Comparison of four IoT wireless technologies

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Comparison of four IoT wireless technologies [Copy link]

It is predicted that there will be approximately 50 billion devices using wireless communication by 2020. According to data from the GSM Alliance, mobile handsets and personal computers account for only 1/4 of them, and the rest are autonomous interconnected devices that communicate with other machines in a non-user interactive manner. Currently our Internet is rapidly developing into a world wide web of interconnected wireless devices - the Internet of Things (IoT).

To better serve end users, utilities and municipalities are beginning to expand smart metering systems to address the growing amount of real-time data. Smart meters allow utilities to view customer energy consumption information more frequently and more effectively, and to quickly identify, isolate, and resolve power failures. Consumers can also access relevant information through interconnection. Indoor network devices can report their status and energy consumption in real time, and can respond to information sent by utilities. With smart energy and smart home systems, consumers will be more convenient and efficient, for example, controlling the activation of dishwashers when electricity rates are lowest, or reminding users to add detergent in a timely manner.

Core Features and Capabilities of Wireless Network Technologies

Wi-Fi is a communication technology based on the 2.4GHz frequency band. It excels at quickly transmitting large amounts of data between two nodes, but it also consumes a lot of energy, and in a star configuration, each AP is limited to no more than 15-32 clients.

Bluetooth is another 2.4GHz technology that is targeted at portable devices and is primarily a point-to-point solution supporting only a few nodes.

ZigBee shares the same wireless spectrum as Bluetooth and Wi-Fi, but is designed only to meet the specialized needs of low-power nodes.

Table 1 summarizes the core features and capabilities of current wireless network technologies

ZigBee: An Optimized Solution for Wireless Mesh Networks

ZigBee is an open wireless mesh network technology based on global standards. Unlike traditional network architectures, such as star and point-to-point, mesh networks use the lowest cost node to provide reliable coverage for all locations within a building (see the network topology options comparison in the figure below). ZigBee uses a dynamic, autonomous routing protocol based on AODV (Ad Hoc On-demand Distance Vector) routing technology. In AODV, when a node needs to connect, it broadcasts a route request message, and other nodes look up in the routing table. If there is a route to the target node, it will feedback to the source node. The source node selects a reliable route with the least hops and stores the information in the local routing table for future needs. If a routing line fails, the node can simply choose another alternative routing line. If the shortest route between the source and the destination is blocked due to walls or multipath interference, ZigBee can adaptively find a longer but available routing line.

Network topology comparison

For example, wireless sensor networks based on Silicon Labs EM35x Ember ZigBee SoCs and EmberZNet PRO protocol stacks provide self-configuring and self-healing mesh network connectivity that can scale to hundreds or thousands of nodes in a single network. The rapid development of "ZigBee Certified Products" is made possible by Ember AppBuilder, which hides protocol stack details and focuses on ZAP (ZigBee Application Profiles). Through a graphical interface, developers can quickly select the properties required for the application, and AppBuilder automatically generates the required code.

To maximize the flexibility of ZigBee networks, efficient debugging tools are needed. The complexity of mesh networks makes it more difficult to use traditional network analysis tools (such as Packet Sniffer). In fact, since packets may traverse multiple hops to reach their destination, many intermediate transmissions are beyond the scope of the analyzer. For this problem, the only solution is to use Silicon Labs Desktop Network Analyzer, which is a powerful analysis tool that can display the full picture of each packet sent and received in the network in a graphical interface, and has a built-in protocol analysis and visual tracking engine, so that developers can coordinate network communication and device tasks.

In some cases, a mesh network is not a good choice because the node density is too low to provide effective failover support. For example, a road or rail network topology requires nodes to be deployed at wide spacings along long, narrow paths. Similarly, the external facilities of a campus are too sparse for a mesh network. In these environments, a star topology is more appropriate because it can span longer distances and is more reliable.

Sub-GHz: Ideal for long-range and low-power communications

Wireless propagation is inversely proportional to frequency, and sub-GHz radios have advantages in low power consumption, long-distance communication, or the ability to penetrate walls. For many applications, 433MHz has become a global alternative to 2.4GHz (but Japan does not allow it for wireless applications). Designs based on 868MHz and 915MHz are available for the US and European markets. There are many unlicensed or licensed frequency bands available, which gives system integrators the choice of optimizing performance in certain specific areas or designing systems in cooperation with utility companies over a wide area. In this diversity, sub-GHz spectrum has less interference compared to 2.4GHz. Frequency bands with less interference can improve the overall performance of the network and reduce the number of retransmissions during transmission.

Third-party and standards-based stacks are available for sub-GHz radios, but many vendors still choose proprietary solutions for their specific needs. Many wireless protocols face the problem that the interface is constantly active "listening" to communications in the network. Data transmission consumes more energy than data reception, but transmissions are short-lived and have long time intervals, so the long-term average energy consumption is usually lower. In many wireless protocols, the receiver does not know when a message is coming. Therefore, it has to keep listening in order not to lose any data, so the receiver cannot completely turn off energy consumption even if there is no message. This situation will limit the battery autonomy of the node, requiring the battery to be replaced or recharged regularly.

Sub-GHz transceivers, such as the Silicon Labs Si446x EZRadioPRO IC, support a frequency range from 119MHz-1050MHz, a maximum link budget of 146dB, and only 50nA current consumption in sleep mode. To mitigate the effects of multipath fading, the EZRadioPRO chip supports dual antennas and integrates antenna diversity logic algorithms on the chip. By combining frequency hopping and clock synchronization techniques, system integrators can implement sub-GHz networks across kilometers between coordinators and end nodes, while the end nodes can operate for more than ten years on a single battery. This allows system integrators to use a small number of coordinators to reliably cover a specific area and place end nodes where the main power supply cannot be connected.

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