Measurement, Analysis, and Understanding of the Error Vector Magnitude (EVM) of Navigation Signals

摘要

The Navigation payload onboard the navigation satellite mainly contains the data transmitters used to broadcast the navigation messages at L band and S band carriers towards the user's community. Each data transmitter consists of navigation signal generation unit, the modulator, the up-converter and a final power amplifier, mainly the traveling wave tube amplifier (TWTA). The error vector magnitude (EVM) of the navigation signal is one of the most important performance parameters of the navigation satellite. EVM is the modulation related parameter which represents the combined effect of both amplitude and phase imbalance of the navigation signal. EVM accounts for the total noise / imperfections (in the form of white Gaussian noise, color noise, interference, spurious and distortion) present in the payload downlink path. Hence, the EVM of the navigation payload is the quantitative measure of the bit error rate performance of the payload downlink path. The EVM measurement technique, the various factors affecting the EVM values, the measured values of EVM, their understanding and analysis for the navigation payloads of a number of IRNSS (Indian Regional Navigation Satellite System) satellites have been discussed in depth in this paper.