USE OF GUARD BANDS IN MULTIPOINT-TO-POINT ORTHGONAL FREQUENCY DIVISION MULTIPLEXING COMMUNICATION
Systems for use of guard bands in multipoint-to-point orthgonal frequency division multiplexing communication are provided. In one embodiment, an orthogonal frequency division multiplexing (OFDM) system comprises: a host unit; a plurality of remote units using a multiple access scheme to communicate at the same time with the host unit using OFDM; and wherein when at least one tone within the OFDM system carries an upstream alignment signal from at least one remote unit to the host unit to assist in aligning at least one of frequency, timing, and amplitude of transmissions from the at least one remote unit to improve orthogonality of an OFDM waveform received at the host unit, the at least one tone is separated from payload bearing tones within the OFDM system by a guard band of frequency spectrum.
1 . A multipoint-to-point, orthogonal frequency division multiplexed (OFDM) communication system comprising:
a plurality of remote units; and
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 orthogonal tone within the OFDM waveform carries at least one upstream alignment signal from at least one remote unit for assisting in aligning at least one of frequency, timing, and amplitude of transmissions from the at least one remote unit to improve orthogonality of the OFDM waveform received at the host unit; and
wherein when the at least one orthogonal tone carries the at least one upstream alignment signal the at least one orthogonal tone is separated from payload bearing tones within the OFDM waveform by a guard band of frequency spectrum.
2 . The OFDM communication system of claim 1 wherein the at least one orthogonal tone is permanently assigned to carry alignment signals to improve orthogonality of the OFDM waveform received at the host unit.
3 . The OFDM communication system of claim 1 wherein the guard band is permanently restricted from carrying payload data.
4 . The OFDM communication system of claim 1 wherein the guard band is sized to include a plurality of orthogonal tones within the OFDM waveform.
5 . The OFDM communication system of claim 1 wherein the guard band is sized to include at least ten orthogonal tones within the OFDM waveform.
6 . The OFDM communication system of claim 1 wherein the guard band is sized to reduce corruption of upstream signals from other remote units caused by said at least one upstream alignment signal from said at least one remote unit.
7 . An orthogonal frequency division multiplexing (OFDM) system comprising:
a host unit; and
a plurality of remote units using a multiple access scheme to communicate at the same time with the host unit using OFDM; and
wherein when at least one tone within the OFDM system carries an upstream alignment signal from at least one remote unit to the host unit to assist in aligning at least one of frequency, timing, and amplitude of transmissions from the at least one remote unit to improve orthogonality of an OFDM waveform received at the host unit, the at least one tone is separated from payload bearing tones within the OFDM system by a guard band of frequency spectrum.
8 . The OFDM system of claim 7 wherein the guard band is sized to include a plurality of orthogonal tones within the system.
9 . The OFDM system of claim 7 wherein the at least one tone is permanently assigned to carry signals that assist in aligning transmissions from the plurality of remote units.