OFDM Receiver I-Q Mismatch Correction Circuit
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Solution Overview
Problem
Existing OFDM receivers face challenges in effectively correcting quadrature mismatch, particularly in wide-band applications where frequency-dependent mismatches occur, leading to distortion and interference.
Innovation Solution
A receiver is designed with a frequency domain equalization and I-Q mismatch correction circuit that performs per-tone corrections on frequency domain samples, using multipliers, complex conjugate units, and adaptation algorithms to adjust coefficients and minimize decision errors, thereby addressing both channel distortion and I-Q mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frequency domain equalization is performed to correct channel distortion, then signal quality improves, but I-Q mismatch correction is not addressed leading to residual distortion
Solution Approach 1:
The patent combines frequency domain equalization and I-Q mismatch correction into a single unified circuit block. The frequency domain equalization unit and I-Q mismatch correction unit operate simultaneously on the same frequency domain samples, sharing common resources such as the FFT output and decision feedback mechanisms. This merging approach corrects both channel distortion and I-Q mismatch in one processing stage, eliminating residual distortion that would remain if only equalization were performed.
Solution Approach 2:
The frequency domain equalization and I-Q mismatch correction circuit performs multiple functions: it equalizes channel frequency response, corrects I-Q mismatch, and provides decision feedback for adaptive coefficient adjustment. By making the circuit multi-functional, the system addresses both channel distortion and I-Q mismatch without requiring separate dedicated circuits, thereby improving signal quality while correcting multiple types of distortion simultaneously.
2Measurement precision
If per-tone correction is applied to correct frequency-dependent I-Q mismatch, then mismatch accuracy improves, but computational complexity increases
Solution Approach 1:
The patent divides the frequency spectrum into individual tones and applies per-tone correction factors to each frequency component. Instead of applying a single correction factor across the entire bandwidth, the system calculates and applies frequency-dependent correction factors specific to each tone. This segmentation approach enables accurate correction of frequency-dependent I-Q mismatch while allowing the use of efficient per-tone processing algorithms that reduce overall computational complexity compared to time-domain methods.
Solution Approach 2:
The patent transforms the I-Q mismatch correction problem from the time domain to the frequency domain by applying FFT to convert time-domain samples into frequency-domain samples. This parameter change enables the use of frequency-dependent correction factors that can be applied as simple complex multiplications in the frequency domain, significantly reducing computational complexity compared to time-domain convolution-based correction methods while maintaining high correction accuracy.
3Measurement precision
If decision feedback is used to adaptively adjust correction coefficients, then correction accuracy improves, but processing time increases
Solution Approach 1:
The patent implements decision feedback that operates periodically at symbol boundaries rather than continuously. At each symbol boundary, the system makes hard decisions on the received symbols and uses these decisions to update the equalization and mismatch correction coefficients for the next symbol. This periodic update mechanism achieves high correction accuracy through adaptive learning while minimizing processing time by avoiding continuous coefficient adjustment, allowing parallel processing within each symbol period.
Data Source
AI summary
An OFDM receiver includes a demodulator unit being coupled to a received signal for demodulating both an in-phase (I) component and a quadrature-phase (Q) component of the received signal; a serial to parallel unit for converting the output of the demodulator to a plurality of parallel paths, each path corresponding to a particular tone and having a plurality of time-domain samples; a fast Fourier transform circuit for generating frequency domain samples from the time-domain samples; and a equalization and I-Q mismatch correction circuit being coupled to the fast Fourier transform circuit for performing both frequency domain equalization and I-Q mismatch correction on at least one frequency domain sample being output by the fast Fourier transform circuit.