OFDM Symbol Interleaving With Dynamic Permutation Codes
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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 and even symbols.
Innovation Solution
A data processing apparatus with a symbol interleaver that uses a linear feedback shift register and permutation circuit to generate pseudo-random bit sequences and change permutation codes for each OFDM symbol, ensuring that data symbols are mapped efficiently across sub-carriers, reducing the likelihood of successive data bits being mapped to the same sub-carrier, thereby enhancing error correction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed permutation code is used for interleaving data symbols onto sub-carriers, then the addressing scheme is simple and deterministic, but successive data bits may be mapped to the same sub-carrier reducing error correction effectiveness
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 different symbols, improving error correction effectiveness while maintaining a manageable complexity through the systematic variation pattern.
Solution Approach 2:
The patent changes the permutation code parameter based on the OFDM symbol index. By varying this parameter dynamically, the system optimizes the mapping of data bits to sub-carriers for each symbol, preventing systematic mapping patterns that would reduce error correction performance. This parameter change approach resolves the contradiction by introducing variability without requiring complete redesign of the addressing architecture.
2Reliability
If different permutation codes are used for each OFDM symbol to improve data symbol distribution, then error correction performance is enhanced, but the complexity of the address generator increases
Solution Approach 1:
The address generator is designed to dynamically select different permutation codes based on the OFDM symbol index. This dynamic behavior allows the system to enhance data symbol distribution across sub-carriers for each symbol while managing complexity through a systematic selection mechanism rather than requiring multiple independent address generators.
Solution Approach 2:
The patent implements periodic action by cycling through different permutation codes in a systematic pattern based on the OFDM symbol index. This periodic variation ensures that data symbols are well-distributed across sub-carriers across different symbols, improving error correction performance. The regular, predictable pattern of code changes keeps the address generator complexity manageable through deterministic behavior.
3Reliability
If more memory is used in the interleaver to store data symbols for interleaving, then the interleaving process can be more effective, but the device size and cost increase
Solution Approach 1:
The patent optimizes the interleaving effectiveness by changing the permutation code parameter for each OFDM symbol rather than increasing memory size. This approach achieves better data symbol distribution and interleaving effectiveness through intelligent addressing patterns, avoiding the need for larger memory structures and thus controlling device size and cost.
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 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 permutation code is changed from one OFDM symbol to another, 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.