Patent ID: 7133352

Claim:
In a unidirectional or broadcasting communication system using OFDM transmission from a base station to subscriber units, means for achieving a bi-directional channel comprising: A. transmitting means in the subscriber units for transmitting signals that are orthogonal to signals transmitted from the base station and are also orthogonal to signals from other subscriber units; B. receiving means in the base station for receiving and processing together signals from a plurality of subscriber units; C. Automatic Frequency Control (AFC) means at the base station for detecting deviations in a frequency of the signals transmitted from each subscriber unit and for sending correction signals indicative of the deviations, to each subscriber unit; D. control means in each subscriber unit for correcting the transmit frequency responsive to the correction signals received from the base, so that the signals received at the base from each subscriber have a frequency corrected for that deviation, wherein said base station further includes means for transmitting Automatic Synchronization Control (ASC) signals to each subscriber, for correcting deviations in a transmit time of each subscriber, and wherein each subscriber further includes means for adjusting the transmit time therein responsive to said ASC signals, so that all the subscribers in an uplink channel will be received at the base during a same time window.