SYSTEMS AND METHOD FOR ORTHOGONAL FREQUENCY DIVISIONAL MULTIPLEXING
Systems and methods for orthogonal frequency division multiplexing are provided. In one embodiment, a multi-carrier modem comprising: a receiver configured to receive symbols from at least one of a plurality of spectrally overlapping carrier signals to produce an output; a transmitter configured to modulate symbols onto at least one of a plurality of the spectrally overlapping carrier signals; a processor coupled to the receiver, wherein the processor applies a Fourier transform to the output from the receiver; and a controller programmed to instruct the transmitter to transmit at least one symbol comprising a ranging pattern when a predetermined instruction is received by the receiver.
1 . A multi-carrier modem, the modem comprising:
a receiver configured to receive symbols from at least one of a plurality of spectrally overlapping carrier signals to produce an output;
a transmitter configured to modulate symbols onto at least one of a plurality of the spectrally overlapping carrier signals;
a processor coupled to the receiver, wherein the processor applies a Fourier transform to the output from the receiver; and
a controller programmed to instruct the transmitter to transmit at least one symbol comprising a ranging pattern when a predetermined instruction is received by the receiver.
2 . The modem of claim 1 , further comprising:
a variable delay;
wherein the variable delay is configured to vary a timing of transmissions transmitted by the transmitter.
3 . The modem of claim 1 , the controller further programmed to instruct the variable delay to vary a timing of transmissions transmitted by the transmitter when a delay adjustment instruction is received by the receiver.
4 . The modem of claim 1 , wherein the Fourier transform is based on one of a Fast Fourier Transform (FFT) and a Discrete Fourier Transform (DFT).
5 . A multi-carrier modem, the modem comprising:
a receiver configured to de-modulate symbols from at least one of a plurality of spectrally overlapping carrier signals;
a transmitter configured to modulate symbols onto at least one of a plurality of the spectrally overlapping carrier signals;
a processor coupled to the transmitter, wherein the processor outputs data for transmission by the transmitter, wherein the processor applies an inverse Fourier transform to the data transmitted by the transmitter;
a controller programmed to compare a phase of a ranging tone received from at least one of a plurality of remote units with a synchronizing tone transmitted to the plurality of remote units.
6 . The modem of claim 5 , the controller further programmed to instruct the transmitter to transmit an adjustment instruction modulated using the inverse Fourier transform to the at least one of the plurality of remote units, the adjustment instruction instructing the at least one of the plurality of remote units to vary a phase of transmissions transmitted from the at least one of the plurality of remote units.
7 . The modem of claim 6 , the controller further programmed to instruct the transmitter to transmit an adjustment instruction modulated using the inverse Fourier transform, the adjustment instruction instructing the at least one of the plurality of remote units to vary the phase of the ranging tone.
8 . The modem of claim 5 , wherein the inverse Fourier transform is based on one of an inverse Fast Fourier Transform (FFT) and an inverse Discrete Fourier Transform (DFT).