Cell Reselection Reporting in CELL_FACH State
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Solution Overview
Problem
In wireless communication networks, particularly in the CELL_FACH state, user equipment (UE) faces challenges with cell reselection during data transmission, leading to data loss and increased interference, as it is forbidden to perform cell reselection while having a common E-DCH resource, resulting in potential loss of coverage and higher drop call probabilities.
Innovation Solution
The network configures UE to report cell reselection criteria via System Information Broadcast (SIB), allowing UE to inform the network of satisfied reselection criteria, even with a common E-DCH resource, and suspending uplink transmissions until cell reselection is complete, thereby preventing data loss and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If UE is forbidden to perform cell reselection while having a common E-DCH resource, then data transmission reliability is improved, but mobility adaptability deteriorates
Solution Approach 1:
The network sends a configuration message in advance to prohibit the UE from performing cell reselection when having a common E-DCH resource. This preliminary prohibition prevents the UE from moving to a new cell during data transmission, ensuring reliability while the network maintains control over when reselection is permitted.
2Ease of operation
If UE performs cell reselection without informing the network, then mobility freedom is improved, but data loss increases
Solution Approach 1:
The UE is configured to send a measurement report to the network when cell reselection criteria are satisfied. This feedback mechanism allows the network to be aware of the UE's reselection intent and take appropriate actions (such as suspending downlink data transmission) to prevent data loss while still allowing the UE to perform cell reselection.
3Reliability
If UE continues monitoring source cell after reselection, then data reception reliability is improved, but energy consumption increases
Solution Approach 1:
The network sends a configuration message in advance to prohibit the UE from performing cell reselection when having a common E-DCH resource. This preliminary prohibition prevents the UE from moving to a new cell during data transmission, ensuring reliability while the network maintains control over when reselection is permitted.
Data Source
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AI summary
If a UE determines that a cell reselection should be performed, it does so without informing the network ahead of time. The network is only aware of the change after having received a cell update transmitted by the UE in a new (target) cell. In the meantime, the original (source) Node-B may continue transmitting the data it has remaining in the buffer for that UE. This data will be lost since the UE is no longer monitoring that cell. Enhanced Uplink in CELL FACH state was introduced in Release 8. When a UE has a common E-DCH resource, the UE can perform measurements which may be later used to perform cell re-selection; however, the UE is not allowed to perform cell re-selection while the UE has a common E-DCH resource. Only when the UE has released the common E- DCH resource can the UE perform a cell re-selection. Thus, if the UE has a common E- DCH resource and moves from one cell to another, the UE cannot perform cell reselection to the new cell. Accordingly, the UE may lose coverage and the RRC connection. These problems are solved by the present application, in that the SIB includes information instructing the UE (10) to report to the network (11) whenever cell reselection criteria are satisfied (102). The UE 10 periodically or continuously monitors neighboring cells (16) for possible cell reselection (104), comparing measurements against the cell reselection criteria received in the SIB. If the cell reselection criteria are satisfied (106), the UE (10) transmits to the network (11) an indication that cell reselection criteria are satisfied (108). In this manner, the network (11) is alerted to a pending cell reselection event, and take appropriate action to avoid the loss of data stockpiled at the Node-B (14) of the cell (12) to which the UE (10) is currently connected.