942 IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 22, NO. 5, JUNE 2004 MH-TRACE: Multihop Time Reservation Using Adaptive Control for Energy Efficiency Bulent Tavli, Student Member, IEEE, and Wendi B. Heinzelman, Member, IEEE Abstract—In this paper, we propose multihop time reservation using adaptive control for energy efficiency (MH-TRACE), which is a medium access control (MAC) protocol that combines advantageous features of fully centralized and fully distributed networks for energy-efficient real-time packet broadcasting in a multihop radio network. We introduce a novel clustering algorithm that dynamically organizes the network into two-hop clusters. MH-TRACE clusters are just for coordinating channel access and minimizing interference; thus, ordinary nodes are not static members of any cluster. Time is organized into cyclic superframes, which consist of several time frames, to support reservation-based periodic channel access for real-time traffic. Each clusterhead chooses the frame with least interference based on its own measurements for the operation of its cluster. Energy dissipation for receiving unwanted or collided data packets or for waiting in idle mode is avoided through the use of information summarization packets sent prior to the data transmissions by the source nodes. Through the use of transmission schedules within each cluster, managed by the clusterheads, intracluster data collisions are completely eliminated and intercluster collisions are minimized. We investigated MH-TRACE through extensive simulations and theoretical analysis. Our results show that MH-TRACE outperforms existing distributed MAC protocols like IEEE 802.11 and sensor MAC, in terms of energy efficiency and throughput, approaching the theoretical maximum throughput and theoretical minimum energy dissipation. Index Terms—Energy efficiency, multiaccess communication, protocols, quality-of-service (QoS), real-time systems, speech communication. I. INTRODUCTION A D HOC NETWORK architectures for mobile radios have many application areas in several scenarios that involve groups of people. Examples of such groups are military units (e.g., a squadron of soldiers), search and rescue teams, and tourists in interactive group trips. The ad hoc network architecture for these applications should be capable of sup- porting broadcasting of real-time traffic like voice, which is the primary means of conveying information in interactive human groups. To support such real-time broadcast traffic, the network protocol must provide support for quality-of-service (QoS), such as bounding delay and reducing packet drops. Furthermore, the network protocol should avoid unnecessary Manuscript received June 1, 2003; revised November 30, 2003. This work was supported in part by the University of Rochester, Center for Electronic Imaging Systems, and in part by Harris Corporation, RF Communications Division. The authors are with the Department of Electrical and Computer Engineering, University of Rochester, Rochester, NY 14627 USA (e-mail: tavli@ece.rochester.edu; wheinzel@ece.rochester.edu). Digital Object Identifier 10.1109/JSAC.2004.826932 energy dissipation, since light-weight mobile radios are battery operated and have limited energy. A. Quality-of-Service (QoS) Achieving energy-efficient broadcasting of streaming data, such as voice, with stringent QoS requirements in a mobile wire- less ad hoc network is a challenging task. Although many pro- tocols are proposed in the literature [1]–[5], neither energy effi- ciency nor support for real-time streaming media are completely solved issues in ad hoc networks due to their highly dynamic topologies and limited network resources. QoS for streaming media necessitates timely delivery of packets (low delay) and low packet drop ratio. In broadcasting scenarios, where acknowledged data delivery is not possible, QoS of the streaming media is determined primarily by the medium access control (MAC) layer. One solution to meet the delay and packet delivery requirements for voice is to use periodic time-frame-based medium access with automatic renewal of channel access, where the frame rate is matched to the periodic rate of the voice sources [6], [7]. This ensures that flows are uninterrupted, but it requires central control to coordinate channel access. Although it is quite straightforward to coordinate channel access in single-hop networks [8], regu- lating and optimizing channel access with partial information about the network status is a challenging task in multihop networks. B. Energy Efficiency Energy efficiency of a wireless network can be achieved by jointly optimizing the transmit power [9], minimizing idle lis- tening periods [5], avoiding reception of collided packets [8], and avoiding overhearing irrelevant transmissions [4]. In addi- tion, energy saving mechanisms should not prevent the nodes from receiving or transmitting necessary data or control packets. Several MAC protocols have been developed with the goal of minimizing energy dissipation of the nodes. Sensor (SMAC) [5] is an energy-efficient MAC protocol designed specifically for sensor networks and built on top of 802.11. The authors make the observation that the main sources of energy ineffi- ciency in 802.11 are idle listening and overhearing packets des- tined for other nodes. In SMAC, idle listening is reduced by periodically shutting the radios off. All the nodes in the net- work synchronize through synchronization packet broadcasts in a master–slave fashion to match their nonsleep periods. Further- more, overhearing is avoided by entering the sleep mode after receiving the request-to-send (RTS) and/or clear-to-send (CTS) 0733-8716/04$20.00 © 2004 IEEE