Multiple user access method using OFDM

• US 5,815,488 A
• Filed: 09/28/1995
• Issued: 09/29/1998
• Est. Priority Date: 09/28/1995
• Status: Expired due to Term

• Current Assignee: TC Technology LLC (Charter Communications Incorporated)
• Original Assignee: Cable Television Laboratories Incorporated
• Inventors: Williams, Thomas H., Prodan, Richard S.
• Primary Examiner(s): TON, DANG T
• Application Number:
  US08/535,593
• Time in Patent Office: 1,097 Days
• Field of Search: 370/20, 370/21, 370/22, 370/23, 370/30, 370/69.1, 370/120, 370/71, 370/73, 370/57, 370/18, 370/19, 370/95.1, 370/205, 370/206, 370/208, 370/209, 370/210, 370/314, 370/320, 370/321, 370/324, 370/335, 370/336, 370/337, 370/344, 370/343, 370/342, 370/347, 370/441, 370/442, 380/34, 375/200, 375/205, 375/237, 375/238, 375/239, 375/261, 375/298, 455/38.1
• US Class Current: 370/206
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601

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.

Claims

1. A method for enabling a plurality of remote locations to transmit data to a central location comprising the steps of:

at each remote location, coding data to be transmitted by translating each group of one or more bits of said data into a transform coefficient associated with a particular baseband frequency in a particular subset of orthogonal baseband frequencies allocated to the remote location, the particular subset of orthogonal baseband frequencies allocated to each remote location being chosen from a set of orthogonal baseband frequencies, the subsets of baseband frequencies allocated to each remote location being mutually exclusive.

at each remote location, using an electronic processor, performing an inverse orthogonal transformation on said transform coefficients to obtain a block of time domain data;

at each remote location, utilizing a modulator to modulate said block of time domain data onto a carrier signal for transmission to said central location, said carrier signal having the same carrier frequency for each remote location;

receiving at said central location from one or more of said remote locations, one or more blocks of time domain data modulated on one or more of said carrier signals;

using a demodulator, demodulating said one or more blocks of time domain data from the carrier frequency signal.

performing said orthogonal transformation on said demodulated time domain data to reconstruct said transform coefficients, and

translating said transform coefficients into said data to be translated from each remote location.

2. A method for enabling a plurality of remote locations to transmit data to a central location comprising the steps of:

at each remote location, coding data to be transmitted by translating each group of one or more bits of said data into a transform coefficient associated with a particular baseband frequency in a particular subset of orthogonal baseband frequencies allocated to the remote location, the particular subset of orthogonal baseband frequencies allocated to each remote location being chosen from a set of orthogonal baseband frequencies, the subsets of baseband frequencies allocated to each remote location being mutually exclusive;

at each remote location, using an electronic processor, performing an inverse orthogonal transformation on said transform coefficients to obtain a block of time domain data;

at each remote location, utilizing a modulator to modulate said block of time domain data onto a carrier signal for transmission to said central location, said carrier signal having the same carrier frequency for each remote location.

receiving at said central location from one or more of said remote locations, one or more blocks of time domain data modulated on one or more of said carrier signals;

using a demodulator, multiplying said received one or more blocks of time domain data with in-phase and quadrature carrier signals to obtain in-phase and quadrature baseband signals, converting said in-phase and quadrature baseband signals to digital form, and using an electronic processor, performing said orthogonal transform using said in-phase and quadrature baseband signals as real and imaginary values, respectively, to demodulate said one or more blocks of time domain data from the carrier frequency signal, and

performing said orthogonal transformation on the demodulated time domain data to reconstruct said transform coefficients.