In short: PoC radio, push-to-talk over a cellular network, is the obvious replacement for the DMR and TETRA handsets that lose range between container stacks, but on a public 4G network it fails in the same places for a different reason. Ports that run PoC over their own private 5G network get the group-call features they wanted with coverage they control, and should still keep a direct-mode radio in the cab for the day the network is down.
Key Takeaways
- The stacks eat the signal — Six containers high is fifteen metres of steel, and a UHF handset on the far side of a block from its repeater is talking to nobody.
- PoC on a public network moves the problem — Push-to-talk over EE or Vodafone is only as good as the operator's coverage on the quay, which was planned for the town behind it.
- Private 5G makes PoC a port system — Radios sited for the terminal, priority for voice, and one network for handsets, cab terminals and cameras, with DMR kept for direct-mode fallback.
In a nutshell
What is PoC radio and why are ports looking at it?
PoC radio is push-to-talk carried over a cellular data network instead of a dedicated radio channel, and ports are looking at it because their two-way radio systems were built for a smaller, lower terminal than the one they now run.
A conventional port radio system is a fleet of DMR or TETRA handsets and in-cab units talking through one or more repeaters on the port's own Ofcom business radio licence. It is simple, tough and independent, and the handsets survive being dropped from a straddle carrier. Its weakness is physics. The repeater covers what it can see, and a modern container terminal is a landscape of steel boxes that changes shape every shift.
Push-to-talk over cellular replaces the repeater with a data network and the radio channel with an app or a dedicated PoC handset from Motorola, Hytera, Sepura or Tait. Group calls, talk groups, priority calls, location on a map, text, and now video, all ride on the same connection. The feature list is long and the hardware is cheap by radio standards. The question every port radio manager asks first is where the coverage comes from, and the brochures rarely answer it.
Why does walkie talkie range collapse in a container yard?
Because a container block is a moving wall of steel, and a handheld radio at ground level between two blocks has no line of sight to anything.
A standard container is 2.59 metres high. Stacked five or six high, a block is 13 to 16 metres of solid steel, hundreds of metres long, and the yard is made of dozens of them with lanes between. A UHF signal at 400 MHz, which is where most port DMR systems sit, penetrates buildings reasonably well but does not pass through a stacked container block; it goes round or over, losing strength on every bounce. Stand in a lane with the repeater mast on the far side of three blocks and the handset shows a full battery and an empty channel.
The ordinary fixes each have limits. Raising the repeater helps the middle of the yard and does little for the lanes. Adding repeaters means more licences, more masts and, in a DMR system, careful planning so that the sites do not interfere with each other. In-cab radios with roof antennas do better than handhelds, which is why the cab crews cope and the ground staff, lashers, checkers and reefer technicians, are the ones saying "say again" into a dead channel. The dead spots also move. A yard planner reshuffles blocks to suit the next vessel, and the coverage map drawn at commissioning is fiction a month later.
For the terminals that have automated part of the yard, the problem compounds. Remote-controlled cranes, reefer monitoring and pedestrian-detection systems each arrive with their own wireless requirement, and each is being asked to work in the same shadows.
Can PoC radio replace DMR or TETRA at a port?
For day-to-day operational voice, yes, and the larger UK terminals are already part way through the change. For the safety-critical fallback, not entirely, and the honest answer is a hybrid.
The features favour PoC. Talk groups can be created per vessel, per shift or per contractor in minutes rather than by reprogramming handsets. Dispatchers see every user on a map. A call to the first-aider can pre-empt the channel. Video from a handset at an incident reaches the control room. The 3GPP mission-critical push-to-talk standards, MCPTT from Release 13 onwards, define call set-up times and priority behaviour that match what TETRA users are accustomed to, and the blue-light services' own move from the Airwave TETRA network to the 4G-based Emergency Services Network, however late it is running, signals where the technology is going.
The counter-argument is real. A DMR handset in direct mode talks to another handset a few hundred metres away with no infrastructure at all. If the repeater fails, the yard still has radio. A PoC handset with no network is a brick, and a port evacuation is the wrong moment to discover that. Battery life on a cellular handset is shorter than on a radio. And the coverage question does not go away; it changes owner.
We think the terminals doing this well keep both. Operational voice, data and location move to PoC on the port network. A reduced DMR fleet stays in cabs and with supervisors, licensed and tested, for the direct-mode fallback and the emergency channel. Gateways from Motorola and others bridge the two so that a talk group can span both systems during the transition. The mistake is to treat it as a swap and decommission the radio licence in the first year.
Why does PoC on a public network disappoint on the quayside?
Because the public operators planned their masts for the town, the A road and the ferry queue, and the quayside behind the port fence is a low priority they cannot easily fix.
A port is a poor customer for a mobile operator. The ground staff who need coverage are a few hundred people on a few hundred acres that are mostly steel, and the site is hard to build in: masts need port approval, the geometry changes, and the terminal cannot stop for a cell-site installation. So the macro cells outside the fence do their best, and their best fails in the same lanes the UHF repeater failed in, with the added disadvantage that the port cannot move the mast.
Congestion adds to the shadow. A cruise ship alongside at Southampton puts several thousand phones on the same cells as the terminal's PoC handsets. A Dover or Holyhead ferry queue does the same. Public LTE and 5G give data users a fair share of capacity, and a group call set-up that takes half a second on a quiet cell can take several on a busy one, or fail. PoC on a public SIM from a UK operator works well in a town-centre depot and works badly on a quay, and we have listened to more than one radio manager who trialled it, concluded that PoC was the problem, and went back to a system with dead spots.
Roaming multi-network SIMs help at the margins by picking the best public signal available, but they cannot create signal where no operator has built, and they inherit every operator's congestion.
What does PoC over private 5G change?
It gives the port the coverage decision, which is the decision that made the old radio system work in the first place.
A private 5G network is planned for the terminal and nothing else. Radios go where the yard needs them, on light towers, cranes and the roofs of workshops, on Ofcom's shared access licence in the 3.8 to 4.2 GHz band at power the port controls. Coverage is designed against the stack plan rather than the town plan, and the port can add a small cell when the layout changes without asking anyone's permission. The result is a cellular signal in the lanes that the public operators could never justify and the UHF repeater could never reach.
Voice gets priority. A private core can give the PoC application a guaranteed slice of the network, so that a group call sets up in the time the MCPTT standard expects regardless of what the cameras and cab terminals are doing. That is the property a public network cannot sell to a single tenant and the property a port radio system always had.
The same network then carries everything else. The reefer monitoring, the checker's handheld, the straddle carrier's terminal-operating-system link, the pedestrian-detection cameras and the gate ANPR all share the coverage the port built for voice. This is why we consistently argue that a port should buy coverage once and run its systems over it, rather than tolerate a separate wireless island for each. PoC is often the application that first justifies the network, because voice is the one system every port already accepts it must pay for.
The trade-off is ownership. A private network is capital expenditure and an operations responsibility, and a small terminal or a fishing harbour with a dozen radio users will not justify it for voice alone. For that operator, an upgraded DMR repeater or PoC on a public SIM with a DMR fallback is the sensible choice, and we say so. The argument for private 5G is strongest at the container, ro-ro and bulk terminals where the yard is large, the steel is dense and voice is only one of six systems fighting for wireless.
What should a port keep from its old radio system?
Its licence, its emergency channel and its habit of testing.
The Ofcom business radio licence is cheap to hold and slow to reacquire, and a DMR channel in direct mode is the last-resort system that keeps working when nothing else does. Keep a fleet of handsets and cab units on it, keep the emergency talk group there, and keep the radio checks that every shift already does. Then move operational voice onto PoC over the private network, group by group, starting with the ground staff who suffer the dead spots most.
The first test is the one the UHF system failed. Take a PoC handset on the new network into the lane between the two tallest blocks, call the control room, and listen for the reply. If the network was planned for the terminal, the call connects. If it was not, the port has learned that before it moved the fleet.