March 25, 2018
March 25, 2018
March 27, 2018
TITLE Simple Student-Built IQ Modulator/Demodulators for Wireless Communication Laboratory Digital Communication Link Demonstrations
ABSTRACT Instrumentation Vector Signal Generators (VSG) and Vector Signal Analyzers (VSA) are great tools to demonstrate wireless communication link characteristics but are often too expensive for equipping every station in a digital communications laboratory. Software Defined Radios (SDR) equipment are also great tools for demonstrating wireless links as there are models now that are relatively inexpensive and have great performance.
The laboratory exercise discussed in this contribution provides many of the learning outcomes possible with VSA/VSG equipment with additional insights at the hardware level that might not be evident using SDRs. The laboratory exercise in this contribution centers on having students build IQ modulators/demodulators that can be used to demonstrate digital communication links. The required construction parts include semi-rigid coaxial cable, surface mount frequency mixers, and surface mount resistors that cost $12. A pre-lab handout and introductory laboratory lecture illustrate how IQ modulators are used to generate arbitrary digital modulation constellations in the I-Q plane. An example completed IQ modulator is shown to students demonstrating the basics of high frequency signal routing with short lead lengths and good grounding. Each student then individually solders together the IQ modulator assembly in a process that can be done in about 2 hours. A wireless communication link is then demonstrated by having one student using their assembly as an IQ modulator and a student partner using their assembly as an IQ demodulator. The IQ modulator uses a function generator input and the IQ demodulator uses an oscilloscope as the receiver. Students can directly witness the importance of having the local oscillator of the transmitter phase locked to the local oscillator of the receiver in order for the digital communication link to be successful. Students also compare Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and higher order constellations as part of the characterization of the digital links.
Student feedback on the IQ Modulator/Demodulator laboratory project centers on how the soldering and high frequency layout of the project are eye-opening compared to early laboratory activities in the curriculum. Students also report a much more in-depth understanding of I-Q modulation techniques as they use more capable VSA/VSG and SDR equipment in future laboratory sessions.
The intent is to present this as a poster paper and the author would give some live demonstrations of the laboratory exercise.
Derickson, D. (2018, March), Simple Student-Built IQ Modulator/Demodulators for Wireless Communication Laboratory Digital Communication Link Demonstrations Paper presented at 2018 ASEE Zone IV Conference, Boulder, Colorado. https://peer.asee.org/29625
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