An unprecedented rate of growth in the number of vehicles has resulted in acute road congestion problems worldwide, especially in many developing countries. In this article, we present Road-RFSense, a practical RF sensing--based road traffic estimation system for developing regions. Our first contribution is a new mechanism to sense road occupancy, based on variation in RF link characteristics, when line of sight between a transmitter-receiver pair is obstructed. We design algorithms to classify traffic states into two classes, free-flow versus congested, at timescales of 20 seconds with greater than 90% accuracy. We also present a traffic queue length measurement system, where a network of RF sensors can correlate the traffic state classification decisions of individual sensors and detect traffic queue length in real time. Deployment of our system on a Mumbai road gives correct estimates, validated against 9 hours of image-based ground truth. Our third contribution is a large-scale data-driven study, in collaboration with city traffic authorities, to answer questions regarding road-specific classification model training. Finally, we explore multilevel classification into seven different traffic states using a larger set of RF-based features and careful choice of classification algorithms.

In this work, we describe our experiences in building a low cost and low power wireless mesh network using IEEE 802.15.4 technology to provide telephony services in rural regions of the developing world. 802.15.4 was originally designed for a completely different application space of non-real-time, low data rate embedded wireless sensing. We use it to design and prototype a telephony system, which we term as Lo 3 (Low cost, Low power, Local voice). Lo 3 primarily provides two use cases; (1) local and broadcast voice within the wireless mesh network, and (2) remote voice to a phone in the outside world. A Lo 3 network can cost as less as $2K, and can last for several days without power "off the grid", thus making it an ideal choice to meet cost and power constraints of rural regions. We test deployed a full-fledged Lo 3 system in a village near Mumbai, India for 18 hours over 3 days. We established voice calls with an end-to-end latency of less than 120ms, with an average packet loss of less than 2%, and a MOS of 3.6 which is considered as good in practice. The users too gave a positive response to our system. We also tested Lo 3 within our department where it can be used as a wireless intercom service. To our knowledge, Lo 3 is the first system to enable such a voice communication system using 802.15.4 technology, and show its effectiveness in operational settings.

No abstract

An accelerometer based on an automatic force-balance principle has been developed with a view to measuring linear acceleration from 0.01 to 1.0 g, with overall accuracy of 0.1% under static as well as dynamic conditions in the frequency range from 0 to 70 Hz. The analysis of errors of components of various blocks and its experimental verification, the exact determination of damping ratio, and the phenomenon of reduction of undamped natural frequency arising out of the so called 'piston effect', caused by the highly viscous damping fluid, are some of the highlights in the determination of the performance. Finally, it is concluded that this linear accelerometer, using a new technique of calibration and an accurate measuring device, can be considered as a standard accelerometer. Principal symbolsA = gain of the /1-circuit {} = Bl = gain of the B-circuit B = flux density b = coefficient of damping D = diameter of feedback coil h = damping factor /," = current in calibrating coil I O ut -current in feedback coil K o = stiffness of the spring Kp = introduced stiffness K v = A 2 A 3 A^A S m = mass of the movable system n = transformation ratio n e = ratio of applied frequency to equivalent frequency n 0 = ratio of applied frequency to natural frequency N = number of turns of the feedback coil N t = number of turns on the primary side of transformer N 2 -number of turns on the secondary side of transformer R = matched output resistance on the secondary side of the transformer R in = input resistance of the transformer on primary side of the transformer a = relative value of actuating quantity £ 0 = damping ratio (open-loop) Paper 4933A (S4), first £ e = damping ratio (closed-loop) co = applied frequency cop = introduced frequency (closed-loop system) co e = equivalent frequency (closed-loop system) co 0 -undamped natural frequency (open-loop system)

No abstract