Ground Network Receiver

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Description

The Ground Network Receiver is a communication component that aggregates multiple Ground Stations into a single logical receiver endpoint. It extends the base Receiver class and provides unified access calculations across a distributed network of ground stations, eliminating the need to configure individual receivers at each station. The receiver automatically selects the closest ground station with visibility to the transmitting spacecraft, enabling seamless handover between stations as spacecraft move through their orbits.

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Example Use Cases

• Deep Space Network: Model a coordinated network of globally distributed ground stations for continuous spacecraft coverage.
• LEO Constellation Support: Aggregate multiple regional ground stations to maximize contact time with low Earth orbit satellites.
• Mission Operations: Simplify telemetry reception by treating an entire ground network as a single communication endpoint.
• Coverage Analysis: Evaluate network-wide visibility and handover performance without configuring individual station links.
• Ground Station Redundancy: Automatically route communications through the nearest available station.

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Module Implementation

The ground network receiver attaches to a Ground Station and maintains a list of associated stations. Unlike standard receivers where each ground station requires its own antenna, this component provides a single receiver that spans multiple geographic locations.

Station Registration

When the receiver is attached to a ground station, that station is automatically added to the network:

$$\text{Stations}\leftarrow \text{Stations}\cup \{\text{Parent}\}$$

Additional stations can be registered dynamically using AddGroundStation(). The receiver prevents duplicate registrations:

$$\text{AddGroundStation}(S):S\notin \text{Stations}\Rightarrow \text{Stations}\leftarrow \text{Stations}\cup \{S\}$$

Stations can also be removed from the network:

$$\text{RemoveGroundStation}(S):S\in \text{Stations}\Rightarrow \text{Stations}\leftarrow \text{Stations}\setminus \{S\}$$

Link Registration

When the Telemetry System creates links to the ground network receiver, the receiver disables standard celestial access calculations:

$$\text{IsAccessCalculated}=\text{false}$$

This flag indicates that the receiver will compute access internally using ground station tracking data rather than relying on the telemetry system’s line-of-sight calculations.

Closest Station Selection

For each link, the receiver determines which ground station is closest to the transmitting spacecraft:

$$S^{\ast }=\underset{S\in \text{Stations}}{\mathrm{argmin}}\Vert {\mathbf{r}}_S-{\mathbf{r}}_{\text{tx}}{\Vert }^2$$

where ${\mathbf{r}}_S$ is the position of station $S$ and ${\mathbf{r}}_{\text{tx}}$ is the position of the transmitter in the local inertial frame.

The squared distance is used for computational efficiency:

$$d^2=\Vert {\mathbf{r}}_S-{\mathbf{r}}_{\text{tx}}{\Vert }^2=({\mathbf{r}}_S-{\mathbf{r}}_{\text{tx}})\cdot ({\mathbf{r}}_S-{\mathbf{r}}_{\text{tx}})$$

Access Override Calculation

The receiver overrides the standard access calculation by querying each link’s closest ground station for visibility:

$$\text{IsAccessOverride}=\text{TrackObject}(\text{Root}).\text{IsAccessible}$$

where TrackObject invokes the ground station’s access tracking system, which accounts for:

• Minimum elevation angle constraints
• Maximum range limitations
• Planetary body occlusion

The receiver index is also updated to identify which station is handling the link:

$$\text{ReceiverIndex}=\text{IndexOf}(S^{\ast },\text{Stations})$$

This index enables the Telemetry System to correctly attribute interference calculations to links sharing the same physical station.

Antenna Position for Link Budget

When computing link budget parameters such as distance and pointing losses, the receiver reports the position of the closest ground station rather than its own position:

$${\mathbf{r}}_{\text{antenna}}=\{\begin{array}{ll}{\mathbf{r}}_{S^{\ast }}& \text{if }{S}^{\ast }\ne \text{null}\\ {\mathbf{r}}_{\text{self}}& \text{otherwise}\end{array}$$

This ensures that link distance calculations reflect the actual geometric relationship between the spacecraft and the receiving station.

Ground Station Link Bypass

Unlike standard Receiver components attached to ground stations, the ground network receiver does not create a Ground Station Link model on its parent station. This prevents duplicate access tracking since the receiver manages access calculations internally across all registered stations.

Update Sequence

Each simulation step, the receiver performs the following operations:

Step	Operation
1	Loop through all connected links
2	Determine closest station to each transmitter
3	Query station access for transmitter’s root object
4	Set access override flag based on station visibility
5	Update receiver index for interference tracking

This process occurs before the Telemetry System performs link budget calculations, ensuring that access states are current when computing signal and noise power.

Integration with Telemetry System

The ground network receiver integrates with the Telemetry System through the standard Receiver interface. Links are created automatically when compatible Transmitters exist on other root objects. The key difference is that access calculations bypass the telemetry system’s celestial occlusion checks in favour of the ground station tracking system.

The receiver inherits all standard receiver functionality including:

• Packet reception and buffering
• Propagation delay modelling
• Bit error application
• Bandwidth-limited processing
• Data reassembly and decoding

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Assumptions/Limitations

• The receiver assumes all registered ground stations are compatible with incoming transmissions; frequency and bandwidth matching is handled by the standard link budget calculations.
• Station selection is based purely on geometric distance; signal quality or station loading are not considered.
• Handover between stations is instantaneous; no handover delay or data loss is modelled during transitions.
• The receiver does not model antenna slew time at individual ground stations.
• All registered stations are assumed to be operational; station outages or maintenance windows are not tracked.
• The receiver index used for interference calculations assumes one active link per station; multiple spacecraft visible to the same station may have incorrect interference attribution.
• Ground station access constraints (elevation, range) are inherited from each station’s configuration; the receiver does not impose additional constraints.
• The parent ground station’s position is only used if no stations are registered; otherwise, it serves as the default entry in the station list.
• Station removal during active communication may cause temporary link disruption until the next access calculation cycle.