Hybrid Timeslot Design for IEEE 802.15.4 TSCH to Support Heterogeneous WSNs

The IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) protocol defines two types of timeslots for communications, namely dedicated and shared timeslots. An upper layer in the protocol stack uses these timeslots to design a communication schedule for the network links, based on the required bandwidth for each link. Considering a network with time-varying data traffic generation by each node, the bandwidth requirements are changing over time for each link. This leads to poor efficiency of a predefined schedule when there is no data traffic for the dedicated timeslots, or there is too much data traffic injected to the shared timeslots. In this paper, we propose a new type of timeslot, called hybrid timeslot. A hybrid timeslot acts as a dedicated timeslot for a specific link, when there are packets available to be transmitted on that link. Otherwise, it acts as a shared timeslot that can be accessed by other links, using a contention-based mechanism. The hybrid timeslot has backward compatibility with the TSCH protocol and is functional with a few adaptations in the parameter setup of the TSCH protocol. Experimental and simulation results show that for heterogeneous networks using hybrid timeslots improves communication latency without reliability penalty.