Georgios Y. Lazarou

A bit-map-assisted energy-efficient MAC scheme for wireless sensor networks

Low-energy characteristics of wireless sensor networks (WSNs) pose a great design challenge for MAC control design. Recent studies have proposed different intra-cluster communication bit-map-assisted (BMA) MAC protocol for large-scale cluster-based WSNs. BMA is intended for event-driven applications, where sensor nodes transmit data to the cluster head only if significant events are observed. In addition, we provide the energy and packet latency analytical models for BMA, conventional TDMA, and energy efficient TDMA (E-TDMA) when used as intra-cluster MAC schemes. Our results show that BMA is superior for the cases of low and medium traffic loads, relatively few sensor nodes per cluster, and relatively large data packet sizes. In addition, BMA performs better than the TDMA-based MAC schemes in terms of average packet latency.

A cluster-based power-efficient MAC scheme for event-driven sensing applications

In developing an architecture for wireless sensor networks (WSNs) that is extensible to hundreds of thousands of heterogeneous nodes, fundamental advances in energy efficient communication protocols must occur. In this paper, we first propose an energy-efficient and robust intra-cluster communication bit-map assisted (BMA) MAC protocol for large-scale cluster-based WSNs and then derive energy models for BMA, conventional TDMA, and energy efficient TDMA (E-TDMA) using two different approaches. We use simulation to validate these analytical models. BMA is intended for event-driven sensing applications, that is, sensor nodes forward data to the cluster head only if significant events are observed. It has low complexity and utilizes a dynamic scheduling scheme. Clustering is a promising distributing technique used in large-scale WSNs, and when combined with an appropriate MAC scheme, high energy efficiency can be achieved. The results indicate that BMA can improve the performance of wireless sensor networks by reducing energy expenditure and packet latency. The performance of BMA as an intra-cluster MAC scheme relative to E-TDMA depends on the sensor node traffic offer load and several other key system parameters. For most sensor-based applications, the values of these parameters can be constrained such that BMA provides enhanced performance.

Describing network traffic using the index of variability

Commonly used measures of traffic burstiness do not capture the fluctuation of traffic variability over the entire range of time-scales. In this paper, we present a measure of variability, called the Index of Variability (Hv(tau)), that depicts the degree of variability (burstiness) of a typical network traffic process at each time-scale and is analytically tractable for many traffic models. As an illustration, we derive the closed-form expressions of Hv(tau) for two traditional traffic models and generate a variety of two-dimensional (2D) and three-dimensional (3D) Index-of-Variability curves. These curves demonstrate that the Index of Variability can help in determining the complexities of the network traffic variability over the network performance relevant time-scales. We then introduce a practical method for estimating the Index-of-Variability curve from a given traffic trace. Using this method, we estimate the Index-of-Variability curves for 12 long NLANR network traffic traces. The results indicate that the variability of real network traffic varies with time-scales and that the Index of Variability has the ability to discern qualitative differences between traffic traces obtained from different networks. Thus, the Index of Variability offers the potential to gain insights into the dynamics of network traffic that existing tools do not offer.

ATM WAN performance tools, experiments, and results

Practical experiments in a wide-area ATM network environment are essential to gain a better understanding of the factors affecting ATM performance. This article summarizes the main lessons learned through the authors practical experiences with ATM and how these can be applied to performance tuning. In order to achieve maximum performance from an ATM WAN, factors ranging from the transport protocol to the equipment used and the network conditions must be carefully taken into consideration. The authors also discuss some of the software-based throughput measurement tools available for the evaluation of high speed network performance, with particular emphasis on NetSpec.

A stochastic model for short-lived TCP flows

In this paper, we propose a new model for the slow-start phase based on the discrete evolutions on the congestion window, and we use this slow-start model together with our improved TCP steady-state model to develop an extensive stochastic model which can more accurately predict the throughput and latency of short-lived TCP connections as functions of loss rate, round-trip time (RTT), and file size. The result from simulation experiments show that our models performance predictions are up to 20% more accurate than the predictions obtained from the models proposed in [N. Cardwell et al., Mar. 2002] and [B. Sikdar et al., 2001].

Experimental and simulation performance results of TCP/IP over high-speed ATM over ACTS

To assist in the design and understanding of future global networks, this paper describes the practical and simulation experiences gained from a TCP/IP on ATM network over a high speed satellite link and presents performance comparison studies of such networks with the same host/traffic configurations over local area (LAN) and wide area (WAN) networks. It was found that the satellite systems deliver performance similar to the terrestrial networks regardless of their path latencies in cases where the communication channels exhibit a low bit error rate (BER). NASAs Advanced Communications Technology Satellite (ACTS), with its special characteristics and high data rate satellite channels, and the ACTS ATM Internetwork (AAI) were used in these experiments to deliver broadband traffic. Network performance tests were carried out using application-level software (ttcp, Netspec) on OC-3 and OC-12 ATM satellite links.

Using measurements to validate simulation models of TCP/IP over high speed ATM wide area networks

Predicting the performance of high speed wide area ATM networks (WANs) is a difficult task. Evaluating the performance of these systems by means of mathematical models is not yet feasible. As a result, the creation of simulation models is usually the only means of predicting and evaluating the performance of such systems. We use measurements to validate simulation models of TCP/IP over high speed ATM wide area networks. Validation of simulations with measurements is not common; however, it is needed so that simulation models can be used with confidence to accurately characterize the performance of ATM WANs. In addition, the appropriate level of fidelity of the simulation models needs to be determined. The results show that feasible simulations models can accurately predict the performance of complex high speed ATM wide area networks.

Connectivity planning and call admission control in an on-board cross-connect based multimedia GEO satellite network

This paper addresses end-to-end connectivity planning and call admission control for a high capacity multi-beam satellite network with on-board cross-connectivity. On board satellite switching is a technology designed to offer multimedia services, especially in demographically dispersed areas. Nevertheless, full on-board switching techniques are far from maturity. Their implementations have been proven expensive and difficult. There are also high risks involved in launching satellites for the stationary orbit surrounding the earth. As a substitute, a satellite network with on-board cross-connect is devised in this paper. Connectivity planning and call admission control mechanisms associated with such a network are also presented. Simulation studies are conducted to show the effectiveness of the proposed mechanisms.

Automatic scaling range selection for long-range dependent network traffic

In this paper, we present an adaptive search algorithm to automatically select the scaling range in the wavelet-based Hurst parameter estimation method. This algorithm is recursive and adaptive in nature, and it can select a scaling range consistent with human visual selection. In addition, it can be easily extended to automatically find the (approximately) linear regions of any curve. We tested our algorithm on 13 NLANR network traffic traces. The results show that our algorithm works well for the cases of monofractal traffic.

A microstrip line-fed multi-resonant slot antenna in the 4G/LTE band for smartphones

A microstrip line-fed slot antenna is presented in this paper to operate in the entire 4G/LTE band. The slot antenna has the letter ‘L’ shape, and when excited with a transmission line generates multiple modes. These modes are combined to obtain the large bandwidth for covering most of the 4G/LTE band. Several feedlines have been studied to enhance the bandwidth. The slot width is also varied to achieve large impedance bandwidth. The radiation patterns are provided showing the behavior of the antenna. This antenna can be further optimized to provide polarization diversity in the 4G/LTE systems. The slot antenna is located in the upper portion of the ground plane, leaving a large area available for accommodating electronic circuitry for wireless communications or display technology in modern smartphones. This area can also be utilized to incorporate millimeter wave antennas to make the device compatible for future 5G wireless systems.