Reduction of error floor of differential PSK in mobile radio channels by adaptive sampling

We investigate the error floor of both differential BPSK and differential /spl pi//4-QPSK with adaptive sampling in two-delay fading channels where the excess delay is smaller than a bit length. For "basic" DBPSK (i.e., using rectangular pulseshape), the error floor can be eliminated completely, but has finite values for pulses with raised-cosine spectrum. For a/4 DQPSK, the error floor is reduced by only a factor on the order of two as compared to fixed sampling.