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Designing and Implementing Future Aerial Communication Networks
Sathyanarayanan Chandrasekharan, Karina Gomez, Akram Al-Hourani, Sithamparanathan Kandeepan, Tinku Rasheed, Leonardo Goratti, Laurent Reynaud, David Grace, Isabelle Bucaille, Thomas Wirth, Sandy Allsopp
TL;DR
The paper addresses how aerial platforms can complement terrestrial networks for wireless coverage during temporary events and emergencies. It reports the design, implementation, and trial of LTE-A aerial base stations using Helikites. The trial was encouraging, while onboard power efficiency remained important for achieving a longer-lasting solution.
Problem
The paper examines how to provide rapidly deployable, reliable aerial wireless coverage for public safety during and after large-scale temporary events.
Method
The authors design and implement LTE-A aerial base stations on tethered Helikites, with airborne batteries, antennas, and RRH equipment connected by optical fiber to ground-based network components.
Results
Trials of the Helikite-mounted LTE-A system were encouraging for serving users on the ground and supporting temporary-event and emergency Internet access.
Takeaways & Limitations
Helikite-enabled LTE-A platforms can provision Internet access during temporary events and emergencies, with improved onboard power efficiency needed for greater stability.
Takeaways & Limitations
Mechanical constraints, payload limits, and inefficient power provision affect the selected technology, operating altitude, and endurance of AeNB deployments.
Abstract
from arXiv · showhide
Providing "connectivity from the sky" is the new innovative trend in wireless communications. High and low altitude platforms, drones, aircrafts and airships are being considered as the candidates for deploying wireless communications complementing the terrestrial communication infrastructure. In this article, we report the detailed account of the design and implementation challenges of an aerial network consisting of LTE Advanced (LTE-A) base stations. In particular, we review achievements and innovations harnessed by an aerial network composed of Helikite platforms. Helikites can be raised in the sky to bring Internet access during special events and in the aftermath of an emergency. The trial phase of the system mounting LTE-A technology onboard Helikites to serve users on the ground showed not only to be very encouraging but that such a system could offer even a longer lasting solution provided that inefficiency in powering the radio frequency equipment in the Helikite can be overcome.
I. INTRODUCTION
Aerial communication networks are being explored to extend wireless coverage for emergencies, temporary events, rural areas, and emerging markets. The ABSOLUTE project focuses on designing and validating LTE-A aerial base stations using low-altitude platforms integrated with terrestrial and satellite networks.
- Aerial networks target public safety, temporary large-scale events, and Internet access in rural, remote, and emerging regions.
- CAPANINA, Google Loon, and Facebook projects illustrate efforts to provide broadband or Internet connectivity from high-altitude platforms, balloons, aircraft, and satellites.
- ABSOLUTE designed and implemented LTE-A aerial base stations using low-altitude platforms for rapidly deployable public-safety coverage during and after temporary emergencies.
- The project aimed for a reliable aerial network that could integrate rapidly with satellite and LTE-A terrestrial networks while remaining flexible, scalable, and interoperable.
- The article reviews aerial platforms, regulatory aspects, implementation details, and communication challenges and limitations of aerial base stations.
A. Drones Characteristics
Drones provide flexible low-altitude platforms but are constrained by payload capacity and short battery-powered autonomy. These limitations made them unsuitable for ABSOLUTE scenarios requiring substantial LTE equipment at higher altitudes.
- Drones generally operate at low or very low altitudes because their payload and autonomy capacities are limited.
- Typical drone payloads range from a few dozen grams for micro-drones to 5–7 kilograms for larger drones.
- Drone batteries power propulsion, telemetry, and payload, producing expected autonomy of approximately 10 to 40 minutes.
- Drones were unsuitable for ABSOLUTE scenarios requiring at least 10 kg of LTE equipment carried at hundreds or thousands of meters.
- Stratospheric aircraft offer longer endurance and payload options, but their cost limited their selection for ABSOLUTE.
D. Helikites Characteristics
Helikites combine helium and wind lift in tethered aerostatic platforms suited to low-altitude communications. Their payload, endurance, cost, and regulatory characteristics support deployment in varied weather and operational settings, although aerial networks remain subject to extensive regulation.
- A Helikite combines a helium balloon and a kite into a tethered aircraft using helium and wind for lift.
- Helikites can fly at high altitudes in high winds and operate in several weather conditions because aerodynamic lift counters wind effects.
- Helikites can carry more payload than other aerostats in both high- and low-wind conditions.
- Helikites require no electrical power for a ballonet, lose little helium through their gas-tight inner balloon, and are comparatively inexpensive.
- Aerial-network operation is governed by platform category, control method, altitude, location, emergency status, flight safety, and spectrum-protection requirements.
- Regulatory challenges include licensing, interference with terrestrial services, and the need for further work on efficient spectrum use.
IV. AERIAL NETWORK IMPLEMENTATION
The implemented AeNB separates airborne radio equipment from ground-based baseband and core-network equipment, connecting both segments through optical fiber. The architecture was designed around a Helikite-mounted RRH and antennas.
- The AeNB architecture places most LTE base-station equipment in the ground eNB-BB and the radio-frequency equipment in an airborne RRH near the antennas.
- An optical-fiber link connects the RRH to the eNB-BB, reducing coaxial feed-line losses and increasing cell-site construction flexibility.
- Figure 1 presents the LTE-based aerial base station as a combination of airborne RRH and antennas with terrestrial eNB-BB, EPC, and satellite systems.
- The AeNB comprises an aerial RRH-and-antenna segment and a terrestrial eNB-BB, distributed EPC, and satellite segment linked by fiber.
A. Aerial Segment
The aerial segment integrates a Helikite with lightweight LTE equipment, antennas, batteries, and fiber-optic tethering to support airborne base-station operation.
- The Helikite carries the battery, antenna, and remote radio head, making the aerial segment the most challenging part of AeNB design and implementation.
- The 34m3 desert star Helikite combines helium and wind for lift and includes weather testing and an automatic GPS-integrated cut-down device.
- The remote radio head supports frequencies up to 6 GHz, optimized current consumption of 1.7-1.8 A, two transceivers, and cognitive spectrum allocation.
- Lightweight metalized-foam helix antennas were shaped for quasi-uniform cell illumination, with orientation, polarization, aperture, and MIMO requirements addressed.
- A pendulum mount maintains vertical antenna orientation despite balloon inclination, while a 500m flying line and twin-fiber cable connect the airborne system.
B. Terrestrial Segment
The terrestrial segment provides the LTE baseband and distributed core functions, connecting the deployable network to satellite backhaul and the airborne radio unit.
- The eNB-BB offers a cost-effective LTE solution for flexible terrestrial deployments and connects to the distributed-EPC for end-to-end management.
- The baseband cabinet contains a MicroTCA rack for eNB baseband boards, a server for distributed-EPC and SIP software, access peripherals, and routing and power equipment.
- The terrestrial cabinet connects by Ethernet to a deployable Ka-band satellite terminal and by optical fiber to the remote radio head.
C. Testing Campaign Results
The testing campaign evaluated user-equipment attachment to an airborne LTE-A base station and examined how aerial-terrestrial propagation differs from terrestrial communication.
- The initial campaign tested user-equipment attachment to an AeNB flying 25m above ground with 23 dBm transmission power.
- Measurements were collected for two different types of user equipment during the ABSOLUTE validation phase.
- Air-to-ground signals propagate through free space before encountering urban shadowing, scattering, and other man-made effects, unlike terrestrial propagation.
- The A2G channel model uses free-space path loss plus environment-dependent excessive path loss, with line-of-sight and non-line-of-sight propagation groups.
B. Optimal Positioning of Aerial Platform
Aerial-platform positioning requires balancing coverage benefits from higher elevation against increased free-space loss and energy demands, while clustering and relaying address network efficiency and outages.
- B. Optimal Positioning of Aerial Platform: Higher altitude increases the line-of-sight probability and coverage radius, but also increases distance and the free-space path-loss component.
- B. Optimal Positioning of Aerial Platform: The trade-off between free-space and excessive path loss permits altitude optimization for maximum coverage under a maximum allowed path-loss.
- B. Optimal Positioning of Aerial Platform: The ABSOLUTE demonstration limited platform altitude to 150m because of Helikite payload constraints, while mechanical properties and regulations constrain operational altitude.
- C. Clustering and Relaying: Clustering groups ground terminals so one node collects and forwards members’ information, significantly improving energy efficiency and reducing connection congestion.
- C. Clustering and Relaying: Relaying enables nearby user equipment to forward information from terminals with bad channel conditions, providing coverage extension and capacity improvement.
D. Wireless Backhauling and Self-organization
The aerial network uses wireless backhauling and self-organization to connect cells, monitor changing network conditions, and manage spectrum dynamically. A distributed EPC and cognitive radio functions support standalone aerial base-station operation.
- Wireless backhauling and self-organization: AeNBs use wireless backhauling for inter-cell and Internet connectivity in dynamic network conditions.The aerial base stations exchange information for handovers, network topology, and channel conditions.
- Wireless backhauling and self-organization: Cognitive algorithms assess network conditions and support radio resource management decisions.They provide awareness during network setup and help select suitable radio resources.
- Dynamic spectrum management: Dynamic spectrum sharing is considered because dedicated spectrum may not be available for future full-scale deployments.The intended system would share spectrum with an incumbent LTE-A system.
- Dynamic spectrum management: Spectrum sensing and a Radio Environment Map produce prioritized lists of unused LTE channels and sub-channels.The SDR collects occupancy measurements, while the database stores and processes radio-environment information for the target area.
- Standalone aerial base stations: Standalone AeNB operation requires a distributed EPC embedded near the base-station side rather than centralized equipment.The Flexible Management Entity virtualizes and decentralizes a simplified LTE core network for a single cell and its subscribers.
E. Limitations and Remaining Challenges
Aerial LTE-A deployment is constrained by mechanical, regulatory, access, testing, and power-system challenges. The paper identifies Helikite-based LTE-A as suitable for temporary events and emergencies, while several infrastructure and energy questions remain open.
- Limitations and challenges: Telecom equipment and aerial platforms are not designed for each other, making payload and energy constraints central to AeNB design.These constraints affect the access technology selected, the operating altitude, and the achievable coverage area.
- Limitations and challenges: Terrestrial access requirements constrain tethered-platform placement, while altitude and coverage raise cross-border, military, and civil-aviation regulatory issues.The terrestrial segment must reach the target area to use the AeNB’s ground coverage fully.
- Limitations and challenges: Limited testing and trial capabilities can restrict the preliminary results available for evaluating multi-AeNB systems.The passage connects this boundary to the cost of implementing aerial platforms.
- Helikite-based implementation: The ABSOLUTE design uses Helikites carrying battery, antenna, and RRH equipment, with a ground tether and optical-fiber connection to the eNB-BB.The paper presents Helikites as a longer-enduring, inexpensive, and easier-to-use alternative.
- Conclusions and remaining work: Helikite-enabled aerial platforms and LTE-A can provision Internet access during temporary events and emergencies.The solution could become more stable if onboard power reliability and efficiency improve, including possible powering over optical fiber.
- Conclusions and remaining work: Inter-aerial-platform links and efficient energy sources for communication equipment remain open research issues.The paper identifies these topics as future work.
BIOGRAPHIES
The biographies describe contributors from academic, industrial, standards, and aerial-platform backgrounds. Their experience spans wireless networks, future-network research, stratospheric platforms, 5G design, and Helikite operations.
- BIOGRAPHIES: Akram Al-Hourani is an RMIT PhD candidate with seven years of mobile-telecom radio-planning experience and ICT project-management experience.He has also received Australian government and Orange Labs scholarships.
- BIOGRAPHIES: Sithamparanathan Kandeepan is an RMIT academic and IEEE Senior Member with experience at NICTA and CREATE-NET.He has served in leadership roles within IEEE communications and cognitive-network organizations.
- BIOGRAPHIES: Tinku Rasheed leads the Future Networks R&D Area at Create-Net and works on wireless communications, end-to-end architectures, services, and patents.His background combines industrial and academic research experience.
- BIOGRAPHIES: Isabelle Bucaille has worked on digital processing, HiperLAN2 standardization, stratospheric platforms, secured wireless products, and 5G PHY and MAC design.Her career includes engineering and system-definition roles at ISEP and THALES Communications.
- BIOGRAPHIES: Sandy Allsopp designed the Helikite aerostat and has extensive experience manufacturing and operating aerostats and conducting radio-relay trials.He is also the holder of Helikite patents and designs.