TIDUEO0C July 2019 – March 2021
Smart utility meters with battery power, including gas, water and heat meters, represent a significant market opportunity for various wireless communication technologies such as: Sub-1 GHz, BLE, NB-IoT, and others. With these technologies come trade-offs that must be considered to select the appropriate protocol. For instance, Sub-1 GHz offers up to 1600 m of range at data rates maxing out a 500 kbps. These specifications are ideal for applications like metering, smoke detectors, or temperature sensors in buildings. However, when greater throughput is required, a higher frequency protocol may be more optimal, such as BLE, which can support ranges from 200 m to 400 m (LR) at 2.4 GHz, with a capped throughput of 2 Mbps. BLE is designed to support ultra-low power consumption, with the ability to survive off a coin cell for several years. Applications range from wireless keyboards to heart rate monitors, making it the most widely used wireless technology.
This design focuses mainly on NB-IoT which claims to ensure reliable connectivity deep inside buildings. NB-IoT boasts a range of 1 km in urban settings with a throughput peaking in the tens of kbps. Other NB-IoT promoted characteristics include low device unit cost, an improved outdoor and indoor penetration coverage compared with existing wide-area technologies, secure connectivity, and strong authentication as well as simplified network topology and deployment. The latter seems a major advantage versus all existing LPWA technologies, all of which require installation and maintenance of a proprietary RF network, comprising multiple data collectors, or data concentrator devices, or both.
Narrowband IoT (NB-IoT) is a 3rd Generation Partnership Project (3GPP) standards-based low-power wide area (LPWA) technology which uses licensed spectrum and can coexist alongside 3G and 4G cellular networks. NB-IoT deployment is underway in Europe and North America with multiple operators introducing services for smart devices such as vehicles, connected healthcare monitors, wearable devices, smart meters, asset tracking, and many others. NB-IoT is not equal to LTE CAT-M (also known as LTE-M) IoT technology used by some US mobile operators because NB-IoT is a separate network and not part of the operator’s existing LTE network. The extensive availability of the sensor network paves the way for innovative and cost-effective NB-IoT solutions in virtually all business areas, including industrial transport and logistics, industrial automation, and the public sector.
The main advantage of 3GPP-standardized, cellular LPWA solutions is that they have the support of a huge existing ecosystem, and can therefore both be deployed and scaled up more rapidly, as well as having a single regulatory body that enforces the standard and controls interoperability across vendors and mobile operators. This LPWA standard is supported by 3GPP in Release 13 and Release 14 of their specifications.
Once a wireless technology has been selected, in this case NB-IoT, the power requirements must be investigated to choose an appropriate battery architecture. If a designer decides to use a single LiMnO2 primary cell as their power source, then a boost configuration will be required to maintain, for example, 3.3 V from a battery that varies between 3.2 V down to 2.0 V across its lifetime. Alternatively, when two in-series cells are selected, a buck converter must be utilized. Using a buck will enable the two in-series cell voltage to be reduced to a value specified by a wireless module. The main trade-off between using a 1s or 2s configuration is cost and size versus battery lifetime. Both the 1s and 2s configurations are explored in this reference design.