The city grows downwards; communication cannot be left behind
Large-scale underground space follows from the way cities densify. From the surface downwards, transport, utilities and storage facilities stack layer on layer — and building, governing and maintaining all of it depends on a properly designed private communications system.
Conventional radio cannot carry underground governance
The underground environment makes maintenance genuinely difficult — a great deal of labour is spent for very little effect.
Equipment faults are always handled after the event, with no clear view of system state and a standing risk of communications going down.
Conventional radio carries voice only and cannot extend into the checkpoints of an operating process, which holds back everything built on it.
Consolidated zones make even a long, narrow space controllable
Different end coverage and access methods are chosen to suit the structure and function of each space, then consolidated at one zone node that provides signal access for every purpose. Zones run independently and in parallel and support roaming between them — which sharply reduces the risk of the whole system going down at once.
Converged digital multi-service network
A digital base station strengthens voice and data output, and transport is digital fibre end to end — bringing fire, operations and public safety networks together into one consolidated design, built for the long distances and later extensions a tunnel demands.
FM broadcast in, emergency override out
The moment a vehicle enters the tunnel it loses contact with the outside, and radio is the only channel still reaching the driver. The same RFoF coverage base that carries the private network brings FM broadcast into the tunnel — and lets the control centre override it with one action in an emergency.
Remote units have dual source inputs and receive the primary and standby signals at the same time, so a changeover does not interrupt transmission. OMU and ORU are cascaded into a fibre ring: where a star topology would leave part of the tunnel degraded after a fibre fault, the ring keeps everything working — and the interleaved dual-ring structure raises reliability further.
A 22-carrier channel-selective unit receives the FM signal, amplified through digital OMU and ORU to cover the full length of the tunnel.
The channel unit is controlled from the control centre, switching between FM broadcast and the override audio channel, with zone selection, audio playback or live microphone.
A client-server architecture keeps primary and standby databases in sync; a primary failure switches to the backup OCC automatically without losing override capability.
Receiving equipment in each tunnel polls audio quality on every channel, while the NetFlex platform monitors OMU and ORU parameters live and raises alarms.
Tunnel projects
From arterial city tunnels to underground complexes, the private network runs in service across a series of landmark projects.
Every section underground, inside the network
Tunnels, utility corridors, underground complexes — a consolidated zoned private network, built once and maintainable for the long run.
Tunnel system key facts
Leaky feeder + fiber
Continuous coverage along linear structures
FM injection
Public FM broadcast carried into the tunnel
Override
Operators can break into broadcast for evacuation messages
Section handover
Radios move between sections without manual switching
Tunnel and corridor coverage FAQ
The questions we hear most often on selection, certification and delivery.
Didn’t find your question? Ask an engineer →Fiber repeaters distribute signal along the tunnel and feed leaky (radiating) cable or antennas section by section, so coverage follows the alignment rather than depending on portal sites.
Yes. FM broadcast can be injected into the same distribution, and the control room can override it to broadcast emergency or evacuation instructions.
Yes. The same fiber and leaky-feeder approach is used for utility corridors, with ORUs placed per section and status reported to the management system.
Yes. Sections can be migrated one at a time, so operations continue on the existing system until each section is commissioned.