Adaptive Quorum: A Traffic Aware Power Saving Mechanism for Multi-hop Mobile Ad-hoc Networks Seyed Ali Hosseininezhad Golnoosh Saeedi Nejad Keyvan Rahimizadeh Mehdi Dehghan Amirkabir University of Technology, Tehran, Iran Amirkabir University of Technology, Tehran, Iran Amirkabir University of Technology, Tehran, Iran Amirkabir University of Technology, Tehran, Iran seyedali@aut.ac.ir golnoosh.s@gmail.com rahimizadeh@aut.ac.ir dehghan@aut.ac.ir Abstract ⎯ In this paper we propose a method for adaptive power saving based on Cyclic Quorum method. Quorum based protocols can make a guarantee for upper delay bounds which a node can experience before it can see the next hop in active state. These methods are useful for multi-hop ad-hoc networks which do not have any global synchronization between their nodes. We try to make Cyclic Quorum protocol adaptive to changes in traffic condition of network. We have shown that using Adaptive Quorum, nodes can be power conservative up to 3.5 times more than IEEE 802.11 in low traffic conditions. This method presents throughput and delay efficiencies to be very close to what network can experience while nodes are always on. This method also considers different quality of service requirements for making decisions to change the power efficiency. Independency of MAC layer from other network layers is also observed and therefore no information is needed from routing layer. Keywords ⎯ Adaptive Power Saving, Quorum based Protocols, IEEE 802.11 , Multi-hop Ad-hoc. 1. Introduction One of the problems in ad-hoc wireless networks is power limitation of devices participating in network configuration. Being responsible for sending the packets of other nodes, each node in ad-hoc networks plays a vital role in whole network connectivity. But it is not possible to use unlimited power supplies due to nodes mobility and therefore power limitation is a challenge for these networks. The power consumption of network interfaces in three states of sending, receiving and standby are similarly high. Hence, if transceiver modules try to lessen their active times, battery life will augment. For this reason, various methods have been developed. Some of these methods, for instance, decrease transmission power when receivers are nearby and there is no need to transmit packets with maximum power. In some other methods, it is supposed that all the transmitters have one transmission power level and their signal strength cannot be altered. In such algorithms, it is desirable to avoid unreasonable power consumption through shutting down the transceiver module when there is no packet to be sent or received by that node. There are two problems to be investigated in these methods. Firstly, power saving percentage should be surveyed. The more power consumption reduces, the more algorithm approaches its goal which is reaching the point that each node is active just when it is sending or receiving packets. Secondly there is a trade-off between power saving ratio and the delay imposed on packets; because each packet has to be buffered until the next node is activated and consequently, packet end-to-end delay increases. This yields to lower network throughput which obliges the sender to wait more before it can deliver its data. In consequence, power consumption augments, which is contrary to the algorithm’s main goal. Thereupon, streams which need quality of service and are sensitive to end-to-end delay (such as video conferencing) cannot achieve their eligible service. 2. Related Work 2.1. 802.11 PSM IEEE 802.11 standard [1] is the protocol most discussed in research. In this protocol, two options regarding power management are considered. In the first, network interface card operates normally and is active the whole time. In the other, namely PSM 1 , network interface card can have two states: active and inactive. Being in active state, node is ready to send or receive packets. In contrast, other nodes cannot communicate with a node in inactive state. In this protocol, time is divided to intervals, called BI 2 . In each BI, all nodes are synchronized and at the beginning of each BI all of them try to send beacons. In case that network is managed and use access points, beacons are merely sent by AP 3 . In ad-hoc networks, due to absence of a central synchronization point, all nodes are bound to send beacons. It is possible to synchronize all nodes by sending beacon from any node, only when all nodes are in each other’s communication range. After sending beacon, it is time to send ATIM 4 packets. ATIM packets do not contain data and they are aimed to inform other nodes that they have packets in their buffer waiting to be sent. Each node which receives this packet and does not find its address in destinations list can change its state to inactive until the next BI. But those nodes which are among the destinations enlisted in ATIM packet need to send ATIM-acknowledge and remain active until the end of BI. 802.11 PSM is designed for 1 Power Saving Mode 2 Beacon Interval 3 Access Point 4 Ad-hoc Traffic Indication Message ISBN 978-89-5519-136-3 -322- Feb. 17-20, 2008 ICACT 2008