Handoff Calls Research Articles

Adaptive bandwidth framework for provisioning connection-level QoS for next-generation wireless cellular networks

The next generation of wireless cellular networks is expected to support real-time multimedia services with different classes of traffic and diverse bandwidth requirements. Bandwidth is a scarce resource in wireless networking that needs to be carefully allocated amid competing connections with different quality of service (QoS) requirements. In this paper, an adaptive framework for supporting multiple classes of multimedia services with different QoS requirements in wireless cellular networks is proposed. The framework combines the following components: (1) a threshold-based bandwidth allocation policy that gives priority to handoff calls over new calls and prioritizes among different classes of handoff calls by assigning a threshold to each class; (2) an efficient threshold-type call admission control (CAC) algorithm; and (3) a bandwidth adaptation algorithm (BAA) that dynamically adjusts the bandwidth of ongoing multimedia calls to minimize the number of calls receiving lower bandwidth than they had requested. Numerical results show that the proposed adaptive multimedia framework outperforms existing non-adaptive schemes in terms of the handoff call dropping probability and effective utilization.

Priority-Determined Multiclass Handoff Scheme With Guaranteed Mobile QoS in Wireless Multimedia Networks

The provision of multiclass services is gaining wide acceptance and will be more ubiquitous in future wireless and mobile systems. The crucial issue is to provide the guaranteed mobile quality of service (QoS) for arriving multiclass calls. In multimedia cellular networks, we should not only minimize the dropping rate of handoff calls, but also control the blocking rate of new calls at an acceptable level. This paper proposes a novel multiclass call-admission-control mechanism that is based on a dynamic reservation pool for handoff requests. In this paper, we propose the concept of servicing multiclass connections based on priority determination through the combined analysis of mobile movement information and the desired QoS requirements of multimedia traffic. A practical framework is provided to determine the occurrence time of handoff-request reservations. In our simulation experiments, three kinds of timers are introduced for controlling the progress of discrete events. Our simulation results show that the individual QoS criteria of multiclass traffic such as the handoff call-dropping probability can be achieved within a targeted objective and the new-call-blocking probability is constrained to be below a given level. The proposed scheme is applicable to channel allocation of multiclass calls over high-speed wireless multimedia networks.

Prioritized Handover Requests in Cellular Mobile System with Subrating for Integrated Voice/Data Traffic

Priority to hand off attempts in cellular radio network dealing with integrated traffic has proven to be one of the important issue to improve the grade of service (GOS) of such system. We propose prioritized fixed channel assignment strategy with subrating to protect the interest of handoffs in cellular radio network. To reduce the drop calls, finite buffering for handoffs of voice calls are allowed. The integrated voice/data traffic is originated from infinite population. Analytical results for the blocking probability of new and handoff attempts for each traffic group are derived by using steady state queue size distribution of the number of attempts in the system. We also derive expressions for blocking probabilities, delay probabilities and carried load etc. Since data/voice traffic users are usually, finite in numbers, finite population model has also been discussed. An iterative algorithmic procedure has been presented and validated by assigning the parameters of the system in order to compute performance measures. The optimal allocation of channels among new and handoff calls has been ascertained by formulating discrete capacity allocation problem. Numerical experiment has been performed to obtain optimum number of guard channels.

Capacity optimization in multiservice mobile wireless networks with multiple fractional channel reservation

In this paper, the multiple fractional channel reservation (MFCR) strategy for service differentiation is proposed. MFCR overcomes the integer nature of traditional channel reservation schemes (also referred to as guard channel, trunk reservation, or cutoff priority) that precludes them to achieve maximum system capacity in single- and multiservice environments. Contrary to the rest of the channel reservation schemes previously proposed in the literature on the topic, MFCR reserves, on average, real numbers of channels to prioritize new and/or handoff calls in multiple service environments. Given a set of requirements on new call blocking and forced termination probabilities for each service type, MFCR maximizes system capacity while meeting the quality of service (QoS) constraints in multiservice mobile cellular networks. It finely controls the communication service quality, by varying the average numbers of reserved channels by a fraction of one. Determining the right amount of resources (cutoff threshold or number of reserved channels) to prioritize each call type and to satisfy all QoS constraints in multiservice environments, however, is a difficult task. Selecting the optimal prioritization order is not an easy process either, as it is affected by QoS constraints, system characteristics, and resource sharing. Thus, an heuristic algorithm to determine the optimum numbers of reserved (resources) channels to achieve maximum system capacity when using the MFCR is also proposed. To our knowledge, the capacity optimization problem considering individual QoS constraints had only been addressed in single service environments. Also, a comprehensive survey on channel reservation strategies proposed in the literature has been included.

Optimizing the QoS of high speed moving terminals in cellular networks

AbstractThis paper presents a dynamic guard channel assignment technique based on a two‐layer cellular architecture which optimizes the blocking probability performance of high‐speed moving terminals (HSMT) and handoff calls of low‐speed moving terminals (LSMT), in a congested urban area. The lower layer of the proposed architecture is based on a microcellular solution, for absorbing the traffic loads of LSMT. The higher layer is based on a macro‐cell umbrella solution, for absorbing the traffic load of the HSMT. The results show that using the optimum number of channels and adjusting dynamically the number of guard channels in each layer, the blocking probability of the HSMT and the handoff blocking probability of LSMT is optimized having the minimum bad effect on the new call blocking probability of LSMT. Copyright © 2003 John Wiley & Sons, Ltd.

Channel assignment for initial and handoff calls to improve the call-completion probability

The paper focuses on how to assign channels for initial and handoff calls. Previous schemes give priority to handoff calls by queuing handoff calls, reserving some channels for handoff calls, or subrating existing calls for handoff calls. We queue both initial and handoff calls. We take this idea from derivations of the optimal value for an approximation to the call-completion probability. Our goal is to have higher call-completion probability and still keep forced-termination probability low. We propose four schemes: SFTT (single-queue, FIFO, timeout, average timeout), SPTT (single-queue, priority, timeout, average timeout), DFTS (dual-queues, FIFO, timeout, statistical TDM), and DPTS (dual-queues, priority, timeout, statistical TDM). The four schemes, along with the NPS and FIFO schemes, were simulated and compared. For the SFTT scheme, we also simulated different average timeouts for initial calls. All four proposed schemes have better call-completion probabilities than the NPS and FIFO schemes. Call-completion probabilities can be improved by implementing a priority scheme which serves the waiting call with the least remaining time first. The implementation of statistical multiplexing also has the effect of increasing call-completion probability when the average new-call arrival rates are high. However, both the priority scheme and statistical multiplexing may increase forced-termination probability.

Multimedia call admission control in mobile networks: a dynamical reservation-pool approach

The effective delivery of Multimedia traffic in next generation mobile cellular communication environment will become an increasingly important issue as cell sizes shrink to accommodate continuously large demand for high capacity. To provide the guaranteed mobile QoS for arriving multi-class calls, we should not only consider the regular latency requirement, but also minimize the dropping rate of handoff calls while at the same time controlling the blocking rate of new calls. In this paper, a new multi-class call admission control mechanism is proposed that is based on dynamically forming a reservation-pool for handoff requests. The prerequisite of this scheme is that wireless components can estimate future trajectory of mobile hosts with high degree of accuracy, which is possible in today’s increasingly improved position location techniques such as GPS. In this work, we first develop the notion of servicing various multi-class connections based on priority determined using the combined analysis of mobile movement information and the desired QoS requirements of multimedia traffic. We also provide a practical framework for determining the occurrence time of handoff request reservations. For our simulation experiments, three kinds of timers are introduced for controlling the progress of discrete events. The simulation results show that the individual QoS criteria of multi-class traffic such as the handoff call dropping probability can be achieved within a targeted objective and the new call blocking probability is constrained to be below a given level. The proposed scheme is applicable to channel allocation of multi-class calls over high-speed multimedia wireless ATM networks.

Resource management in LEO satellite networks

To provide truly global coverage needed by increased Personal Communication Services (PCS), a new generation of mobile satellite networks has been proposed. These low Earth orbit (LEO) mobile satellite networks handle multimedia traffic and can be used for non-real-time as well as real-time service to remote areas. Due to the many handoffs, resource management and connection admission control are important tasks for fair bandwidth sharing and QoS guarantees. Because the total link capacity has to be divided among several carriers and given the limited buffer capacity of the ATM switch, resource management is vital. It ensures the ability of the network to provide users with their negotiated QoS while protecting the network and the end-systems from congestion. We introduced a simple connection admission control (CAC) priority policy based on the delay and cell loss requirements for the investigated types of traffic. We took into account the handoff status of the satellite beams involved. Thus, we propose an onboard buffer architecture with separated buffers for new calls and intra-satellite handoff calls. The priority scheme applied is as follows: highest priority is given to CBR, followed by rt-VBR, nrtVBR and ABR.

On uplink call level QoS in DS-CDMA networks

Quality of service (QoS) in direct sequence code division multiple access networks with multiple traffic types can be described with a number of measures. One such measure is the handoff QoS deterioration probability, defined as the probability that the handoff into a new cell or sector of the network will cause violation of the signal to interference and noise ratio requirements for other users (the outage condition). In order to prevent outage events upon handoff for various traffic types, we propose a two tier admission policy. In the first tier, network capacity is calculated on the basis of a given bound on outage probability. Since this may not suffice to reduce the handoff QoS deterioration probability, in the second tier we reserve extra bandwidth for handoff calls below the threshold determined by tier 1 admission. The modified, two tier admission control algorithm is executed only when a call is admitted into the network, so that the admitted calls can freely execute handoffs using the reserved bandwidth. Three different tier 2 policies that differ in complexity and performance have been investigated through analytical modeling. The first policy reserves a fixed number of guard channels out of the soft capacity of the network. In the second policy, the number of reserved channels is proportional to the estimated handoff call arrival rate. In the third policy, the number of reserved channels is obtained through a convex function of the estimated handoff call arrival rate; an additional tuning parameter controls the level of handoff deterioration probability at a given new call arrival rate. The third policy has been found to offer the best performance under increasing traffic load. Analytical results for this tier 2 policy have been verified through simulation for voice traffic only, and mixed voice and data traffic.

A MAC Protocol for New and Handoff Calls with Finite Population

A MAC protocol for new and handoff calls with a finite population of users, rather than with an infinite user population as in dynamic channel reservation scheme (DCRS), is considered. Similar to DCRS, we divide the wireless channels into shared channels and reserved channels. The handoff calls access any available channel with probability of one, while the new calls access a shared channel with probability of one and access a reserved channel with a request probability. We propose three simpler formulae than that used in the existing DCRS in setting the request probability. In addition, the handoff calls in our proposed protocol are allowed to queue in a finite buffer. To evaluate the system performance, a mathematical model based on queuing theory, rather than a simulation method used in DCRS, is developed. It is a general model that can be adopted for any types of request probabilities including DCRS. Suggestions of how to get the optimum values of the design parameters are also given.

Performance of Channel Carrying for Handoff in a DCA Cellular Network

Channel carrying allows a mobile station to continue the use of its currently occupied channel when it hands off to a new cell. Since in a dynamic channel assignment (DCA) system, generally, any channel can be used by any cell, channel carrying can be more easily implemented than in a fixed channel assignment (FCA) system which supports channel carrying through borrowing channels or extending channel reuse distance. Therefore, this paper investigates different channel carrying strategies maybe used in the distributed timid DCA scheme with the seamless handoff policy (DCA-DT/SLH), namely, channel carrying first (CCF) and channel carrying last (CCL). This study shows that (1) CCL generally outperforms CCF; (2) in DCA-DT/SLH without channel carrying, handoff calls may suffer higher dropping probabilities than new calls if no priority is given to handoff calls while channel carrying can easily avoid such undesirable situation; and (3) channel carrying in DCA-DT/SLH is comparable and even better than the guard channel (GC) in FCA and can also slightly improve the performance of GC in DCA-DT/SLH.

A Dynamic Reservation-Based Call Admission Control Algorithm for Wireless Networks Using the Concept of Influence Curve

In this paper a dynamic channel reservation and call admission control scheme is proposed to provide QoS guarantees in a mobile wireless network using the concept of influence curve. The basic idea behind the proposed scheme is that a moving user, in addition to its requirements in the current cell, exerts some influence on the channel allocation in neighboring cells. Such an influence is related to the moving pattern of the users and is calculated statistically. Furthermore we developed a general analytical model to calculate the corresponding blocking probabilities for wireless networks with multiple platforms, which removes the commonly used assumption that new calls and handoff calls have same channel holding time. The numerical results demonstrate that our scheme outperforms traditional channel reservation schemes and can effectively adapt to the real time network conditions.

Multiple fractional channel reservation for optimum system capacity in multi-service cellular networks

The multiple fractional channel reservation (MFCR) strategy for service differentiation is proposed. It reserves, on average, real numbers of channels to prioritise new and/or handoff calls in multiple service environments. Also, an algorithm to determine the optimum numbers of reserved channels to achieve maximum system capacity when using the MFCR strategy is proposed.

A Call Admission Control Mechanism Using Mobility Graph in Mobile Multimedia Networks

One of the important issues in providing efficient multimedia traffic on a mobile computing environment is to guarantee the mobile host (client) with consistent QoS (Quality of Service). However, the QoS negotiated between the client and the network in one cell may not be honored due to client mobility, causing hand-offs between cells. In this paper, a call admission control mechanism is proposed to provide a consistent QoS guarantee for multimedia traffic on a mobile computing environment. Each cell can reserve fractional bandwidth for hand-off calls to its adjacent cells. It is important to determine the right amount of bandwidth reserved for hand-off calls because the blocking probability of new calls may increase if the amount of reserved bandwidth is more than necessary. An adaptive bandwidth reservation based on a mobility graph and a 2-tier cell structure is proposed to determine the amount of bandwidth to be reserved in the cell and to control dynamically its amount according to network conditions. We also propose a call admission control based on this bandwidth reservation and ``next-cell prediction'' scheme using a mobility graph. In order to evaluate the performance of our call admission control mechanism, we measure metrics such as blocking probability of new calls, dropping probability of hand-off calls, and bandwidth utilization. The simulation results show that the performance of our mechanism is superior to that of existing mechanisms such as NR-CAT2, FR-CAT2, and AR-CAT2.

Performance of Reuse Partitioning in Cellular Systems with Mobile Users

Reuse partitioning (RP) is a simple technique that can be used to increase the traffic capacity in a cellular system. With RP, a cell is divided into several concentric regions, each associated with a different cluster size. In this article, a traffic model is developed to analyze the impact of mobile users on a two-region RP system using fixed channel assignment. The influence of user speed and cell size on the new call blocking probability, Pb, and the call dropping probability, Pd, is investigated. A simpler model that can be used to estimate Pb and Pd in some cases is described. The effect on system capacity of reserving some channels for handoff calls is also studied. It is found that even though prioritized handoff can reduce Pd, it may also degrade the capacity. The accuracy of the analysis is verified using simulation for three mobility models.

Analytic modeling of handoffs in wireless cellular networks

In this paper, we report our recent work on closed form solutions to the blocking and dropping probability in wireless cellular networks with handoff. First, we develop a performance model of a cell in a wireless network where the effect of handoff arrival and the use of guard channels are included. Fast recursive formulas for the loss probabilities of new calls and handoff calls are given. Algorithms to determine the optimal number of guard channels and the optimal number of channels are developed. To determine the handoff arrival rate into a cell, a fixed-point iteration scheme is proposed, and the uniqueness of the fixed-point is shown. Then, we allow for failure and repair of channels and hence provide a performability analysis for cellular systems. We present a hierarchical model combining both performance and availability and its closed form solution. Performability measures of interest are explicitly given.

PCS networks with correlated arrival process and retrial phenomenon

In this paper, the arrival of new calls and handoff calls to 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. A new call will retry again if the first attempt is blocked. The PCS network consists of homogeneous cells and each cell consists of a finite number of channels. Under the general conditions that all random variables involved have general phase type (PH) distribution, we develop an explicit expression of the infinitesimal generator matrix of the Markov chain governing the network and find its complexity. This hits been a difficult matrix to obtain, judging from the works in the literature. It is very complex to develop and has not been previously obtained by other researchers. Some methods to find the stationary probability of the network are discussed. Particularly, we introduce an effective method, from which we can obtain the new call blocking probability and the handoff call failure probability. Also, the busy period of the orbit is introduced. This is an interesting measure from the viewpoint of network provider; its distribution and expectation are then obtained. The results presented in this paper can be used to provide some guidelines to performance evaluation for PCS network design.

Optimizing the handover call blocking probability in cellular networks with high speed moving terminals

This letter presents a two-layer cellular architecture which optimizes the handoff blocking probability performance of high-speed moving terminals (HSMT) in a congested urban area. The lower layer of the proposed architecture is based on a microcellular solution, for absorbing the traffic loads of both the low-speed moving terminals (LSMT) and the new calls of HSMT. The higher layer is based on a macrocell umbrella solution, for absorbing the traffic load of the existed handoff calls of the HSMT. The results show that using the optimum number of channels in each layer, the handoff call blocking probability of the HSMT is optimized having the minimum effect on the call blocking probability of the microcellular layer.

Actual call connection time characterization for wireless mobile networks under a general channel allocation scheme

Actual call connection time (ACCT) is the total time that a mobile user engages in communications over a wireless network during a call connection. Due to limited network resources of wireless mobile networks, a call connection may be prematurely disconnected and the ACCT for the call in general may not be the same as the requested call connection time (RCCT). The ACCT depends not only on the RCCT, but also on the network resource allocation scheme and network traffic. We characterize the ACCT and related performance metrics for wireless mobile networks under a newly proposed general channel allocation scheme. This scheme generalizes the nonprioritized scheme, the reserved channel scheme, the queueing priority scheme and the subrating scheme in such a way as to reduce the blocking probability of the handoff calls while keeping the ACCT as long as possible. Explicit formulae for the distribution and the expectation of the ACCT are obtained. The call completion probability, the call drop probability, and the average actual call connection times for both the complete calls and the incomplete calls are derived. The results can form the basis for designing better billing rate schemes by differentiating incomplete calls and complete calls.

Call admission control for CDMA mobile communications systems supporting multimedia services

The call admission control (CAC) belongs to the category of resource management. Since the radio spectrum is very scarce resource, CAC is one of the most important engineering issues for mobile communications. In this paper, we propose a CAC scheme for direct sequence code-division multiple-access cellular systems supporting mobile multimedia communications services. There are multiple call classes in multimedia services and the required signal-to-interference ratio (SIR) varies with call classes. Call admission decision in the proposed scheme is based on SIR measurement. We take account of the traffic asymmetry between uplink and downlink, which is the most important characteristic of multimedia traffic. In addition, the proposed scheme guarantees the priority of handoff call requests over new call requests. We evaluate the performance of the proposed scheme using Markov analysis. The performance measures which we focus on are the system throughput and the blocking probabilities of handoff calls and new calls. The outage probability of a call in progress is also calculated, which is the probability that the measured bit energy-to-noise density ratio of the call is smaller than the required value for maintaining adequate transmission quality. We present some numerical examples with practically meaningful parameter values and, as a result, show that the proposed CAC scheme can operate well in the mobile multimedia systems such as the International Mobile Telecommunications-2000 (IMT-2000) systems.