Channel Holding Time in Wireless Cellular Communications with General Distributed Session Time and Dwell Time

Channel holding time is fundamental to teletraffic analysis of wireless cellular networks. This quantity depends on user's mobility which can be characterized by the dwell time, and the traffic model which is associated with the unencumbered session time. In this paper, under a general assumption on the distributions of unencumbered session time and dwell time, the characteristics of new call channel holding time and handoff call channel holding time are investigated. Analytical formulae for the distributions of new call channel holding time and handoff call channel holding time are derived     

A Mobility Model and Performance Analysis in Wireless Cellular Network with General Distribution and Multi-Cell Model

Multi-cell mobility model and performance analysis for wireless cellular networks are presented. The mobility model plays an important role in characterizing different mobility-related parameters such as handoff call arrival rate, blocking or dropping probability, and channel holding time. We present a novel tractable multi-cell mobility model for wireless cellular networks under the general assumptions that the cell dwell times induced by mobiles’ mobility and call holding times are modeled by using a general distribution instead of exponential distribution. We propose a novel generalized closed-form matrix formula to support the multi-cell mobility model and call holding time with general distributions. This allows us to develop a fixed point algorithm to compute loss probabilities, and handoff call arrival rate under the given assumptions. In order to reduce computational complexity of the fixed point algorithm, the channel holding time of each cell is down-modeled into an exponentially distributed one for purposes of simplification, since the service time is insensitive in computing loss probabilities of each cell due to Erlang insensitivity. The accuracy of the multi-cell analytic mobility model is supported by the comparison of the simulation results and the analytic ones.     

A PCS network with correlated arrival process and splitted-ratingchannels

The arrival of calls (i.e., new and handoff calls) in a personal communications services (PCS) network are modeled by a Markov arrival process (MAP) in which we allow correlation of the interarrival times among new calls, among handoff calls, as well as between these two kinds of calls. Each cell of the network consists of a finite number of channels and a buffer with finite size for handoff calls. There exist some channels among each cell which can be used by splitting the original rate into two channels with different rates if necessary when a handoff call arrives and finds all the channels busy. We obtain the stationary joint probability of number of calls in the cell and the phase of the arrival process, the blocking probability of a new call, the forced termination probability of a handoff call, and the mean dwell time of a handoff call in the buffer. Finally, we obtain the distribution and the mean of the cell's busy period, the distribution and the mean of the first time to split the cth channel, and some other interesting performance measures for the network. Some explicit results for special cases obtained by Lin et al. (see IEEE Trans. Vech. Technol., vol.45, no.1, p.122-30, 1996 and vol.43, no.3, p.704-12, 1994), Tekinary et al. (1992) and by Yoon et al. (1993) can also be directly obtained from the general conclusion. The results presented can provide guidelines for field data processing in PCS network design and performance evaluation     

Mobility patterns in microcellular wireless networks

This study investigates mobility patterns in microcellular wireless networks, based on measurements from the 802.11 based system that blankets the Carnegie Mellon University campus. We characterize the distribution of dwell time, which is the length of time that a mobile device remains in a cell until the next handoff, and sign-on interarrival time, which is the length of time between successive sign-ons from the same mobile device. Many researchers have assumed that these distributions are exponential, but our results based on empirical analysis show that dwell time and sign-on interarrival time can be accurately described using heavy-tailed arithmetic distributions that have infinite mean and variance. We also show that the number of handoffs per sign-on can be modeled accurately with a heavy-tailed distribution.     

MEO卫星通信系统的小区驻留时间分布

在MEO卫星移动通信系统中,确定小区驻留时间分布对于合理地规划切换策略具有十分重要的意义。指出了地球固定覆盖与卫星固定覆盖两种方式下小区驻留时间分布的不同原因。提出了计算和仿真卫星固定覆盖方式下小区驻留时间分布的方法,得出了数值结果,并与地球固定覆盖方式下的小区驻留时间分布进行了比较。     

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.     

Performance analysis of cognitive radio networks with generalized call holding time distribution of secondary user

In cognitive radio networks (CRNs), spectrum handoff probability and expected number of spectrum handoffs are important parameters in the evaluation of network performance and design. This paper presents an analytical model for spectrum handoff probability and spectrum handoff rate for CRNs under general distribution of call holding time of secondary users (SUs). The standardized analytical forms of spectrum handoff probability and handoff rate of secondary network under negotiated scenario are derived for a complete service call duration. The effect of mobility parameters: departure rate of SUs (\(\upmu )\) and departure rate of spectrum holes (\(\uplambda )\) on spectrum handoff are also reported in this paper. Extensive results for all the proposed analytical models are obtained and presented in this paper. Analytical results show that exponential and Erlangian distribution functions are not suitable for call holding time of SU in the analysis of spectrum handoff in CRNs. Moreover, the superiority of lognormal distribution function ascertains its use for call holding time of SU in spectrum handoff estimation for better CRN performances. The Monte-Carlo simulation is also performed for spectrum handoff probability to validate the analytical model.     

Heterogeneous Wireless Networks: Configuration and Vertical Handoff Management

Vertical handoff is one of the most important issues for the next generation heterogeneous wireless networks. However, in many situations, unbeneficial vertical handoffs occur across intersystem heterogeneous networks cause network performance degradation. Therefore, we propose a novel configuration architecture that can be deployed in the next generation of wireless networks. Second, we propose a predictive and adaptive Vertical Handoff Decision Scheme that optimizes the handoff initiation time as well as selection of the most optimal network. The proposed vertical handoff decision algorithm considers the technology type as well as the Signal to Interference Ratio (SIR), the Mobile Station (MS) velocity, the user preferences, the applications requirements and the terminal capabilities as the most important factors to make vertical handoff decision. In order to minimize handoff costs, the proposed decision algorithm uses the dwell timer concept. The handoff costs are analyzed in terms of unnecessary and unbeneficial handoffs rate.The simulation results show that the reduction of unnecessary handoffs proposed in our vertical handoff decision scheme reduces the handoff blocking probability, the packets loss rate and the handoff overhead     

Performance analysis of fractional guard channel policies in mobile cellular networks

In this letter, recursive formulas for the new call blocking and handoff failure probabilities for Fractional Guard Channel (FGC) policies in cellular networks are derived. The effect of users' mobility on the maximum system capacity achieved with the Guard Channel (GC), the Limited Fractional Guard Channel (LFGC), and the Uniform Fractional Guard Channel (UFGC) strategies is then evaluated. Results show that maximum system capacity decreases exponentially as the mean cell dwell time decreases and that the relative capacity gain of each scheme depends on the mean cell dwell time. It was also found that LFGC outperforms GC and UFGC under any mobility condition.     

基于运动趋势的模糊逻辑垂直切换算法

随着无线异构网络的融合,移动性管理技术成为其关键问题,而切换管理又是移动性管理的重要部分。针对垂直切换管理提出了一种基于运动趋势的模糊逻辑垂直切换算法。算法分为预判定、模糊逻辑控制及切换判决3个过程。首先,在预判定阶段根据MN的运动趋势及接收信号强度滤除掉不适宜接入WLAN的网络信息,从而有效减少不必要的数据量和系统开销;其次,将接收信号强度、网络的可用带宽和网络开销送入模糊逻辑控制器,通过参数的归一量化最终得到网络综合性能值(VCPN);最后,通过综合考虑VCPN和驻留时间来进行网络切换判决。仿真结果显示,该算法能够有针对性地做出切换判决,有效消除乒乓效应,提高网络切换性能。     

Performance analysis of a preemptive and priority reservation handoff scheme for integrated service-based wireless mobile networks

We propose an analytical model for integrated real-time and non-real-time services in a wireless mobile network with priority reservation and preemptive priority handoff schemes. We categorize the service calls into four different types, namely, real-time and non-real-time service originating calls, and real-time and non real-time handoff service request calls. Accordingly, the channels in each cell are divided into three parts: one is for real-time service calls only, the second is for non-real-time service calls only, and the last one is for overflow of handoff requests that cannot be served in the first two parts. In the third group, several channels are reserved exclusively for real-time service handoffs so that higher priority can be given to them. In addition, a realtime service handoff request has the right to preempt non-real-time service in the preemptive priority handoff scheme if no free channels are available, while the interrupted non-real-time service call returns to its handoff request queue. The system is modeled using a multidimensional Markov chain and a numerical analysis is presented to estimate blocking probabilities of originating calls, forced termination probability, and average transmission delay. This scheme is also simulated under different call holding time and cell dwell time distributions. It is observed that the simulation results closely match the analytical model. Our scheme significantly reduces the forced termination probability of real-time service calls. The probability of packet loss of non-real-time transmission is shown to be negligibly small, as a non-real-time service handoff request in waiting can be transferred from the queue of the current base station to another one.     

Modeling node mobility for reliable packet delivery in mobile ip networks

In this paper, we analyze node mobility for reliable packet delivery in mobile IP networks. In mobile IP, packets destined to roaming nodes are intercepted by their home agents and delivered via tunneling to their care of addresses (CoA). A mobile node may roam across multiple subnets. At each boundary crossing, a handoff is initiated such that the CoA is updated and a new tunnel is established. We consider both basic mobile IP handoff and smooth handoff. We find that reliable packet delivery in mobile IP networks can be modeled as a renewal process, because the retransmission over a new tunnel after each boundary crossing is independent of the previous history. We then derive the probability distribution of boundary crossings for each successful packet, based on which the packet reliable delivery time can be obtained. Our analytical model is derived based on a general distribution of residence time in a subnet and a general distribution of successful retransmission attempts in each subnet. The results can be readily applied to any distributions for both items. We also provide numerical examples to calculate the probability distribution of boundary crossings, and conduct simulations to validate our analytical results     

Channel reservation for handoff calls in a PCS network

Some new performance measures and channel reservation for handoff calls for maximizing the service provider's revenue in a personal communications service (PCS) network, with general cell residence time and general requested call holding time, are investigated. Here, each cell within the PCS network consists M channels, but only when at least m+1 (0⩽m<μ) channels are available will a new originating call be accepted. A handoff attempt is unsuccessful if no channel in the target cell is available. Some new performance measures of the system such as the modified offered load (MOL) approximations of the blocking probability of new and handoff calls, the distribution and the mean actual call holding time of a new call and related conditional distributions and the expectations, as well as the boundary of the mean of the actual call holding time of an incomplete call and a complete call are obtained. A necessary and sufficient condition for maximizing the provider's revenue is achieved for any general cost structure if it is an increasing function of the actual call holding time. In order to be fair to the customers with incomplete call and complete call, two different kinds of holding costs are considered for the different customers. In both situations, the optimal controlling value m of handoff priority is obtained by maximizing the service provider's revenue     

Stochastic control of path optimization for inter-switch handoffsin wireless ATM networks

One of the major design issues in wireless ATM networks is the support of inter-switch handoffs. An inter-switch handoff occurs when a mobile terminal moves to a new base station connecting to a different switch. Apart from resource allocation at the new base station, inter-switch handoff also requires connection rerouting. With the aim of minimizing the handoff delay while using the network resources efficiently, the two-phase handoff protocol uses path extension for each inter-switch handoff, followed by path optimization if necessary. The objective of this paper is to determine when and how often path optimization should be performed. The problem is formulated as a semi-Markov decision process. Link cost and signaling cost functions are introduced to capture the tradeoff between the network resources utilized by a connection and the signaling and processing load incurred on the network. The time between inter-switch handoffs follows a general distribution. A stationary optimal policy is obtained when the call termination time is exponentially distributed. Numerical results show significant improvement over four other heuristics     

A Robust Analytical Model of Mobile IP Handoff with Multiple Traffic Profiles

Mobile IP has been developed to provide the continuous information network access to mobile users. The performance of Mobile IP mobility management scheme is dependent on traffic characteristics and user mobility. Consequently, it is important to assess this performance in-depth through these factors. This paper introduces a novel analytical model of handoff management in mobile IP networks. The proposed model focuses on the effect the traffic types and their frame error rates on the handoff latency. It is derived based on general distribution of both successful transmission attempts and the residence time to be applicable in all cases of traffic characteristics and user mobility. The impact of the behavior of wireless connection, cell residence time, probability distribution of transmission time and the handoff time is investigated. Numerical results are obtained and presented for both TCP and UDP traffics. As expected, the reliability of TCP leads to higher handoff latency than UDP traffic. It is shown that, higher values of FER increase the probability of erroneous packet transfer across the link layer. A short retransmission time leads to end the connection most likely in the existing FA; however a long retransmission time leads to a large delivery time. The proposed model is robust in the sense that it covers the impact of all the effective parameters and can be easily extended to any distribution.     

A Homogeneous PCS network with Markov Call Arrival Process and Phase Type Cell Residence Time

In this paper, the arrival of calls (i.e., new and handoff calls) in a personal communications services (PCS) network is modeled by a Markov arrival process (MAP) in which we allow correlation of the interarrival times among new calls, among handoff calls, as well as between these two kinds of calls. The PCS network consists of homogeneous cells and each cell consists of a finite number of channels. Under the conditions that both cell's residence time and the requested call holding time possess the general phase type (PH) distribution, we obtain the distribution of the channel holding times, the new call blocking probability and the handoff call failure probability. Furthermore, we prove that the cell residence time is PH distribution if and only if the new call channel holding time is PH distribution; or the handoff call channel holding time is PH distribution; or the call channel holding time is PH distribution;provided that the requested call holding time is a PH distribution and the total call arrival process is a MAP. Also, we prove that the actual call holding time of a non-blocked new call is a mixture of PH distributions. We then developed the Markov process for describing the system and found the complexity of this Markov process. Finally, two interesting measures for the network users, i.e., the duration of new call blocking period and the duration of handoff call blocking period, are introduced; their distributions and the expectations are then obtained explicitly.     

The Complementary Use of 3G WCDMA and GSM/GPRS Cellular Radio Networks

The traffic performance of integrated 3G wide-band code division multiple access (WCDMA) and GSM/GPRS network is evaluated. This type of network links two cellular radio systems which have different set of frequency bands and the same coverage size. The base station of 3G WCDMA is installed on an existing GSM/GPRS site. Dual-mode mobile terminals use handoff to establish calls on the better system. The soft handoff or inter-frequency hard handoff occurs when mobile terminals of 3G WCDMA or GSM/GPRS move between two adjacent cells, respectively. The inter-system hard handoffs are used between 3G WCDMA and GSM/GPRS systems. The data rate conversions between different systems, soft handoff region size, multiple data rate multimedia services, and the effect of the mobile terminal mobility on the user mean dwell time in each system are considered in the study. The simulation results demonstrate that a great traffic performance improvement on the complementary use of 3G WCDMA and GSM/GPRS cellular radio networks compared with the use of GSM/GPRS cellular radio networks. When high-data rate transmission is chosen for low-mobility subscribers, both the handoff failure probability, and carried traffic rates increase with the new call generation rate. However, both rates decrease conversely with the increasing new call generation rate as soon as the new call generation rate exceeds a critical value. This causes the integrated networks saturation. The higher mean speed for the mobile terminals produces lower new call blocking probabilities and total carried traffic. The new call blocking probabilities and total carried traffic increase with the size of the soft handoff region.     

蜂窝重叠情况下移动IP切换延时分析

从理论上首次对移动 IP 切换过程中的切换延时和乱序分组进行了建模和分析,分别得到了各自的概率分布公式。并且根据这个结果,优化了重叠区域的半径。结果表明:本模型准确地描述了移动 IP 的切换行为,它对于评价移动 IP 的切换性能非常有用。     

高铁场景下C网切换时长的研究

在高速铁路场景下,列车时速最高可达到350 km/h,留给扇区间切换的时间很短。通过对普速、高速、高铁三种场景下码分多址（CDMA）系统切换时长进行比较研究,得出：软切换、更软切换时长随着移动台移动速度的增加有所变长;切换加比切换去所用的切换时长要长;从软切换和更软切换时长的分析来看,建议采用400 ms作为软切换时长的参考值,而350 ms作为更软切换时长的参考值。最后,提出高铁场景下小区重叠覆盖区域大小的建议。     

LEO卫星通信系统覆盖时间和切换次数分析

针对近地轨道(LEO)卫星移动通信系统,该文提出一种分析不同用户覆盖时间及切换次数的方法。在充分考虑地面用户随机分布特性的基础上,建立了卫星和波束对随机用户的覆盖时间统计模型,推导了星间切换及波束间切换平均次数下限值的计算方法。最后通过铱星通信系统模型(包括铱星星座参数,地面站参数和阵列天线波束模型)对该方法进行了仿真分析,结果显示该方法能很好地近似用户随机覆盖时间统计特性及平均切换次数的下限值。