Ahmed Doha

Performance Evaluation of Reservation Medium Access Control in IEEE 802.16 Networks

The IEEE 802.16 technology is increasingly being considered for fixed and mobile voice and high speed data access. The success of IEEE 802.16 in a mobile or mesh network environment is contingent on its ability to embrace and sustain dynamic traffic conditions. To this end, we study the reservation multiple access protocol of the IEEE 802.16 standard to understand the protocol performance and potentials. Basically for its primary role in controlling the protocol performance, we emphasize the design of the contention-based reservation period. We present an analytical model for computing the contention delay, data transmission delay, and throughput resulting from different contention period allocations under dynamic traffic conditions. We illustrate the performance compromises and remedies with respect to the contention period allocation. Based on the analytical model and performance evaluation results, we institute a research base to enhance the performance of the reservation multiple access protocol in IEEE 802.16 standard.

The influence of product life cycle on the efficacy of purchasing practices

Purpose – The purpose of this study is twofold. First, to examine the contingent role of the product life cycle on the efficacy of purchasing practices. Second, to use the results of the first investigation to explore the adequacy of the profit‐maximization framework for explaining purchasing decision making. This second investigation is motivated by growing evidence on the role of institutional factors in explaining supply chain management practices.Design/methodology/approach – Survey data from a sample of North American manufacturing firms, across four standard industry sectors, are analysed using ANOVA and linear regression, to examine the hypotheses.Findings – The results indicate that product life cycle has a contingent effect on the efficacy of some purchasing practices but not on others. Interestingly, the results suggest that the profit‐maximization framework is capable of explaining only some purchasing decisions but not others; firms adopt certain purchasing practices in certain product life cy...

Access delay analysis in reservation multiple access protocols for broadband local and cellular network

This work analyzes reservation request access delay in reservation multiple access protocols in light of frame contention slot allocation. Variations of the reservation MAC protocol are widely used in local and cellular network technologies. We derive an analytical model for access delay of reservation request packets that reflects the impact of per-frame number of contention slots on access delay of a request packet. We obtain insightful observations on this relation and as a result show that a new family of delay and throughput constrained dynamic contention slot allocation schemes can be developed.

Opportunistic performance enhancement of reservation multiple access protocols of wireless broadband networks

Most of todays broadband networks, including the recently ratified IEEE 802.16 standard, employ reservation based multiple media access control. A problem pertinent to reservation MAC protocols is the division of frame slots between the contention and data transmission processes. In most of the reservation MAC protocols no specific ratio is standardized, leaving proprietary solutions address the local network environment. As both processes are equally important for maintaining efficient delay and throughput performance, a solution must consider the timely varying traffic load. For example, heterogeneity and cooperation of networks promote access technologies that can sustain waves of increasing traffic load. In this paper, we start by instituting a framework for efficient allocation of frame resources to the contention and data transmission processes in light of the delay and throughout performance. We then propose a dynamic resource allocation controller based on a Markovian optimization model, where the optimization parameters are tuned according to specific preferential criteria of service providers. Our model achieves opportunistic performance improvements, on a per frame basis, over the best-case static allocation. Through simulation, we study the merits of our proposed optimized controller with respect to the framework. We show by illustrative examples and numerical results that the controller successfully fulfills the framework objectives.

Measuring firms’ imitation activity

Although imitation is more abundant and prevalent than innovation in firms’ product and process development activities, it has been understudied in research on innovation and R&D management. For example, a valid and reliable objective firm-level measure of the intensity of imitation activity is lacking in the extant literature. This measure is necessary to understand the antecedents and consequences of firms’ imitation activity, which has implications for R&D management. In this paper, we present novel methods that employ patent infringement litigations data to improve on the validity and reliability of measuring firms’ imitation activity. We validate our proposed measure by presenting a first model and test of R&D as a multiple-output production function with R&D expenditure as the primary input, and innovation and imitation as joint outputs. This is in contrast to current R&D models as a single-output production function of either innovation or imitation. This study uses a sample of 227 public firms from the computer, semiconductor, and pharmaceutical industries in the United States during 1991–2010.