US 5,815,488 A
Multiple user access method using OFDMGeneral
US 5,815,488 A
Multiple user access method using OFDM
Tech Center:
2700
Examiner:
Dang Ton
Art Unit:
2732
Inventors:
THOMAS H. WILLIAMS; RICHARD S. PRODAN
Assignee:
Priority:
09/28/95
Filed:
09/28/95
Granted:
09/29/98
Expiration:
09/28/15
Abstract
A communication method enables a plurality of remote locations to transmit data to a central location. The remote locations simultaneously share a channel and there is a high degree of immunity to channel impairments. At each remote location, data to be transmitted is coded by translating each group of one or more bits of the data into a transform coefficient associated with a frequency in a particular subset of orthonormal baseband frequencies allocated to each remote location. The particular subset of orthonormal baseband frequencies allocated to each location is chosen from a set of orthonormal baseband frequencies. At each remote location, an electronic processor performs an inverse orthogonal transform (e.g., an inverse Fourier Transform) on the transform coefficients to obtain a block of time domain data. The time domain data is then modulated on a carrier for transmission to the central location. Preferably, the time intervals for data transmission at the different remote locations are aligned with each other. In one embodiment of the invention, all of the baseband frequencies are allocated to a single particular remote location for one time slot. At the remote location, data is received from a plurality of remote locations. The data is demodulated to obtain baseband time domain data. The orthogonal transform is performed on this data to obtain transform coefficients. Each transform coefficient is associated with a baseband frequency. The central location keeps track of which baseband frequencies are allocated to which remote location for subsequent translation of each transform coefficient.