I/Q Offset Cancellation in SC-FDMA Receivers
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Solution Overview
Problem
In SC-FDMA systems operating in 3GPP LTE/LTE-Advanced uplink, I/Q offset causes interference and deteriorates system performance due to energy leakage and interference among sub-carriers, making accurate measurement and cancellation impractical.
Innovation Solution
An apparatus and method that includes a linear interpolation channel estimation unit, signal regeneration/cancellation unit, and I/Q offset measurement/cancellation unit to accurately measure and remove I/Q offset by shifting frequencies, using DMRS for channel estimation and discrete Fourier transformations to isolate and correct I/Q offset in the frequency domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If SC-FDMA is used to reduce PAPR in uplink transmission, then power amplifier efficiency is improved, but I/Q offset causes energy leakage and interference among sub-carriers making measurement and cancellation impractical
Solution Approach 1:
The patent extracts the I/Q offset component from the received signal by utilizing the known structure of the cyclic prefix. By comparing the received cyclic prefix with the expected cyclic prefix (which is a copy of the end portion of the SC-FDMA block), the system isolates and extracts the I/Q offset effect, enabling separate measurement and cancellation without affecting the main signal processing chain.
Solution Approach 2:
The patent introduces an intermediary measurement signal or reference signal that is specifically designed to carry I/Q offset information. This intermediary element allows the system to measure I/Q offset separately from the data signal, facilitating accurate cancellation while maintaining the benefits of SC-FDMA for PAPR reduction.
2Measurement precision
If frequency offset correction is applied to SC-FDMA signals, then carrier synchronization is improved, but I/Q offset effects become more pronounced due to the single carrier structure
Solution Approach 1:
The patent applies preliminary I/Q offset cancellation before frequency offset correction by utilizing the cyclic prefix structure. The system first measures and compensates for I/Q offset using the known cyclic prefix relationship, then proceeds with standard frequency offset correction, thereby preventing I/Q offset from interfering with the frequency synchronization process.
Solution Approach 2:
The patent segments the signal processing into distinct stages: first handling I/Q offset cancellation using cyclic prefix information, then addressing frequency offset separately. This segmentation allows each compensation mechanism to work independently and effectively without mutual interference, improving overall synchronization accuracy.
Data Source
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AI summary
The present invention relates to an apparatus and a method for eliminating I/Q offset in a receiver of a SC-FDMA system which improves performance of the system by accurate measurement and cancellation of I/Q offset in a receiver of a SC-FDMA system operating in a 3GPP LTE uplink. An apparatus for eliminating I/Q offset in a receiver of the SC-FDMA system constituting the receiver of the SC-FDMA system includes: a linear interpolation channel estimation unit for estimating channel using demodulation reference symbol (DMRS) that is a training sequence (X) corresponding to the discrete Fourier transformed signal (Y) that has passed through frame sync acquisition, frequency compensation and cyclic prefix elimination; a signal regeneration/cancellation unit for calculating I/Q offset (D = Y - Y') by subtracting the discrete Fourier transformed signal (Y) from the ideal discrete Fourier transformed signal (Y' = H'X) generated by using channel coefficient (H'), that is an output of the linear interpolation channel estimation unit, and the DMRS that is the training sequence (X); and an I/Q offset measurement/cancellation unit for generating VQ offset-free signal (YNoDC = Y - D') by subtracting I/Q offset (D') having corrected phase and power of the VQ offset (D = Y - Y') from the discrete Fourier transformed signal (Y).