Distributed power control in ad-hoc wireless networks

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Abstract
Mobile ad-hoc networking involves peer-to-peer communica- tion in a network with a dynamically changing topology. Achieving energy efficient communication in such a network is more challenging than in cellu- lar networks since there is no centralized arbiter such as a base station that can administer power management. In this paper, we propose and evaluate a power control loop, similar to those commonly found in cellular CDMA networks, for ad-hoc wireless networks. We use a comprehensive simula- tion infrastructure consisting of group mobility, group communication and terrain blockage models. A major focus of research in ad-hoc wireless net- working is to reduce energy consumption because the wireless devices are en- visioned to have small batteries and be incapable of energy scavenging. We show that this power control loop reduces energy consumption per trans- mitted byte by 10 - 20%. Furthermore, we show that it increases overall throughput by 15%. Ad-hoc wireless networking is receiving renewed attention. It enables many interesting usage scenarios but poses several chal- lenges. Traditionally, wireless networking has been applied to cellular telephony and Internet connectivity via radio modems. These systems provide single hop connectivity to a fix ed, wired base station. Ad-hoc wireless network systems attempt to form multi-hop networks without pre-configured network topologies. There is peer-to-peer interaction among nodes, unlike in cellular networks where nodes communicate with a centralized base sta- tion. Ad-hoc networks are characterized by dynamically chang- ing topologies, a direct result of the mobility of the nodes. Such systems can offer many advantages. They do not rely on exten- sive and expensive installations of fix ed base stations through- out the usage area. With the availability of multiple routes to the same node or base station, they can perform route selection, based on various metrics such as robustness and energy cost. Nodes can communicate directly with each other when possi- ble, rather than using a distant, intermediate base station. This can help conserve energy and improve throughput. These sys- tems enable various applications, ranging from the monitoring of herds of animals to supporting communication in military bat- tlefields (1) and civilian disaster recovery scenarios. Many of these applications require that nodes be mobile and be deployed with little network planning. The mobility of nodes limits their size, which in turn limits the energy reserves avail- able to them. Thus energy conservation is a key requirement in the design of ad-hoc networks. In wireless networks, bandwidth is precious and scarce. Simultaneous transmissions in domains which use the same bandwidth interfere with each other. Thus bandwidth re-use is also important. Power control helps combat long term fading effects and inter- ference. When power control is administered, a transmitter will use the minimum transmit power level that is required to commu- nicate with the desired receiver. This ensures that the necessary and sufficient transmit power is used to establish link closure. This minimizes interference caused by this transmission to oth- ers in the vicinity. This improves both bandwidth and energy consumption. However, unlike in cellular networks where base stations make centralized decisions about power control settings, in ad-hoc networks power control needs to be managed in a dis- tributed fashion. In this paper, we present a power control loop for ad-hoc wire- less networks. We describe the details of this algorithm in Sec- tion II. In Section III we describe the simulation infrastructure that we have built to simulate realistic ad-hoc networks. We have made an effort to model the node mobility, communication traf- fic and environment likely to be experienced in typical scenarios. We evaluate our power control loop in Section IV. Our power control loop improves energy consumption and throughput by 10-20% and 15% respectively in our simulation models.

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