Metro-area wireless trial links 99.3% of smart meters
Sensus has revealed details of a smart metering trial using 400MHz point-to-multi-point radio with multi-km range, claiming 99.3% of meters were covered.
Proposed as an alternative to communicating through phone networks or ZigBee-like mesh networks, the system was “built with battery life and building penetration in mind”, Sensus marketing director Andy Slater told Electronics Weekly.
Sensus is based in the US, where more than ten million smart meter and grid end points are connected to the firm’s networks.
The trial was implemented by SmartReach, a collaboration of: Arqiva, BT, Detica, Sensus and ScottishPower. It included 5,000 smart electricity meters in two areas: central Glasgow, and Lochwinnock – a rural area 20 miles from Glasgow “renown for having poor cellular coverage”, said Slater.
“Densely populated Glasgow presents a different kind of communications challenge, with meters located deep inside buildings, including basements,” said SmartReach.
According to Slater, 99.3% coverage was achieved with no optimisation of, for example, basestation position.
In the system, each meter can always see at least two basestations (although it is dedicated to one), and one basestation can cope with up to 50,000 meters “depending on how much data is requested”, said Slater.
Lochwinnock had four basestations – which in general, according to Slater, consist of an antenna on an existing mast plus around 400mm of 19in rack, which includes back-up battery.
This trial followed one in Ipswich that got 100% coverage from three basestations, and a water meter trial in Reading with Thames water which achieved 100% coverage despite the meters being underground beneath metal covers, said Slater.
Range is from 5km, and up to 20km in open countryside. This drops to 3-5km for buried water meters.
Link noise is kept down by using narrowband signals and modest data rates, neither of which Slater will discuss in detail. The centre frequency is just above 400MHz and adjacent to the Tetra band, he said.
At the meter end, the entire transceiver including 15 year battery and folded dipole for a water meter is around 50x37x37mm. There is no provision for an external antenna in this case.
The meter transmits accumulated measurements a small number of times a day, perhaps three, set by the utility company. Immediately following each transmission, the receiver is powered up briefly to allow commands to be sent back to the meter.
To allow for ad-hoc readings, for example during a customer phone call to the utility company, the receiver is also powered up for a few milliseconds at a fixed time during each minute – with this time spread around the minute in different meters.
According to Slater, if this system was chosen instead of GSM, Arqiva could roll-out enough base stations for 100% national coverage in 18 months.
“For the under 1%, we may have to do some engineering,” said Slater. “As sure as we can be at this time, we will get 100% coverage.”
For situations where link budget is insufficient for a reliable connection, there are options including repeaters and external aerials.