Various embodiments of the systems and methods described herein may be used to compute a minimum variance unbiased estimator by receiving a first OFDM signal at a pilot tone, receiving a second OFDM signal sent in the same frequency band and determining a differential phase metric between the first OFDM signal and the second OFDM signal. Advantageously, multiple supply voltages to the row decoder and a switching circuit for transferring the voltages over hierarchic-mode enabled conduction paths are provided. Therefore, the power feeding time of a battery is extended in a portable device such as laptop computer. The compartments are attached together proximate the tops of the compartments, and the bottoms of the compartments are free from being attached to each other. The catch on the piston is locked in one direction and pivots in the opposite direction such that the rack engages with the piston when it moves in a first direction and the rack disengages with the piston when it is moved in a second direction opposite the first direction.