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A Survey of Wireless Networks for Future Aerial COMmunications (FACOM)

Aygün Baltaci, Ergin Dinc, Mustafa Ozger, Abdulrahman Alabbasi, Cicek Cavdar, Dominic Schupke

arXiv:2111.04175v1cs.NIeess.SP

TL;DR

Aerial vehicles have diverse connectivity demands, and the survey finds no unified networking solution that meets them all. It reviews use cases, requirements, technologies, and architectures, concluding that heterogeneous, multi-technology networks are needed.

  • Problem

    Aerial vehicle use cases have diverse QoS demands, and the survey identifies a lack of a unified networking solution to meet them.

    Source: §VII · p. 37

  • Method

    The survey examines aerial connectivity demands and evaluates potential ways to meet them using different wireless technologies, reviewing more than 500 studies.

    Source: §I · p. 3, §VII · p. 37

  • Results

    The technology-to-use-case match study finds no unified networking solution that meets all aerial connectivity demands.

    Source: §VII · p. 37

  • Takeaways & Limitations

    Further investigations should realize heterogeneous, multi-technology architectures to support FACOM use cases.

    Source: §VII · p. 37

    Small-scale UAVs cannot carry heavy satellite terminals, and dish antennas are not integrable to their payloads.

    Source: E. Hardware and Certification · p. 37

Abstract

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Electrification turned over a new leaf in aviation by introducing new types of aerial vehicles along with new means of transportation. Addressing a plethora of use cases, drones are gaining attention and increasingly appear in the sky. Emerging concepts of flying taxi enable passengers to be transported over several tens of kilometers. Therefore, unmanned traffic management systems are under development to cope with the complexity of future airspace, thereby resulting in unprecedented communication needs. Moreover, the increase in the number of commercial airplanes pushes the limits of voice-oriented communications, and future options such as single-pilot operations demand robust connectivity. In this survey, we provide a comprehensive review and vision for enabling the connectivity applications of aerial vehicles utilizing current and future communication technologies. We begin by categorizing the connectivity use cases per aerial vehicle and analyzing their connectivity requirements. By reviewing more than 500 related studies, we aim for a comprehensive approach to cover wireless communication technologies, and provide an overview of recent findings from the literature toward the possibilities and challenges of employing the wireless communication standards. After analyzing the network architectures, we list the open-source testbed platforms to facilitate future investigations. This study helped us observe that while numerous works focused on cellular technologies for aerial platforms, a single wireless technology is not sufficient to meet the stringent connectivity demands of the aerial use cases. We identified the need of further investigations on multi-technology network architectures to enable robust connectivity in the sky. Future works should consider suitable technology combinations to develop unified aerial networks that can meet the diverse quality of service demands.

I. INTRODUCTION

Emerging UAV, eVTOL, and airplane operations create diverse connectivity needs, while communication options differ in coverage and QoS capabilities. The survey frames FACOM as a heterogeneous connectivity ecosystem and reviews aerial use cases, requirements, and potential solutions.

I. INTRODUCTION

  • FACOM brings together aerial connectivity use cases and potential solutions because vehicle types have diverse QoS needs and existing technologies face distinct coverage and reliability challenges.The survey presents DA2GC, SatCom, HAPCom, and A2A as technologies to evaluate against those demands.Source: §I · pp. 1, 3
  • GEO offers wide coverage but is unsuitable for latency-sensitive applications; LEO and HAPCom support real-time connectivity but face service interruptions from rapid handovers.DA2GC coverage is primarily limited to flights over the ground, while A2A requires vehicle proximity for end-to-end connectivity.Source: §I · p. 3

A. Nomenclature and Definitions

  • The survey focuses on external RF communications for non-military aerial vehicles from take-off through landing, excluding optical, wired, onboard, and ground-operation communications.Aerial platforms that provide connectivity, including aerial base stations, are also outside its literature review; HAPs are treated separately from other UAVs.Source: §I · p. 3, A. Nomenclature and Definitions · p. 3

I. INTRODUCTION

  • The survey categorizes use cases and their demands, reviews more than 500 studies, matches technologies to QoS needs, and covers architectures, testbeds, and open questions.It also presents a vision for future eVTOL connectivity.Source: §I · p. 3

A. Nomenclature and Definitions

  • The survey distinguishes airplanes, eVTOLs, and UAVs as aerial platforms and treats airplanes and UAVs that provide connectivity as outside its scope.It separates HAPs from other UAVs because of their distinct flight characteristics at very high altitudes.Source: A. Nomenclature and Definitions · pp. 3–4, • eVTOL · p. 4

• eVTOL:

  • Egress and ingress links denote AV-to-ground and ground-to-AV transmission; communication reliability combines measures including service availability, packet delivery, continuity, and integrity.The survey uses low, medium, and high reliability ranges because concrete requirements for particular aerial applications are not yet defined.Source: • eVTOL · pp. 4–5

B. Related Works

The survey derives aerial connectivity demands from vehicle applications and evaluates technologies across airplanes, eVTOLs, and UAVs. It reviews prior surveys and FACOM studies, including requirements, technology matching, multi-link options, architectures, and testbeds.

B. Related Works

  • Earlier surveys addressed UAV networking, cellular feasibility, and FANET routing; this review focuses mainly on studies from 2018 to 2021.The authors compare their survey with selected related surveys in Table III.Source: B. Related Works · p. 5, Table III · p. 6
  • The survey takes a top-down approach to derive connectivity requirements from applications, highlights eVTOL demands, and matches technologies to aerial applications.Its technology scope includes cellular and IEEE systems as well as satellites and HAPs.Source: B. Related Works · p. 5
  • The review examines heterogeneous multi-link connectivity for BVLoS remote piloting and surveys proposed AV and UTM architectures and open-source flight and networking platforms.The authors note that stringent remote-piloting requirements are difficult to achieve with a single link.Source: B. Related Works · p. 5

II. USE CASES AND CONNECTIVITY REQUIREMENTS

  • The paper discusses connectivity use cases for each aerial-vehicle type and analyzes both egress-link and ingress-link requirements.The airplane use cases include ATM, ACARS, single-pilot operations, and massive data transfer.Source: §II · p. 5, A. Airplanes · p. 6

A. Airplanes

  • Airplane ATM relies primarily on voice over VHF, while VDL-2 supports A2G data transfer up to 31.5 kbps; VHF systems were expected to saturate by 2020–2025 before the pandemic.Future airplane connectivity applications and architecture are illustrated in Figures 4 and 5.Source: 1) ATM · p. 6, Figure 4 · p. 7, Figure 5 · p. 7

1) ATM:

  • Future ATM systems envision an all-IP network instead of a specialized closed network, while initiatives such as SESAR, SANDRA, and NextGen develop future ATM capabilities.Network mobility remains a concern, and high-capacity, reliable connectivity is still needed throughout all flight phases.Source: 1) ATM · pp. 6–7

2) Aircraft Communication Addressing and Reporting System (ACARS):

The section describes airplane ACARS and single-pilot connectivity, massive data transfer, and connectivity requirements, then introduces eVTOL operations and their use cases.

2) Aircraft Communication Addressing and Reporting System (ACARS):

  • ACARS connects airplanes with airline operation control centers and other ground entities using VHF and satellite links; its messages are limited to 1960 bytes.Egress links carry requests such as weather updates and clearance requests, while ingress links return requested information.Source: 2) Aircraft Communication Addressing… · p. 7

3) Single-Pilot Operations (SPOs):

  • Single-pilot operations divide flight-related tasks between an onboard captain and a ground operator, making reliable, robust airplane-ground connectivity key to ground monitoring and operational support.NASA's vision replaces the onboard first officer with a ground operator.Source: 3) Single-Pilot Operations (SPOs) · p. 7, Figure 6 · p. 7

4) Massive Data Transfer:

  • An Airbus A320 generates 10 GB of data per flight hour, so massive data transfer requires high-rate connectivity during the short interval before the next flight.The transfer includes collected sensor data and onboard-computer data.Source: 4) Massive Data Transfer · pp. 7–8

5) Connectivity Requirements:

  • NASA requires up to 10^-8 communication reliability for SPO; the authors say eight uncorrelated links, each with 99.9% reliability, can meet that demand.The section also gives a 20 Mbps rate with a 300 ms latency threshold for full SPO above 10 km at 1000 km/h, and a 45 Mbps requirement for massive data transfer with an assumed 100 ms latency.Source: 5) Connectivity Requirements · p. 8

B. eVTOLs

  • eVTOLs are electric vertical-takeoff-and-landing vehicles aimed mainly at short-to-medium-range passenger transport, with use cases including airport shuttles, air taxis, and air ambulances.The paper presents eVTOL connectivity use cases in Figures 7 and 8.Source: B. eVTOLs · p. 8, Figure 7 · p. 8, Figure 8 · p. 8

1) Detect and Avoid:

The section links eVTOL and UAV operations to connectivity needs for detect-and-avoid, vertiports, and UTM. It describes UTM services and the information exchange required among air vehicles, operators, and other entities.

1) Detect and Avoid:

  • Detect-and-avoid systems detect conflicting aircraft, obstacles, events, and weather, then determine preventive maneuvers; connectivity supports timely alerts to remote pilots or other aircraft.A2A reachability is essential for detecting unknown objects early enough to avoid collisions, and its requirement depends on vehicle type, speed, and flight characteristics.Source: 1) Detect and Avoid · pp. 8–9

2) Vertiport Connectivity:

  • Near vertiports, eVTOLs need short-range, robust connectivity to receive ground assistance for precise take-off and landing.Between flights, operators also offload sensor and onboard-computer data for maintenance.Source: 2) Vertiport Connectivity · p. 9

3) Unmanned Traffic Management (UTM):

  • UTM addresses the greater operation numbers, vehicle density, lower cruising altitudes, and varied pilot and automation capabilities that conventional ATM cannot accommodate.UTMs may operate regionally and need inter-UTM handoffs for cross-region flights; robust real-time exchange supports eVTOL regulation, conflict resolution, flight requests, and trajectory updates. UTM services include C2 connectivity, tracking, flight planning, and authorization.Source: 3) Unmanned Traffic Management (UTM) · pp. 9–10

4) Piloting:

eVTOL piloting ranges from onboard pilots through remote operation to full autonomy, with communication needs shaped by human involvement and the vehicle’s reliance on connectivity. Remote piloting is the most connectivity-critical case, motivating heterogeneous multi-link architectures.

4) Piloting:

  • An onboard eVTOL pilot is expected in the first integration phase, whereas RPO uses ground pilots and onboard cameras and sensor data to support remote operation.In RPO, one pilot controls an aircraft at a time; different pilots may handle long or international flights, and transfers between providers require seamless CNPC handover for control and video streams.Source: 4) Piloting · p. 10, Figure 10 · p. 11
  • FAO removes the remote pilot but may retain a ground supervisor, while UAS includes both remotely piloted systems and fully autonomous systems.The paper distinguishes RPAS as a remotely piloted aircraft, operator, and communication link, with certification standards like manned aircraft,,.Source: 4) Piloting · p. 10

5) Connectivity Requirements:

  • RPO is the most connectivity-critical eVTOL scenario: control depends on the ground link, requiring real-time, robust, secure exchange over asymmetric video and control traffic.Multiple or 360° cameras, redundant avionics, and tight latency demands contribute to the higher data-rate requirements than for UAVs.Source: 5) Connectivity Requirements · pp. 11, 13, 4) Piloting · p. 11
  • Vertiport assisted take-off and landing is assumed to need low data rate but high reliability and tight latency, while massive data-transfer assumptions are scaled from airplane use cases.For detect-and-avoid, communication must remain robust when a remote pilot maneuvers to avoid conflicts.Source: 5) Connectivity Requirements · p. 12
  • The authors relate connectivity reliability to aviation safety objectives: DALs map function criticality to failure-rate ranges, including 10^-7 per flight hour for a catastrophic connectivity failure condition.The failure-rate thresholds are discussed against EASA eVTOL safety objectives, and conventional-airplane DALs.Source: 5) Connectivity Requirements · p. 12
  • 10^-5 per flight hour is the expected upper communication reliability rate for RPO, while a catastrophic connectivity failure in a single-passenger eVTOL could require 10^-7 per flight hour.The paper notes that wireless links face unpredictable fading and shadowing, complicating such high reliability.Source: 5) Connectivity Requirements · p. 12
  • Fully autonomous operation has more relaxed assumed requirements: up to 1 Mbps for flight updates, a 500 ms latency bound, and 15 Mbps broadband capacity.The authors base these assumptions on onboard handling of real-time operations and the rarity of ground-supervisor involvement; total passenger broadband demand varies with passenger count.Source: 5) Connectivity Requirements · p. 12
  • Current wireless technologies cannot provide the RPO reliability rate of 10^-5, leading the authors to foresee heterogeneous, multi-link network architectures.RF channel conditions fluctuate over the environment and flight, making high reliability and seamless connectivity difficult to ensure throughout a flight.Source: 5) Connectivity Requirements · pp. 12–13

C. UAV

UAVs span diverse sizes and operating environments, with connectivity use cases organized around command-and-control and payload traffic. Application scenarios include vision-based work, delivery, and data collection, each with different operating and communication characteristics.

C. UAV

  • UAVs range across three EASA size and mass categories, and their maximum operating altitude is usually 90–150 m, subject to national regulation.The listed categories are maximum dimensions and MTOM of 1 m and 5 kg, 3 m and 200 kg, and 8 m and 600 kg.Source: C. UAV · p. 13
  • UAV payload connectivity is divided into vision-based applications and non-vision applications, with the latter split into periodic and event-driven sporadic communication.UTM handles command-and-non-payload communication and coordinates UAV operations.Source: C. UAV · p. 13

1) Application Scenarios of UAVs:

  • Vision-based UAV applications include inspection, infrastructure construction, mapping, traffic surveillance, cinematography, monitoring, and search and rescue.These aircraft usually fly below 300 m at low speed or while hovering to capture high-quality imagery; connectivity needs depend on video quality.Source: 1) Application Scenarios of UAVs · p. 13
  • Delivery UAVs typically fly at low altitudes and medium speed, with connectivity used for destination-waypoint uploads and package tracking.Research on these services also addresses monitoring, scheduling, and route optimization.Source: 1) Application Scenarios of UAVs · p. 13
  • IoT data-collection UAVs gather sensor data directly or from distributed sensors; non-visual data collection can use higher altitudes and more latency-tolerant, lower-volume links than vision applications.Energy-efficiency studies address trajectory, collection time, device transmit power and positioning, wireless charging, edge computing, and underwater collection.Source: 1) Application Scenarios of UAVs · pp. 13–14
  • Agricultural UAVs support field sensing and imagery as well as tasks such as disease detection, crop spraying, irrigation, fruit counting, and planned harvesting.Agriculture UAVs accounted for 80% of global UAV revenues in 2017.Source: 1) Application Scenarios of UAVs · p. 14

2) Connectivity Requirements and Specifications of UAV Applications:

This section examines UAV applications’ varied flight profiles and communication needs, including operation-dependent CNPC requirements and stringent QoS demands that may call for multiple technologies. It also covers aviation authorization and restrictions for cellular FACOM spectrum, alongside studies of bandwidth needs and proposed spectrum-sharing and reuse mechanisms.

2) Connectivity Requirements and Specifications of UAV Applications:

  • UAVs may fly up to 300 m, typically at 10–15 m/s, in urban or rural areas; vision applications can need 10 ms latency, versus seconds for IoT.The survey characterizes flight profiles and notes that IoT applications generally do not require real-time transmission.Source: 2) Connectivity Requirements and… · p. 14

3) Connectivity Requirements for CNPC:

  • VLoS control and telemetry may require 5–150 kbps, FAO somewhat less, while BVLoS information links can demand high rates for first-person-view video.VLoS rates depend on UAV type and the number of exchanged parameters.Source: 3) Connectivity Requirements for CNPC · p. 14
  • CNPC latency depends on operation: VLoS/BVLoS requirements range from 50–100 ms in 3GPP reports to bounds of 155–300 ms in other specifications and studies.For FAO, latency can be relaxed up to 5 s when onboard controllers make flight decisions, but must remain low if ground components participate.Source: 3) Connectivity Requirements for CNPC · p. 14
  • DAL-based estimates place VLoS/BVLoS reliability requirements at 10−3–10−4, relaxed to 10−2–10−3 for FAO.The cited standards also specify 99.9% CNPC reliability, while RTCA specifies >99.976% availability and >99.9% communication continuity.Source: 3) Connectivity Requirements for CNPC · pp. 14–15

III. COMMUNICATION TECHNOLOGIES

  • The survey reviews FACOM wireless technologies as DA2GC, SatCom, HAPCom, and A2A, organizing studies by airplanes, eVTOLs/helicopters, and UAVs.It presents this technology categorization in Figure 13.Source: §III · p. 15

A. Direct Air-to-ground Communication

1) Cellular Networks:

  • Cellular studies report 5G DA2GC and LEO outperforming 4G, planar arrays offering 1.2 Gbps average airplane downlink, and measured commercial-style links reaching 26–30 Mbps downlink.The 1.2 Gbps estimate uses 50–100 MHz bandwidth and 500–1000 antenna elements; the 26–30 Mbps result used a 20 MHz, 2.6 GHz link at 10 km altitude.Source: 1) Cellular Networks · p. 15
  • In 4G measurements at 2.6 GHz using a UAV, maximum latency reached 2.5–3 s at 300 m, exceeding remote-piloting requirements and indicating degraded current cellular performance at high altitudes.Studies also describe severe air-coverage problems; dedicated A2G networks could significantly reduce them but require interference-free coverage across varying altitudes and costly deployment.Source: 1) Cellular Networks · pp. 16, 18
  • Licensed cellular bands require aviation-regulator permission; unlicensed LAA benefits from global harmonization but is suitable only for non-safety applications because it lacks regulation.Source: 1) Cellular Networks · p. 19
  • ITU reports 34 MHz is sufficient for RPO over terrestrial networks; an ECC study of one aerial UE up to 10 km says density limits and no-fly zones are needed to protect ground UEs.Source: 1) Cellular Networks · p. 19
  • 1.4 MHz is sufficient for current UAV CNPC demand at 99.9% communication reliability, with a projected need extending to 5 MHz in 20 years.Source: 1) Cellular Networks · p. 19
  • Proposals improve spectrum use by placing UAV control-plane allocation on A2A links to assign empty spectrum to A2G, and dedicating separate ground and aerial antennas for cellular spectrum reuse.Source: 1) Cellular Networks · p. 19

2) IEEE Networks:

IEEE technologies offer accessible, cost-efficient options for some aerial use cases, but reliability, certification, coverage, and spectrum constraints limit their suitability. The reviewed studies show distinct uses and trade-offs across WiFi, WiMAX, and ZigBee.

2) IEEE Networks:

  • Unlicensed spectrum and short communication ranges make IEEE protocols challenging for safety-critical or BVLoS operations, despite their availability and cost efficiency.The review notes reliability and certifiability concerns under aviation safety requirements.Source: 2) IEEE Networks · p. 19
  • 30% higher video quality than legacy multicast was measured with an RTP-based, rate-adaptive point-to-multipoint streaming framework over IEEE 802.11a.The framework supported live multicast video streaming over multiple UAVs.Source: 2) IEEE Networks · p. 20
  • Emerging WiFi standards add features relevant to aerial IoT and low-latency use, including sub-1-GHz coverage up to 1 km in 802.11ah and multi-link operation in 802.11be.The review also reports 802.11ax rates above 6 Gbps and planned scheduling through target wake time.Source: 2) IEEE Networks · p. 20
  • WiFi is mainly feasible for airplane and eVTOL cabin applications, but safety-critical cabin use requires reliability modifications and scarce spectrum limits supported applications.For UAV A2A links, remote-control interference in the 2.4 GHz band made WiFi unsuitable in one experimental study.Source: 2) IEEE Networks · pp. 19–20
  • WiMAX can provide coverage up to 50 km and data rates up to 70 Mbps on the IL and 28 Mbps on the EL, with potential for UAV agriculture and disaster-relief uses,.A study considered WiMAX for UAV rescue and monitoring in Alpine environments.Source: 2) IEEE Networks · p. 20
  • ZigBee has been studied for FACOM machine-type communication, including runway anomaly detection, aircraft hydraulic-leak detection, and UAV formation control –.Its coverage range below 100 m and use of unlicensed spectrum constrain deployment scenarios [290].Source: 2) IEEE Networks · p. 20

3) Other Networks:

Other networks span specialized low-power, aeronautical, surveillance, and long-range options for aerial connectivity. Their potential is use-case-specific, with constraints including interference, range, and spectrum scalability.

3) Other Networks:

  • UWB’s anti-multipath capability and low power use suit low-power aircraft applications, but UAV links may need RF-front-end protection against strong electromagnetic-pulse interference,.A low-profile 29 x 39 mm antenna design was presented to reduce UAV air drag.Source: 3) Other Networks · pp. 20–21
  • LoRa is a low-power, low-rate technology for long-range machine communication; one UAV V2X study sent data 10 km at 0 dBm.Other discussed uses include aircraft-structure vibration monitoring and coexistence with ATM radars in the 800 MHz European band.Source: 3) Other Networks · p. 21
  • LoRa and 3G modems have been proposed together for secure BVLoS remote-piloting links, while LoRa with a low-latency MAC improved reliability over WiFi in tests with 10 UAVs and 20 robots.The swarm tests also allowed high swarm density and larger coverage.Source: 3) Other Networks · p. 21
  • AeroMACS provides secure airport C-band communication, with reported rates up to 18.2 Mbps on the IL and 6.8 Mbps on the EL.A UAV mobility analysis found it could support speeds up to 130 km/h.Source: 3) Other Networks · p. 21
  • LDACS is an aviation-spectrum terrestrial platform with an OFDM architecture and rates up to 1.43 Mbps using 500 kHz bandwidth.It targets future civil-aviation voice and data, including A2G and A2A links, and may complement satellite communication.Source: 3) Other Networks · p. 21
  • ADS-B supports surveillance and collision-avoidance uses, but excessive UAV numbers can saturate its spectrum and limit scalability [318],.The paper proposes ground-based sense-and-avoid using cellular position reports to a ground base station, which informs other aircraft and ATM.Source: 3) Other Networks · p. 22

B. Satellite Networks

Satellite networks offer different coverage, capacity, and latency trade-offs for aerial connectivity, while terminal constraints and handovers shape their suitability. The section outlines satellite bands and handover types and emphasizes evaluating their effects on service continuity.

1) Background:

  • Satellite spectrum choices trade capacity and propagation constraints: Ka-band offers lower bandwidth cost, while Q/V bands are investigated for high-rate broadband but are highly sensitive to atmospheric conditions such as rain.C- and Ku-band spectrum is a major constraint for satellite operators.Source: 1) Background · p. 22
  • Satellite terminals can challenge aerial size, weight, and power limits: an Inmarsat machine-to-machine terminal can demand up to 50 W during transmission, and mmWave use further raises power requirements.Large antennas and advanced beamtracking and beamsteering are also challenges for mobile aerial vehicles.Source: 1) Background · p. 22
  • Satellite handovers include link-layer changes such as spotbeam, satellite, or inter-satellite-link handovers, and network-layer IP-address changes; hard handovers break before make, while soft handovers make before break.These categories reflect dynamic satellite connectivity and coverage or mobility changes.Source: 1) Background · p. 23
  • Because handover effects matter to connectivity and reliability is essential for CNPC, the paper identifies make-before-break as a mitigation approach to avoid interruption before handover.The authors call for evaluating service-interruption scenarios in FACOM.Source: 1) Background · p. 23

2) Satellite Constellations:

Satellite constellations present differing coverage, latency, and terminal trade-offs, while handovers and link conditions pose challenges for aerial use. HAPs offer another stratospheric connectivity option, with operational and technology constraints.

2) Satellite Constellations:

  • GEO offers global coverage but its usual 700–800 ms latency, heavy terminals up to 30 kg, and high costs constrain mission-critical use and large-scale deployment.The paper still identifies GEO as a possible primary link for selected applications.Source: 2) Satellite Constellations · p. 23
  • MEO can offer an intermediate latency-coverage balance: O3b end-to-end latency is around 130 ms, though large user terminals may be difficult to integrate into eVTOLs and UAVs.Current O3b networks use Ka-band with beam coverage around 700 km in diameter.Source: 2) Satellite Constellations · p. 23
  • Multiple spot beams support high-throughput satellite capacity through frequency reuse and directive beams, while user-centric services can use steerable beams.The figure contrasts seamless large coverage from conventional single-beam operation with QoS-aware user-centric services from multiple beams.Source: Figure 16 · p. 23, 2) Satellite Constellations · p. 24
  • LEO constellations offer latency similar to ground networks and potentially small, light terminals, supporting high-rate and mission-critical aerial services, but rapid handovers can interrupt connectivity and reduce availability.Phased-array antennas may mitigate this by connecting simultaneously to different spot beams before a main-beam handover.Source: 2) Satellite Constellations · p. 24

3) Challenges and Future Solutions:

  • LEO’s 7 km/s movement challenges reliable inter-satellite links and introduces Doppler effects, while its 5–15-year lifespan raises long-term service-continuity concerns,.Source: 2) Satellite Constellations · p. 24
  • Increasing satellites and spot beams can raise handover rates; beam tracking methods and phased-array airborne antennas are among the approaches discussed for managing tracking and connectivity challenges,,,.Gogo claims up to 100 Mbps with steerable phased-array antennas for airplanes,.Source: 3) Challenges and Future Solutions · p. 24
  • GEO latency makes time-critical FACOM use impractical, while LEO latency is described as comparable in magnitude to DA2GC; rotor-blade blockage also affects helicopter-to-satellite links and may be relevant to eVTOLs, –,.The reviewed work includes random linear coding to avoid retransmission latency and several techniques for mitigating rotor blockage.Source: 3) Challenges and Future Solutions · p. 24

1) Background:

  • HAPs operate quasi-stationarily at 17–25 km and can provide wide coverage and low propagation delay, but require station monitoring and antenna stabilization, while airship technology remains immature.HAP systems can provide indoor coverage and use spot beams; their stated total cost is about 50–300 million USD.Source: 1) Background · pp. 24–25

2) Spectrum Allocation:

The survey reviews HAP spectrum, architecture, uses, and challenges, then introduces FANETs as an aerial ad-hoc option. HAPs can offer broad, dynamic connectivity, but displacement and networking challenges constrain reliability.

2) Spectrum Allocation:

  • At 47 GHz, HAPCom requires twice the power needed at 28 GHz for service availability, while 18–32 GHz is less sensitive to rain attenuation than 47 GHz.The survey lists L-, S-, C-, K-, Ka-, and V-band allocations for HAPCom.Source: 2) Spectrum Allocation · pp. 25–26

3) Architecture and Design:

  • HAPCom can use relay-station or onboard-processing base-station architectures; displacement can interrupt backhaul and weaken edge-cell link budgets.Multiple ground-station links, displacement limits, or resource allocation between HAPs are proposed responses, but displacement can still destabilize coverage and handovers.Source: 3) Architecture and Design · p. 26

4) The Role of HAPCom in FACOM:

  • HAPs can extend urban coverage, increase capacity or reliability, collect sensing data, and support navigation and positioning.The survey also reviews HAP-assisted FANET neighbor discovery, satellite free-space-optics quantum key distribution, and HAP-to-ground propagation studies.Source: 4) The Role of HAPCom in FACOM · p. 26

5) Future Challenges:

  • HAP displacement and AV movement challenge beam alignment, link budgets, routing, and handovers; despite these constraints, HAPs can provide cost-efficient, dynamic connectivity with high-rate and low-latency services.The survey notes that changing topology can stale routing information, while frequent handovers warrant further study.Source: 5) Future Challenges · p. 26, 3) Architecture and Design · p. 26

D. A2A

  • FANETs connect aerial vehicles directly or relay information without a ground system, and can address resource-management issues from using satellite resources for rising in-flight entertainment demand.FANET nodes move faster and more freely than MANET nodes, but their mobility is more predictable and node density lower.Source: D. A2A · p. 26

1) A2A Standards:

The surveyed A2A standards span cellular vehicle links, IEEE 802.11p, and LDACS, with reported performance varying by technology and study. Airplane and eVTOL A2A solutions must also address coverage, mobility, routing, and antenna constraints.

1) A2A Standards:

  • 2.9 km communication distance at 20 m altitude was achieved with IEEE 802.11p, but another study found it could not support bursty video traffic.Experimental 2.4 GHz channel studies found attenuation similar to free-space pathloss and weaker multipath at higher altitudes; at 60 GHz, one study found a slightly higher pathloss exponent than free-space.Source: 1) A2A Standards · p. 27
  • IEEE 802.11p outperformed cellular V2X in one comparison, while a separate numerical study found NR-V2X superior in reliability, latency, and data rate.The survey also reports work comparing underlay and overlay spectrum sharing for C-V2V A2A links.Source: 1) A2A Standards · p. 27

2) Challenges and Potential Solutions of A2A for FACOM:

  • 37 Mbps throughput was reported for A2A coverage up to 340 km when extending DA2GC coverage, while the same study reported DA2GC reach up to 432 km.The survey also notes that line-of-sight A2A connectivity can reach 740 km because of Earth’s curvature.Source: 2) Challenges and Potential Solutions… · pp. 27–28

1) A2A Standards:

  • For LDACS A2A, STDMA was reported as a better candidate than ALOHA when the available bandwidth is divided into 0.5 MHz subchannels.Another study considered A2A transmissions on A2G spectrum whenever the channel is free.Source: 2) Challenges and Potential Solutions… · p. 28

2) Challenges and Potential Solutions of A2A for FACOM:

  • Airplane A2A design must account for high-speed mobility, link stability, and path interruption, while airborne antennas need steerability and low weight and drag.Beamforming, beamtracking, and dual-radio designs are discussed as potential approaches; one UAV simulation reported a 35.8% increase in link robustness.Source: 2) Challenges and Potential Solutions… · pp. 28–29
  • 68.2 kbps with a latency of 184 ms was measured for an oceanic FANET routing scenario, versus 38.3 kbps with a latency of 401 ms in a continental scenario.The survey describes stable routes and clusters, trajectory-based routing, and packet path diversity as approaches for airplane networking.Source: 2) Challenges and Potential Solutions… · pp. 28–29

E. Multi-link Connectivity

The survey argues that a single wireless link may provide data rate but not both ultra-reliable communication and ubiquitous coverage, motivating heterogeneous multi-link designs. Its match study assigns candidate technologies to use cases and identifies practical limits on technology choice.

E. Multi-link Connectivity

  • A single wireless link may provide sufficient data rate, but cannot achieve both ultra-reliable communication and ubiquitous coverage across environments.The survey calls for evaluating heterogeneous backhaul and technology combinations against a 10^-5 communication reliability target for eVTOL remote piloting and airplane single-pilot operations.Source: E. Multi-link Connectivity · pp. 29–30
  • The survey distinguishes technology, network, base-station, and frequency diversity as ways to combine links, with different scopes for the resulting diversity.Multiple parallel links can improve robustness but add networking cost, so the survey recommends optimizing link count for the use case.Source: E. Multi-link Connectivity · pp. 29–30
  • Dual-operator connectivity maintained 99.9% Packet Error Ratio (PER) at all altitudes on the IL, compared with a 97.6% minimum reliability rate for a single MNO.The cited field studies found multi-link performance gains, but note that independently designed MNO networks make reliability at every time instance challenging.Source: E. Multi-link Connectivity · p. 29

F. Connectivity Options vs. FACOM use cases: Match Study

  • The match study compares data rate, latency, reliability, coverage, and spectrum against aerial-use-case requirements, and identifies preferred technologies per use case.It excludes HAPs as they lack a specific connectivity standard and generally omits WiFi for limited coverage and single-hop operation.Source: F. Connectivity Options vs. FACOM use… · pp. 30–31
  • For airplane services, the survey selects LDACS for VoIP and digital messaging, but envisions cellular plus LEO connectivity for future single-pilot operations.Cellular is proposed for continental flights and LEO for intercontinental flights; LDACS is considered insufficient for the high data rates of future SPOs.Source: F. Connectivity Options vs. FACOM use… · p. 31
  • For eVTOLs, the survey pairs cellular with LEO for remote piloting, mMTC with eMBB for cabin and vertiport needs, and C-V2V for detect-and-avoid links.It also considers LDACS for UTM communications and AeroMACS for vertiports; C-V2V and IEEE 802.11p are limited to eVTOL DAA links because their range is under 1 km.Source: F. Connectivity Options vs. FACOM use… · p. 31
  • The diverse technology mix must coexist, and deployment and operating costs motivate choosing technologies that can serve multiple applications.Source: F. Connectivity Options vs. FACOM use… · p. 31

IV. SYSTEM ARCHITECTURES FOR FACOM

The survey reviews proposed airplane, UAV, and UTM architectures, then catalogs open-source simulation and emulation platforms. It highlights both architecture-specific design trade-offs and the platforms’ differing research capabilities.

A. Network Architectures for Airplanes

  • For airplane connectivity, a centralized A2G core is described as offering en-route harmonization and flexible QoS and resource allocation, while ocean coverage remains a difficult case.A proposed North Atlantic network places ground base stations on stationary ships along fiber cables, with each base station covering about 370 km; the survey questions its operational feasibility and notes ship movement can alter beam directions.Source: A. Network Architectures for Airplanes · p. 32, Figure 20 · p. 33

B. Network Architectures for UAVs

  • UAV A2A architectures include centralized and decentralized forms: multi-cluster suits differing flight characteristics and tasks, while a single cluster suits similar UAVs.Centralization minimizes CNPC latency, decentralized architectures are more robust for A2A links, and a secondary cluster head can replace a primary head when its battery falls below a threshold.Source: B. Network Architectures for UAVs · p. 32, Figure 21 · p. 33

C. 5G System Architectures for UTMs

  • Proposed UTM architectures add gateways and network functions to coordinate UTM services, while future work should address dedicated UTM-eVTOL ground networks and heterogeneous cellular-LEO architectures.The survey notes that existing ground-network sidelobes may not reliably cover eVTOLs at altitudes up to 1 km.Source: C. 5G System Architectures for UTMs · p. 33

V. OPEN SOURCE SIMULATION AND EMULATION PLATFORMS

  • The survey categorizes open-source platforms for UAV, airplane, and ATM simulation, comparing simulation or emulation type, flight and networking capabilities, and features.Platforms combining flight and network simulation can support networking experiments with less implementation effort.Source: §IV · p. 32, §V · p. 33
  • Platform choice depends on the research task: AVENS supports FANET simulation, UAVSim supports satellite-network simulation, and FlyNetSim supports multilink emulation.Some platforms also combine simulation and emulation to help deploy custom algorithms from software to hardware; the survey leaves detailed platform evaluation outside its scope.Source: §V · pp. 33–34

VI. OPEN RESEARCH CHALLENGES IN FACOM

FACOM research must address varied vehicle, flight, and QoS requirements while developing capacity and coordination for heterogeneous aerial networks. The section identifies AI, unified-network design, and capacity as open challenges.

A. Artificial Intelligence

  • AI could support aerial multilink networking by optimizing routing and link selection, predicting handovers, and helping meet CNPC reliability and latency demands.Prior work covers aerial base-station placement and prediction, channel modeling, routing, and ground coverage.Source: A. Artificial Intelligence · p. 34

B. Diversity and Unified Network Design

  • AV diversity across flight characteristics, altitudes, mobility, and SWaP complicates unified designs; heterogeneous links can improve robustness but are complex, costly, and hardware-intensive.The section calls for new MAC/IP architectures and adapted or novel multilink transport protocols; multiple radio interfaces also challenge SWaP requirements.Source: B. Diversity and Unified Network Design · pp. 34, 36
  • The section identifies open-source UAV flight/network simulators and airplane simulators without networking support.The provided table captions establish the scope of these simulator lists, but not their individual entries.Source: Table XXI · p. 35, Table XXII · p. 36
  • Coordinating same-network and cross-network handovers is difficult with limited UE handover information, while prediction may support routing and congestion control.SDN and network slicing are also proposed for unified resource control and priority-traffic isolation.Source: B. Diversity and Unified Network Design · p. 36

C. Network Capacity

  • 75 Mbps per aircraft is the capacity EAN can provide, and the section calls for more capacity as high-throughput UAV applications grow.Possible approaches include more ground stations or high-throughput satellites; beamforming and higher-order modulation can improve link robustness, while interference mitigation is another research need.Source: C. Network Capacity · p. 36

D. Spectrum Regulation

The survey examines spectrum, hardware, and other research challenges, then concludes that diverse aerial connectivity demands call for heterogeneous technologies whose suitable combinations remain unresolved.

D. Spectrum Regulation

  • Aeronautical safety spectrum is globally harmonized but scarce and costly to serve, licensed spectrum can support high rates but lacks global harmonization, and unlicensed spectrum is unsuitable for safety applications.The section also notes uncertainty about cellular authorization to use aeronautical safety spectrum for CNPC and the need for licensed spectrum for UTM airspace regulation.Source: D. Spectrum Regulation · pp. 36–37

E. Hardware and Certification

  • Onboard communication hardware must balance size, weight, and power constraints; small UAVs cannot carry heavy satellite terminals, and aviation certification requires failure-resilient hardware.Flexible hardware such as SDRs may enable multipurpose onboard RF systems, though standardization and commercialization can take time.Source: E. Hardware and Certification · p. 37

F. Other Research Challenges

  • Future work includes data dissemination for eVTOL and airplane MTC use cases, energy-efficient A2G networks for eVTOLs, and secure communications for critical aerial missions.The section relates these topics to prior UAV dissemination, energy-optimization, and security studies.Source: F. Other Research Challenges · p. 37

VII. CONCLUSION

  • Each AV type has distinct use cases and QoS metrics, while eVTOL operations reach 1 km versus commercial UAVs at 150 m and require robust multi-pilot networking and handovers.Dedicated A2G solutions exist, but network capacity needs improvement as demands increase.Source: §VII · p. 37
  • UTM must connect distinct entities for low-altitude regulation, with new handoff mechanisms needed for inter-region and cross-border flights..Source: §VII · p. 37
  • Cellular networks are prominent for urban FACOM, LDACS is a potential RPO option, and satellites may complement ground systems, though high-mobility satellite performance is uncertain.The conclusion also identifies unlicensed spectrum and lack of multi-hop architecture as IEEE-standard disadvantages for FACOM.Source: §VII · p. 37
  • A single wireless solution does not meet all aerial-use-case demands, so heterogeneous architectures are needed, but suitable technology combinations and parallel-link counts remain unresolved.The survey particularly leaves open which combinations suit RPOs.Source: §VII · pp. 37–38
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