Emulated Cell Border for High Speed Train Handovers
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Solution Overview
Problem
High-speed trains experience abrupt Doppler shifts when handovering between cells, leading to radio link failures due to the UE's inability to correctly determine frequency offsets, which reduces system capacity and causes interruptions in cellular communication.
Innovation Solution
The solution involves configuring antenna nodes to form downlink beams in the same direction along the track, with controlled transmitter power levels to emulate a cell border, allowing UEs to smoothly transition between cells without experiencing abrupt Doppler shifts, thereby ensuring successful handovers and reducing radio link failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transmitting antennas are placed close to the track to provide coverage, then coverage quality is improved, but Doppler shift increases due to small angle between trajectory and antenna line
Solution Approach 1:
The system segments the cell coverage into multiple directional beams (first direction and second direction) transmitted from different antenna nodes. This segmentation allows the UE to receive signals from multiple directions simultaneously, reducing the impact of Doppler shift from any single antenna direction while maintaining coverage quality.
Solution Approach 2:
The system applies different transmit power levels to different antenna nodes based on their local characteristics and position relative to the UE. By controlling the power of individual antenna nodes, the system optimizes the signal quality in each local direction while managing the overall Doppler shift impact across the cell boundary.
2Stability of the object's composition
If unidirectional beam arrangement is used to reduce Doppler shift variability, then Doppler shift stability is improved, but abrupt Doppler shift occurs at cell boundaries during handover
Solution Approach 1:
The cell structure is segmented into multiple directional beams from different antenna nodes. During handover, the UE transitions from receiving signals primarily from one directional beam to another, with both beams active in the overlap region. This segmentation allows gradual transition and maintains Doppler shift stability while enabling reliable handover.
Solution Approach 2:
The system merges the coverage of multiple antenna nodes transmitting in different directions to create an extended overlap region. By combining the signals from first and second direction beams with controlled power levels, the system creates a seamless transition zone that maintains both Doppler stability and handover reliability.
3Reliability
If cell overlap region is extended to enable smooth handover, then handover reliability is improved, but downlink signal power distribution becomes unbalanced
Solution Approach 1:
The system applies different transmit power levels to different antenna nodes within the overlap region based on their specific local conditions and distance to the UE. This localized power control balances the downlink signal power distribution across the extended overlap region while maintaining handover reliability.
Solution Approach 2:
The system dynamically adjusts the transmit power parameter of antenna nodes based on the UE's position and the required handover conditions. By changing the power parameter locally in different regions of the cell, the system achieves both extended overlap for reliable handover and balanced power distribution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration stabilizes the Doppler shift experienced by UEs and network nodes, reduces inter-carrier interference, and enhances the carrier-to-noise ratio, allowing for higher modulation orders and improved system throughput.
Implementation Method 1
causing the one or more first antenna nodes to each form downlink beams in a same direction along the track as one another
Implementation Method 2
Transmitter power levels of each of the one or more first antenna nodes are controlled such that: downlink signal power distributed through the emulated cell border
Implementation Method 3
the received signal may display a significant Doppler shift. The Doppler shift forces the UE to increase its demodulation frequency when moving towards the cell, and decrease it when moving away from the cell
Data Source
Figure 1(a)~1(e)
Figure 2
Figure 3~4
AI summary
A first network node has first antenna nodes located along a track and associated with a first cell. Some of them serve a first cell overlap region that overlaps a second cell overlap region of second antenna nodes connected to a second network node. Some first antenna nodes form downlink beams in a same direction with power levels controlled such that respective amounts of overlap between the downlink beams and respective power levels of the downlink beams jointly cause the first cell's overlap region to emulate a cell border for a user equipment travelling at high speed. Emulated cell border signal power is lower at locations closer to an emulated cell outer edge than at more distant locations. Emulated cell border length is sufficient to cause the travelling user equipment to be within the emulated cell border long enough to successfully perform a handover between the first and second cells.