Cell Reselection in Enhanced Cell_FACH State
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Solution Overview
Problem
Current 3GPP Release 6 specifications do not support High Speed Downlink Packet Access (HSDPA) operation in the Cell_FACH state, leading to difficulties in retrieving HSDPA configuration information and timely MAC-hs reset during cell reselection, resulting in inefficient HSDPA communication and potential data loss.
Innovation Solution
A method and apparatus for cell update in the Cell_FACH state, where system information is read from the target cell to configure the MAC-hs entity based on HS-DSCH common system information, using a common H-RNTI or reserved H-RNTI for HSDPA transmission, and performing a MAC-hs reset after cell reselection to ensure seamless HSDPA communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If HSDPA operation is implemented in Cell_FACH state, then downlink throughput is improved, but device complexity increases due to MAC-hs entity configuration requirements
Solution Approach 1:
The patent applies preliminary action by pre-configuring HSDPA parameters and MAC-hs entity settings in the Cell_FACH state before actual HSDPA data transmission begins. This allows the device to have HSDPA capability ready and configured, enabling seamless transition to high-speed data transmission when needed, thus improving downlink throughput while managing complexity through advance preparation.
2Speed
If cell reselection is performed autonomously by WTRU, then mobility speed is improved, but reliability deteriorates due to lack of synchronized MAC-hs reset
Solution Approach 1:
The patent implements feedback mechanisms where the WTRU monitors cell reselection events and provides feedback triggers for MAC-hs entity reset. When autonomous cell reselection occurs, the WTRU detects the change and initiates appropriate MAC-hs reset procedures, ensuring that the high-speed downlink configuration is properly synchronized with the new serving cell, thus maintaining data transmission reliability during fast mobility.
Solution Approach 2:
The patent applies preliminary action by preparing MAC-hs reset procedures in advance of actual cell reselection completion. The WTRU pre-configures reset timing and parameters so that when cell reselection occurs autonomously, the MAC-hs entity can be reset synchronously with the new cell activation, preventing data loss and ensuring reliable HSDPA operation during mobility.
3Reliability
If dedicated H-RNTI is assigned by SRNC, then communication reliability is improved, but loss of time increases during cell reselection due to H-RNTI reassignment
Solution Approach 1:
The patent applies universality by enabling the common H-RNTI to serve multiple functions: it acts as both a general identifier for Cell_FACH state communications and as a functional H-RNTI for HSDPA operations. This eliminates the need for separate dedicated H-RNTI assignment during cell reselection, as the common H-RNTI can be reused immediately in the target cell, thus maintaining communication reliability while avoiding time loss associated with reassignment procedures.
Data Source
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AI summary
Performing cell reselection (update) when a source cell is in a Cell_FACH state and a target cell supports enhanced Cell_FACH. Problem: target cell supports Enhanced Cell_FACH (i.e. Cell_FACH state in which High-Speed Downlink Packet Access, HSDPA, is used, supported or available), but source cell supports non-enhanced Cell_FACH. Solution: selecting the target cell that supports Enhanced Cell_FACH; reading system information broadcast from the target cell, the system information including high speed downlink shared channel, HS-DSCH, common system information; clearing an HS-DSCH radio network temporary identity, H-RNTI, associated with a source cell; clearing a cell RNTI, C-RNTI, associated with the source cell; resetting an HS-DSCH medium access control, MAC-ehs, entity configured in the source cell; configuring a MAC-ehs entity based on the HS-DSCH common system information; and receiving high speed downlink packet access, HSDPA, transmission in the target cell.