Some of the first commercial DMR Tier III trunked radio networks in the world – if not the very first – can be found in the Central American republic of Guatemala, where a variety of radio systems for public and private users are operated by a local company, Corporación Radio Electrónica (Crelosa). Their General Manager is Stuart Scott, who, as a new electronic engineering graduate, started the company in 1988 to provide communications for a family business.

Crelosa today

Since starting Crelosa, he has gathered experience of a whole spectrum of two-way radio technologies, from basic two-way radio upwards, pioneering trunked radio technology in the region and installing systems by the score. Among these have been community repeaters, proprietary trunked systems, the British-developed MPT1327 standard, the US LTR and LTR-net trunking technologies, plus add-on features such as telephone interconnects. 

“I grew up with radios and I really love radios. It’s such an amazing thing to work with radio.”

Today, Crelosa’s operations incorporate 19 DMR radio sites, on which it bases six shared-subscriber networks and 14 private systems. Among their customers and users are government bodies, police, firefighters, and Transurbano, Guatemala City’s integrated metropolitan transit operator.

Transport and telemetry

Mr. Scott singles out Transurbano as making particularly full use of DMR technology – beginning with its backwards compatibility with analogue trunking. “We’ve got more than 1500 units working on the DMR system, most of them installed in buses”, he explains. “They started using analogue and then finally we changed them to digital – and the difference between digital and analogue was huge.”

“We use telemetry, text messaging and GPS. Everything has been Hytera. We created our own application to manage our clients’ needs, especially for this client itself. We do data intensive systems – for example, GPS positioning. I believe GPS works really well with DMR.”

With telemetry capability, Crelosa has been able to help with revenue protection as well as fleet management. 

“Remember, on the buses you have an entrance and an exit”, Mr. Scott explains. “The idea is for people not to enter through the exit, because you can get a free ride easily if you enter through the exit! 

"So telemetry tells you two or three things: first of all, when the exit door is open, it tells you; it will tell you when the exit button is triggered. If the exit button is triggered and the door does not open, you’ve got a problem. And if the exit door opens and you did not hit the exit button, you’ve got a problem. So basically it will tell you when things are not working properly.”

“The other telemetry is emergency or panic buttons. We have two panic buttons – one at the rear and one at the driver’s side. You press the panic button and automatically it will show the guy at the monitoring centre that there is an emergency. This happens!”

“The guy in the monitoring centre presses a button and is able to make the microphone on the bus go live for a specific time. We have installed it for 30-second transmit, then a 10-second delay, and then he can talk to the guy. And then the system automatically goes back into transmit mode."

“This way”, he continues, “the driver can communicate with the monitoring centre, without pressing the PTT or making any other intervention. Crelosa has exploited DMR’s telemetry capabilities at its own radio sites too." he adds.

“At every repeater site that we have, even though we have microwaves and we have video feeds and everything, we have hooked up a digital radio with telemetry so that it tells you when they open and when they close the doors of the repeater site. And there’s another one when they arm or disarm the alarm of the repeater site. We can see when they open the door or when they close it.”

And he offers an afterthought: 

“Remember, I’m not a factory, I’m a customer – I’m buying things and testing all the radios. We test all the radios here really well.”

Confidential comms

“With digital, it sounds loud, it sounds good”, Mr. Scott declares. “We don’t have any more hisses and whistles.” But DMR has brought other important benefits for customers such as the firefighters, because their radio traffic during an incident can no longer be intercepted through scanners or stolen radios.

“The firefighters changed to digital after having a lot of problems with conventional, not only because of the coverage itself but because of the intrusions”, he says. “Firemen wanted to be more secretive in their communications because somehow when they got there, there was someone else before them.” 

Reporters from the tabloid press and even representatives of funeral homes often arrived suspiciously early on the scene of an incident.

“They needed a confidential system,” Mr. Scott sums up. “And the cheapest and most efficient system is DMR. We sat down with them. We saw Tetra (for them it was off the market, very expensive); we saw Apco 25 (very expensive as well, because the terminal units in Apco 25 are far gone in pricing). So they decided to go with DMR.”

Pseudo trunking

After testing DMR radios from a couple of manufacturers, the firefighters decided upon a Hytera system – and a major reason for this choice was the doubling of capacity made possible by Hytera’s support for ‘pseudo trunking’ or ‘dual-slot trunking’. 

“If one slot is occupied, then the radio will use the next one”, he explains. “It’s not a great solution because it only gives you one more timeslot – but in reality that makes a world of difference to the client."

“Normally the system works in Timeslot 1. You program all the units there, so that your units normally are figuring out if Timeslot 1 is occupied. If it is occupied, automatically they will go to Timeslot 2. And the receiving radios will continue to sample either of the timeslots."

Though the digital signal is inherently resistant to eavesdropping, a DMR feature especially welcomed by the firefighters is its digital voice encryption capability. 

“Hytera has one of the best encryption protocols in the market because you can have, on DMR, three scenarios: 16 bits, 128 and 256 bits. We’ve given them the capacity to change their own keys by themselves. This way, the client himself is able to control the privacy in their communications."

Connecting with IP

Another Hytera system feature he values is the ability to interconnect repeaters using IP data links, enabling wide-area coverage to be provided simply. 

“Once you operate pseudo-trunking single-site, the first thing that your client wants is more coverage”, he explains. “That means that you have to install repeaters.”

“The interesting part here is that the Hytera product has the automatic roaming capability installed into the system, without an extra option. When we buy from the factory, it comes in with all the bells and whistles, so it’s easier for us just to program whatever we need.”

“But the scenario of roaming works really well. Here’s an interesting hint: there is something called beacon programming on the repeater. It means that if no one is speaking – if there’s no traffic flowing through that repeater – the repeater has to have a beacon to tell any radio scanning on DMR that the repeater is on, and it’s working and it’s ready to receive signals. This way, the radio can actually do the roaming into that site.”

“That is a big tip”, he laughs. “Either you have a client who actually uses a repeater so that the radio can find it, or you do your beacon very often.”

But he continues: “DMR wide-area networking has a wonderful capacity for management and administration, simply because you are able to programme all the repeaters on the radio. You can even tell it that, for example, your radio can only access Repeaters 1, 2 and 3 – not 4, 5 and 6. We can do that. And if you want 1, 5, 6 – not a problem.”

“If the radio gets stolen, we can turn it off or radio-kill. We can take that ID off the system, so he will not be able to get into the system and communicate.

Traffic loading

A conventional, one-slot trunking system can support up to 45 radios and three or four company fleets, Mr. Scott finds, although even that modest level of loading can lead to contention. “On pseudo-trunking, you can actually pump the system up to 75 units and have about 6–7 companies operating with almost no collisions whatsoever”, he says. “But here is one of the factors that made a big difference with Hytera. Pseudo-trunking gave us an edge on loading capabilities with our clients.”

“Obviously you have to be very efficient in choosing, because you cannot choose two taxi companies on the same system, because they are going to flood it! But you have to mix and match and be very comprehensive upon the type of client you are going to use with the pseudo-trunking system.”

Split affections

For Crelosa, a very special feature of Hytera’s DMR radios is their support for unconventional transmit/receive frequency splits. These are commonly required in Guatemala and other Central American countries, in place of the tidy 10 MHz or 5 MHz splits usual in Europe. “Specifically, for Guatemala, you’d sometimes get 1 MHz while sometimes you get 3 MHz and sometimes you get 10 MHz”, Mr. Scott observes. “Well, my friend, welcome to Guatemala.”

The solution to this problem, he continues, is simple enough: you approach your radio manufacturer and you ask them to change their entire programming scheme.

“Well, Hytera did it”, he adds. “And Hytera, in version 2.0, will have that difficult channel split. For that, with humility, I have to thank the people at Hytera, because they have been listening to me.”

Customer challenges

Crelose was originally running analogue, LTR and digital mobile services for business and government. With the growing demands in communication, Crelosa gradually realised the inferiority of analogue in communication and data services. End users often complained about its network due to unclear audio quality and blind areas in communication. Some taxi services held back from using it because it couldn’t provide GPS in large capacities. 

Public Safety users didn't want to continue with the service due to the high rent of the P25 equipment. So Crelosa decided to replace the existing network in stages with Hytera DMR Trunking Pro.

Hytera working with Crelosa

  • Hytera DMR Trunking Pro based on Hytera infrastructure was adopted for Crelosa in 2012.
  • At the first stage, four DMR trunking base stations were installed to cover the centre of Guatemala.
  • Compared with the analogue network, the newly built DMR trunking system provides double the user and traffic capacity, which can support more than 4,000 end users.

Solution highlights

  • DMR Trunking Terminal – Besides superior audio quality, a major feature for Hytera DMR products is the doubling of capacity, which gives customer an edge on loading capabilities. And the TDMA two time-slots technology, which improves battery saving, is also welcomed by the customer. 
  • Powerful Dispatching Capability – Another Hytera system feature the customer values is the ability to interconnect network using IP data links with Hytera's DWS dispatching system, enabling versatile data services like SMS, status message and GPS data to be provided simply.
  • Remote Network Management – With the network management system, Crelosa is able to realise remote user management and status monitor at the control center, even through all the base stations are installed far away from the city center.
  • Large Network Coverage – Adopting tri-diversity receiving and large coverage technologies, Hytera DMR trunking Pro perfectly meets the customer's coverage requirements.

“I have fallen in love with Hytera because of the way Hytera works – they bring you into a family. That’s very difficult for me to explain, but it’s a family feeling that really pushes you forward into much, much more than a business relationship. I have had G S Kok here, the head of engineering, asking personally what I would prefer to have in our next radio. And everything that Hytera has promised to me, it has come true."

Stuart Scott, General Manager
Corporación Radio Electrónica (Crelosa)
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5 January 2017