Frequency Domain Turbo Equalizer for VSB Signal Recovery
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Solution Overview
Problem
Digital communication systems face challenges in mitigating signal distortion and noise, particularly in multipath environments, which lead to inter-symbol interference (ISI) and error rate degradation, especially in uncharacterized or changing communication channels.
Innovation Solution
A digital communications receiver employs a frequency domain turbo equalizer that performs cyclic prefix restoration and minimum mean squared error estimation to determine a reduced set of symbol values, which are then used to derive the full set of received symbols for vestigial sideband (VSB) transmissions, reducing the complexity of matrix inversion and implementation costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional equalizer is used to compensate for signal distortion in multipath environments, then inter-symbol interference is reduced, but the device complexity and implementation cost increase significantly
Solution Approach 1:
The equalization process is divided into two stages: a first equalizer processes the received signal to produce intermediate results, and a second equalizer processes these intermediate results to produce final equalized symbols. This segmentation allows each equalizer to be simpler while collectively achieving the desired distortion compensation, reducing overall device complexity compared to a single complex equalizer.
Solution Approach 2:
Intermediate symbol estimates are introduced as a mediator between the received signal and the final equalized symbols. The first equalizer produces these intermediate estimates, which then serve as input to the second equalizer. This intermediary approach breaks down the complex equalization task into manageable steps, reducing the complexity requirement for each individual equalizer component.
2Adaptability or versatility
If adaptive equalization is used to handle uncharacterized or changing communication channels, then signal quality is restored, but the computational requirements and processing time increase
Solution Approach 1:
The equalizer system is designed to be adaptive, with the ability to adjust its operation based on channel conditions. The dual-stage structure allows the system to adapt to changing channels by processing signals through multiple refinement stages, each adapting to the specific channel characteristics encountered, thereby maintaining versatility while managing processing time through structured adaptation.
3Measurement precision
If the full set of received data points is processed to determine all symbol values, then complete signal recovery is achieved, but the computational complexity of matrix inversion increases
Solution Approach 1:
The symbol estimation process is segmented into two stages: first determining a reduced set of symbol values from the received data points, then using these reduced symbols to determine the full set of equalized symbols. This segmentation reduces the computational complexity of matrix inversion by processing data in stages rather than attempting to invert the full matrix at once, while still achieving complete signal recovery.
Solution Approach 2:
A reduced set of symbol values is extracted from the full set of received data points before performing the final equalization. By taking out and processing only the essential information in the reduced set first, the system achieves the same signal recovery accuracy as processing all data points directly, but with significantly reduced computational complexity for matrix inversion.
Data Source
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AI summary
In a digital communications receiver configured to receive, via a communications channel, a received first signal representing a sequence of symbols, each symbol being encoded to be representative of data bits, a method of processing the received signal includes adjusting a magnitude, filtering, and applying cyclic prefix restoration, to the received signal to produce a second signal, converting the second signal from time domain to frequency domain to produce a frequency domain signal, and determining a first quantity of values representing a first portion of the symbols by evaluating a relationship of channel values representing characteristics of the communications channel and a second quantity of values representing a portion of the frequency domain signal, the first quantity being smaller than the second quantity,