A Comparison of Digital Modulation Methods for Small Satellite Data Links

The selection of a good modulation scheme for a satellite data link should involve careful consideration of several factors. Bit-error-rate (BER), initial cost, power consumption, circuit complexity, channel linearity, reliability, and bandwidth must be considered and weighed in the selection process. This paper examines and compares various modulation methods applicable to small satellite data links. The performance of frequency-shift keying (FSK), bi-phase-shift keying (BPSK), quadrature-phase-shift keying (QPSK), offset QPSK (OQPSK), minimum-shift keying (MSK), and on-off keying (OOK) are compared. The use of a non-linear transmitter amplifier is normally desirable because of its power efficiency. Because of this, a near constant envelope modulation scheme is desired. Power efficiency and bandwidth efficiency may also be important. In regards to these and other criteria, OQPSK has good characteristics and is recommended.