Portland State University. Department of Electrical and Computer Engineering
Term of Graduation
Date of Publication
Master of Science (M.S.) in Electrical and Computer Engineering
Electrical and Computer Engineering
1 online resource (xvi, 92 pages)
An L-band uplink communication system was designed and validated in the lab for a CubeSat satellite operating in low Earth orbit (LEO). This paper investigates communication link analysis, discusses the design strategy for an inexpensive CubeSat receiver operating in L-band with a moderate power Earth station transmitter, and validates the link budget with prototype hardware using an anechoic chamber.
A receiver's required carrier-to-noise ratio (CNR) establishes the basis for a link budget. The requirement for a digital communication link is set by the bit-error-rate (BER) requirement of a chosen communication protocol which is inversely related to the energy per bit to noise power spectral density (Eb/N0) of a chosen modulation scheme. The carrier power level can be controlled; however, noise power and specifically thermal noise power can only partially be controlled. Through investigation of thermal noise power effects on receiver front-end hardware, a low power and low system noise temperature receiver was designed utilizing a downconverter with inexpensive commercial off-the-shelf (COTS) components. In addition, the link analysis minimized Earth station transmit power; however, for the purpose of this thesis a simple low power transmitter was designed.
Preliminary measurements of the designed receiver and transmitter were taken to evaluate performance. Measured system noise temperature of the receiver was used for link analysis which compared to calculations. For link budget validation, closed system testing with injected noise power was conducted for a validation baseline before testing in an anechoic chamber which allowed for antenna testing in a controlled thermal noise environment. A Y-factor with correction measurement method was used with a spectrum analyzer to precisely set expected carrier and noise power levels at the receiver's front-end. The same method was used to verify the integrity of the anechoic chamber by measuring the receiver's antenna noise temperature. Measurement results compared closely to theoretical BER vs. Eb/N0 plots after a revised CNR to Eb/N0 relationship was conceived for the binary frequency-shift keying (BFSK) modulation schemes used. In addition, a small and expected modulation implementation loss was shown, and performance limitations of the sub-gigahertz transceiver IC were discovered.
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Mastrogiannis, Evangelos, "Theoretical and Experimental Validation of a CubeSat's L-Band Communication System" (2020). Dissertations and Theses. Paper 5564.