Smart Meter Design Considerations
By Anna Ukovich, Ph.D.
March 31, 2021
By Anna Ukovich, Ph.D.
March 31, 2021
For smart meters, precise engineering yields optimal results. In the case of battery-powered meters, which often need to function in the field for a decade or longer, it’s essential to keep power consumption at a minimum. With many hardware and connectivity options on the market today, smart meter designers face a host of decisions. Here’s a look at some of the most critical smart meter design considerations to clear the confusion.
When designers choose technology for their smart meters, they want to rest assured that the device will still connect in 10 or 20 years. Unlicensed providers of wireless wide-area networking such as LoRaWAN make that promise, contrasting their offering with the constantly changing world of cellular standards. While that’s a powerful story, it’s important to remember that cellular technology stays in place for many years, even as new standards emerge. For example, 2G was introduced in the 1990s, but it’s still operational almost 30 years later. Today’s cellular standards will continue to be supported in the long term, making cellular LPWA a safe and viable choice for smart meter designs. Cellular LPWA operates on licensed spectrum and is governed by 3GPP standards adopted by mobile network operators worldwide.
Since they deal with personal and sensitive data, utilities are very attentive to security concerns. While some hardware options promise to reduce power consumption, it’s essential to weigh those advantages against potential security threats. In IoT networks, devices are only as secure as the weakest link in their hardware and software components. Integrators should work with trusted hardware and connectivity providers that can offer proven track records to minimize vulnerabilities. They should also note government security requirements in regions where they plan to deploy. For example, some countries have specific rules for smart meters around security; in some other countries, there are bans and restrictions for mission-critical infrastructure applications such as smart meters.
Cellular LPWA suits the connectivity needs of smart meters. The choice of the right technology under its umbrella involves considerations regarding the data rate required by the smart meter application (both in normal operation and in the case of firmware over-the-air upgrades) and the geographical deployment area.
Narrowband IoT (NB-IoT) is capable of supporting tens of kilobits per second (Kbps) (up to over one hundred in case of NB2), while LTE-M (Cat M1) can support several hundreds of Kbps. In terms of geographical coverage, integrators should look at which technology is available in the countries where they plan to deploy and whether it’s wise to have a fallback connectivity option (such as 2G) if coverage is lacking in some locations. In general, cellular connectivity is available worldwide, while deployments of unlicensed technologies are region-specific.
For battery-powered smart meters, power consumption is one of the most significant design considerations. There are several ways to optimize smart meter devices to minimize power consumption over time. Hardware is one factor — some chipsets and modules use more power than others, so it’s crucial to look closely at options, particularly noting how much energy is expended when the device is in deep-sleep idle.
Cellular LPWA offers additional strategies for reducing power consumption with operation design. LTE-M (Cat M1) and narrowband IoT (NB-IoT) include two features that can reduce consumption and stretch battery life, Power Saving Mode (PSM) and extended Discontinuous Reception (eDRX). PSM allows the smart meter to go into sleep mode when it isn’t actively transmitting or receiving data. eDRX is useful in case the smart meter device needs to be reachable at any time while still allowing some latency.
Once you have the above covered, it’s crucial to scrutinize your candidate wireless modules’ power consumption specifications. Review vendor-published specifications to shortlist vendor options and then obtain empirical data on power measurements made at their labs and these measurements’ conditions. This review is critical because, even though all wireless chipsets must comply with strict standards and protocols, different vendors achieve these standards with varying design strategies and technologies, which result in materially different power consumption performance.
The size of the module is another design consideration, with many integrators opting for small modules. Gas and water meters are often very compact and integrated with manufacturing, making module size an important factor. Several newer form factors on the market, such as the Telit xE310 product family, are ideal for compact smart meter applications.
Signal coverage is another essential consideration for smart meter designs. Some meters may be deployed underground or within buildings, while others will need coverage in remote areas worldwide. Integrators should investigate coverage in the areas they hope to deploy and determine which technologies will yield the most reliable connectivity. For example, NB-IoT and Cat M1 have coverage enhancement techniques to provide better coverage than higher 4G categories if devices are deployed underground or indoors.
Smart meters have distinctive needs. Unlike smartphones and similar devices, they don’t need to send and receive large amounts of data, and they don’t always need to be reachable. In this realm, long latency is allowable and can contribute to power optimization. Designers must determine how often their meters need to check in with the network and send data — whether that’s once a day or once a week — and then decide whether the devices will be available on demand or only able to check in at appointed times. For cellular devices, this determines whether PSM or eDRX can be used to save power. eDRX allows designers to have the best of both worlds — the ability to conserve energy in sleep mode while retaining the ability to summon them as needed. There will still be some latency with eDRX, and the more latency is acceptable, the more power the device will save.
How can a microamp make a decade of difference in battery life? The idea seems incredible, but such design precision yields exponential benefits over time. Today’s smart meter integrators perform a delicate dance of trade-offs between hardware, functionality and connectivity standards to create battery-powered meters that can see successful deployment for 10 years or longer. Telit’s portfolio of low-power cellular modules, global connectivity options and engineering design resources we offer from 20 years of enabling the utility industry can help you design a solution to extend device battery life materially and ensure the longevity of function for smart meters.