Demetrios Kazakos

Multi-threshold bandwidth reservation scheme of an integrated voice/data wireless network

Due to the limited nature of the bandwidth of wireless links, it is essential to design wireless mobile networks that furnish effective and dynamic bandwidth allocation policies which not only ensure that the system guarantee potentially different QoS requirements and provide the necessary service differentiation from diverse applications, but also simultaneously and fully utilize the scarce wireless bandwidth available. To achieve this goal, we propose a generalized analytical model to investigate the performance of an integrated voice/data wireless mobile network in terms of various performance metrics which include, but are not limited to, voice-call blocking probability, forced termination probability, total channel utilization, and total carried traffic. A complete sharing system with multiple thresholds based on the guard channel policy is proposed and then analyzed using a two-dimensional Markov process.

Editorial: quality of service in mobile ad hoc networks

Mobile ad hoc networking is a challenging task due to thelack of resources residing in the network as well as the fre-quentchangesinnetworktopology.Althoughmuchresearchhas been directed to supporting quality of service (QoS) inthe Internet and traditional wireless networks, present re-sults are not suitable for mobile ad hoc network (MANET).QoS support for mobile ad hoc networks remains an openproblem, drawing interest from both academia and indus-try under military and commercial sponsorship. MANETshave certain unique characteristics that pose several diffi-culties in provisioning QoS, such as dynamically varyingnetwork topology, lack of precise state information, lack ofcentral control, error-prone shared radio channels, limitedresource availability, hidden terminal problems, and inse-cure media, and little consensus yet exists on which ap-proaches may be optimal. Future MANETs are likely to be“multimode” or heterogeneous in nature. Thus, the routerscomprising a MANET will employ multiple, physical-layerwireless technologies, with each new technology requiring amultiple access (MAC) protocol for supporting QoS. Abovethe MAC layer, forwarding, routing, signaling, and admis-sion control policies are required, and the best combinationofthesepolicieswillchangeastheunderlyinghardwaretech-nology evolves.In response to the above demand for mobile ad hocnetworks, this special issue aims at providing a timely andconcise reference of the current activities and findings in therelevant technical fields, and focuses as well on the state-of-the-art and up-to-date efforts in design, performance anal-ysis, implementation and experimental results for variousQoS issues in MANETs.Webelievethatallofthesepapersnotonlyprovidenovelideas, new analytical models, simulation and experimentalresults, and handful experience in this field, but also simu-late the future research activities in the area of the quality ofserviceformobileadhocnetworks.Abriefsummaryofeachpaper is listed as follows.The first paper by Qi He et al. first identifies two criti-cal issues leading to the TCP performance degradation: (1)unreliable broadcast, since broadcast frames are transmittedwithout the request-to-send and clear-to-send (RTS/CTS)dialog and Data/ACK handshake, so they are vulnerable tothehiddenterminalproblem;and(2)falselinkfailurewhichoccurs when a node cannot successfully transmit data tem-porarily due to medium contention. Secondly, the authorspropose a scheme to use a narrow-bandwidth, out-of-bandbusy-tonechanneltomakereservationforbroadcastandlinkerror detection frames only. The proposed scheme is sim-ple and power efficient, because only the sender needs totransmit two short messages in the busy tone channel beforesending broadcast or link error detection frames in the datachannel. Analytical results show that the proposed schemecan dramatically reduce the collision probability of broad-cast and link error detection frames. Extensive simulationswith different network topologies further demonstrate thatthe proposed scheme can improve TCP throughput by 23%to150%,dependingonusermobility,andeffectivelyenhanceboth short-term and long-term fairness among coexistingTCP flows in multi-hop wireless ad hoc networks.The second paper by Deying Li et al. discusses the en-ergy efficient QoS topology control problem for nonhomo-geneous ad hoc wireless networks. Given a set of nodes withdifferent energy and bandwidth capacities in a plane, andgiven the end-to-end traffic demands and delay bounds be-tween node pairs, the problem is to find a network topol-ogy that can meet the QoS requirements, and the maximumenergy utilization of nodes is minimized. Achieving this ob-jective is vital to the increase of network lifetime. We con-sider two cases of the problem: (1) the traffic demands arenot splittable, and (2) the traffic demands are splittable. For

Piecewise Linear Companders are Robust

This paper considers the design of a robust quantizer for the class of input signal distributions having given quantiles and otherwise arbitrary shape. The quantizer model that consists of a compander and a uniform quantizer is utilized. The case of large number of quantization points is considered, and we use Bennetts and Gershos approximation to the mean rth power distortion measure. We demonstrate that the piecewise linear compander provides robust quantization for the class of all input probability distributions having only their quantiles specified. The optimum robust solution is provided through the determination of all the required parameters. The problem is resolved for the case of block quantizers as well, and we show that the robust solution corresponds to a piecewise constant output point density function. The least favorable input multivariable density function is the piecewise uniform one

Special issue: modeling and performance evaluation of radio resource QoS for next‐generation wireless and mobile networks

Next generation wireless and mobile communication systems are rapidly evolving to satisfy the demands of various network users. Due to the great success and enormous impact of IP networks, high-speed transmission is now possible for both indoor and outdoor wireless systems, internet access and web browsing have become the ruling paradigm for the next generation systems. It is envisioned that new generation wireless networks and hand-held terminals will support a wide variety of multimedia services such as multimedia web browsing, video and news on demand, mobile office system, stock market information, and so on, to mobile users anywhere, anytime in an uninterrupted and seamless way with low-powered handsets. The characteristics of wireless links, as well as the desire to maintain connectivity while on the move, offer significant challenges to provisioning quality of service and the related performance is of central interest. Since the resources (such as time, frequency and code) in the wireless segments of such networks are very limited, over-dimensioning the network resource is equivalent to poor capital investment, while congestion at busy hours could mean lost calls and lost revenues. It is therefore critical for wireless network designers to utilize these resources efficiently and effectively. In response to the above demand for next generation wireless and mobile communication systems, this special issue aims at providing a timely and concise reference of the current activities and findings in the relevant technical fields. The primary goal is to address the key technical issues pertaining to the integrated new systems and present novel technical contributions. Ten papers are selected for publication in this special issue from over 50 submissions. Each paper was reviewed carefully by at least two reviewers. The reviewers’ reports not only correct some deficiencies of the submissions but also greatly improve the quality of this special issue. We believe that all of these papers not only provide novel ideas, new analytical models, simulation and experimental results, and handful experience in this field, but also simulate the future research activities in the area of resource allocation strategies in next generation wireless networks. A brief summary of each paper is listed as follows. The first paper by Y. Fang presents a survey on a new analytical approach his research team have developed in the last few years to evaluate the performance of wireless cellular networks under more realistic assumptions. This approach is particularly applied to the analysis of call connection performance and mobility management under assumptions that many time variables such as call holding time, cell residence time, channel holding time, registration area (RA) residence time and inter-service time are assumed to be generally distributed, and show how to obtain more general analytical results. The second paper by A. Jamalipour, V. Mirchandani, and M. Kibria first reviews some of the state of art techniques in the area of QoS and resource management based mobility. They then propose an augmented 4G/B3G architecture that addresses key limitations in the salient 4G architectures examined in the literature. Their proposed novel augmentations in mobility, QoS, and resource management schemes consolidate operation of the 4G architecture. The other defining attributes of their proposed 4G architecture are that it is open, hierarchical, layered, and modular with cross-layer coordination and distributed network functionalities.

Performance evaluation of a soft hand off scheme in CDMA cellular networks

Code division multiple-access (CDMA) schemes are widely used in cellular communications system because they provide high quality, reduced interference and result in high system capacity. In CDMA systems since one carrier frequency is being used, a phenomenon known as soft hand off occurs when a user changes radio resources from one base station to another. In this paper, we propose a soft hand off scheme using a two cell and roaming user probability approach, to properly illustrate the hand off process between the cells of interest. The proposed scheme assumes that calls entering the soft region are immediately assigned two channels. This assumption helps to reduce the blocking probability of new calls in the soft region as opposed to other schemes which do not explicitly cater for such calls. A three dimensional Markov process is created to describe and develop the stochastic behavior of the calls in the system. Performance measures such as new call blocking probability, hand off call blocking probability, channel efficiency, total carried traffic are deduced

Robust Estimation for Multivariate Time Series

In this paper we present some new results on the problem of robust estimation for stationary multiple time series processes. For these processes, we consider the prediction, smoothing and causal filtering problem in cases for which the minimum achievable mean square error is expressed in a closed form in terms of the spectral density matrix of the signal. We consider three convex classes of spectral uncertainties, and develop robust solutions for these cases

New Performance Bounds in Signal Parameter Estimation under Mismatch

In this paper we develop a new upper bound for the mean square estimation error of a parameter that takes values on a bounded interval. The bound is based on the discretization of the region into a finite number of points, and the determination of the estimate by a maximum likelihood procedure. It is assumed that inaccurate versions of the true spectra are utilized in the implementation of the maximum likelihood estimator. As a special case, we develop new upper bounds to the performance of time delay estimation schemes

When are two multivariate random processes indistinguishable

Prediction error identification methods have been recently the objects of much study, and have wide applicability. The maximum likelihood (ML) identification methods for Gaussian models and the least squares prediction error method (LSPE) are special cases of the general approach. In this paper, we investigate conditions for distinguishability or identifiability of multivariate random processes, for both continuous and discrete observation time T. We consider stationary stochastic processes, for the ML and LSPE methods, and for large observation interval T, we resolve the identifiability question. Our analysis begins by considering stationary autoregressive moving average models, but the conclusions apply for general stationary, stable vector models. The limiting value for T → ∞ of the criterion function is evaluated, and it is viewed as a distance measure in the parameter space of the model.The main new result of this paper is to specify the equivalence classes of stationary models that achieve the global minimization of the above distance measure, and hence to determine precisely the classes of models that are not identifiable from each other. The new conclusions are useful for parameterizing multivariate stationary models in system identification problems. Relationships to previously discovered identifiability conditions are discussed.

Improved quality of service for WCDMA networks and coexistence with indoor wireless technologies

In this paper we use a WCDMA network simulator to evaluate the different performance criteria. We also simulate a transmit diversity scheme and use the results of the diversity scheme in the simulator to evaluate the QoS (quality of service) enhancements obtained. Further we explore the possibility of a coexistence of a WCDMA network with the WIPAS (wireless IP access system).

Numerical analysis for the optimal reserved channel numbers in reserved channel scheme with hybrid revenue of incomplete and complete calls

In this note, a revenue scheme based on the channel reservation scheme in a wireless system is investigated. Here, the revenue function is considered to be a weighted function for the actual call connection time (ACCT) ([Wei Li and A.S. Alfa, 2000], [Wei Li et al., 2002]) of incomplete call and the ACCT of the complete call, which is a challenge method in the updated wireless networks. We numerically show that the strategy of reserving a small numbers of the channels is better than that of reserving a larger number of channels for this revenue structure. The idea and the technique are expected to be applied to other advanced communications systems.