Almost Blank Subframe Patterns for Interference Reduction
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Solution Overview
Problem
In heterogeneous wireless networks, time division approaches for minimizing interference lead to inaccurate radio resource management, RLM, and CSI measurements, causing erratic behaviors such as failed connections and unnecessary handovers due to interference from femto and pico cells.
Innovation Solution
Implementing almost blank subframes (AB subframes) where only critical information is transmitted, allowing UEs to perform measurements during specific subframes, and determining AB subframe patterns based on signal strength to minimize interference and ensure accurate measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If time division approaches are used to minimize interference between base stations, then interference between cells is reduced, but measurement accuracy deteriorates leading to inaccurate RRM, RLM, and CSI measurements
Solution Approach 1:
The time domain is segmented into different subframe types (normal subframes and almost blank subframes) with distinct functions. Normal subframes carry regular traffic while almost blank subframes are dedicated for measurements with minimal interference, allowing both interference reduction and accurate measurements to coexist through temporal segmentation.
Solution Approach 2:
Almost blank subframes are configured periodically with a specific pattern that repeats over time. This periodic structure allows UEs to know when to expect low-interference subframes for measurements, enabling accurate measurements while maintaining overall network throughput through regular traffic in other subframes.
2Duration of action of stationary object
If femto and pico cells transmit continuously to maintain service, then user service continuity is improved, but measurement accuracy for macro cells deteriorates due to persistent interference
Solution Approach 1:
Different subframes have different transmission qualities configured for different cells. During almost blank subframes, femto and pico cells reduce or eliminate transmissions in specific resource elements, creating local low-interference windows that allow accurate macro cell measurements while maintaining overall service continuity through normal subframes.
3Area of stationary object
If UEs perform measurements during all subframes, then measurement coverage is improved, but measurement accuracy deteriorates due to interference from ongoing transmissions
Solution Approach 1:
The network pre-configures UEs with knowledge of almost blank subframe patterns before measurements are performed. This preliminary configuration allows UEs to proactively schedule their measurements during the predetermined low-interference subframes, ensuring accurate measurements without needing to wait for or detect interference conditions in real-time.
Data Source
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AI summary
A mobile station in a wireless communication network is disclosed. The mobile station includes a transceiver coupled to a processor configured to rank a plurality of detected cells according to a signal level metric of the plurality of cells, to determine a first pattern of time periods during which a highest ranked cell is configured to transmit only a restricted set of information, and to perform measurements of cells other than the highest ranked cell, of the plurality of cells, only during the first pattern of time periods.