STEM newsletter

Modelling public safety radio networks

30 October 2006

All over Europe, a number of PMR (Professional Mobile Radio) networks are being installed. These networks are often used by public safety authorities: the most recent example is a PMR system in Germany for which the tender process is ongoing. However, PMR systems are also used in industrial environments that have high requirements for reliability and safety, for example, airports or the production facilities of car manufacturing, chemical or power supply industries. DOK SYSTEME has carried out STEM-based cost calculations on behalf of the German government for the public safety network in Germany. This TETRA network will have more than 4000 base stations.

Choosing an appropriate technology

In the early stages of the German tender process, there was a big debate about whether to choose a GSM-based proposal from Vodafone or a PMR solution. The mobile operator wanted to offer a service based on its GSM network, extended by the GSM ASCI feature set that had been developed for the European rail companies (ETCS). Vodafone got as far as carrying out a field trail with the extended functionality designed to meet the requirements of the public authorities.

At a certain point, however, the government changed its strategy and focused finally on a PMR solution. Modern PMR systems are based on either the ETSI TETRA standard, or the proprietary TETRAPOL system (EADS). These two digital trunked radio systems are successors of the old analogue systems that have reached the end of their life cycle. Currently we are seeing a big market boom in PMR all over Germany.

In September 2006, EADS finally won the contract with a TETRA system that had been taken over from Nokia. The next steps will be the network roll-out and the procurement of TETRA handsets.

Critical network dimensioning

The radio traffic design of trunked PMR networks is different from more familiar radio networks such as GSM or UMTS, and a traffic-driven approach can’t be used for a PMR STEM model. The main reason for this is that measurements of the traffic on public safety networks such as those of police or fire brigade forces show no typical traffic pattern over time, as is found on public telecoms networks. Thus a typical main busy hour can’t be found. Therefore traffic engineering has to be pre-planned and the dimensioning has to be done for critical events.

Splitting the costs using templates

As mentioned above, the network in Germany will have over 4000 base stations. The cost will be split between the central government and 16 federal states. Thus the STEM model had to do this cost split using STEM template elements in an intensive way. Achieving this just by using Excel spreadsheets would have taken significantly more time. The simplified example below illustrates the principle that was used.

Simplified example of cost split between geographical template elements

Using Excel for inputs and results

It has proved to be very helpful to use standardised Excel input matrixes for personnel and infrastructure costs. Using this approach for cost-driven models, even big STEM models can be built in a short period of time. Another advantage is that these input matrixes can be readily discussed with people who are not familiar with STEM, for example with clients during project meetings.

Also very useful was the use of the Excel STEM add-in to import results into a spreadsheet. Cash flow and P&L computations for all the German stakeholders became very simple by using a standardised naming convention for the resource elements. (Due to differences in German commercial and public law, some changes had to be made in the P&L tables compared to the original STEM results sheets.)

Wider applications

The model discussed here was for a large-scale, national roll-out. Nevertheless, a STEM-based PMR model could be easily scaled down to smaller TETRA networks.

A similar methodology could also be used for other radio technologies, and the dimensioning elements in STEM are flexible enough to allow the modeller to choose between the ‘critical network dimensioning’ described here, and the more typical busy-hour approach used for dimensioning carrier networks.

Dr.-Ing. Jan Steuer is a Managing Partner at DOK SYSTEME since 2003. Previously he worked with Siemens’ Carrier and Enterprise Division in the UK. Jan received his doctorate in the area of radio communications from the University of Hanover, Institute for Communications, where he worked as a research assistant for several years and published several papers, and currently lectures on UMTS.

DOK SYSTEME GmbH is a small German consulting company with 30 employees, specialising in ITC business and technology consulting.

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