Constant Envelope Bandlimited BPSK Signal

A modified BPSK modulation technique using premodulation filtering is presented. The modified BPSK modulator achieves a smooth phase transition from 0 to π rad by going through an intermediate value of
\pi/2
rad. The resultant PSK signal has a very low AM component, particularly suitable for data transmission through nonlinear channels. Experimental tests performed in a channel having a high degree of AM nonlinearity (AM-to-AM conversion), have shown that the modified BPSK signal, when passed through a hard-limiter, has a spectrum with greatly reduced spectral sidelobes compared to the conventional BPSK signal. The modified BPSK signal has spectral lines at the carrier frequency plus multiples of the signaling frequency, which in some cases might be useful for timing recovery in the demodulation process.