Patent ID: 6141317
Filing Date: 2000-10-31
Classification: H04L

Abstract:
A multi-point communications system having an allocated bandwidth dedicated to communications for the multi-point communications system, the multi-point communications system comprising:a head end unit disposed at a primary site, the head end unit including a transmitter for transmitting OFDM/DMT (Orthogonal Frequency Division Multiplexing/Discrete Multi Tone) modulated data over a predetermined number of bins across a transmission medium to a plurality of remote transceivers, the transmitter of the head end unit transmitting OFDM/DMT modulated data corresponding to a first data stream to a first one of the plurality of remote transceivers over one or more bins of a first subset of the predetermined number of bins and OFDM/DMT modulated data corresponding to a second data stream to a second one of the plurality of remote transceivers over one or more bins of a second subset of the predetermined number of bins, the transmitter having at least an X QAM (Quadrature Amplitude Modulation) mode of transmission for transmitting X QAM modulated data in any given one of the first and second subsets of bins and a Y QAM mode of transmission for transmitting Y QAM modulated data in any given one of the first and second subset of bins, where X and Y are different integer numbers reflecting a constellation size used for data transmission in a bin and where X>Y, the head end also monitoring bandwidth used in the system and comparing the used bandwidth to a predetermined bandwidth threshold value;the first transceiver receiving the OFDM/DMT data from the transmission medium over the one or more bins of the first subset of bins and transmitting one or more data segments to the head end unit corresponding to measurements of signal-to-noise ratios for the one or more bins of the first subset of bins, the head end unit using the one or more data segments to direct the first transceiver to receive in either the X QAM mode or the Y QAM mode on the one or more bins of the first subset of bins without substantially effecting the data rate of the received first data stream when the predetermined bandwidth threshold value is exceeded and the measured signal-to-noise ratios (SNR) in the one or more bins of the first subset of bins is above a predetermined SNR threshold value;the second transceiver receiving the OFDM/DMT data from the transmission medium over the one or more bins of the second subset of bins and transmitting one or more data segments to the head end unit corresponding to measurements of signal-to-noise ratios for the one or more bins of the second subset of bins, the head end unit using the one or more data segments to direct the second transceiver to receive in either the X QAM mode or the Y QAM mode on the one or more bins of the first subset of bins without substantially effecting the data rate of the received first data stream when the predetermined bandwidth threshold value is exceeded and the measured signal-to-noise ratios in the one or more bins of the second subset of bins is above a predetermined SNR threshold value.