Implicit Satellite Handover via Ephemeris Data
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Solution Overview
Problem
In wireless communications via non-geostationary satellites, maintaining continuous connectivity is challenging due to satellite movement, as existing systems require significant control signaling overhead to agree on the serving satellite, and the gateway lacks real-time knowledge of user equipment channel conditions.
Innovation Solution
User equipment and gateways independently identify and select a default satellite based on ephemeris data and elevation angles for implicit handover, with the option to initiate explicit handover using performance metric data and a lock bit to minimize signaling overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional explicit handover signaling is used to agree on serving satellite, then handover reliability is improved, but control signaling overhead increases
Solution Approach 1:
The UE device independently selects the serving satellite based on ephemeris data and elevation angle calculations, and the gateway independently determines the serving satellite using the same criteria. This self-service mechanism eliminates the need for extensive back-and-forth signaling to agree on satellite selection, thereby reducing control signaling overhead while maintaining handover reliability.
Solution Approach 2:
Both the UE device and gateway pre-calculate elevation angles and identify potential serving satellites before handover is needed. By having this information prepared in advance using ephemeris data and independent calculations, the system avoids time-consuming signaling exchanges during actual handover events.
2Quantity of substance
If implicit handover with independent satellite selection is used, then control signaling overhead is reduced, but handover reliability may deteriorate due to gateway lacking channel condition knowledge
Solution Approach 1:
The UE device provides feedback to the gateway by transmitting an explicit handover message when channel conditions are insufficient. This feedback mechanism allows the gateway to learn about actual channel conditions from the UE's perspective and make informed decisions about serving satellite selection, thereby maintaining reliability while using minimal signaling.
Solution Approach 2:
Instead of continuous explicit signaling, the system uses implicit handover for normal conditions and only activates explicit handover messaging when channel conditions deteriorate. This partial action approach maintains reliability during critical moments while minimizing overall signaling overhead during normal operation.
3Measurement precision
If explicit handover message with lock bit is transmitted, then handover control precision is improved, but use of energy increases
Solution Approach 1:
The system uses periodic implicit handover updates based on ephemeris data and elevation angle changes, and only activates energy-intensive explicit handover messages when channel conditions warrant it. This periodic action with conditional escalation provides precise control when needed while conserving energy during normal periodic updates.
Solution Approach 2:
The lock bit parameter in the explicit handover message provides precise control over handover behavior with minimal additional signaling. By changing this single binary parameter, the system achieves fine-grained control precision without proportionally increasing energy consumption, as the entire handover control mechanism remains efficient.
Data Source
AI summary
A communications system may include user equipment (UE) device, satellites, and a gateway. The UE and gateway may perform implicit handover in which the UE and gateway independently identify the same serving satellite using ephemeris data, without additional signaling overhead. The UE may also characterize its channel conditions. When insufficient, the UE may transmit an explicit handover message to the gateway via a different satellite visible to the UE. The explicit handover message may include a satellite identifier and a lock bit. The gateway may use the satellite identifier to convey wireless data with the UE via the different satellite during the next cycle. The gateway may use the lock bit to know how to perform handover away from the different cycle during subsequent cycles. In this way, the UE may direct handover, given that the gateway has no knowledge of the channel condition at the UE.