Low Power Collision-Tolerant Media Access Control with On-Off Accumulative Transmission

In this paper, a cross-layer collision-tolerant (CT) media access control (MAC) scheme is proposed to achieve reliable low power communications for one-hop asynchronous wireless sensor networks (WSNs). Unlike conventional MAC schemes that discard and retransmit signals colliding at a receiver, the CT-MAC extracts the salient information from the colliding signals by leveraging on the signal processing capability in the physical layer with a new on-off accumulative transmission (OOAT) scheme. Nodes employing OOAT delivers information to a base station (BS) through asynchronous duty-cycled transmission (on-off transmission) of multiple identical sub-symbols (accumulative transmission). The on-off transmission reduces collision probability at the BS, and the accumulative transmission in the time-domain enables the simultaneous detection of colliding signals in the spatial-domain. An optimum maximum likelihood sequence estimation detector with time-varying trellis structure is employed by the BS to perform detection over the colliding signals.