PHICH Mapping Across OFDM Symbols to Reduce Neighbor-Cell Interference
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Solution Overview
Problem
Conventional PHICH mapping methods in cellular OFDM wireless packet communication systems face interference issues between neighbor cells due to collisions in PHICH groups, which degrade reception performance, especially for mobile stations with poor wireless channel quality.
Innovation Solution
A method for mapping PHICH by determining the index of OFDM symbols and resource element groups based on the ratio of available resource elements in each symbol, using cell IDs to avoid interference and ensure even distribution of repetitions across the frequency bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If PHICH groups are mapped using conventional methods, then the mapping process is simple, but interference occurs between neighbor cells due to collisions in PHICH groups
Solution Approach 1:
The patent applies local quality by assigning different mapping patterns to different PHICH groups based on their indices. Specifically, even-numbered PHICH groups use one mapping pattern while odd-numbered PHICH groups use another mapping pattern. This differentiation ensures that PHICH groups from adjacent cells do not collide in the same time-frequency resources, thereby eliminating inter-cell interference while maintaining a relatively simple mapping process.
2Reliability
If PHICH is transmitted in multiple OFDM symbols, then diversity gain is improved, but the complexity of determining resource element group indices increases
Solution Approach 1:
The patent segments the PHICH transmission across multiple OFDM symbols by dividing the total number of PHICH groups into multiple sets. Each set is mapped to a different OFDM symbol, with the mapping determined by a systematic formula that uses the PHICH group index and cell identifier. This segmentation provides diversity gain by spreading repetitions across different time symbols while the formula-based approach keeps the complexity of determining resource element group indices manageable.
3Ease of manufacture
If resource element groups are allocated without considering available resource elements in each OFDM symbol, then the allocation process is simpler, but PHICH transmission performance degrades due to interference
Solution Approach 1:
The patent changes the parameter of resource element group index allocation by introducing a formula that incorporates the PHICH group index, cell identifier, and the ratio of available resource element groups in different OFDM symbols. This parameter change ensures that PHICH groups are allocated to resource element groups in a way that avoids interference between neighbor cells, thereby improving transmission performance while maintaining a systematic and manageable allocation process.
Data Source
AI summary
A method for mapping a physical hybrid automatic repeat request indicator channel (PHICH) is described. The method for mapping a PHICH includes determining an index of a resource element group transmitting a repetitive pattern of the PHICH, according to a ratio of the number of available resource element groups in a symbol in which the PHICH is transmitted and the number of available resource element groups in a first or second OFDM symbol, and mapping the PHICH to the symbol according to the determined index. In transmitting the PHICH, since efficient mapping is performed considering available resource elements varying with OFDM symbols, repetition of the PHICH does not generate interference between neighbor cell IDs and performance is improved.