Femtocell Frequency Sub-channel Selection for Macrocell Interference
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Solution Overview
Problem
Current hand-off methods in cellular networks fail to address interference from private femtocell transmitters, which can cause coverage holes and increased interference, especially when a mobile device is not authorized to access the femtocell.
Innovation Solution
A femtocell determines the soft-frequency-reuse information of an overlapping macrocell to select and assign frequency sub-channels for its users, reducing interference by transmitting on cell-center user frequency sub-channels, and the macrocell reassigns cell-center users to higher power sub-channels when they approach the femtocell.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a mobile device uses hand-off method to switch to the strongest signal transmitter, then communication quality is improved, but interference from femtocell transmitters cannot be resolved when the device is not authorized to access the femtocell
Solution Approach 1:
The patent changes the frequency parameter by assigning different frequency sub-channels to cell-center and cell-edge users. The femtocell transmits on cell-center frequency sub-channels while the macrocell transmits on cell-edge frequency sub-channels, creating frequency separation that reduces interference without requiring hand-off to the femtocell.
2Area of stationary object
If femtocell transmits at lower power levels, then coverage area is reduced, but interference with macrocell transmissions increases when mobile devices are in proximity
Solution Approach 1:
The patent segments the frequency spectrum into different sub-channels, assigning cell-center frequency sub-channels to the femtocell and cell-edge frequency sub-channels to the macrocell. This frequency segmentation allows both transmitters to operate simultaneously with minimal interference, even when coverage areas overlap.
3Object-affected harmful factors
If macrocell reassigns cell-center users to higher power sub-channels when they approach femtocell, then interference resistance is improved, but network complexity increases
Solution Approach 1:
The patent implements dynamic frequency assignment where the macrocell controller monitors mobile device locations and dynamically reassigns users from cell-center frequency sub-channels to cell-edge frequency sub-channels when they approach femtocell coverage areas. This dynamic adaptation reduces interference while maintaining network efficiency.
Data Source
AI summary
Disclosed is a method for a femtocell to reduce interference with an overlapping macrocell. The femtocell determines soft-frequency-reuse (“SFR”) information of the macrocell. From that information, the femtocell determines which frequency subchannels are assigned by the macrocell for its cell-center users and which frequency subchannels are assigned for cell-edge users. (Cell-edge users are given a higher transmission power profile in order to overcome potential interference with neighboring macrocells.) Then, the femtocell selects from the cell-center user frequency sub-channels for transmission to the femtocell's users. By transmitting on the cell-center user frequency sub-channels, the femtocell reduces interference with the overlapping macro cell. The femtocell continues to update its knowledge of the macrocell's SFR information and re-assigns frequency sub-channels as the SFR changes. If the macrocell detects that one of its cell-center users is “close enough” to the femtocell, then the macrocell re-assigns the cell-center user as a cell-edge user to overcome interference.