Adaptive channel allocation for wireless PCN

In cellular networks, forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. In order to maintain an acceptable call dropping probability rate, we propose, in this paper, two new guard channel schemes: an adaptive one – New Adaptive Channel Reservation (NACR) – and a dynamic one – Predictive Reservation Policy (PRP). In NACR, for a given period of time, a given number of channels is guarded in each cell for handoff traffic. In PRP, the number of reserved channels depends on the actual number of calls in progress in the neighboring cells. An approximate analytical model of NACR is presented. A Tabu search method has been implemented in order to optimize the Grade of Service. Discrete event simulations of PRP and NACR were run. The effectiveness of the proposed methods is emphasized on a complex configuration.     

Adaptive resource allocation for prioritized call admission over anATM-based wireless PCN

In future personal communications networks (PCNs) supporting network-wide handoffs, new and handoff requests will compete for connection resources in both the mobile and backbone networks. Forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. The previously proposed guard channel scheme for radio channel allocation in cellular networks reduces handoff call blocking probability substantially at the expense of slight increases in new call blocking probability by giving resource access priority to handoff calls over new calls in call admission control. While the effectiveness of a fixed number of guard channels has been demonstrated under stationary traffic conditions, with nonstationary call arrival rates in a practical system, the achieved handoff call blocking probability may deviate significantly from the desired objective. We propose a novel dynamic guard channel scheme which adapts the number of guard channels in each cell according to the current estimate of the handoff call arrival rate derived from the current number of ongoing calls in neighboring cells and the mobility pattern, so as to keep the handoff call blocking probability close to the targeted objective while constraining the new call blocking probability to be below a given level. The proposed scheme is applicable to channel allocation over cellular mobile networks, and is extended to bandwidth allocation over the backbone network to enable a unified approach to prioritized call admission control over the ATM-based PCN     

Traffic management in a multicode CDMA system supporting softhandoffs

A traffic management scheme is proposed in a multicode code-division multiple-access system supporting soft handoff that uses guard channels and a queue for real-time traffic. Preemptive queue control gives priority to queued handoff calls. Handoff traffic is derived as a function of the new call arrival rate, the size of the soft handoff region, mobile speed, the new call blocking probability, and the handoff failure probability. System performance with K types of calls is analyzed by introducing a concept of effective channel. The effects of the number of guard channels, the number of effective channels, system capacity, and other factors are numerically investigated. The effectiveness of the proposed queue control scheme is also observed in terms of handoff processing delay     

基于排队理论的信道分配算法研究

针对蜂窝移动通信系统,基于排队理论提出了一种信道分配方案。该方案将信道分为2部分:语音信道和数据保护信道。预留数据保护信道用于补偿数据丢包率,同时对语音业务设置FIFO排队缓冲器,切换呼叫优先占用缓冲器以确保切换优先。当语音信道空闲时,数据业务可以占用语音信道,一旦有语音呼叫请求到来且无可用语音信道,数据业务应释放占用的语音信道,在数据缓存器中排队等待。仿真结果表明该方案不仅降低了新增呼叫阻塞率和切换掉话率,而且提升了数据业务的性能。     

Optimizing the QoS of high speed moving terminals in cellular networks

This 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.     

A distributed adaptive guard channel reservation scheme for cellular networks

In this paper, a distributed adaptive guard channel reservation (DAGCR) scheme is proposed to give priority to handoff calls. This scheme is built upon the concept of guard channels and it uses an adaptive algorithm to search automatically the optimal number of guard channels to be reserved at each base station. The quality‐of‐service (QoS) parameters used are the new and handoff call blockings. Simulation studies are performed to compare the present algorithm with the static guard channel policy. Simulation results show that this proposed algorithm guarantees the handoff call blocking probability to remain below the targeted threshold up to a substantially high offered load with a minimal blocking to new calls up to a moderate offered load and also shows significantly high channel utilization in all offered load conditions. This scheme is examined over a wide range of offered load. Thus, it seems the proposed scheme is very useful in controlling the blocking performances in wireless cellular networks. Copyright © 2006 John Wiley & Sons, Ltd.     

Design and Analysis of a Channel Assignment Scheme for CDMA/TDMA Mobile Networks

In this paper, a channel assignment scheme is proposed for use in CDMA/TDMA mobile networks carrying voice and data traffic. In each cell, three types of calls are assumed to compete for access to the limited number of available channels by the cell: new voice calls, handoff voice calls, and data calls. The scheme uses the movable boundary concept in both the code and time domains in order to guarantee the quality of service (QoS) requirements of each type. A traditional Markov analysis method is employed to evaluate the performance of the proposed scheme. Measures, namely, the new call blocking probability, the handoff call forced termination probability, the data call loss probability, the expected number of handoff and the handoff link maintenance probability are obtained from the analysis. The numerical results, which are validated by simulation, indicate that the scheme helps meet the QoS requirements of the different call types.     

Teletraffic performance evaluation of microcellular personalcommunication networks (PCN's) with prioritized handoff procedures

Evaluates four handoff priority-oriented channel allocation schemes. These give priority to handoff calls by reserving channels exclusively for handoff calls. The measurement-based handover channel adaptive reassignment scheme (MHAR-A) exclusively uses reserved handover channels for newly originated calls if a certain criterion is satisfied. All four schemes studied differ from the conventional guard channel-based handover priority-oriented channel allocation scheme. To study the schemes, a personal communication network (PCN) based on city street microcells is considered. A teletraffic simulation model accommodating a fast moving vehicle is developed, and the performance parameters are obtained. The performances of all four schemes are compared with the nonpriority scheme and the conventional guard channel-based handover priority-oriented channel allocation scheme. It was found that some of the channel allocation algorithms studied improved the teletraffic capacity over the nonpriority and the conventional guard case. Also, the probability of new call blocking and carried traffic was improved for three of the schemes when compared to the conventional guard scheme. The MHAR-A scheme did not perform up to expectation. Nevertheless, it can be used to finely control the communication service quality equivalent to the control obtained by varying the number of handoff channels in a fraction of one. Increasing the number of reserved handover channels in fraction of one can never be achieved in the conventional guard channel-based handover priority-oriented channel allocation scheme     

Traffic model and performance analysis for cellular mobile radio telephone systems with prioritized and nonprioritized handoff procedures

A traffic model and analysis for cellular mobile radio telephone systems with handoff are described. Three schemes for call traffic handling are considered. One is nonprioritized and two are priority oriented. Fixed channel assignment is considered. In the nonprioritized scheme the base stations make no distinction between new call attempts and handoff attempts. Attempts which find all channels occupied are cleared. In the first priority scheme considered, a fixed number of channels in each cell are reserved exclusively for handoff calls. The second priority scheme employs a similar channel assignment strategy, but, additionally, the queueing of handoff attempts is allowed. Appropriate analytical models and criteria are developed and used to derive performance characteristics. These show, for example, blocking probability, forced termination probability, and fraction of new calls not completed, as functions of pertinent system parameters. General formulas are given and specific numerical results for nominal system parameters are presented.     

Fixed and dynamic bandwidth allocation strategies for wireless mobile integrated services networks

Performance evaluation of two bandwidth allocation strategies in wireless mobile integrated services networks is carried out. Performances of the proposed strategies are compared with those of the traditional guard channels and threshold strategies. In the study, a single wireless cell which is accessed by voice and non-voice traffic types producing, respectively narrowband and wideband calls is considered. In the proposed strategies a number of channels are reserved in a fixed or dynamic fashion for the use of originating wideband calls in addition to the guard channels allocated for the handoff calls. The results indicate that the two strategies have comparable advantages and by manipulating the number of reserved channels, desired performance levels can be achieved. The dynamic reservation based strategy makes the system fairer for the originating wideband calls while maintaining low handoff dropping probability and acceptable channel utilization levels. On the other hand, the fixed reservation strategy provides a lower handoff call dropping at comparable channel utilization levels. The tradeoff is between improving the handoff call dropping versus the originating wideband call blocking. Both strategies provide better performance for the originating wideband calls compared with that provided by the traditional guard channels strategy.

Analysis of a hybrid cutoff priority scheme for multiple classes of traffic in multimedia wireless networks

In this paper, we propose and analyze the performance of a new handoff scheme called hybrid cutoff priority scheme for wireless networks carrying multimedia traffic. The unique characteristics of this scheme include support for N classes of traffic, each may have different QoS requirements in terms of number of channels needed, holding time of the connection and cutoff priority. The proposed scheme can handle finite buffering for both new calls and handoffs. Futhermore, we take into consideration the departure of new calls due to caller impatience and the dropping of queued handoff calls due to unavailability of channels during the handoff period. The performance indices adopted in the evaluation using the Stochastic Petri Net (SPN) model include new call and handoff blocking probabilities, call forced termination probability, and channel utilization for each type of traffic. Impact on the performance measures by various system parameters such as queue length, traffic input and QoS of different traffic has also been studied. This revised version was published online in June 2006 with corrections to the Cover Date.     

On optimal call admission control in cellular networks

Two important Quality-of-Service (QoS) measures for current cellular networks are the fractions of new and handoff “calls” that are blocked due to unavailability of “channels” (radio and/or computing resources). Based on these QoS measures, we derive optimal admission control policies for three problems: minimizing a linear objective function of the new and handoff call blocking probabilities (MINOBJ), minimizing the new call blocking probability with a hard constraint on the handoff call blocking probability (MINBLOCK) and minimizing the number of channels with hard constraints on both of the blocking probabilities (MINC). We show that the well-known Guard Channel policy is optimal for the MINOBJ problem, while a new Fractional Guard Channel policy is optimal for the MINBLOCK and MINC problems. The Guard Channel policy reserves a set of channels for handoff calls while the Fractional Guard Channel policy effectively reserves a non-integral number of guard channels for handoff calls by rejecting new calls with some probability that depends on the current channel occupancy. It is also shown that the Fractional policy results in significant savings (20-50\%) in the new call blocking probability for the MINBLOCK problem and provides some, though small, gains over the Guard Channel policy for the MINC problem. Further, we also develop computationally inexpensive algorithms for the determination of the parameters for the optimal policies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimizing the handover call blocking probability in cellularnetworks 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     

Analysis of a hierarchical cellular system with reneging anddropping for waiting new and handoff calls

We analyze a hierarchical cellular system with finite queues for new and handoff calls. Both the effect of the reneging of waiting new calls because of the callers' impatience and the effect of the dropping of queued handoff calls as the callers move out of the handoff area are considered, besides the effect of the guard channel scheme. We successfully solve the system by adopting the multidimensional Markovian chain and using the transition-probability matrix and the signal-flow graph to obtain the average new-call blocking probability, the forced termination probability, and the average waiting time of queued new and handoff calls. We further investigate how the design parameters of the buffer sizes and guard channel numbers in macrocell and microcells affect the performance of the hierarchical cellular system. The results show that provision of a buffering scheme and guard channel scheme can effectively reduce the new call blocking probability and the forced termination probability in the hierarchical cellular system, and the effectiveness is more significant in the macrocell than in the microcells     

Modeling and performance analysis for soft handoff schemes in CDMA cellular systems

This paper investigates the features of a cellular geometry in code-division multiple-access (CDMA) systems with soft handoff and distinguishes controlling area of a cell from coverage area of a cell. Some important characteristics of the cellular configuration in soft handoff systems are used to propose a new design of efficient call admission control (CAC) in CDMA systems. Then, the paper constructs a continuous-time Markov chain (CTMC) model for CAC in CDMA with a soft handoff queue, obtains closed-form solutions, and thus develops loss formulas as performance indices such as the new blocking probability and the handoff dropping probability. In order to determine handoff traffic arrival rate, a fixed-point strategy is developed. Algorithms are also provided to stably compute loss probabilities and to determine the optimal number of guard channels. A new soft handoff scheme-eliminating pseudo handoff calls (EPHC)-is proposed to improve channel utilization efficiency based on mobility information. As an application of the loss formulas, the proposed modeling techniques are used to evaluate and compare the performance of conventional and proposed EPHC soft handoff schemes. Numerical results show the effectiveness of the proposed Markov chain models and the benefits of the new soft handoff scheme.     

Adaptive Resource Management in Mobile Wireless Networks Using Feedback Control Theory

Emerging mobile wireless networks are characterized by significant uncertainties in mobile user population and system resource state. Such networks require adaptive resource management that continuously monitor the system and dynamically adjust resource allocations for adherence to the desired system performance requirements. We propose adaptive resource management technique based on control theory. The controller dynamically solves resource allocation problem using feedback control laws. In the base algorithm, the number of guard channels is dynamically adjusted by feeding back the current handoff call dropping probability. The base algorithm is then enhanced in two ways: feeding back the instantaneous number of handoff calls and by probabilistically implementing a fractional number of guard channels. We study the effects of parameter choices on the performance of the proposed algorithms using discrete event simulation. Simulation results indicate that the feedback controllers can guarantee the predetermined call dropping probability under a variety of traffic conditions, and so can utilize the scarce wireless resource efficiently by accepting more new calls.     

Performance analysis of a dynamic handoff scheme in wireless networks with heterogeneous call arrival processes

The Guard Channel Scheme (GCS) and Handoff Queueing Scheme (HQS) are the popular and practical strategies to prioritize handoff calls in wireless cellular networks. A key issue of giving handoff calls the higher priority is how to achieve a tradeoff among the handoff call blocking probability, new call blocking probability and handoff delay. This paper extends GCS and HQS and presents an efficient handoff scheme that dynamically manages the channels reserved for handoff calls depending on the current status of the handoff queue. A three-dimensional Markov model is developed to analyze the performance of this scheme and investigate the desirable performance tradeoff. The Poisson process and Markov-Modulated-Poisson-Process (MMPP) are used to model the arrival processes of new and handoff calls, respectively. The accuracy of this model is evaluated through the extensive comparison of the analytical results to those obtained from discrete-event simulation experiments. Performance measures in terms of the mean number of calls in the system, aggregate response time, aggregate call blocking probability, handoff call blocking probability, new call blocking probability and handoff delay are evaluated. The analytical model is used to investigate the effects of the number of channels originally reserved for handoff calls, the number of dynamic channels, and the ratio of the rate of handover calls to the aggregate arrival rate on the system performance.     

An adaptive channel preemption model for small‐cell embedded large‐cellular networks

In this paper, we present an analytical model of adaptive channel preemption (ACP) for small‐cell embedded large‐cellular (SCELC) networks. An SCELC network consists of a fixed base station (FBS) with large coverage and many embedded base stations (EBS) with relatively small coverage. Channel capacity in an FBS cell may become insufficient when traffic is unexpectedly increased particularly in some special occasion. This paper considers two aspects of dynamically allocating channels for an SCELC network. First, by increasing one or more EBS cells within an FBS cell, the proposed ACP can reduce blocking probability of new calls. Second, to reduce dropping probability of handoff calls, the proposed ACP allows a handoff call to preempt an on‐going call, when the latter is located in an EBS cell or in the overlapping area of two adjacent FBS cells. For the purpose of performance evaluation, we build an analytical model with 4‐tuple Markov chains. Numerical results reveal that embedding one or more EBS cells inside an FBS cell needs to be done carefully since it results in a tradeoff between the reduction of new‐call blocking probability and the increase of handoff‐call dropping probability. Copyright © 2011 John Wiley & Sons, Ltd.     

Dynamic channel management scheme to increase performance index of cellular networks

A dynamic channel management scheme (DCMS), using both a one-layer cellular architecture (OLCA) and a two-layer cellular architecture (TLCA), for use in areas with random offered traffic load, is presented. The philosophy of DCMS is based either on OLCA or TLCA, and is proposed for optimisation of the handoff blocking probability performance of high-speed moving terminals and the call blocking probability of the rest of the calls in a congested urban area, with random offered traffic load. Also, the number of channels assigned to microcells and the umbrella cell, is regulated dynamically achieve to the foregoing objectives.     

An adaptive measured-based preassignment scheme withconnection-level QoS support for mobile networks

This paper presents a new adaptive bandwidth allocation scheme to prevent handoff failure in wireless cellular networks, known as the measurement-based preassignment (MPr) technique. This technique is particularly useful in micro/pico cellular networks which offers quality-of-service (QoS) guarantee against call dropping. The proposed MPr scheme distinguishes itself from the well-known guarded channel (GC) based schemes in that it allows the handoff calls to utilize a prereserved channel pool before competing for the shared channels with new call arrivals. The key advantage of the proposed MPr scheme is that it enables easy derivation of the number of channels that needs to be reserved for handoff based on a predetermined handoff dropping probability, without the need for solving the often complex Markov chain required in GC schemes, thus, making the proposed MPr scheme simple and efficient for implementation. This is essential in handling multiple traffic types with potentially different QoS requirements. In addition, the MPr scheme is adaptive in that it can dynamically adjust the number of reserved channels for the handoff according to the periodical measurement of the traffic status within a local cell, thus completely eliminating the signaling overhead for status information exchange among cells mandated in most existing channel allocation schemes. Numerical results and comparisons are given to illustrate the tradeoff