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LEO Satellites in 5G and Beyond Networks: A Review from a Standardization Perspective

Tasneem Darwish, Gunes Karabulut Kurt, Halim Yanikomeroglu, Michel Bellemare, Guillaume Lamontagne

arXiv:2110.08654v1cs.NI

TL;DR

Integrating satellite and terrestrial networks requires coordinated 3GPP standardization beyond historically separate ecosystems. This survey reviews that work across use cases, NR, management, orchestration, and future integration needs, concluding that further efforts are needed for full SatNet and 5G+ integration.

  • Problem

    Satellite and terrestrial networks have historically been standardized independently, creating a need to address their integration within 5G and beyond.

  • Method

    The paper comprehensively reviews 3GPP satellite-network standardization activities from Releases 14 through 18 across use cases, NR adaptation, and management and orchestration.

  • Results

    The review identifies satellite-access use cases, summarizes requirements for their realization, discusses NR adaptations and potential solutions, and describes management and orchestration requirements.

  • Takeaways & Limitations

    Further standardization is needed to achieve full integration of SatNets and 5G+ from the physical layer through the application layer.

Abstract

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Low Earth Orbit (LEO) Satellite Network (SatNet) with their mega-constellations are expected to play a key role in providing ubiquitous Internet and communications services in the future. LEO SatNets will provide wide-area coverage and support service availability, continuity, and scalability. To support the integration of SatNets and terrestrial Fifth Generation (5G)networks and beyond, the satellite communication industry has become increasingly involved with the 3rd Generation Partnership Project (3GPP) standardization activities for 5G. In this work, we review the 3GPP standardization activities for the integration of SatNets in 5G and beyond. The 3GPP use cases of SatNets are highlighted and potential requirements to realize them are summarized as well. The impacted areas of New Radio(NR) are discussed with some potential solutions. The foreseen requirements for the management and orchestration of SatNets within 5G are described. Future standardization directions are discussed to support the full integration of SatNets in SixthGeneration (6G) with the goal of ubiquitous global connectivity.

I. INTRODUCTION

LEO SatNets are being integrated with terrestrial 5G through expanding 3GPP standardization, motivated by connectivity demands and the distinct coverage and continuity benefits of satellite systems. This survey reviews that work across use cases, NR, management, orchestration, and future 6G directions.

  • I. INTRODUCTION: Growing device connectivity, stringent QoS demands, and continuous-connectivity needs challenge terrestrial telecommunications.The cited motivation includes an estimate of 3.5 billion 5G subscriptions by the end of 2026 and traffic from billions of sensors and devices.
  • I. INTRODUCTION: LEO mega-constellations can provide service continuity, wide-area coverage, availability for critical communications, and network scalability.Their satellite-to-satellite networking capability supports their role in future integrated networks.
  • I. INTRODUCTION: 3GPP classifies satellite systems as Non-Terrestrial Networks that complement terrestrial networks, while this survey focuses on satellites in 5G and beyond.The review distinguishes satellite communication work from separate HAPS and UAV standardization tracks.
  • I. INTRODUCTION: 3GPP considered satellite communications from Release 14 onward across NR, architectures, use cases, scenarios, management, and orchestration.The survey comprehensively reviews these standardization activities with a focus on 3GPP work.
  • A. Motivation and contributions: The survey covers 3GPP activities from Release 14 to Release 18, satellite-access use cases, NR adaptation, management and orchestration, other organizations, and 6G directions.The paper is organized around satellite network elements, standardization, architectures, NR, management, non-3GPP efforts, and future integration directions.

II. SATELLITE ACCESS NETWORK ELEMENTS AND CHARACTERISTICS IN 3GPP STANDARDIZATION

3GPP characterizes satellite access through its platforms, links, gateways, payloads, and orbital configurations, while emphasizing coverage, continuity, scalability, and service-extension roles for 5G.

  • 3GPP roles and characteristics: SatNets can provide 5G service in unserved and underserved areas, upgrade limited terrestrial networks, support continuity, and enable network scalability.The listed applications include isolated and remote areas, moving platforms, critical communications, and multicast or broadcast delivery toward network edges.
  • Satellite access network elements: A satellite access network includes user equipment, a service link, a space platform carrying a payload, inter-satellite links, gateways, and feeder links.The space platform may use bent-pipe or regenerative payload configurations.
  • Payload configurations: Bent-pipe payloads perform radio-frequency filtering, frequency conversion, and amplification, whereas regenerative payloads additionally perform base-station-like processing.Regenerative payloads can include demodulation, decoding, switching or routing, coding, and modulation.
  • Satellite access network elements: Inter-satellite links support satellite constellations and may operate in radio-frequency or optical bands.The cited architecture describes ISLs specifically for regenerative payloads and constellations of satellites.
  • Orbital configurations: 3GPP distinguishes GEO, NGSO, LEO, MEO, and HEO orbital categories by altitude, motion relative to Earth, and coverage characteristics.GEO satellites at 35,786 km can provide continuous coverage, while NGSO service continuity requires constellations whose required size increases as altitude decreases.
  • Orbital configurations: LEO satellites operate from 500 km to 2,000 km, with orbital-plane inclination angles from 0 to 180 degrees.The cited description places LEO constellations above the International Space Station and debris and below the first Van Allen belt.

III. OVERVIEW OF SATELLITE ACCESS NETWORK 3GPP STANDARDIZATION AND USE CASES

3GPP progressively incorporated satellite access into 5G standardization, beginning with deployment scenarios and requirements and expanding toward NTN studies, satellite use cases, and NR adaptation.

  • 3GPP standardization overview: 3GPP initiated satellite-communication consideration in Release 14 through a study on scenarios and requirements for next-generation access technologies.This marked the beginning of the release-based standardization path reviewed by the paper.
  • 3GPP standardization overview: Release 14 identified satellite extensions for areas without terrestrial coverage and for services such as broadcasting and delay-tolerant communications.Release 15 analyses further described satellites' role in 5G, with emphasis on NR for industrial and mission-critical services.
  • NTN standardization: The growing integration effort led 3GPP to define Non-Terrestrial Networks, with satellites treated as the main case and other aerial systems as special cases.Release 17 work addressed NTNs for 5G systems supporting underserved areas and other satellite-enabled scenarios.

A. 3GPP standardization activities for satellite access networks

3GPP standardization activities progressively addressed satellite integration into 5G across releases, covering architectures, NR, management, and use cases. The defined use cases emphasize continuity, ubiquity, and scalability, with requirements for selecting, combining, and managing terrestrial and satellite access.

  • Release activities: Releases 15–18 launched studies and work items covering satellite access, NR support, 5G architecture integration, and management and orchestration.Release 15 initiated studies on NR and satellite access; Releases 16–18 continued architecture, integration, NTN, and related evolution activities.
  • Release activities: Release 17 work on NR support for NTN consolidated physical-layer impacts, evaluated LEO and GEO scenarios through link- and system-level simulations, and identified upper-layer requirements.The associated architecture work also examined interactions between the core network and RAN.
  • Use cases: 3GPP identified service continuity, service ubiquity, and service scalability as the three main satellite-access use-case categories.These categories cover movement between terrestrial and satellite networks, access in unserved or underserved areas, and satellite multicasting, broadcasting, or terrestrial traffic off-loading.
  • Requirements: Realizing satellite access requires guaranteed-QoS continuity, optimum network selection, support for mMTC and NB-IoT, satellite-aware latency handling, and traffic distribution across access types.The requirements also call for cooperation between mobile and satellite operators and QoS indicators adapted to GEO, MEO, and LEO access.
  • Requirements: 3GPP requirements include selecting or rejecting satellite connections based on supported indicators and available accesses, while multi-access systems select combinations using priority, pre-emption, QoS, and availability.These requirements support access decisions across heterogeneous terrestrial and satellite networks.

IV. SATELLITE ACCESS IN 5G AND ITS ARCHITECTURE ASPECTS

3GPP characterized satellite access networks by terminal type and bandwidth, then mapped satellite components onto NG-RAN through transparent, regenerative, and multi-connectivity architectures. These options differ in where radio processing and inter-satellite connectivity are implemented.

  • Access networks: 3GPP described broadband satellite access for mobile VSATs and narrow- or wide-band access for terminals with omni- or semi-directional antennas.Broadband service links operate above 6 GHz and provide at least 50 Mbps downlink, while narrow-band service below 6 GHz refers to less than 1 or 2 Mbps downlink.
  • Architecture mapping: The satellite access architecture is compared with the 3GPP NG-RAN logical architecture to identify how satellite network components map onto 5G.This mapping is the basis for integrating satellite access networks into 5G.
  • Architecture types: Transparent satellite-based NG-RAN uses payloads for frequency conversion and RF amplification, with multiple satellites potentially connected to one ground gNB.The satellite payload does not perform signal regeneration in this architecture.
  • Architecture types: Regenerative satellite-based NG-RAN performs signal regeneration onboard and provides inter-satellite links, with either gNB or gNB-DU processing on the payload.The inter-satellite link may use radio or optical interfaces defined by 3GPP or other organizations.
  • Architecture types: Multi-connectivity can involve transparent or regenerative satellites with gNB or gNB-DU functions onboard.Figure 3 illustrates these satellite access architectures and their mapping onto the 5G architecture.

V. ADAPTING NEW RADIO FOR SATELLITE NETWORKS

Satellite deployment introduces propagation, mobility, channel, resource, and topology constraints that differ from cellular systems. These constraints affect signaling timing, synchronization, handover, access control, and link availability in NR.

  • Deployment constraints: Satellite channels require distinct multipath and Doppler models, with outdoor and line-of-sight conditions needed for satellite communication.For narrowband signals and frequency bands below 6 GHz, the time disparity may be ignored.
  • Deployment constraints: Moving satellite cells create propagation-delay differences between cell-edge and cell-centre UEs, while high-speed UEs may require support up to 1,000 km/h.The delay difference increases as satellite altitude decreases and can affect contention-based access when UE position is unknown.
  • Deployment constraints: Satellite propagation delays increase round-trip signaling times, especially at access and transport levels.Propagation delay is a central difference between satellite and terrestrial deployment scenarios.
  • Deployment constraints: NGSO satellite motion produces stronger Doppler effects that continuously modify carrier frequency, phase, and spacing.The Doppler effect depends on frequency band and relative satellite velocity with respect to the UE.
  • Deployment constraints: Handover must support continuity between terrestrial and non-terrestrial access, including regenerative and bent-pipe satellites, preparation, failure handling, and lossless transfer.Handover may arise from mobility within an NTN or between NTN and cellular networks.
  • Deployment constraints: Satellite topology places access control mainly at satellite base-station, gateway, or hub level, making pregrants, SPS, or grant-free access beneficial.The remote location of access control can prevent an optimal response time compared with cellular systems.

B. NR impacted areas and potential solutions

Satellite-specific delay, mobility, power, and topology constraints affect numerous NR procedures. Potential adaptations address random access, timing, synchronization, retransmissions, mobility, protocols, and waveform power efficiency.

  • NR impacts: Satellite constraints impact NR features, motivating potential solutions across radio procedures and system operation.The review identifies impacted areas using 3GPP TR 38.811 and TR 38.821.
  • Mobility: LEO beams retain UEs for only a few minutes, requiring rapid paging and handover to avoid inefficient satellite-resource use and possible data loss.Moving beams do not correspond one-to-one with fixed ground tracking or registration areas used for paging.
  • Access and timing: Moving satellites cause delay variations that exceed NR’s 1 ms-or-less TTI, making TA alignment important for synchronized uplink reception.The alignment must account for rapid changes in the UE–base-station distance through the satellite.
  • Retransmission procedures: Satellite RTT can exceed conventional HARQ timers and parallel-process limits, so simply scaling HARQ processes linearly with RTT may be infeasible for memory-constrained UEs.The delay also affects the number of active HARQ processes at gNBs.
  • Retransmission procedures: LEO one-way delay changes continuously, requiring larger ARQ buffers while limiting retransmissions because packets remain buffered until acknowledgment or timeout.For a 600 km orbit, the one-way propagation delay is given as 2–7 ms.
  • Physical-layer procedures: Satellite power limits and long control-loop delays restrict power control, which is expected to track slower variations rather than fast fading.The limited power margin also affects automatic coding and modulation.
  • Access and timing: Long RTT requires modified PRACH design and procedures because satellite cells can involve large common and relative propagation delays.If common propagation delay is compensated, PRACH design depends on the remaining relative delay; thousands-of-kilometers time advance can require further modification.
  • Waveforms: Low-PAPR waveforms are desired because satellite power amplifiers become nonlinear near saturation, while increasing backoff reduces amplifier efficiency.NR downlink CP-OFDM has higher PAPR than the underlying single-carrier modulation.

VI. MANAGEMENT AND ORCHESTRATION WITH INTEGRATED SATELLITE COMPONENTS IN A 5G NETWORK

Management and orchestration studies address how satellite components can be integrated into 5G networks. The work defines reference architectures and groups requirements around slicing, satellite-component management, and monitoring, while noting substantial mobility-related impacts and limited NTN-management standardization.

  • Orchestration manages and controls network services and resources on an integrated basis for optimization and faster, more flexible allocation.
  • The study defines two reference architectures: one integrating satellite NR-RAT and terrestrial RAT within a 3GPP RAN, and one integrating a non-3GPP satellite RAN.
  • Management and orchestration requirements are organized into network slice management, satellite-component management, and satellite-component monitoring.
  • Satellite integration mainly affects scenarios where gNB components are onboard LEO or MEO satellites, because they move faster than the earth and introduce long-delay monitoring challenges.
  • 3GPP concluded that 5G Self-Organizing Network concepts require enhancement for mobile non-terrestrial gNBs, although NTN-management standardization remains limited.

VII. OTHER STANDARDIZATION ORGANIZATIONS

Satellite integration standardization extends beyond 3GPP across international, regional, industry, and national organizations. These efforts address architectures, spectrum, transport, virtualization, edge computing, management, use cases, and satellite-specific technologies.

  • ITU Standardization: ITU standardization envisions an access-network-independent IMT-2020 architecture with a common core network supporting multiple radio access technologies.
  • World Radio Conference: WRC revises international rules governing radiofrequency spectrum and geostationary and non-geostationary satellite orbits.
  • World Radio Conference: WRC-19 adopted deployment milestones requiring non-GSO systems to deploy 10% of a constellation within two years, 50% within five years, and the full constellation within seven years.
  • IETF and ETSI: IETF work includes multipath deployments using fixed gateways and satellites for 5G backhauling, while ETSI addresses NFV, MEC, millimeter-wave transmission, and non-IP networking.
  • Other organizations: Other initiatives cover satellite management and orchestration, spectrum coordination, future-network roadmaps, and use cases spanning IoT, smart cities, maritime and aviation, transport infrastructure, and emergency disasters.

A. Satellite and aviation standardization

Satellite and aviation organizations contribute standards for satellite broadcasting, space-data interoperability, and aircraft connectivity. Their work spans satellite links, broadband return channels, telemetry and telecommand, and aviation network infrastructure and security.

  • Digital Video Broadcasting: DVB defines satellite broadcasting and return-channel specifications supporting broadband telecommunication services via satellite.
  • Consultative Committee for Space Data Systems: CCSDS develops data-system and information-system standards to promote interoperability and cross-support among cooperating space agencies.
  • Consultative Committee for Space Data Systems: The CCSDS Space Link Service defines telemetry and telecommand links between Earth and space probes.
  • Airlines Electronic Engineering Committee: AEEC develops aviation engineering standards for avionics, networks, cabin systems, aircraft IP connectivity, and security using open standards.

VIII. STANDARDIZATION FOR 6G SATELLITE COMMUNICATIONS NETWORKS

6G satellite-network standardization must address the mobility and signaling consequences of rapidly changing LEO topology. Frequent handovers, moving tracking areas, and high paging loads require new mobility-management mechanisms for integrated terrestrial-NTN networks.

  • Mobility management: LEO satellites offer shorter propagation delays and higher data rates than GEO satellites but cause frequent handovers and time-varying communication channels.
  • Mobility management: LEO handovers include intra-satellite beam changes, inter-satellite transfers, and inter-access-network transfers between satellite, aerial, and terrestrial networks.
  • Mobility management: Thousands of users may need simultaneous or near-simultaneous handovers, creating large network loads that conventional schemes cannot efficiently manage.
  • Mobility management: MIPv6 and PMIPv6 were not designed for SatNets with rapidly changing topologies in which the gNB itself moves with the LEO satellite.
  • Mobility management: Moving tracking areas accommodate LEO footprints but create high paging loads, while dual connectivity and vertical handovers require novel mechanisms for seamless integrated-6G mobility.

B. Routing

Routing in LEO SatNets must accommodate dynamic topology, congestion, and application-specific QoS requirements. Standardization should also support interoperability and integrated-network compatibility.

  • Routing: LEO routing must adapt to frequent topology changes and limited ISL lifetimes while meeting application-specific QoS requirements.Relevant QoS measures include packet delivery delay and packet delivery ratio.
  • Routing: Delay-tolerant routing suits delay-tolerant applications, whereas multi-path routing supports applications requiring high bandwidth.
  • Routing: Routing standards should support interoperability among different satellite constellations and operators.
  • Routing: SDN-based SatNet solutions should be considered in standardization to improve compatibility and interoperability among integrated network components.
  • Routing: Dynamic spectrum allocation is necessary but difficult because unpredictable user and satellite mobility complicate spectrum management.
  • Routing: Further standardization is needed for full SatNet and 5G+ integration from the physical layer through the application layer.
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