Quality of Service (QoS) and network slicing in Non Terrestrial Networks (NTN) introduce constraints that differ significantly from terrestrial 5G deployments.

While 5G NR natively supports QoS flows and end to end slicing, satellite integration creates challenges in:

1. Latency
2. Jitter
3. Bandwidth variability
4. Beam mobility
5. Resource isolation

This article examines how 5G Release 17 addresses NTN QoS and where practical limitations remain.

1. 5G QoS Framework Refresher

The 5G QoS model is defined in:

• 3GPP TS 23.501 – System Architecture
• 3GPP TS 23.502 – Procedures
• 3GPP TS 38.300 – NR overall description

Key components:

1. QoS Flows identified by QFI
2. 5QI standardized characteristics
3. GBR and Non GBR services
4. Reflective QoS
5. Network slicing via S-NSSAI

These mechanisms apply to NTN, but performance envelopes differ.

2. NTN Latency Impact on QoS

Typical round trip times:

1. GEO: ~500–600 ms
2. LEO: ~20–40 ms
3. MEO: ~100–150 ms

Implications:

1. HARQ timing must be adapted
2. RLC retransmissions increase jitter
3. GBR guarantees become harder to enforce
4. URLLC support is constrained in GEO

Reference:

• 3GPP TR 38.811 – Study on NR to support NTN

In GEO scenarios, conversational voice QoS must tolerate large delay budgets.

In LEO, near terrestrial performance becomes feasible.

3. Beam Mobility and QoS Continuity

In LEO NTN, beams move relative to Earth.

Challenges:

1. Frequent beam handovers
2. Dynamic path loss variation
3. Scheduling instability
4. Temporary buffering during gateway switching

QoS continuity depends on:

1. Fast beam reselection
2. Predictive mobility using ephemeris data
3. Core network assisted session continuity

Defined in:

• 3GPP TR 38.821 – NTN solutions

4. Network Slicing in NTN

Network slicing is standardized in:

• 3GPP TS 23.501
• 3GPP TS 28.530 (Management and orchestration)

In NTN, slicing must account for:

1. Satellite power constraints
2. Shared feeder links
3. Multi beam resource pooling
4. Limited spectrum allocations (ITU coordinated)

Unlike terrestrial networks, physical resource isolation is constrained by:

1. Shared satellite transponders
2. Beam overlap regions
3. Gateway bottlenecks

True slice isolation may require:

1. Beam level resource partitioning
2. Feeder link redundancy
3. Dedicated gateway clusters

5. QoS Differentiation Challenges

Terrestrial 5G can dynamically adjust scheduling every millisecond.

In NTN:

1. Long RTT reduces feedback agility
2. Beam wide congestion affects multiple slices
3. Power constraints limit peak throughput
4. Weather conditions impact high frequency links

Practical effects:

1. eMBB may dominate capacity
2. mMTC remains feasible
3. URLLC over GEO is not practical
4. Mission-critical services require regenerative architectures

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6. Slice SLA Enforcement in NTN

Service Level Agreements require monitoring of:

1. Latency
2. Packet loss
3. Throughput
4. Availability

In NTN, SLA violations may occur due to:

1. Gateway outages
2. Satellite handovers
3. Rain fade events
4. Beam power reallocation

Mitigation strategies:

1. Multi gateway diversity
2. Adaptive coding and modulation
3. Cross layer scheduling awareness
4. Predictive traffic shaping

7. Architectural Trade Off

Transparent Payload:

1. QoS control centralized at ground gNB
2. Higher feeder link dependency
3. Increased delay sensitivity

Regenerative Payload:

1. Faster scheduling decisions onboard
2. Reduced backhaul latency
3. Improved slice isolation

Regenerative designs are better suited for advanced slicing models.

8. Key Engineering Insight

NTN slicing is not merely logical separation.

It must integrate:

1. Satellite power allocation
2. Beam geometry
3. Feeder link planning
4. ITU spectrum constraints

QoS in NTN is a multi layer optimization problem.

Conclusion

5G Release 17 enables NTN QoS and slicing within the standard 5G framework. However, real world deployment requires:

1. Latency aware service mapping
2. Beam aware resource scheduling
3. Power constrained slice planning
4. Gateway diversity engineering

In NTN, QoS is limited not by protocol design, but by orbital physics and satellite power budgets.