A study on DSSS transceivers using OQPSK modulation by IEEE 802.15.4 in AWGN and flat Rayleigh fading channels

IEEE 802.15.4 defines physical layer specifications for compatible interconnections amongst devices using low-power transceivers. However, error performances of these transceivers must be discreetly studied to investigate the transceiver's energy expense on wireless communication. This paper reports a simulation-based study on the transceivers conducting direct sequence spreading spectrum (DSSS) processing and Offset Quadrature Phase Shift Keying (OQPSK) modulation specified by IEEE 802.15.4. The study focuses on evaluating the bit error rate (BER) performances of these transceivers in Additive White Gaussian Noise (AWGN) and Rayleigh flat-fading channels. A Matlab-based simulator is developed to simulate the signal processing components of the DSSS transceivers such that the input/output signals of each component and the transceiver's BER curve can be drawn. The derived BER curves are found greatly degrading from the corresponding theoretical BER. The degradation may stem from the peculiar transceiver design and inferior orthogonality of the standard chip sequences. To redeem this degradation without changing the transceiver structure, the standard chip sequences are replaced with w-sequences possessing better orthogonality. Signals transmitted via the transceivers exploiting w-sequences are found to significantly outperform the counterpart via the transceivers using the standard sequences in withstanding noise and fading effects.