OFDM Interleaver Addressing for Sub-Carrier 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 odd symbols and varying modes like 2k, 8k, and 4k.
Innovation Solution
A data processing apparatus with an address generator using a linear feedback shift register and permutation circuit to generate addresses for interleaving data symbols across OFDM sub-carriers, employing a sequence of permutation codes to change the order of bits from one OFDM symbol to another, optimizing the interleaving process for improved error correction, particularly using the odd interleaving process for all modes with less than half the maximum sub-carriers.
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 successive data bits may map to the same sub-carrier causing correlated fading and reduced error correction performance
Solution Approach 1:
The patent applies dynamics by making the permutation code variable rather than fixed. The address generator selects different permutation codes from a set of available codes based on the OFDM symbol index, creating a dynamic addressing scheme that adapts to each symbol while maintaining deterministic behavior. This resolves the contradiction by introducing temporal variation to prevent systematic mapping patterns without requiring complex adaptive algorithms.
Solution Approach 2:
The patent changes the parameter of the permutation code itself across different OFDM symbols. By varying which permutation code from the set is applied to each symbol, the system transforms the static addressing parameter into a dynamic one that changes systematically over time. This ensures that successive data bits are distributed across different sub-carriers, improving error correction performance while maintaining manageable complexity through the use of a predefined code set.
2Reliability
If different permutation codes are used for different OFDM symbols, then data symbols are better distributed across sub-carriers improving error correction, but the address generation and control logic becomes more complex
Solution Approach 1:
The patent implements periodic action by cycling through a set of permutation codes in a systematic sequence across successive OFDM symbols. Rather than using complex adaptive selection, the system applies permutation codes periodically according to a predetermined pattern based on the symbol index. This achieves good data distribution and error correction performance while keeping the control logic simple and deterministic.
Solution Approach 2:
The patent applies preliminary action by pre-defining a set of permutation codes that are prepared in advance for use across different OFDM symbols. The system does not need to generate or select codes dynamically during operation; instead, the appropriate code is already determined by the symbol index. This reduces runtime complexity while maintaining the benefits of variable permutation for improved data integrity.
3Adaptability or versatility
If standard interleaving is applied to all OFDM modes, then the system is simple to implement, but it is not optimal for modes with fewer sub-carriers where only odd interleving should be used
Solution Approach 1:
The patent applies local quality by tailoring the interleaving approach to the specific characteristics of different OFDM modes. The system determines the appropriate interleaving strategy (standard or odd-only) based on the operating mode and applies the corresponding permutation codes selectively. This ensures optimal performance for each mode type without requiring complex adaptive algorithms, as the appropriate code set is selected based on predefined mode characteristics.
Data Source
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AI summary
A data processing apparatus maps input symbols to be communicated onto a predetermined number of sub-carrier signals of an Orthogonal Frequency Division Multiplexed (OFDM) symbol. 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 twelve register stages with a generator polynomial for the linear feedback shift register of Riʹ11=Ri-1ʹ0⊕Ri-1ʹ1⊕Ri-1ʹ4⊕Ri-1ʹ6, and the permutation code forms, with an additional bit, a thirteen bit address. The permutation code is changed from one OFDM symbol to another, thereby providing an improvement in interleaving the data symbols for an 8K operating mode of an OFDM modulated system such as a Digital Video Broadcasting (DVB) standard such as DVB-Terrestria12 (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.