A low-energy adaptive and distributed MAC protocol for wireless sensor-actuator networks

We present a novel low-energy and delay-adaptive (LEAD) MAC for
wireless sensor-actuator networks that combines the effectiveness of CSMA,
TDMA and CDMA while eliminating their pitfalls. The important components
of LEAD-MAC are: (a) to minimize the total network energy consumption
with the intent to have minimum residual energy networks; (b) to
keep a minimum bound on the experienced delay that has an optimal mapping
toward any sensor network application (e.g., time-stringent traffic); and
(c) most important of all, to maintain an application-specific optimal equilibrium
between the above mentioned constraints for a promised QoS. The
sensors are intelligently scheduled (application dependent TDMA-slots) by
the actuators based on trees obtained by the ADP to insure a high delivery
rate while maintaining a low delay and a highly reduced total network energy
consumption per successful transmission. The actuator and its sensors in a
cluster have their transmissions encapsulated by a CDMA code to avoid an
access of energy-wastage due to inter-cluster interference. The presence of
actuators among sensors in the network is optimally utilized according to the
fundamental laws of economics for maximum group performance to obtain
efficient delay-energy trade-offs.
Through mathematical analysis and ns2-simulation results, we show that
LEAD-MAC greatly improves the sensor-actor system lifetime and achieves
an optimistic trade-off between the packet delay and sensor energy consumption.
LEAD-MAC is independent of network size, node density and network
topology.