A bidirectional communication system is provided. In one embodiment, a system comprises a host unit and a plurality of remote units using a multiple access scheme to communicate at the same time with the host unit using orthogonal frequency division multiplexing (OFDM). The host unit repeatedly performs an analysis of a transmission characteristic of at least one upstream signal from at least one remote unit. The at least one remote unit makes adjustments to the transmission characteristic based on the analyses performed by the host unit to assist the host unit in demodulating a plurality of upstream signals from the plurality of remote units.