WTRU CSG Cell Search Gap Management
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Solution Overview
Problem
Current LTE systems lack a comprehensive solution for wireless transmit/receive units (WTRUs) to autonomously identify and report Closed Subscriber Group (CSG) cells, particularly in terms of criteria for tuning away from serving cells, measurement gap types, and network notification protocols, leading to inefficiencies in CSG cell detection and mobility management.
Innovation Solution
A method and apparatus for WTRUs to request and manage measurement/cell-search gaps, configure frequency and PCID information, and autonomously tune away to read Master Information Blocks (MIB) and System Information Blocks (SIB) of neighboring CSG cells, with mechanisms for handling handover requests and refusals in both active and idle modes, ensuring efficient CSG cell identification and reporting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If WTRU autonomously tunes away from serving cell to read MIB and SIB of CSG cells, then CSG cell detection capability is improved, but time required for cell identification increases
Solution Approach 1:
The WTRU is pre-configured with a white list containing PCIDs of CSG cells before autonomous operation. This preliminary configuration enables the WTRU to directly search for and identify target CSG cells without needing to read and process all neighboring cell information, significantly reducing the time required for CSG cell detection while maintaining autonomous detection capability
Solution Approach 2:
The invention extracts only the necessary identification information (PCID) from the complete cell information set and places it in a white list for prioritized searching. By focusing search efforts on pre-identified CSG cell PCIDs rather than all neighboring cells, the system achieves faster CSG cell detection without requiring full autonomous tuning away procedures for all cells
2Measurement precision
If WTRU requests measurement gap allocation from network, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The WTRU autonomously determines whether a measurement gap is needed by checking if its current DRX cycle is sufficient for reading MIB and SIB. Only when the DRX cycle is insufficient does the WTRU request a measurement gap from the network. This self-service approach reduces unnecessary signaling and simplifies measurement gap management while maintaining measurement precision when required
Solution Approach 2:
The measurement gap allocation is made dynamic based on the WTRU's actual needs. The system transitions between using DRX cycles for measurements and requesting dedicated measurement gaps from the network, depending on whether the current DRX configuration is sufficient. This dynamic adaptation reduces device complexity by avoiding permanent complex measurement gap management mechanisms
3Use of energy by moving object
If WTRU uses DRX gap for reading MIB and SIB, then energy consumption is reduced, but measurement precision deteriorates
Solution Approach 1:
The WTRU first attempts to perform CSG cell identification using only the DRX gap, which is a partial measurement approach that consumes less energy. The system accepts that this partial action may not always provide sufficient measurement precision, but it is the preferred first approach due to lower energy consumption. Only when this partial action proves insufficient does the system transition to requesting a full measurement gap
Data Source
AI summary
A method and apparatus for searching for closed subscriber group (CSG) cells are described. A wireless transmit/receive unit (WTRU) transmits, to a network of CSG cells, a measurement/cell-search gap request message including a cause value having at least one bit that indicates whether the request message was transmitted due to a manual cell search command or a WTRU autonomous determination. The WTRU receives a measurement/cell-search gap allocation message from the network in response to the measurement/cell-search request message. The WTRU also may determine whether it has a discontinuous reception (DRX) gap that is long enough to read a master information block (MIB) and a system information block (SIB) of a neighboring CSG cell. If the DRX gap is not long enough, the WTRU may transmit a measurement/cell-search gap request message to the network, or autonomously tune away from a cell currently serving the WTRU to read the MIB and SIB.