Frequency-Dependent IQ Imbalance Estimation in Wireless Communication
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Solution Overview
Problem
In wireless communication systems, in-phase/quadrature (IQ) imbalance due to temperature changes or aging of modulators leads to reduced signal-to-noise ratio (SNR) and data rate, as the in-phase and quadrature signals are not consistently 90° out-of-phase, causing errors in bitstream demodulation.
Innovation Solution
User equipment (UEs) estimate frequency-dependent IQ imbalance and transmit these estimates to network nodes or radio units, which determine compensation filter coefficients to correct for IQ imbalance, reducing complexity and frequency of updates by leveraging the capabilities of UEs, network nodes, and radio units.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If IQ imbalance correction is performed at the network node or radio unit with high precision, then signal-to-noise ratio and data rate are improved, but computational complexity and update frequency increase
Solution Approach 1:
The patent divides the IQ imbalance correction task into two segments: (1) UE performs IQ imbalance estimation and transmits results to network node, (2) network node determines filter coefficients and transmits to radio unit for actual correction. This segmentation distributes computational complexity across different devices, reducing the burden on any single component while maintaining correction effectiveness.
Solution Approach 2:
The patent introduces FDIQI estimates as an intermediary element between the IQ imbalance problem and the correction process. Instead of directly computing complex correction parameters at the network node, the system uses UE-generated estimates as intermediate data that simplifies the subsequent coefficient determination process, reducing overall computational complexity.
2Reliability
If filter coefficients are updated frequently to maintain accurate IQ imbalance correction, then communication reliability is improved, but latency and processing overhead increase
Solution Approach 1:
The patent implements dynamic update timing for filter coefficients based on actual system conditions. Rather than using fixed frequent updates, the system adapts the update frequency to match the rate at which IQ imbalance actually changes (typically slow due to temperature and aging effects), reducing unnecessary updates and associated latency while maintaining correction accuracy.
Solution Approach 2:
The UE performs self-service by autonomously estimating its own IQ imbalance characteristics and providing these estimates to the network node. This eliminates the need for the network node to continuously monitor and re-estimate imbalance parameters, reducing update frequency and latency while maintaining accurate correction.
3Measurement precision
If IQ imbalance estimation is performed at the network node, then correction accuracy is improved, but feedback complexity and processing load increase
Solution Approach 1:
The patent inverts the traditional approach by having the UE (the receiving end) perform the IQ imbalance estimation instead of the network node (the transmitting end). Since IQ imbalance affects the received signal, the UE is better positioned to accurately estimate the imbalance. This inversion reduces feedback complexity because the estimation is performed locally at the UE without requiring complex network-side processing.
Data Source
AI summary
An apparatus for wireless communication includes a memory and a processor coupled to the memory. The processor is configured to: receive one or more signals for determining frequency dependent in-phase quadrature imbalance (FDIQI) estimates; generate one or more FDIQI estimates based on the one or more signals; and transmit the one or more FDIQI estimates to a network node.