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We consider two classes of multiserver retrial queueing systems. For the first class, the rate of retrial requests depends on the number of customers on the orbit, and for the second class, the rate is constant. The input flow is assumed to be a regenerative one and the service time has an arbitrary distribution. Based on the synchronization of the input flow and an auxiliary service process, we establish necessary and sufficient stability conditions for models of both classes., 1. Introduction We consider a multiserver queueing system in which primary customers arrive according to a regenerative flow X with rate [lambda] [1]. The system has m stochastically identical servers. [...]

In this paper, we present findings from a three-year research project funded by the US Institute of Museum and Library Services that examined how advanced broadband measurement capabilities can support the infrastructure and services needed to respond to the digital demands of public library users across the US. Previous studies have identified the ongoing broadband challenges of public libraries while also highlighting the increasing digital expectations of their patrons. However, few large-scale research efforts have collected automated, longitudinal measurement data on library broadband speeds and quality of service at a local, granular level inside public libraries over time, including when buildings are closed. This research seeks to address this gap in the literature through the following research question: How can public libraries utilize broadband measurement tools to develop a better understanding of the broadband speeds and quality of service that public libraries receive? In response, quantitative measurement data were gathered from an open-source broadband measurement system that was both developed for the research and deployed at 30 public libraries across the US. Findings from our analysis of the data revealed that Ookla measurements over time can confirm when the library's internet connection matches expected service levels and when they do not. When measurements are not consistent with expected service levels, libraries can observe the differences and correlate this with additional local information about the causes. Ongoing measurements conducted by the library enable local control and monitoring of this vital service and support critique and interrogation of the differences between internet measurement platforms. In addition, we learned that speed tests are useful for examining these trends but are only a small part of assessing an internet connection and how well it can be used for specific purposes. These findings have implications for state library agencies and federal policymakers interested in having access to data on observed versus advertised speeds and quality of service of public library broadband connections nationwide., INTRODUCTION The COVID-19 pandemic exposed the severity of the digital divide in the United States. During this time, lack of access to computers and the internet has been highlighted among [...]

VANET is the spontaneous evolving creation of a wireless network, and clustering in these networks is a challenging task due to rapidly changing topology and frequent disconnection in networks. The cluster head (CH) stability plays a prominent role in robustness and scalability in the network. The stable CH ensures minimum intra- and intercluster communication, thereby reducing the overhead. These challenges lead the authors to search for a CH selection method based on a weighted amalgamation of four metrics: befit factor, community neighborhood, eccentricity, and trust. The stability of CH depends on the vehicle's speed, distance, velocity, and change in acceleration. These all are included in the befit factor. Also, the accurate location of the vehicle in changing the model is very vital. Thus, the predicted location with the Kalman filter's help is used to evaluate CH stability. The results have shown better performance than the existing state of the art for the befit factor. The change in dynamics and frequent disconnection in communication links due to the vehicle's high speed are inevitable. To comprehend this problem, a graphing approach is used to evaluate the eccentricity and the community neighborhood. The link reliability is calculated using the eigengap heuristic. The last metric is trust; this is one of the concepts that has not been included in the weighted approach to date as per the literature. An adaptive spectrum sensing is designed for evaluating the trust values specifically for the primary users. A deep recurrent learning network, commonly known as long short-term memory (LSTM), is trained for the probability of detection with various signals and noise conditions. The false rate has drastically reduced with the usage of LSTM. The proposed scheme is tested on the real map of Chengdu, southwestern China's Sichuan province, with different vehicular mobilities. The comparative study with the individual and weighted metric has shown significant improvement in the cluster head stability during high vehicular density. Also, there is a considerable increase in network performance in energy, packet delay, packet delay ratio, and throughput., Author(s): Muhammad Asim Saleem [1]; Zhou Shijie [1]; Muhammad Umer Sarwar [2]; Tanveer Ahmad [3]; Amarah Maqbool [4]; Casper Shikali Shivachi (corresponding author) [5]; Maham Tariq [4] 1. Introduction A [...]

The basic concern of a Communication System is to transfer information from its source to a destination some distance away. Textual documents also deal with the transmission of information. Particularly, from a text categorization system point of view, the information encoded by a document is the topic or category it belongs to. Following this initial intuition, a theoretical framework is developed where Automatic Text Categorization (ATC) is studied under a Communication System perspective. Under this approach, the problematic indexing feature space dimensionality reduction has been tackled by a two-level supervised scheme, implemented by a noisy terms filtering and a subsequent redundant terms compression. Gaussian probabilistic categorizers have been revisited and adapted to the concomitance of sparsity in ATC. Experimental results pertaining to 20 Newsgroups and Reuters-21578 collections validate the theoretical approaches. The noise filter and redundancy compressor allows an aggressive term vocabulary reduction (reduction factor greater than 0.99) with a minimum loss (lower than 3 percent) and, in some cases, gain (greater than 4 percent) of final classification accuracy. The adapted Gaussian Naive Bayes classifier reaches classification results similar to those obtained by state-of-the-art Multinomial Naive Bayes (MNB) and Support Vector Machines (SVMs). Index Terms--Data communications, text processing, data compaction and compression, clustering, classifier design and evaluation, feature evaluation and selection.

The aim of the discrete simulation framework is to deal with issues of the next generation of wireless cellular networks (e.g., multimedia traffic, radio resource management and mobility ... etc) and to provide a platform for current and future investigations involving wireless cellular networks. The simulator is built from the scratch to enable customization requirements of any research and to provide the freedom to understand, configure protocol modules, draw desired topologies and specifies the movement paths of the mobile users and to plot the necessary performance graphs. In order to evaluate and validate the performance of the designed simulator, a simulation model for the wireless cellular network and mobile environment deployed. The performance of the developed simulator compared with the performance characteristics of existing algorithms. Simulation results verify the developed simulator is able to recapture the results of both the numerical result and simulation results of the comparative system utilizing an idealistic platform. In addition the simulator incorporates detail algorithms for the correlated components between the entities of the cellular networks and the development of the discrete simulator. Key words: Discrete simulation, wireless cellular network, performance modeling, INTRODUCTION The growth in complexity of communication systems increases the time and effort required for analysis and design, the need to insert new technologies into commercial products quickly requires that [...]

This paper describes a two-level simulated annealing heuristic for the joint problem of object placement and request routing in a Content Distribution Network (CDN) with constraints pertaining to server capacity and end-to-end object transfer delay. A CDN is a technology that is used to efficiently distribute electronic content throughout an existing network. The two-level solution procedure is composed of an outer and an inner simulated annealing algorithms. Computational experiments are conducted by comparing the proposed procedure with several truncated exact solution algorithms on randomly generated Internet topologies. Keywords: telecommunications; content distribution network; object placement; request routing; simulated annealing

This article proposes a solution methodology for the design of a wide area telecommunication network. This study is motivated by the Alberta SuperNet project, which provides broadband Internet access to 422 communities across Alberta. There are two components to this problem: the network design itself, consisting of selecting which links will be part of the solution and which nodes should house shelters; and the loading problem which consists of determining which signal transport technology should be installed on the selected edges of the network. Mathematical models are described for these two subproblems. A tabu search algorithm heuristic is developed and tested on randomly generated instances and on Alberta SuperNet data. Keywords: heuristic; network design; telecommunications

We study broadcast systems that distribute a series of data updates to a large number of passive clients. The updates are sent over a broadcast channel in the form of discrete packets. We assume that clients periodically access the channel to obtain the most recent update. Such scenarios arise in many practical applications, such as distribution of traffic information and market updates to mobile wireless devices. Our goal is to design broadcast schedules that minimize the waiting time, i.e., the amount of time the client needs to wait in order to obtain the most recent update. We assume that each client has a different access pattern depending on the channel conditions, computing power, and storage capabilities. We introduce and analyze optimal universal schedules that guarantee low waiting time for any client, regardless of its behavior. Index Terms--Broadcast systems, data updates, universal schedules, waiting time.

Phase estimation using polyspectrum slices (PEP) methods are proposed for solving the phase estimation problem of nonminimum phase systems. PEP algorithms exhibit better performances than classical methods for band-limited systems.

A best practice guide for building empirical models for predicting performance variables of computing systems is presented. The practice guide assists in configuring modeling approaches systematically for best estimation, and prediction results.

Hybrid ALOHA is a novel medium access control (MAC) protocol for collision-free channel estimation and simultaneous multiuser transmission. The article presents the achievement of significant performance improvement with the hybrid ALOHA protocol as compared to the traditional ALOHA protocol.

The proposed approach to the optimal coordination of midterm planning can be used by vertically integrated utilities as well as the ISOs in electricity markets. The approach coordinates the optimal maintenance scheduling of generating units and transmission lines, within the outage scheduling horizon of weeks to months, with the security-constrained unit commitment of available components. The proposed model provides hourly schedules for maintenance outages, generation unit commitment, and transmission flows based on hourly load curves. In addition, the approach calculates the optimal allocation of fuel and emission allowance for thermal units in a vertically integrated utility, and energy allocation in electricity markets. This paper discusses that a seamless coordination of midterm and short-term optimization schemes will effectively improve the security of electricity services and reduce the chance of blackouts in aging power systems. The proposed approach highlights a trade-off between calculation speed and accuracy for large-scale implementations. A six-bus system is used for detailed analyses, and further results presented for the IEEE-118 system exhibit the effectiveness of the proposed midterm planning approach. Index Terms--Lagrangian relaxation, maintenance outage scheduling for generators and transmission lines, mixed integer programming, resource allocation and utilization, transmission network security, unit commitment.

This paper describes the use of an interactive evolutionary algorithm for the identification and selection of direct load control actions in electrical distribution networks. The evolutionary algorithm accommodates a progressive articulation of the decision maker's preferences by changing aspiration or reservation levels used in the fitness assessment of the individuals in the population (load control strategies). Genetic operators have revealed as an adequate way to supply the evolutionary process with relevant information about the search results. Besides contributing to reduce the scope of the search, and thus the computer effort, this also enables the identification of solutions more in accordance with the decision maker's evolving preferences. Index Terms--Direct load control, electrical distribution networks, energy, evolutionary algorithms, interactive approach, multi-objective models.

This paper decomposes the effects of the transition from an average cost distribution tariff to a cost causation-based distribution tariff, in terms of time and location, that uses nodal prices to recover losses and an 'extent-of-use' method to recover fixed network costs based on use at coincident peak. Our decomposition is designed so that the effects of using coincident peak and location for fixed network charges, as well as using marginal losses under constraints recovering the exact amount of losses, and recovering exactly the cost of network service in total can be isolated and analyzed separately. We apply our tariff transition and decomposition method to an example network with data from Uruguay to isolate the various effects with and without a distributed generation (DG) resource. We show moving to coincident peak charges and to fully charging for marginal losses while rebating the merchandising surplus through the fixed charges have the greatest effects on changes in distribution tariff charges. DG provides countervailing cost changes to distribution tariffs for loads through loss reductions and the implicit 'creation' of new network capacity for which it is paid. The interaction of all these effects may lead to outcomes that are counter-intuitive, which further supports the need to decompose the tariff changes to fully understand the reasons for the direction and magnitude of changes in tariff charges in the transition to tariffs based more on cost causation. Index Terms--Distributed generation, distribution networks, fixed cost allocations, loss allocations, tariffs.

This paper develops a quantification of the most important benefits brought about by the systematic operation of customer-owned back-up generators by distribution utilities or load-serving entities. The back-up reciprocating or internal combustion engine is the most widespread form of distributed generation, demonstrating high penetration levels in commercial and industrial areas. If the load-serving entity can oversee the operation of some of these units during strategic hours, important benefits can be realized, not only for the utility, but also for the owner of the unit and the society in general as shown in the results. The most important benefits of this coordinated operation are identified and quantified, using real cost data and pricing from a real North American electricity market. Index Terms--Distributed generation, distribution network, economic benefits, load serving entity.

In this note, we investigate the problem of remote stabilization via communication networks involving some time-varying delays of known average dynamics. This problem arises when the control law is remotely implemented and leads to the problem of stabilizing an open-loop unstable system with time-varying delay. We use a time-varying horizon predictor to diesign a stabilizing control law that sets the poles of the closed-loop system. The computation of the horizon of the predictor is investigated and the proposed control law explicitly takes into account an estimation of the average delay dynamics. The resulting closed loop system robustness with respect to some uncertainties on the delay estimation is also considered. Simulation results are finally presented. Index Terms--Networked control systems, stabilization with time-varying delays, state predictor.

The transmission capacity (TC) of a wireless ad hoc network is defined as the maximum spatiai intensity of successful transmissions such that the outage probability does not exceed some specified threshold. This work studies the improvement in TC obtainable with successive interference cancellation (SIC), an important receiver technique that has been shown to achieve the capacity of several classes of multiuser channels, but has not been carefully evaluated in the context of ad hoc wireless networks. This paper develops closed-form upper bounds and easily computable lower bounds for the TC of ad hoc networks with SIC receivers, for both perfect and imperfect SIC. The analysis applies to any multiuser receiver that cancels the K strongest interfering signals by a factor z [member of] [0, 1]. In addition to providing the first closed-form capacity results for SIC in ad hoc networks, design-relevant insights are made possible. In particular, it is shown that SIC should be used with direct sequence spread spectrum. Also, any imperfections in the interference cancellation rapidly degrade its usefulness. More encouragingly, only a few--often just one--interfering nodes need to be canceled in order to get the vast majority of the available performance gain. Index Terms--Ad hoc networks, successive interference cancellation, transmission capacity (TC).

Third Generation Partnership Project working group proposes the high-speed downlink packet access to speed up downlink transmission for the universal mobile telecommunication system, where the time-division-based high-speed downlink shared-channel (HS-DSCH) approach is adopted. Our previous work proposed the shared-channel assignment and scheduling (SCAS) scheme to efficiently schedule the DSCH to serve different connections, which guarantees the requested transmission rate for each connection. However, limitations exist in the SCAS scheme: 1) the requested transmission rates of connections must be two's power numbers of the basic transmission rate and 2) all served connections should be rescheduled while a new request is granted, which introduces extra rescheduling overhead to the system. This paper proposes the elastic shared-channel assignment and scheduling (eSCAS) scheme to overcome these limitations. We formally prove the correctness of the eSCAS scheme. An analytical model and simulation experiments are conducted to compare the performance for eSCAS and SCAS. Our study shows that eSCAS can significantly improve the acceptance rate for new connections without increasing the rescheduling overhead. Index Terms--High-speed downlink packet access (HSDPA), high-speed downlink shared-channel (HS-DSCH), orthogonal variable spreading factor (OVSF), scheduling, universal mobile telecommunication system (UMTS).

It has been demonstrated that turbo codes substantially outperform other codes, e.g., convolutional codes, both in the non-fading additive white Gaussian noise (AWGN) channel as well as multiple-transmit and multiple-receive antenna fading channels. Moreover, it has also been reported that turbo codes perform very well in fast fading channels, but perform somewhat poorly on slow and block fading channels of which the broadband fixed wireless access (FWA) channel is an example. In this paper, we thoroughly compare the performance of turbo-coded and convolutional-coded broadband FWA systems both with and without antenna diversity under the condition of identical complexity for a variety of decoding algorithms. In particular, we derive mathematical expressions to characterize the complexity of turbo decoding based on state-of-the-art Log-MAP and Max-Log-MAP algorithms as well as convolutional decoding based on the Viterbi algorithm in terms of the number of equivalent addition operations. Simulation results show that turbo codes do not offer any performance advantage over convolutional codes in FWA systems without antenna diversity or FWA systems with limited antenna diversity. Indeed, turbo codes only outperform convolutional codes in FWA systems having significant antenna diversity. Index Terms--Algorithms, communication system performance, complexity theory, concatenated coding, convolutional codes, decoding, fading channels, iterative methods, trellis codes.

Ultra-wideband wireless transmission has attracted considerable attention both in academia and industry. For high-rate and short-range transmission, direct sequence based ultra-wideband (DS-UWB) systems are a strong contender for consumer market applications. Due to the large transmission bandwidth, the UWB channel is characterized by a long root-mean-square delay spread and the RAKE receiver cannot always overcome the resulting intersymbol interference. We therefore study equalization for DS-UWB systems. This paper is comprised of two parts. In this first part, we consider DS-UWB with binary phase-shift keying (BPSK) modulation, which is the mandatory transmission mode for DS-UWB systems promoted by the UWB Forum industry alliance. We derive matched filter bounds for optimum equalization taking into account practical constraints like receiver filtering, sampling, and the number of RAKE fingers when RAKE preprocessing is applied at the receiver. Our results show that chip-rate sampling is sufficient for close-to-optimum performance. For analysis of suboptimum equalization strategies we further study the distribution of the zeros of the channel transfer function including RAKE combining. Our findings suggest that linear equalization is well suited for the lower data rate modes of DS-UWB systems, whereas nonlinear equalization is preferable for high-data rate modes. Moreover, we devise equalization schemes with widely linear processing, which improves performance while not increasing equalizer complexity. Simulation and numerical results confirm the significance of our analysis and equalizer designs and show that low-complexity (widely) linear and nonlinear equalizers perform close to the pertinent matched filter bound limit. Index Terms--Direct sequence UWB, equalization, RAKE receiver, statistical channel characterization, ultra wideband (UWB), widely linear processing.

Universal mobile-telecommunication system supports IP multimedia services through the IP multimedia corenetwork subsystem OMS). This paper proposes a prepaid application server (PAS) to handle both the prepaid calls and messaging services in the IMS. When both voice and messaging are simultaneously offered, a potential problem is that the delivery of a message during a call may result in force-termination of that call due to credit depletion. To address this issue, we describe a strategy to determine if a prepaid message can be sent out during a call session. We propose an analytic model to investigate the performance of this strategy. This paper provides guidelines to select appropriate input parameters for the PAS. Index Terms--Billing, diameter protocol, IP multimedia corenetwork subsystem (IMS), session initiation protocol (SIP), VoIP.

The problem of efficient video communications over multiple-input-multiple-output (MIMO) wireless systems is of great significance due to the high capacity of the multiple antenna system. The high data rates provided by the MIMO system can be traded off with diversity gain by using different channel-coding schemes. Also, by using different video source-coding methods, high compression gain can be traded off with the error resilience gain. One should jointly consider source coding and channel coding when designing a MIMO wireless video system. However, little is known so far about what combinations of channel-coding and source-coding methods have the best overall performance in a MIMO system. In this paper, by comparing the performances of several different typical combinations through both theoretical and simulation studies, we show that no single combination is the best for the entire range of channel conditions, but rather, different combinations may be best for a subrange. Index Terms--Diversity, error resilience, joint source--channel coding, layered coding (LC), multiple description coding (MDC), multiple input--multiple output (MIMO), space--time coding, video coding.

We treat the performance analysis and optimization of an interleave-division-multiplexing (IDM) multiple-inputsingle-output (MISO) system with partial channel state information (CSI) at the transmitters and an iterative (turbo) receiver. We propose a general methodology to analyze and evaluate the performance of such an IDM-MISO system. In particular, an SNR tracking method is proposed to calculate the output SNR of the soft-input soft-output IDM detector. The extrinsic mutual information transfer chart technique is employed to analyze the performance of the entire system. More specifically, the repetition decoder and the low-density parity check decoder are considered for the uncoded IDM system and the coded IDM system, respectively. Furthermore, based on the above analytical framework, we present the optimal transmit strategy for the IDM-MISO system with an imperfect CSI at the transmitter. Extensive simulations are performed to demonstrate the performance of the proposed IDM schemes under the MISO channels with different correlation statistics. Our results show that the proposed IDM-MISO scheme can outperform the existing space-time block code schemes in the low-rate transmission scenario. Index Terms--Interleave-division-multiplexing (IDM), iterative receiver, low-density parity check (LDPC), multiple-inputsingle-output (MISO), power allocation.

The novel pulses, which not only meet the power spectral mask of the Federal Communications Commission (FCC) but also preserve orthonormality at the correlation receiver, have been proposedby Kim et al. for high data rate communications in indoor ultra-wideband (UWB) systems. The proposed multiple orthonormal pulses comply with the FCC spectral mask without additional frequency shifting or bandpass filters, and furthermore, provide enhanced bit-error rate (BER) performance, compared with a well-known Gaussian monocycle and modified Hermite pulses. This paper analyzes the impact of the proposed pulses' properties, such as their auto- and cross-correlations, on the correlation receiver of the UWB system based on the pulse position modulation. The performance of the proposed pulses are compared with different waveforms under various conditions, such as multipath fading, timing mismatch, and multiuser interference. We also discuss a modulation scheme using the multiple orthogonal pulses to achieve the enhancement of data rate and the impact of the correlation characteristics of the proposed waveforms on the BER performance. Simulation results demonstrate the effectiveness of the proposed orthonormal pulses in various conditions, comparing with different waveforms. Index Terms--Bit-error rate (BER) performance, modulation, multiuser interference (MUI), orthogonal pulses, ultra-wideband (UWB).