Patent ID: 8406115

Claim:
A multi-carrier modem, the modem comprising: a receiver configured to receive a waveform comprising a plurality of spectrally overlapping carrier signals from at least two of a plurality of remote units, wherein the plurality of spectrally overlapping carrier signals are modulated using an inverse Fourier transform algorithm; a transmitter; a processor coupled to the transmitter, wherein the processor outputs data for transmission by the transmitter, wherein the processor applies an inverse Fourier transform algorithm to the data provided to the transmitter; a controller programmed to calculate an elapsed time value for each of the at least two of a plurality of remote units, the elapsed time value representing an elapsed time between transmitting a ranging signal to a remote unit and receiving a signal from the remote unit in response to the ranging signal; the controller further programmed to reducing any difference between at least two elapsed time values by instructing at least one of the plurality of remote units to adjust a delay.