Patent ID: 6937623

Claim:
In a bi-directional data transmission system that facilitates communications between a plurality of remote units and a central unit using a symbol-based discrete multi-carrier transmission scheme that has a multiplicity of discrete sub-channels provided for facilitating upstream communications between the plurality of remote units and the central unit, an apparatus for transmitting data from a selected remote unit to the central unit, comprising: a serial to parallel converter for receiving said data and converting said data to parallel data; an encoder coupled to said serial to parallel converter for encoding said parallel data according to one of a first and a second modulation schemes responsive to a control signal, said first modulation scheme being operative during a polled transmission mode and requires a receiver at said central unit to have prior knowledge of the identity of said selected remote unit for decoding, said second modulation scheme being operative during a fast access transmission mode and does not require the receiver at said central unit to have prior knowledge of the identity of said selected remote unit for decoding; an IFFT modulator coupled to said encoder for modulating encoded data from said encoder; and a parallel to serial converter coupled to said IFFT modulator for converting modulated data from said IFFT modulator to a serial format for transmission to said central unit.