Performance of SRC-filtered ODQPSK in mobile radio communications

The differential detection of OQPSK signals in a mobile radio environment is discussed. Two implementations, square-root-raised-cosine-filtered offset differential quadrature phase shift keying (SRC-ODQPSK) and constant envelope ODQPSK (CE-ODQPSK), are evaluated using computer simulation. It is demonstrated that a compact spectrum and low envelope variation of the modulated signal are achievable using SRC-ODQPSK. Its bit-error-rate (BER) performance is superior to that of π/4-DQPSK in hardlimited and fast Rayleigh fading channels. It has also been found that the CE-ODQPSK signal has a power spectral density (PSD) which is comparable to that of Gaussian minimum shift keying (GMSK) (BT = 0.4). In an additive white Gaussian noise (AWGN) channel, it outperforms one-bit and two-bit differentially detected GMSK (BT = 0.4) by 4 dB and 1.5 dB, respectively, at a BER of 10^-4. The good spectral and envelope properties, superior error performance, and simple receiver configurations make SRC- and CE-ODQPSK attractive for use in power- and bandwidth-limited mobile radio communications