Transmission of information from large groups of sensors using synthetic aperture radar and modulated reradiation, and, Quasi-regular LDPC code design for QAM constellations
Abstract
This thesis consists of two parts. In the first part, we develop a remote data collection system to extract information from a number of passive sensors. Active transmitters on sensors, being inherently energy expensive, pose a bottleneck to long battery life. We propose modulated reradiation of radar illumination by sensor nodes as a means to transmit information. A Synthetic Aperture processing technique is developed to decode the transmitted information and simultaneously obtain a geographic map of the sensor locations. Modulated re-radiation be achieved by switching a load on the sensor antenna. Load modulation consumes negligible power compared to an active transmitter, thus reducing the overall power consumption of the sensor. To eliminate the clutter interference in the imaging process due to the presence of unwanted targets, a nonlinear antenna load is used and the reradiated harmonics are processed. In the second part, we develop an LDPC coded modulation scheme for bandwidthefficient data transmission using QAM modulation. The underlying LDPC code is a rate 1/2 quasi-regular code having a low check degree of 5. The code is designed to offer different levels of protection to each bit position in the modulation symbol. Edges attached to different bit positions are treated differently and constraints are imposed on the check node connections to maximize the reliability of the outgoing messages from the check nodes. With a suitable choice of the constellation labeling and by using iterative demodulation, the code is shown to provide excellent performance on an AWGN channel at reasonably short block lengths.
Degree
Ph.D.
Advisors
Bell, Purdue University.
Subject Area
Electrical engineering|Remote sensing
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