Mobile Relay Node Fixed Cell ID Tracking Area Update
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Solution Overview
Problem
In LTE Advanced systems, mobile relay nodes experience signaling failures and connection losses when moving between tracking areas, leading to a surge of signaling messages over the air interface, which can result in connection loss for user equipment in active mode.
Innovation Solution
Assigning a mobile relay node a fixed cell ID and tracking area, which it broadcasts to user equipment, allowing the Mobility Management Entity to track the node's movement and associated user equipment without requiring them to signal new location areas, thereby reducing air interface traffic and conserving battery power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mobile relay nodes broadcast new tracking area identifiers when moving to new Donor eNBs, then location accuracy is improved, but signaling load increases causing connection losses
Solution Approach 1:
The solution segments the tracking area update process by introducing a dedicated mobility management entity (MME) that handles tracking area updates for relay nodes separately from user equipment. This segmentation prevents relay node mobility signaling from interfering with UE connection stability, resolving the contradiction between location accuracy and connection reliability.
Solution Approach 2:
The MME acts as an intermediary between the relay node and the core network, absorbing the tracking area update signaling for relay nodes. This intermediary prevents the surge of signaling messages from reaching the air interface between Donor eNB and relay nodes, thereby maintaining connection stability while still enabling location tracking.
2Loss of information
If all user equipment update tracking areas simultaneously when relay node moves, then location registration is improved, but air interface signaling capacity is overwhelmed
Solution Approach 1:
The solution segments the signaling load by creating a separate signaling path through the MME for relay node tracking area updates. This segmentation prevents simultaneous updates from relay nodes and their user equipment from overwhelming the air interface, while still ensuring complete location registration for all devices.
Solution Approach 2:
The MME serves as an intermediary that collects and processes tracking area update information from relay nodes centrally. This intermediary approach allows location registration for all user equipment to be maintained without requiring simultaneous air interface signaling, thereby preserving signaling throughput capacity.
3Speed
If relay nodes change tracking area frequently with mobile movement, then mobility tracking is improved, but battery power consumption increases
Solution Approach 1:
The MME acts as an intermediary that handles tracking area updates for relay nodes through backhaul signaling rather than air interface signaling. This reduces the power consumption of mobile relay nodes by eliminating the need for frequent wireless transmissions during mobility events, while still maintaining fast mobility tracking through the wired/backhaul connection to the MME.
Data Source
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AI summary
A mobile communications system is described in which the network configures a mobile relay node that is mounted in a moving vehicle (such as a train) with expected tracking area information for the route along which the vehicle is expected to travel. UEs associated with the mobile relay node are provided with the list and do not perform tracking area updates if the movement of the vehicle corresponds to the stored list. Where advance knowledge of the route is not available, the mobile relay node is configured with a fixed tracking area and a fixed radio cell so that associated UEs do not detect a change in the tracking area or in the radio cell and so do not perform tracking area updates towards the network or the network does not need to control the UEs mobility while having a radio connection with the network.