An efficient cross layer based channel reservation method for vehicular networks

The swift growth of the mobile users and limited availability of bandwidth lead to the requirement of effective channel allocation process. Channel allocation becomes tedious in vehicular ad hoc network, as the mobility of the nodes is high. So, in this paper, we propose a method called as cross layer based channel reservation with preemption (CCRP) method that performs channel allocation process by estimating the handoffs in vehicular ad hoc networks. The time estimated is communicated from physical layer to medium access control layer using a cross‐layer design. The reusability concept is used, and the channels are divided into three groups. The different cells acquire different groups based on the database status and exclusively to avoid interference. Preemption is incorporated to give the highest priority to real time originating calls and real time handoff calls. The performance of the proposed method, CCRP, is compared with the legacy systems such as cooperative reservation of service channels and very fast handover scheme in terms of dropping probability, blocking probability, and handoff latency. The results show that the proposed algorithm, CCRP, performs better in comparison. Copyright © 2013 John Wiley & Sons, Ltd.     

基于无线ATM的快速切换管理新方案

未来的移动通信网应发展成以异步传模式（ＡＴＭ） 为基础,支持多媒体业务的网络。为了在这种环境下实现无缝隙、快速切换,提出了在相邻基站间备用永久虚连接（ＰＶＣ） 的一种快速切换管理方案,并计算了给定ＰＶＣ 带宽时的切换阻塞概率。本方案与Ａｃａｍ ｐｏｒａ 的虚连接树（ＶＣＴ） 相比,有效地节省了有线链路资源,并在切换过程中保持本地小区序列的完整性     

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     

A Predictive Bandwidth Reservation Scheme Using Mobile Positioning and Road Topology Information

In cellular networks, an important practical issue is how to limit the handoff dropping probability efficiently. One possible approach is to perform dynamic bandwidth reservation based on mobility predictions. With the rapid advances in mobile positioning technology, and the widespread availability of digital road maps previously designed for navigational devices, we propose a predictive bandwidth reservation scheme built upon these timely opportunities. In contrast to the common practice of utilizing only incoming handoff predictions at each cell to compute the reservations, our scheme is more efficient as it innovatively utilizes both incoming and outgoing handoff predictions; it can meet the same target handoff dropping probability by blocking fewer new calls. The individual base stations are responsible for the computations, which are shown to be simple enough to be performed in real-time. We evaluate the scheme via simulation, along with five other schemes for comparison. Simulation results show that those schemes that rely on positioning information are significantly more efficient than those that do not. Our scheme's additional use of the road topology information further improves upon this advantage, bringing the efficiency closer to the bound set by a benchmark scheme that assumes perfect knowledge about future handoffs.     

基于预留信道和强占优先相结合的接入策略

报道了一种用于话音／数据综合的蜂窝移动通信系统中的基于预留切换信道和强占优先策略相结合的业务接入方案。在本方案中为具有越区切换请求的话音呼叫提供了预留切换信道和强占数据业务的优先权相结合的接入策略。同时为了提高系统总的承载话音的业务量,也为新近产生的话音呼叫提供了一定的强占数据业务的优先权。结果表明：我们的方案可以为移动用户提供更好的服务质量。     

An Efficient Scheme to Reduce Handoff Dropping in LEO Satellite Systems

The problem of handoffs in cellular networks is compounded in a low earth orbit (LEO) satellite-based cellular network due to the relative motion of the satellites with respect to a stationary observer on earth. Typically, the velocity of motion of mobiles can be ignored when compared to the very high velocity of the footprints of satellites. We exploit this property of LEO satellite systems and propose a handoff scheme based on a channel sharing approach that results in a substantial decrease in handoff dropping. For the same handoff dropping performance, our scheme has significantly lower new call blocking probability than the conventional reservation scheme. We also present an analytical approximation that is in very good accord with simulation results.     

A framework of handoffs in wireless overlay networks based on mobile IPv6

Although there are various wireless access network technologies with different characteristics and performance level have been developed, no single network that can satisfy the anytime, anywhere, and any service wireless access needs of mobile users. A truly seamless mobile environment can only be realized by considering vertical and horizontal handoffs together. With the advantages of Mobile IPv6, a more comprehensive and integrated framework of heterogeneous networks can be developed. In this paper, we discuss the issues related to handoffs including horizontal and vertical handoffs. We present a scheme for integrating wireless local area network and wide area access networks, and propose a micromobility management method called HiMIPv6+. We also propose a QoS-based (quality-of-service-based) vertical handoff scheme and algorithm that consider wireless network transport capacity and user service requirement. Our prototype evaluations and the simulations show that our framework performs as expected.     

A learning approach for prioritized handoff channel allocation in mobile multimedia networks

An efficient channel allocation policy that prioritizes handoffs is an indispensable ingredient in future cellular networks in order to support multimedia traffic while ensuring quality of service requirements (QoS). In this paper we study the application of a reinforcement-learning algorithm to develop an alternative channel allocation scheme in mobile cellular networks that supports multiple heterogeneous traffic classes. The proposed scheme prioritizes handoff call requests over new calls and provides differentiated services for different traffic classes with diverse characteristics and quality of service requirements. Furthermore, it is asymptotically optimal, computationally inexpensive, model-free, and can adapt to changing traffic conditions. Simulations are provided to compare the effectiveness of the proposed algorithm with other known resource-sharing policies such as complete sharing and reservation policies     

An adaptive resource reservation for vehicular mobile networks

This paper presents the time‐based bandwidth reservation (TBR) algorithm, suitable for handoff management in cellular systems. TBR is based on real‐time measurements of mobile stations (position, velocity and acceleration). The scheme consists in sending reservation requests to the neighboring cells based on an extrapolation of the user's motion. The originality of our approach lies in dynamically adjusting the amount of time for which bandwidth has to be allocated and reserved in a cell. In addition, we propose an optimal channel requests arrangement (CRA) algorithm in order to improve the performance of TBR in terms of resource utilization. Finally, we propose VTBR, an adapted and extended version of TBR for better support of vehicular network specificities where service degradation or forced call termination may occur owing to frequent handoffs. Detailed simulation results for TBR and VTBR schemes and a comparison with the guard channel scheme are presented. The results show that TBR and VTBR can efficiently improve the flow dropping probability. Copyright © 2008 John Wiley & Sons, Ltd.     

Channel management in microcell/macrocell cellular radio systems

In this paper, we study spectrum management in a two-tier microcell/macrocell cellular system. Two issues are studied: micro-macro cell selection and frequency spectrum partitioning between microcells and macrocells. To keep the handoff rate in a two-tier cellular system at an acceptable level, low mobility users (with speed υ0 ) should undergo handoffs at microcell boundaries, and high mobility users (with speed υ>V₀) should undergo handoffs at macrocell boundaries. The mobile determines user mobility from microcell sojourn times and uses it for channel assignment at call origination and handoff. The probability of erroneous assignment of a mobile to a microcell or macrocell is shown to be significantly lower than previous approaches. We investigate the optimal velocity threshold, V₀, and propose that it may be dynamically adjusted according to traffic load. Finally, we propose a systematic way for finding an optimal partition of frequency spectrum between microcells and macrocells. This partitioning is based on the traffic load and velocity distribution of mobiles in the system     

Handoff performance in wireless DS‐CDMA networks

This paper analyses the performance of DS‐CDMA networks in the presence of call handoffs. We show that a handoff may violate the SINR requirements for other users, and thus cause an outage in the target cell. We propose to use the probability of such events as a possible metric for quality of service in networks with multiple traffic types, and derive the corresponding QoS parameters. A two‐level admission policy is defined: in tier 1 policy, the network capacity is calculated on the basis of the bound on outage probability. However, this policy does not suffice to prevent outage events upon handoffs for various traffic types, and henceforth, we propose an extension that reserves extra bandwidth for handoff calls, thus ensuring that handoff calls will not violate the outage probability bound. The overhead imposed by the extension is negligible, as the complete two‐tier admission control algorithm is executed only when a call is admitted into the network. Once admitted, calls can freely execute handoffs using the reserved bandwidth. The modified second‐tier bandwidth reservation policy is adaptive with respect to the traffic intensity and user's mobility and we show that it can provide satisfactory call (flow) quality during its lifetime. Analytical results for the QoS have been verified by the simulations. Copyright © 2002 John Wiley & Sons, Ltd.     

Probabilistic channel reservation scheme for mobilepico/microcellular networks

Channel reservation based on the handoff probability of a call arriving in an adjacent cell is proposed as a more flexible and dynamic means of providing handoff priority in mobile pico/microcellular networks in which frequent handoff events are to be expected. A basic probabilistic channel reservation scheme is described and shown to yield improvements in performance, especially in terms of channel utilization by successfully completed call, over the well-known static trunk reservation policy     

Mitigating location management traffic via aggregation in multi-hop cellular networks

In high mobility areas such as shopping malls and transportation stations, mobile users tend to move in and out in a bursty fashion, and hence location update (LU) and paging signaling cause substantial traffic burden to the cellular networks, leading to signaling congestion. This poses a great challenge to the system design for wireless cellular systems. Traditional cellular systems cannot cope with this situation very well. However, with the ad hoc operational mode recently introduced into the cellular systems, the added multi-hop relaying via mobile devices provides a new way to mitigate location management traffic. In this paper, based on this new architecture, we propose a novel scheme, called aggregative location management, which aggregates multiple location updates into group location updates. For the scenarios of high capacity transit (HCT) systems, we use this grouping scheme to alleviate the signaling traffic when mobile users in an HCT move into new location areas. For other scenarios with mass arrivals of LU requests, we develop a generic aggregative location management scheme in which LU requests can be first aggregated by designated mobile devices and then are periodically sent to the location registers. Performance evaluation is carried out and shows their significant effectiveness.     

Channel Allocation Scheme for Handoff Control in Wireless Ad Hoc Network with Group Mobility

Because a wireless ad hoc network does not have a fixed backbone network and the mobile base station moves randomly, the conventional channel allocation scheme cannot efficiently predict group mobility and is not feasible to support a burst handoff traffic due to group mobility. In this paper, we propose an channel allocation scheme to solve this problem. Our scheme efficiently support burst handoff using guard channel and hello message in wireless ad hoc network with group mobility. We developed an analytical Markov model for the proposed scheme and evaluate our scheme in terms of new call and handoff blocking probability and channel utilization via simulation study. Simulation results show that our scheme offers better performance than the conventional schemes.     

Adaptive quality of service handoff priority scheme for mobilemultimedia networks

For various advantages including better utilization of radio spectrum (through frequency reuse), lower mobile transmit power requirements, and smaller and cheaper base station equipment, future wireless mobile multimedia networks are likely to adopt micro/picocellular architectures. A consequence of using small cell sizes is the increased rate of call handoffs as mobiles move between cells during the holding times of calls. In a network supporting multimedia services, the increased rate of call handoffs not only increases the signaling load on the network, but makes it very difficult for the network to guarantee the quality of service (QoS) promised to a call at setup or admission time. This paper describes an adaptive QoS handoff priority scheme which reduces the probability of call handoff failures in a mobile multimedia network with a micro/picocellular architecture. The scheme exploits the ability of most multimedia traffic types to adapt and trade off QoS with changes in the amount of bandwidth used. In this way, calls can trade QoS received for fewer handoff failures. The call level and packet level performance of the handoff scheme are studied analytically for a homogeneous network supporting a mix of wide-band and narrow-band calls. Comparisons are made to the performance of the nonpriority handoff scheme and the well-known guard-channel handoff scheme     

Immune optimization algorithm for solving vertical handoff decision problem in heterogeneous wireless network

In heterogeneous wireless network environment, wireless local area network (WLAN) is usually deployed within the coverage of a cellular network to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. Vertical handoffs between the WLAN and the cellular network maybe occur frequently. As for the vertical handoff performance, there is a critical requirement for developing algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a mathematical model for vertical handoff decision problem, and propose a multi-objective optimization immune algorithm-based vertical handoff decision scheme. The proposed scheme can enable a wireless access network not only to balance the overall load among all base stations and access points but also maximize the collective battery lifetime of mobile terminals. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed scheme.     

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     

Mobile ad hoc relaying for upward vertical handoff in hybrid WLAN/cellular systems

One of the main issues in hybrid wireless networks is vertical handoff. Dropping probability is one of the important parameters that must be considered in planning the wireless communication systems. However, there has not been much effort in dropping rate reduction in loosely coupled hybrid wireless networks. In loosely coupled WLAN/cellular systems the system administrator of the WLAN is different from the cellular one. Therefore, in these situations, reducing the dropping probability based on classical methods such as using reserved guard channels is difficult. A handoff from a WLAN to a cellular system occurs when a multi-mode device moves out of the WLANs coverage area. This is an upward vertical handoff in a hybrid network. In this paper, we propose to employ ad hoc relaying during the upward vertical handoff in a hybrid WLAN/cellular system. Two-hop and multi-hop relaying approaches, which we propose in this paper, improve the dropping probability regardless of the number of reserved channels. Simulation results support the effectiveness of the proposed methods. Also, practical routing protocols are proposed in order to implement the suggested relaying methods.     

Vertical handoffs in wireless overlay networks

No single wireless network technology simultaneously provides a low latency, high bandwidth, wide area data service to a large number of mobile users. Wireless Overlay Networks - a hierarchical structure of room-size, building-size, and wide area data networks - solve the problem of providing network connectivity to a large number of mobile users in an efficient and scalable way. The specific topology of cells and the wide variety of network technologies that comprise wireless overlay networks present new problems that have not been encountered in previous cellular handoff systems. We have implemented a vertical handoff system that allows users to roam between cells in wireless overlay networks. Our goal is to provide a user with the best possible connectivity for as long as possible with a minimum of disruption during handoff. Results of our initial implementation show that the handoff latency is bounded by the discovery time, the amount of time before the mobile host discovers that it has moved into or out of a new wireless overlay. This discovery time is measured in seconds: large enough to disrupt reliable transport protocols such as TCP and introduce significant disruptions in continuous multimedia transmission. To efficiently support applications that cannot tolerate these disruptions, we present enhancements to the basic scheme that significantly reduce the discovery time without assuming any knowledge about specific channel characteristics. For handoffs between room-size and building-size overlays, these enhancements lead to a best-case handoff latency of approximately 170 ms with a 1.5% overhead in terms of network resources. For handoffs between building-size and wide-area data networks, the best-case handoff latency is approximately 800 ms with a similarly low overhead. This revised version was published online in June 2006 with corrections to the Cover Date.     

Dynamic QoS Allocation for Multimedia Ad Hoc Wireless Networks

In this paper, we propose an approach to support QoS for multimedia applications in ad hoc wireless network. An ad hoc network is a collection of mobile stations forming a temporary network without the aid of any centralized coordinator and is different from cellular networks which require fixed base stations interconnected by a wired backbone. It is useful for some special situations, such as battlefield communications and disaster recovery. The approach we provide uses CSMA/CA medium access protocol and additional reservation and control mechanisms to guarantee quality of service in ad hoc network system. The reason we choose CSMA protocol instead of other MAC protocols is that it is used in most of currently wireless LAN productions. Via QoS routing information and reservation scheme, network resources are dynamically allocated to individual multimedia application connections.