Determining transmitter impairments using offset local oscillators
AssigneeNational Instruments Corporation
InventorsStephen L. Dark, Christopher J. Behnke
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Abstract
Systems and methods for measuring transmitter and/or receiver I/Q impairments are disclosed, including iterative methods for measuring transmitter I/Q impairments using shared local oscillators, iterative methods for measuring transmitter I/Q impairments using intentionally-offset local oscillators, and methods for measuring receiver I/Q impairments. Also disclosed are methods for computing I/Q impairments from a sampled complex signal, methods for computing DC properties of a signal path between the transmitter and receiver, and methods for transforming I/Q impairments through a linear system.
Claims20
A method for determining I/Q impairments of a transmitter, the method comprising:
- (a) supplying 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) computing 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) removing 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) updating the current estimate of the I/Q impairments of the transmitter based on the path-compensated I/Q impairments.
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.
Dependencies are inferred from the claim text.