Channel Estimate Interpolation Circuit for OFDM Bandwidth Edge
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Solution Overview
Problem
In OFDM-based radio baseband systems, generating virtual waveforms of channel estimate values outside the bandwidth using FFT interpolation results in significant differences from actual waveforms, and existing solutions require complex circuitry to perform additional processing steps, leading to increased circuit size.
Innovation Solution
A channel estimate interpolation circuit that selectively performs FFT or inverse-FFT operations, using linear interpolation between channel estimate values at bandwidth ends, followed by inverse-FFT and FFT operations with data component replacement to minimize differences and reduce circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple linear interpolation is used to generate virtual waveform outside bandwidth, then circuit complexity is reduced, but the difference between virtual waveform and actual waveform becomes large
Solution Approach 1:
The patent segments the waveform generation process into two distinct parts: (1) using simple linear interpolation for points outside the bandwidth where reference signals are unavailable, and (2) using FFT-based interpolation for points within the bandwidth where reference signals exist. This segmentation allows each method to be applied where it is most effective, maintaining low circuit complexity for out-of-bandwidth points while improving accuracy for in-bandwidth points.
Solution Approach 2:
The patent changes the interpolation parameter (method) based on the position of the frequency component. For frequency components outside the bandwidth, linear interpolation parameters are used to keep circuit complexity low. For frequency components within the bandwidth, FFT-based interpolation parameters are used to improve waveform accuracy. This parameter change resolves the contradiction by adapting the method to the specific requirements of each region.
2Measurement precision
If FFT interpolation is used to improve interpolation accuracy, then waveform accuracy is improved, but circuit size increases due to additional processing circuits
Solution Approach 1:
The patent applies segmentation by dividing the frequency domain into in-bandwidth and out-of-bandwidth regions. FFT interpolation is applied only to the in-bandwidth region where it provides accuracy improvements, while linear interpolation handles the out-of-bandwidth region. This selective application reduces the overall circuit size compared to applying FFT interpolation across the entire frequency range.
Solution Approach 2:
The patent implements partial action by applying the computationally intensive FFT interpolation only partially - specifically only to the frequency components within the bandwidth where reference signals are available. This partial application achieves waveform accuracy improvement where needed while avoiding the full circuit complexity overhead that would result from applying FFT interpolation to all frequency components.
3Device complexity
If linear interpolation is used for channel estimate values outside bandwidth, then circuit complexity is minimized, but the difference from actual channel estimate values becomes large
Solution Approach 1:
The patent segments the channel estimate calculation into two paths: one for in-bandwidth subcarriers using FFT interpolation to achieve high accuracy, and another for out-of-bandwidth subcarriers using simple linear interpolation to maintain low circuit complexity. This segmentation allows the system to achieve acceptable channel estimate accuracy across all subcarriers without incurring the full circuit complexity of FFT-based methods everywhere.
Solution Approach 2:
The patent changes the interpolation parameter based on the subcarrier position relative to the bandwidth. For out-of-bandwidth subcarriers, linear interpolation parameters are used to minimize circuit complexity. For in-bandwidth subcarriers, FFT-based parameters are used to improve accuracy. This adaptive parameter selection resolves the contradiction between circuit complexity and channel estimate accuracy.
Data Source
AI summary
To more accurately generate a virtual waveform of channel estimate values outside a bandwidth upon their interpolation in OFDM system while preventing the circuit size from increasing, a converter (104) performs a linear interpolation between channel estimate values corresponding to reference signals arranged at both ends of a predetermined bandwidth among first channel estimate values estimated based on reference signals, thereby estimating second channel estimate values corresponding to subcarriers outside the bandwidth. The converter (104) performs an inverse-FFT operation for channel estimate values obtained by merging the first and second channel estimate values to obtain a first delay profile, replaces with zero data components delayed for a predetermined threshold time or more in the first delay profile, performs an FFT operation for a delay profile obtained by the replacement to obtain third channel estimate values, and extracts therefrom channel estimate values corresponding to the subcarriers outside the bandwidth.