Predictive channel reservation for handoff prioritization in wireless cellular networks

Analytic modeling of handoffs in wireless cellular networks

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.

Interactive transparent networking–modeling examples of snoop and WTCP protocols

A promising approach for implementing channel assignment and control in cellular mobile telephone networks is the virtually fixed channel assignment (VFCA) scheme. In VFCA channels are allocated to cells according to the fixed channel assignment (FCA) scheme, but cells are allowed to borrow channels from one another. As such, VFCA maintains the efficiency of FCA, but adds the flexibility lacking in FCA. One feature of a VFCA network is that, to prevent co-channel interference, it requires several channels to be locked to serve a single call that borrows a channel. This feature raises the concern that VFCA may lead to chain reaction in channel borrowing among cells and cause the network performance to degrade, especially under heavy traffic conditions. In this paper, we propose the virtually fixed channel assignment with recall (VFCAWR) scheme: The network is implemented according to VFCA, but a cell can recall a locked channel to service an arriving handoff call, which occurs when a mobile unit crosses the boundary of its cell. We model the network as a three-dimensional Markov chain and derive its steady-state performance. Through modification of this basic model, we evaluate two dynamic channel assignment strategies, the virtual channel reservation (VCR) strategy and the linear switch-over (LSO) strategy, which exploit the unique borrowing/recall capability of VFCAWR to reduce the weighted cost of blocking fresh and handoff calls by reserving several virtual channels (the channels that may be borrowed from adjacent cells when necessary) for handoff calls. We validate the analytical models by simulation; the simulation test cases show that our models accurately predict the system performance measures of interest. Numerical and simulation results also show that both dynamic strategies outperform conventional channel reservation schemes based on fixed channel assignment and hybrid channel assignment.

This paper proposes a novel adaptive time- threshold based bandwidth allocation scheme (ATTS) for voice handoff calls in cellular wireless networks. The proposed scheme overcomes the flaws of the fixed time-threshold based bandwidth allocation scheme (FTTS) in the total admitted traffic and the blocking probability of new calls. In proposed scheme, bandwidth threshold for non-prioritized handoff calls and new calls can be varied adaptively based on instantaneous handoff call and new call arrival rates. This makes it possible that there is the increasing number of new calls which have successfully occupied bandwidth units in ATTS scheme when traffic load is heavier. Simulation results show that the proposed scheme improves new call blocking probability and bandwidth utilization with traffic load of given cell increasing while keeps low total handoff call dropping probability compared with FTTS scheme. The proposed scheme provides good QoS guarantees for both mobile users and service provider.

To guarantee the real-time transmission for time-sensitive traffic, we need to take delay-bound quality-of-service (QoS) into account when designing the wireless cellular networks. The traditional powerful QoS guarantee technique, called the homogeneous statistical QoS provisioning, assumes that the QoS provisioning of each link can be individually processed. In order to further significantly increase the global system throughput, the available resources of all links need to be jointly controlled, which is typically suitable for downlink transmissions over wireless cellular networks. Under this setup, we need to consider the diverse delay-bound QoS provisionings for different links at the same time, which represents the new heterogeneous statistical QoS provisioning framework and imposes many new challenges not encountered before in wireless networks. To overcome these problems, in this paper we propose the heterogeneous statistical QoS provisioning framework for high-speed downlink transmissions in wireless cellular networks. In particular, we formulate the optimization problem to maximize the downlink throughput subject to heterogeneous statistical delay-bound QoS requirements. For solving this optimization problem, we develop the heterogeneous-QoS-driven power allocation scheme to derive the closed-form solutions which can maximize the global system throughput while guaranteeing the heterogeneous delay-bound QoS for the entire wireless cellular networks. We show that the heterogeneous-QoS-driven power allocation provides more generic framework for downlink transmissions. The extensive simulation results obtained show that our proposed heterogeneous-QoS-driven power allocation scheme can achieve the global optimization of wireless resource efficiency, thus significantly increasing the global system throughput as compared with the homogeneous statistical delay-bound QoS provisioning schemes.

Network protocols in cellular wireless data networks must update routes as a mobile host moves between cells. These routing updates combined with some associated state changes are called handoffs. Most current handoff schemes in wireless networks result in data loss or large variations in packet delivery times. Unfortunately, many applications, such as real-time multimedia applications and reliable transport protocols, adapt to long term estimates of end-to-end delay and loss. Violations and rapid fluctuations of these estimates caused by handoff processing often result in degraded performance. For example, loss during handoff adversely affects TCP performance [4], and high packet loss and variable delays result in poor real-time multimedia performance. In this paper, we describe a multicast-based protocol that eliminates data loss and incurs negligible delays during a handoff. The basic technique of the algorithm is to anticipate a handoff using wireless network information in the form of received signal strengths and to multicast data destined for the mobile host to nearby base stations in advance. This routing, combined with intelligent buffering techniques at the base stations, enables very rapid routing updates and eliminates data loss without the use of explicit data forwarding. We have implemented this protocol using IP Multicast and Mobile IP-like routing. In our implementation, handoffs typically take between 8 and 15 ms to complete and result in no data loss.

In order to utilize network resources efficiently and reduce regional congestion, associating mobile stations (MSs) with proper base stations (BSs) is of crucial importance in wireless cellular networks. There have been several load-aware proposals in literature, where most are classified into so-called closed-form approaches. In such approaches, each MS independently and deterministically selects the BS which is expected to provide the highest throughput. The throughput is estimated by a closed-form equation based on the assumption of the Proportional Fair (PF) user scheduler that ensures temporal fairness. However, the closed-form approaches do not perform well when the closed-form equation is not available, e.g., general α-fair user scheduler, where temporal fairness is not guaranteed, or deterministic BS association may make wrong decisions, e.g., under the dynamics of mobility or flow arrivals/departures. In this paper, we propose a novel BS association scheme, called ViSE (Virtual Scheduling based Emulation) to tackle such challenges. It emulates an optimal BS association by running a notion of virtual scheduler, and each MS randomly determines its associated BS with the probability proportional to the throughput virtually allocated by the virtual scheduler. We demonstrate through extensive simulations under various practical scenarios that ViSE outperforms the existing algorithms in terms of user schedulers with diverse fairness and robustness to network dynamics.

Many handover algorithms are proposed in the literature. However, to make a better handover and keep the QoS in wireless networks is very difficult. In this paper, we propose a new handover system based on fuzzy logic. The proposed system uses 3 parameters for handoff decision: the change of signal strength of the present Base Station (BS), signal strength from the neighbor BS, and the distance between Mobile Station (MS) and BS. The performance evaluation via simulations shows that proposed system can avoid ping-pong effect and has a good handover decision.

Achieving maximum network throughput while providing fairness is one of the key challenges in wireless cellular networks. This goal is typically met when the load of base stations (BSs) is balanced. In a recent study, it was confirmed that the preamble sequence, which is mainly used for cell identification and synchronization, can be used as an implicit load indicator for long term load balancing in cellular networks. In this paper, we further explore its viability as an implicit information indicator, and present distributed load balancing schemes based on the properties of the preamble sequence. These schemes empower the mobile stations (MSs) to implicitly obtain information about the load status of BSs for intelligent cell-site selection. By utilizing the two characteristic and important properties of preamble sequences, which are high auto-correlation and low cross-correlation, we propose both network and user side algorithms that work together to enable the MSs to associate with BSs with relatively low load in the long term. We evaluate our algorithms for fairness to the MSs in terms of resources and throughput, and confirm through simulations that the preamble sequence can indeed be used as a leverage for better cell-site selection leading to a high degree of fairness in the system.

Handoff calls’ joining behavior and incentive mechanism in wireless cellular networks with retrial orbit

Enhancing system capacity while maintaining quality of service is an important issue in wireless cellular networks. In this paper, we present a localized channel sharing scheme to address this problem. Our basic idea is to allow channels to be shared between adjacent cells at the expense of a smaller initial allocation of channels per cell. We show that this tradeoff results in a better utilization of network resources. An important feature of our sharing scheme is that channel management is localized between adjacent cells, and no global coordination or optimization is required, thus making it suitable for implementation. The sharing scheme can also facilitate handoff processing. We provide numerical results comparing our scheme with the channel reservation technique, and find a significant performance improvement over a wide range of traffic parameters and a variety of quality of service requirements.

Channel reservation techniques have been extensively used in cellular networks in order to meet the quality of service (QoS) requirements. An influence-based channel reservation and call admission control scheme is proposed to provide the QoS guarantee in a mobile wireless network. The basic idea behind the proposed scheme is that a moving user; in addition to its requirements in the

A novel general analytical model for the unencumbered call session time distribution is proposed in cellular wireless networks, and the fact is observed that the unencumbered call session time distribution could be derived by using the cell residence time distribution and the average number of cells traveled by a mobile station with an unencumbered call.

We demonstrate in the paper that the applied mobility model has great influences on the system performance of mobile cellular networks. We develop a novel mobility model with Abrupt Event Influence (AEI), as well as the system model, to study to what extent the influences will be, with focusing on the mobility model simulation. We concern the parameters that determine the system performance of mobile cellular networks. We show in this paper that these parameters vary while user mobility changes, but the effects are interactive. Since handoff calls are given a higher priority over new calls and GC mechanism is employed, our analysis shows that a mature mobile cellular network should make use of user mobility characteristics and dynamically adjust its reservation threshold of the handoff call requests. Extensive simulation results validate our analysis.