networks
rigs or oil and gas refi neries, even those onshore, are, in his words, “an RF designer’s nightmare”. He said that with huge amounts of steel, metal and concrete these environments are very diffi cult to predict or simulate. “More decisions need to be made based on ‘educated
Real-time information R
guesses’ than trying to simulate actual signals”, Koski said, “since simulations will fail miserably, and more time needs to be spent on fi nding the correct solution. Often the use of antennas is doomed to fail in these kinds of challenging environments, which often require leaky feeders to achieve good and stable coverage.” He added, as an aside, that in off -shore and refi nery
ecently launched by Motorola is the second generation of TETRA RF Automated Coverage Evaluation System (TRACES), an optimization tool
which allows public safety network operators to collect, visualize and evaluate real-time data from mission-critical TETRA networks. It allows them to view usage patterns and identify and react to coverage black spots, thereby maintaining a stable network at all times for users in the fi eld. This new version, which recently won two categories at the International TETRA Awards, builds a detailed picture of the entire mission critical network by automatically and continuously capturing network performance data from actual user devices and base stations. This real-time Information also allows network operators to monitor their compliance against typical KPI and SLA criteria. The system is designed to be fl exible, easy to install and modular and can
be customized to mission critical network operator needs whether they solely manage a network or whether they also have their own fl eet of users. Its Uplink Measurement Report (UMR) module enables operators to collect real- time data over GPS signals and radios while they are in use in the fi eld giving a comprehensive view of network coverage from an end-user perspective, without actually owning any radios at all.
On infrastructure issues, Taylor also said that as passive
intermodulation (PIM) can impact TETRA, just as with cellular cell sites, base stations need to be able to ‘report’ interference problems, which may result in channel change requirements. “A ‘monitoring network’ might be used where you deploy a number of fi xed units and make test calls to those units, or you call certain radios periodically and check for quality issues. Increasingly, there are processes being incorporated into TETRA networks to continuously monitor performance to ensure no problems are arising. T ey have good reporting and alarm systems which allow users to feed information back easily to the network operator, which can then be acted upon to rectify problems, eg if the coverage behind a building during a fi re is bad it must be easy for fi re department users to report such critical information. In such cases, the operator may want to optimize the network. So, for instance, if call handover is not good and is the apparent problem, the operator can use the neighbour list to aid in making necessary adjustments at the base station.” When it comes to RF design factors and alternative
optimization techniques required for network deployments in unusual scenarios, such as off shore installations, Taylor said that the spinning turbines of wind farms could pose problems for RF design, as the spin can create a refl ector eff ect and must be taken into account; water also creates interference problems as RF behaves strangely over water, but there are optimization tools to handle this challenge. Koski added that unusual installations, like off shore
18
scenarios, potentially explosive atmospheres mean that equipment used must be certifi ed and this includes all the RF lines. “Often I see people who believe that you should only take care of the power supply and the AC or DC voltage connections. Sure, this is important, but it is not suffi cient on its own. Most of the standard units and equipment in TETRA are able to produce enough RF power needed to create a spark, which is not a good thing in a potentially explosive atmosphere and, hence, is why all the antenna ports coming from radios, BTSs or repeaters, need to be ATEX certifi ed.”
A sharing footnote Cell site sharing – where TETRA infrastructure shares the cell sites of cellular players – is taking place, but this comes with its own set of pros and cons. David Taylor agrees that such sharing activities make sense as long as the RF design works. “We’re talking diff erent spectrum, 380-400MHz versus 900/1800MHz, where intermodulation would need to be controlled, though I haven’t seen much of this. What would most likely be the biggest issue is wideband noise. “However, the most typical form of sharing at the moment
is sharing the same cell site compound, although using diff erent masts. T ere would need to be separate criteria for battery back-up for TETRA as we’re talking critical communications rather than simply public telephony. So, battery supplies and equipment like UPS [uninterruptible power supply] would need to be separate.” Peter Jackson, director, at infrastructure specialists CCI,
agreed that usually it is not the RF infrastructure that is shared, but the supporting structures such as the towers, with TETRA having its own equipment shelter, feeders and antennas, all due to the fact that the emergency services are critical communications users.
Unusual installations, like offshore rigs or oil and gas refi neries are, in the words of Jyrki Koski, chief executive offi cer at Creowave, “an RF designer’s nightmare”
TE TRA TODAY Issue 14 2013
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