Mass simulcast paging

Many public safety organisations are wary of relying on mobile phones to communicate quickly with staff – though paging is seen as ‘old’ technology its ability to reach numerous staff members simultaneously and penetrate remote areas and indoors makes it an attractive option

Mass simulcast paging

For a decade or more, radio paging has been seen by many as a has-been technology, the poor relation to mobile telephony. And yet paging has stubbornly refused to fade away, and is now actually attracting renewed attention.

Throughout that time, paging has remained common in hospitals and medical centres where, as an individual or team alerting technology, it is favoured because it poses little threat of interference with sensitive medical electronics.

However, it is in the wide area, simultaneous mass communication role that paging is now being re-cast, and this is because there are some things that simulcast paging does uniquely well. As governments and civil emergency organisations focus on how to respond to challenges including increasing terrorism and natural events such as earthquakes and extreme weather, those unique qualities of paging are once again pushing it centre stage.

For many types of emergency situations, public safety organisations have no initial need for two-way communications. Often what’s needed upfront is simple, quick and ultra-reliable distribution of  the ‘what, where and when’ details of an incident to the people who need to know.

Such information is by definition mission-critical. Mobile phone networks suffer from congestion issues during high volume traffic conditions, such as during an emergency, and even in times of light loading they are unable to guarantee delivery of messaging and voicemail.

At Sacramento County in the US, which deployed its own private simulcast paging system to alert fire, police and medical response teams, telecommunications supervisor James Marshall expressed the problem in blunt terms: ‘Cellphones are not a viable method of paging. If you send a voicemail message to an individual, it can be anywhere from two minutes to two hours before that message goes through.’

Paging is able to achieve the guaranteed immediacy that messaging by mobile telephony simply cannot. It works in locations where other messaging technology often struggles to achieve coverage, penetrating remote areas, underground and within buildings. Simultaneous delivery to tens, hundreds or even thousands of people is typically made within five to 30 seconds.

Moreover, networks can be cost-effectively configured with built-in redundancy so that in the event of a natural disaster or some other event destroying one or more transmitter sites, coverage is still sufficient to deliver vital messages to every person.

Even allowing for the additional cost of building in such fault tolerance, paging is comparatively much less expensive to buy and operate than mobile telephony. These lower costs mean self-ownership and self-operation of mass paging is becoming increasingly common as large organisations realise they can afford to insulate themselves from the potential uncertainties of services provided by third parties, and ensure conflict-free, instant and fully redundant communications.

Simulcast paging

So, what does a contemporary simulcast paging system look like and what are its key attributes?

In the Middle East, multiple types of national paging services are provided to government agencies and other users by a private operator – among its clients are first responders, police, rescue and security organisations, plus news and media companies.

The operator in question was faced with a dilemma when its technology vendor revealed that due to declining demand it was ending support for its paging platform. This not only threatened the stability of the network but also undermined the plans for expansion. Having such a vital national resource effectively frozen in time, and at the mercy of equipment failures, was simply unacceptable, so the operator began an urgent search for ways to update its network.

The solution it found was a high-speed Simulcast Paging System, the latest generation of a product line from Zetron that has a 25-year track record of reliable service around the world. The system uses GPS timing information to synchronise the transmission of digital signals to within microseconds and comprises a source unit, the Model 600 Wireless Data Manager, and destination units, known as Model 620 Wireless Data Encoders.

The link between source and destination units is any type or combination of types of link that can reliably transport data. The system is designed for non-proprietary transmitters, so it’s ideal for the cost-effective build-out of new transmitter sites for public or private paging system operators, as well as for upgrading existing sites. 

Standard features of the Zetron system included encoding for POCSAG (512, 1200 and 2400 baud) and basic FLEX (1600), support for up to 1,000 destinations with TNPP routing and zoning capabilities, multi-frequency transmitter control, Trimble Acutime 2000 compatible GPS interface, traditional two-level digital transmitter interface, and multiple user-definable input/output ports. It also offers the option of enhanced four-level FLEX (3200 and 6400 baud) for the I20 transmitter interface, and support for other GPS devices. 

At the same time as looking for a proven technology platform to replace its existing end-of-life network, the operator also wanted to strengthen the redundancy of satellite links between its central control room and the multiple transmission sites around the country.

An earlier 12-hour service outage caused by a satellite problem had exposed weaknesses in the original scheme of terrestrial UHF as the fail-over link between the central site and transmitters.
Fully automatic backup

With the operational integrity of the network paramount, the need for a solution that delivered a practical alternative backup route became a major driver and it led the operator to identify the Zetron system as the only viable alternative that supported fully automatic IP backup.

Another vitally important system deliverable was the ability to prioritise messages and predictably manage high traffic and congestion in the event of a major incident – it was not acceptable for critical messages to be stuck in a traffic queue. The Model 600 uses sophisticated batching algorithms that result in maximum efficiency for normal traffic and the ability for critical messages to be sent immediately, or ‘break through’, even when the system is under high load.

As well as making an informed decision to resolve the sourcing challenge, the company also had to make sure the new system integrated into the existing back office systems, which are used to generate the messages. They worked closely with Zetron to test and simulate different connection scenarios in parallel with the existing infrastructure, ensuring that when the system was installed it worked seamlessly.

The focus then switched to finding a way to deploy Zetron’s advanced platform without the massive cost of replacing all the existing C-Net Nucleus transmitters at the same time. A team of engineers worked on the integration problem and developed a plan that was approved by both the operator and Zetron. Exhaustive tests were carried out on the configuration and within a relatively short space of time these were successfully concluded.

Finally, the work of implementing the Zetron solution began, with the phased re-configuration of the Nucleus transmitters and the installation of over 120 Zetron Model 620 platforms at more than 70 sites throughout the country.

Using proven technology and innovative thinking, this programme gave the operator the ability to offer its users a reliable, effective and robust service while at the same time enabling it to plan with confidence for a new generation of services. Despite being prematurely written-off, paging is continuing its move back to centre stage in the mission-critical arena.

Written by Wireless magazine
Wireless magazine

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