Method and apparatus for producing wide null antenna patterns

• US 6,061,023 A
• Filed: 11/03/1997
• Issued: 05/09/2000
• Est. Priority Date: 11/03/1997
• Status: Expired due to Term

• Current Assignee: CDC Propriete Intellectuelle
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Daniel, Sam Mordochai, Ma, Stephen Chih-Hung, Warble, Keith Vaclav, Pan, Shao-Wei, Wang, Shay-Ping Thomas
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/963,485
• Time in Patent Office: 918 Days
• Field of Search: 342/383, 342/378, 342/373, 342/354
• US Class Current: 342/354
• CPC Class Codes: G01S 7/2813 Means providing a modification of the radiation pattern for cancelling noise, clutter or interfering signals, e.g. side lobe suppression, side lobe blanking, null-steering arrays specially adapted to secondary radar systems G01S13/762; aerials or aerials systems H01Q21/29, H01Q25/00
• CPC Class Codes: H01Q 3/2611 Means for null steering; Adaptive interference nulling
• CPC Class Codes: H04B 7/2041 Spot beam multiple access
• CPC Class Codes: H04W 84/06 Airborne or Satellite Networks space-based or airborne stations H04B7/185

Abstract

An enhanced digital beamformer (EDBF) (210, FIG. 2) is provided for use in a transceiver subsystem (200, FIG. 2) for mitigating interference and increasing the frequency reuse factor in communication systems. The EDBF is used to produce wide nulls (520, FIG. 5) in at least one steerable antenna beam pattern. By directing wide nulls at undesired signals, the EDBF provides a more efficient processing of antenna beam patterns in communication systems. The EDBF is used in geostationary satellites, non-geostationary satellites, and terrestrial communication devices. The EDBF combines a unique algorithm, a special processor, and an array antenna to significantly improve the capacity of current and future communication systems, while remaining compatible with existing modulation techniques.

Claims

1. A method of operating a satellite for mitigating interference from K undesired signals, wherein K is an integer, said method comprising the steps of:

identifying a first number of desired signals for reception by said satellite;

determining a beam direction for one of said first number of desired signals;

tracking said beam direction as said satellite moves;

identifying a second number of undesired signals within said satellite'"'"'s field of view (FOV), said second number of undesired signals including said K undesired signals;

determining a null direction for at least one of said K undesired signals;

tracking said null direction as said satellite moves; and

mitigating said interference from said at least one of said K undesired signals by providing at least one wide null directed at said at least one of said K undesired signals, said at least one wide null comprising a third number of nulls that is periodically redirected as said satellite moves, wherein said third number of nulls are determined using an enhanced digital beam forming (EDBF) algorithm and an enhanced transformation matrix, said EDBF algorithm further comprising the steps of;

a) creating an enhanced transformation matrix, said enhanced transformation matrix being initially empty;

b) determining N beam directions identifying angles of arrival for N desired signals within said first number of desired signals;

c) identifying a J(th) beam direction, said J(th) beam direction identifying an angle of arrival for a J(th) desired signal within N desired signals;

d) determining K null directions identifying angles of arrival for said K undesired signals within said second number of undesired signals;

e) constructing K sets of angles, a set of angles being constructed for a null direction;

f) constructing a list by combining said angle of arrival for said J(th) beam direction with said K sets of angles;

g) computing a steering matrix using said list;

h) calculating a standard transformation matrix using said steering matrix;

i) appending a first row of said standard transformation matrix to said enhanced transformation matrix;

j) discarding said J(th) beam direction;

k) rotating said list in a left direction;

l) incrementing J;

m) returning to step c)and repeating steps c) through m), when J is not greater than N; and

n) ending when J is greater than N.

2. The method as claimed in claim 1, wherein said method includes the step of operating said satellite to mitigate interference at a terrestrial-based interfering signal receiver, said step further comprises the steps of:

identifying a transmit signal for transmission by said satellite;

determining a beam direction for said transmit signal;

identifying said terrestrial-based interfering signal receiver;

determining a null direction for said terrestrial-based interfering signal receiver; and

mitigating interference at said terrestrial-based interfering signal receiver by providing at least one wide null directed at said terrestrial-based interfering signal receiver.

3. The method as claimed in claim 1, wherein said mitigating step further comprises the step of:

determining said beam direction and said null direction using angles of arrival in two dimensions.

4. The method as claimed in claim 1, wherein said mitigating step further comprises the step of:

determining said beam direction and said null direction using angles of arrival in three dimensions.

5. The method as claimed in claim 1, wherein step e) further comprises the step of:

locating said set of angles symmetrically about said null direction within a coverage range.

6. The method as claimed in claim 1, wherein step e) further comprises the step of:

locating said set of angles randomly about said null direction within a coverage range.

7. A method of operating a transmitter to mitigate interference using an enhanced digital beamformer adapted for use with an array antenna, said array antenna having a plurality of radiating elements for providing a plurality of steerable antenna beam patterns, said enhanced digital beamformer providing at least one control matrix for controlling said plurality of steerable antenna beam patterns, said method comprising the steps of:

transmitting at least one steerable beam pattern, said at least one steerable beam pattern including at least one beam at a first level in a desired signal direction and a plurality of undesired signals, wherein said plurality of undesired signals determine an interference level;

reducing said interference level using said enhanced digital beamformer and said at least one control matrix, wherein a first original angle of arrival associated with said desired signal direction is combined with a set of nulls associated with original angles of arrival of said plurality of undesired signals to produce a list of angles of arrival;

adjusting said at least one control matrix to increase said first level; and

re-adjusting said at least one control matrix to provide at least one set of nulls, wherein said at least one set of nulls reduces said interference level, wherein said re-adjusting step further comprises the steps of;

a) identifying a first beam direction, said first beam direction identifying an angle for transmission of said at least one beam;

b) determining a number of directions, said directions identifying angles of transmission for said plurality of undesired signals;

c) constructing a first set of angles for said first beam direction wherein said first set of angles is centered about said first beam direction;

d) constructing sets of angles for said number of directions, wherein said sets of angles are centered about said number of directions;

e) constructing a list by combining said angle for transmission for said first beam direction with said sets of angles for said number of directions, said list not including said first set of angles;

f) computing a steering matrix using said list;

g) calculating a transformation matrix using said steering matrix;

h) appending a first row of said transformation matrix to an enhanced transformation matrix;

i) dropping said first beam direction;

j) rotating said list in a left direction;

k) designating a next direction in said number of directions as said first beam direction;

l) returning to step a) and repeating a) through l), when said next direction is available; and

m) ending when said next direction is not available.

8. The method as claimed in claim 7, wherein said method further comprises the step of:

repeating said adjusting step and said re-adjusting step a number of times in order to increase said first level.

9. The method as claimed in claim 7, wherein said method further comprises the step of:

repeating said adjusting step and said re-adjusting step a number of times in order to decrease said interference level.