This paper proposes a half-chip offset QPSK (Quadrature Phase Shift Keying) modulation CDMA (Code Division Multiple Access) scheme to allow the simple differential detection while realizing a compact spectrum in nonlinear channels for wireless LAN systems. The experimental results show the proposed scheme achieves excellent Pe (probability of error) performances in ACI (adjacent channel interference) and CCI (co-channel interference) environments. Moreover, by employing time diversity and high-coding-gain FEC (Forward Error Correction), the half-chip offset QPSK-CDMA scheme realizes an improvement of 3.0 dB (in terms of Eb/No at a Pe of 105) in Rician fading environments with a Doppler frequency fD of 10 Hz and a delay spread of 40 nsec.