Testing Infrastructure – an ongoing process

Testing is an ongoing process that continues well beyond system installation and commissioning. The test and measurement (T&M) processes for TETRA are arguably more critical and exacting than for other technologies such as ‘plain old cellular,’ as they address a critical communications technology and from infrastructure development and manufacture to deployment and ongoing everyday operations, the continuous T&M process requires equipment for field engineering teams to monitor the physical network, which are various and wide ranging in their capabilities.

One of the leading companies providing advanced test and measurement solutions to the sector is Aeroflex. TETRA Today spoke with product marketing manager, EMEA, for the company, Lyndon Zielke, who began by saying that one of the very first and key issues requiring TETRA infrastructure test and measurement is verifying the performance of that equipment before it’s sold and delivered to the customer. “The production process is never going to be 100% perfect, and you will always need to calibrate for modulator errors, RF output power levels, RF frequency error, and receiver sensitivity.” But, as Zielke added, that doesn’t negate the need, on actual deployment, for further tests. “When deploying and commissioning, the installer too, will once again need to verify performance before the system can be handed over to the customer.”

Looking from a slightly different perspective, Wolf Seidl, product management Drive Test for Authorities, Aerospace & Defense, TETRA at Rohde & Schwarz in Munich, considered the need for both effective indoor and outdoor performance of the network. He stressed the need for the digital radio network for public safety and security (PSS) not only to be able to ensure smooth communications in the open but also for the coordination of emergency personnel inside facilities and structures, such as buildings, sport stadiums, road and rail tunnels, to be guaranteed. He said having the right T&M equipment available would ensure, through test, that when infrastructure inside facilities is connected to the PSS digital radio network, the influence on the area outside the facility is not negatively impacted and the quality of open area coverage remains good.

In view of the fact that TETRA systems are often used for critical communications, Lyndon Zielke pointed out that they, therefore, require more ‘critical testing’ than other communications technologies. “Testing of TETRA requires equipment that can find problems in the system before they become severe enough to interfere with optimal communication. This means that the equipment employed must be able to determine when a TETRA system is not operating at its peak performance,” Zielke said. “Since a system consists of both the infrastructure and the subscribers it is not enough to test only one part of the system, but rather all pieces of the system must constantly be tested and evaluated.”

When testing TETRA mobiles, as opposed to cellular devices, he added that these must be tested with their “ ‘live’ personality programming and not with a test ‘SIM’, in order to also check their configuration.” This testing will often include GPS testing, since most critical communications radios include GPS for location information. He added that while an undetected problem in a cellular system can mean loss of revenue, a similar problem with TETRA systems, often used as we know for critical communications can, therefore, mean loss of life in extreme cases. Hence, the importance of ongoing and accurate T&M is essential.

Continuing his view of the importance of the network plan and coverage monitoring inside and outside structures, R&S’ Wolf Seidl painted the picture of the complexity of some of the scenarios to be evaluated. “Due to its lower frequency, digital PSS radio features lower building attenuation than is the case with GSM mobile radio networks, for example. Nevertheless, the Q factor for basic coverage is not comparable with the coverage that we are familiar with from mobile radio networks. Depending on the nature of the building (reinforced concrete, metalized windows) and distance from the base station, the supply from outside will cover only part of the building. Boosting the density of base station sites with the goal of providing supply for all buildings from outside is technically and economically difficult to achieve.” He added that one of the complexities of TETRA is that compared to conventional GSM, UMTS and LTE networks for commercial mobile services, is that TETRA networks have a significantly higher number of network operators, whether they be public authorities as well as private licensees, including: municipal utilities, local public transport, airports and refineries, as well as the military. As a result, Seidl said that co-channel occupancy, overreach and insufficient network planning can lead to mutual interference. “This is where T&M solutions such as the Rohde & Schwarz drive-test solution make it possible to measure and analyze these factors independently of the manufacturer.

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