Inter-carrier Bandwidth Control for IQ Imbalance Compensation
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Solution Overview
Problem
Dual-carrier double conversion receivers in carrier aggregation systems are sensitive to IQ imbalance due to shared, gain- and phase-imbalanced LOs and mixers, leading to inter-carrier coupling and making digital compensation of IQ imbalance challenging, especially when carriers have different bandwidths.
Innovation Solution
The frequency response of signal processing elements in receiver branches is set to not fully attenuate received signals in a frequency band of interest wider than the carrier bandwidth, allowing for digital estimation and compensation of IQ imbalance by making interfering signals appear in the IQ imbalance-induced inter-carrier image, facilitating joint compensation across branches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the frequency response of signal processing elements is set to fully attenuate adjacent channel signals, then interference rejection is improved, but digital IQ imbalance compensation becomes impossible due to loss of interfering signal information
Solution Approach 1:
The frequency response is configured to provide partial attenuation of adjacent channel signals rather than complete attenuation. This partial action preserves sufficient interfering signal information for IQ imbalance estimation while still providing some interference rejection, resolving the contradiction between interference rejection and information preservation
Solution Approach 2:
The patent converts the harmful effect of adjacent channel interference into a beneficial resource for IQ imbalance compensation. By allowing interfering signals to appear in the inter-carrier image through controlled frequency response, the system uses these previously harmful signals to enable digital compensation of IQ imbalance
2Measurement precision
If the frequency response is widened to preserve interfering signal information for IQ imbalance compensation, then digital compensation capability is improved, but adjacent channel interference rejection deteriorates
Solution Approach 1:
The frequency response is set to partially pass adjacent channel signals rather than completely blocking them. This partial transmission provides enough interfering signal information for accurate IQ imbalance compensation while maintaining sufficient attenuation to reject harmful interference, balancing both requirements
3Adaptability or versatility
If a direct conversion receiver is used for each carrier, then carrier aggregation capability is improved, but hardware complexity and cost increase
Solution Approach 1:
The patent merges multiple carrier reception capabilities into a single receiver architecture. By using one receiver to process multiple carriers simultaneously with appropriately configured frequency responses, the system eliminates the need for separate direct conversion receivers for each carrier, reducing hardware complexity while maintaining carrier aggregation capability
Solution Approach 2:
The single receiver is designed with multi-functional capability to handle multiple carriers. Through configurable frequency responses that allow controlled passing of adjacent channel signals, the receiver can perform both primary carrier reception and IQ imbalance compensation for multiple carriers, achieving universality without requiring dedicated hardware for each function
Data Source
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AI summary
Digital IQ imbalance estimation and compensation in a carrier aggregation environment is facilitated by shaping the frequency response of receiver branches. In particular, in a multi - carrier receiver, the frequency response of signal processing elements in at least one receiver branch is set to not fully attenuate received signals in a frequency band of interest. The frequency band of interest is greater than the carrier bandwidth of the received signal processed by that receiver branch. In some embodiments, the received signal is not attenuated, and adjacent interfering signals are partially attenuated. This allows information regarding the interfering signals to appear in an IQ imbalance- induced, inter- carrier image of the signals in anther receiver branch, facilitating digital estimation and compensation of IQ imbalance.