1. EVM Validation for Leapfrog Return Link
Sachin Weerasooriya – University of Illinois at Urbana Champaign
Leif Park Jordan – Harvey Mudd
Supervisor – David Schmitz
Motivation
Measure EVM of Leapfrog return link modem in Matlab to determine how well IQ data is transmitted
Error Vector Magnitude (EVM): Measure used to quantify the performance of a digital radio transmitter/receiver
Goals
Filter signal
Develop method to demodulate transmitted data
Detect timing and frequency offsets
Recover transmitted IQ symbols
Display various metrics
EVM, IQ spread, IQ imbalance, transmit power variation
Filtration
Root raised cosine (RRC) filter used in User Terminal (UT)
Reduces inter-symbol interference
Must use pair of RRC filters to properly recover data
Data passed through Matlab generated RRC filter
Example of pulse shaping filter
Recovering Bursts
Bursts contain both a timing and frequency offset.
Timing Recovery
Determine timing offset using blind timing estimation equation
Blind timing estimation not sensitive to frequency error
Frequency Recovery: Linear Phase Error
Signal with frequency offset has linearly increasing phase
Linear trend determines phase error in data
Can compare entire signal with expected symbols
Very accurate but more computation required
Can average phase error in each amble to create best fit
Less data points but more susceptible to noise and less accurate
Frequency Recovery: Cross-Correlation
Cross correlation with desired symbols determines any time lag present in transmitted signal
As signal s become similar, correlation score increases
Hypothesize various frequencies and narrow in on value with the largest correlation
Recovered Symbols
Once signal processing is done, symbols are recovered
EVM Results
Motivation & Goals
Results
Signal Processing