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Resource allocation is a fundamental problem in connection-oriented networks. A preemption mechanism would provide available and reliable services to new connections with higher priority by tearing down existing connections of lower priority. However, end users of the existing connections that are preempted will suffer service disruptions. The duration spent and the work done for these connections are wasted, leading to lower useful utilization of the overall network resources. Soft preemption can alleviate this by rerouting a connection that is about to be preempted before actually tearing it down so that the interruption of ongoing service can be avoided. In this paper, we focus on minimizing the service disruptions caused as a result of preemption by proposing algorithms that incorporate the soft preemption feature. A centralized algorithm is developed to select the network links that have a high number of reroutable connections in order to minimize service disruptions. For feasible deployment, a decentralized preemption algorithm that uses local information is subsequently proposed. Simulation results indicate that these approaches not only reduce the service disruption but also lead to higher network throughput than what can be achieved by existing preemption algorithms. Index Terms--Connection-oriented, preemption, reroute, soft preemption.

In this paper, the sensitivity of the handoff dwell time (HDT) model on wireless mobile network performance is studied. We present an approach on the basis of the universal approximation property of phase-type (PH) distribution in order to address the intractable numerical issue caused by HDT. We first obtain the steady state probability under the general HDT. The performance metrics from the perspective of base station (BS) as well as from the point view of call are developed. The PH-type HDT is then assumed to derive the numerically tractable expressions for the performance metrics. Finally, the truncated Gaussian HDT is approximately fitted by the PH distribution via expectation maximization algorithm to reuse the closed form analytical expression. The comparison shows that, in terms of the BS performance, the handoff blocking probability exhibits a significant discrepancy whenever one uses the exponential or truncated Gaussian HDT distribution, while the new call blocking probability is less sensitive to different HDT. In addition, HDT has little impact on the call performance with respect to the call completion probability and total waiting time. Both the analytical model and the approximation approach are verified by simulation. Index Terms--Call completion probability, call performance, cell residence time, channel holding time, handoff, handoff call blocking probability, handoff dwell time, new call blocking probability, queueing priority, wireless network.

Byline: Yan Zhang (1), Boon-Hee Soong (1) Keywords: blocking probability; channel holding time; handoff dwell time; mobility model Abstract: In this paper, we have studied the impact of the handoff dwell time (HDT) on the channel holding time (CHT) modeling and examined how it affects the mobile network performance evaluation. Realistic mobility model is constructed that includes the effect of HDT and we derive the important relationship between the critical parameters such as cell residence time (CRT), call holding time, CHT and HDT. Queueing priority scheme utilizing the HDT is applied to evaluate the HDT effect on performance indices in terms of the new call and handoff call blocking probabilities. It is observed that the relative error between the realistic new call blocking probability and conventional one can reach 70% and the conventional handoff blocking probability can even double the realistic one under the same specific practical condition. Next, we compare the new call and handoff call blocking probabilities when exponential handoff dwell time distribution is replaced by truncated Gaussian distribution with both the same mean and standard deviation in the discrete event simulation. A considerable gap between the handoff call blocking probabilities is shown, which indicates that the performance indices are sensitive to the handoff dwell time distribution. Author Affiliation: (1) School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore, 639798, Singapore Article History: Registration Date: 01/01/2004 Article note: Zhang Yan received the B.S. degree in communication engineering from the Nanjing University of Post and Telecommunication, People's Republic of China, in 1997 and the M.S. degree in electrical engineering from the Beijing University of Aeronautics and Astronautics in 2000. After graduation, he worked as senior software engineer in Xinwei Telecom Technology Co., Datang Telecom Group, China, where he has been working on the CDMA base station software development. He is currently pursuing Ph.D. degree in School of Electrical and Electronics Engineering, Nanyang Technological University, Singapore. His research interests include call admission control and resource management in wireless multimedia systems, PCS network traffic load and performance evaluation. Dr. Soong Boon-Hee received his B. Eng. (Hons. I) degree in electrical and electronic engineering from University of Auckland, New Zealand, and the Ph.D. degree from the University of Newcastle, Australia, in 1984 and 1990, respectively. He is currently an associate professor with the School of Electrical and Electronic Engineering, Nanyang Technological University. From October 1999 to April 2000, he was a visiting research fellow at the Department of Electrical and Electronic Engineering, Imperial College, UK, under the Commonwealth Fellowship Award. He also served as a consultant for Mobile IP in a recent technical field trial of Next-Generation Wireless LAN initiated by InfoComm Development Authority (IDA), Singapore. He has supervised a number of postgraduate students in the area of optimization and planning of mobile communication networks. He has been teaching a number of subjects related to the field of network performance. His area of research interests includes ad-hoc networks, mobility issues, mobile IP, optimization of wireless networks, routing algorithms, queueing theory system theory, quality of service issues in high-speed networks, and signal processing. He has published a total of 60 international journals and conferences. He is a member of IEEE.

Performance of a reverse link code-division multiple-access (CDMA) system with fast close-loop power control algorithms is studied. It is found that if fast close-loop power control algorithm functions effectively, the speed of the mobile unit is in the range such that its Doppler frequency is less than one tenth of the power control updating rate. This paper also proposes a new predictive power control algorithm with better performance in terms of system capacity than the conventional and adaptive step size algorithms. An increase in system capacity as high as 22% compared with the conventional algorithm can be achieved depending on the mobile velocity. Index Terms - CDMA systems, cellular communications, power control algorithm.