Resolving Colliding HNB Signals via Upper Layer ID Verification
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Solution Overview
Problem
In the context of 3GPP LTE, the identification of Home Evolved Node-B (HNB) cells is challenging due to potential collisions of physical layer synchronization signals, especially in environments with numerous HNBs from different operators, which complicates cell selection and reselection procedures for wireless transmit/receive units (WTRUs).
Innovation Solution
A method and apparatus for selecting or reselecting an HNB among colliding physical layer signals involve configuring a WTRU with a white-list of HNB IDs, allowing it to detect and synchronize with broadcast channels, and using upper layers to resolve collisions by checking upper layer IDs and performing measurements to determine the most suitable cell for camping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If HNBs are identified at the physical layer by means of a reserved physical layer synchronization signal, then the identification speed is improved, but the reliability deteriorates due to signal collisions between multiple HNBs
Solution Approach 1:
The identification process is segmented into two stages: physical layer synchronization signal detection for initial cell discovery, followed by upper layer broadcast channel detection for definitive HNB identification. This segmentation allows the system to maintain fast initial detection while ensuring reliable final identification through hierarchical verification
Solution Approach 2:
The upper layer broadcast channel acts as an intermediary that resolves conflicts between colliding physical layer signals. When multiple HNBs transmit identical or colliding synchronization signals, the broadcast channel provides additional identification information that enables the WTRU to distinguish between them and select the appropriate HNB
2Measurement precision
If the WTRU reads the RRC layer broadcast channel to acquire HNB ID, then the identification accuracy is improved, but the performance requirement deteriorates due to the large number of HNBs in vicinity
Solution Approach 1:
The system performs preliminary cell search and synchronization at the physical layer before the WTRU enters connected mode. The HNB ID is acquired from broadcast channels during idle mode cell selection, not during connected mode measurements, thereby avoiding performance degradation while maintaining identification accuracy
Solution Approach 2:
The WTRU performs partial reading of broadcast channel information only for cells that pass initial physical layer synchronization and signal quality thresholds. This partial action approach reduces the overall processing burden compared to reading all broadcast channels, while still ensuring accurate HNB identification for suitable cells
3Reliability
If cell planning techniques are used to prevent signal collision, then the reliability is improved, but the adaptability deteriorates in environments with hundreds of HNBs from multiple operators
Solution Approach 1:
Instead of relying on manual cell planning to prevent collisions, the system enables WTRUs to autonomously resolve signal collisions through self-service mechanisms. The WTRU independently detects colliding signals, acquires HNB IDs from broadcast channels, and performs measurements to select the most suitable HNB, thereby maintaining reliability without constraining deployment flexibility
Solution Approach 2:
The system changes the identification parameters from relying solely on physical layer synchronization signals to incorporating upper layer broadcast channel information. This parameter change allows the system to maintain reliability in high-density deployments by using additional identification dimensions while preserving full deployment flexibility
Data Source
AI summary
A method and apparatus for selecting or reselecting a home Node-B (HNB), (i.e., a closed subscriber group (CSG) cell), among cells having colliding physical layer signals are disclosed. Once the identity (ID) of an HNB is determined, measurements needed to support cell selection or reselection are performed. A broadcast channel that broadcasts an HNB ID is detected and synchronized to, and information obtained from the broadcast channel is forwarded to a non-access stratum (NAS). The broadcasted HNB ID is checked against an HNB white-list provided by the NAS to determine whether the HNB is suitable for a wireless transmit/receive unit (WTRU). The WTRU selects the HNB to camp on, or changes from a cell currently serving the WTRU to the HNB if it is determined to be more suitable than the current serving cell.