OFDM LDPC De-Interleaving for Burst-Error-Resistant Decoding
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Solution Overview
Problem
Existing OFDM communication systems face challenges in error correction, particularly in terrestrial broadcast channels with correlated fading, where LDPC codes struggle with burst errors and erasures due to the interleaving of data bits onto sub-carrier signals, leading to reduced decoding performance.
Innovation Solution
A data processing apparatus that combines a bit interleaver and a symbol interleaver to perform parity interleaving and column twist interleaving on LDPC codes, ensuring that error-susceptible code bits are mapped to strong bits of orthogonally modulated symbols, thereby increasing resistance to burst errors and maintaining performance in AWGN communication paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data bits are separated onto different data symbols and communicated on different sub-carrier signals, then error correction coding performance is improved, but device complexity increases due to the need for symbol interleavers and address generators
Solution Approach 1:
The patent divides the interleaving process into two distinct stages: bit-level interleaving (separating LDPC code bits across symbols) and symbol-level interleaving (mapping symbols to sub-carriers). This segmentation allows each interleaver to be optimized independently, improving error correction performance while managing complexity through modular design.
Solution Approach 2:
The patent introduces a dual-dimensional interleaving approach where data is first interleaved across the symbol dimension (time) and then across the sub-carrier dimension (frequency). This two-dimensional approach maximizes error dispersion in both time and frequency domains, achieving superior error correction performance.
2Reliability
If LDPC codes are used for error correction, then decoding performance is improved in AWGN channels, but resistance to burst errors and erasures deteriorates in terrestrial broadcast channels with correlated fading
Solution Approach 1:
The patent applies bit interleaving as a preliminary action before symbol mapping and transmission. By预先 separating LDPC code bits across different symbols and sub-carriers, the system prepares the data to resist burst errors before they occur during transmission through correlated fading channels.
Solution Approach 2:
The patent converts the harmful effect of correlated fading into a benefit by using it to validate and optimize the interleaving strategy. The interleaving pattern is specifically designed to exploit the statistical properties of fading channels, transforming the correlated nature of fading from a source of burst errors into a mechanism that disperses errors into independent events that LDPC codes can handle more effectively.
3Reliability
If symbol interleaving is applied to map data symbols onto sub-carrier signals, then data integrity is improved, but the complexity of address generation and permutation increases
Solution Approach 1:
The patent employs dynamic address generation for the symbol interleaver, where the read-out addresses are generated based on the write-in addresses through a permutation function. This dynamic approach allows the same hardware structure to adapt to different interleaving patterns and modes, reducing overall system complexity while maintaining data integrity.
Solution Approach 2:
The patent introduces an address generator as an intermediary component that mediates between the symbol interleaver memory and the control logic. This intermediary handles the complex address permutation and generation tasks, simplifying the control logic and making the system more manageable while ensuring correct data mapping.
Data Source
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AI summary
A data processing apparatus is arranged in operation to recover data bits from data symbols received from a predetermined number of sub-carrier signals of an Orthogonal Frequency Division Multiplexed (OFDM) symbol to form an output bit stream. The data processing apparatus comprises a symbol de-interleaver operable to read-into and out from the predetermined number of data symbols from the OFDM sub-carrier signals in accordance with a set of addresses, with the effect that the data symbols are de-interleaved from the OFDM sub-carrier signals into the output symbol stream. A de-mapping unit is operable to generate from the data symbols of the output symbol stream parity interleaved LDPC encoded data bits by converting each of the data symbols of the output symbol stream representing a modulation symbol of the OFDM sub-carrier signals into data bits corresponding to a modulation scheme. An inverse permuter is adapted to perform an inverse permutation process so that a plurality of the LDPC encoded data bits corresponding to a value of 1 in an arbitrary row of an information matrix corresponding to information bits of an LDPC code, which was used to encode the data bits, is not incorporated into the same symbol. An LDPC decoder is adapted to perform LDPC decoding on the LDPC encoded data bits on which the inverse permutation process has been performed to form the output data bits. The symbol de-interleaver includes an address generator operable to generate the set of addresses. The set of addresses are generated by an address generator which has been optimised to interleave the data symbols on to the sub-carrier signals of the OFDM carrier signals for a given operating mode of the OFDM system, such as a 4K operating mode for DVB-T2 or DVB-C2.