IrLAP protocol performance analysis of IrDA wireless communications

The IRDA IrLAP protocol is analytically modelled. Throughput performance is examined with bit error rate, window size, and turnaround times. It is shown that for the proposed 16 Mbit/s and 127 frame maximum window size extension the link BER quality becomes critical if maximum throughput is to be achieved. A window size of 60 is less sensitive to bit error rate variations. Reducing the minimum turnaround time is always beneficial     

IrBurst Modelling and Performance Analysis in the Presence of Transmission Errors

IrBurst is a session/presentation layer protocol dedicated for high speed large volume information transfer over IrDA links. The protocol is developed by IrDA in order to complement the existing protocol OBEX which is best suited for small files. This paper presents a mathematical model for IrBurst over the IrDA protocol stacks taking into account the presence of bit errors and multiple simultaneously applications. The performance of IrBurst is examined considering TinyTP buffer sizes and the number of IrBurst application connections as parameters. The contribution of this work is to develop a mathematical model for IrBurst, investigate the compatibility of IrBurst to low layer protocols, as well as providing suitable design guidelines for IrDA devices for high performance of IrBurst. Pi Huang received the B.Sc. degree in Electrical and Electronic Engineering from University of Central Lancashire, U.K., in 2001, the M.Sc. degree in Telecommunications from University College London, U.K., in 2002 and the Ph.D degree in the Personal Wireless Networks and Outdoor Optical Links from Bournemouth University, U.K., in 2006. He is currently working in wireless solution division of British Telecom. His research focuses on performance modelling and analysis as well as discrete-event simulation of wireless communication protocols and wireless communication networks. He has published over 20 papers in the areas of wireless communications. Anthony C. Boucouvalas has worked at GEC Hirst Research Centre, and became Group Leader and Divisional Chief Scientist until 1987, when he joined Hewlett Packard (HP) Laboratories as Project Manager. He joined Bournemouth University in 1994 and became a Professor in Multimedia Communications in 1996, and in 1999 became Director of the Microelectronics and Multimedia Research Centre. His current research interests span the fields of wireless communications, optical fibre communications and components, multimedia communications, and human-computer interfaces, where he has published over 200 papers. He has contributed to the formation of IrDA as an industry standard and he is now a Member of the IrDA Architectures Council. He is a Fellow of Fellow of the Royal Society for the encouragement of Arts, Manufacturers and Commerce, (FRSA) and a Fellow of IEE, (FIEE). In 2002 he became a Fellow of the Institute of Electrical and Electronic Engineers (FIEEE), for contributions to optical fibre components and optical wireless communications. He is an Editor of numerous Journals and in the Organising committee of many conferences.     

Performance Analysis of the Advanced Infrared (AIr) CSMA/CA MAC Protocol for Wireless LANs

Advanced Infrared (AIr) is a proposed standard of the Infrared Data Association (IrDA) for indoor infrared LANs. AIr Medium Access Control (MAC) employs Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) techniques with Request To Send/Clear To Send (RTS/CTS) frame exchange to address the hidden station problem. A long Collision Avoidance Slot (CAS) duration, that includes the beginning of the CTS frame, is defined to cope with collisions caused from hidden stations. AIr MAC employs linear adjustment of the Contention Window (CW) size to minimize delays emerging from the long CAS duration. This paper provides a simple and accurate analytical model for the linear CW adjustment that calculates AIr throughput assuming a finite number of stations and error free channel transmissions. Validity of the model is verified by comparing analysis with simulation results. By examining the first derivative of the throughput equation, we derive the optimum CW size that maximizes throughput as a function of the network size. In the case of the AIr protocol, where a collision lasts exactly one CAS, different conclusions result for maximum throughput as compared with the corresponding conclusions for the similar IEEE 802.11 protocol. Using the proposed model, we present an extensive AIr throughput performance evaluation. The effectiveness of physical and link layer parameters on throughput performance is explored. The proposed long CAS duration combined with CW linear adjustment are proven quite effective. Linear CW adjustment combined with the long CAS duration offer an efficient collision avoidance scheme that does not suffer from collisions caused from hidden stations.     

OBEX Over IrDA: Performance Analysis and Optimization by Considering Multiple Applications

OBEX (Object Exchange Protocol) is a session protocol designed to exchange all kind of objects between portable devices using different ad hoc wireless links including IrDA and Bluetooth. This paper develops a mathematical model for OBEX over the IrDA protocol stack by considering multiple applications and presence of bit errors. The model is also verified by simulation results. We derive throughput equations and carry out an optimization study focusing on four major parameters: OBEX packet size, TinyTP (IrDA transport layer) buffer size, IrLAP (IrDA link layer) frame and window size. Equations are derived for the optimum IrLAP window and frame sizes. Numerical results show significant improvement on OBEX performance using the optimized parameters. The major contribution of this work is the modelling of OBEX including the low layer protocols and optimization of the overall throughput by appropriate parameter selection     

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co‐ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Heat transport limitations and reaction scheme of partial oxidation of methane to synthesis gas over supported rhodium catalysts

The partial oxidation of methane to synthesis gas over supported Rh catalysts is investigated, paying particular attention to removing heat transport limitations and identifying the reaction conditions within the kinetic-controlling regime. The results obtained suggest that the reaction follows the sequence of total oxidation to CO₂ and H₂O, followed by reforming reactions to synthesis gas.     

Cutoff frequencies in optical fibers of arbitrary refractive index profile using the resonance technique

We present a very simple and accurate numerical method for calculating the cutoff frequencies of arbitrary refractive index profile optical fibers, including discrete numerical data from profile measurements. From Maxwell's equations we derive a transmission line equivalent circuit for any mode of an optical fiber which is cutoff frequency dependent. The problem of finding the cutoff frequency of a mode is transformed into finding the resonance frequency of the equivalent circuit. The algorithm uses no Bessel or other complicated functions and could be implemented on small microcomputers.     

High-isolation single-mode wavelength-division multiplexer/demultiplexer

A single-mode fibre-optic wavelength-division multiplexer/demultiplexer with excellent isolation is reported. The device utilises a fused biconical structure similar to that of 3 dB couplers and exhibits an insertion loss of 0.04 dB and a wavelength isolation of 43 dB at 1.300 ?m and 30 dB at 1.523 ?m.     

Intensity noise in lightwave fibre systems using LED transmitters

Excess noise in fibre-optic systems using LED transmitters is analysed. The relative excess noise (REN) of a commercially available single-mode LED source was measured to be -128+or-1.0 dB Hz/sup -1/. REN is shown to be significant in single-mode fibre systems in which the detected optical power is greater than -25 dBm.<>