OFDM Preamble Timing Error and Frequency Offset Estimation
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Solution Overview
Problem
High-speed portable Internet systems face challenges in accurately estimating timing errors and frequency offsets due to inter-symbol interference (ISI) and frequency offset-induced orthogonality loss between subcarriers, which affect decoding performance and synchronization in OFDM methods.
Innovation Solution
A method involving a preamble symbol extraction and pseudo noise (PN) sequence multiplication is used to estimate timing errors and frequency offsets, employing a preamble extractor, PN generator, multiplexer, timing error determining unit, and frequency offset estimator to compensate for these errors, thereby enhancing time-frequency synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If OFDM method is used to reduce inter-symbol interference, then ISI is efficiently reduced, but frequency offset causes orthogonality loss and interference between subchannels
Solution Approach 1:
The patent applies preliminary action by performing frequency offset estimation and compensation before the FFT operation and symbol detection. The receiver estimates the frequency offset using correlation methods on the received signal, then compensates for it by adjusting the local oscillator frequency or applying a corrective phase rotation to the received signal before further processing. This preliminary compensation ensures that orthogonality is restored before critical operations occur.
Solution Approach 2:
The patent implements feedback by continuously monitoring the received signal for frequency offset conditions and adjusting the compensation mechanism accordingly. The receiver uses correlation-based estimation to detect frequency offset, feeds this information back to the frequency compensation unit, which then adjusts the local carrier frequency or applies corrective phase rotation. This closed-loop feedback mechanism maintains orthogonality despite varying channel conditions.
2Measurement precision
If receiver tuning is inappropriate due to channel characteristics, then frequency offset occurs, but prior art methods do not correctly estimate timing error and frequency offset due to multipath ISI
Solution Approach 1:
The patent applies the extraction principle by isolating and removing the multipath ISI component from the received signal before performing frequency offset estimation. The receiver first estimates and compensates for timing error to properly align the received signal with the expected symbol boundaries. Then it extracts the frequency offset information using correlation methods on the timing-corrected signal, separating the frequency offset effect from the multipath interference effect for accurate measurement.
Solution Approach 2:
The patent performs preliminary timing error compensation before frequency offset estimation to eliminate the confounding effect of multipath ISI. By first correcting the timing alignment using correlation-based timing error estimation on the received signal, the system prepares the signal in a state where frequency offset can be accurately measured without contamination from misalignment-induced ISI. This sequential preliminary correction enables precise measurement of both parameters.
Data Source
AI summary
The present invention relates to a method for estimating a timing error and a frequency offset in a high-speed portable Internet system and a method thereof. A predetermined preamble symbol is added to an OFDM frame to be transmitted by a transmitter according to an exemplary embodiment of the present invention, an IFFT operation is performed, and then a pseudo noise is multiplexed by the preamble symbol to estimate the timing error and the frequency offset. A receiver receives an OFDM symbol, extracts the preamble symbol from the OFDM symbol, and multiplexes the extracted preamble symbol by a local pseudo noise, which is equal to the pseudo noise used by the transmitter but is shifted.