OFDM Interleaver Addressing for DVB-T2 4K Error Resilience
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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 data symbols across sub-carrier signals, but current interleaving schemes are not optimal, especially for the 4K mode, leading to inefficiencies in error correction and data integrity.
Innovation Solution
A data processing apparatus with an interleaver memory and address generator using a linear feedback shift register and permutation circuit to generate addresses for interleaving and de-interleaving data symbols, employing an odd interleaving process and cycling through different permutation codes to reduce the likelihood of successive data bits being mapped to the same sub-carrier, thereby improving error correction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data symbols are mapped onto sub-carrier signals using conventional interleaving schemes, then the mapping process is simple and fast, but successive data bits may be mapped to the same sub-carrier leading to correlated fading and poor error correction performance
Solution Approach 1:
The patent applies dynamics by making the permutation code variable rather than fixed. Different permutation codes are used for different OFDM symbols, specifically alternating between two permutation codes for consecutive symbols. This dynamic approach ensures that successive data bits are distributed across different sub-carriers, breaking the correlation caused by fading and improving error correction performance without requiring a completely complex new system architecture
Solution Approach 2:
The patent changes the parameter of permutation code selection dynamically. By alternating between two predefined permutation codes (e.g., code A for even symbols and code B for odd symbols), the system modifies the mapping pattern without changing the fundamental interleaver structure. This parameter change approach resolves the contradiction by improving reliability through better bit distribution while maintaining relatively simple device complexity
2Reliability
If a fixed permutation code is used for interleaving, then the device complexity is low and operation is simple, but successive data bits may consistently map to the same sub-carrier positions across different OFDM symbols
Solution Approach 1:
The patent implements periodic action by alternating between two permutation codes in a regular pattern across consecutive OFDM symbols. This periodic switching ensures that data bits are distributed differently across sub-carriers in alternating symbols, preventing consistent mapping to the same sub-carrier positions. The periodic nature maintains operational simplicity through a predictable pattern while significantly improving data integrity by breaking fading correlations
3Reliability
If conventional address generation is used, then the address generator is simple, but it cannot effectively separate encoded symbols on different sub-carrier signals to improve error correction coding performance
Solution Approach 1:
The address generator is made dynamic by incorporating a mechanism to switch between two different permutation codes. This dynamic address generation ensures that encoded symbols are separated across different sub-carrier positions in alternating OFDM symbols, improving error correction coding performance by breaking fading correlations while maintaining relatively manageable complexity through the use of only two predefined codes
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 Riʹ10=Ri-1ʹ0⊕Ri-1ʹ2, and the permutation code forms, with an additional bit, a twelve bit address. The address generator includes an offset generator operable to add an offset to the formed twelve bit address, and 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.