Spreading with Walsh code for π/2-DBPSK modulated WBAN systems

The IEEE has proposed a narrowband PHY for the IEEE standard of wireless body area network. To maintain small phase transition of the π/2-DBPSK modulated signal and ensure simple receiver design, repetition code is used where lower data rate is needed. In this paper, we suggest to replace the repetition code by Walsh code to improve the interference cancelation capability of the system. Spreading-before-modulation approach is suggested to retain the merit of small phase transition. Three receivers, including frequency discriminator, differential demodulator and coherent receiver, are developed for the proposed scheme. We show that the proposed scheme, with slightly increased complexity, can improve the signal to interference ratio by about 2 dB, which increases with increasing packet length.