Optimized Beamforming for Satellite Communication

• US 20100194630A1
• Filed: 04/14/2010
• Published: 08/05/2010
• Est. Priority Date: 03/30/2006
• Status: Active Grant

• Current Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: Draganov, Alexandr, Weinberg, Aaron
• Granted Patent: US 8,130,140 B2
• Time in Patent Office: Days
• US Class Current: 342/354
• CPC Class Codes: H04B 7/2041 Spot beam multiple access

Abstract

A method for determining beamforming weights used onboard a satellite and ground-based beamforming weights used in a ground-based station as part of a satellite communication system. This beamforming method is a two-stage beamforming process that requires a reduced downlink bandwidth between the satellite and the ground-based station yet achieves optimal signal-to-noise ratio for bandwidth allocated for the downlink. values for the fixed onboard beamforming weights are computed to yield a maximum,

$\underset{A}{\max }\left(\underset{U}{\min }\frac{S}{N}{}_{W=\stackrel{⋓}{W}}\right),$

where the maximum is computed over all possible fixed weights A represented by an L×M matrix, the minimum is computed over all possible positions of remote communication devices U, and the signal-to-noise ratio (S/N) is computed for the optimal set of ground-based beamforming weights W={hacek over (W)}.

Claims

1. A method of determining weights to be used onboard a satellite for a signal transmitted from a communication device and received at each of a plurality of antenna elements, comprising:

selecting initial values for onboard beamforming weights;

for each of a plurality of positions of a remote communication device in the field of view of the satellite;

applying the onboard beamforming weights to M signals derived from a signal received from the remote communication device at the M plurality of antenna elements of the satellite and combining the resulting signals to produce L downlink signals, where L is less than M;

computing optimal ground-based beamforming weights for combining the L downlink signals;

applying the optimal ground-based beamforming weights to the L downlink signals and combining the resulting signals to produce a beamformed output signal;

computing a signal-to-noise ratio of the beamformed output signal;

determining the minimal signal-to-noise ratio for said plurality of positions; and

selecting values for said onboard beamforming weights to maximize the minimal signal-to-noise ratio of the beamformed output signal.

2. The method of claim 1, wherein selecting comprises computing values for said onboard beamforming weights using an algorithm for constrained multivariable optimization.

3. The method of claim 1, wherein selecting comprising computing values for the fixed weights that yield a maximum,

4. The method of claim 1, and further comprising determining whether a change in said onboard beamforming weights will improve the minimum signal to noise-ratio of the beamformed output signal for any of said plurality of positions.

5. The method of claim 4, wherein selecting comprises computing values for said onboard beamforming weights only when it is determined that a change in said onboard beamforming weights will improve the minimum signal to noise-ratio of the beamformed output signal.

6. The method of claim 1, and further comprising selecting the number L of downlink signals to be used based on a tradeoff between the number of downlink channels and a bandwidth or signal-to-noise ratio required for the downlink signals.

7. A satellite communication method requiring reduced downlink bandwidth, comprising:

receiving at M plurality of antennas of a satellite a signal transmitted from a remote communication device, to produce M plurality of receive signals each associated with detection of the signal transmitted by the remote communication device at a corresponding one of the M plurality of antennas;

applying a set of fixed beamforming weights to the M plurality of receive signals to produce L plurality of weighted signals, where L is less than M;

transmitting each of the L plurality of weighted signals on a corresponding one of L plurality of downlink channels to a ground-based station;

receiving at the ground-based station the L plurality of downlink channel signals from the satellite;

applying ground-based beamforming weights to the plurality of downlink channel signals; and

combining the plurality of weighted downlink channel signals to produce a beamformed receive signal.

8. The method of claim 7, wherein for any position of a remote communication device with respect to the satellite the ground-based beamforming weights are set to values that maximize a signal-to-noise ratio of the beamformed receive signal, and the fixed beamforming weights are selected to maximize a minimum signal-to-noise ratio of the received beamformed signal with respect to position of a remote communication device.

9. The method of claim 8, and further comprising computing values for said onboard beamforming weights using an algorithm for constrained multivariable optimization.

10. The method of claim 7, and further comprising computing values for the fixed weights that yield a maximum,

11. The method of claim 7, and further comprising selecting the number L of downlink channel to be used based on a tradeoff between the number of downlink channels and a bandwidth or signal-to-noise ratio required for the downlink channel signals.