The Effect of Handoff Dwell Time on the Mobile Network Performance

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.Zhang Yan received the B.S. degree in communication engineering from the Nanjing University of Post and Telecommunication, Peoples 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.     

A Modified Distributed Call Admission Control Scheme and Its Performance

Call admission control is one of the key elements to guarantee the handoff call dropping probability in cellular networks. Among numerous proposals in the literature, the distributed call admission control policy (DCAC) seems to be promising, due to its simplicity and adaptability to changing traffic. However, one crucial assumption used in DCAC is that the actually admitted new calls has to obey a Poisson process to enter the network after the call admission control. Given the dynamic and distributed nature of the control process, this can neither be validated nor be easily implemented. In this paper, we will first discuss a generalized DCAC which eliminates the above assumption and can be used in general environments. Then, a mobility-aware DCAC is introduced, which considers the difference of handoff support between low and high mobility calls in making the CAC decision in order to improve channel utilization. The performance of the modified DCAC scheme is investigated through simulation studies.     

蜂窝移动网中基于MMPP业务输入模型的系统性能分析

文章针对现有的以Poisson过程作为输入业务流模型分析系统性能的不足,提出采用马尔可夫调制泊松过程(MMPP)作为输入业务流来分析系统的呼叫阻塞率和掉话率.数值和仿真结果表明,MMPP能够较好的对蜂窝移动网中的业务输入流近似建摸,它考虑了业务流本身的相关特性和突发特性,可以更加准确的用于分析系统性能.     

A Decomposable Random Walk Model for Mobility in Wireless Communications

In this paper we develop models to represent the time until boundary crossing and associated statistics in cellular wireless networks. We propose modeling the terminal movements within a cell by a discrete two-dimensional random walk process. We note that in such an environment mobile units tend to move in roughly a straight line, with occasional backtracking, for a significant period of time before changing direction. We determine the time until crossing an exit point from a circular cell by choosing a random direction from the starting point to an exit point. The user would actually be moving in fluctuating directions until reaching this exit point. Subsequently, we calculate the expected time to reach the exit point as a function of the constant speed of travel and the propensity to change direction en route. The model is rather general and has the potential to be used for highly irregular cell shapes when boundary crossing is not distance-based but determined by propagation attenuation-based criterion.     

Integrating Distributed Channel Allocation and Adaptive Handoff Management for QoS-Sensitive Cellular Networks

Next generation high-speed cellular networks are expected to support multimedia applications, which require QoS provisions. Since frequency spectrum is the most expensive resource in wireless networks, it is a challenge to support QoS using limited frequency spectrum. In the literature, two orthogonal approaches are used to address the bandwidth utilization issue and the QoS provision issue; that is, channel allocation schemes have been proposed to improve bandwidth efficiency, whereas handoff management schemes, based on bandwidth reservation, have been proposed to guarantee a low connection dropping rate. However, little effort has been taken to address both issues together. In this paper, we integrate distributed channel allocation and adaptive handoff management to provide QoS guarantees and efficiently utilize the bandwidth. First, we present a complete distributed distributed channel allocation algorithm and propose techniques to reduce its message complexity and intra-handoff overhead. Second, we integrate the proposed distributed channel allocation algorithm with an adaptive handoff management scheme to provide QoS guarantees and efficiently utilize the bandwidth. Detailed simulation experiments are carried out to evaluate the proposed methodology. Compared to previous schemes, our scheme can significantly reduce the message complexity and intra-handoff overhead. Moreover, the proposed scheme can improve the bandwidth utilization while providing QoS guarantees.     

A Call-Admission Control (CAC) Algorithm for Providing Guaranteed QoS in Cellular Networks

Future broadband wireless access systems are expected to integrate various classes of mobile terminals (MTs), each class with a different type of quality of service (QoS) requirement. When the load on a wireless network is high, the guarantee of QoS for each class of MTs is a challenging task. This study considers two classes of MTs—profiled MTs and nonprofiled or regular MTs. It is assumed that profiled users require a guaranteed QoS. The measure of QoS is the probability of forced termination of a call that was allowed to access the network. Two previous handoff prioritization schemes—(i) prerequest scheme and (ii) guard channel scheme—decrease handoff failure (and hence forced termination). In this work, we compare and contrast both the schemes through extensive simulation and we find that neither guard channel nor channel prerequest scheme can guarantee a desired level of QoS for the profiled MTs. We then propose a novel call-admission control (CAC) algorithm that can maintain any desired level of QoS, while the successful call completion rate is very high. In the proposed algorithm, the new call arrival rate is estimated continuously, and when the estimated arrival rate is higher than a predetermined level, some new calls are blocked irrespective of the availability of channels. The objective of this new call preblocking is to maintain a cell's observed new call arrival rate at no more than the predetermined rate. We show that the proposed method can guarantee any desired level of QoS for profiled users.     

Q-Win – A New Admission and Handoff Management Scheme for Multimedia LEO Satellite Networks

Low Earth Orbit (LEO) satellite networks are deployed as an enhancement to terrestrial wireless networks in order to provide broadband services to users regardless of their location. In addition to global coverage, these satellite systems support communications with hand-held devices and offer low cost-per-minute access cost, making them promising platform for Personal Communication Services (PCS). LEO satellites are expected to support multimedia traffic and to provide their users with the negotiated Quality of Service (QoS). However, the limited bandwidth of the satellite channel, satellite rotation around the Earth and mobility of end-users makes QoS provisioning and mobility management a challenging task. One important mobility problem is the intra-satellite handoff management. The main contribution of this work is to propose Q-Win, a novel call admission and handoff management scheme for LEO satellite networks. A key ingredient in our scheme is a companion predictive bandwidth allocation strategy that exploits the topology of the network and contributes to maintaining high bandwidth utilization. Our bandwidth allocation scheme is specifically tailored to meet the QoS needs of multimedia connections. The performance of Q-Win is compared to that of two recent schemes proposed in the literature. Simulation results show that our scheme offers low call dropping probability, providing for reliable handoff of on-going calls, good call blocking probability for new call requests, while maintaining bandwidth utilization high.     

The extended connection‐dependent threshold model for call‐level performance analysis of multi‐rate loss systems under the bandwidth reservation policy

Firstly, we reviewed two extensions of the Erlang multi‐rate loss model, whereby we can assess the call‐level QoS of telecom networks supporting elastic traffic: (i) the extended Erlang multi‐rate loss model, where random arriving calls of certain bandwidth requirements at call setup can tolerate bandwidth compression while in service; and (ii) the connection‐dependent threshold model, where arriving calls may have several contingency bandwidth requirements, whereas in‐service calls cannot tolerate bandwidth compression. Secondly, we proposed a new model, the extended connection‐dependent threshold model. Calls may have alternative bandwidth requirements at call setup and can tolerate bandwidth compression while in service. We proposed a recurrent formula for the efficient calculation of link occupancy distribution and consequently call blocking probabilities, link utilization, and throughput per service class. Furthermore, in the proposed model, we incorporated the bandwidth reservation policy, whereby we can (i) equalize the call blocking probabilities of different service classes, (ii) guarantee specific QoS per service class, and (iii) implement different maximum bandwidth compression/expansion rate per service class so that the network supports both elastic and stream traffic. The accuracy of the new model is verified by simulation. Moreover, the proposed model performs better than the existing models. Finally, we generalize the proposed model by incorporating service classes with either random or quasi‐random arrivals. Copyright © 2011 John Wiley & Sons, Ltd.