Determining Transmitter Impairments Using Offset Local Oscillators

A computer system for determining I/Q impairments of a transmitter, the computer system comprising:

• a processor;
• and
• memory storing program instructions, wherein the program instructions, when executed by the processor, cause the processor to:
• (a) supply a pre-compensation transformation to a pre-compensation circuit of the transmitter, wherein the pre-compensation circuit is configured to apply the pre-compensation transformation to a tone in order to obtain an adjusted signal, wherein the pre-compensation transformation is configured to pre-compensate for a current estimate of the I/Q impairments of the transmitter, wherein the transmitter is configured to transmit a transmit signal based on the adjusted signal;
• (b) compute raw I/Q impairments based on a frequency-shifted signal, wherein the frequency-shifted signal is a result of frequency shifting a sampled signal by an amount of offset between a local oscillator (LO) of the transmitter and a local oscillator of a receiver, wherein the sampled signal has been captured by a receiver in response to said transmission of the transmit signal;
• (c) remove a current estimate of a signal path from the raw I/Q impairments to obtain path-compensated I/Q impairments, wherein the signal path includes a path from an I/Q modulator of the transmitter to a demodulator of the receiver;
• and
• (d) update the current estimate of the I/Q impairments of the transmitter based on the path-compensated I/Q impairments.

A non-transitory computer-readable memory medium for determining I/Q impairments of a transmitter, wherein the memory medium stores program instructions, wherein the program instructions, when executed by a processor, cause the processor to:

• (a) supply a pre-compensation transformation to a pre-compensation circuit of the transmitter, wherein the pre-compensation circuit is configured to apply the pre-compensation transformation to a tone in order to obtain an adjusted signal, wherein the pre-compensation transformation is configured to pre-compensate for a current estimate of the I/Q impairments of the transmitter, wherein the transmitter is configured to transmit a transmit signal based on the adjusted signal;
• (b) compute raw I/Q impairments based on a frequency-shifted signal, wherein the frequency-shifted signal is a result of frequency shifting a sampled signal by an amount of offset between a local oscillator (LO) of the transmitter and a local oscillator of a receiver, wherein the sampled signal has been captured by a receiver in response to said transmission of the transmit signal;
• (c) remove a current estimate of a signal path from the raw I/Q impairments to obtain path-compensated I/Q impairments, wherein the signal path includes a path from an I/Q modulator of the transmitter to a demodulator of the receiver;
• and
• (d) update the current estimate of the I/Q impairments of the transmitter based on the path-compensated I/Q impairments.