2 resultados para Low Autocorrelation Binary Sequence Problem
em Duke University
Resumo:
*Designated as an exemplary master's project for 2015-16*
The American approach to disparities in educational achievement is deficit focused and based on false assumptions of equal educational opportunity and social mobility. The labels attached to children served by compensatory early childhood education programs have evolved, e.g., from “culturally deprived” into “at-risk” for school failure, yet remain rooted in deficit discourses and ideology. Drawing on multiple bodies of literature, this thesis analyzes the rhetoric of compensatory education as viewed through the conceptual lens of the deficit thinking paradigm, in which school failure is attributed to perceived genetic, cultural, or environmental deficiencies, rather than institutional and societal inequalities. With a focus on the evolution of deficit thinking, the thesis begins with late 19th century U.S. early childhood education as it set the stage for more than a century of compensatory education responses to the needs of children, inadequacies of immigrant and minority families, and threats to national security. Key educational research and publications on genetic-, cultural-, and environmental-deficits are aligned with trends in achievement gaps and compensatory education initiatives, beginning mid-20th century following the Brown vs Board declaration of 1954 and continuing to the present. This analysis then highlights patterns in the oppression, segregation, and disenfranchisement experienced by low-income and minority students, largely ignored within the mainstream compensatory education discourse. This thesis concludes with a heterodox analysis of how the deficit thinking paradigm is dependent on assumptions of equal educational opportunity and social mobility, which helps perpetuate the cycle of school failure amid larger social injustices.
Resumo:
Backscatter communication is an emerging wireless technology that recently has gained an increase in attention from both academic and industry circles. The key innovation of the technology is the ability of ultra-low power devices to utilize nearby existing radio signals to communicate. As there is no need to generate their own energetic radio signal, the devices can benefit from a simple design, are very inexpensive and are extremely energy efficient compared with traditional wireless communication. These benefits have made backscatter communication a desirable candidate for distributed wireless sensor network applications with energy constraints.
The backscatter channel presents a unique set of challenges. Unlike a conventional one-way communication (in which the information source is also the energy source), the backscatter channel experiences strong self-interference and spread Doppler clutter that mask the information-bearing (modulated) signal scattered from the device. Both of these sources of interference arise from the scattering of the transmitted signal off of objects, both stationary and moving, in the environment. Additionally, the measurement of the location of the backscatter device is negatively affected by both the clutter and the modulation of the signal return.
This work proposes a channel coding framework for the backscatter channel consisting of a bi-static transmitter/receiver pair and a quasi-cooperative transponder. It proposes to use run-length limited coding to mitigate the background self-interference and spread-Doppler clutter with only a small decrease in communication rate. The proposed method applies to both binary phase-shift keying (BPSK) and quadrature-amplitude modulation (QAM) scheme and provides an increase in rate by up to a factor of two compared with previous methods.
Additionally, this work analyzes the use of frequency modulation and bi-phase waveform coding for the transmitted (interrogating) waveform for high precision range estimation of the transponder location. Compared to previous methods, optimal lower range sidelobes are achieved. Moreover, since both the transmitted (interrogating) waveform coding and transponder communication coding result in instantaneous phase modulation of the signal, cross-interference between localization and communication tasks exists. Phase discriminating algorithm is proposed to make it possible to separate the waveform coding from the communication coding, upon reception, and achieve localization with increased signal energy by up to 3 dB compared with previous reported results.
The joint communication-localization framework also enables a low-complexity receiver design because the same radio is used both for localization and communication.
Simulations comparing the performance of different codes corroborate the theoretical results and offer possible trade-off between information rate and clutter mitigation as well as a trade-off between choice of waveform-channel coding pairs. Experimental results from a brass-board microwave system in an indoor environment are also presented and discussed.
