Laura Marie Feeney

Investigating the energy consumption of a wireless network interface in an ad hoc networking environment

Energy-aware design and evaluation of network protocols requires knowledge of the energy consumption behavior of actual wireless interfaces. But little practical information is available about the energy consumption behavior of well-known wireless network interfaces and device specifications do not provide information in a form that is helpful to protocol developers. This paper describes a series of experiments which obtained detailed measurements of the energy consumption of an IEEE 802.11 wireless network interface operating in an ad hoc networking environment. The data is presented as a collection of linear equations for calculating the energy consumed in sending, receiving and discarding broadcast and point-to-point data packets of various sizes. Some implications for protocol design and evaluation in ad hoc networks are discussed.

An energy consumption model for performance analysis of routing protocols for mobile ad hoc networks

A mobile ad hoc network (or manet) is a group of mobile, wireless nodes which cooperatively form a network independent of any fixed infrastructure or centralized administration. In particular, a manet has no base stations: a node communicates directly with nodes within wireless range and indirectly with all other nodes using a dynamically-computed, multi-hop route via the other nodes of the manet.Simulation and experimental results are combined to show that energy and bandwidth are substantively different metrics and that resource utilization in manet routing protocols is not fully addressed by bandwidth-centric analysis. This report presents a model for evaluating the energy consumption behavior of a mobile ad hoc network. The model was used to examine the energy consumption of two well-known manet routing protocols. Energy-aware performance analysis is shown to provide new insights into costly protocol behaviors and suggests opportunities for improvement at the protocol and link layers.

Spontaneous networking: an application oriented approach to ad hoc networking

An ad hoc network must operate independent of a preestablished or centralized network management infrastructure, while still providing administrative services needed to support applications. Address allocation, name resolution, service location, authentication, and access control policies represent just some of the functionality that must be supported-without preconfiguration or centralized services. In order to solve these problems, it is necessary to leverage some aspect of the environment in which the network operates. We introduce the notion of a spontaneous network, created when a group of people come together for some collaborative activity. In this case, we can use the human interactions associated with the activity in order to establish a basic service and security infrastructure. We structure our discussion around a practical real-world scenario illustrating the use of such a network, identifying the key challenges involved and some of the techniques that can be used to address them.

Multi-rate Relaying for Performance Improvement in IEEE 802.11 WLANs

It is well known that the presence of nodes using a low data transmit rate has a disproportionate impact on the performance of an IEEE 802.11 WLAN. ORP is an opportunistic relay protocol that allows nodes to increase their effective transmit rate by replacing a low data rate transmission with a two-hop sequence of shorter range, higher data rate transmissions, using an intermediate node as a relay. ORP differs from existing protocols in discovering relays experimentally, by optimistically making frames available for relaying. Relays identify themselves as suitable relays by forwarding these frames. This approach has several advantages compared with previously proposed relay protocols: Most importantly, ORP does not rely on observations of received signal strength to infer the availability of relay nodes and transmit rates. We present analytic and simulation results showing that ORP improves the throughput by up to 40% in a saturated IEEE 802.11b network.

Evaluating Battery Models in Wireless Sensor Networks

Recent measurements highlight the importance of battery-aware evaluation of energy efficiency in wireless sensor networks. However, existing battery models been not investigated in the context of the low duty cycle, short duration loads that are typical of sensor networks. We evaluate three battery models with regard to their applicability in the WSN context. Our evaluation focuses on how the models reflect two key battery discharge behaviors, the rate capacity effect and charge recovery. We find that the models handle the former better than the latter and are more sensitive to a load’s peak current than to its timing.

Simulation and evaluation of unsynchronized power saving mechanisms in wireless ad hoc networks

Power saving mechanisms in wireless ad hoc network nodes mainly switch off the transmission and reception hardware for a maximal amount of time and turn it on again within a given interval. Many approaches aim to synchronize the state changes of the nodes in the network through distributed beacon generation and introduce mechanisms where nodes synchronously wake up at designated points of time to exchange announcements about pending traffic. Synchronization however is difficult to achieve, in particular in ad hoc networks. This paper describes the simulation, evaluation and refinement of a recently proposed power saving approach based on asynchronous wake-up patterns and wake-up announcements integrated with AODV. We show that significant improvements of the connectivity under low wake ratios can be achieved by carefully designed forwarding strategies of AODV route request messages.

A geometric derivation of the probability of finding a relay in multi-rate networks

Relaying can improve performance of a wireless network, especially when transmission modes with different distance/cost tradeoffs are available. Examples of such modes include data rates or transmission power. This paper geometrically analyzes the probability that a high-cost direct transmission can be replaced by a combination of low-cost relay transmissions. The main result of the analysis is a technology-agnostic characterization of a communication systems amenability to relaying strategies and some recommendations for how to structure such systems

Spontnet: experiences in configuring and securing small ad hoc networks

In contrast with work focusing on routing problems in mobile ad hoc networks, we address the problem of system configuration in such networks. In particular, we are interested in ways to instantiate the configuration infrastructure - naming, addressing, authentication, and key distribution

How do the dynamics of battery discharge affect sensor lifetime

needed to establish small-to-medium scale ad hoc networks supporting collaborative applications. We argue that, in such spontaneous networks, much of the necessary infrastructure can be derived from the face-to-face human interactions that these networks are intended to facilitate. This approach has the additional advantage of being intuitive for the nonexpert user. We describe Spontnet, our prototype implementation of a simple ad hoc network configuration utility based on these ideas. Spontnet allows users to distribute a group session key without previous shared context and to establish shared namespace. Two applications, a simple Web server and a shared whiteboard, are provided as examples of collaborative applications that could be useful in a spontaneous networking environment.

Towards trustworthy simulation of wireless MAC/PHY layers: a comparison framework

Evaluation of energy consumption and device lifetime in battery-powered wireless sensor networks (WSN) is almost exclusively based on estimates of the total charge (i.e. mA-h) consumed by the device. In reality, batteries are complex electro-chemical systems and their discharge behavior depends heavily on the timing and intensity of the applied load. However, there is very little empirical data or reliable models available for the kinds of batteries and loads that are typically used in WSN. The effect of battery dynamics on sensor lifetime is therefore not well understood. We characterize CR2032 Li coin cells using carefully controlled synthetic loads and a wide range of WSN-typical load parameters. Our results are the first to quantify in-depth the discharge behavior of primary batteries in the WSN context. We report that in some common cases, observed lifetimes can differ from predicted ones by almost a factor of three. Furthermore, loads with similar average currents - which would be expected to have similar lifetimes - can vary significantly in the amount of capacity they can utilize, with short duration loads generally faring better. The results show that energy evaluation based on a mA-h consumed model has significant limitations. This has important implications for the design and evaluation of WSN applications, as well as for practical problems in network dimensioning and lifetime prediction.