Low-altitude airspace refers to areas extending up to 1,000 meters vertically above ground level, potentially stretching to 3,000 meters depending on regional needs, with current research prioritizing sub-600-meter altitudes. The low-altitude economy encompasses aviation activities involving both manned and unmanned aircraft, driving synergistic growth across manufacturing, operations, and service sectors. This economy spans agriculture, industry, and public services, characterized by extensive domain coverage, intricate supply chains, and diverse applications.
5G-Advanced (5G-A) Integrated Sensing and Communication (ISAC) technology embeds sensing capabilities within communication systems. It leverages existing spectral resources, hardware, and signal processing units to simultaneously enable data transmission and environmental perception. This integration enhances spectrum efficiency, hardware utilization, and information processing, forming a unified architecture as shown below. Compared to 5G, 5G-A delivers 10× higher peak data rates, ultra-low latency under 1 ms, and massive connection density exceeding 1 million devices per km², enabling robust low-altitude information services.
The proliferation of 5G infrastructure offers an ideal foundation for deploying ISAC-enabled networks. This synergy elevates low-altitude information services, enhances data sharing, and drives cost-efficient digital transformation for low-altitude economies. Critical applications include agricultural monitoring, aerial mapping, logistics, security patrols, emergency response, and live broadcasting.
Technical Requirements for Low-Altitude UAV Networking
Low-altitude UAV operations impose distinct technical demands across scenarios. Key metrics include throughput, latency, reliability, and positioning accuracy, varying significantly by use case:
| Application | Downlink Rate | Uplink Rate | Latency | Reliability | Positioning Accuracy |
|---|---|---|---|---|---|
| Agricultural Spraying | 500 kbps – 1 Mbps | 5 – 10 Mbps | < 100 ms | 99% | 1 – 3 meters |
| Aerial Mapping | 1 – 2 Mbps | 20 – 50 Mbps | < 200 ms | 99.9% | < 0.5 meters |
| Logistics/Inspection | 1 – 3 Mbps | 10 – 30 Mbps | < 50 ms | 99.99% | < 1 meter |
| Live Broadcasting | 300 kbps – 1 Mbps | 50 – 100 Mbps | < 200 ms | 99% | 2 – 5 meters |
| Formation Flying | 2 – 5 Mbps | 5 – 20 Mbps | < 20 ms | 99.999% | < 0.1 meters |
Control commands demand ultra-reliable low-latency communication (URLLC) with < 20 ms end-to-end latency, while video uplink requires enhanced mobile broadband (eMBB) up to 100 Mbps. Signal propagation challenges in urban canyons or dense environments necessitate advanced path loss modeling:
$$PL(d) = PL_0 + 10n\log_{10}(d) + X_\sigma$$
Where \(PL_0\) is reference path loss, \(n\) is the environment-dependent exponent, \(d\) is distance, and \(X_\sigma\) represents shadowing effects. Throughput is bounded by Shannon’s formula:
$$C = B \log_2\left(1 + \frac{S}{N + I}\right)$$
Here, \(C\) is capacity, \(B\) is bandwidth, \(S\) is signal power, \(N\) is noise, and \(I\) is interference—critical for optimizing low-altitude UAV performance.
Comprehensive Networking Strategy
Overall Deployment Architecture
Two primary models exist for low-altitude coverage, each with distinct trade-offs:
| Mode | Description | Coverage Height | Cost Efficiency | Interference Management |
|---|---|---|---|---|
| Mode 1 | Public network slices with User Plane Function (UPF)下沉 near flight control platforms | Below 50 meters | High (reuses infrastructure) | Challenging (co-frequency) |
| Mode 2 | Dedicated aerial base stations with isolated spectrum | 50 – 600 meters | Moderate (new hardware) | Optimal (frequency isolation) |
Mode 2 is generally preferred for dedicated low-altitude UAV operations due to superior interference control. The SINR (Signal-to-Interference-plus-Noise Ratio) is calculated as:
$$\text{SINR} = \frac{P_r}{\sum I_i + N}$$
Where \(P_r\) is received power and \(I_i\) denotes interference sources. Dedicated frequencies minimize \(\sum I_i\), crucial for urban deployments.
Core Network Architecture
ISAC integration employs two core network frameworks:
| Architecture | Sensing Function (SF) Placement | Latency | Scalability | Use Case |
|---|---|---|---|---|
| Tight Coupling | SF integrated within 5G Core (5GC) | Moderate (20 – 50 ms) | High (wide-area) | City-wide surveillance |
| Loose Coupling | SF collocated with Baseband Unit (BBU) | Low (< 10 ms) | Limited (localized) | Industrial campuses |
Tight coupling uses the Network Exposure Function (NEF) for capability openness, while loose coupling enables edge processing. The optimal choice balances latency \(L\) and data volume \(V\):
$$L \propto \frac{V}{B \cdot \eta}$$
Where \(B\) is bandwidth and \(\eta\) is processing efficiency.
Transport Network Strategy
Existing 5G transport segments are reused with network slicing:
- Fronthaul (AAU-DU): Carries I/Q data, latency < 100 μs
- Midhaul (DU-CU): Supports packetized data, latency < 10 ms
- Backhaul (CU-Core): Manages aggregated traffic, latency < 20 ms
Slice-specific resource allocation ensures QoS. For a slice demanding bandwidth \(B_s\) and latency \(L_s\), resources are reserved as:
$$R_s = \alpha B_s + \beta \frac{1}{L_s}$$
Here, \(\alpha\) and \(\beta\) are network-specific coefficients.
Radio Access Network Design
Key steps include:
- Site Planning: Density optimization using hexagonal cell models with radius \(r\):
$$r = \frac{c}{4\pi f \sqrt{\epsilon}}$$
\(c\): light speed, \(f\): frequency, \(\epsilon\): permittivity. - Antenna Design: Elevation beamforming with downtilt angle \(\theta\):
$$\theta = \tan^{-1}\left(\frac{h_{\text{BS}} – h_{\text{UAV}}}{d}\right)$$
\(h_{\text{BS}}\): base station height, \(h_{\text{UAV}}\): UAV altitude, \(d\): horizontal distance. - Interference Coordination: Dynamic frequency allocation using fractional frequency reuse (FFR).
Case Study: Metropolitan Deployment
A Yangtze River Delta city deployed 101 dedicated low-altitude base stations using Mode 2 (dedicated AAUs, 3.5 GHz + 4.9 GHz bands). Key metrics at varying altitudes:
| Altitude (m) | Avg. RSRP (dBm) | < -105 dBm Coverage (%) | Avg. Uplink Throughput (Mbps) | < 25 Mbps Areas (%) |
|---|---|---|---|---|
| 1.5 | -98.2 | 38.7 | 18.3 | 45.1 |
| 100 | -87.6 | 12.4 | 63.8 | 8.9 |
| 300 | -82.1 | 5.3 | 89.5 | 2.1 |
Performance improves with altitude due to reduced obstructions. At 1.5m, urban clutter causes severe attenuation modeled as:
$$L_{\text{urban}} = 20\log_{10}\left(\frac{4\pi d}{\lambda}\right) + \gamma d + L_{\text{building}}$$
\(\lambda\): wavelength, \(\gamma\): clutter loss coefficient, \(L_{\text{building}}\): building penetration loss. Future enhancements will integrate satellite networks for seamless coverage.
Conclusion
5G-A ISAC provides a foundational framework for scalable low-altitude UAV networking, addressing diverse requirements through integrated sensing, flexible core architectures, and dedicated radio planning. Field results confirm significant performance gains at operational altitudes above 100m, though urban canyons require advanced mitigation. As regulations evolve, cross-layer integration with terrestrial and non-terrestrial networks will unlock ubiquitous low-altitude connectivity, driving economic growth across logistics, agriculture, and public safety sectors globally.