OFDM Receiver Frequency Offset Correction Using Unallocated Subcarriers
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Solution Overview
Problem
OFDM receivers face significant challenges in accurately correcting frequency offset errors, particularly in LTE-V2X systems, due to factors like local oscillator inaccuracies, timing mismatches, and Doppler shifts, leading to energy leakage from allocated to unallocated subcarriers, which degrades signal quality and increases interference.
Innovation Solution
The proposed solution involves a frequency offset correction mechanism that utilizes both allocated and unallocated subcarriers to estimate and correct frequency offset errors, enhancing the robustness of BCH decoding by harvesting energy that has leaked onto unallocated subcarriers, thereby improving signal-to-noise ratio and reducing block error rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If frequency offset correction uses only allocated subcarriers, then device complexity is reduced, but measurement precision of frequency offset estimation deteriorates
Solution Approach 1:
The frequency offset correction mechanism is designed to work with both allocated and unallocated subcarriers, making the system multi-functional. The same correction logic processes different types of subcarriers uniformly, improving estimation accuracy without significantly increasing complexity.
Solution Approach 2:
The system changes the parameter of subcarrier utilization from only allocated subcarriers to include both allocated and unallocated subcarriers. This parameter change expands the data source for frequency offset estimation, improving precision while maintaining manageable complexity through efficient processing.
2Measurement precision
If frequency offset correction utilizes both allocated and unallocated subcarriers, then measurement precision of frequency offset estimation is improved, but device complexity increases
Solution Approach 1:
The patent extracts and utilizes the previously discarded unallocated subcarriers as useful data sources for frequency offset estimation. By taking out these unused resources and repurposing them, the system improves measurement precision without requiring entirely new hardware structures.
Solution Approach 2:
The unallocated subcarriers, which were previously serving no functional purpose, now serve the frequency offset correction function. The system makes the existing subcarrier structure work for multiple purposes, reducing the need for additional dedicated components.
3Loss of energy
If energy from unallocated subcarriers is harvested for correction, then loss of energy is reduced, but device complexity increases
Solution Approach 1:
The patent converts the harmful effect of energy leakage onto unallocated subcarriers into a beneficial resource. The leaked energy that was previously considered waste or interference is now harvested and utilized to improve the frequency offset correction, reducing overall energy loss while using existing system components.
Solution Approach 2:
Instead of discarding the energy present on unallocated subcarriers, the system recovers and utilizes this energy for frequency offset correction. This recovery process improves energy efficiency by making use of previously wasted signal energy.
Data Source
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AI summary
A system for use with an OFDM-receiver. The system comprising a frequency-offset-correction-block; and a sub-band-demapping-block. The sub-band-demapping-block is configured to receive an input-signal and determine within the input signal: one or more allocated-frequency-sub-bands allocated to convey an information-signal (PSS, SSS and BCH); and one or more unallocated-frequency-sub-bands. The sub-band-demapping-block can then provide the allocated-frequency-sub-bands and the unallocated-frequency-sub-bands to the frequency-offset-correction-block. The frequency-offset-correction-block is configured to: receive a frequency-offset-estimation-signal representative of a frequency-offset-error of the input-signal relative to a local oscillator of the OFDM-receiver; and apply a frequency-correction-algorithm to the allocated-frequency-sub-bands and at least a subset of the unallocated-frequency-sub-bands, based on the frequency-offset-estimation-signal, to produce a frequency-corrected-signal which compensates for the frequency-offset-error of the input-signal. Even though in Sidelink synchronization subframes there is no data allocated to the neighbouring unallocated-subcarriers, a frequency-offset-correction block can use them to improve the frequency offset robustness of BCH decoding. The reason is that in case of frequency-offset-error, energy leaks onto these unallocated-subcarriers. By including them in a frequency offset correction input, the energy that leaked onto them can advantageously be harvested. As a result, the BCH decoding performance can be improved substantially.