By Peder Martin Evjen, co-founder and managing director, Radiocrafts ASIndustrial Wireless Sensor Networks (WSN) and the Industrial IoT (Internet of Things) require solutions that are reliable, secure and low power running off batteries. Wireless M-Bus is a solution already widely used in smart metering applications. The 169 MHz variant of Wireless M-Bus is also a suitable alternative to other LPWAN technologies for the Industrial IoT.
Wireless M-Bus for industrial sensor networks
The reading of utility meters is very similar to applications in the industry where sensors or actuators need to be read or operated at a distance. Very often, these sensors are battery operated and it is difficult to install wires to reach them. Adding to this, there are requirements to the security and the reliability of the data communication. All of these issues have already been addressed in the development of the Wireless M-Bus standard. Therefore we will find that Wireless M-Bus is also a good alternative as a communication standard for industrial wireless sensor networks in general.
Wireless M-Bus as LPWAN
Low Power Wide Area Networks (LPWAN) are used to communicate with objects that are distributed over larger areas than a house or building. Solutions at 868 MHz and cellular technology already exist. However, if the distance is limited to few kilometers, and operation cost is essential, an interesting alternative to these solutions is the use of long-range narrowband radio in some newly opened license-free bands at VHF frequencies. This is exactly what Wireless M-Bus at 169 MHz is offering, providing the benefits of no subscription cost and reduced complexity.
The relatively low frequency (VHF band) combined with high transmission power (up to 500 mW), enables radio communication at long-range. In addition, narrowband radio (12.5 kHz) is used to get the best radio receiver sensitivity. A communication range of 3-4 km in urban environment has been demonstrated using ultra-narrowband radio modules at 169 MHz (see Radiocrafts Application Note AN021).
Wireless M-Bus in metering
Wireless M-Bus is the preferred standard for wireless utility meter reading and heat cost allocators. The standard is rooted in the wired M-Bus user group that was very active in the 90's. Initially the M-Bus user group created the wired M-Bus standard, but later the specification was enhanced, and Wireless M-Bus was introduced. This standardisation work was transferred to CEN, technical committee TC294, that created the new European standard EN 13757 "Communication system for meters and remote reading of meters". Radiocrafts is an active contributing member of the CEN TC294 working groups developing the standard, and a leading provider of radio modules based on the standard. The standard currently (as of June 2017) consists of 6 parts, covering wired and wireless communication, repeaters, and application layers with security. Wireless M-Bus is a radio and data link specification described in EN 13757-4. The application layer for M-Bus is specified in EN 13757-3.
The 868 MHz variant (S, T and C mode) is widely used for short range reading of meters, in a home, or in drive-by systems. However, many water and gas meters are placed in basements or outdoor locations that are harder to reach, requiring a better radio technology. The 169 MHz band, using narrowband radio (mode N), was therefore introduced in the 2013 edition. Today, there are tens of millions of Wireless M-Bus units in the field, used to read and protect the large values of energy and water supplies.
Either WSN sensors are a part of energy management systems in buildings, or related to industrial process monitoring. Radiocrafts provides compact module solutions simplifying the design of hardware and software in terms of the wireless communication protocol and sensor interfaces.
Industrial IoT using 169 MHz for LPWAN
LPWAN (Low Power Wide Area Network) has become an important part and enabler of the IoT (Internet of Things). What separates LPWAN from other technologies in the IoT space, is range and geographical coverage. The idea behind LPWAN is to cover a large area, even a city or a country, with a radio network using very low-power radio technology enabling many years of battery lifetime. This means sensors and actuators can be spread over a large geographical area, or even be mobile. Typically the amount of data to be transmitted is very small, usually only a few bytes as reading a sensor. This is quite the opposite of the high bandwidth offered by the latest generations of cellular phone technologies (3G and 4G). In order to reduce the cost of the infrastructure (reducing the number of gateways), the communication range for LPWAN is important. Ultra-narrowband radio technology is a solution to achieve this.
The main three players in the LPWAN market we see today are Sigfox, LoRa and NB-IoT (LTE). Sigfox and LoRa two use license-free bands at 868/915 MHz, while NB-IoT is using a part of the 4G licensed spectrum. Although the term “narrowband” (NB) is used for the new LTE standard, it is not narrowband in a strict sense. By using 200 kHz wide channels, it is more “narrow” than the full LTE bandwidth, but much wider than the real narrowband (10-25 kHz) which is now often referred to as “ultra” narrowband.
Furthermore, LoRa is not using narrowband technology, but a kind of spread-spectrum based on frequency chirps. The bandwidth is typically 100 – 200 kHz, depending on the data rate used.
Among these three it is only Sigfox that use a true narrowband radio. The uplink is 100 bps (in Europe), using a 10 kHz bandwidth.
However, all three technologies require either some special base stations with signal processing (as for LoRa), or using a subscription based cellular network operated by a telecom provider (as for Sigfox and LTE). For some applications, this can be an advantageous solution, but for others it is not. When the application requires country-wide or city-wide coverage, Sigfox technology can be a suitable solution.
An alternative to these technologies is the Wireless M-Bus using ultra narrowband modulation at 169 MHz. The benefits of this solution are summarised in Figure 3. This variant of the standard has gained great popularity, for example in France. It is used by GRdF for gas meters, and by Suez for water meters. Based on this experience, they recently founded the Wize Alliance, to promote this solution for general smart city applications. In Italy too, the 169 MHz variant is being used for gas meters. Radiocrafts is also part of pilot projects in many other countries based on this new long-range technology.
About the author
Peder Martin Evjen is co-founder and managing director of Radiocrafts. He has more than 25 years’ experience in radio technology. He is a member of several standardization groups for wireless communication in meter reading and building automation, and represents Norway in CEN TC294. He has a M.Sc. degree from the Technical University of Trondheim in Norway.