Predictive and adaptive bandwidth reservation for hand-offs in qos-sensitive cellular networks

Predictive

and Adaptive Bandwidth Reservation QoS-Sensitive Cellular Networks
Sunghyun Choi and Kang G. Shin
Real-Time Department of Electrical Computing Engineering Laboratory and Computer Science

for Hand-Offs *

in

The University Ann Arbor,

of Michigan 48109-2122

Michigan

E-mail: {shchoi,kgshin}@eecs.umich.edu
Abstract How to control hand-off drops is a very importantQualityof-Service (QoS) issue in cellular networks. In order to keep the hand-off dropping probability below a pre-specified target value (thus providing a probabilistic QoS guarantee), we design and evaluate predictive and adaptive schemes for the bandwidth reservation for the existing connections’ handoffs and the admission control of new connections. We first develop a method to estimate usermobility based on an aggregate history of hand-offs observed in each cell. This method is then used to predict (probabilistically) mobiles’ directions and hand-off times in a cell. For each cell, the bandwidth to be reserved for hand-offs is calculated by estimating the total sum of fractional bandwidths of the expected hand-offs within a mobility-estimation time window. We also develop an algorithmthat controls this winand effective response to dow for efficient use of bandwidth (1) time-varying traffic/mobility and (2) inaccuracy of mobility estimation. Three different admission-control schemes for new connection requests using this bandwidth reservation are proposed. Finally, we evaluate the performance of the proposed schemes to show that they meet our design goal and outperform thestatic reservation scheme under various scenarios. 1 Introduction efforts to support QoS guarantees in wireless/mobile networks have also been reported [2,3,9]. In addition to packetbound, throughput, and level QoS issues (like packet-delay packet-error probability) considered in [2,3,9], connectionlevel QoS issues (related to connection establishment and management) need to be addressed inwireless/mobile networks, because users are expected to move around during communication sessions, causing hand-offs between cells. The current trend in cellular networks is to reduce cell size to accommodate more mobile users in a given area, and it will cause more frequent hand-offs, thus making connection-level QoS even more important. One of the most important connection-level QoS issues is how tocontrol (or reduce) hand-off drops due to lack of available channels in the new cell, since mobile users should be able to continue their on-going sessions. We will consider two connection-level QoS parameters: the probability PCB of blocking new connection requests and the probability PHD of dropping hand-offs. Ideally, we would like to have no hand-off drops so that on-going connections may bepreserved as in a QoS-guaranteed wired network. However, this requires the network to reserve bandwidth in all cells a mobile might pass through; this is not possible in most cases, because the mobile’s direction is not known Moreover, this per-connection/mobile reservation a priori. will severely under-utilize, and hence quickly deplete, bandwidth, which will, in turn, cause high PCB. Each cell can,instead, reserve fractional bandwidths of on-going connections in its adjacent cells, and this aggregate reserved bandwidth (of multiple on-going connections) can be used solely for hand-offs, not for new connection requests. The problem is then how much of bandwidth in each cell should be reserved for hand-offs. In this paper, we present a predictive and adaptive scheme for bandwidth reservationand admission control that keeps the hand-off dropping probability below a target value, PHD,~~~~~~. Since it is practically impossible to completely eliminate handoff drops, the best one can do is to provide some form of probabilistic QoS guarantees by keeping PHD below a prespecified value. Our scheme is predictive as it estimates the directions and hand-off times of on-going connections in...