Showing papers by "Samir R. Das published in 2015"

Network-side positioning of cellular-band devices with minimal effort

Abstract: We address the problem of network-side localization where cellular operators are interested in localizing cellular devices by means of signal strength measurements alone. While fingerprinting-based approaches have been used recently to address this problem, they require significant amount of geo-tagged (‘labeled’) measurement data that is expensive for the operator to collect. Our goal is to use semi-supervised and unsupervised machine learning techniques to reduce or eliminate this effort without compromising the accuracy of localization. Our experimental results in a university campus (6 sq. km) demonstrate that sub-100m median localization accuracy is achievable with very little or no labeled data so long as enough training is possible with ‘unlabeled’ measurements. This provides an opportunity for the operator to improve the model with time. We present extensive analysis of the error characteristics to gain insight and improve performance, including understanding spatial properties and developing confidence measures.

Phase-based Ranging of RFID Tags with Applications to Shopping Cart Localization

Abstract: In this work, we investigate the problem of localizing RFID tags using a ranging method used in frequency-modulated radars. The idea is to exploit the phase change of the tag response due to frequency changes that normally happen as the RFID reader frequency hops. We demonstrate the general feasibility of this technique in ranging standard RFID tags using commodity readers. We then use it for a localization application - localizing shopping carts in supermarket aisles. We show that the ranging and localization accuracies are very good (median errors 5cm and 10cm respectively) even at distances over 4m making the technique competitive with existing techniques that require more complex set up.

Ez-Channel

Abstract: There is a significant interest in new wireless multiple access protocols that adaptively split a wide frequency channel into multiple sub-channels-perhaps of varying widths-and assign these sub-channels to competing transmissions. Existing protocols suffer from various limitations such as considerable protocol overhead, dependence on a centralized controller, and use of fixed-size channels. We introduce Ez-Channel, a novel MAC protocol that parsimoniously utilizes the OFDM sub-carriers to perform channelization and assignment of sub-channels to competing links. In addition to circumventing hidden and exposed terminal problems, Ez-Channel adapts channel assignments to the network topology. To eliminate the need for a centralized controller and to avoid an overwhelming amount of information exchange, the protocol uses a randomization technique enabling provably efficient localized decision making. Our extensive analytical and simulation studies show that Ez-Channel yields significant throughput improvements as compared to the state-of-the-art protocols.

Reconfigurable wireless data center network using free-space optics

Abstract: A reconfigurable free-space optical inter-rack network includes a plurality of server racks, each including at least one switch mounted on a top thereof, where each top-mounted switch includes a plurality of free-space-optic link connector, each with a free-space optical connection to a free-space-optic link connector on another top-mounted switch, a single ceiling mirror above the plurality of server racks that substantially covers the plurality of server racks, wherein the single ceiling mirror redirects optical connections between pairs of free-space-optic link connectors to provide a clear lines-of-sight between each pair of connected free-space-optic link connectors, and a controller that preconfigures a free-space optical network connecting the plurality of server racks by establishing connections between pairs of free-space-optic link connectors, and that reconfigures connections between pairs of free-space-optic link connectors in response to network traffic demands and events.

Inter-node communication system and method

Abstract: Provided is a system for data transmission in a wireless network including a plurality of sets of directional antennas with each set of directional antennas rotatably mounted on a common axis and each antenna of each set of directional antennas focused in a different sector emanating from a respective common axis, and a memory includes routing information identifying aligned sectors of adjacent sets of directional antennas. Detection of rotation of a set of directional antennas beyond a threshold amount identifies a changed alignment of adjacent sectors. Upon identification of the changed alignment of the adjacent sectors, revised routing information is provided to the plurality of sets of directional antennas. Upon identification of the changed alignment of the adjacent sectors, a data packet is rebroadcast between adjacent sets of directional antennas utilizing directional antennas identified by the revised routing information.