Digital beamforming in a satellite communication system

• US 6,016,124 A
• Filed: 04/06/1998
• Issued: 01/18/2000
• Est. Priority Date: 04/07/1997
• Status: Expired due to Fees

• Current Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Original Assignee: Nortel Networks Corporation
• Inventors: Chang, Jue, Lo, Wing
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): PHAN, DAO LINDA
• Application Number:
  US09/055,374
• Time in Patent Office: 652 Days
• Field of Search: 342/354, 342/373, 370/335, 370/342, 370/441, 370/479, 370/916
• US Class Current: 342/373
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H04B 7/18515 Transmission equipment in satellites or space-based relays
• CPC Class Codes: H04B 7/2041 Spot beam multiple access

Abstract

A plurality of bit stream formatters formats and codes the digital information signals that are to be transmitted. A symbol generator generates I and Q symbols from the formatted information signals. These symbols are input to the beamforming matrix that is connected directly to the symbol generators. The beamforming matrix generates baseband beam signals from the I and Q symbols. Baseband, pulse-shaping, low-pass filters are connected to the beamforming matrix. The low-pass filters each generate an antenna feed signal from each of the baseband beam signals.

Claims

1. A reduced rate beamforming network comprising:

a plurality of digital input signals that represent voice or data messages;

a plurality of bit stream formatters, each bit stream formatter coupled to one of the plurality of digital input signals to generate a predetermined format signal;

a plurality of symbol generators, each symbol generator coupled to one of the plurality of bit stream formatters, each symbol generator transforming the predetermined format signal into a series of symbols;

a beamforming matrix connected directly to the plurality of symbol generators, the beamforming matrix generating a plurality of baseband beam signals from the plurality of series of symbols; and

a plurality of baseband low-pass filters coupled to the beamforming matrix, each of the filters coupled to a different baseband beam signal of the plurality of baseband beam signals, the low-pass filters generating a plurality of antenna feed signals from the plurality of baseband beams signals.

2. A ground-based, satellite beamforming system comprising:

a plurality of baseband digital radios for generating baseband, digital information signals;

a baseband beamforming network comprising;

a plurality of bit stream formatters, each bit stream formatter coupled to one of the plurality of digital information signals to generate a predetermined format signal;

a plurality of symbol generators, each symbol generator coupled to one of the plurality of bit stream formatters, each symbol generator transforming the predetermined format signal into a series of symbols;

a beamforming matrix connected directly to the plurality of symbol generators, the beamforming matrix generating a plurality of baseband beam signals from the plurality of series of symbols; and

a plurality of baseband low-pass filters coupled to the beamforming matrix, each of the filters coupled to a different baseband beam signal of the plurality of baseband beam signals, the low-pass filters generating a plurality of antenna feed signals from the plurality of baseband beams signals;

a plurality of coherent multiplexers, each multiplexer coupled to a different baseband beamforming network, each multiplexer combining the plurality of antenna feed signals from the coupled baseband beamforming network into a multiplexed signal;

a plurality of radio frequency modulators, each modulator coupled to a different coherent multiplexer, the modulators modulating each multiplexed signal to a predetermined frequency to produce a modulated signal; and

a radio frequency front end coupled to the radio frequency modulator, the radio frequency front end producing a radio frequency feeder signal from the plurality of modulated signals.

3. A method for performing baseband beamforming in a multi-frequency, multi-beam, beamforming network, the method comprising the steps of:

formatting a plurality of digital signal bit streams to generate a plurality of predetermined digital format signals;

generating a series of symbols, at a baseband frequency, from each of the predetermined format signals;

generating antenna feed signals from each of the plurality of series of symbols; and

generating filtered antenna feed signals from the antenna feed signals by pulse-shaping and low-pass filtering the antenna feed signals.