Performance evaluation of hierarchical cellular CDMA networks with soft handoff queueing

We consider hierarchical cellular code-division multiple-access networks supporting soft handoff, where users with different mobility are assigned to different layers, i.e., microcells in the lower layer are used to carry slow users, whereas macrocells in the upper layer are for fast users, and handoff queues are provided for handoff calls that cannot obtain the required channel immediately, so that forced termination probability can be reduced. According to whether handoff queues are provided in microcells and/or macrocells, four different call admission control schemes are proposed and studied. We derive the mathematical model of the considered system with multidimensional birth-death process and utilize Gauss-Seidel iterative method to find the steady-state probability distribution and thus the performance measures of interest: new call blocking probability, handoff failure probability, and forced termination probability. Analytical results show that providing handoff queues in both microcells and macrocells can achieve largest performance improvement. Furthermore, handoff queue size greater than a threshold is shown to have little effect on performance measures of interest. Last but not least, the studied two-tier system is compared with a one-tier counterpart. It is shown that the two-tier system performs better in terms of average number of handoffs per fast call.     

A Call-Admission Control (CAC) Algorithm for Providing Guaranteed QoS in Cellular Networks

Future broadband wireless access systems are expected to integrate various classes of mobile terminals (MTs), each class with a different type of quality of service (QoS) requirement. When the load on a wireless network is high, the guarantee of QoS for each class of MTs is a challenging task. This study considers two classes of MTs—profiled MTs and nonprofiled or regular MTs. It is assumed that profiled users require a guaranteed QoS. The measure of QoS is the probability of forced termination of a call that was allowed to access the network. Two previous handoff prioritization schemes—(i) prerequest scheme and (ii) guard channel scheme—decrease handoff failure (and hence forced termination). In this work, we compare and contrast both the schemes through extensive simulation and we find that neither guard channel nor channel prerequest scheme can guarantee a desired level of QoS for the profiled MTs. We then propose a novel call-admission control (CAC) algorithm that can maintain any desired level of QoS, while the successful call completion rate is very high. In the proposed algorithm, the new call arrival rate is estimated continuously, and when the estimated arrival rate is higher than a predetermined level, some new calls are blocked irrespective of the availability of channels. The objective of this new call preblocking is to maintain a cell's observed new call arrival rate at no more than the predetermined rate. We show that the proposed method can guarantee any desired level of QoS for profiled users.     

Q-Win – A New Admission and Handoff Management Scheme for Multimedia LEO Satellite Networks

Low Earth Orbit (LEO) satellite networks are deployed as an enhancement to terrestrial wireless networks in order to provide broadband services to users regardless of their location. In addition to global coverage, these satellite systems support communications with hand-held devices and offer low cost-per-minute access cost, making them promising platform for Personal Communication Services (PCS). LEO satellites are expected to support multimedia traffic and to provide their users with the negotiated Quality of Service (QoS). However, the limited bandwidth of the satellite channel, satellite rotation around the Earth and mobility of end-users makes QoS provisioning and mobility management a challenging task. One important mobility problem is the intra-satellite handoff management. The main contribution of this work is to propose Q-Win, a novel call admission and handoff management scheme for LEO satellite networks. A key ingredient in our scheme is a companion predictive bandwidth allocation strategy that exploits the topology of the network and contributes to maintaining high bandwidth utilization. Our bandwidth allocation scheme is specifically tailored to meet the QoS needs of multimedia connections. The performance of Q-Win is compared to that of two recent schemes proposed in the literature. Simulation results show that our scheme offers low call dropping probability, providing for reliable handoff of on-going calls, good call blocking probability for new call requests, while maintaining bandwidth utilization high.     

Admission control scheme for soft handoff in DS-CDMA cellular systems supporting voice and stream-type data services

The soft handoff call requests of real-time services in third-generation (3G) direct-sequence code-division multiple access (DS-CDMA) and first- and second-generation cellular systems are more important than new call requests from the viewpoint of quality of service (QoS). Rejection of soft handoff requests causes forced termination of an ongoing real-time call, which is a severer problem than blocking of new call attempts. An admission control scheme that can guarantee a higher QoS for the soft handoff requests of real-time services in 3G DS-CDMA systems is proposed for delay-sensitive voice and delay-tolerant stream-type data services. The proposed scheme (P-Scheme) accommodates both voice and data services by utilizing the full bandwidth. However, voice soft handoff call requests are given priority over new voice call and stream-type data packet requests by suppressing interference from stream-type data services according to voice soft handoff requests, and by varying interference levels. Performance of the P-Scheme is evaluated using a Markovian model. Results are compared with a conventional reservation scheme (C-Scheme) that reserves resources exclusively for voice soft handoff requests. Numerical results show that system performance can be significantly improved using the proposed P-Scheme, compared with the conventional C-Scheme, when various types of service are supported in third-generation DS-CDMA systems.     

An innovative channel management strategy for highly reliable handoff in cellular networks

In this paper, we have resolved the problem of forced call termination that occurs when mobile traffic is concentrated on a hot‐spot cell in cellular networks. Enhanced Channel Management Scheme (ECMS) is an innovative way to increase the flexibility of channel usage over non‐uniform traffic distribution. ECMS exploits mobile hosts initiated or active in overlapping areas between cells. The scheme consists of three phases to monitor the status of channels on each base station and to make a channel reservation using the availability list maintained for the candidate‐MH selection. When the traffic load in a cell is intolerably high, ECMS invokes the load‐balancing procedure to distribute its traffic to adjacent cells. The reserved channels are used to support the safe and fast handoff. From the simulation, we observed that ECMS outperformed other compatible channel assignment schemes such as directed handoff schemes in blocking probability and channel utilization. Copyright © 2002 John Wiley & Sons, Ltd.     

Adaptive channel reservation for call admission control to support prioritized soft handoff calls in a cellular CDMA system

This paper proposes a prioritized call admission control (CAC) model to support soft handoff calls with quality of service (QoS) assurances for both the uplink and downlink connections in a CDMA system. CAC is formulated as a combinatorial optimization problem in which the problem objective is to minimize the handoff forced termination rate. The model, which is based on the adaptive channel reservation (ACR) scheme for prioritized calls, adapts to changes in handoff traffic where the associated parameters (reserved channels, and new and handoff call arrival rates) can be varied. To solve the optimization model, iteration-based Lagrangean relaxation is applied by allocating a time budget. We express our achievements in terms of the problem formulation and performance improvement. Computational experiments demonstrate that the proposed ACR scheme outperforms other approaches when there are fewer rather than more channels, and it reduces the handoff call blocking rate more efficiently when the handoff traffic is heavily loaded. Moreover, the model can be adapted to any kind of reservation service.     

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.     

Adaptive channel reservation scheme for soft handoff in DS-CDMAcellular systems

Soft handoff techniques in direct-sequence code-division multiple-access (DS-CDMA) systems provide mobile calls with seamless connections between adjacent cells. Channel reservation schemes are used to give high priority to more important soft handoff attempts over new call attempts. However, since the number of soft handoff attempts varies according to environmental conditions, fixed reservation schemes for handoff attempts can be inefficient. An adaptive channel reservation scheme is herein proposed to control the size of reservation capacity according to varying the number of soft handoff attempts. The proposed scheme also includes a balancing procedure between soft handoff failure and new call blocking to maximize the system capacity. To evaluate the performance of the proposed scheme, a Markovian model is developed that considers the interference-limited capacity effect of DS-CDMA systems. The analytical result shows that the proposed scheme yields a considerable enhancement in terms of new call blocking and soft handoff failure probabilities when compared with the conventional fixed channel reservation scheme     

A call admission control scheme for packet data in CDMA cellular communications

In wireless cellular communication systems, call admission control (CAC) is to ensure satisfactory services for mobile users and maximize the utilization of the limited radio spectrum. In this paper, we propose a new CAC scheme for a code division multiple access (CDMA) wireless cellular network supporting heterogeneous self-similar data traffic. In addition to ensuring transmission accuracy at the bit level, the CAC scheme guarantees service requirements at both the call level and the packet level. The grade of service (GoS) at the call level and the quality of service (QoS) at the packet level are evaluated using the handoff call dropping probability and the packet transmission delay, respectively. The effective bandwidth approach for data traffic is applied to guarantee QoS requirements. Handoff probability and cell overload probability are derived via the traffic aggregation method. The two probabilities are used to determine the handoff call dropping probability, and the GoS requirement can be guaranteed on a per call basis. Numerical analysis and computer simulation results demonstrate that the proposed CAC scheme can meet both QoS and GoS requirements and achieve efficient resource utilization.     

DiffServ resource allocation for fast handoff in wireless mobileInternet

The next-generation wireless networks are evolving toward a versatile IP-based network that can provide various real-time multimedia services to mobile users. Two major challenges in establishing such a wireless mobile Internet are support of fast handoff and provision of quality of service (QoS) over IP-based wireless access networks. In this article, a DiffServ resource allocation architecture is proposed for the evolving wireless mobile Internet. The registration-domain-based scheme supports fast handoff by significantly reducing mobility management signaling. The registration domain is integrated with the DiffServ mechanism and provisions QoS guarantee for each service class by domain-based admission control. Furthermore, an adaptive assured service is presented for the stream class of traffic, where resource allocation is adjusted according to the network condition in order to minimize handoff call dropping and new call blocking probabilities     

A Hopfield neural-network-based dynamic channel allocation withhandoff channel reservation control

As channel allocation schemes become more complex and computationally demanding in cellular radio networks, alternative computational models that provide the means for faster processing time are becoming the topic of research interest. These computational models include knowledge-based algorithms, neural networks, and stochastic search techniques. This paper is concerned with the application of a Hopfield (1982) neural network (HNN) to dynamic channel allocation (DCA) and extends previous work that reports the performance of HNN in terms of new call blocking probability. We further model and examine the effect on performance of traffic mobility and the consequent intercell call handoff, which, under increasing load, can force call terminations with an adverse impact on the quality of service (QoS). To maintain the overall QoS, it is important that forced call terminations be kept to a minimum. For an HNN-based DCA, we have therefore modified the underlying model by formulating a new energy function to account for the overall channel allocation optimization, not only for new calls but also for handoff channel allocation resulting from traffic mobility. That is, both new call blocking and handoff call blocking probabilities are applied as a joint performance estimator. We refer to the enhanced model as HNN-DCA++. We have also considered a variation of the original technique based on a simple handoff priority scheme, here referred to as HNN-DCA+. The two neural DCA schemes together with the original model are evaluated under traffic mobility and their performance compared in terms of new-call blocking and handoff-call dropping probabilities. Results show that the HNN-DCA++ model performs favorably due to its embedded control for assisting handoff channel allocation     

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.     

Enabling seamless multimedia wireless access through QoS‐based bandwidth adaptation

Effective support of real‐time multimedia applications in wireless access networks, viz. cellular networks and wireless LANs, requires a dynamic bandwidth adaptation framework where the bandwidth of an ongoing call is continuously monitored and adjusted. Since bandwidth is a scarce resource in wireless networking, it needs to be carefully allocated amidst competing connections with different Quality of Service (QoS) requirements. In this paper, we propose a new framework called QoS‐adaptive multimedia wireless access (QoS‐AMWA) for supporting heterogeneous traffic with different QoS requirements in wireless cellular networks. The QoS‐AMWA framework combines the following components: (i) a threshold‐based bandwidth allocation policy that gives priority to handoff calls over new calls and prioritizes between different classes of handoff calls by assigning a threshold to each class, (ii) an efficient threshold‐type connection admission control algorithm, and (iii) a bandwidth adaptation algorithm that dynamically adjusts the bandwidth of an ongoing multimedia call to minimize the number of calls receiving lower bandwidth than the requested. The framework can be modeled as a multi‐dimensional Markov chain, and therefore, a product‐form solution is provided. The QoS metrics—new call blocking probability (NCBP), handoff call dropping probability (HCDB), and degradation probability (DP)—are derived. The analytical results are supported by simulation and show that this work improves the service quality by minimizing the handoff call dropping probability and maintaining the bandwidth utilization efficiently. Copyright © 2006 John Wiley & Sons, Ltd.     

Techniques for providing QoS in Mobile Cellular Networks Based on CAC and Resource Reservation at the Origin and Destination

Next generation mobile cellular networks will have to support multimedia services. These applications, however, are very different in relation to Quality of Service (QoS) requirements, imposing restrictive requirements for this type of environment because of its limited bandwidth. This work proposes alternative Call Admission Control (CAC) schemes combined with end-to-end bandwidth reservation. This work aims to attend the different multimedia services according to their different QOS requirements, as well as reducing the rate of call losses during the procedures of handoff, prioritizing users already using the network. Simulation results show that it is possible to guarantee satisfactory levels of handoff losses, maintaining the continuity of the calls and increasing user satisfaction.     

多业务无线蜂窝移动通信系统的一种呼叫允许控制策略

第三代移动通信系统要求支持宽带多媒体业务,如话音、视频、数据等多种业务,不同业务有不同的QoS要求。本文提出的多业务无线蜂窝移动通信系统中一种基于QoS的呼收允许控制策略,对不同业务的切换呼叫给予不同的优先权。本文分析了两种呼叫允许控制（CAC）算法,一种是各种业务的切控呼叫无缓冲器,不进入排队系统;另一种是各种业务的切换呼叫设置有缓冲器,进入排除系统,并且话音、视频业务的切切呼叫比数据业务的切换呼叫有更高的优先权,系统的空闲信道应首先分配给话音、视频业务的切换呼叫,再分配给数据业务的切换呼叫。在分析两种CAC算法的呼叫阻塞概率、切换失败概率以及系统吞吐量的基础上,给出了计算机仿真结果。     

Handoff Performance in Wireless Mobile Networks with Unreliable Fading Channel

Handoff is an indispensable operation in wireless networks to guarantee continuous, effective, and resilient services during a Mobile Station (MS) mobility. Handoff counting, handoff rate, and handoff probability are important metrics to characterize the handoff performance. Handoff counting defines the number of handoff operations during an active call connection. Handoff rate specifies the expected number of handoff operations during an active call, or equivalently, the average handoff counting. Handoff probability refers to the probability that an MS will perform a handoff before call completion. In the literature, the fading channel is not incorporated in deriving these metrics. In addition, the teletraffic parameters are usually simplified into exponentially distributed variables for the sake of analytical tractability. In this paper, we derive the formulas for these metrics over Rayleigh fading. In particular, the results can demonstrate the explicit relationship between the handoff metrics and the physical layer characteristics, e.g., carrier frequency, maximum Doppler frequency, and fade margin. Furthermore, the formulas are developed with the generalized teletraffic parameters. Numerical examples are presented to demonstrate the impact of physical layer on the handoff metrics. The techniques and the results are significant for both deploying practical wireless networks and evaluating the system resilience over an unreliable radio channel.     

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.     

Predictive mobility support for QoS provisioning in mobile wirelessenvironments

With the proliferation of wireless network technologies, mobile users are expected to demand the same quality of service (QoS) available to fixed users. This paper presents a predictive and adaptive scheme to support timed-QoS guarantees in pico- and micro-cellular environments. The proposed scheme integrates the mobility model into the service model to achieve efficient network resource utilization and avoid severe network congestion. The mobility model uses a probabilistic approach to determine the most likely cluster to be visited by the mobile unit. The admission control is invoked when a new call arrives or an existing call performs a handoff to verify the feasibility of supporting the call. The performance of the proposed schemes is compared to the shadow cluster scheme. The performance of the proposed scheme under different traffic patterns is also presented     

Route optimization in mobile ATM networks

This paper presents an algorithm for optimizing the route of a connection that becomes suboptimal due to operations such as handoffs and location-based reroutes, and applies this algorithm to the handoff management problem in mobile ATM (Asynchronous Transfer Mode) networks based on the PNNI (Private Network-to-Network Interface) standard. The route optimization algorithm uses hierarchical route information of the connection and summarized topology and loading information of the network to determine a “crossover node” such that adjusting the connection from that crossover node results in an optimally routed connection. Handoff management schemes that perform local rerouting of connections have been proposed in order to support fast handoffs. These methods result in suboptimally routed connections. In this paper, we demonstrate how this route optimization algorithm can be used to optimize the route of a connection after such a handoff is executed, as the second phase of a two-phase handoff scheme. This route optimization procedure can also be executed as part of the handoff procedure resulting in a one-phase handoff scheme. Applying this route optimization algorithm, we propose two one-phase schemes, the one-phase optimal scheme and the one-phase minimal scheme. A comparative performance analysis of one- and two-phase handoff schemes is presented. Measures of comparison are handoff latency and the amount of network resources used by a connection. Handoff latency in the one-phase optimal scheme is greater than that in the two-phase schemes, and handoff latency in the one-phase minimal scheme is smaller than that in the two-phase schemes. The one-phase methods show a significant increase in efficiency of the connection compared to the two-phase methods. This revised version was published online in June 2006 with corrections to the Cover Date.     

NACR: A New Adaptive Channel Reservation in Cellular Communication Systems

Future Personal Communication Networks (PCN) will employ microcells and picocells to support a higher capacity, thus increasing the frequency of handoff calls. Forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. The proposed guard channel schemes for radio channel allocation in cellular networks reduce handoff call blocking probability at the expense of increases in new call blocking probability by giving resource access priority to handoff calls over new calls in call admission control. Under uniform traffic assumptions, it has been shown that a fixed number of guard channels leads to good performance results. In a more realistic system, non-uniform traffic conditions should be considered. In this case, the achieved call blocking probability may deviate significantly from the desired objective. In this paper, we propose a new adaptive guard channel scheme: New Adaptive Channel Reservation (NACR). In NACR, for a given period of time, a given number of channels are guarded in each cell for handoff traffic. An approximate analytical model of NACR is presented. Tabu search method has been implemented in order to optimize the grade of service. Discrete event simulations of NACR were run. The effectiveness of the proposed method is emphasized on a complex configuration.