OFDM Symbol Interleaving Using LFSR Address Permutation
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Solution Overview
Problem
DVB-T and DVB-H systems face challenges in error correction due to correlated fading in terrestrial broadcast channels, which affects the integrity of data communication, particularly in the 2k, 8k, and 4k modes, where existing interleaving schemes do not optimally separate symbols across sub-carrier signals.
Innovation Solution
A symbol interleaver using a permutation code and generator polynomial is implemented to optimally map data symbols onto OFDM sub-carrier signals, with an address generator that generates write and read addresses for the interleaver memory, allowing for improved interleaving and de-interleaving in both the transmitter and receiver, specifically utilizing odd and even symbol interleaving modes to enhance error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing interleaving schemes are used in DVB-T and DVB-H systems, then the implementation is straightforward with standard address generators, but the symbols are not optimally separated across sub-carrier signals, reducing error correction performance
Solution Approach 1:
The patent applies parameter changes by modifying the address generation process to use a permutation code that changes the mapping pattern between input symbols and sub-carrier signals. The address generator uses a generator polynomial to create permuted addresses that optimally separate symbols across sub-carriers, improving error correction performance without requiring a completely new interleaver architecture
Solution Approach 2:
The patent segments the address generation process into distinct components: a linear feedback shift register for base address generation, a permutation circuit for reordering addresses, and a final address output stage. This segmentation allows each component to be optimized independently while maintaining overall system functionality
2Reliability
If symbols are separated across more sub-carrier signals to improve error correction, then the error correction coding performance increases, but the device complexity and memory requirements increase
Solution Approach 1:
The patent implements dynamic address generation where the permutation code and generator polynomial adapt the mapping pattern based on the specific DVB-T or DVB-H mode being used. The address generator dynamically creates different address sequences for different operational modes, allowing optimal symbol separation for each mode without requiring separate dedicated memory structures for each mode
Solution Approach 2:
The patent creates a universal address generator that can operate across multiple DVB-T and DVB-H modes (2k, 8k, and 4k modes) using a single permutation circuit and generator polynomial structure. This multi-functional approach allows the same hardware to achieve optimal symbol separation for different sub-carrier configurations without proportionally increasing memory requirements
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-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.