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

ABSTRACT

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.

KEYWORDS:

• Bit error rate (BER)
• Code division multiple access (CDMA)
• Error vector magnitude (EVM)
• Navigation signal generation unit (NSGU)
• Signal constellation

ACKNOWLEDGEMENTS

The authors are thankful to the Deputy Director, ICA, Shri V. K. Hariharan and Group Director, SCG, Smt. U. N. Vasanthakumari for their constant encouragements and motivations for writing this paper. The authors also extend their sincere gratitude to the IRNSS Project Director (Space segment), Shri V. Ramanathan for giving the opportunity to carry out this work. Finally, the authors are very much thankful to Mr Kamalakar (Ex Director, LEOS/ISRO) for giving the precious time and effort during verifying the paper meticulously.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Md. Tosicul Wara

Md. Tosicul Wara. He is a scientist at ISRO Satellite Centre. He joined ISRO in 1993. His field of interest includes satellite communication, global navigational satellite system (GNSS), and microwave measurement and instrumentations. He is a fellow of the Institution of Electronics & Telecommunication Engineers (IETE).

Raghavendra M. R.

Raghavendra M. R. He is a scientist at ISRO Satellite Centre. He joined ISRO in the year 1992. His research interest includes RF communication systems, digital signal processing, design and development of analog and digital demodulators. Presently, he is the head of GEOSAT RF & Payload Checkout Division (GRCD) at ISRO Satellite Centre. E-mail: [email protected]

Kodandaram M.

Kodandaram M. He received his Bachelor's Degree in Electronics and Communication Engineering in the year 2009 with distinction. He joined ISRO in the year 2010. His area of interests includes satellite communication, satellite based navigational system, and microwave measurement and instrumentations. E-mail: [email protected]

Bhuvaneshwari M. S.

M. S. Bhuvaneswari. She joined ISRO Satellite Centre in 1987 after graduating in electronics and communication. Currently, she is heading one of the checkout sections of Spacecraft Checkout Group. Measurement and process automation, innovative software and measurement development, visualization and data mining are her areas of interest. E-mail: [email protected]