The Interference Puzzle: Managing Coverage and Coexistence at 60,000 Feet

Part 4 of a 20-Part Bridge Series on HAPS Usage and Deployment in the United States.

1. Why Interference Is the Gating Issue for HAPS

For HAPS to move from trials to commercial reality, interference and coexistence must be addressed. The platform itself can be designed, launched and operated, but if it cannot share spectrum safely with existing services, its role will remain limited.

Interference is the gating issue because:

• HAPS sits high enough to “see” an enormous footprint.

• Its downlink and uplink signals can overlap with many terrestrial cells and microwave links.

• It must coexist with satellite systems using similar or adjacent bands.

• Regulators are rightly cautious about any new service that changes the interference environment over large regions.

2. Coverage Geometry at Altitude

From 20 km altitude, the radio horizon is vastly larger than from a terrestrial tower. That has two sides:

• Positive: A single HAPS footprint can cover a region the size of a small state.

• Negative: Any interference error is also wide-area by nature.

Key geometric considerations include:

• The elevation angles seen by user devices and terrestrial nodes.

• The footprint size as a function of frequency and power.

• The shapes and overlaps of cells projected onto the ground if the HAPS payload uses beamforming.

Even without specific numeric models, the principle is clear: altitude amplifies error. Good design demands conservative assumptions and robust protections.

3. Coexistence with Terrestrial Networks

HAPS will most likely share or neighbour bands already in use by macro and fixed wireless networks. Coexistence strategies include:

3.1 Geographic separation

Restricting HAPS operations to:

• Specific regions where terrestrial use is sparse

• Offshore or remote areas

• Well-defined corridors (e.g. logistics or maritime lanes)

3.2 Spectral separation

Using:

• Guard bands

• Dedicated sub-bands

• Dynamic frequency selection to avoid occupied channels

3.3 Power and pattern control

Managing:

• Maximum EIRP towards the ground

• Beam shapes, tilts and sidelobe levels

• Adaptive power control tied to interference measurements

The objective is to avoid raising the interference floor for terrestrial systems beyond acceptable limits.

4. Coexistence with Satellite Systems

HAPS will also need to coexist with GEO and LEO satellites using similar spectrum:

• Uplinks from users to HAPS must not create excessive interference into satellite receivers.

• HAPS downlinks must avoid harmful overlap with satellite downlink footprints.

• Earth stations and gateways require particular care, as they operate at higher power levels.

Principles include:

• Coordination within international frameworks (ITU allocations and regional agreements).

• Directional antenna design on both HAPS and ground terminals.

• Careful siting and pattern shaping for gateways.

Again, high-level policy and technical guidelines can be defined without exposing any proprietary customer work.

“At 60,000 feet, good spectrum planning is not an engineering nice-to-have; it is the difference between a strategic asset and a regulatory dead end.”

5. The Trade-Offs: Coverage vs Capacity vs Interference

HAPS designers and operators must constantly juggle three competing dimensions:

1. Coverage – the size of the footprint and depth of indoor/outdoor service.

2. Capacity – total throughput per platform and per user.

3. Interference – the impact on other systems and on the HAPS service itself.

Pushing hard on coverage (large cells at high power) increases interference risk and can reduce effective capacity. Conversely, using more, smaller beams with lower power improves control but complicates payload design and spectrum management.

Strategic choices must reflect the use-case priority:

• Frontier and underserved coverage → coverage first, modest capacity, conservative power.

• Industrial or public safety hotspots → higher capacity in smaller areas, stricter beam control.

6. Spectrum Planning Principles for Boards and Regulators

Without revealing any specific modelling, there are clear principles that stakeholders should insist on:

• Technology neutrality, spectrum discipline – allow multiple technologies, but require rigorous planning and interference testing.

• Layered protection – use geographic, spectral and power controls together, not in isolation.

• Progressive licensing – start with conservative parameters and expand as experience and data accumulate.

• Transparent monitoring – mandate measurement and reporting of interference events and performance.

The goal is to enable innovation while protecting incumbents, not to freeze the spectrum landscape.

7. Operational Safeguards and Monitoring

HAPS platforms can be built with:

• Real-time spectrum sensing and interference detection

• Remote configuration of channels, beams and power levels

• Integration with terrestrial network management systems

• Automation and AI-assisted optimisation (within predefined guardrails)

These features allow operators to react to emerging interference patterns rather than relying solely on static design assumptions.

8. Board-Level “So What?” for Operators and Policy Makers

For boards, investment committees and regulators, the questions are:

• What interference protections must be non-negotiable?

• Which bands and geographies are realistic candidates for early HAPS use?

• How can we use pilot deployments to build a shared evidence base without exposing customers or incumbents to undue risk?

• How do we ensure that HAPS becomes an asset to the ecosystem, not a source of endless coordination disputes?

Handled correctly, the interference puzzle becomes manageable. Handled badly, it can stall HAPS for a decade.

9. Conclusion – Getting Coexistence Right the First Time

HAPS will only scale if regulators, operators and technology providers take interference seriously from day one. That means conservative initial assumptions, strong safeguards and transparent performance monitoring.

The reward is significant: a new coverage and resilience layer for the US, integrated safely into the existing spectrum landscape.

If your organisation is exploring how high-altitude platforms, non-terrestrial networks or frontier communications could support your strategy, Bridge Connect US can help.

Our advisors work with executives, boards and public-sector leaders across telecoms, digital infrastructure and emerging technologies to clarify the opportunities, the risks and the practical next steps.

To discuss your priorities in confidence - or to understand where HAPS and other NTN solutions may fit within your US connectivity roadmap - contact Bridge Connect US for an initial conversation.

We help you move from uncertainty to strategic clarity.