Magnitude modulation for small satellite Earth terminals using QPSK and OQPSK

This paper investigates the design and application of data magnitude modulation to reduce power amplifier back-off for QPSK and OQPSK modulations for small satellite Earth stations. The coefficients for data magnitude modulation are obtained by using an iterative design loop. The parameters of this loop are tuned to obtain maximum gain. Roll-off factors from 10% to 100% are considered, with emphasis on small roll-off values for increased bandwidth efficiency. It is shown that a gain of almost 6dB can ideally be obtained for a roll-off factor of 10%. Error correction coding is used to compensate for the increased sensitivity to noise of the magnitude modulated data. The loss due to this increased sensitivity is reduced from almost 5.5dB to 1.2dB for a roll-off factor of 10% by using high rate product codes, thus giving an overall gain of 4.8dB. Trade offs between spectral regrowth and implementation are addressed.