COMMUNICATION TECHNOLOGY Understanding WIRELESS M-BUS By Vivek Mohan, Silicon Labs for the European Smart Meter Market Connectivity for the Internet of Things The term Internet of Things (IoT) has gained enormous popularity with the explosion of wireless sensor networks, smart meters, home automation devices and wearable electronics. The IoT spans long-range outdoor networks such as the smart grid and municipal lighting as well as shorter-range indoor networks that enable the connected home, residential security systems and energy management. Wireless connectivity and standards-based software protocols provide critical enabling technology for the IoT. A case in point is wireless connectivity for smart metering systems. One of the most useful wireless protocols for smart metering to emerge in recent years is Wireless M-Bus, which is widely used for metering applications across Europe. What is wireless M-Bus? Meter-Bus (M-Bus) is based on European standards for smart meter communication. This connectivity can be wired or wireless, and the standard specifies the communication link between smart meters and data collectors, as shown in Figure 1. The standard also applies to heat cost allocators and drive-by or stationary remote meter reading devices. Based on sub-GHz frequency bands (169 MHz, 434 MHz and 868 MHz), wireless M-Bus uses a simple star type of network configuration with a protocol that is optimised for the needs of smart meter devices. The sub-GHz frequencies enable better propagation characteristics than higher frequencies such as 2.4 GHz. The longer range allows the radio waves to reach difficult wireless locations such as underground installations or meters behind several walls and obstructions. IP addressability and mesh networking are not specified in the standard although meters are individually addressable and may support relaying or routing of messages in some modes. The lower data rates and small packet lengths support a low-power, long-range solution with a small software stack implementation. The frequencies, modulation (FSK based) and bandwidths required by the standard make it spectrally efficient compared to spread spectrum-based protocols. Standards and organisations Figure 1: Connected Metering System Architecture 30 Several European standards and organisations are relevant to wireless M-Bus. In Europe, all sub-GHz wireless devices must comply with ETSI EN 300 220, which sets the emission limits in METERING INTERNATIONAL ISSUE – 3 | 2015