OFDM De-Interleaving With Variable Permutation Codes for 4K DVB-T2
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Solution Overview
Problem
Existing OFDM systems, such as DVB-T and DVB-H, face challenges in error correction due to correlated fading in terrestrial broadcast channels, which can be mitigated by effectively interleaving symbols across sub-carrier signals, but current interleaving schemes are not optimal, especially for the 4k mode, leading to inefficiencies in data communication integrity.
Innovation Solution
A data processing apparatus with a de-interleaver and address generator using a linear feedback shift register and permutation circuit to generate pseudo-random bit sequences and addresses, which changes permutation codes for each OFDM symbol to improve symbol mapping and reduce the likelihood of consecutive data bits being mapped to the same sub-carrier, employing an odd interleaving process to optimize memory usage and error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed permutation code is used for interleaving data symbols onto sub-carrier signals, then the addressing scheme is simple and deterministic, but consecutive data bits may be mapped to the same sub-carrier leading to poor error correction performance
Solution Approach 1:
The patent applies dynamics by making the permutation code variable rather than fixed. The address generator selects from multiple permutation codes (first, second, third codes) based on the OFDM symbol index, creating a dynamic addressing scheme that adapts to different symbols. This dynamic approach ensures that consecutive data bits are mapped to different sub-carriers across successive OFDM symbols, improving error correction performance without requiring overly complex address generation logic.
Solution Approach 2:
The patent changes the parameter of the permutation code itself - switching between different permutation codes (first code, second code, third code) depending on the OFDM symbol being processed. This parameter change in the addressing scheme allows the system to vary the mapping pattern dynamically, preventing consecutive data bits from consistently mapping to the same sub-carrier positions, thereby improving reliability while maintaining manageable complexity through structured code selection.
2Reliability
If memory is used to store all data symbols for de-interleaving, then complete de-interleaving can be achieved, but memory requirements increase significantly
Solution Approach 1:
The patent applies segmentation by dividing the data symbol processing into different groups based on the OFDM symbol index. Instead of treating all data symbols uniformly, the system segments them into groups that use different permutation codes for addressing. This segmentation allows the de-interleaver to process symbols in manageable groups, reducing the memory footprint required to store all symbols simultaneously while still achieving complete de-interleaving through the structured addressing scheme.
Solution Approach 2:
The patent employs preliminary action by pre-defining multiple permutation codes (first, second, third codes) that can be selected based on the OFDM symbol index. This preliminary preparation of addressing patterns allows the system to efficiently manage memory usage during de-interleaving, as the address generator can directly select the appropriate pre-defined code without requiring complex real-time computation, thereby reducing memory requirements while maintaining data integrity.
3Device complexity
If the same permutation code is used for all OFDM symbols, then the address generator is simple to implement, but the interleaving pattern repeats leading to correlated fading issues
Solution Approach 1:
The patent applies periodic action by cycling through multiple permutation codes (first code, second code, third code) in a systematic pattern based on the OFDM symbol index. Instead of using a single static permutation code, the system periodically switches between different codes, creating a repeating but varied interleaving pattern. This periodic variation prevents the same mapping pattern from repeating continuously, thereby mitigating correlated fading issues while maintaining implementation simplicity through the structured, predictable code selection sequence.
Data Source
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AI summary
A data processing apparatus maps symbols received from a predetermined number of sub-carrier signals of Orthogonal Frequency Division Multiplexed (OFDM) symbols into an output symbol stream. The data processor includes an interleaver memory which reads-in the predetermined number of data symbols for mapping onto the OFDM sub-carrier signals. The interleaver memory reads-out the data symbols on to the OFDM sub-carriers to effect the mapping, the read-out being in a different order than the read-in, the order being determined from a set of addresses, with the effect that the data symbols are interleaved on to the sub-carrier signals. The set of addresses are generated from an address generator which comprises a linear feedback shift register and a permutation circuit. The linear feedback shift register has eleven register stages with a generator polynomial for the linear feedback shift: register of R'i[10] = R'i-1 [0] ⊕ R'i-1 [2], and the permutation code forms, with an additional bit, a twelve bit address. The data processing apparatus is operable to de-interleave the first and second sets of data symbols into the output data stream in accordance with an odd interleaving process, thereby providing an improvement in interleaving the data symbols for a 4K operating mode of an OFDM modulated system such as a Digital Video Broadcasting (DVB) standard such as DVB-Terrestrial2 (DVB-T2). This is because there is a reduced likelihood that successive data bits which are close in order in an input data stream are mapped onto the same sub-carrier of an OFDM symbol.