Apparatus and method for remote beam forming for satellite broadcasting systems

• US 8,098,612 B2
• Filed: 05/16/2008
• Issued: 01/17/2012
• Est. Priority Date: 05/21/2007
• Status: Active Grant

• Current Assignee: Spatial Digital Systems Inc
• Original Assignee: Spatial Digital Systems Inc
• Inventors: Chang, Donald Chin-Dong
• Primary Examiner(s): TRAN, PHUC H
• Application Number:
  US12/122,462
• Publication Number:
  US 20080291864A1
• Time in Patent Office: 1,341 Days
• Field of Search: 370315-316, 370/338, 370/501, 370/532
• US Class Current: 370/316
• CPC Class Codes: H04B 7/1851 Systems using a satellite or space-based relay H04B7/18508, H04B7/18521 take precedence; providing specific services H04B7/18523 - H04B7/18576
• CPC Class Codes: H04B 7/2041 Spot beam multiple access
• CPC Class Codes: H04L 27/265 Fourier transform demodulators, e.g. fast Fourier transform [FFT] or discrete Fourier transform [DFT] demodulators H04L27/26524 takes precedence
• CPC Class Codes: H04N 7/20 Adaptations for transmission via a GHz frequency band, e.g. via satellite
• CPC Class Codes: H04W 16/14 Spectrum sharing arrangements between different networks

Abstract

A satellite broadcasting system is achieved in which remote beam forming processors located among distributed ground stations are used to control downlink beam footprints and pointing directions. Digital beam forming techniques allow a single satellite downlink broadcast antenna array to generate multiple simultaneous downlinks that can be pointed independently and that may contain distinct information content. By allocating some of the uplink back-channel elements as null channels, continuous calibration of the uplink channel can be performed, improving the performance of the downlink broadcast array and the quality of the broadcast for users. By wavefront multiplexing, all of the uplink channel elements propagate through the all of the available propagation channels simultaneously, eliminating the need for complex and costly individual array-element calibration equipment using on-board or ground-based references.

Claims

1. For an integer N that is greater than one and an integer M that is greater than N−

1, a satellite broadcasting system includes;

a satellite segment comprising;

a downlink broadcast antenna array including N elements;

a wavefront de-multiplexer having at least N outputs configured to drive corresponding ones of the N downlink broadcast antenna array elements, and M inputs;

a frequency-domain de-multiplexer unit configured to demultiplex and frequency-convert uplink signals; and

an uplink receive antenna configured to receive the uplink signals;

a ground segment comprising;

at least one digital beam forming (DBF) processor configured to multiply a content data stream with an N-component beam weight vector (BWV) to create an N-component product vector;

a wavefront multiplexer having at least N inputs driven by corresponding ones of the N-component product vector, and M outputs;

a frequency-domain multiplexer unit configured to frequency up-convert and modulate the M outputs of the wavefront multiplexer to generate the uplink signals; and

an uplink transmit antenna configured to transmit the uplink signals; and

a user segment comprising at least one user receiving at least one beam from the downlink broadcast antenna array of the satellite segment.

2. The satellite broadcasting system of claim 1, wherein:

the at least one DBF processor of the ground segment further includes an N-component complex multiplier configured to multiply the content data stream with the N-component BWV; and

the N-component BWV further comprises N configurable complex coefficients, each of which includes an amplitude portion and a phase portion.

3. The satellite broadcasting system of claim 1, wherein the wavefront multiplexer of the ground segment comprises an M-by-M Butler matrix.

4. The satellite broadcasting system of claim 1, wherein the wavefront de-multiplexer of the satellite segment comprises an M-by-M Butler matrix.

5. The satellite broadcasting system of claim 1, wherein the frequency-domain multiplexer unit of the ground segment further comprises:

M digital-to-analog converters adapted to synthesize M analog waveforms from corresponding ones of the M outputs of the wavefront multiplexer;

M frequency up-converters adapted to frequency up-convert corresponding ones of the M analog waveforms to radio frequency; and

a frequency multiplexer adapted to combine the M analog waveforms after up-conversion to radio frequency to form composite signals that are the uplink signals.

6. The satellite broadcasting system of claim 1, wherein the ground segment is further adapted to include at least one of a solid-state power amplifier, a traveling wave-tube amplifier, and a klystron to amplify the uplink signals before transmission by the uplink transmit antenna.

7. The satellite broadcasting system of claim 1, wherein the frequency-domain de-multiplexer unit of the satellite segment further comprises:

a de-multiplexer adapted to extract M analog uplink waveforms from the uplink signals received by the uplink receive antenna; and

M frequency converters adapted to frequency convert corresponding ones of the M analog uplink waveforms to a downlink radio frequency.

8. The satellite broadcasting system of claim 1, wherein the satellite segment is further adapted to include at least N solid-state power amplifiers connected to corresponding ones of the at least N outputs of the wavefront de-multiplexer.

9. The satellite broadcasting system of claim 1, wherein:

the wavefront multiplexer of the ground segment is further adapted to include M-N null inputs;

the satellite segment further includes a cost function unit having M-N inputs; and

the wavefront de-multiplexer of the satellite segment is further adapted to include M-N outputs that are connected to corresponding ones of the M-N inputs of the cost function unit;

wherein M is further constrained to be greater than N; and

wherein the cost function unit is adapted to measure a deviation of the M-N inputs of the cost function unit from null in order to measure imbalances in an uplink channel.

10. The satellite broadcasting system of claim 9, wherein the satellite segment is further adapted to correct for measured imbalances in the uplink channel by adjusting phases and amplitudes of outputs of the frequency-domain de-multiplexer unit.

11. The satellite broadcasting system of claim 9, wherein:

the satellite segment is further adapted to downlink an index of measured imbalances in the uplink channel to the ground segment; and

the ground segment is further adapted to pre-compensate for the index of measured imbalances in the uplink channel by adjusting phases and amplitudes of inputs of the frequency-domain multiplexer unit.

12. For an integer N that is greater than one and an integer M that is greater than N, a satellite broadcasting system includes:

a satellite segment comprising;

a downlink broadcast antenna array including N elements;

a cost function unit adapted to measure deviations from null;

a receive-side Butler Matrix having M inputs and M outputs, wherein N of the M outputs are configured to drive corresponding ones of the N downlink broadcast antenna array elements, and the other M-N outputs are configured to drive the cost function unit;

a frequency-domain de-multiplexer unit configured to demodulate and frequency-convert uplink signals; and

an uplink receive antenna configured to receive the uplink signals;

a ground segment comprising;

at least one digital beam forming (DBF) processor configured to multiply a content data stream with an N-component beam weight vector (BWV) to create an N-component product vector;

a transmit-side Butler Matrix having M inputs and M outputs, wherein N of the M inputs are driven by corresponding ones of the N-component product vector, and the other M-N inputs are driven by null signals;

a frequency-domain multiplexer unit configured to frequency up-convert and modulate the M outputs of the receive-side Butler Matrix to generate the uplink signals; and

an uplink transmit antenna configured to transmit the uplink signals; and

a user segment comprising at least one user receiving at least one beam from the downlink broadcast antenna array of the satellite segment.

13. The satellite broadcasting system of claim 12, wherein:

the at least one DBF processor of the ground segment further includes an N-component complex multiplier configured to multiply the content data stream with the N-component BWV; and

the N-component BWV further comprises N configurable complex coefficients, each of which includes an amplitude portion and a phase portion.

14. The satellite broadcasting system of claim 13, wherein the frequency-domain multiplexer unit of the ground segment further comprises:

M digital-to-analog converters adapted to synthesize M analog waveforms from corresponding ones of the M outputs of the transmit-side Butler Matrix;

M frequency up-converters adapted to frequency up-convert corresponding ones of the M analog waveforms to radio frequency; and

a multiplexer adapted to combine the M analog waveforms after up-conversion to radio frequency to form composite signals that are the uplink signals.

15. The satellite broadcasting system of claim 12, wherein the ground segment is further adapted to include at least one of a solid-state power amplifier, a traveling wave-tube amplifier, and a klystron to amplify the uplink signals before transmission by the uplink transmit antenna.

16. The satellite broadcasting system of claim 12, wherein the frequency-domain de-multiplexer unit of the satellite segment further comprises:

a de-multiplexer adapted to extract M analog uplink waveforms from the uplink signals received by the uplink receive antenna; and

M frequency converters adapted to frequency convert corresponding ones of the M analog uplink waveforms to a downlink radio frequency.

17. The satellite broadcasting system of claim 12, wherein the satellite segment is further adapted to include N solid-state power amplifiers connected to N of the M outputs of the receive-side Butler Matrix.

18. The satellite broadcasting system of claim 12, wherein:

the cost function unit is adapted to measure a deviation of the M-N inputs of the cost function unit from null in order to measure imbalances in an uplink channel; and

the satellite segment is further adapted to correct for the measured imbalances in the uplink channel by adjusting phases and amplitudes of outputs of the frequency-domain de-multiplexer unit.

19. The satellite broadcasting system of claim 12, wherein:

the cost function unit is adapted to measure a deviation of the M-N inputs of the cost function unit from null in order to measure imbalances in an uplink channel;

the satellite segment is further adapted to downlink the measured imbalances in the uplink channel to the ground segment; and

the ground segment is further adapted to pre-compensate for the measured imbalances in the uplink channel by adjusting phases and amplitudes of inputs of the frequency-domain multiplexer unit.

20. For an integer N that is greater than one and an integer M that is greater than N, in a satellite broadcasting system comprising a ground segment, a user segment, and a satellite segment including at least one downlink broadcast antenna array having N elements, a method of generating multiple simultaneous beams from the downlink broadcast antenna array that are controlled by the ground segment comprises:

multiplying input content data streams by N-component beam weight vectors (BWVs) to create N-component product vectors in the ground segment;

padding the N-component product vectors with nulls until the product vectors reach a dimension of M;

creating an element-by-element sum of the M-component product vectors after padding to create an M-component composite vector;

performing an M-component spatial Fourier transform on the M-component composite vector to create an M-component transformed vector;

frequency up-converting the M-component transformed vector by mixing each of M components of the M-component transformed vector with M distinct closely spaced carrier frequency references to create M radio-frequency signals;

combining the M radio-frequency signals into composite frequency-domain-multiplexed (FDM) uplink signals;

transmitting the FDM uplink signals to a satellite;

de-multiplexing the uplink signals after receipt by the satellite;

frequency converting the uplink signals after de-multiplexing by mixing M components of the uplink signals after de-multiplexing with M distinct closely spaced frequency references to create an M-component downlink vector;

performing a spatial Fourier transform of the M-component downlink vector to create an M-component transformed downlink vector;

applying N of M components of the M-component transformed downlink vector to corresponding ones of the N array elements of the downlink broadcast antenna array.

21. The method of claim 20, wherein the step of performing an M-component spatial Fourier transform on the M-component composite vector further comprises running the M-component composite vector through an M-by-M Butler Matrix.

22. The method of claim 20, wherein the step of performing a spatial Fourier transform of the M-component downlink vector further comprises running the M-component downlink vector through an M-by-M Butler Matrix.

23. The method of claim 20, wherein the step of applying N of M components of the M-component transformed downlink vector to corresponding ones of the N array elements of the downlink broadcast antenna array further comprises:

applying the remaining M-N components of the M-component transformed downlink vector to a cost function unit; and

measuring a deviation of the remaining M-N components from null in order to calculate uplink channel imbalances.

24. The method of claim 23, further comprising correcting for uplink channel imbalances by applying corrections to amplitudes and phases of the M-component downlink vector.

25. The method of claim 23, further comprising:

downlinking uplink channel imbalances to the ground segment;

correcting for uplink channel imbalances by applying pre-corrections to amplitudes and phases of the M-component transformed vector.