Abstract:Feher patented Quadrature Phase Shift Keying(FQPSK)，which is suitable for deep space communication，is introduced at first. In order to improve its envelope fluctuation，a modified FQPSK modulation—Constant Envelope FQPSK(CEFQPSK) that has an absolutely constant envelope is presented. This modulation method not only keeps the high bandwidth efficiency, Interference and Jitter Free(IJF) features of FQPSK，but also improves the power efficiency of the radio frequency amplifiers to the utmost. In order to generate signal at high speed and real-time，several optimized technologies are adopted and these two modulation technologies are implemented by using DSP of TI.