Virtual Backhaul Connectivity for Enhanced Coverage in Fiber-Less Areas

• More than half the world’s population lacks proper internet connectivity, especially in rural and remote areas, limiting opportunities and motivating 5G-era Sustainable Development Goals to bridge the digital divide.Source: INTRODUCTION · p. 1
• By September 2021, only 30% of rural inhabitants could access full-fiber capabilities, with cost, terrain, and network design contributing to weak rural coverage.Source: INTRODUCTION · p. 1
• 5G NR’s IAB divides bandwidth between wireless backhaul and access and offers fiber-like speeds (“virtual fiber”), but still depends on fiber PoPs that constrain rural deployment,.Source: INTRODUCTION · p. 1
• Since Release 15 approval in March 2017, 3GPP has proposed integrating NTN—including LEO satellites and HAPs/LAPs—into 5G NR for wider coverage and throughput, potentially addressing fiber-less IAB constraints.These platforms have also been applied for emergency response, backhauling, data collection, and IoT in remote areas.Source: INTRODUCTION · p. 1

Rural and remote areas

• Rural and remote areas lack investment because low potential subscriber density limits returns, while long fiber routes and difficult last-mile terrain add costs.These areas also lack sufficient funds to build base stations and wireless networks.Source: EXAMPLES OF FIBER-LESS REGIONS · p. 2

Low-income neighborhoods in urban and suburban regions

• Low-income urban and suburban neighborhoods can be difficult to connect because unauthorized buildings are crowded together and access to resources such as the electrical grid is limited.Source: EXAMPLES OF FIBER-LESS REGIONS · p. 2

Post-disaster locations

• Natural disasters can leave locations fiber-less temporarily because damaged cellular infrastructure, including base stations and fiber networks, cannot be restored quickly while reconstruction planning proceeds.Source: EXAMPLES OF FIBER-LESS REGIONS · p. 2

IAB NETWORKS: VIRTUAL FIBER

• Terragraph and WeLink use mmWave for high-bandwidth service, deploy quickly and economically, and work best with line of sight (LoS),.Terragraph is described as “wireless fiber” or “virtual fiber” and as less costly than conventional fixed wireless access networks.Source: IAB NETWORKS: VIRTUAL FIBER · p. 2
• IAB can expand fiber networks and provide high-speed, low-cost coverage in fiber-less settings, including homes, schools, public safety, smart cities, and businesses.It can serve fixed users through fixed-access connections or Wi-Fi access points.Source: IAB NETWORKS: VIRTUAL FIBER · p. 2
• Client nodes (CNs) sit near buildings and connect customer equipment to distribution nodes (DNs); DNs link to each other and PoPs, supporting paths up to 15 hops.Because DNs provide both access and backhaul, optimizing their spectrum allocation can maximize network capacity.Source: IAB NETWORKS: VIRTUAL FIBER · p. 2
• Plan CN placement around customer equipment and PoPs, keep PoPs more than 250 m apart, and favor vertical sites where each DN can have multiple LoS links.Streetlights are typical DN sites; signal lights and utility poles are alternatives, though not every possible location will be usable.Source: IAB NETWORKS: VIRTUAL FIBER · p. 2
• Pre-install candidate DNs, remove those without PoP paths within 15 hops, then test traffic and capacity and optimize DN resource allocation through routing.DN density and PoP distribution affect the share of DNs that can form physical paths to PoPs.Source: IAB NETWORKS: VIRTUAL FIBER · p. 3
• Test the minimum share of pre-installed DNs to retain for each PoP so that unused nodes can be removed without wasting PoP capacity.Too few reserved DNs can prevent the actual network rate from reaching peak capacity.Source: IAB NETWORKS: VIRTUAL FIBER · p. 3

FWA and IAB

• Unlike FWA’s last-mile access role, IAB can carry FWA node connections over mmWave radios and enable network-wide fiber-less backhaul.The paper describes a joint radio/free-space optical design as a possible next-generation backhaul approach.Source: HYBRID IAB-BASED SOLUTIONS · pp. 3–4

Conventional IAB solution

• Conventional IAB offers low-cost, fiber-like-speed backhaul, but reliance on fiber PoPs can restrict service across fiber-less residential areas.Low-income areas may lack capacity for multiple PoPs, and PoPs may be border-limited to reduce cable costs; the proposed design can jointly use radio and free-space optical links.Source: HYBRID IAB-BASED SOLUTIONS · pp. 3–4

Hybrid IAB + NTN solution

• Hybrid IAB + NTN uses balloons and satellites to address fiber PoPs’ spatial limits and potentially reduce costs, but requires access to NTN platforms.The figure illustrates satellites assisting an IAB system in a residential block.Source: HYBRID IAB-BASED SOLUTIONS · p. 4, Figure 2 · p. 4

HYBRID IAB-BASED SOLUTIONS

• The paper proposes IAB and hybrid IAB-based solutions to enhance fiber-less-area connectivity and introduces concrete IAB use cases in the following section.Source: HYBRID IAB-BASED SOLUTIONS · p. 4

Rural and remote locations

• Rural networks can support smart agriculture and environmental monitoring, with LoS common on flat farms but less likely in forests or mountains.Rural areas generally span 1 km2 to 10 km2; DNs may use wind turbines, meteorological stations, and solar insecticidal lamps, and their positions may need manual adjustment. Agricultural-field mmWave path loss has been studied.Source: USE CASES AND PROOF OF CONCEPT · p. 4

Low-income neighborhoods

• Low-income urban or suburban neighborhoods can use backhaul for remote learning and smart transportation, with LoS possible between most DNs.These neighborhoods are often in areas larger than 10 km2; utility poles and streetlights can connect adjacent nodes, and mmWave channels in streets and residential areas have been tested.Source: USE CASES AND PROOF OF CONCEPT · p. 4

Post-disaster locations

• After disasters, IAB networks can help detect the environment and communicate to speed reconstruction, while temporary streetlights and utility poles enable rapid network restoration.These areas have often lost high buildings and base stations; temporary stable structures can provide LoS between adjacent nodes and support quickly assembled DNs.Source: USE CASES AND PROOF OF CONCEPT · pp. 4–5

USE CASES AND PROOF OF CONCEPT

• IAB and hybrid IAB + NTN can connect unconnected fiber-less areas and super-connect areas already served by communication networks.Both solutions can also complement existing communication networks.Source: USE CASES AND PROOF OF CONCEPT · p. 5

SIMULATIONS

• The simulation models a 4 km × 4 km residential area with LEO satellites at 160–2000 km altitude relaying between PoPs and the core network, using 15 dBW transmit power and shadowed Rician fading for satellite-PoP links.The study treats satellite PoPs as NTN-connected PoPs with reliable core connections; HAP/LAP PoPs are considered to have the same influence.Source: SIMULATIONS · p. 5
• The simulations compare fiber and satellite PoP distributions, including four fiber PoPs placed at block vertices or boundary midpoints, and define Wacs/Wwhole as the access-service share of each DN’s spectrum.Important simulation parameters are listed in Table I.Source: SIMULATIONS · p. 5
• When DN density exceeds 3×10−5 DNs/m2, connected-DN proportions exceed 80% in all strategies except four fiber PoPs at block vertices; four fiber PoPs at boundary midpoints perform better than at vertices.Below 2 × 10−5 DNs/m2, uniformly distributed satellite PoPs connect more DNs than fiber PoPs.Source: SIMULATIONS · p. 5, Figure 3 · p. 5
• As access service occupies a larger share of each DN’s spectrum, the minimum proportion of DNs needed to use PoP resources decreases; at fixed PoP number and capacity, satellite PoPs support more DNs successfully than fiber PoPs.This comparison uses DN density = 5 × 10−5 DNs/m2.Source: SIMULATIONS · p. 5, Figure 4 · p. 6
• At Wacs/Wwhole = 1/6 ≈1.67, an IAB network with 16 satellite PoPs can support at least 1000 CNs with 50 Gbps throughput; at half-spectrum access, only CNs near one-hop DNs are stably supported.The capacity comparison assumes a pre-installed DN density of 5×10−5 DNs/m2 in a 4000 m × 4000 m area.Source: SIMULATIONS · pp. 5–6, Figure 5 · p. 6

Challenge 1. Lack of incentives and regulation

• IAB deployment requires authority approval and professional technicians to manage backhaul networks, placing requirements on operator services.Source: CHALLENGES · p. 6

Challenge 2. Pre-deployment strategies of different scenarios

• Different IAB and hybrid IAB-based solutions create distinct opportunities and challenges, while feasibility depends on regulatory decisions about fiber PoPs and support from satellites, LAPs, or HAPs.Hybrid solutions can overcome spatial limitations to obtain better actual network capacity, making pre-deployment choices difficult.Source: CHALLENGES · p. 6

Challenge 3. Network design optimization

• Individualized or adaptive spectrum allocation is harder and more expensive, while resilient operation may require each DN to connect to more than two neighbors.Adaptive routing and NTN assistance can also improve network resilience.Source: CHALLENGES · p. 6

Challenge 4. LoS

• Terrain, road signs, or buildings can block line of sight between adjacent DNs, complicating construction even where fiber-less areas generally satisfy LoS conditions.The paper identifies LoS as important for stable DN connections, particularly in rural areas.Source: CHALLENGES · p. 6

Challenge 5. Energy efficiency

• Daily access and backhaul services require substantial energy; grid-connected streetlights, solar power, and energy-reducing adaptive routing are possible mitigations.Source: CHALLENGES · p. 6

Challenge 6. Decrease in node capacity

• Real-time multi-hop routing can fully use a DN’s capacity for forwarding, reducing how many CPEs and CNs can access the backhaul system.Source: CHALLENGES · p. 6

Challenge 7. User fairness

• Providing users in different locations of the same residential area with the same good QoS remains a fairness challenge that routing and spectrum management may address.Source: CHALLENGES · p. 6

Challenge 8. Vertical integration

• Vertical management of terrestrial and non-terrestrial operator resources can increase throughput and reduce hybrid IAB + NTN costs, but faces market competition and resource-allocation challenges.Source: CHALLENGES · pp. 6–7

CONCLUSION

• When access spectrum is 0.1–0.25 of total spectrum, the most CNs can connect to the core network; a lower access-spectrum proportion lets more DNs work simultaneously.The study considers unified spectrum pre-allocation and examines the minimum reserved-DN proportion under different allocation schemes, including the minimum pre-installed-DN proportion PoPs can serve during congestion to optimize actual network capacity.Source: CONCLUSION · p. 7
• Sufficient pre-installed DN density establishes paths to PoPs for most DNs, while NTN topology flexibility enables more efficient backhaul paths and reduces link-testing cost.Source: CONCLUSION · p. 7
• Conventional IAB relies on fiber PoPs, whose capacity is difficult to fully utilize topologically, especially in low-income areas; hybrid IAB uses HAPs, LAPs, and satellites.Source: CONCLUSION · p. 7
• The article discusses the characteristics and development needs of fiber-less regions and the challenges facing IAB solutions.Source: CONCLUSION · p. 7