OFDM Frequency Offset Correction via Cyclic Prefix Buffering
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Solution Overview
Problem
Existing wireless communication systems, particularly those using mmW frequencies, face challenges in correcting large and rapidly varying frequency offsets, which lead to inter-carrier interference and increased symbol error rates due to phase noise and oscillator drifts, limiting their performance in real-world, non-line-of-sight environments.
Innovation Solution
The Iris technique employs a time-domain processing method that buffers received OFDM symbols, measures the average frequency offset using the cyclic prefix, and applies a correction signal using a numerically controlled oscillator to mitigate frequency offsets on a per-symbol basis, minimizing processing delay and computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing baseband processing techniques are used to correct frequency offsets, then large but stable frequency offsets can be corrected, but rapidly varying frequency offsets cannot be corrected efficiently, leading to residual offsets and inter-carrier interference
Solution Approach 1:
The patent implements a dynamic frequency offset correction approach where the correction process is repeated iteratively across multiple OFDM symbols. The system adapts to rapidly varying frequency offsets by continuously updating correction estimates for each symbol, transforming the static correction approach into a dynamic one that tracks time-varying conditions.
Solution Approach 2:
The patent employs feedback mechanisms where residual frequency offsets are estimated and used to refine correction estimates in subsequent iterations. The system uses feedback from channel estimates and pilot symbols to continuously improve frequency offset correction accuracy, addressing rapidly varying offsets through iterative refinement.
2Productivity
If symbol durations are increased to improve data transmission, then more data can be transmitted per symbol, but oscillators exhibit larger drifts over larger time-scales, exacerbating frequency offset effects
Solution Approach 1:
The patent segments the frequency offset correction process into per-symbol operations. Instead of attempting to correct frequency offsets over long symbol durations, the system applies correction independently to each OFDM symbol, breaking down the large time-scale drift problem into manageable per-symbol correction steps.
Solution Approach 2:
The patent implements periodic frequency offset correction by applying correction estimates to each successive OFDM symbol in a repeating cycle. This periodic application of correction across multiple symbols addresses oscillator drift that accumulates over time, maintaining orthogonality despite longer symbol durations.
3Quantity of substance
If mmW systems operate at higher frequencies to provide greater spectrum, then orders of magnitude greater spectrum is available, but frequency offsets exhibit high magnitudes and high variations over time, leading to high symbol error rates
Solution Approach 1:
The patent implements dynamic frequency offset correction that adapts to the high-rate variations characteristic of mmW systems. By updating correction estimates for each OFDM symbol and using iterative refinement, the system tracks rapidly varying frequency offsets that occur at mmW frequencies, maintaining reliability despite high magnitudes and variations.
Solution Approach 2:
The patent replaces traditional mechanical or hardware-based frequency stabilization approaches with signal processing-based correction in the baseband domain. By using digital signal processing to estimate and correct frequency offsets after reception, the system addresses mmW frequency instability without requiring ultra-stable hardware oscillators at high frequencies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Iris significantly reduces symbol error rates by effectively correcting large and rapidly varying frequency offsets, outperforming existing methods, especially at larger FFT sizes, and maintaining orthogonality of OFDM subcarriers, thereby enhancing the reliability of mmW wireless communication systems.
Implementation Method 1
applies a correction signal based on the frequency offset parameter to the buffered portion to generate an at least partially corrected signal
Data Source
AI summary
Exemplary communication apparatus can comprise a receiver; a computer arrangement; and a non-transitory medium comprising computer-executable instructions that cause the apparatus to: receive a signal comprising a plurality of symbols in a first domain; store a portion of the signal comprising at least one symbol in a buffer; determine a frequency offset parameter relating to the buffered portion; apply a correction signal based on the offset parameter to the buffered portion to generate an at least partially corrected signal in the first domain; and transform the at least partially corrected signal into a second domain. In some embodiments, the first domain is a time domain, the second domain is a frequency domain, and the symbols are OFDM symbols. The corrected signal can be further transformed into a third domain. Further, exemplary methods and computer-readable media can be provided embodying one or more procedures the apparatus is configured to perform.