A two-way radio is one that allows you to transmit and receive, that’s the difference with the radio devices that we have at home that allow us to listen to the music or keep informed. In this way, through one of these terminals, users can have a conversation with other similar terminals, as long as they are in the same frequency.
Within this communication method, in a conventional system, if the user wishes to talk to another one, he should do so through the channel that has been previously assigned to him, and if it’s busy, it will be impossible to transmit his message. In the same way, If at a given time he wants to communicate with a different group, he should manually change the channel.
In front of this, the trunked (or cellular) one is a two-way system that, unlike conventional systems, uses a channel access control to dynamically manage the traffic.
It is therefore a more automated and complex system, but it adds interesting advantages, such as a greater spectrum efficiency and a higher number of users. In this system, users don’t depend on a specific channel to transmit their messages, they share all the frequencies and, if one of them wants to talk, the system dynamically provides him a free channel to do so. If at that moment, there weren’t any free channel, he would be allocated to a queue till one of them was released.
Let’s see an example. In a bank office, there is only one queue in which clients wait their turn, and the first in the row have to go to the first available window. In a conventional radio system, using the same example, each customer should go to a window that have been previously assigned, y he would have to wait if his window were busy, although the other were completely free.
But, in addition, the trunked system offers more advantages, such as that it’s possible to develop more conversation groups with different combinations of users regardless of the number of channels, just taking advantage of the times when they are not used. Furthermore, you can stablish priorities for some calls or send short messages without occupying the channel.
As a summary, in conventional systems there isn’t infrastructure to manage the connection among the different terminals, and the terminals itself connect each other or, at the most, through a signal repeater. Because of this, the scope of the communications depends on the transmission RF power of the terminals, and the conditions of the operation land.
On the other side, the infrastructure that manages communications does exist in cellular systems. In this way, communication flux is: Source terminal – nearest base station- switching node – nearest base station – destination terminal. This makes it more suitable for regional or national deployments, allowing calls from devices that are very far away from each other, something that would be impossible to do radio to radio.