Call Blocking Probability Research Articles

Blocking probabilities in mobile communications networks with time-varying rates and redialing subscribers

Call-blocking probabilities are among the key performance measures in mobile communications networks. For their analysis, mobile networks can be modelled as networks of Erlang loss queues with common capacity restrictions dictated by the allocation of frequencies to the cells of the network. However, due to the time-varying load offered to the cells of such networks, blocking probabilities usually cannot be obtained in closed form. The relation between networks of Erlang loss queues and networks of infinite server queues, for which the time-dependent occupancy distribution is multidimensional Poisson, suggests to use that distribution as approximate distribution for the network of Erlang loss queues. This paper extends this so-called Modified Offered Load (MOL) approximation to networks of Erlang loss queues, and also allows subscribers that find their call blocked to redial to continue their call. For GSM networks operating under Fixed Channel Allocation, it is shown that blocking probabilities are increasing in the redial rates so that the MOL approximation that is most accurate for maximal redial rates turns out to be fairly accurate for the resulting upper bound for blocking probabilities. The accuracy is explicitly evaluated in an application of the results towards blocking probabilities in a hot spot travelling along a road through a GSM network.

Computing blocking probabilities in multiclass wavelength-routing networks with multicast calls

We present an approximate analytical method to compute efficiently the call-blocking probabilities in wavelength-routing networks with multiple classes of both unicast and multicast calls. Our approach involves the following steps. We start with an approximate solution to a linear single-class unicast network which we developed earlier. Next, all classes of calls on a particular route are aggregated to give an equivalent single-class model. We then extend the path decomposition algorithms that we have developed for single-class networks to handle mesh networks with multiple classes of calls. We show how to use these path decomposition algorithms to decompose large networks with multicast paths into smaller subsystems with only linear paths, which, in turn, are solved by the product-form approximation algorithm. We also consider a state-dependent Poisson arrival process for multicast calls which is more accurate in capturing the behavior of these calls.

Blocking probabilities in circuit-switched wavelength division multiplexing networks under multicast service

We evaluate the call-blocking probabilities in optical networks which support multicast (or multipoint) service. Due to the difficulty of the problem, we restrict our attention to the case of completely connected networks, for which the blocking probabilities act as a lower bound for other topologies. Nodes may, or may not be equipped with wavelength converters. In both cases, routing can be done either directly, using one hop, or indirectly, and even in the latter case the number of hops can be either restricted to two hops, or unrestricted. We evaluate the blocking probability by first estimating the load offered to each link, and then use the iterative-reduced load approximation method to refine this estimate. Using this estimate, we then obtain the probabilities of blocking and success. Numerical examples are presented, and are compared to simulation.

Optimization for adaptive bandwidth reservation in wireless multimedia networks

In future wireless multimedia networks, user mobility management for seamless connection regarding realtime multimedia applications is one of the most important problems. In this paper we propose an opportunity-cost concept-based approach for adaptive bandwidth reservation with admission control for handover calls utilizing network traffic information. Excessive reservation guarantees low blocking probability of handover calls at the cost of high blocking probability of new calls. According to our survey, however, it may degrade bandwidth utilization while no prioritization for handover admissions degrades quality of service (QoS) for ongoing calls. We consider both QoS assurance and bandwidth utilization in order to optimize the amount of bandwidth to reserve for handover admissions. We believe that our scheme could be utilized as a guideline for cost-effective radio resource allocation in mobile multimedia networks.

Optimal prioritized channel allocation in cellular mobile systems

Under the cutoff priority discipline, the optimal prioritized channel allocation problem is formulated, which minimizes the weighted average blocking probability of handoff calls while ensuring the prespecified grade of service for new calls and the co-channel interference constraints. We use the concept of pattern to deal with the problem more conveniently. Using Lagrangean relaxation and subgradient optimization techniques, we obtain high-quality solutions with information about their deviations from true optimal solutions. Computational experiments show that our method works very well. Scope and Purpose Channel allocation is one of the most important problems in the design of cellular mobile systems. Since the number of cells of forthcoming networks will increase rapidly, this problem will be of even greater importance in the future. In cellular mobile systems, a new channel should be assigned by the new base when a call enters an adjacent cell. It provides continuation of ongoing calls as the user travels across cell boundaries, and is called handoff. The handoff call is forced to terminate before completion if there are no channels available in the new cell. However, in many practical situations, the blocking of a handoff call attempt is critical since it will result in a disconnection of the call in the middle of conversation. Thus, for reducing the blocking probability of handoff calls, several algorithms based on the cutoff priority scheme have been introduced in the literature. In the cutoff priority scheme, priority is given to handoff calls by exclusively reserving some channels called guard channels for them. In this article, we formulate a prioritized channel allocation problem under the cutoff priority scheme in general multicell environments, and suggest an efficient algorithm to solve that problem.

Output and delay process analysis for slotted CDMA wireless communication networks with integrated voice/data transmission

This paper presents the output and delay process analysis of integrated voice/data slotted code division multiple access (CDMA) network systems with random access protocol for packet radio communications. The system model consists of a finite number of users, and each user can be a source of both voice traffic and data traffic. The allocation of codes to voice calls is given priority over that to data packets, while an admission control, which restricts the maximum number of codes available to voice sources, is considered for voice traffic so as not to monopolize the resource. Such codes allocated exclusively to voice calls are called voice codes. In addition, the system monitoring can distinguish between silent and talkspurt periods of voice sources, so that users with data packets can use the voice codes for transmission if the voice sources are silent. A discrete-time Markov process is used to model the system operation, and an exact analysis is presented to derive the moment generating functions of the probability distributions for packet departures of both voice and data traffic and for the data packet delay. For some cases with different numbers of voice codes, numerical results display the correlation coefficient of the voice and data packet departures and the coefficient of variation of the data packet delay as well as average performance measures, such as the throughput, the average delay of data packets, and the average blocking probability of voice calls.

Performance evaluation of telecommunication systems with forcible cutoff control scheme

The rapid growth of computer-communication services means that telephone-conversation traffic must compete for system resources with computer-communication traffic carried by dial-up connections to the Internet or intranets over public telephone switching networks. The traffic characteristics differ for the two types of service; for example, the mean holding time and peak traffic periods are different. However, because dial-up connection calls occupy circuit lines for a long time, the grade of service (GoS) of telephone-conversation calls may deteriorate during periods of peak demand. Another problem is that since a telephone switching network is dimensioned to satisfy the required GoS for telephone calls during peak demand periods, there will be surplus resources, and a significant opportunity cost, during off-peak periods. One way to efficiently use these surplus switching-network resources is to offer fixed-cost best-effort dial-up connection service during off-peak periods for telephone traffic. This also makes the demand for dial-up connections less likely to affect the GoS of telephone-conversation calls during peak periods. We propose a priority control scheme for such an off-peak service. This scheme works as follows in a telephone switching system where both high-priority telephone-conversation calls and low-priority dial-up connection calls are offered. When a call arrives at the system and there are adequate resources available for an ordinary telephone-conversation call, a high-priority telephone call or a low-priority dial-up connection call can be connected. However, if a high-priority call arrives at the system and there are not enough resources available to allow connection, an already connected dial-up connection call is forcibly cut off to enable connection of the high-priority telephone call, and thus guarantee the GoS of telephone calls. We evaluate the performance of a telecommunication system based on this scheme by using a Markov model. We derive the call-blocking probabilities for both call types and the ratio of the amount of traffic that is forcibly cut off to the amount of offered traffic in the system, and show calculated results. We also discuss some guidelines for offering services using this scheme. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(6): 78–87, 2000

DIDA: a Distributed, Dynamic and Adaptive VP bandwidth management scheme for ATM networks

Virtual Path (VP) provisioning has gained wide acceptance as an effective resource management technique for improving transmission efficiency in ATM networks. VP bandwidth management in particular could absorb short-term fluctuations in traffic and improve call-blocking probability. In this paper, we propose a distributed and dynamic VP bandwidth management scheme called DIDA, which absorbs medium scale traffic fluctuations and improves the call blocking probability. The proposed scheme incorporates an adaptive traffic estimator that is suitable even for VPs carrying heterogeneous traffic. Simulation studies conducted on DIDA show that the adaptive estimator of DIDA improves the call blocking probability in an ATM network, with VPs carrying heterogeneous traffic while maintaining fairness among different call types at the same time.

Proposal of Asynchronous Time Division Multiple Access Radio HighwayUsing Chirp Multiplexing Transform

Asynchronous TDMA bus-link systems using chirp multiplexing transform (CMT) are proposed for radio highway networks to provide the flexible construction of fiber-optic radio access networks and the possibility of the universal use of these networks among future diverse radio services. The CMT equipped at the radio base station performs two functions. One is the conversion of FDM multiple radio services into signals with a TDMA format and the other is the time compression of the generated signal in order to allow asynchronous access. As a result, the proposed systems can realize the unified transmission of multiple radio services and the switching of them in the optical stage (photonic routing) in the networks according to the type of radio service. The realization of such photonic routing of the radio service would greatly benefit the goal of a seamless and universal network available to different types of radio service. The relationship between the pulse-loss probability performance and the call-blocking probability performance is theoretically analyzed. The effect on the performance of traffic partiality in the covered area and the way the performance can be improved are theoretically investigated. Finally, one of the ways to determine the network size covered by a bus link and the number of connected radio base stations is introduced.

A path decomposition approach for computing blocking probabilities in wavelength-routing networks

We study a class of circuit-switched wavelength-routing networks with fixed or alternate routing and with random wavelength allocation. We present an iterative path decomposition algorithm to evaluate accurately and efficiently the blocking performance of such networks with and without wavelength converters. Our iterative algorithm analyzes the original network by decomposing it into single-path subsystems. These subsystems are analyzed in isolation, and the individual results are appropriately combined to obtain a solution for the overall network. To analyze individual subsystems, we first construct an exact Markov process that captures the behavior of a path in terms of wavelength use. We also obtain an approximate Markov process which has a closed-form solution that can be computed efficiently for short paths. We then develop an iterative algorithm to analyze approximately arbitrarily long paths. The path decomposition approach naturally captures the correlation of both link loads and link blocking events. Our algorithm represents a simple and computationally efficient solution to the difficult problem of computing call-blocking probabilities in wavelength-routing networks. We also demonstrate how our analytical techniques can be applied to gain insight into the problem of converter placement in wavelength-routing networks.

Throughput evaluation of a satellite-switched CDMA (SS/CDMA) demand assignment system

This paper presents throughput evaluation of a satellite-switched code-division multiple-access (SS/CDMA) system which operates under demand assignment control. SS/CDMA provides both multiple access and switching to a geostationary multibeam satellite. Multiple access is resolved by space, frequency, and code division. Space division is introduced by the multibeam antennas that provide frequency reuse in each beam. The spectrum is then channelized into frequency bands where each band is accessed by code division for both the uplink and downlink. The satellite on-board performs the switching function, which is also based on compatible code-multiplexed switching. The switch may route both circuit calls and data packets which are assigned upon request. The on-board code-division switch operates under the control of a channel assignment algorithm. We provide channel assignment algorithms for optimum, suboptimum, and random switch operation. The system throughput has been evaluated for each case and compared. Performance analysis has been carried out for the case of the optimum switch scheduling. The analysis is based on a discrete-time Markovian model, and provides the call-blocking probabilities and data packet delays. Computer simulations have been used to evaluate the performance of the optimum, suboptimum, and random cases. It is shown that the circuit call-blocking probabilities achieved for these cases are almost the same. The optimum algorithm achieves the minimum data packet delay, while the performance of the suboptimum algorithm is slightly better than the random one. Furthermore, data packets may be routed via the switch with limited delays, even with a heavy load of circuit calls.

On optimal converter placement in wavelength-routed networks

Wavelength converters increase the traffic-carrying capacity of circuit-switched optical networks by relaxing the wavelength continuity constraints. We consider the problem of optimally placing a given number of wavelength converters on a path to minimize the call-blocking probability. Using a simple performance model, we first prove that uniform spacing of converters is optimal for the end-to-end performance when link loads are uniform and independent. We then show that significant gains are achievable with optimal placement compared to random placement. For nonuniform link loads, we provide a dynamic programming algorithm for the optimal placement and compare the performance with random and uniform placement. Optimal solutions for bus and ring topologies are also presented. Finally, we discuss the effect of the traffic model on the placement decision.

Handoff ordering using signal prediction priority queuing in personal communication systems

Handoffs in a mobile cellular communications environment will become an increasingly important issue as cell sizes shrink to accommodate an increasingly large demand for services. A new handoff ordering method is proposed which can be used to provide rapid handovers with a smaller percentage of dropped calls than other methods. Signal prediction priority queuing (SPPQ) is a generic queuing method which can be adapted to almost any handover technique for the benefit of decreased dropped calls. In typical personal communication systems (PCSs) environment, it is shown that for realistic call-blocking probabilities (2%-6%), SPPQ leads to about 15% fewer dropped calls compared to first-in-first-out (FIFO) queuing. This benefit comes at the expense of a slight increase (<1%) in blocked call percentage. The proposed SPPQ scheme is also compared to a previously developed method called measurement-based priority scheme (MBPS), and, based on worst case scenarios, it is shown to outperform MBPS as well.

Adaptive Control of Bandwidth Allocation and Routing in High-Speed Networks

In this paper, a real-time rearrangement policy for Virtual Paths (VPs) in a robust logical network, built on top of the physical layer of a general network, is introduced. This policy tends to recover services in case of failure, in the sense that a VP's capacity could be enlarged or decreased depending on its usage over time. End-to-end separated VPs are established beforehand, and a set of non ordered alternative paths can be used in case of unavailability of resources, in order to meet the required Quality of Service (QoS) for each class. A new adaptive bandwidth reallocation scheme is investigated, in which a reassignment of bandwidth may take place on-line, if required. To realize this scheme, a bandwidth pool is proposed to react to a high blocking probability of new incoming calls. A service separation and a route separation scheme have been chosen. The high percentage of blocking which may characterize service separation is subject to be decreased in the proposed mechanism.

Design of a power-spectrum-based ATM connection admission controller for multimedia communications

This paper proposes a power-spectrum-based connection admission controller design in asynchronous transfer mode (ATM) switches for multimedia communications. The controller contains a power-spectrum-indexed table for managing multimedia call requests, where traffic characteristics of call requests are described by the power spectrum. The power-spectrum can be obtained from the claimed traffic parameters of peak rate, mean rate, and peak rate duration; the power-spectrum has been shown to have a dominant effect on system performance. The results show that the proposed power-spectrum-based connection admission control method achieves higher system utilization and lower call-blocking probability than the equivalent-capacity allocation method.

Call blocking probabilities for dynamic and fixed assignment of a single channel in a linear cellular array

We consider the problem of assigning a single channel in a linear cellular array, and compare the call blocking probabilities for dynamic and fixed channel assignment (DCA and FCA). Our principal concern is the derivation of closed-form expressions for these blocking probabilities as a function of the array size and traffic load, assuming a Markov traffic model. The limiting behavior of the blocking probabilities for DCA and FCA relative to increasing array size and extreme traffic loads is also discussed. Moreover, it is shown that there is a unique cross-over traffic load such that DCA has a lower blocking probability than FCA for traffic loads less than the cross-over load, and vice versa.

Admission policies for integrated voice and data traffic in CDMA packet radio networks

The authors derive optimal admission policies for integrated voice and data traffic in packet radio networks employing code division multiple access (CDMA) with direct-sequence spread spectrum (DS/SS) signaling. The network performance is measured in terms of the average blocking probability of voice calls and the average delay and packet loss probability of data messages. The admission scheme determines the number of newly arrived voice users that are accepted in the network so that the long-term blocking probability of voice calls is minimized. In addition, new data arrivals are rejected if the mean delay or the packet loss probability of data exceeds a desirable prespecified level. A semi-Markov decision process (SMDP) is used to model the system operation. Then, a value iteration algorithm is used to derive the optimal admission control. Two models for the other-user interference of the CDMA system are considered: one based on thresholds and another based on the graceful degradation of the CDMA system performance, and their performance is compared. These admission policies find application in emerging commercial CDMA packet radio networks including cellular networks, personal communication networks, and networks of LEO satellites for global communications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of a cutoff priority cellular radio system with finite queueing and reneging/dropping

Queueing of new or handoff calls can minimize blocking probabilities or increase total carried traffic. This paper investigates a new cutoff priority cellular radio system that allows finite queueing of both new and handoff calls. We consider the reneging from the system of queued new calls due to caller impatience and the dropping of queued handoff calls by the system as they move out of a handoff area before being accomplished successfully. We use signal-flow graphs and Mason's formula to obtain the blocking probabilities of new and handoff calls and the average waiting times. Moreover, an optimal cutoff parameter and appropriate queue sizes for new and handoff calls are numerically determined so that a proposed overall blocking probability is minimized. >

Comparisons of channel-assignment strategies in cellular mobile telephone systems

Two novel channel-assignment strategies are proposed: the locally optimized dynamic assignment (LODA) strategy and the borrowing with directional channel-locking (BDCL) strategy. Their performance is compared with the fixed-assignment (FA) strategy (currently used on certain systems) and the borrowing with channel ordering (BCO) strategy (the strategy that has given the lowest blocking probability in previous research). Computer simulations on a 49-cell network for both uniform and nonuniform traffic showed that the average call-blocking probability of the BDCL strategy is always the lowest. The LODA performance is comparable with that of BCO under nonuniform traffic conditions but is inferior under uniform traffic conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis for spectrum efficiency in single cell trunked and cellular mobile radio

Spectrum efficiencies for single-cell trunked and cellular mobile radio systems are analyzed, taking into consideration fading circumstances and call blocking probability. Two kinds of transmit power control methods are considered. One retains area mean power at the receiver constant and the other retains local mean power constant. For single-cell trunked systems, it has been shown how spectrum efficiency is limited by the required traffic quality or permitable adjacent channel interference. A narrower channel spaced system shows superiority to wide-band systems, if an adjacent channel interference protection ratio is lower than about -40 dB and a few percent interference probability is permitted. On comparing cellular systems, superiority in spectrum efficiency is determined by the product of protection ratio and channel spacing. Call blocking probability and interference have little effect on spectrum efficiency comparison. For both systems, the two kinds of transmit power control and the two interchannel interference criteria show no significant difference between their effects on spectrum efficiency.