Tone allocation in multipoint-to-point communication using orthgonal frequency division multiplexing

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 at least one of the plurality of remote units transmits to the host unit using at least a first orthogonal tone within the OFDM system allocated to the first remote unit by the host unit;
• wherein the host unit sends an adjustment signal to the at least one remote unit 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 after the at least one remote unit has begun transmission using the first orthogonal tone but before the at least one remote unit has completed its transmission, the host unit allocates to the at least one remote unit a different orthogonal tone within the OFDM system different than said first orthogonal tone.