Active Set Configuration for Inter-Symbol Interference Mitigation
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Solution Overview
Problem
Existing methods for configuring and managing active sets in OFDM-based networks face challenges with Inter-Symbol Interference (ISI) due to cells with delayed signal arrival times, leading to degradation in Signal-to-Interference and Noise Ratio (SINR) and increased overhead in cyclic prefix extension, which affects user mobility and system capacity.
Innovation Solution
Implementing new schemes for active set configuration and management that assess and mitigate ISI by selectively adding or removing cells from the active set based on their power delay profiles and delay offsets, using triggers to suppress or inhibit transmissions from cells causing significant ISI, and adjusting the FFT window positioning to minimize interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If cells with delayed signal arrival times are added to the active set to improve coverage and mobility, then the active set size and coverage area increase, but Inter-Symbol Interference (ISI) increases leading to SINR degradation
Solution Approach 1:
The network node performs preliminary assessment of the power delay profile and delay offset of candidate cells before adding them to the active set. This preliminary action identifies cells that would cause excessive ISI due to delayed signal arrival, preventing their addition to the active set and thus avoiding SINR degradation while maintaining coverage through alternative cells
Solution Approach 2:
The patent converts the potentially harmful effect of delayed signal arrivals into a useful selection criterion. By measuring and evaluating the power delay profile and delay offset, the system identifies which cells' delayed signals would be harmful (excessive ISI) and excludes them, while allowing cells with acceptable delay characteristics to contribute to coverage extension
2Object-affected harmful factors
If cyclic prefix is extended to accommodate delayed signals from cells in the active set, then ISI is reduced and signal quality improves, but overhead increases affecting system capacity
Solution Approach 1:
Instead of uniformly extending the cyclic prefix for all cells, the patent applies selective quality control by evaluating each candidate cell's power delay profile and delay offset locally. Cells are individually assessed to determine whether their delayed signals would cause excessive ISI, and only cells meeting the delay criterion are added to the active set, avoiding the need for universal CP extension
Solution Approach 2:
The patent changes the selection parameter for active set configuration from purely signal strength-based to include delay-based criteria (power delay profile and delay offset). This parameter change enables the system to select cells that provide coverage extension without introducing excessive delay, thereby avoiding ISI problems and the need for increased cyclic prefix overhead
3Reliability
If the active set is configured to include multiple serving cells for multi-connectivity, then user mobility and robustness improve, but the complexity of active set management and configuration increases
Solution Approach 1:
The network node uses feedback from uplink signals received at candidate cells to assess the power delay profile and delay offset. This feedback mechanism enables automated evaluation of candidate cells' suitability for active set inclusion, reducing the complexity of manual configuration and management while maintaining reliable multi-connectivity
Solution Approach 2:
The system performs self-assessment of candidate cells by measuring the uplink signal characteristics (power delay profile) at each candidate cell. This self-service capability allows the network to autonomously identify suitable cells for the active set based on their inherent delay characteristics, simplifying the management process while ensuring reliable mobility support
Data Source
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AI summary
There is provided a method comprising: determining an information on an inter-symbol interference between signals on a same frequency resource and a same time resource from one or more first cells and one or more second cells, wherein an active set of the apparatus comprises at least the one or more second cells, the inter-symbol interference is an estimated inter-symbol interference if at least one of the one or more first cells is not in the active set, and the inter-symbol interference is a measured inter-symbol interference if the active set consists of the one or more first cells and the one or more second cells; and deciding whether or not to inform a network comprising the one or more first cells and the one or more second cells on the information on the inter-symbol interference.