Gabriel Bengo | Portfolio

At 8:42 p.m. the lights stutter on a campus. LTE drops to one bar. In the library, a first-year rubs his eyes—his sister is having an asthma attack, and he can’t reach an ambulance. His phone whispers to a nearby phone over Bluetooth, hops across a hallway of laptops, lands on a palm-sized LoRa radio by the window, and the message rides a sub-GHz chirp across the motorway to the hospital. No towers. No fiber. Still connected.

That’s the claim: a city-scale, offline-first network you can build with shelf parts—resilient in outages, cheap to deploy, and good enough for what matters most: messages, alerts, and coordination.

Bluetooth covers the last 100 meters; LoRa covers the last 10 kilometers. Dense, short-range device-to-device where people are; sparse, long-range backhaul where people aren’t. Together you get reach, redundancy, and absurdly low cost.

How It Works: Campus to Clinic

Phones talk to phones (local hops). Your app opens a peer-to-peer channel over Bluetooth. Nearby phones relay a few hops indoors—lecture halls, cafeterias, dorms. Note: iOS/Android don’t ship as full Bluetooth Mesh relays; you implement foreground/background scanning in the app, and—if you want reliability—sprinkle in tiny always-on relays (ESP32s) in hallways. Smartphones do not natively support the Bluetooth Mesh stack as mesh nodes; vendors provide provisioning/control apps, not system-level relays.
Pocket radios bridge to long-range. A R500–R1 200 (~US$25–$60) LoRa+BLE node (e.g., LILYGO T-Beam, Heltec WiFi LoRa 32 V3) pairs to a phone over BLE and forwards your text onto LoRa. These boards are widely sold in this price window.
Rooftop gateways hear kilometers away. A few outdoor LoRaWAN gateways on campus roofs hear those chirps for 2–5 km in urban conditions (10–15 km+ rural line-of-sight). This isn’t marketing fluff; range bands like ~3 km dense urban / ~15 km rural are repeatedly documented.
Cross the motorway, land at the clinic. Mount a low-power LoRa Relay node on a light pole or add a single additional gateway along the corridor. The LoRaWAN Relay spec extends coverage in hard corners; relays are limited to ~16 devices and aren’t gateway replacements, but they’re perfect for bridging gaps.
No internet? Still fine. Run a local LoRaWAN Network Server (LNS) like ChirpStack on a small PC—or even on the gateway OS—so messages route, queue, and deliver without WAN. ChirpStack Gateway OS includes an option with the full network server stack.

The Cost Breakdown

Indoor gateways (campus buildings, clinics): The Things Indoor Gateway typically US$79–$99.
Outdoor gateways (rooftops/masts): RAK WisGate Edge Pro typically US$372–$525 (model dependent). Kerlink iStation around €520–€570 ex-VAT.
Pocket LoRa+BLE nodes (for responders, patrols, RA desks): US$25–$60 per unit (LILYGO/Heltec variants).
BLE relay vitamins (ESP32 boards to densify halls): US$7–$20 each.
Power & mounts (PoE injectors, small solar kits for a subset, brackets), permits & labor: varies most by city.

Back-of-napkin for a mid-sized urban core (~400 km² with overlap):

30 outdoor gateways @ $450 ≈ $13.5k
30 indoor gateways @ $90 ≈ $2.7k
200 pocket LoRa+BLE radios @ $45 ≈ $9k
300 ESP32 relays @ $12 ≈ $3.6k
Mounts/solar/PoE/backhaul/permits/labor/spares ≈ $40–$55k

Total hardware + install: ~US$69–$83k. Depending on geography and mast access, you still clear the “~$100k to cover a city for text/alerts” claim with margin.

Why Africa Should Lead This Play

Spectrum alignment. South Africa—and much of Southern Africa—use the EU863–870 LoRa plan, simplifying procurement and roaming.
Load-shedding resilience. Small solar + batteries keep gateways alive; LoRa’s power budget is tiny and duty-cycle constrained by design (EU868 sub-bands commonly 0.1–1%), which encourages bursty, efficient traffic instead of brittle continuous links.
Public health and safety. Offline triage, ambulance-to-clinic updates, campus panic beacons, and civil-defense alerts continue even during wide-area outages or conflict when networks are targeted.
Industrial spillover. Once the backbone exists, water meters, leak sensors, power substations, and traffic telemetry ride for free.

Treat this like roads and water: public infrastructure. Governments fund the backbone; startups build the apps.

A Visual Walkthrough

Campus: phones create Bluetooth clusters in lecture halls; a few ESP32s keep hallways stitched.
Rooftops: two outdoor gateways blanket the campus.
Motorway: one or two solar relays or a single extra rooftop gateway bridge 8–12 km across a corridor.
Clinic: two gateways cover intake and emergency; a pocket LoRa radio at the ambulance bay bridges phones when LTE is saturated.

Result: end-to-end store-and-forward text in seconds to tens of seconds—without leaving the region.

Technical Deep Dive

Why LoRa Reaches When LTE Doesn’t

Modulation. LoRa uses chirp spread spectrum; you trade data rate for link budget. Typical data rates are ~0.3–50 kbps depending on spreading factor and bandwidth.
Sensitivity. With modern silicon, receivers hit ~−126 dBm @ SF7/125 kHz and ~−139 to −141 dBm @ SF12/125 kHz, which is why multi-kilometer urban and double-digit-kilometer rural links are ordinary.
Range reality. Expect ~2–5 km in dense urban and ~10–15 km rural line-of-sight; longer over water or high-elevation.

What Bluetooth Is (and Isn’t) Good For

Great at: fast device-to-device bursts, dense indoor hops, phone accessories.
Not magic: phones aren’t native mesh relays; your app must manage scanning/advertising and will hit OS background limits. Vendors themselves say smartphones don’t natively support Bluetooth Mesh as nodes. Also, plan for ~8 concurrent BLE connections on a typical phone. Use tiny mains-powered relays to stabilize the mesh.

A Resilient Architecture

Edge: Phones ↔ BLE ↔ pocket LoRa node (for people who move); ESP32 BLE relays for rooms that don’t.
Backbone: LoRaWAN gateways (8–16 channels) on campuses, clinics, civic rooftops.
Network server: ChirpStack local to the city/region; ChirpStack Gateway OS bundles the full stack option for running directly at the edge.
Coverage extenders: LoRaWAN Relay for dead spots; relays support a small set of devices (~16)—use judiciously.

Expected Throughput and UX

Payloads: texts + metadata (tens to a few hundred bytes) fit within LoRaWAN envelopes at practical data rates.
Latency: BLE hop (milliseconds) + LoRa time-on-air (hundreds of ms to seconds at high spreading factors) + possible duty-cycle queuing. EU868 sub-bands enforce 0.1–1% duty-cycle; design for bursts and backoff.

Security Model

App-layer end-to-end encryption (X25519 + AES-GCM; libsodium/Noise) so relays/gateways see only ciphertext.
Don’t repeat the Bridgefy failure mode (tracking, impersonation, DoS); that literature is clear.
LoRaWAN already adds network + application session keys; keep application keys off gateways.

Spectrum & Compliance in Southern Africa

South Africa: EU863–870 band; plan channels and duty-cycle budgets accordingly.

Bill of Materials (Starter Kit)

1× Outdoor gateway (rooftop, PoE) — RAK WisGate Edge Pro / similar. Unit cost: US$372–$525
3× Indoor gateways (CS building, library, clinic) — TTIG or SenseCAP M2. Unit cost: ~US$79–$120
15× Pocket LoRa+BLE radios (security, RA desk, clinic intake) — LILYGO/Heltec. Unit cost: US$25–$60
30× ESP32 BLE relays (hallways/common rooms). Unit cost: US$7–$20
1× Edge box running ChirpStack (NUC/RPi) or on-gateway ChirpStack OS
Mounts, PoE injectors, surge protection, a few solar kits

This is commodity gear. The scarce resource is deployment discipline: RF surveys, mast access, power, grounding, and a clean channel plan.

Policy: Build Corridors, Not Islands

Start with density. Fund five campus-clinic pairs. Roof gateways, corridor relays, one local LNS.
Open standards only. LoRaWAN + ChirpStack; app-layer E2E encryption.
Build a corridor. Stitch campuses to hospitals along motorways using relays and a handful of outdoor gateways.
Finance like infrastructure. Think streetlights: capex + modest O&M, with local firms building apps on top.
Train locally. RF survey + install skill in TVETs; procurement through local integrators.

The Physics: Does it Work?

Range: 2–5 km dense urban; ~10–15 km rural—documented across Semtech/TTN and vendor literature.
Data rate: ~0.3–50 kbps—exactly the envelope needed for reliable text/alerts.
Sensitivity: ~−126 dBm (SF7) to ~−139/−141 dBm (SF12) with modern chipsets.
Duty cycle: EU868 sub-bands at 0.1–1%; you’re designing for bursts, not streams—perfect for messaging and telemetry.
Cost: Indoor gateways at ~$79–$120; robust outdoor units ~$372–€570+. The city-backbone math pencils out under ~$100k for text/alert coverage.

Build This, and Make it World-Class

Ship the simple app: default to Bluetooth, escalate to LoRa, sync opportunistically when any phone sees the internet again. Be honest in the UX—“Messages may take ~20 s; photos queue until online.” Put a live mesh-health map on a wall where people can see it. Measure what you’ve built. Improve it. Then open the corridor to the next city.

Africa doesn’t need to wait for anyone’s permission to keep campuses, clinics, and neighborhoods stitched together when it matters—during load-shedding, undersea cable cuts, or conflict. This is radios, math, and civic will.

Somewhere tonight, on a campus, the message will get through.