FORWARD-LOOKING TONE ALLOCATION IN MULTIPOINT-TO-POINT COMMUNICATION USING ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING

1 . A multipoint-to-point, orthogonal frequency division multiplexed (OFDM) communication system comprising:

a plurality of remote units;

a host unit that includes a demodulator;

wherein each of the remote units transmits an upstream OFDM signal using a multiple access scheme to the host unit demodulator using at least one of a plurality of orthogonal tones within an OFDM waveform;

wherein the host unit receives the upstream OFDM signals from a plurality of the remote units, the tones of the upstream signals being substantially orthogonal when received at the host unit;

wherein portions of upstream OFDM signals from at least two of the remote units arrive at the host unit at the same time;

wherein the host unit demodulator demodulates said portions;

wherein the host unit sends an adjustment signal to at least one of the remote units instructing the at least one remote unit to adjust the timing of transmissions from the remote unit to improve orthogonality of the OFDM waveform received at the host unit, and

wherein the host unit allocates at least one of the tones to the at least one remote unit based at least in part on channel quality information for the at least one tone.

2 . The OFDM communication system of claim 1 wherein the host unit determines channel quality for the at least one tone based at least in part on an error rate history for the at least one tone.

3 . The OFDM communication system of claim 1 wherein the host unit determines channel quality for the at least one tone based at least in part on a signal-to-noise ratio for the at least one tone.

4 . The OFDM communication system of claim 1 wherein the host unit allocates the at least one tone to the at least one remote unit based at least in part on a comparison of channel quality information for a plurality of unallocated tones.

5 . The OFDM communication system of claim 4 wherein the comparison of channel quality is a comparison of length of low-error rate history for the plurality of unallocated tones.

6 . The OFDM communication system of claim 4 wherein the comparison is performed by ranking the plurality of unallocated tones based at least in part on channel quality information.

7 . The OFDM communication system of claim 6 wherein the ranking is performed based at least in part on type of service to be transmitted.

8 . The OFDM communication system of claim 1 wherein the host unit stores a channel quality database table for the plurality of tones, and wherein the channel quality database table is used by the host unit in determining which tones to allocate to remote units.

9 . A system comprising:

a host unit;

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);

wherein the host unit sends an adjustment signal to at least one of the remote units instructing the at least one remote unit to adjust the timing of transmissions from the remote unit to improve orthogonality of OFDM transmissions received at the host unit from the plurality of remote units;

wherein the host unit allocates orthogonal tones within the system to the plurality of remote units; and

wherein the host unit switches the tone allocation for at least one remote unit from a first tone to a second tone based at least in part on channel quality information for the second tone.

10 . The system of claim 9 wherein the host unit switches the tone allocation based at least in part on channel quality information for the first tone.

11 . The system of claim 10 wherein the host unit switches the tone allocation after detecting that the first tone has become corrupted.

12 . The system of claim 9 wherein the channel quality information includes at least one of error rate information and signal-to-noise ratio information.

13 . The system of claim 12 wherein the signal-to-noise ratio information is estimated using equalizer error information.