Double Layer MRC Equalizer for OFDM ICI Cancellation
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Solution Overview
Problem
In OFDM-based digital communications, inter-carrier-interference (ICI) degrades system performance by destroying carrier orthogonality in time-varying Doppler fading channels, leading to reduced carrier-to-noise ratio (C/N) performance.
Innovation Solution
The implementation of a double layer diversity combining equalizer with ICI canceling techniques, comprising an encoded data estimator, a pair of ICI estimators, and a pair of diversity combining equalizers, specifically using maximal ratio combining (MRC) to compensate for multi-path interference and subtract ICI terms, enhancing C/N performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diversity combining techniques are used to improve C/N performance, then carrier-to-noise ratio is improved, but inter-carrier-interference destroys carrier orthogonality and degrades system performance
Solution Approach 1:
The patent segments the equalization process into two distinct layers: a first diversity combining equalizer that processes received signals from multiple channels, and a second diversity combining equalizer that processes ICI-subtracted signals. This segmentation allows each layer to specialize in handling specific types of interference, with the first layer addressing multi-path interference and the second layer addressing residual ICI, thereby resolving the contradiction between improving C/N and managing ICI
Solution Approach 2:
The patent applies preliminary ICI cancellation by estimating and subtracting ICI terms from the received signals before the final diversity combining equalization. The ICI estimators calculate interference terms based on channel state information and transmitted data, which are then subtracted from the received signals. This preliminary action removes the harmful ICI component before the signals undergo final equalization, preventing ICI from degrading system performance while maintaining the benefits of diversity combining
2Reliability
If ICI cancellation is applied to restore OFDM carrier orthogonality, then system performance is improved, but device complexity increases
Solution Approach 1:
The patent implements multi-functionality by having the diversity combining equalizers serve dual purposes: they perform both traditional multi-path interference equalization and ICI cancellation operations. The first diversity combining equalizer handles received signals while the second processes ICI-subtracted signals, allowing the system to achieve both equalization and interference cancellation functions within a unified receiver architecture, thereby improving system performance without proportionally increasing device complexity
3Reliability
If double layer diversity combining equalization with ICI canceling is implemented, then C/N gain is improved, but computational requirements increase
Solution Approach 1:
The patent applies partial action by implementing ICI cancellation only for the most significant interference components rather than attempting to eliminate all interference. The ICI estimators focus on calculating and subtracting the dominant ICI terms that have the greatest impact on system performance, while accepting that some residual interference may remain. This approach achieves substantial C/N gain (2-4 dB for AWGN channels and 5.5-8 dB for Doppler channels) without the excessive computational burden of complete interference elimination
Data Source
AI summary
An apparatus, method, and system for reducing a C/N in an OFDM receiver using diversity combining techniques in the presence of ICI, wherein the apparatus comprises an encoded data estimator adapted to estimate data received in the OFDM receiver; a pair of ICI estimators operatively connected to the encoded data estimator and adapted to calculate an inter-carrier-interference term of the data; and a pair of diversity combining equalizers adapted to compensate multi-path interference of the data, wherein a first one of the diversity combining equalizers is operatively connected to the encoded data estimator, and a second one of the diversity combining equalizers is operatively connected to the pair of ICI estimators. The diversity combining equalizer may comprise a MRC diversity combining equalizer. Preferably, the encoded data estimator, the pair of ICI estimators, and the pair of diversity combining equalizers are implemented on a DVB-T/H diversity SoC.