System and method for closed-loop signal distortion

1. An automatic equalizing circuit and system for a closed-loop satellite communication system comprising:

a transmitter system configured to receive a digital data input signal and send a transmit signal to a satellite in space;

a satellite repeater at the satellite configured to receive the transmit signal, process the transmit signal and send the processed signal toward Earth;

a receiver system on Earth configured to receive the processed signal from the satellite repeater; and

an automatic equalizer on Earth between the receiver system and the transmitter system, the automatic equalizer comprising at least a backward complex infinite impulse response (IIR) filter and a forward finite impulse response (FIR) filter in series with a Nyquist filter, the automatic equalizer configured to:

measure an impulse response of a communication channel from the signal received by the receiver system, the communication channel comprising at least the transmitter system and the satellite repeater;

calculate an inverse filter response for the communication channel based on the impulse response; and

digitally modulate the digital data input signal with the inverse filter response in the digital domain to pre-distort the digital data input signal before it is sent by the transmitter system.

2. The automatic equalizing circuit and system of claim 1 , wherein the automatic equalizer comprises a modulator programmed to generate a known pseudorandom noise signal having a bandwidth substantially equal to the digital data input signal and pass the known pseudorandom noise signal through the communication channel to measure the impulse response of the communication channel.

3. The automatic equalizing circuit and system of claim 1 , wherein the automatic equalizer is configured to pre-distort the digital data input signal to compensate for amplitude versus frequency group delay by positioning the automatic equalizer in the receiver system.

4. The automatic equalizing circuit and system of claim 1 , wherein the automatic equalizer is configured to pre-distort the digital data input signal to compensate for amplitude and group delay versus frequency by passing the digital data input signal through a forward complex finite impulse response (FIR) filter in series with a backward complex infinite impulse response (IIR) filter either before or after a series Nyquist filter before passing the digital data input signal to a modulator in the transmitter system.

5. The automatic equalizing circuit and system of claim 4 , wherein the automatic equalizer is configured to calculate a plurality of pre-distortion coefficients for a leading portion of the impulse response and then pass those coefficients to the forward complex finite impulse response (FIR) filter, and to calculate a plurality of pre-distortion coefficients for a trailing portion of the impulse response and then pass those coefficients to the backward complex infinite impulse response (IIR) filter.

6. The automatic equalizing circuit and system of claim 1 , wherein the automatic equalizer is configured to equalize independent of an output frequency of a modulator for the transmitter system.

7. The automatic equalizing circuit and system of claim 6 , wherein the automatic equalizer comprises a forward complex finite impulse response (FIR) filter in series with a backward complex infinite impulse response (IIR) filter that is coupled in series with a Nyquist filter before being coupled to the modulator for the transmitter system.

8. The automatic equalizing circuit and system of claim 1 , wherein pre-distortion coefficients for the impulse response are pre-calculated for the communication channel and stored in association with the automatic equalizing circuit.

9. A method of automatically equalizing a communication channel for a satellite communication system, the method comprising:

measuring an impulse response of a communication channel from a signal received by a receiver system, the communication channel comprising at least a transmitter system on Earth and a satellite repeater in space;

calculating an inverse filter response for the communication channel based on the impulse response; and

digitally modulating a digital data input signal for the transmitter system with the inverse filter response in the digital domain to pre-distort the digital data input signal before it is sent by the transmitter system to the satellite repeater by passing the digital data input signal through a forward complex finite impulse response (FIR) filter in series with a backward complex infinite impulse response (IIR) filter either before or after a series Nyquist filter before passing the digital data input signal to a modulator in the transmitter system.

10. The method of claim 9 , wherein measuring the impulse response of the communication channel comprises generating a known pseudorandom noise modulated binary phase shift keyed signal having a bandwidth substantially equal to the digital data input signal and passing the known pseudorandom noise modulated binary phase shift keyed signal through the communication channel.

11. The method of claim 9 , wherein calculating the inverse filter response comprises calculating a plurality of pre-distortion coefficients for a leading portion of the impulse response and passing those coefficients to the forward complex finite impulse response (FIR) filter, and calculating a plurality of pre-distortion coefficients for a trailing portion of the impulse response and then passing those coefficients to the backward complex infinite impulse response (IIR) filter.

12. The method of claim 11 , wherein pre-distortion coefficients for at least one of the leading portion and the trailing portion of the impulse response are pre-calculated for the communication channel and stored in association with an automatic equalizing circuit located between and in communication with a receiver system and a transmitter system.

13. The method of claim 11 , wherein measuring the impulse response of the communication channel comprises, before calculating the plurality of pre-distortion coefficients, generating a known pseudorandom noise modulated binary phase shift keyed signal having a bandwidth substantially equal to the digital data input signal and passing the known pseudorandom noise modulated binary phase shift keyed signal through the communication channel.

14. The method of claim 9 , further comprising equalizing the communication channel independent of an output frequency of the communication channel.

15. A method of pre-distorting a digital data input to a modulator for a satellite communication system, the method comprising:

receiving a digital data input for a satellite communication system at a digital processor and then at an automatic equalizer coupled between a transmitter system and a receiver system of a communication channel for the satellite communication system, the communication channel comprising at least a transmitter system on Earth and a satellite repeater in space;

receiving a received satellite signal passed from the receiver system at the automatic equalizer;

passing an output of the automatic equalizing circuit to a modulator of the transmitter system; and

automatically equalizing the communication channel in the digital domain independent of an output frequency of the communication channel by passing the digital data input signal through a forward complex finite impulse response (FIR) filter in series with a backward complex infinite impulse response (IIR) filter either before or after a series Nyquist filter before passing the digital data input signal to the modulator of the transmitter system.

16. The method of claim 15 , further comprising, within the automatic equalizer:

measuring an impulse response of the communication channel from the received satellite signal;

calculating an inverse filter response for the communication channel based on the impulse response measured; and

digitally modulating the digital data input signal for the transmitter system with the inverse filter response in the digital domain to pre-distort the digital data input signal before it is sent by the transmitter system to the satellite repeater.

17. The method of claim 15 , wherein calculating the inverse filter response comprises calculating a plurality of pre-distortion coefficients for a leading portion of the impulse response and passing those coefficients to the forward complex finite impulse response (FIR) filter, and calculating a plurality of pre-distortion coefficients for a trailing portion of the impulse response and then passing those coefficients to the backward complex infinite impulse response (IIR) filter.

18. The method of claim 17 , further comprising pre-calculating the pre-distortion coefficients for at least one of the leading portion and the trailing portion of the impulse response and storing the pre-distortion coefficients in the automatic equalizer.

19. The method of claim 17 , wherein measuring the impulse response of the communication channel comprises generating a known pseudorandom noise modulated binary phase shift keyed signal having a bandwidth substantially equal to the digital data input signal and passing the known pseudorandom noise modulated binary phase shift keyed signal through the communication channel.