What is PTT Over Cellular Radio

Conventional radio systems normally have one or more radio channels assigned to them to operate on. these channels are often assigned by government bodies to each user, and a licence fee is often charged. Range of these conventional system is often limited to a few Km or tens of Km unless expensive infrastructure is installed with multiple radio sites and high equipment costs.

Although there is still a place for these conventional radio system, The new PTT over cellular technology can offer a real alternative to conventional radio with virtually no limit to range and very low hardware and running costs.

PTT over cellular stands for (Press to talk over cellular) sometimes abbreviated to PoC or referred to as Network radio. these radio units often look the same as a conventional radio but utilise the GSM mobile phone network as a relay station to relay calls a few meters, up to hundreds even thousands of Km.

A Poc handset or Car mount radio is effectively a mobile data device, Devices come in many form, but essentially they have a SIM card inside and connect to one of the Mobile network operators to provide the service. For a POC device to work it must have 3 things.

1) A GSM ideally 3 G or 4 G mobile phone network

2) A sim card to send data over that network or multi network SIM card

3) a POC server that  relays the calls.

FACTORS TO CONSIDER WHEN CHOOSING CONVENTIONAL RADIO OR PoC

Conventional radio advantages

  • Total independent of any network so will work regardless of location
  • when used in a single country running costs are low.
  • Fast connection time and minimal delay in voice traffic

Conventional radio disadvantages

  • Range of a basic system can be limited to a few Km so full track coverage cant be guaranteed unless a repeater booster is used. 
  • Repeater boosters are expensive and need to be re configured if you have to change radio channels (typically when traveling abroad)
  • A radio licence is required for each country the system is used in, this can be expensive and time consuming to compete in Europe and internationally.
  • The radio channels used for digital radio are extremely condensed, this presents problems getting clear communications in very noisy environments.
  • interference from other radio users can be a big problem and can result in missed calls.

PoC advantages

  • Greater range than Conventional radio as long as there is good mobile network coverage.
  • Clearer speech with high quality audio and tolerates high noise better.
  • Greater flexibilty for multi car teams, users are able to monitor multiple channels without the need for channel scanning.
  • Users can be given specific rolls, like engineer, crew,  car, manager or listen only. a specific roll can be assigned access to differnt channels and be assigned a priority level. Priority levels allow high prority users to override low priorty user calls.
  • Sytem configuration via a web portal. This allows sytem re-confiuration live, and changes made to each user with over the air programming.

PoC disadvantages

  • PoC calls have a short delay, from when the user talks to when  it is heard by the other team members. this is called latency. Typiclly this delay is around  500 miliseconds and not noticable during conversations on track.
  • PoC is reliant on good 4 or 5G network coverage, at race tracks this is normally not an issue, we use roaming Sim cards so if one network is not avaialble then another can be used.
  • If the network used is very congested then the latency time may be extended, this is very rare but can happen.