Intermediate Frequency compression/expansion technique improves linearity performance in digital radio system

The aim of this paper is to present a new method to improve radio link performance when very complex modulation schemes, such as 64 and 128 QAM, are used. It is wanted to achieve a sort of relief for the whole radio links in particular as regard linearity and, in general, as far as much more critical aspects are concerned. In practice it is suggested to introduce an IF gain compression (AM/AM distortion) before the QAM signal is sent to the transmitter and an equal and opposite AM/AM distortion (expansion) before the signal is sent to the demodulator. In this way the IF signal is restored owing to the fact that no AM/AM distortion is altogether introduced. As a consequence the overall radio link system, that is to say the IF sections, the MW mixer, the low noise amp, the power amp and so on, are working in a much more linear and relaxed condition. In fact the peak power to the average power ratio of the modulated signal is reduced owing to the IF compression. Moreover the system results much more resistant as regard temperature variations and electrical parameters spread just by adding a very simple and low cost structure.