Electronic Design

Ultra-Narrow-Band Telemetry Radios Optimized For Meter Reading

Companies have been working for years to create an affordable and practical wireless automatic meter reading (AMR) system. The data radio is less of a problem, but collecting all that data from hundreds of thousands to millions of homes and businesses wirelessly and getting it back to the utility is a huge issue. Some companies are working with ZigBee radios in a mesh or multipoint-to-point system that uses machine-to-machine (M2M) cellular radios back to the utility.

Plextek’s low-cost Ultra Narrow Band (UNB) telemetry platform targets automatic remote meter reading and smart metering applications. It eliminates the complex and costly need for a mesh network or the use of cellular backhaul. The UNB system also includes a low-cost, low-power module for integration into the customer’s meter and a cost-optimized basestation (see the figure). Each basestation can handle up to 5000 client meters. Four basestations can be connected to one controller unit. ADSL or other IP-based networks can handle the backhaul.

The two-way Plextek technology not only permits AMR, the customer meter also can receive information from the utility network for smart control of heating and air conditioning and other heavy loads. The units operate in the 868-MHz (Europe) and 902- to 928-MHz (U.S.) unlicensed bands. And, this unique system is truly ultra-narrow-band. The data rate from meter to basestation is a low 62.5 bits/s and from basestation to meter is 500 bits/s, both using minimal bandwidth in the spectrum.

Those rates aren’t a typo. High speed simply isn’t a requirement in this application. Plextek has traded off speed for longer range and higher reliability of the radio link. Typical range is 2 to 6 km in urban areas and up to 20 km in rural areas where line of sight is possible. A key factor in this extended range and reliability is the use of digital signal processing in the receiver to provide increased sensitivity even in the presence of noise and interference in these usually crowded unlicensed bands. The protocol also includes forward error correction, error detection, automatic retransmissions, power control, and other features to ensure a solid connection.

With energy conservation becoming a larger priority and governments increasingly requiring power reductions to lower carbon impact, automatic meter reading and smart control are major parts of the solution. “As power usage in homes increases through an ever-growing number of electrical and entertainment devices, we are blissfully unaware of the resulting increase in kWh usage,” says Colin Smithers, managing director of Plextek. “With prices soaring, consumers are now beginning to demand the ability to have more control over their usage, and operators are keen to reduce consumption and better manage supplies.”

Solutions like Plextek’s UNB will ultimately bring about the energy savings that we all want.

Plextek Ltd.


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