End-to-end delay margin balancing approach for routing in multi-class networks

This paper presents Quality of Service (QoS) based routing and priority class assignment algorithms. It introduces an end-to-end delay margin balancing approach to routing, and uses it to formulate a nonlinear optimization problem. In a single-class network, the formulation is shown to be convex; however in a multi-class priority network, it is only convex within specific regions, and is infeasible otherwise. A centralized off-line computation technique is proposed to calculate both the route configuration and end-to-end priority assignment. A gradient-based solution in the convex region and a heuristic to overcome the multi-class discontinuity are derived. An approximation of the optimization problem is developed for on-line distributed processing is then presented. Using the approximation, arriving traffic flows can use vector routing tables to search for routes. Compared with minimum-hop, minimum-delay, and min-interference routing algorithms, the proposed approach enables the single-class network to accommodate more users of different end-to-end delay requirements. In a multi-class priority network, results show that using the objective function to combine route and priority class assignment further increases the supportable network traffic volume. Mohamed Ashour received his B.Sc. (1991) and M.Sc. (1997) in Electrical Engineering from Ain Shams University, Cairo, Egypt. He worked for Hughes and General Dynamics as a Telecommunications Engineer. Currently, he is a Ph.D. Candidate in the Department of Electrical and Computer Engineering of McGill University, Montreal, Quebec, Canada. His current area of research is focused on traffic engineering, routing, and QoS provisioning in DiffServ and MPLS Networks. He is also interested in multi-class queuing analysis of long-range traffic, and QoS provisioning in ad hoc networks and satellite communications. Tho Le-Ngoc obtained his B. Eng. (with Distinction) in Electrical Engineering in 1976, his M.Eng. in Microprocessor Applications in 1978 from McGill University, Montreal, and his Ph.D. in Digital Communications 1983 from the University of Ottawa, Canada. During 1977–1982, he was with Spar Aerospace Limited as a Design Engineer and then a Senior Design Engineer, involved in the development and design of the microprocessor-based controller of Canadarm (of the Space Shuttle), and SCPC/FM, SCPC/PSK, TDMA satellite communications systems. During 1982–1985, he was an Engineering Manager of the Radio Group in the Department of Development Engineering of SRTelecom Inc., developed the new point-to-multipoint DA-TDMA/TDM Subscriber Radio System SR500. He was the System Architect of this first digital point-to-multipoint wireless TDMA system. During 1985–2000, he was a Professor the Department of Electrical and Computer Engineering of Concordia University. Since 2000, he has been with the Department of Electrical and Computer Engineering of McGill University. His research interest is in the area of broadband digital communications with a special emphasis on Modulation, Coding, and Multiple-Access Techniques. He is a Senior Member of the Ordre des Ingénieur du Quebec, a Fellow of the Institute of Electrical and Electronics Engineers (IEEE), a Fellow of the Engineering Institute of Canada (EIC), and a Fellow of the Canadian Academy of Engineering (CAE). He is the recipient of the 2004 Canadian Award in Telecommunications Research, and recipient of the IEEE Canada Fessenden Award 2005.     

A cellular finite element model for the cutting of softwood across the grain

In this paper, the mechanics of cutting wood across the grain are reexamined. A hybrid cellular/macroscopic finite element model of wood was developed to simulate the effects of cell collapse during the cutting process. Initially, the model was used to simulate the compression test across the grain. The linear elastic and cell collapse behaviours of the compression tests were sucessfully simulated. The model was then used to simulate two orthogonal cutting processes, wedge cutting and chip-forming cutting. The cellular/macroscopic model revealed that during the cutting process, the load compresses the wood until cell wall buckling occurs ahead of the tool. The collapse of the supporting cell wall results in a localized tensile stress in the longitudinal direction of the cell at the tip of the tool. It is postulated that this longitudinal tensile stress would lead to microfibrils being pulled out of the matrix and hence to failure of the cell wall. Therefore, the cellular/macroscopic model has been used to explain the mechanics of severing wood fibres during the process of cutting wood across the grain.     

Diversity Analysis of Relay Selection Schemes for Two-Way Wireless Relay Networks

One-way wireless relay networks have recently received a lot of attention due to their ability to provide spatial diversity in fading wireless environment. Moreover, performing single-relay selection is a very attractive method due to its cost effective implementation and superior performance. However, one-way relay networks with the half-duplex signalling suffer from a spectral efficiency loss. To overcome such a drawback, two-way wireless relay networks have been proposed and these are also the networks considered in this paper. The paper analyzes the diversity orders of various relay selection schemes, including the best-relay selection, best-worse-channel selection, and maximum-harmonic-mean selection. The analysis is done for the amplify-and-forward protocol and under the two-step and three-step transmission procedures. In particular, it is shown that full diversity orders of R and R + 1 can be achieved in a R-relay wireless network with the two-step and three-step procedures, respectively. Numerical and simulation results are provided to verify our analysis.     

Performance evaluation and application of channel offset schemes inindoor channel assignments

We deal with channel offset schemes and their application in three-dimensional (3-D) frequency reuse environments with ideal cubic microcells. Formulas are derived to calculate channel reuse distances (CRDs) and interchannel usage distances (IUDs) for a given offset degree. For an indoor personal communication network (PCN), an algorithm is proposed for fixed channel assignment with channel offset. The spectral efficiency of channel offset schemes is discussed and the results show that compared to the channel offsetless scheme, channel offset schemes make more efficient use of limited spectrum resources     

Performance analysis of CFDAMA-PB protocol for packet satellitecommunications

Combined free/demand-assignment multiple-access (CFDAMA) schemes are suitable for broad-band packet satellite communications systems serving a finite number of bursty data sources. The performance analysis of the CFDAMA using piggy-backed (PB) reservation is presented. The probability generating function (PGF) of the packet delay is developed. The performance is evaluated in terms of three performance measures: average packet delay, variance of packet delay, and cumulative probability distribution of packet delay. Performance comparison with other pertinent schemes shows CFDAMA-PB to be superior for a wide range of user population sizes     

Performance analysis of M-PAM signaling with Tomlinson-Harashima precoding over ISI channels

An analytical method is developed to evaluate the symbol error probability of multilevel pulse amplitude modulation system using Tomlinson-Harashima precoding over inter-symbol interference channels. Analytical and simulation results are in an excellent agreement for different values of M.     

Exact lower bounds on the codelength of three-steppermutation-decodable cyclic codes

The exact lower bounds on codelength n for three-step ( T, U) permutation decodable binary cyclic codes of even-valued error number t (t⩾4) are presented. Since the derivation of these results involves only the error position, the results are applicable to cyclic codes over GF(2^m)     

Analysis of a new multiaccess/switching technique for multibeamsatellites in a prioritized ISDN environment

A performance analysis to compute the packet loss, call blocking, and packet delays of a typical user in an integrated voice-data-video satellite internetworking environment is discussed. The uplink technique used is a hybrid packet/circuit switched approach of the demand assignment type, while the downlink is a time-division-multiplexing (TDM) technique. Onboard the satellite, a baseband nonblocking switch is used to route the packets from input to output ports. Various amounts of input and output buffering as well as priority rules and blocking resolution algorithms are used. The authors conduct a performance analysis for the problems at hand and identify the best ranges for the different parameters involved     

Outage Probability with Correlated Lognormal Interferers using Log Shifted Gamma Approximation

The computation of outage probability in cellular radio system has been extensively studied. The Signal-to-Interference-plus-Noise Ratio (SINR) distribution involves the sum of lognormal distributions due to dominant effect of shadowing in both the signal and interference components. Since no closed-form expression can be found for the sum of lognormal distributions, many approximation methods and bounds were proposed in the past. In this paper, Log Shifted Gamma (LSG) approximation is proposed to calculate the sum of correlated lognormal random variables (RVs), hence the outage probability, accurately with a wide range of dB spreads, number of interferers M, correlation coefficients r among interference components, and noise power N. Overall, LSG approximation shows consistent accuracy due to its flexibility over the classical lognormal approximation, especially with small correlation coefficients r and/or large dB spreads.     

Performance evaluation of a switch using priority-based dynamic capacity allocation scheme

Performance-analysis of a switching system using priority-based dynamic capacity allocation is presented. The system provides connectivity between a number of point-to-multipoint communication access clusters. The scheduling of traffic transmission at each access cluster is based on a priority scheme with priority given to real-time (rt) traffic over nonreal-time (nrt) traffic. An analytical model is developed to evaluate the covariance functions of both rt and nrt traffic arriving at the output ports. Aggregate traffic arrival streams are approximated to 2-state Markov-modulated Poisson processes (MMPPs) by matching their statistical characteristics. Analytical and simulation results on performance of an example 4 /spl times/ 4 switch for different traffic loads are discussed.