Compensate for imbalance between in-phase and quadrature components
RF Impairments Correction
The I/Q Imbalance Compensator mitigates the effects of an amplitude and phase imbalance between the in-phase and quadrature components of a modulated signal. The supported modulation schemes include OFDM, M-PSK, and M-QAM, where M > 2.
This block accepts up to three input ports, of which one is
the input signal. When you set the Source of compensator
coefficient parameter to
Estimated from input
signal, two additional input ports are enabled. The
first is enabled when you set the Source of adaptation step
size parameter to
Input port and
the second is enabled when you check the Coefficient adaptation
input port box. The two options are independent. Additionally,
you can check the Estimated coefficient output port box
to create an optional output port from which the estimated compensator
coefficients are made available.
When you set the Source of compensator coefficient parameter
Input port, only one possible configuration
is possible (input signal port, coefficient input port, and output
Specify the source of the compensator coefficients as
from input signal or
If set to
Estimated from input signal,
the compensator calculates the coefficients from the input signal.
If set to
Input port, all other properties
are disabled and you must provide the coefficients through the input
port. The default value is
Estimated from input signal.
Specify the initial coefficient used by the internal algorithm
to compensate for the I/Q imbalance. The default value is
Specify the source of the adaptation step size as
port. If set to
specify the step size in the Adaptation step size field.
If set to
Input port, you must specify
the step size through an input port. The default value is
Specify the step size of the adaptation algorithm as a real
scalar. This parameter is available only when Source of
adaptation step size is set to
The default value is
Select this check box to create an input port that permits a
signal to control the adaptation process. If the check box is selected
and if the input signal is
true, the estimated
compensation coefficients are updated. If the adaptation port is not
enabled or if the input signal is
false, the compensation
coefficients do not change. By default, the check box is not selected.
Select this check box to provide the estimated compensation coefficients to an output port. By default, the check box is not selected.
This block implements the algorithm, inputs, and outputs described
comm.IQImbalanceCompensator reference page. The object properties correspond
to the block parameters.
This example shows how to use the I/Q Imbalance Compensator block to remove the effects of an amplitude and phase imbalance on a modulated signal.
Open the model, doc_iqimbcomp, from the MATLAB command prompt.
The model includes these blocks:
Double-click the I/Q Imbalance block. You can see that the I/Q amplitude imbalance (dB) parameter is set to 5 and the I/Q phase imbalance (deg) parameter is also set to 5.
Run the model. In the Signal with I/Q Imbalance constellation diagram, observe the effects of the amplitude imbalance and phase imbalance on the 8-PSK signal.
Look at the Compensated Signal constellation diagram. Observe that the signal is not well aligned with the reference constellation (shown in red).
Increase the simulation time from 20 seconds to 100 seconds and run the model again. You can see that the constellation is now well aligned with the reference constellation. This is because the compensation algorithm is adaptive; consequently, it requires time to accurately estimate the I/Q imbalance.
Try changing other simulation parameters such as the step size in the I/Q Imbalance Compensator block, the amplitude and phase imbalance in the I/Q Imbalance block, the modulation type etc. Observe the effects on the Compensated Signal constellation diagram.
|Port||Supported Data Types|
 Anttila, L., M. Valkama and M. Renfors. “Blind Compensation of Frequency-Selective I/Q Imbalances in Quadrature Radio Receivers: Circularity-Based Approach”. Proc. IEEE ICASSP. 2007, pp. III-245 -III-248.
 Kiayani, A., L. Anttila, Y. Zou, and M. Valkama, “Advanced Receiver Design for Mitigating Multiple RF Impairments in OFDM Systems: Algorithms and RF Measurements”. Journal of Electrical and Computer Engineering. Vol. 2012.