OFDM Symbol Interleaving With LFSR Address Permutation
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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 odd and even OFDM symbols.
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 addresses, allowing for efficient mapping and de-mapping of data symbols across OFDM sub-carriers, with a focus on odd interleaving to improve error correction and memory efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed permutation code is used for interleaving 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 permutation code changes based on the OFDM symbol index, creating a dynamic addressing scheme that adapts to different symbols. This ensures that successive data bits are mapped to different sub-carriers across symbols, mitigating correlated fading while maintaining manageable complexity through a systematic variation pattern.
Solution Approach 2:
The patent changes the permutation code parameter based on the OFDM symbol index. By varying this key parameter dynamically, the system achieves better error correction performance through improved symbol distribution across sub-carriers, while the change follows a predictable pattern that controls the overall system complexity.
2Reliability
If separate interleaver memories are used for odd and even OFDM symbols, then the interleaving can be optimized for each symbol type independently, but the memory requirements and device complexity increase
Solution Approach 1:
The patent merges the interleaving operations for odd and even OFDM symbols into a single interleaver memory structure. By combining these operations and using a dynamically varying permutation code, the system achieves the benefits of optimized interleaving for different symbol types while reducing memory requirements and device complexity compared to maintaining separate memory structures.
Solution Approach 2:
The single interleaver memory is designed to handle both odd and even OFDM symbols universally. The same memory structure performs multiple functions by adapting the permutation code based on the symbol type, eliminating the need for separate dedicated memories while maintaining optimization for each symbol type.
3Reliability
If the permutation code changes for each OFDM symbol, then the distribution of data bits across sub-carriers is improved reducing correlated fading, but the complexity of the address generator increases
Solution Approach 1:
The patent implements periodic action by changing the permutation code in a systematic, repeating pattern based on the OFDM symbol index. This periodic variation ensures uniform distribution of data bits across sub-carriers over time, mitigating correlated fading, while the regular pattern keeps the address generator complexity manageable through predictable, cyclical behavior rather than arbitrary changes.
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 ten register stages with a generator polynomial for the linear feedback shift register of Riʹ9=Ri-1ʹ0⊕Ri-1ʹ3, and the permutation code forms, with an additional bit, an eleven bit address. The permutation code is changed from one OFDM symbol to another, thereby providing an improvement in interleaving the data symbols for a 2K 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.