Citizen-operated MANET with Wifi HaLow

September 2025

A recent DIY build showed a sub-$110 node delivering core behavior of far pricier tactical radios¹. This article documents a layered MANET using 802.11ah (Wifi HaLow) for the IP backbone, LoRa/ELRS for telemetry, and optional analog VTX for low-latency video, with hot-swappable power and a hardened enclosure. The goal is straightforward: resilient, permissionless networking using unlicensed spectrum and parts anyone can buy.^[2]

High-level design

Such system may separate roles by bitrate and reliability. A HaLow backbone carries IP traffic and apps. A low-power LoRa/ELRS plane persists presence, GPS, and commands when links degrade. An optional analog VTX path carries instantaneous video outside the IP mesh to sidestep duty-cycle and QoS contention. Nodes self-form and self-heal; any node may inject internet if a Starlink or LTE modem is attached. The result is a topology that continues to coordinate even when the backbone is impaired, and that scales by adding radios and antennas rather than bespoke infrastructure.

        ┌───────────────┐
        │  Internet GW  │◄──── Starlink/LTE
        └───────┬───────┘
                │
        ┌───────▼────────┐     Optional Analog VTX
        │   HaLow IP     │◄──────────────────────────► Cameras
        │   Backbone     │
        └───────┬────────┘
                │
        ┌───────▼────────┐
        │  Local Wifi    │  Phones/Laptops/ATAK
        └───────┬────────┘
                │
        ┌───────▼────────┐
        │ LoRa/ELRS C2   │  GPS/telemetry/commands
        └────────────────┘

Hardware stack

A node could center on a Raspberry Pi 4² for driver maturity and power draw that remains manageable with two 21700 cells. The HaLow interface is a Mini-PCIe module (e.g., WM6108-class) on a Pi HAT or USB-bridge; local access uses the Pi’s 2.4/5 GHz radio or a USB NIC for better antennas. Telemetry attaches via SPI/UART LoRa or ELRS modules. Analog VTX is a separate transmitter at 5.8 GHz (or 900 MHz where permitted). The enclosure is 3D-printed ASA with gasket channels and bulkhead RF connectors; with O-rings and gland fittings the design meets IP67 for rain and immersion tests, provided pressure equalization and thermal paths are handled.^[4]

Power comes from a dual-cell UPS HAT with parallel 21700 slots. Parallel wiring keeps bus voltage constant while summing capacity; the HAT performs seamless source switchover between cells and USB-C input. This enables hot-swap with no downtime by replacing one cell at a time. The only caveat is voltage sag if the remaining cell is near empty or of poor quality; decent INR/IMR cells and conservative cutoff thresholds remove the edge cases.^[5]

For fixed sites, a 12 V LiFePO4 pack and DC-DC rails power the node, RF amplifiers, and an outdoor HaLow panel. Solar charge controllers fit naturally in this topology.

RF and PHY choices

Wifi HaLow (802.11ah) runs in sub-1 GHz ISM^[6] 902-928 MHz in the US, 920-928 MHz in Japan, and 920-925 MHz in Taiwan. Narrow channels and OFDM provide range and penetration superior to 2.4/5 GHz while sustaining megabit-class throughput. In practice, field links with modest antennas deliver single-digit Mbps over kilometers line-of-sight; urban clutter shortens reach but remains usable. Some regions apply duty-cycle or EIRP constraints; continuous HD streaming is unwise unless rules allow and links are engineered for it.^[7]

LoRa/ELRS form the low-bitrate plane. LoRa’s chirp spread spectrum trades speed for reach and energy efficiency; ELRS favors fast control loops. Both move GPS, text, and sensor data at kilobit scales across wide areas and keep the mesh coordinated when the backbone is saturated or jammed.

Analog VTX at 5.8 GHz gives near-zero-latency video for piloting and situational awareness. It is simple and proven but unencrypted; keep it for observations, not sensitive feeds. Running video out-of-band prevents IP congestion and avoids HaLow duty-cycle headroom issues.

Antenna selection matters more than radio choice. Omnidirectional stubs serve client access; directional Yagi or panel antennas on HaLow lift SNR and push range. Use low-loss coax, weatherproof bulkheads, and verified impedance matches.

Software stack

OS and device layer

OpenWrt provides a small, router-centric base with LuCI for field changes. When a full Linux is preferred, Debian-based images work fine; keep services container-light and disable anything not required. GPIO and I²C buses expose power and thermal telemetry for graceful throttling.

Mesh and IP policy

B.A.T.M.A.N. advanced simplifies mobility by presenting a virtual L2 segment. For larger or more mobile topologies, OLSRv2 or BMX7 at L3 keeps broadcast storms in check and gives more predictable routing under churn. QoS rules prioritize LoRa/ELRS gateways and push-to-talk over bulk transfers. Shaping with tc prevents single flows from monopolizing air time.

Clients ─► Local Wifi  ─► br0
                    ┌─────────────┐
HaLow (ah0) ────────┤ bat0 (L2)   ├──► wg0 (E2E tunnel, optional)
LoRa/ELRS GW ───────┤ policy tags ├──► ifb (shaper)
                    └─────────────┘

Security

Link-layer protection starts with WPA3-SAE for simplicity. For higher assurance, WPA3-EAP-TLS enforces mutual certificate authentication against a small RADIUS/PKI running on a gateway node. End-to-end encryption rides over the mesh with WireGuard or IPsec. Private keys sit in a hardware secure element (ATECC608A or a TPM) to reduce key-exfiltration risk if a node is captured. Certificates are short-lived and renewed through a bootstrap token flow.

Services and apps

ATAK works well over the mesh, benefiting from multicast for markers and presence. Voice rides on Mumble/Opus or a slim WebRTC PTT. A gateway node can run a caching proxy for repeated fetches, an MQTT broker for telemetry, and a small registry for service discovery. Internet injection is just NAT and a default route advertisement from the gateway node.

Power and hot-swap behavior

The UPS HAT presents a regulated output to the Pi while charging cells from USB-C. With parallel cells, removing one leaves bus voltage unchanged; the surviving cell takes the entire load. Hot-swap then becomes a four-step cadence: pull one, insert fresh, pull the other, insert fresh. To avoid brownouts, set conservative swap thresholds, log undervoltage events, and observe recovery curves of chosen cells. For unattended sites, LiFePO4 packs, shunt gauges, and a small supercap buffer during RF bursts keep rails stable.^[8]

Performance envelope

Expect a kilometer-scale HaLow hop with omnidirectional antennas in mixed terrain; with elevation and panels, several kilometers at modest MCS. Throughput sits in the 1-10 Mbps range per hop under typical settings. Latency resembles Wifi and supports PTT and interactive apps. LoRa/ELRS persists presence at a few kbps regardless of backbone health. Analog VTX adds the immediate video path that IP often can’t match under tight duty-cycle or interference.

Regulatory stance

Operate within ISM limits for your region. HaLow’s allowable channels and power differ by jurisdiction; analog VTX allocations vary as well. Plan for interference and coexistence. If you add RF amplification, keep filters tight and logs auditable. Permissionless does not mean undisciplined; spectrum etiquette preserves utility for everyone sharing the band.^[9]