System and method for analysis of intermodulation dispersion

• US 6,259,899 B1
• Filed: 11/04/1998
• Issued: 07/10/2001
• Est. Priority Date: 11/04/1998
• Status: Expired due to Term

• Current Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Original Assignee: Hughes Electronics Corporation (Rtx Corporation)
• Inventors: Berman, Arnold L., Mandell, Michael I.
• Primary Examiner(s): Hunter, Daniel
• Assistant Examiner(s): Gantt, Alan T.
• Application Number:
  US09/185,780
• Time in Patent Office: 979 Days
• Field of Search: 455/102, 455/103, 455/114, 455/115, 455/16-22, 375/296, 330/124 R, 330/154, 330/149
• US Class Current: 455/115.4
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

A system and method for determining dispersion of intermodulation power in a satellite communication system or any other system which can be mathematically modeled as a matrix multiplication followed by an instantaneous nonlinearity and another matrix multiplication include determining a matrix (V) representing amplitudes and frequencies of signals generated by a digital processor and input to a plurality of amplifiers. A matrix (M) representing signal propagation from the amplifiers to a destination is used to determine the intermodulation power at the destination within each transmitted beam at each intermodulation distortion frequency. The intermodulation distortion frequencies are determined based on sums and differences of component frequencies corresponding to the user signals. By considering only third-order intermodulation effects and performing a frequency domain analysis, the present invention is computationally efficient enough to analyze cellular communications systems containing a large number of individual users, a large number of amplifiers, and a complex multi-beam antenna. The improvement of signal to intermodulation power ratio when going from the amplifiers on a satellite to the received signals on the ground.

Claims

1. A method for analyzing distortion in a satellite communication system having at least one element characterized by a nonlinear response, the method comprising:

generating a mathematical input matrix representing a plurality of signals having associated frequencies and amplitudes at an input to the at least one element;

repeatedly calculating distortion for each element based on a product of the amplitudes of a second plurality of the signals at an associated distortion frequency determined by a sum and difference of component frequencies for all possible distortion frequencies of the plurality of signals; and

multiplying the distortion by a mathematical output matrix representing the satellite communication system to determine distortion in a received beam.

2. The method of claim 1 wherein the satellite communication system generates a plurality of beams to transmit the signals to a destination, the method further comprising:

determining the transmitted signal power for each of the plurality of beams at each of the plurality of frequencies;

determining the signal power in each of the at least one element at each of the plurality of frequencies; and

determining the signal power received at the destination for each of the plurality of beams at each of the plurality of frequencies.

3. The method of claim 1 wherein the distortion is intermodulation distortion and each distortion frequency is an intermodulation distortion frequency and wherein the step of calculating comprises:

calculating a third-order intermodulation product for each intermodulation frequency determined by a first component frequency plus a second component frequency minus a third component frequency.

4. The method of claim 3 further comprising:

determining a first ratio corresponding to transmitted signal power divided by intermodulation power on the satellite for each of the at least one element at a selected one of the plurality of frequencies.

5. The method of claim 4 further comprising:

determining a second ratio corresponding to received signal power divided by received intermodulation power at a selected one of the plurality of frequencies within a selected one of a plurality of beams transmitted from the satellite to a destination.

6. The method of claim 5 further comprising:

determining a third ratio representing an improvement in the signal to intermodulation power ratio corresponding to the second ratio divided by the first ratio.

7. The method of claim 6 further comprising:

selecting an operating point for the at least one element based on the third ratio.

8. A computer readable storage medium having stored therein data representing instructions executable by a computer for determining dispersion of intermodulation power in a satellite communications system having at least one element with a nonlinear response, the computer readable storage medium comprising:

instructions for receiving a numerical input matrix representing a plurality of signals having associated frequencies and amplitudes at an input to the at least one element;

instructions for repeatedly calculating distortion for each element based on a product of the amplitudes of a second plurality of the signals at an associated distortion frequency determined by a sum and difference of component frequencies for all possible distortion frequencies of the plurality of signals; and

instructions for multiplying the distortion by a numerical output matrix representing the satellite communication system to determine distortion in a received beam.

9. The computer readable storage medium of claim 8 further comprising:

instructions for determining transmitted signal power for each of a plurality of beams at each of the plurality of frequencies.

10. The computer readable storage medium of claim 8 further comprising:

instructions for determining the signal power in each of the at least one element at each of the plurality of frequencies.

11. The computer readable storage medium of claim 8 further comprising:

instructions for determining signal power received at a destination for each of the plurality of beams at each of the plurality of frequencies.

12. The computer readable storage medium of claim 9 further comprising:

instructions for determining a first ratio corresponding to transmitted signal power divided by distortion power on the satellite for each of the at least one element at a selected one of the plurality of frequencies;

instructions for determining a second ratio corresponding to received signal power divided by received distortion power at a selected one of the plurality of frequencies within a selected one of a plurality of beams transmitted from the satellite to a destination; and

instructions for determining a third ratio representing an improvement in the signal to intermodulation power ratio corresponding to the second ratio divided by the first ratio.

13. A method for determining dispersion of intermodulation power in a satellite communication system including a digital processor in communication with a plurality of amplifiers, the amplifiers connected to a plurality of antenna feed elements via a hybrid matrix and a feedmap matrix, the system transmitting a plurality of signals at a plurality of frequencies within a plurality of beams to at least one destination, the method comprising:

determining a mathematical matrix representing amplitudes and frequencies of signals generated by the digital processor and input to the plurality of amplifiers;

determining a mathematical matrix representing signal propagation from the plurality of amplifiers to the at least one destination;

calculating a plurality of intermodulation distortion frequencies based on combinations of subsets of the plurality of signals;

calculating intermodulation power output from each of the plurality of amplifiers for each of the plurality of intermodulation distortion frequencies; and

calculating intermodulation power at the at least one destination within each of the plurality of beams at each of the plurality of intermodulation distortion frequencies.

14. The method of claim 13 wherein the step of calculating intermodulation power at the at least one destination comprises performing a matrix multiplication of the mathematical matrix representing propagation of the signals from the amplifiers by a mathematical matrix representing the intermodulation power output from each of the plurality of amplifiers.

15. The method of claim 13 wherein the step of calculating a plurality of intermodulation distortion frequencies comprises adding frequencies of corresponding first and second ones of the plurality of signals and subtracting a frequency corresponding to a third one of the plurality of signals.

16. The method of claim 13 wherein the step of calculating a plurality of intermodulation distortion frequencies comprises calculating each intermodulation distortion frequency using sums and differences of frequencies corresponding to a subset of the plurality of signals.

17. The method of claim 13 further comprising:

determining transmitted signal power for each of the plurality of beams at each of the plurality of frequencies;

determining amplifier signal power for each of the plurality of amplifiers at each of the plurality of frequencies; and

determining received signal power at the at least one destination for each of the plurality of beams at each of the plurality of frequencies.

18. The method of claim 17 further comprising:

determining a first ratio corresponding to transmitted signal power divided by intermodulation distortion power on the satellite for each of the plurality of amplifiers at a selected one of the plurality of frequencies;

determining a second ratio corresponding to received signal power divided by received intermodulation distortion power at a selected one of the plurality of frequencies within a selected one of a plurality of beams transmitted from the satellite to the at least one destination; and

determining a third ratio representing an improvement in the signal to intermodulation power ratio corresponding to the second ratio divided by the first ratio.

19. A method for analysis of intermodulation dispersion in satellite systems having amplifiers coupled to an antenna array, the method comprising:

calculating only third-order intermodulation products for each intermodulation frequency to improve computational efficiency;

calculating improvement in signal to intermodulation ratio between the amplifiers on the satellite and received signals on the ground based on the intermodulation products without requiring specification of the operating point of the amplifiers or calculating signal to intermodulation ratio at either the amplifiers or on the ground.

20. The method of claim 19 further comprising:

selecting an operating point for the amplifiers based on the calculated improvement in signal to intermodulation ratio.

21. The method of claim 19 wherein the step of calculating third-order intermodulation products comprises separately tracking contributions of each user signal based on a corresponding amplitude and frequency to quantify spatial scattering of the intermodulation products.