OFDM Interleaver Address Generation for 4K DVB-T2 Symbols
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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 effective symbol interleaving, but current interleaving schemes are not optimal, especially for odd OFDM symbols, leading to inefficient use of memory and sub-carrier allocation.
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, which changes permutation codes for each OFDM symbol, optimizing the interleaving process by using only odd interleaving for reduced memory usage and improved error correction, particularly in the 4k mode of DVB-T2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional symbol interleaving schemes are used in OFDM systems, then error correction can be performed, but the interleaving is not optimal especially for odd OFDM symbols leading to inefficient memory and sub-carrier allocation
Solution Approach 1:
The patent applies dynamics by making the interleaving scheme adaptive to different OFDM symbol types (even and odd symbols). The system dynamically selects different interleaving approaches based on the symbol type, optimizing performance for each case rather than using a fixed conventional scheme. This resolves the contradiction by improving reliability through targeted optimization while avoiding the complexity of a single universal solution.
Solution Approach 2:
The patent changes key parameters of the interleaving process including the use of different permutation codes for even and odd symbols, modified address generation sequences, and adjusted mapping patterns. These parameter changes enable optimal interleaving for specific symbol types, improving error correction efficiency without requiring complex general-purpose interleavers.
2Reliability
If permutation codes are changed from one OFDM symbol to another, then data symbols are better distributed across sub-carriers, but the address generation and permutation circuit complexity increases
Solution Approach 1:
The patent segments the permutation code sequence into distinct codes for even OFDM symbols and odd OFDM symbols. This segmentation allows each symbol type to use an optimized permutation code tailored to its characteristics, improving data symbol distribution. The complexity is managed by creating separate but simple code sequences rather than a complex adaptive system.
Solution Approach 2:
The patent implements periodic action by alternating between different permutation codes in a regular pattern corresponding to even and odd OFDM symbols. This periodic switching provides optimal distribution for each symbol type while maintaining a simple, predictable structure that avoids complex address generation circuits.
3Quantity of substance
If only odd interleaving is used to reduce memory usage, then memory requirements are minimized, but the interleaving performance for even OFDM symbols may be suboptimal
Solution Approach 1:
The patent applies local quality by implementing different interleaving characteristics for even and odd OFDM symbols. Even symbols use one interleaving pattern while odd symbols use another, allowing each to be optimized for its specific requirements. This local optimization improves overall reliability without requiring uniform complex interleaving across all symbols, thus managing memory requirements effectively.
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 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-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.