Systems and method for orthogonal frequency divisional multiplexing
View Patent ↗Systems and methods for orthogonal frequency division multiplexing are provided. In one embodiment, a multi-carrier modem comprises: a receiver configured to receive a waveform comprising a plurality of spectrally overlapping carrier signals from at least two of a plurality of remotes, the carrier signals are modulated using an inverse Fourier transform; a transmitter; a processor coupled to the transmitter, the processor outputs data for transmission to the transmitter, the processor applies an inverse Fourier transform to the data provided to the transmitter; a controller programmed to instruct the transmitter to transmit timing adjustments to the at least two of the plurality of remotes, the timing adjustments instruct the at least two of the plurality of remotes to adjust transmission timing so that transmitted symbols associated with frames of a predetermined multiframe structure are received in sequence from the at least two of the plurality of remotes based on the structure.
1. A remote service unit using minimum allocations in a multipoint-to-point communication system, the remote service unit comprising:
a transceiver communicatively coupled with a host unit in a multipoint-to-point configuration, the transceiver configured to communicate with the host unit via a composite orthogonal frequency division multiplexing (OFDM) waveform of adjacent spectrally overlapping sub-carriers, wherein the transceiver further includes:
at least one converter generating an analog signal based on a stream of time domain in-phase and quadrature phase data; and
a radio frequency transmitter for transmitting a radio frequency signal based on the analog signal;
a multi-carrier modem coupled to the transceiver and configured to modulate upstream payload data onto a plurality of OFDM sub-carriers transmitted by the transceiver, the multi-carrier modem synchronized with the host unit such that the upstream payload data transmitted by the transceiver and other upstream OFDM signals from other transceivers received at the host unit combine to form the composite OFDM waveform, wherein the multi-carrier modulator further includes:
at least one symbol mapper that maps data into symbols using quadrature amplitude modulation (QAM) symbol mapping and phase-shift keying (PSK) symbol mapping; and
a Fast Fourier Transform (FFT) engine, between the at least one symbol mapper and the transceiver, that receives a frame of parallel data, the Fast Fourier Transform (FFT) engine generating time domain in-phase and quadrature phase data from the parallel data;
wherein the remote unit receives channel allocations from the host unit, wherein whenever a channel allocation is made for transport of upstream payload data, the channel allocation provides a plurality of OFDM sub-carriers.
2. The remote service unit of claim 1 , wherein the transceiver further comprises a wireless radio frequency transmitter for transmitting a radio frequency signal comprising the plurality of distinct OFDM subcarriers.
3. The remote service unit of claim 1 , wherein the transceiver comprises:
a transmitter component; and
a receiver component.
4. The remote service unit of claim 1 , wherein the OFDM sub-carriers are selected based on an allocation received from the host unit, wherein each allocation received for transmitting upstream payload to the host unit comprises at least a plurality of contiguous OFDM subcarriers within the composite OFDM waveform.
5. The remote service unit of claim 1 , wherein the remote service unit uses the phase-shift keying (PSK) symbol mapping when transmitting control data to the host unit.
6. The remote service unit of claim 1 , wherein the remote service unit receives the channel allocation based at least in part on information about the data to be transmitted by the remote service unit.
7. The remote service unit of claim 1 , wherein the synchronization of the remote service unit OFDM sub-carriers in time is at least in part based on the remote service unit making timing adjustments to its upstream transmissions to the host unit to equalize a round trip delay of transmissions between the remote service unit and the host unit with transmissions between at least one of the other transceivers and the host unit.
8. The remote service unit of claim 1 , wherein the synchronization of the remote service unit OFDM sub-carriers in time is at least in part based on the remote service unit making timing adjustments to its upstream transmissions based on information received from the host unit to align at the host unit multiframes transmitted by the remote service unit with multiframes transmitted to the host unit by at least one of the other transceivers.
9. The remote service unit of claim 1 , wherein the remote service unit repeats a follow-up synchronization procedure to maintain timing synchronization within the composite OFDM waveform.
10. The remote service unit of claim 1 , wherein the OFDM waveform is a frequency spectrum divided into at least 480 orthogonal sub-carriers.
11. The remote service unit of claim 1 , wherein the remote service unit uses a data modulation technique wherein a symbol generated by the symbol mapper is modulated onto a single orthogonal sub-carrier.
12. The remote service unit of claim 1 , wherein the multicarrier modulator further includes a component between the symbol mapper and the FFT engine, the component receiving symbols generated by the symbol mapper and outputting the parallel data to the FFT engine.
13. The remote service unit of claim 12 , wherein the component is a buffer.