Smart antennas are a specific type of directional antenna able to dynamically control the gain as a function of direction. This contrasts with more traditional directional antennas, where the dynamic ability is missing, and with omnidirectional antennas, which are designed to have equal gain in all directions.

It is well known that algorithms for measuring available path capacity at the IP layer by active probing tend to be more accurate when using long probe trains. This is due to the bias errors introduced by short probe trains. However, long trains have other disadvantages, such as delay, overhead, and increased risk for packet loss, especially for high probe rates. Router queue sizes also limit the maximum probe train length. In this paper, a robust method is proposed for reducing measurement bias caused by short probe trains. The method is robust in the sense that it gracefully handles lost packets and outliers, such as caused by non-Poisson cross traffic. The proposed method has been combined with the BART estimator for measuring available path capacity, and successfully tested in a multi-hop local IP network for industrial use. The principle should be generally applicable to estimators of available path capacity based on active probe trains.

This paper presents a new method, BART (bandwidth available in real-time), for estimating the end-to-end available bandwidth over a network path. It estimates bandwidth quasi-continuously, in real-time. The method has also been implemented as a tool. It relies on self-induced congestion, and repeatedly samples the available bandwidth of the network path with sequences of probe packet pairs, sent at randomized rates. BART requires little computation in each iteration, is lightweight with respect to memory requirements, and adds only a small amount of probe traffic. The BART method uses Kalman filtering, which enables real-time estimation (a.k.a. tracking). It maintains a current estimate, which is incrementally improved with each new measurement of the inter-packet time separations in a sequence of probe packet pairs. The measurement model has a strong non-linearity, and would not at first sight be considered suitable for Kalman filtering, but we show how this non-linearity can be handled. BART may be tuned according to the specific needs of the measurement application, such as agility vs. stability of the estimate. We have tested an implementation of BART in a physical test network with carefully controlled cross traffic, with good accuracy and agreement. Test measurements have also been performed over the Internet. We compare the performance of BART with that of pathChirp, a state-of-the-art tool for measuring end-to-end available bandwidth in real-time

A common view in snake robot research is that serpentine locomotion is only possible when there is nonuniform friction. This paper demonstrates that this view is incorrect, through a simple and easily reproducible experiment. We also present a theoretical kinematical analysis, which explains the experiment.

Connectors for self-reconfiguring robots need to fulfill a wide range of requirements. We discuss these properties, with emphasis on geometrical shape and latching. We describe the DRAGON modular connector, whose most distinctive features are its ability to self-align and its strength. It weighs 170 g, but holds over 70 kg load. It is able to self-align /spl plusmn/15 mm (O/5) lateral offsets, and /spl plusmn/45/spl deg/ directional and rotational offsets.

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.

We describe a principle for tactile sensing which allows acquisition of data from a sensor array using a single wire. The basic idea is to construct the sensor array as a filter. Sensor excitation changes filter characteristics, and can be recovered through the filter's impulse response. The method is also applicable to distributed sensor arrays of other scalar fields than mechanical pressure, such as heat, proximity, or radiation. We discuss the general principle, together with theoretical analysis and experimental data for a particular design.

In order to perform operations such as slip-free locomotion and vertical climbing, autonomous snake robots need joints with special properties. The most important of these are their being torsion-free, and having large pitch range. We discuss these requirements, and derive an actuated, torsion-free joint design which combines a /spl plusmn/135/spl deg/ pitch range with an unlimited roll range. The joint has been built and tested, and some data are given for a prototype, employed in an experimental snake robot.

Autonomous snake robot locomotion in rough terrain depends on the robot's ability to rise from a horizontal position to a vertical. At first sight, lifting N body segments seems to require O(N) dynamic torque. However, in this paper we describe a practical algorithm, which requires only O(1) dynamic torque. The algorithm is applicable to a wide range of snake robot morphologies. The algorithm requires little space, and control is simple, since motion occurs only in a plane. Analysis of the algorithm reveals a strong relation between the maximum dynamic torque required and the joint pitch range. We discuss some consequences for the design of snake robots. For instance, we show that an adjustment of the mass center of the robot's end segment can reduce the maximum dynamic torque. We study the implications for some snake robot joint designs, including Dragon I, an autonomous snake robot constructed for the study of unconventional locomotion.

This paper deals with the communication in task-sharing between two autonomous six-legged robots equipped with object and goal sensing, and a repertoire of contact and light-following behaviors. The performance of pushing an elongated box towards a goal region is difficult for a single robot and improves significantly when performed cooperatively, but requires careful coordination between the robots. We present and experimentally demonstrate an approach that utilizes cooperation at three levels: sensing, action, and control, and takes the advantage of a simple communication protocol to compensate for the robots' noisy and uncertain sensing.