TX IQ Imbalance Estimation via Artificial CFO
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Solution Overview
Problem
Existing methods struggle to accurately estimate and separate transmitter (TX) and receiver (RX) IQ imbalances in communication systems, especially when carrier-frequency offset (CFO) is small or zero, leading to noise enhancement and inability to accurately compensate for IQ imbalances in multichannel systems.
Innovation Solution
A computer-implemented method that introduces a controlled, known carrier frequency offset (CFO) during calibration to estimate TX and RX IQ imbalances using a pre-defined training sequence and least-squares estimation, allowing for accurate separation and compensation of IQ imbalances without noise enhancement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing estimation methods are used when CFO is small or zero, then the system can operate with natural frequency alignment, but noise enhancement occurs and accurate separation of TX and RX IQ imbalances becomes impossible
Solution Approach 1:
The patent applies preliminary action by introducing a known artificial CFO during a calibration phase before actual data transmission. This preliminary step creates a controlled environment where the total IQ imbalance can be accurately measured and separated into TX and RX components, avoiding noise enhancement that would occur with natural small CFO values.
Solution Approach 2:
The patent changes the CFO parameter from its natural small or zero value to a controlled non-zero artificial value during calibration. This parameter change enables accurate IQ imbalance estimation by ensuring the CFO is large enough to prevent noise enhancement while remaining controllable and removable in subsequent processing.
2Ease of operation
If existing methods are used to estimate TX IQ imbalance after RX compensation, then the process follows a sequential approach, but accurate separation fails when CFO is small or zero
Solution Approach 1:
The patent performs preliminary joint estimation of both TX and RX IQ imbalances during a calibration phase with artificial CFO, rather than sequential estimation. This preliminary joint measurement captures the total imbalance accurately, enabling subsequent separation without the failures that occur in sequential methods when CFO is small.
Solution Approach 2:
The patent segments the total IQ imbalance measurement into distinct TX and RX components through mathematical separation after joint estimation. By first measuring the combined effect and then separating the components, the method achieves accurate individual estimates that sequential methods cannot achieve when CFO is small.
3Measurement precision
If artificial CFO is introduced during calibration, then accurate IQ imbalance estimation is achieved, but an additional calibration step is required
Solution Approach 1:
The patent introduces a preliminary calibration phase that, while adding a step, simplifies the overall process by enabling accurate one-time estimation of both TX and RX imbalances. This preliminary measurement avoids the need for complex iterative sequential estimation that would be required without artificial CFO.
Data Source
AI summary
A computer-implemented method of estimating IQ imbalance in a communication system including a transmitter and a receiver. The method includes: defining a system model in which a transmitted signal is affected by TX IQ imbalance, carrier frequency offset (CFO) and RX IQ imbalance; controlling a local oscillator at the transmitter to introduce a known carrier frequency offset (CFO) during a calibration; and estimating unknown parameters in the system model using a pre-defined training sequence to determine the TX IQ imbalance and the RX IQ imbalance.