Saltar al contenido principal

Bilateral and Multilateral Spectrum Coordination

In the satellite industry, spectrum management is where policy meets engineering. Before a satellite operator can record their frequency assignments in the Master International Frequency Register (MIFR) and claim international protection, they must successfully coordinate their frequencies with other operators whose filings overlap. This chapter details the technical and regulatory mechanics of bilateral and multilateral spectrum coordination.

The Article 9 Coordination Framework​

Under the ITU Radio Regulations, the process of resolving potential interference is governed by Article 9. While the Advance Publication Information (API) phase publishes a network's general parameters, the Coordination Request (CR/C) phase publishes the precise technical characteristics of the system, initiating the formal coordination process.

The ITU defines different coordination paths depending on the orbital configurations and service classes involved:

  • Section I (No. 9.7): Mandates coordination between Geostationary (GSO) networks operating in the same frequency bands.
  • Section II (No. 9.11A / 9.12 / 9.13): Mandates coordination involving Non-Geostationary (NGSO) systems. This includes NGSO-to-NGSO systems and NGSO-to-GSO networks in specific bands.

Coordination is typically conducted bilaterally (between two national administrations representing their respective operators) or multilaterally (involving several administrations at once, which is common in congested bands like Ka-band).

Coexistence Criteria: Triggering Coordination​

How do regulators and operators know when coordination is legally required? The ITU uses specific engineering calculations to establish trigger thresholds.

1. The Delta T over T (ΔT/T) Metric​

Defined in Appendix 8 of the Radio Regulations, ΔT/T measures the percentage increase in the equivalent noise temperature of a "victim" satellite receiver caused by the transmissions of a "new" satellite network.

  • The Threshold: If the calculated ΔT/T exceeds 6%, the new network is legally deemed to have a potential for interference, and coordination is mandatory.
  • Limitations: ΔT/T is a simple, conservative metric. It does not account for actual traffic patterns or detailed antenna patterns. It acts merely as a gatekeeper to determine if closer study is needed.

2. The Interference-to-Noise Ratio (I/N)​

Once coordination is triggered, operators move to more detailed analyses using the Interference-to-Noise (I/N) ratio. This compares the power of the interfering signal (I) at the receiver to the thermal noise level of the receiver (N).

  • Standard Thresholds: Operators negotiate target I/N levels. A common long-term target is -6 dB or -10 dB. An I/N of -6 dB means the interfering signal is 6 decibels below the receiver's thermal noise floor, which increases the receiver's total equivalent noise by approximately 1 dB.

:::tip The Library Analogy Imagine a quiet reading room in a library (the receiver's thermal noise floor). If one person whispers at a very low level (e.g., I/N = -10 dB), it does not disrupt your reading. However, if multiple people start whispering at the same time, the cumulative background noise rises, eventually making it impossible to concentrate. Satellites must coordinate to ensure their individual "whispers" do not collectively raise the background noise above acceptable limits. :::

3. The Interference Budget (ITU-R S.1432)​

To prevent the cumulative "library noise" from destroying communications, ITU-R Recommendation S.1432 allocates a satellite network's allowable error performance degradation (interference budget) to different sources:

  • 20% of the noise budget is allocated to continuous interference from other co-frequency GSO networks.
  • 6% is allocated to transient interference from NGSO constellations.
  • 74% is reserved for the network's own internal noise and thermal noise floor.

GSO vs. NGSO Sharing & Article 22​

The relationship between Geostationary (GSO) and Non-Geostationary (NGSO) systems is one of the most contentious areas of spectrum engineering.

Because GSO satellites remain in fixed positions relative to Earth, their ground antennas point at a single spot in the sky. If an NGSO satellite passes directly through that line of sight, it will cause massive main-beam interference.

The Article 22 Priority Mandate​

To protect the massive historical investments in GSO systems, Article 22 of the ITU Radio Regulations establishes a strict priority rule: :::important Article 22 (No. 22.2) Non-geostationary-satellite systems must not cause unacceptable interference to, and cannot claim protection from, geostationary-satellite networks in the fixed-satellite service (FSS) and broadcasting-satellite service (BSS). :::

Equivalent Power Flux-Density (EPFD)​

To make No. 22.2 enforceable, engineers developed the concept of Equivalent Power Flux-Density (EPFD). EPFD mathematical algorithms calculate the aggregate power flux-density produced at any point on the Earth's surface by all active satellites in an NGSO constellation:

  • epfd↓ (Downlink): Protects GSO earth stations from NGSO satellite downlinks.
  • epfd↑ (Uplink): Protects GSO satellite receivers from NGSO earth station uplinks.
  • epfd_is (Inter-satellite): Protects GSO satellite receivers from NGSO cross-links.

If an NGSO constellation's filing complies with the strict EPFD limits defined in Article 22, it is legally assumed to have satisfied its obligation not to cause unacceptable interference to GSO networks.

Technical Mitigation Techniques​

When coordination analyses reveal that interference thresholds will be exceeded, engineering teams must agree on technical mitigation techniques to allow coexistence:

  1. Spatial and Angular Separation:
    • In-line Event Avoidance: NGSO systems temporarily switch off beams or shift frequencies when an active satellite passes within a specific angular threshold (e.g., 1.5° to 3°) of a GSO earth station's line of sight to its GSO satellite.
  2. Frequency and Polarization Isolation:
    • Guard Bands: Shifting frequency allocations slightly to leave a sliver of unused spectrum between adjacent channels.
    • Cross-Polarization: Operating on opposite polarizations—such as Left-Hand Circular Polarization (LHCP) vs. Right-Hand Circular Polarization (RHCP), or Horizontal (H) vs. Vertical (V) linear polarization. This provides up to 20 to 30 dB of isolation.
  3. Geographical Gateway Isolation:
    • Placing large gateway earth stations in remote, rural areas to isolate them from terrestrial mobile networks (like 5G) operating in shared bands (e.g., C-band).

Next Steps​

Further Reading​