FQPSK-L: An Improved Constant Envelope Modulation Scheme for QPSK

A new constant envelope modulation scheme and architecture for QPSK by cubic spline interpolation methods which increase spectral efficiency and power efficiency, named FQPSK-L, is presented. This modulation technique is an extension of the Feher Quadrature Shift Keying (FQPSK) patented technologies, see Ref [1]. Being a constant envelope modulation, FQPSK-L can operate with class C power amplifier without spectrum regrowth. We achieve a more compact spectrum with comparable bit error rate performance. For example, FQPSK-L is about 20% more spectral efficient than GMSK BTb=0.3 from 40 to 70 dB attenuation point. Moreover, FQPSK-L intrinsically has spikes at fc ± 0.5fb, fc ± 1.0fb, fc ± 1.5fb, ... which are useful for carrier recovery, symbol time recovery and fading compensation. In Rayleigh fading channel, FQPSK-L outperform GMSK BTb=0.3 by 0.8 dB. FQPSK-L is an excellent scheme for wireless and satellite communications which require high spectral and power efficiency.