Stacked carrier discrete multiple tone communication system

• US 6,512,737 B1
• Filed: 09/08/2000
• Issued: 01/28/2003
• Est. Priority Date: 02/24/1997
• Status: Expired due to Term

• Current Assignee: The DIRECTV Group, Inc. (AT&T, Inc.)
• Original Assignee: BeamReach Networks, Inc.
• Inventors: Agee, Brian G.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): Duong, Frank
• Application Number:
  US09/658,761
• Time in Patent Office: 872 Days
• Field of Search: 370/206, 370/208, 370/210, 370/320, 370/335, 370/342, 370/441, 375/130, 375/140, 375/144, 375/146, 375/147, 375/148, 375/346, 375/347, 375/348, 375/267, 375/278, 375/284
• US Class Current: 370/208
• CPC Class Codes: H04B 1/692 Hybrid techniques using combinations of two or more spread spectrum techniques
• CPC Class Codes: H04B 7/06 at the transmitting station
• CPC Class Codes: H04B 7/086 using weights depending on external parameters, e.g. direction of arrival [DOA], predetermined weights or beamforming
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/026 using code division

Abstract

A “stacked-carrier” spread spectrum communication system based on frequency domain spreading that multiplies a time-domain representation of a baseband signal by a set of superimposed, or stacked, complex sinusoid carrier waves. In a preferred embodiment, the spreading energizes the bins of a large fast Fourier transform (FFT). This provides a considerable savings in computational complexity for moderate output FFT sizes. Point-to-multipoint and multipoint-to-multipoint (nodeless) network topologies are possible. A code-nulling method is included for interference cancellation and enhanced signal separation by exploiting the spectral diversity of the various sources. The basic system may be extended to include multi-element antenna array nulling methods also for interference cancellation and enhanced signal separation using spatial separation. Such methods permit directive and retrodirective transmission systems that adapt or can be adapted to the radio environment. Such systems are compatible with bandwidth-on-demand and higher-order modulation formats and use advanced (maximum-SINR) despreader adaptation algorithms.

Claims

1. A method of digitally communicating comprising the steps of:

spreading, at a first station, digital information onto each of a plurality of stacked carrier signals using a distinct spreading gain for each stacked carrier signal, each of said plurality of stacked carrier signals having a channel bandwidth that is separable from said channel bandwidth of other of said plurality of stacked carrier signals;

transmitting each of said stacked carrier signals across a wireless medium from said first station to a second station;

receiving, at said second station using a multi-element antenna array, said transmitted plurality of stacked carrier signals as received stacked carrier signals;

channelizing on each element of said array each of said received stacked carrier signals to identify a baseband signal for each of said-received stacked carrier signals;

despreading by applying despread weights that are different than said spreading gains to each of said received baseband signals and combining said received baseband signals to obtain a baseband signal that compensates for interference and maximizes a signal to noise and interference ratio, said despreading step using a linear combiner dimensionality which is composed of spectral dimensions and spatial dimensions,

wherein said spatial and spectral dimensions are variable for a plurality of different ones of said first stations; and

wherein each of said distinct spreading gains associated with each of said plurality of stacked carrier signals is linearly independent and non-orthogonal.