Sub-channel Signal Interleaving for OFDMA Cell Boundary Interference
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Solution Overview
Problem
In IEEE 802.16e communication systems, the use of the same sub-channels with the same modulation and coding scheme by adjacent cells leads to increased interference for mobile subscriber stations at cell boundaries, especially when the frequency reuse factor is 1, causing signal strength issues and decoding errors.
Innovation Solution
The implementation of a sub-channel signal interleaving method that allocates distinct interleaving patterns to each base station, using cyclic-shifted and offset-modulo orthogonal sequences to differentiate sub-channels, thereby minimizing interference between adjacent cells by varying the mapping order of modulation symbols across sub-carriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If adjacent cells use the same sub-channels with the same modulation and coding scheme, then frequency reuse efficiency is improved, but interference between adjacent cells increases
Solution Approach 1:
The patent applies local quality by assigning different interleaving patterns to different base stations. Each base station uses a unique interleaving pattern (e.g., BS1 uses pattern P1, BS2 uses pattern P2) for mapping modulation symbols to sub-channels. This creates local differentiation in the frequency domain, allowing adjacent cells to reuse the same sub-channels while maintaining distinguishable signal characteristics that reduce interference.
2Productivity
If the frequency reuse factor is 1, then spectrum utilization is improved, but signal strength and decoding accuracy for mobile stations at cell boundaries deteriorate
Solution Approach 1:
The patent implements preliminary action by pre-establishing and assigning different interleaving patterns to each base station before communication begins. The base stations use these pre-assigned patterns to map modulation symbols to sub-channels in a differentiated manner. This preliminary differentiation ensures that even when adjacent cells reuse the same sub-channels with frequency reuse factor of 1, the mobile station can distinguish between signals from different base stations, maintaining signal strength and decoding accuracy at cell boundaries.
Data Source
AI summary
A method of allocating sub-channel signal interleaving patterns to BSs forming a wireless communication system that divides a frequency band into a plurality of sub-carriers and including a plurality of sub-channels, which are a set of predetermined adjacent sub-carriers. The method includes: creating a basic orthogonal sequence having a length identical to a number of the sub-carriers forming the sub-channel; creating a plurality of sequences having a same length as the basic orthogonal sequence by cyclic-shifting the basic orthogonal sequence a predetermined number of times or performing a modulo operation based on a number of the sub-carriers forming the sub-channel, after adding a predetermined offset to the cyclic-shifted basic orthogonal sequence; selecting a predetermined number of sequences corresponding to a number of the BSs from among the plurality of sequences; and allocating the selected sequences as the sub-channel signal interleaving patterns for the BSs.