CORDIC-Based Inverse Channel Estimation for OFDM Systems
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Solution Overview
Problem
Digital data transmission systems face challenges in accurately estimating and compensating for channel transfer function imperfections, particularly in non-stationary channels, leading to bit errors and inefficiencies in OFDM and single-carrier systems due to high computational burdens and costs associated with conventional channel estimation methods.
Innovation Solution
A modified least-squares method combined with the CORDIC algorithm for estimating the inverse channel transfer function, utilizing a CORDIC unit for division and scaling to prevent overflow, and employing Farrow-style interpolation for efficient channel equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional channel estimation methods are used, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent replaces complex conventional channel estimation algorithms with the CORDIC (COordinate Rotation DIgital Computer) algorithm, which uses iterative geometric rotations to compute channel estimates through simple shift-and-add operations. This substitution of the computational mechanism reduces device complexity while maintaining measurement precision in OFDM and single-carrier systems
Solution Approach 2:
The patent changes the computational parameters by using the CORDIC algorithm's iterative rotation approach with configurable iteration counts. By adjusting the number of iterations and using scaling factors, the system achieves accurate channel estimation with reduced computational burden compared to traditional methods like least-squares or MMSE estimators
2Device complexity
If CORDIC algorithm is used for division, then device complexity is reduced, but loss of information may increase due to overflow
Solution Approach 1:
The patent applies preliminary scaling to the input signals before they enter the CORDIC division unit. By pre-scaling the numerator and denominator values to appropriate ranges, the system prevents overflow during the iterative CORDIC computation while maintaining the accuracy of the division result. This preliminary preparation action ensures that the reduced-complexity CORDIC algorithm does not lose information through overflow
Solution Approach 2:
The patent introduces scaling factors as intermediary elements between the input signals and the CORDIC algorithm. These scaling factors act as mediators that adjust the magnitude of input values to prevent overflow during computation, while being compensatable in the final result to maintain accuracy
Data Source
AI summary
An inverse channel estimation method includes receiving a modulated signal with a pilot. A local reference pilot, matching the received pilot as it was prior to transmission, is divided by a scaled version of the received pilot's power. The division result is scaled again and multiplied with a conjugate value of the received pilot signal, to obtain the inverse channel estimate. Scaling may be performed using bit shifting. The division is performed using a CORDIC algorithm. If multiple pilots are received, interpolation can be performed to provide channel estimates for time and/or frequencies in between. Interpolation can be based on the Farrow method. The received signal may be equalized by multiplying it with the inverse channel estimate.