Modulation of a digital signal to produce a narrow band output with approximately constant envelope

摘要

The transmitted signal results from the modulation of digital data by a modulation function which is a Gaussian function of time t. The digital data comprises a set of bits bk identified by rank k and of duration T. The transmitted signal consists of an indexed sum by rank k of the product of the complex constant j to the power k, of the modulation function h(t-kT) and of the input data. The modulator comprises a signal processor (PR) which splits the input signal into real and imaginary components in the form S = I + jQ. A time base (BDT) generates a clock Ck and a carrier C. The carrier is fed into a de-phaser circuit DEP. Mixer M1 combines the carrier with real signal I and mixer M2 combines the de-phased carrier with the complex component of the signal. The two outputs are then summed.