optimal solution. We present numerical results, which show that the average packet delay and traffic handling capacity of a network, using w/o NC+SIC, NC, SIC and NC+SIC schemes, improves from left to right. The traffic capacity of NC+SIC is double of the w/o NC+SIC. Thus, combined utilization of NC and SIC techniques results in significant performance improvement.

Network coding (NC) has been shown to improve the throughput of multi-hop wireless networks (MWN). Prior work on performance modeling of NC mainly addresses the maximization of throughput. However, these works fail to capture the complete picture since there may be paths in the network for which end-to-end packet delay is prohibitively high. In this paper, we address the problem of delay minimization in MWNs with NC. The objective has been assignment of wireless node capacities in a way that the average packet delay is minimized for a given network topology and the traffic demand matrix. We develop a performance analysis of the system, which models network nodes as M/G/1 queues and takes into account wireless interference. The proposed model is valid both with and without opportunistic listening for any wireless network topology. The model also incorporates network coding-aware routing that routes the flows in a manner that increases coding opportunities. We present numerical results, which show that NC reduces the average packet delay in the network and extends the stable operating region of the network. We also present simulation results, which confirm the accuracy of the analysis.

In vehicular ad hoc networks (VANETs), because all vehicles in range are shown as destination nodes and less time is spent for the medium access process, broadcast communication is considered a highly appropriate technique for the dissemination of safety messages in such networks. However, the lack of request-to-send/clear-to-send handshaking and packet acknowledgment makes the communication more vulnerable to interferences, thus resulting in lower communication reliability. In this paper, we present an analytical model for the performance evaluation of safety message dissemination in vehicular ad hoc networks with two priority classes. In particular, considering the IEEE 802.11 broadcast protocol and using 2-D Markov modeling, we derive the joint distribution of the numbers of low-priority periodic messages, which are in transmission mode and in a backoff process in a highway. Then, the result is used to derive the average dissemination delay of high-priority event-driven messages in the presence of the low-priority traffic in the network. The results are helpful in determining a good tradeoff between network parameters such as vehicles' transmission range, safety traffic generation rate, and medium access control (MAC) parameters to satisfy the required delay bounds for the critical high-priority traffic.

This paper is concerned with optimization of distributed broadband wireless communication (BWC) systems. BWC systems contain a distributed antenna system (DAS) connected to a base station with optical fiber. BWC systems have been proposed as a solution to the power constraint problem in traditional cellular networks. So far, the research on BWC systems have advanced on two separate tracks, design of the system to meet the quality of service requirements (QoS) and optimization of location of the DAS. In this paper, we consider a combined optimization of BWC systems. We consider uplink communications with multiple levels of priority traffic having any renewal arrival and departure processes. We develop an analysis that determines packet delay violation probability for each priority level as a function of the outage probability of the distributed antenna system through the application of results from renewal theory. Then, we determine the optimal locations of the antennas that minimize the antenna outage probability. We also study the trade off between the packet delay violation probability and packet loss probability.

In this paper, we present an analytical study for the performance of message dissemination in vehicular ad hoc networks (VANETs) with two priority classes. It is assumed that the message traffic generated by event-driven safety applications has higher priority compared to the remaining network traffic. First, we derive the distribution of the number of concurrent transmissions of lower priority messages in the system at the steady state, through a birth-death process analysis. The distribution has a simple product form solution. We also derive the percentage of destination node population which cannot receive the message error free due to interference. Subsequently, we determine the average forwarding distance and the number of nodes which receive a high-priority message in the presence of low-priority traffic. Numerical results are provided along with simulation results that confirm the accuracy of the proposed analysis. The distribution of the number of concurrent transmissions is shown to have a bell-shape curve. Results also show that larger transmission ranges do not necessarily improve the per hop safety-message forwarding distance as more nodes may be exposed to interference, especially in networks with higher node densities.

Wireless actuators are small scale devices that can receive/accept instructions and act on their environment. The IP Multimedia Subsystem (IMS) is a key component for 3G networks. It aims at seamless provisioning of multimedia services. Combining actuation capabilities with IMS capabilities will certainly enable novel value added services. This paper proposes an architecture for the integration of wireless actuation with IMS. The cornerstone of the architecture is the actuation control function, a new functional entity that we introduce into the IMS architecture. A proof of concept prototype has also been developed along with an application to demonstrate the potential of such an integration.

In this paper, we study the statistical properties of continuous communication path availability in vehicular ad hoc networks at the steady state. We assume a network of highways with arbitrary topology. The nodes arrive at the network through one of the traffic entry points following a Poisson process and move along a path according to a mobility model. We model the number of clusters in the node population along a path as a Markovian birth-death process. This model enables us to determine the distribution of the number of clusters and continuous communication path availability and unavailability times as functions of mobility and traffic arrival parameters in the path. The numerical results show that the mean path availability duration varies logarithmically with the transmission range. In practice, an adaptive transmission range may be needed to have very high path availability.

This paper develops a stochastic model for data in a wireless sensor network using random field theory. The model captures the space-time behavior of the underlying phenomenon being observed by the network. We then study the size and spatial distribution of the regions of the network that sense statistically extreme values using the theory of extreme excursion regions. Analytical expressions are found for the average size of the data load in a variety of scenarios. These expressions compliment many existing works in the literature that describe algorithms to reduce the data load but cannot evaluate the size and spatial distribution of this load except through simulation. We show that if only the statistically extreme data is transmitted in the network, then the data load can be significantly reduced. Analytical expressions for the total data load are confirmed with simulation. Finally, a simple performance model of a WSN is developed based on a collection of asynchronous M/M/1 servers working in parallel. We derive several performance measures from this performance model. The presented results will be useful in the design of large scale sensor networks.

The nodes of wireless sensor networks (WSNs) have the dual function of gathering information and relaying it to a central collection point, the sink. For the latter function the key is connectivity involving paths over which data is passed from node to node to the sink. We derive connectivity, as expressed by the probability that a node lies on a path to the sink, as a function of the probability that adjacent cells in a grid are connected. This result is then applied to the typical scenario where nodes are randomly scattered throughout the area being monitored. Useful upper and lower bounds for the probability of adjacent cells being connected are derived as a function of the node density in a cell. For battery powered nodes, lifetime is an important factor. The effect of the demise of nodes on the nodal density and, in turn, on network connectivity is quantified.

In this paper, we study the statistical properties of the connectivity of VANETs with user mobility at the steady state. We assume a network of highways with arbitrary topology. The nodes arrive at the network through one of the traffic entry points following a Poisson process and move within the network according to a mobility model. The path of a node within the network is determined through a routing matrix. The system is modeled as a BCMP network of queues. We derive the probability distribution of the node population size within the network. Then, we determine the probability distribution of the cluster size seen by a new node arriving along a path. The presented numericals results illustrate the effect of mobility on connectivity. The results of the paper may be used to study the routing algorithms, throughput or delay in VANETs.

In this paper, we study the statistical properties of the connectivity of vehicular ad hoc networks (VANETs) with user mobility at the steady state. It is assumed that the nodes travel along a single dimensional strip with finite length. The nodes arrive at the service strip through one of the traffic entry points following a Poisson process and move along the strip in the same direction according to a user mobility model until they reach their exit point. The service strip allows the users with different speeds to pass each other. The nodes, which are within the service strip, are able to participate in communications. We derive the probability distribution of the user population size within the service strip and node's location distribution. Then, we determine the mean cluster size, fraction of nodes within the cluster and probability that nodes will form a single cluster. This work shows significance of mobility on the connectivity of ad hoc networks. The results of the paper may be used to avoid traffic congestion in the highways.

In this work, we consider modeling of a wireless sensor network with a TDMA media access protocol with slot reuse. It is assumed that the nodes have two modes of operation, active and sleep modes. We model the sensor network as a Jackson network with node breakdowns. We determine the joint distribution of the queue lengths in the sensor network. From this result, we derive the probability distribution of the number of active nodes and blocking probability of node activation. Then, we present the mean packet delay, average down period of a node as well as the network throughput. Finally, we discuss how the derived results may be used in the design of sensor networks

In this paper, we study the connectivity of an ad hoc network with a dynamic user population. We assume that the nodes arrive at the service area according to a Poisson process and, then travel according to a user mobility model. The nodes, which have not departed the service area, are able to participate in communications. The location of the nodes and the size of the user population within the service area are constantly changing. We study connectivity of this user population at the steady-state. We derive the distribution of the size of user population within the service area, node's location distribution and the distribution of the distance between the two nodes. Then, we determine the mean cluster size, fraction of nodes within the cluster, probability that nodes will form a single cluster and average of the minimum number of hops that it takes for two nodes to communicate. This work shows significance of mobility on the connectivity of ad hoc networks

This paper studies a random packet selection policy for multicast switching. An input packet generates a fixed number of primary copies plus a random number of secondary copies. Assuming a constant number of contending packets during a slot, the system is modeled as a discrete time birth process. A difference equation describing the dynamics of this process is derived, the solution of which gives a closed form expression for the distribution of the number of packets chosen. Then this result is extended to the steady state distribution through a Markov chain analysis. It is shown that the old packets have larger fanout than the fresh packets and the copy distribution of the mixed packets is determined. The packet and copy throughput taking into account the old packets have been obtained. We determined the mean packet delay as well as an upperbound for packet loss probabilities for finite buffer sizes. The asymptotic distribution of the number of packets is also given for large switch sizes under saturation by applying results from the renewal theory. Finally, simulations are done to determine the performance of the switch under mixed (unicast plus multicast) traffic.

The performance analysis of an input access scheme in a high-speed packet switch for broadband ISDN is presented. In this switch, each input port maintains a separate queue for each of the outputs, thus n/sup 2/ input queues in an (n/spl times/n) switch. Using synchronous operation, at most one packet per input and output will be transferred in any slot. We derive lower and upper bounds for the throughput which show close to optimal performance. The bounds are very tight and approach to unity for switch sizes on the order of a hundred under any traffic load, which is a significant result by itself. Then the mean packet delay is derived and its variance is bounded. A neural network implementation of this input access scheme is given. The energy function of the network, its optimized parameters and the connection matrix are determined. Simulation results of the neural network fall between the theoretical throughput bounds.>

A comparison of the performance of two input access mechanisms for multicast switching is presented. The first of these-a cyclic priority input access method-is a derivative of the ring token reservation method which eliminates the unfairness of the ordinary ring token reservation. It has the advantage of being relatively simple and easy to implement. A second approach employs a neural network to resolve output port conflict. While more difficult to implement, it has a delay-throughput performance advantage over the cyclic priority approach. The primary performance measurements are the switch throughput and the packet delay. A key assumption is that all copies of the same packet must be switched in the same slot.>

A random packet selection policy for multicast switching is studied. An input packet generates a fixed number of primary copies plus a random number of secondary copies. Assuming a constant number of contending packets during a slot, the system is modeled as a discrete-time birth process. A difference equation describing the dynamics of this process is derived, the solution of which gives the distribution of the number of packets chosen. This result is extended to the steady-state distribution through an embedded Markov chain analysis. It is shown that the old packets have a larger number of copies than the fresh packets, and the copy distribution is derived. The packet and copy throughputs taking into account the old packets have been determined. The asymptotic distribution of the number of packets chosen is obtained for large switch sizes under saturation by applying results from renewal theory.>

An analysis of the performance, in terms of average message delay, is presented for a system of interconnected ring networks. The system is hierarchical, with local rings served by a high-speed backbone ring through gateway queues. In both the local and the backbone rings, the access technique employed is token passing. Service disciplines, with and without priority, have been studied. In the former, priority is given to inter-ring traffic over local traffic. The study makes use of certain results on average delay in systems where the customer initiating a busy period receives special service for the M/G/1 queue with nonpreemptive priority and for the G/G/1 queue. The analysis, which involved several approximations, was verified by simulation.>

The application of neural networks to the optimum routing problem in packet-switched computer networks, where the goal is to minimize the network-wide average time delay, is addressed. Under appropriate assumptions, the optimum routing algorithm relies heavily on shortest path computations that have to be carried out in real time. For this purpose an efficient neural network shortest path algorithm that is an improved version of previously suggested Hopfield models is proposed. The general principles involved in the design of the proposed neural network are discussed in detail. Its computational power is demonstrated through computer simulations. One of the main features of the proposed model is that it will enable the routing algorithm to be implemented in real time and also to be adaptive to changes in link costs and network topology.

The performance analysis of an input access scheme in a high-speed packet switch for broadband ISDN is presented. In this switch, each input maintains a separate queue for each of the outputs, thus there are n/sup 2/ input queues in a (n*n) switch. Using synchronous operation, at most one packet per input and output will be transferred in any slot. The choice of the packets is done in a manner to maximize the throughput of the switch. Comparison of simulations with analytically derived upper and lower bounds show close to optimal throughput. The mean packet delay is also derived and its variance is bounded. This input access scheme may be implemented using neural networks.>

A study of the performance of a cyclic-priority input access mechanism for a multicast switch is carried out. The method is a derivative of the ring token reservation method which eliminates the unfairness of the ordinary ring token reservation. It has the further advantage of being simple and easy to implement. The primary performance measurements are the switch throughput and the packet delay. A key assumption is that all copies of the same packet must be switched in the same slot.>

A LAN or MAN (local or metropolitan area network) using token passing to allow stations to access the transmission medium is studied. Ibe and Cheng (1989) recently presented an approximate derivation of message delays for an asymmetric single-service token passing with only one type of message. In the present work, this analysis is extended to an operation with nonpreemptive priority queuing. The number of message priority levels and the walktime vary from one station to another. Moreover, the assumed Poisson message arrival process and the message transmission time vary, not only from one station to another, but also from one class to another. The performance, as measured by the mean delay for any message class at any station, is derived. The simulation results show excellent agreement with the analytical results, even under heavy loading. The results confirm earlier findings that the performance at a station is influenced by its position relative to heavily loaded stations.>

The performance of a multicast switch, a space division switch in which a packet at an input port is routed to a subset of the output ports, is discussed. The delay under the assumption of input port buffering is determined. The system is modeled as an independent set of M/G/1 queues. A key assumption in the analysis is that output port contention is settled by random selection among the contending input ports. In order to justify this as well as the other assumptions, a Monte-Carlo simulation of the system is devised. Numerical results from the analysis and simulation of the system are presented.>

Two forms of fast circuit switching are modeled and studied through mathematical analysis and Monte Carlo simulation. The two examples described use the switching technique in an optical-fiber-based local area network with a star topology. The technique is compatible with time-division multiplexing techniques that are used for a range of traffic classes. Further, the technique trades transmission capacity for processing power, which is the critical limitation of the system. By means of a certain independence assumption, the first form of fast circuit switching is modeled as an M/G/1 queue. The results of the analysis show excellent agreement with simulation. The general result is that there is good system throughput, despite simplicity of processing. The second form, in which rather than first-come first-served the discipline is to search for a message whose destination queue is free, is studied by means of simulation alone. The results indicate an improved performance with a modest increase in processing power.>