DESIGN AND REALIZATION OF A HIGH SPEED MULTILEVEL QAM DIGITAL RADIO MODEM WITH TIME-DOMAIN EQUALIZATION

摘要

In order to use the limited radio frequency band efficiently multilevel modulation techniques are frequently employed.The present contribution focusses mainly on the Integration of an adaptive time-domain equalizer Into the demodulator of a 16-state QAM-systemo The choice of the equalizer structure resulting in a linear complex transversal filter of the parallel-In/serial-out type as well as the control algorithms for the coefficients and the carrier Is discussed.These conceptual decisions are heavily Influenced by the advanced technology available for an economic realization of the high speed,high precision circuitry.The experimental results,especially the various system signatures do not only predict a considerable reduction of the relative system outage probability but also show the adequacy of the realized modules for being used in a 64-QAM modem.It is interesting to note,that the system signature for the 64-QAM case is sllghtly Improved over the 16-QAM case In spite of the Increased number of modulation levels.