Reducing signal distortion using I/Q imbalance or DC offset errors
To reduce signal distortion, a remote terminal receives a quadrature-modulated transmitter-check signal from a user terminal. The remote terminal measures an in-phase/quadrature (I/Q) imbalance error and/or a direct current (DC) offset error in the transmitter-check signal. The remote terminal then transmits to the user terminal transmitter-correction information derived from an I/Q imbalance error or a DC offset error. The transmitter-correction information is for counteracting the I/Q imbalance error or the DC offset error at the user terminal.
1. A method for remote assistance with reducing signal distortion in a user terminal, the method comprising:
receiving a quadrature modulated transmitter-check signal at a remote node over a communications network from a user terminal, the transmitter-check signal comprising modulation symbols;
measuring at the remote node an in-phase/quadrature (I/Q) imbalance error and a direct current (DC) offset error in the transmitter-check signal, the I/Q imbalance error corresponding to an average correlation value of I and Q components of the modulation symbols and the DC offset error corresponding to an average I/Q value of the modulation symbols; and
transmitting from the remote node across the network to the user terminal transmitter-correction information derived from the I/Q imbalance error and the DC offset error, wherein the transmitter-correction information is for counteracting an I/Q imbalance error and a DC offset error at the user terminal.
2. The method for remote assistance of claim 1 , wherein the transmitter-correction information comprises the measurements.
3. The method for remote assistance of claim 1 further comprising calculating transmitter-correction parameters from the measurements, the transmitter-correction parameters calculated to counteract the I/Q imbalance error and the DC offset error, wherein the transmitter-correction information comprises the transmitter-correction parameters.
4. The method for remote assistance of claim 1 further comprising transmitting a receiver-check signal over the communications network to the user terminal.
5. The method for remote assistance of claim 4 further comprising:
receiving at the remote node over the communications network from the user terminal receiver-check-signal measurements of I/Q imbalance error and DC offset error of the quadrature modulated receiver-check signal;
calculating at the remote node using the receiver-check-signal measurements transmitter-correction parameters to counteract the I/Q imbalance error and the DC error in the quadrature modulated receiver-check signal; and
transmitting the receiver-correction parameters from the remote node over the communications network to the user terminal.
6. The method of claim 1 further comprising:
transmitting the quadrature modulated transmitter-check signal from the user terminal over the communications network to the remote node;
receiving, from the remote node over the communications network at the user terminal, the transmitter-correction information corresponding to an I/Q imbalance error and a DC offset error measured in the transmitter-check signal; and
utilizing the received transmitter-correction information to set a transmitter-correction module in the user terminal to counteract the I/Q imbalance error and the DC offset error in the transmitter-check signal.
7. The method of claim 6 , wherein utilizing the received transmitter-correction information includes setting transmitter-correction parameters of the transmitter-correction module to counteract the I/Q imbalance error and the DC offset error in the transmitter-check signal.
8. The method for remote assistance of claim 1 , wherein the transmitter-check signal comprises payload data.
9. The method for remote assistance of claim 1 , wherein the modulation symbols of the transmitter-check signal comprise a known test pattern of modulation symbols.
10. The method for remote assistance of claim 9 , wherein the I/Q imbalance error corresponds to a deviation from zero of the average correlation value of the I and Q components of the modulation symbols.
11. The method for remote assistance of claim 1 , wherein the DC offset error corresponds to a deviation from zero of the average I/Q value of the modulation symbols.
12. A remote node comprising:
a remote receiver for receiving a quadrature modulated transmitter-check signal over a communications network from a user terminal, the transmitter-check signal comprising modulation symbols;
a remote transmitter-correction module coupled to the remote receiver and configured to measure an in-phase/quadrature (I/Q) imbalance error and a direct current (DC) offset error in the transmitter-check signal, the I/Q imbalance error corresponding to an average correlation value of I and Q components of the modulation symbols and the DC offset error corresponding to an average I/Q value of the modulation symbols; and
a remote transmitter coupled to the remote-transmitter correction module and configured to transmit transmitter-correction information derived from the I/Q imbalance error and the DC offset error, wherein the transmitter-correction information is for counteracting an I/Q imbalance error and a DC offset error in the user terminal.
13. The remote node of claim 12 , wherein the remote node is a gateway of a satellite communications network.
14. The remote node of claim 12 , wherein the transmitter-correction information comprises the measurements.
15. The remote node of claim 12 further comprising a remote error processor configured to calculate transmitter-correction parameters from the measurements, the transmitter-correction parameters calculated to counteract an I/Q imbalance error and a DC offset error, wherein the transmitter-correction information comprises the transmitter-correction parameters.
16. The remote node of claim 12 , wherein the remote transmitter is further configured to transmit a receiver-check signal over the communications network to the user terminal.
17. The remote node of claim 16 , wherein:
the remote receiver is further configured to receive over the communications network from the user terminal receiver-check-signal measurements of an I/Q imbalance error and a DC offset error in the quadrature modulated receiver-check signal;
the error processor is further configured to calculate using the receiver-check-signal measurements transmitter-correction parameters to counteract an I/Q imbalance error and a DC error in the quadrature modulated receiver-check signal; and
the remote transmitter is further configured to transmit the transmitter-correction parameters over the communications network to the user terminal.
18. The remote node of claim 12 , wherein the transmitter-check signal comprises payload data.
19. The remote node of claim 12 , wherein the modulation symbols of the transmitter-check signal comprise a known test pattern of modulation symbols.
20. The remote node of claim 19 , wherein the I/Q imbalance error corresponds to a deviation from zero of the average correlation value of the I and Q components of the modulation symbols.