Analytical models for call blocking and dropping in sectorized cellular networks with fractional frequency reuse

In this paper, we construct mathematical models to analyze the probabilities of new call blocking and handoff call (HC) dropping for a sectorized cellular network with fractional frequency reuse (FFR). Because a sectorized FFR network (SFN) consists of two areas, the super group (SG) and the regular group (or sectors), three different types of HCs may happen when a mobile station (MS) moves from the SG to a sector, from a sector to the SG, or from one sector to another sector. To characterize three types of HCs, we first derive the area transition probability, which is defined as the reciprocal of MS's average residence time in an area (i.e., sector or SG). Moreover, we construct the model of Markov chains and derive the state transition rates. Then on the basis of the stationary probabilities of Markovian states, we derive the three types of blocking probabilities of new calls and two types of dropping probabilities of HCs. Finally, we conduct extensive numerical simulations. From the results of numerical simulations, we reveal two important rules for choosing the optimal radius of the SG, with which the system blocking and dropping probability can be effectively minimized. Copyright © 2014 John Wiley & Sons, Ltd.     

New call blocking versus handoff blocking in cellular networks

In cellular networks, blocking occurs when a base station has no free channel to allocate to a mobile user. One distinguishes between two kinds of blocking, the first is called new call blocking and refers to blocking of new calls, the second is called handoff blocking and refers to blocking of ongoing calls due to the mobility of the users. In this paper, we first provide explicit analytic expressions for the two kinds of blocking probabilities in two asymptotic regimes, i.e., for very slow mobile users and for very fast mobile users, and show the fundamental differences between these blocking probabilities. Next, an approximation is introduced in order to capture the system behavior for moderate mobility. The approximation is based on the idea of isolating a set of cells and having a simplifying assumption regarding the handoff traffic into this set of cells, while keeping the exact behavior of the traffic between cells in the set. It is shown that a group of 3 cells is enough to capture the difference between the blocking probabilities of handoff call attempts and new call attempts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analytical expressions for blocking and dropping probabilities for mobile streaming users in wireless cellular networks

We consider a wireless cellular network serving streaming traffic. We study in this context the effect of the users mobility on their quality of service (QoS). If the arrival of a new user violates the capacity constraint, then his call is blocked. If the user is first admitted but the capacity constraint is violated later when he attempts to move, then his call is dropped. The blocking and dropping probabilities are the main QoS indicators in this model called forced termination (FT). We introduce an alternative model, called transitions backtrack (TB), where a user backtracks when his motion violates the capacity constraint. In this model, a relevant QoS indicator is the number of times the user backtracks called number of motion blocking per call. We propose some explicit expressions for the above QoS indicators as functions of the mean user speed. These expressions are validated by simulations. In particular we observe that the dropping probability in the FT model is well approximated by the number of motion blocking per call in the TB model which is expressed analytically.     

Analysis of call blocking probability in TDM/WDM networks withtransparency constraint

In this letter we devise and validate by simulation an analytical model to study the performance of TDM/WDM networks using a three-stage switching architecture as an abstract model. We consider the transparency property as a constraint: a new incoming call can be accepted only without modifying the routing of previously accepted calls. We concentrate on the analysis of the call blocking probability by varying the traffic pattern and the configuration of the switching architecture. We show that a very good agreement is obtained between simulation and analytical results     

Dynamic resource allocation in mobile heterogeneous cellular networks

User mobility is a challenging issue in macro and femto cellular networks for the fifth-generation and newer mobile communications due to the time-varying interference and topology experienced. In this paper, we consider an OFDMA-based two-tier network with one macro cell and several femto cells, wherein each macro user and/or femto user can leave or enter its serving cell frequently, referred to as user mobility. A resource allocation problem with different rate requirements of mobile users is then formulated. Assuming well knowledge of the user locations and the channel state information, we propose a dynamic algorithm with static and dynamic parts for a better trade-of between computational complexity and system throughput. The static algorithm, named interference weighted cluster algorithm in this paper, is based on the graph theory to cluster the femtocells by minimizing the interference between clusters, while the dynamic algorithm is to deal with the user mobility by sharing the resource blocks under the constraints of rate requirements. Numerical results are demonstrated to show the effectiveness of the proposed dynamic resource allocation algorithm in terms of capacity, computational time, and outage probability.

     

State-dependent control of call arrivals in layered cellular mobile networks

Layered cellular mobile networks have been widely proposed as a way of accommodating traffic growth in mobile communications. There is a need, however, to give some form of priority to handover attempts over fresh call attempts to ensure that handovers are fast and reliable. A class of call control policies with state-dependent control of fresh call arrivals is considered for this purpose. A modified version of the Value Iteration Algorithm is used to solve a Markov decision model for the optimal call control policy. The network blocking performance under optimal state-dependent control is compared with the performance under a much simpler channel reservation policy for a model of a cellular sub-network. The channel reservation policy is shown to perform nearly as well as the optimal policy at lower loads, where fresh call blocking is less than 5%, indicating that it is both an effective and an efficient method for ensuring good handover performance.     

Outage probability improvement using a conditional cooperative mechanism in heterogeneous wireless networks

The self-similarity nature of network traffic has been discovered to be a ubiquitous phenomenon in communication networks; meanwhile, heterogeneous wireless cooperative relay networks have received considerable interests in both academia and industry fields. The mechanism of cooperative relay selection is very essential for the design of heterogeneous wireless relay networks. In this paper, based on the self-similar nature of network traffic in heterogeneous wireless cooperative relay network, we propose a new relay selection mechanism called conditional relay selection which can effectively decrease the system outage probability. Compared to conventional relay selection mechanism, the proposed mechanism considers the traffic queue condition of the relay nodes rather than just comparing the signal-to-noise ratio (SNR). Through extensive comparisons with traditional cooperative relay selection mechanisms, the proposed scheme can significantly improve the system outage probability.     

Efficient call admission control for heterogeneous services inwireless mobile ATM networks

An efficient call admission control scheme for handling heterogeneous services in wireless ATM networks is proposed. Quality-of-service provisioning of jitter bounds for constant bit rate traffic and delay bounds for variable bit rate traffic is used in the CAC scheme to guarantee predefined QoS levels for all traffic classes. To reduce the forced handoff call dropping rate, the CAC scheme gives handoff calls a higher priority than new calls by reserving an appropriate amount of resources for potential handoff calls. Resource reservation in the CAC scheme makes use of user mobility information to ensure efficient resource utilization. Simulation results show that the proposed CAC scheme can achieve both low handoff call dropping rate and high resource utilization     

Access probability optimization for streaming media transmission in heterogeneous cellular networks

FemtoCaching technology, aiming at maximizing the access probability of streaming media transmission in heterogeneous cellular networks, is investigated in this paper. Firstly, five kinds of streaming media deployment schemes are proposed based on the network topology and the relationship between users and streaming media. Secondly, a matching algorithm for adaptive streaming media deployment is proposed, where the FemtoCaching can be adjusted dynamically. Thirdly, a joint problem is formulated combined with the channel assignment, the power allocation, and the caching deployment. To address this problem, we propose a joint optimization algorithm combining matching algorithm and genetic algorithm to maximize the access probability of streaming media transmission. Simulation experiments demonstrate that: (1) the average access probability of all users accessing streaming media in the network based on the proposed algorithm compared with recent works can be greatly improved, and (2) the performance increases with increasing the number of channels and the storage capacity of micro base stations, but decreases with increasing the number of users.

     

Heuristic RAT selection policy to minimize call blocking probability in next generation wireless networks

In next generation wireless network (NGWN) where multiple radio access technologies (RAT) co‐exist, a joint call admission control (JCAC) algorithm is needed to make a RAT selection decision for each arriving call. RAT selection policy has a significant effect on the overall new call blocking probability in the network. We propose a heuristic RAT selection policy to minimize new call blocking probability in NGWN. The proposed JCAC scheme measures the arrival rate of each class of calls in the heterogeneous wireless network. Based of the measured values of the arrival rates and using linear programming technique, the JCAC scheme determines the RAT selection policy that minimizes overall call blocking probability in the heterogeneous wireless network. Using Markov decision process, we develop an analytical model for the JCAC scheme, and derive new call blocking probability, handoff call dropping probability (HCDP), and call incompletion probability (CIP). Performance of the proposed scheme is compared with the performance of other JCAC scheme. Simulation results show that the proposed scheme reduces new call blocking probability, HCDP, and CIP in the heterogeneous wireless network. Copyright © 2009 John Wiley & Sons, Ltd.     

Distributed call admission control in mobile/wireless networks

The major focus of this paper is distributed call admission control in mobile/wireless networks, the purpose of which is to limit the call handoff dropping probability in loss systems or the cell overload probability in lossless systems. Handoff dropping or cell overload are consequences of congestion in wireless networks. Our call admission control algorithm takes into consideration the number of calls in adjacent cells, in addition to the number of calls in the cell where a new call request is made, in order to make a call admission decision. This is done by every base station in a distributed manner without the involvement of the network call processor. The admission condition is simple enough that the admission decision can be made in real time. Furthermore, we show that our distributed call admission control scheme limits the handoff dropping or the cell overload probability to a predefined level almost independent of load conditions. This is an important requirement of future wireless/mobile networks with quality-of-service (QoS) provisioning     

On blocking probability of multicast networks

Multicast is a vital operation in both broad-band integrated services digital networks (BISDN) and scalable parallel computers. We look into the issue of supporting multicast in the widely used three-stage Clos network or υ(m, n, r) network. Previous work has shown that a nonblocking υ(m, n, r) multicast network requires a much higher network cost than a υ(m, n, r) permutation network. However, little has been known on the blocking behavior of the υ(m, n, r) multicast network with only a comparable network cost to a permutation network. We first develop an analytical model for the blocking probability of the υ(m, n, r) multicast network and then study the blocking behavior of the network under various routing control strategies through simulations. Our analytical and simulation results show that a υ(m, n, r) network with a small number of middle switches m, such as m=n+c or dn, where c and d are small constants, is almost nonblocking for multicast connections, although theoretically it requires m⩾Θ(n(log r/log log r)) to achieve nonblocking for multicast connections. We also demonstrate that routing control strategies are effective for reducing the blocking probability of the multicast network. The best routing control strategy can provide a factor of two to three performance improvement over random routing. The results indicate that a υ(m, n, r) network with a comparable cost to a permutation network can provide cost-effective support for multicast communication     

On call admission control in DS/CDMA cellular networks

Analytical models are proposed for various direct sequence code-division multiple-access (DS/CDMA) call admission control schemes. Many mathematical call admission models for DS/CDMA cellular networks have been proposed. However, they have shortcomings. First, by ignoring the stochastic traffic load variation or call blocking effect, they failed to sufficiently characterize the second moment of other-cell interference. This leads to inaccurate analysis of a real network. Second, the optimal control parameters were often obtained through an exhaustive search which was very time consuming. Finally, the estimation of system capacity in previous models was obtained by using a simple one-slope path-loss propagation model. However, it is well known that a two-slope path loss propagation model is needed in a line-of-sight (LOS) microcell propagation environment. We propose an analytical model for call admission to overcome these drawbacks. In addition, we combine a modified linear programming technique with the built analytical model to find better call admission control schemes for a DS/CDMA cellular network     

A teletraffic performance study of mobile LEO-Satellite cellular networks with gamma distributed call duration

In this paper, the authors develop an analytical model to study the performance of a mobile low earth orbiting (LEO) satellite cellular network. The model assumes that the call duration has a gamma distribution and considers the effect of system parameters such as the number of channels per cell, the number of channels reserved for the handoff, and the cell residence time, on the teletraffic performance of the system. The quality of service (QoS) measures studied in this paper include new call blocking probability, handoff failure probability, premature call-termination probability (CTP), and call dropping probability (CDP). Based on the causal central limit theorem, the authors use a two-parameter gamma distribution to approximate the distribution of the sum of the residence times in the cells. The analytical model presented in this paper may be used with any call-holding-time distribution. The analytical results are validated by a computer simulation.     

Traffic analysis of heterogeneous mobile cellular networks using “wrap-up” cell structure

In this paper, we develop a tool for evaluating performance of a heterogeneous mobile network under different traffic conditions. The traffic condition is specified in a cluster of seven heterogeneous base stations, and “wrap-up” cell structure is applied to account for the traffic that crosses the boundary of the cluster. The performance of the network is specified in metrics which can be computed using the algorithm developed. These metrics relate to call rejection, i.e. the blocking of new calls, and the termination of handoff calls, as well as the carried traffic i.e. the expected number of ongoing calls in a station. These metrics are either measured for a single base station in a cluster, or measured for the average over the whole cluster. We apply the algorithm to some hypothetical data and present the numerical results. We also consider approximating a heterogeneous model with a simpler homogeneous model. Through some numerical results, we demonstrate the magnitude of errors that could result in the approximation.     

Evaluation of call blocking probabilities in LEO satellite networks

In this paper, we present a new method for calculating call blocking probabilities (CBPs) in a low Earth orbit satellite network that carries voice calls. The calculation of the CBPs uses the Erlang‐B formula, but the traffic intensity has been modified to take into the time and location in which the calls are made. Copyright © 2009 John Wiley & Sons, Ltd.     

Point-to-point blocking probability in switching networks with reservation

In this paper reservation algorithms for multi-service switching networks are proposed. Two new approximate methods of the point-to-point blocking probability calculation in the multi-service switching networks are also presented in the paper. These methods can be used for blocking calculation in the switching networks with and without reservation. Special attention is paid to the method for determining the effective availability, which directly affects the accuracy of the final results. The results of analytical calculations are compared with the data of digital simulation of switching networks without and with reservation.     

Estimating the blocking probability in wavelength-routed optical networks

In this work, a new methodology to compute the blocking probability in wavelength-routed optical networks is presented. The proposal is based on an interactive procedure, named Interactive Matrix Methodology (IMM), that executes actualization of the network traffic distribution in order to reach a precise blocking performance. The IMM updates an initial network link load continuously and computes the blocking probability for each output link considering that the traffic among the links is dependent and related with all links and nodes in the network, not only with all links in a given path or route. The simulation results obtained in the same conditions and in several optical network scenarios match very well with the theoretical approximation achieved with this methodology. The advantage of this theoretical methodology is to be fast, accurate and applicable in low load regions, where a discrete event simulation is not precise. Furthermore, this method can be used to compute the estimative of blocking probabilities per node and in the network, including the cases where the number of wavelengths is different on each node.     

Real-time traffic support in heterogeneous mobile networks

Multi-hop mobile wireless networks have been proposed for a variety of applications where support for real-time multimedia services will be necessary. Support for these applications requires that the network is able to offer quality of service (QoS) appropriate for the latency and jitter bounds of the real-time application constraints. In this paper, we analyze the primary challenges of realizing QoS in mobile wireless networks with heterogeneous devices and propose a QoS framework for real-time traffic support. We address the problem in three ways: estimate the path quality for real-time flows, mitigate the impact of node heterogeneity on service performance, and reduce the impact of interfering non-real-time traffic. Specifically, our proposed QoS framework first utilizes a call setup protocol at the IP layer to discover paths for real-time flows, as well as to perform admission control by accurate service quality prediction. The underlying routing protocol also enables transparent path selection among heterogeneous nodes to provide stable paths for real-time traffic delivery. We then use a prioritized MAC protocol to provide priority access for flows with real-time constraints to reduce interference from unregulated non-real-time traffic. We foresee the utility of our proposed solution in heterogeneous mobile networks, such as campus or community-wide wireless networks. In these environments, resource-rich or fixed wireless routers may be leveraged to achieve better service quality when heterogeneity of node capability and movement is significant. Through experimental results, we demonstrate the utility and efficiency of our approach. Yuan Sun received her Ph.D. from the Department of Computer Science at the University of California, Santa Barbara in 2005. She worked with Prof. Elizabeth Belding-Royer in the MOMENT Lab. Her thesis work focused on providing QoS for mobile networks. Dr. Sun is currently employed at Google. Elizabeth M. Belding-Royer is an Associate Professor in the Department of Computer Science at the University of California, Santa Barbara. Elizabeth’s research focuses on mobile networking, specifically ad hoc and mesh networks, multimedia, monitoring, and advanced service support. She is the founder of the Mobility Management and Networking (MOMENT) Laboratory (moment.cs.ucsb.edu) at UCSB. Elizabeth is the author of over 50 papers related to mobile networking and has served on over 40 program committees for networking conferences. Elizabeth served as the TPC Co-Chair of ACM MobiCom 2005 and IEEE SECON 2005, and is currently on the editorial board for the IEEE Transactions on Mobile Computing. Elizabeth is the recipient of an NSF CAREER award, and a 2002 Technology Review 100 award, awarded to the world’s top young investigators. See ebelding for further details. Xia Gao is currently a Staff Engineer at Ubicom. He received his Ph.D of ECE from the University of Illinois at Urbana-Champaign in 2001. Before joining Ubicom, he had worked in DoCoMo Communications Laboratory for 4 years where he conducted research on 3G-4G wireless communication system and handset technologies and WiFi systems. He has published more than 30 conference and journal papers. He has chaired several International conferences and served as TPC members for many others. He is a member of IEEE and a honored member of Sigma Xi. James Kempf is a Research Fellow at DoCoMo USA Laboratories. He holds a Ph.D. from the University of Arizona, Tucson, AZ. Previously, James worked at Sun Microsystems for 13 years, and contributed to numerous research projects involving wireless networking, mobile computing, and service discovery. James is a former member of the Internet Architecture Board, and co-chaired the SEND and Seamoby IETF Working Groups. James continues to be an active contributor to Internet standards in the areas of security and mobility for next generation, Internet protocol-based mobile systems.