Blind Channel Estimation Using CRC in OFDM Guard Interval
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing blind channel estimation methods in OFDM systems are sensitive to channel zeros and have unstable characteristics, leading to complex and impractical channel estimation, which deteriorates frequency band efficiency.
Innovation Solution
A method for stable channel estimation using cross-correlation matrices and singular value decomposition (SVD) on a rank-one matrix, directly estimating the channel impulse response from the cyclic prefix of the guard interval without pilots, incorporating equal gain combining and noise reduction techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If blind channel estimation is performed using conventional methods in OFDM systems, then channel estimation can be achieved without pilots, but the estimation becomes sensitive to channel zeros and unstable
Solution Approach 1:
The patent introduces a Cyclic Redundancy Check (CRC) sequence as an intermediary element inserted into the guard interval of the OFDM signal. This CRC sequence serves as a mediator that enables reliable channel estimation by providing known reference symbols that are not affected by channel zeros, thereby stabilizing the estimation process while maintaining frequency band efficiency
Solution Approach 2:
The patent performs preliminary channel estimation using the CRC sequence embedded in the guard interval before the main data reception. This preliminary action allows the system to obtain initial channel state information that can be used to guide subsequent equalization and decoding processes, improving overall reliability
2Object-affected harmful factors
If the number of carriers or signal period is increased to solve adjacent signal interference, then interference between successive signals is reduced, but carrier stability and Doppler shift make this difficult in practice
Solution Approach 1:
The patent extracts the function of interference mitigation from the main signal structure by placing known CRC sequences specifically in the guard interval. This separation allows the system to handle adjacent signal interference through the known reference symbols without requiring changes to the overall carrier configuration or signal period, thus avoiding the complexity associated with increasing carrier numbers
3Measurement precision
If pilots are used for channel estimation, then accurate channel information can be obtained, but frequency band efficiency deteriorates
Solution Approach 1:
The patent uses the CRC sequence as an intermediary reference that serves dual purposes: it provides accurate channel estimation information similar to pilots, while simultaneously being part of the standard OFDM frame structure without requiring additional dedicated pilot resources. This allows accurate measurement of channel conditions while preserving frequency band efficiency
Solution Approach 2:
The CRC sequence in the guard interval serves multiple functions: it provides channel estimation reference symbols, enables error detection, and maintains frame synchronization. This multi-functionality eliminates the need for separate dedicated pilot sequences, thereby maintaining frequency band efficiency while achieving accurate channel estimation
Data Source
AI summary
A method for stable channel estimation to increase frequency band efficiency that is lost by using a pilot, and to reduce the complexity and the sensitivity to channel zero. The method includes generating an i-th symbol block Si including N carriers, performing an inverse fast Fourier transform (IFFT) operation on the i-th symbol block, and forming an orthogonal frequency division multiplexing (OFDM) symbol block. The method also includes attaching a guard interval sample in front of the i-th OFDM symbol block Ui and forming at least one OFDM symbol block Ui,cp. The method further includes modeling the formed OFDM symbol block Ui,cp with a channel finite impulse response (FIR) filter and estimating channel impulse response using signals yi received through a channel.