LAUSR

Collision problem is critical for the performance of coexisting Wireless Body Area Networks (WBANs). This paper presents a collision analysis of CSMA/CA based MAC protocol in the view of collision probability under duty cycled superframe structure. Firstly, we discuss two types of chief collisions at a micro level (i.e., staggered collisions and direct collisions) in the presence of hidden and exposed terminals, respectively. Then we discuss various direct collisions between RTS/CTS frames in slotted CSMA/CA. Furthermore, we highlight a special type of direct collisions which can neither be detected by interfering nodes nor discovered before the collisions of DATAs (i.e., indiscoverable collisions). A hypothesis, several propositions and conclusions are presented to explain which is the domination of the collisions and how the direct collisions are released. Numerical results verify our conclusions and confirm that the indiscoverable collisions turn out to be another key issue in coexisting WBANs. The simulation in mobile environment with time-varying traffic is carried out to show the impact of collisions on network performance. To the best of our knowledge, this paper is the most comprehensive collision analysis at the micro level for the evolution of CSMA/CA based MAC protocol and the first estimation of indiscoverable collisions in duty cycled WBANs.