Frequency domain I/Q balance compensation, equalization and resampling
Spurious signals in a receiver are rejected using a method of correcting amplitude and phase imbalances in the received signal. A system implementing the method can be built into the receiver or can be used during assembly of the receiver.
1. A method for correcting spurious signals in a receiver, comprising the steps of:
obtaining an original radio frequency (RF) signal;
in the frequency domain, measuring in-phase (I) and quadrature (Q) signals at a plurality of frequencies within the original RF signal;
recording I/Q imbalances in a memory storage device;
calculating preliminary I/Q balance calibration coefficients based on the recorded I/Q imbalances;
determining a complex value for both the I and Q signals at each calibration frequency, wherein the complex values represent an amplitude and phase of both the I and Q signals;
determining a frequency-dependent vector function at each calibration frequency;
converting the frequency-dependent vector functions to the time-domain;
obtaining time-domain coefficients from the converted frequency-dependent vector functions;
converting the time-domain coefficients back to the frequency domain;
frequency reversing the frequency-dependent vector functions;
determining a frequency domain representation of an I/Q balance corrected estimation of the original signal; and
correcting amplitude and phase variation in the receiver based on the I/Q balance corrected estimation of the original signal.
2. The method of claim 1 , wherein a known continuous wave (CW) signal is used in calculating the preliminary I/Q balance calibration coefficients.
3. The method of claim 1 , wherein the step of determining a complex value for both the I and Q signals is accomplished using real-valued Fast Fourier Transforms (FFTs).
4. The method of claim 3 , wherein a sinusoid of each calibration frequency is used to select a calibration point from frequency domain data.
5. The method of claim 4 , wherein the step of determining a complex value for both the I and Q signals at each calibration frequency is interpolated and extended to cover the FFT frequency range.
6. The method of claim 1 , wherein the frequency-dependent vector functions are converted to the time-domain using Inverse Fast Fourier Transform (IFFT).
7. The method of claim 6 , wherein the step of obtaining time-domain coefficients is accomplished with a window function that time-limits the data.
8. The method of claim 1 , wherein an FFT, an overlap-and-save algorithm, or an overlap-and-add algorithm is used to determine the I/Q balance corrected estimations of the original signal.
9. The method of claim 1 , further comprising determining frequency dependent amplitude variation and/or phase variation of the original signal and correct for the variations.
10. The method of claim 9 , further comprising calculating equalization coefficients and determining calibration coefficients for processing and correcting the variations in the signals.
11. The method of claim 10 , further comprising converting a data rate by modifying the equalization coefficients to zero outside a desired passband.
12. The method of claim 10 , further comprising channelizing data by calculating the equalization coefficients for a full input passband.
13. The method of claim 12 , wherein multiple sets of equalization coefficients are used to implement a set of desired output channels.
14. The method of claim 1 , further comprising processing data from an analog to digital converter with the corrected amplitude and phase variation of the receiver.
15. The method of claim 14 , wherein the data is processed with a Finite Impulse Response (FIR) filter using an overlap-and-save or overlap-and-add algorithm.
16. The method of claim 14 , further comprising one of processing the corrected data in the frequency domain or converting the data back to the time domain.
17. A system for correcting spurious signals in a receiver, comprising:
a radio frequency signal source;
a receiver adapted to receive the calibrated signal source;
a memory storage device; and
a processor adapted to implement the method of claim 1 .
18. The system of claim 17 , wherein the processor is built into the receiver.
19. The system of claim 17 , wherein the processor is external to the receiver and calibration is completed during assembly of the receiver.
20. The system of claim 17 , wherein the receiver is a Zero-IF direct conversion receiver.