The international standard of wireless body area networks (WBANs), ie IEEE 802.15.6, was established in Feb. 2012, and this standard decided spreading code as a suppressing interference technology. However, the sequence length of spreading code is fixed, hence it is difficult to guarantee secure communications due to noise and interference from other WBANs. In this paper, we propose utilizing direct sequence impulse radio ultra wideband (DS-IR-UWB) for multi-WBAN systems, and then analyze multi-WBAN systems theoretically, derive equations of inter-WBAN interference, packet error rate (PER) and throughput. Furthermore, to guarantee secure communications, the desired PER is introduced, and then an algorithm is proposed to take the control of sequence length of DS-IR-UWB in order to ensure that the PER of system is always below the desired PER while maximizing the throughput. The numerical evaluation shows that the sequence length of proposed control method is changed according to the SNR and the number of WBANs, it lets the proposed algorithm of control of sequence length outperform the conventional fixed sequence length method.
