With the explosive growth of wireless multimedia applications over the wireless Internet in recent years, the demand for radio spectral resources has increased significantly. In order to meet the quality of service, delay, and large bandwidth requirements, various techniques such as source and channel coding, distributed streaming, multicast etc. have been considered. In this paper, we propose a technique for distributed multimedia transmission over the secondary user network, which makes use of opportunistic spectrum access with the help of cognitive radios. We use digital fountain codes to distribute the multimedia content over unused spectrum and also to compensate for the loss incurred due to primary user interference. Primary user traffic is modelled as a Poisson process. We develop the techniques to select appropriate channels and study the trade-offs between link reliability, spectral efficiency and coding overhead. Simulation results are presented for the secondary spectrum access model.

Common packet channel (CPCH) access is an efficient approach to support packet data transmissions in a wideband code division multiple access (W-CDMA) system. Rather than using a continuous-time analysis approach, this paper presents a discrete-time analysis of the CPCH access scheme to fully characterize the complete CPCH operation process. Previous studies using the continuous-time analysis only models a portion of the CPCH process. We assume that a packet arrival process is Poisson distributed and the service time of each packet is geometrically distributed. The study focuses on examining the number of packet arrivals in each CPCH access slot. Performance is evaluated in terms of normalized throughput and it is observed that CPCH performs better when packet mean service time is larger. The performance results are also compared with previous studies using continuous-time analyses

An efficient channel allocation policy that prioritizes handoffs is an indispensable ingredient in future cellular networks in order to support multimedia traffic while ensuring quality of service requirements (QoS). In this paper we study the application of a reinforcement-learning algorithm to develop an alternative channel allocation scheme in mobile cellular networks that supports multiple heterogeneous traffic classes. The proposed scheme prioritizes handoff call requests over new calls and provides differentiated services for different traffic classes with diverse characteristics and quality of service requirements. Furthermore, it is asymptotically optimal, computationally inexpensive, model-free, and can adapt to changing traffic conditions. Simulations are provided to compare the effectiveness of the proposed algorithm with other known resource-sharing policies such as complete sharing and reservation policies

A reduced-rate retransmission (RRR) scheme is proposed for improving the throughput performance of spread-spectrum packet radio networks. The scheme takes advantages of the available multi-rate scalable source coding techniques. It assumes that several versions of a data packet with different sizes (number of information bits) are available. The transmission of a packet starts from its full-size version. If the full-size version is not correctly received, its half-size version is used in the retransmission. If further retransmissions are needed, the quarter-size version and so on are used. The shrunk packets are transmitted either in a minislot if the processing gain is kept the same, or occupying a slot duration by increasing the processing gain proportionally. In both cases, the effective signal to interference ratio for a packet is increased. As a result, the system throughput is improved. Theoretical and numerical results are provided in this paper which illustrate the throughput improvement. Another advantage of the proposed RRR scheme is that the packet-size reduction provides finer granules for link adaptation. Therefore, it is especially suitable for multimedia applications for which codes of variable rate for the source data are available and which can tolerate gracefully degraded quality of service. The performance of the proposed scheme in fading channels is also addressed.

The slotted ALOHA (S-ALOHA) scheme in Nakagami fading channel with the presence of in-cell and cochannel-cell interference is studied. The cases of asynchronous cochannel-cells are especially considered. The analysis is based on the signal capture model and gives closed-form expressions for the system throughput. Additional channel conditions and system parameters are examined in the study, including a minimal signal power requirement, lognormal shadowing and the cellular cluster size.

In this paper we propose an alternative approach for finding a near-optimal call admission policy that prioritizes handoff requests over new calls in a generic mobile cellular network. The performance measure is formed as a weighted linear function of new call and handoff call blocking probabilities. The problem is formulated as a semi-Markov decision process with average cost criterion. Then, a simulation-based learning algorithm based on temporal difference methodology is used to determine a near-optimal control policy online from interaction with the network without a priori knowledge or estimation of the dynamical model of the network. Simulations are provided to compare the effectiveness of the proposed algorithm with two well-known resource-sharing policies: complete sharing and reservation policies (guard threshold). The learning algorithm adapts to traffic variations and this paper shows that it also gives very close blocking probabilities to the optimal guard threshold approach.

This paper studies the performance of negative acknowledgement- (NAK-) based ARQ which is a conventional selective repeat ARQ except sending an acknowledgment message only when a transmission error occurs. A Markovian error channel model is considered for both forward and feedback channels. The throughput and mean extra delay in terms of RTD (round trip delay) are obtained. The result shows that the throughput of NAK-based ARQ in a noisy feedback environment is as good as that of a selective repeat ARQ scheme with a perfect feedback channel.

In the next generation cellular mobile multimedia networks, a resource allocation policy, which prioritizes handoff requests over new calls while making efficient use of the network resources, will be an essential component for successful operation. In this paper we develop a new handoff prioritized scheme which adapts the allocation policy according to the current traffic conditions. The goal is to minimize the new call blocking while keeping the handoff failures close to a targeted objective. This problem is formulated as a constrained semi-Markov decision process (SMDP) with average cost criterion. A simulation-based learning algorithm is developed to determine a control policy from direct interaction with the network without a priori knowledge of the network dynamics or traffic. Extensive simulations test the effectiveness of the algorithm under a variety of traffic conditions. Comparisons with other resource allocation policies, such as complete sharing and channel reservation, are presented.

This work gives an analytical performance measure of the common packet channel (CPCH) in 3rd Generation Partnership Project (3GPP) wideband code division multiple access (W-CDMA) systems. The CPCH procedure of the channel assignment (CA) mode is modeled as an Erlang loss network, and a technique for analyzing Erlang loss networks is applied to get the expression of the system throughput and delay. The theoretical results are verified with computer simulations.

The authors evaluate the performance of both the fixed buffer allocation (FBA) and the adaptive buffer allocation (ABA) schemes, in which the network nodes are allowed to offer less than the requested buffer size. The performance measures of interest are the blocking probability, file transfer delay, and the adaptation speed for ABA for a given buffer size and the offered load. The authors develop and analyze a quasi-birth-death model of the ABA scheme (with exponential file lengths and negligible delay in carrying out reservation and cancellation procedures). In particular, they develop a recursive computational scheme exploiting the structure of the underlying model. This is supplemented by a first-passage time analysis to evaluate the transient behavior of the control strategy. The authors use both analytic and simulation methods. The results demonstrate that the ABA schemes provide significant advantages over the FBA scheme if the parameters are appropriately chosen. They also provide guidelines on the choice of these parameters.>

Stochastic analyses of the Survivability of communication networks often include a simplifying assumption that failures of, or damages to, various components of the network are statistically independent. This assumption can be quite unrealistic and can lead one to conclusions that are grossly in error. Survivability analyses and syntheses of robust networks should incorporate dependencies introduced by single events that affect large geographical areas. In this paper, we construct a stochastic damage model, analyze it, and apply the results to the survivability analysis of some simple network topologies. We demonstrate how the results can differ significantly from those obtained when independence of damage is assumed. The damage model consists of a Poisson ensemble of events (damage centers) on the plane, of given intensity (level of attack), and a network resource is damaged, and hence dysfunctional, if it lies within a radius ρ (damage radius) of some damage-causing event. Statistical properties of the damage process are obtained (e.g., the covariance function, mean and variance of the damage extent on a line resulting from the Poisson ensemble) and used to evaluate dependence effects. The damage process on a line is shown to be an alternating renewal process corresponding to the busy/idle process of an appropriately definedM/G/\inftyqueue, and standardM/G//inftyand Type-II counter results can thus be exploited to obtain some desired quantities.

We study the performance of a statistical multiplexer whose inputs consist of a superposition of packetized voice sources and data. The performance analysis predicts voice packet delay distributions, which usually have a stringent requirement, as well as data packet delay distributions. The superposition is approximated by a correlated Markov modulated Poisson process (MMPP), which is chosen such that several of its statistical characteristics identically match those of the superposition. Matrix analytic methods are then used to evaluate system performance measures. In particular, we obtain moments of voice and data delay distributions and queue length distributions. We also obtain Laplace-Stieitjes transforms of the voice and data packet delay distributions, which are numerically inverted to evaluate tails of delay distributions. It is shown how the matrix analytic methodology can incorporate practical system considerations such as finite buffers and a class of overload control mechanisms discussed in the literature. Comparisons with simulation show the methods to be accurate. The numerical results for the tails of the voice packet delay distribution show the dramatic effect of traffic variability and correlations on performance.

Abstract Survivability of a node vulnerable network is often assessed in terms of the (node) connectivity of the graph that represents the logical topology of the network. When the damage causing events have widespread impact then, owing to the physical layout of the network facilities, each event can destroy several nodes. As a survivability measure, therefore, we define the generalized connectivity as the minimum number of events (rather than the minimum number of node removals) required to disconnect the network. To model the possible effects of damage causing events, we introduce the notion of a dependence graph on the nodes of the network and a set of admissible cliques in this graph. Nodes that are nonadjacent in the dependence graph are independent, i. e., they cannot be damaged by the same event, and each event destroys an admissible clique of nodes. We present techniques for calculating or bounding the generalized connectivity of given network graphs, and for synthesizing minimum link networks with prescribed generalized connectivity.

In a Variety of overloaded queueing systems (e.g., an overloaded call processing system), long delays can result either in poor service given to the customer or in customers, unknown to the system, turning "bad." For example, in switching systems, long dial tone delays can result in customers initiating dialing before receiving dial tone. In this case the system will not receive all the digits and an unsuccessful call results. This can lead to the system expending real time on unsuccessful services and, therefore, reduces the effective throughput. Thus, there is a need for control Schemes which reduce the load offered to the processor by selectively refusing service to some customers in such a way as to keep delays, for those customers which are selected for service, small. This fact has been recognized and has led to improved strategies for local switches. In this paper we analyze and compare the performance of various queueing and service disciplines for anM/M/1queue. We consider LIFO and FIFO Schemes with customer rejection mechanisms corresponding to pushing out or timing out older customers in queue. Delay distributions for served customers are obtained and comparisons based upon throughput-delay tradeoffs are presented. For the situation where Customers can turn "bad" at a random time after their arrival, we compare the throughput of good customers. The results presented are a mixture of classical results, which are briefly stated, and new results which are developed in more detail. The numerical results show a dramatic effect of the queueing and Service disciplines on the overload performance and a strong dependence of the throughput of successful services on the mechanism for customers turning "bad." Although results are obtained for a single server queue, they can be used to approximately analyze overload control schemes which control access to distributed systems.

Abstract This paper contains the results of an exploratory study aimed at developing a model which could form the basis of a comprehensive analysis of the Air Traffic Control system. This model could be used to evaluate the effects of proposed changes in the system. The results will be presented in three parts. Part I is intended to provide an overview of the results as well as a detailed description of a traffic flow model which computes the means and variances of delays experienced by individual aircraft. Since this model requires as an input a statistical description of the arrival and departure service processes, Part II describes a model which relates these processes to more basic quantities (e.g., aircraft mix, runway configuration). Since the models which are developed represent a physical system, the question of validation arises and is also discussed in Part II. Part III of the paper considers the question of designing a (real‐time) flow control system. It is formulated as a problem of minimizing a measure of system delay subject to constraints on the allowable departure and arrival times. Illustrative results are included through‐out the paper.

Abstract This is the third and final part of a study of the analysis and control of the flow of air traffic. Part I developed a traffic flow model to compute the means and variances of delays experienced by individual aircraft. Part II was concerned with the arrival and departure processes, and with the question of model validation. In this part, we consider an approach to the problem of designing a (real‐time) flow control system. Central to the approach is the problem of minimizing a measure of system delay subject to constraints on the allowable departure and arrival times.