OFDM De-Interleaver Address Mapping for Odd Symbol Fading
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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 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 de-interleaving of data symbols across OFDM sub-carriers, with the ability to change permutation codes for each OFDM symbol to improve error correction and reduce memory usage by using only odd interleaving processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed permutation code is used for interleaving data symbols onto OFDM sub-carrier signals, then the address generation process is simple and deterministic, but the error correction performance deteriorates due to correlated fading in terrestrial broadcast channels
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 interleaving scheme that adapts to different symbols. This resolves the contradiction by introducing variability to improve error correction performance against correlated fading, while the underlying structure remains deterministic and manageable.
Solution Approach 2:
The patent changes the parameter of the permutation code itself, making it a function of the OFDM symbol index. By varying this parameter across different symbols, the system achieves better error correction performance. The change is systematic and controlled, maintaining determinism while improving reliability.
2Reliability
If separate interleaving processes are used for even and odd OFDM symbols, then the error correction performance improves, but the memory requirements and device complexity increase
Solution Approach 1:
The patent creates a universal interleaving process that handles both even and odd OFDM symbols through a single unified algorithm. The permutation code adapts to different symbol types through the index-based variation, eliminating the need for separate interleaving processes. This reduces memory requirements while maintaining improved error correction performance.
Solution Approach 2:
The patent merges the separate even and odd symbol interleaving processes into a single unified process. By combining these operations and using a permutation code that naturally adapts to different symbol types, the system achieves the same error correction benefits with reduced memory usage and simplified architecture.
3Productivity
If a large number of memory locations are allocated for the interleaver memory to handle all OFDM sub-carriers, then all data symbols can be interleaved efficiently, but the memory usage and device complexity increase for modes with fewer sub-carriers
Solution Approach 1:
The patent applies local quality by making the interleaving process adapt to the specific characteristics of each OFDM mode. The permutation code and address generation are tailored to the actual number of sub-carriers in use, rather than allocating memory for the maximum possible number. This optimizes memory usage for each specific operating mode while maintaining interleaving efficiency.
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 R [9] = R -1 [0]⊕ R -1 [3], and the permutation code forms, with an additional bit, an eleven bit address. 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 2K 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.