I. Introduction
Preamble sampling [2], also referred to as LPL (Low Power Listening), is a key technique used by a large number of MAC protocols to save energy in wireless sensor networks. In preamble sampling, nodes save energy by keeping their radios off most of the time to reduce idle listening. To receive frames, nodes periodically wake up for a short time to sample the channel to check whether there is an ongoing transmission on the channel. A transmission is detected when a node finds that a preamble is being transmitted, in which case it keeps its radio on to receive the data frame that is sent just after the preamble. The preamble is used to indicate that a data frame will be transmitted and is long enough to make sure that all potential receivers wake up at least once during its transmission.