George M. Stamatelos

Comparative Performance Evaluation of TCP Variants in WiMAX (and WLANs) Network Configurations

An important application for the IEEE 802.16 technology (also called WiMAX) is to provide high-speed access to the Internet where the transmission control protocol (TCP) is the core transport protocol. In this paper we study through extensive simulation scenarios the performance characteristics of five representative TCP schemes, namely, TCP New Reno, Vegas, Veno, Westwood, and BIC, in WiMAX (and WLANs) networks, under the conditions of correlated wireless errors, asymmetric end-to-end capabilities, and link congestion. The target is to evaluate how the above conditions would affect the TCP congestion control and suggest the best schemes to be employed in WiMAX networks.

Performance evaluation of TCP in IEEE 802.16 networks

An important application for the IEEE 802.16 technology (also called WiMAX) it to provide high-speed access to the Internet where the transmission control protocol (TCP) is the core transport protocol. In this paper we study through extensive simulation scenarios, the performance characteristics of five representative TCP schemes, namely TCP New Reno, Vegas, Veno, Westwood and BIC, in WiMAX networks, under the conditions of correlated wireless errors, asymmetric end-to-end capabilities and link congestion. The target is to evaluate how the above conditions would affect the TCP congestion control, and suggest the best schemes to be employed in WiMAX Networks.

Content-based image retrieval over IEEE 802.11b noisy wireless networks

Mobile devices such as smartphones and tablets are widely used in everyday life to perform a variety of operations, such as e-mail exchange, connection to social media, bank/financial transactions, and so on. Moreover, because of the large growth of multimedia applications, video and image transferring and sharing via a wireless network is becoming increasingly popular. Several modern mobile applications perform information retrieval and image recognition. For example, Google Goggles is an image recognition application that is used for searches based on pictures taken by handheld devices. In most of the cases, image recognition procedure is an image retrieval procedure. The captured images or a low-level description of them are uploaded online, and the system recognizes their content by retrieving visually similar pictures. Taking into account the last comment, our goal in this paper is to evaluate the process of image retrieval/recognition over an Institute of Electrical and Electronics Engineers 802.11b network, operating at 2.4GHz. Our evaluation is performed through a simulated network configuration, which consists of a number of mobile nodes communicating with an access point. Throughout our simulations, we examine the impact of several factors, such as the existence of a strong line of sight during the communication between wireless devices. Strong line of sight depends on the fading model used for the simulations and has an effect on BER. We have used a large number of image descriptors and a variety of scenarios, reported in the relative literature, in order to comprehensively evaluate our system. To reinforce our results, experiments were conducted on two well-known images databases by using 10 descriptors from the literature. Copyright

Optimal Backoff Exponent estimation for environmental monitoring IEEE 802.15.4 star-topology sensor networks

In the IEEE 802.15.4 standard, the Backoff Exponent (BE) index defines the duration of a nodes backoff period during a transmission attempt. In the context of an environmental monitoring research project, we examine the effect of the BE index value in overall network performance. We show that the minimum and maximum assigned values have a significant performance impact and propose a method for calculating the appropriate index value as a function of packet size, data rate and the number of active sensor nodes. In the same context, we also develop a network calculus approach for throughput estimation of IEEE 802.15.4 star topology networks and evaluate it over an extensive range of network configurations.

An amendment to IEEE 802.17 (RPR) for wireless transport

The Resilient Packet Ring (RPR) is a packet network technology designed to provide broadband traffic transport in a metropolitan area according to IEEE 802.17 specifications. Its advantages include flexibility in bandwidth allocation, fairness and traffic shaping criteria for the acceptance of elastic transit traffic, as well as highly reliable transport. Here we focus on possible future amendments to these specifications (such as inclusion of efficient coding / modulation schemes) that would allow RPRs to support reliably wireless traffic as well.

Performance Evaluation of IEEE 802.15.4 Sensor Chains in an Integrated Water Monitoring Framework

In the context of the CYBERSENSORS integrated water management research project, we derive a numerical modelling approach for throughput estimation in an IEEE 802.15.4 wireless sensor network. We focus on the standard-compliant slotted carrier sense multiple access with collision avoidance algorithm. Our approach takes into account the number of nodes in a cluster network, as well as the transmitted packet size. The configuration examined is a chain network formed by wireless sensor nodes where the first node is the source of data packets and the last is the traffic sink. Theoretical estimations are verified using the ns-2 network simulator. We also look into the 3G communication aspects of the platform involved. Hardware implementation and simulation tools are used here to derive a number of design guidelines that will define the system’s architecture.

TCP-BIAD for Enhancing TCP Performance in Broadband Wireless Access Networks

In this paper a new TCP variant, named TCP-Binary Increase, Adaptive Decrease is presented. The suggested congestion control algorithm is a joint approach of Westwood and an enhanced version of BIC, for improving TCP performance in broadband wireless access networks. BIAD has been evaluated with respect to other TCP variants such as Reno, Westwood, BIC, CUBIC, HSTCP and STCP with the use of network simulator 2. The results indicate that the proposed solution achieves high network utilization levels in a wide range of network settings, including wireless channel errors, link asymmetry and congestion. We also evaluated TCP-BIAD when multiple flows share a bottlenecked access link and we show that it demonstrates the fairness features required for network deployment.

Data communications aspects of an IEEE 802.15.4 based monitoring system for integrated water management

Network components of an environmental monitoring system comprising conventional sensor nodes and wireless visual sensor nodes are evaluated in this paper. In the context of the CYBERSENSORS research project, we look into its communications aspects and heterogeneous networks it employs. Hardware implementation and simulation tools are used here to derive a number of design guidelines that will help define the systems future architecture.

Secure sensor data transmission over wireless cellular networks

Significant effort has been recently devoted to research and development of sensor networks for a wide range of possible applications. Here we focus on the design of a biosensor-based, early-warning system that can be used to detect bio-threats and subsequently relay securely this information - through a cellular network and its communications capabilities - to public health surveillance centers for appropriate processing. As such, it represents an alternative approach to population vaccination against specific viruses and biological threats. Issues involving increased security of communications and network dimensioning are addressed in the above context.