Receiver Frequency Offset for Multi-Carrier Signal Quality
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Solution Overview
Problem
Receivers for RF multi-carrier signals are sensitive to deviations in phase and amplitude of mixing signals, leading to signal distortion due to leakage of spectral components from one side of the spectrum to the other.
Innovation Solution
A receiver with in-phase and quadrature mixers and an oscillating means that adds a frequency offset to the mixing signals to minimize the error vector magnitude, allowing spectral components to leak into harmless positions between subcarriers, thereby reducing distortion without requiring exact matching of I-Q mixing signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If exact matching of I-Q mixing signals is implemented to prevent spectral leakage, then signal quality is improved, but device complexity and manufacturing precision requirements increase
Solution Approach 1:
The patent introduces a frequency offset parameter to the local oscillator that shifts the leaked spectral components away from harmful positions. By changing the frequency parameter of the mixing signals, the system allows controlled leakage into harmless regions between subcarriers, eliminating the need for precise I-Q matching while maintaining signal quality
Solution Approach 2:
The patent converts the harmful spectral leakage caused by I-Q mismatch into a beneficial effect by intentionally allowing leakage to occur at a controlled frequency offset. This transforms the harmful leakage into harmless energy distribution between subcarriers, where it does not interfere with signal demodulation
2Device complexity
If frequency offset is added to local oscillator to allow spectral leakage, then device complexity is reduced, but signal distortion increases due to leakage
Solution Approach 1:
By carefully selecting the frequency offset parameter to correspond to a quarter of the subcarrier spacing, the patent ensures that leaked spectral components land precisely in the null regions between subcarriers. This parameter selection transforms potential distortion into harmless energy distribution
Solution Approach 2:
The patent moves the leakage problem from the time domain (where I-Q matching is critical) to the frequency domain, where controlled frequency offset can redirect leakage energy into harmless spectral regions. This dimensional shift allows simplified hardware while maintaining signal integrity
3Manufacturing precision
If I-Q mixing signals are precisely matched to prevent leakage, then manufacturing precision is improved, but sensitivity to temperature and aging effects worsens
Solution Approach 1:
The patent replaces the need for precise amplitude and phase matching with a frequency offset parameter that is inherently more stable against temperature and aging. Frequency drift compensation through offset adjustment is more robust than maintaining precise I-Q balance, which degrades over time and environmental changes
Solution Approach 2:
The system pre-compensates for potential drift and aging effects by continuously adjusting the frequency offset parameter. This preliminary action prevents degradation of signal quality before it occurs, rather than relying on initial precise manufacturing that cannot adapt to environmental changes
Data Source
AI summary
A receiver which is arranged to receive an RF multi-carrier signal (60) comprises an in-phase mixer (51) for frequency down converting the RF multi-carrier signal to an in-phase multi-carrier signal (I) and a quadrature mixer (52) for frequency down converting the RF multi-carrier signal (60) to a quadrature multi-carrier signal. The receiver further comprises a local oscillator (60) arranged to generate in-phase and quadrature mixing signals (64,65) for the in-phase and quadrature mixers (51,52). The local oscillator (60) is further arranged to add a frequency offset to the in-phase and quadrature mixing signals (65, 65) so as to minimize an error vector magnitude of the in-phase and quadrature multi-carrier signals (I, Q).