Improved modulation techniques for wireless communications: raised cosine filtered FQPSK-FQPSK(RC)

An improved spectrally efficient modem scheme is proposed for wireless communications. This new scheme is based on nonlinear base band processor, with additional filtering to reduced the spectral spreading. Its spectral efficiency is improved up to 20%, comparing with GMSK. Additional filtering is a square root of raised cosine filter with a varying between 0.2 and 0.5. The performance of this technique has been evaluated in both AWGN and Rayleigh fading channels. This new spectral efficient modem is as robust as GMSK in interference limited fading environment and increases the capacity 20%.