  Many TDMA- and CSMA-based protocols try to obtain fair channel access and to
increase channel utilization. It is still challenging and crucial in Wireless
Sensor Networks (WSNs), especially when the time synchronization cannot be well
guaranteed and consumes much extra energy. This paper presents a localized and
ondemand scheme ADC to adaptively adjust duty cycle based on quorum systems.
ADC takes advantages of TDMA and CSMA and guarantees that (1) each node can
fairly access channel based on its demand, (2) channel utilization can be
increased by reducing competition for channel access among neighboring nodes,
(3) every node has at least one rendezvous active time slot with each of its
neighboring nodes even under asynchronization. The latency bound of data
aggregation is analyzed under ADC to show that ADC can bound the latency under
both synchronization and asynchronization. We conduct extensive experiments in
TinyOS on a real test-bed with TelosB nodes to evaluate the performance of ADC.
Comparing with B-MAC, ADC substantially reduces the contention for channel
access and energy consumption, and improves network throughput.
