City authorities, service and utility companies are increasingly investing in modern street lighting, smart metering, road monitoring and security solutions that all demand different communication capabilities. Modern smart city wireless networking applications require different data throughputs, operation distances and real-time performance properties. At the same time, cost is an important aspect, since the quantities of smart devices are generally large. Conventional WiFi is frequently not suitable because of short communication range, significant energy consumption and hardware cost. So which communication technologies are most suited for smart city applications?
The most popular smart city communication solutions for Low-Rate Wireless Personal Area Networks (LR-WPANs) are based on the IEEE802.15.4 standard compliant radios. This standard is most widely known as a physical networking layer of Zigbee communication. It supports both the 2.4GHz and sub-gigahertz licence free radio bands. IEEE802.15.4 radio technology is optimized for low power consumption. According to the standard, in the 2.4GHz band the communication speed is fixed to 250kbps resulting in a communication distance of up to 100…150m. The subgigahertz band standard allows to use different data rates and therefore can offer a communication range of 1…2 kilometers for low speed communication i.e. utility meter reporting. Unfortunately, IEE802.15.4 subgigahertz band may be crowded in European cities, since the frequency range allocated for license free use is narrow, only 2MHz (compared to 26MHz in North America).
IEEE802.15.4 is a rather old communication standard developed already 20 years ago. In 2010, Bluetooth Low Energy (BLE) standard was released, and immediately became a strong competitor to the IEEE802.15.4. Bluetooth operates in 2.4GHz range and compared to IEEE802.15.4, provides higher communication speeds (1Mbps) with a shorter communication range of around 50..100m. A significant advantage of BLE technology is its presence on smartphones and other mobile devices. The latest BLE standard 4.2 enables MESH-like multihop communication and is therefore well suited for modern smart city applications. The new BLE 5.0, which is scheduled to be approved next year, should double the communication range and throughput and be very attractive for dense smart city networks, for example street lighting. The future will see devices such as smartphones and cars directly communicating with luminaires or smart poles, without any centralised infrastructure. This, in turn, will create significant opportunities for new location-aware applications.
Some smart city applications need to send small amounts of data over long distances, such as smart water or gas meters. In these cases, communication solutions such as Sigfox narrow band radio technology becomes relevant. Sigfox devices operate in the subgigahertz band offering bidirectional communication. The company owns the required base station infrastructure serving many battery powered radio devices that transmit data packets rarely, i.e. once a month. Sigfox can support tens of thousands of end devices that operate 10 years from a single battery and send data over distances of 10 kilometers in rural, and 2…3 kilometers in urban areas. The company’s business model is based on charging a service fee from every device connected to the Sigfox network. However, it’s questionable whether large companies and public authorities agree to use service fee payment model with a single provider. However, Sigfox infrastructures have been installed in tens of cities in the U.S. and Europe.
Another important low power long range wireless communication technology is promoted by the LoRa Alliance. LoRa technology also operates in the subgigahertz band. The communication range of 2..3 km in dense urban areas is similar to Sigfox and bidirectional communication speed is some kilobits per second depending on the environment. The LoRa Alliance is led by the chip maker Semtech, and the business model is based on chip sales and licensing. Therefore there could be several competing infrastructure providers, thus lowering customers’ risks. LoRa has already been used in some promising smart city applications, for example open IoT network in Amsterdam led by the Things Network.
Significant changes to the low power IoT communication market will arrive with 5G mobile networks, which will also provide certain localization capabilities. However, it is expected that the 5G standards will be globally agreed by 2018 leaving companies time to utilise the other relevant smart city communication technologies for at least the next 4..5 years.