Baseband pulse shaping techniques for pi /4-DQPSK in nonlinearly amplified land mobile channels

The application of two baseband pulse shaping techniques to improve the spectral efficiency obtained by pi /4-DQPSK (differential quadrature phase shift keying) in a nonlinearly amplified land mobile environment is examined. The spectral and bit error rate (BER) performance of these techniques is studied through computer-aided design techniques. It is demonstrated that, by using the shaping methods considered. pi /4-QORC (quadrature overlapped raised cosine) and pi /4-CTPSK (controlled transition PSK), the spectral regeneration after nonlinear amplification can be reduced significantly. Thus, the schemes studied allow closer channel spacing compared to pi /4-DQPSK, the current standard modem scheme for the US digital mobile communications system.<>