  Channel sensing consists of probing the channel from time to time to check
whether or not it is active - say, because of an incoming message. When
communication is sparse with information being sent once in a long while,
channel sensing becomes a significant source of energy consumption. How to
reliably detect messages while minimizing the receiver energy consumption? This
paper addresses this problem through a reconfigurable scheme, referred to as
AdaSense, which exploits the dependency between the receiver noise figure
(i.e., the receiver added noise) and the receiver power consumption; a higher
power typically translates into less noisy channel observations. AdaSense
begins in a low power low reliability mode and makes a first tentative decision
based on a few channel observations. If a message is declared, it switches to a
high power high reliability mode to confirm the decision, else it sleeps for
the entire duration of the second phase. Compared to prominent detection
schemes such as the BMAC protocol, AdaSense provides relative energy gains that
grow unbounded in the small probability of false-alarm regime, as communication
gets sparser. In the non-asymptotic regime energy gains are 30% to 75% for
communication scenarios typically found in the context of wake-up receivers.
