Cell Search Frequency Filtering in Wireless Networks
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Solution Overview
Problem
In UMTS wireless communications networks, mobile devices spend significant time searching for available cells across multiple frequencies, consuming processing power and battery resources, as they must scan all RF channels, which can take up to 2 minutes for a single band and longer for multiple bands.
Innovation Solution
The method involves using signal strength measurements to quickly determine a subset of frequencies to search for cells, storing RSSI measurements for each frequency, and skipping cell detection on frequencies with insufficient signal strength improvement, reducing the number of frequencies to search and thus the overall search time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE scans all RF channels in UTRA bands to find available PLMNs, then the PLMN selection is complete and reliable, but the search time becomes very long (over 2 minutes for band I alone)
Solution Approach 1:
The patent applies preliminary action by performing RSSI measurements on all frequencies before conducting full cell searches. This preliminary scanning identifies frequencies with sufficient signal strength, allowing the UE to skip cell searches on frequencies that are unlikely to contain usable cells, thereby reducing overall search time while maintaining reliable PLMN selection
Solution Approach 2:
The patent segments the PLMN search process into two distinct phases: a preliminary RSSI measurement phase and a selective cell search phase. This segmentation allows the system to quickly filter frequencies based on signal strength criteria before committing to time-consuming cell searches, effectively dividing the search space into promising and non-promising frequencies
2Reliability
If the UE performs cell search on every frequency, then no available PLMN is missed, but processing power and battery resources are significantly consumed
Solution Approach 1:
The patent performs preliminary RSSI measurements on all frequencies before executing cell searches. By evaluating signal strength in advance, the system identifies and skips frequencies that are unlikely to contain usable cells, thereby reducing processing requirements and battery consumption while maintaining complete PLMN detection for frequencies that meet the signal strength threshold
Solution Approach 2:
The patent applies partial action by performing cell searches only on a subset of frequencies that meet the RSSI threshold criteria, rather than exhaustively searching all frequencies. This partial search approach is sufficient for reliable PLMN detection while significantly reducing energy consumption and processing load
3Loss of time
If the UE reduces the number of frequencies to search, then the search time is reduced, but the accuracy of PLMN detection may be compromised
Solution Approach 1:
The patent changes the parameter used for frequency selection from a binary present/absent cell detection to a continuous RSSI measurement threshold. By adjusting the RSSI threshold parameter, the system can control the trade-off between search time and detection accuracy, ensuring that only frequencies with sufficient signal strength are subjected to full cell searches
Data Source
AI summary
A method of creating a candidate list of available cells for access by a wireless communications device, the method comprising, for each of a plurality of supported frequencies: measuring a received signal strength, and suppressing cell detection on a frequency if: a stored result of a determination of whether a cell was previously detected on the frequency is negative; and the measured received signal strength for the frequency is below a threshold criterion.