Comparison of four wireless technologies: Who is more suitable for the IOT field?

Comparison of four wireless technologies: Who is more suitable for the IOT field?

It is predicted that about 2020 devices will be connected via wireless communication by 50 billion. According to data from the GSM alliance, mobile handheld computers and personal computers only account for 1/4 of the total, while the rest are self-interconnected devices that use non-user interaction to communicate with other machines. At present, our Internet is rapidly developing into the World Wide Web-Internet of Things (IoT) for wireless device interconnection ).

To better serve end users, public utilities and the municipal bureau began to expand the intelligent metering system to solve the problem of increasing real-time data. Through smart electric meters, public utilities can more frequently and effectively view customers' energy consumption information, quickly identify, isolate, and solve power failure and other problems. Consumers can also obtain relevant information through interconnection. All indoor network devices can report their status and energy consumption in real time, and respond to information sent by public utilities. With smart energy and smart home systems, consumers will be more convenient and efficient, such as activating dishwashers when the electricity bill is low, or reminding users to add detergents in due time.

Core features and capabilities of wireless network technology

Wi-Fi is a communication technology based on the GHz band. It is good at fast transmission of large amounts of data between two nodes, but consumes high energy at the same time. In star configuration, each AP must have no more than 15-32 clients.

Bluetooth is another 2-4 GHz technology. It is mainly used as a point-to-point solution for portable devices and only supports several nodes.

ZigBee shares the same wireless spectrum with Bluetooth and Wi-Fi, but is only used to meet the special needs of low-power wireless sensor nodes.

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

ZigBee: an optimization solution for Wireless Mesh Networks

Based on global standards, ZigBee is an open wireless mesh network technology. Unlike traditional network architectures, such as star and point-to-point, the mesh network uses the lowest cost node to provide reliable coverage for all locations in the building (see network topology option comparison in the middle ). ZigBee uses dynamic and autonomous routing protocols based On the routing technology of the Ad Hoc On-demand Distance Vector. When a node needs to be connected, the node broadcasts a route request message. Other nodes are located in the routing table. If a route arrives at the target node, the node sends feedback to the source node, the source node selects a route with the least number of hops and stores the information to the local route table for future use. If one route Line fails, the node can simply select another alternative route Line. If the shortest line between the source and destination is blocked due to wall interference or multi-path interference, ZigBee can automatically find a longer but available routing line.

Network Topology comparison

For example, a wireless sensor network based on the Silicon Labs EM35x Ember ZigBee SoC and EmberZNet PRO protocol stack can provide self-configured and self-Repaired mesh network connectivity, it can be expanded to connect hundreds or thousands of nodes in a single network. The rapid development of the "ZigBee authentication product" benefits from the Ember AppBuilder, which hides the details of the Protocol Stack and focuses on the development tools implemented by ZAP (ZigBee Application Profiles. Through the graphical interface, developers can quickly select the attributes required by the application and then automatically generate the required code by AppBuilder.

Efficient debugging tools are required to maximize the flexibility of ZigBee networks. The complexity of the mesh network makes it more difficult to use traditional network analysis tools (such as Packet sniffer. As a matter of fact, many intermediate transmissions are beyond the scope of the analyzer's application, as the package may jump through multiple to reach the destination. Currently, the only solution to this problem is to use the Silicon Labs Desktop Network Analyzer. This analysis tool is powerful, it can display the entire picture of each packet sending and receiving in the network in a graphical interface, and has a built-in protocol analysis and visual tracking engine. developers can coordinate network communication and device tasks.

In some cases, the mesh network is not an appropriate choice, because the node density is too low, so it cannot provide effective Failover Support. For example, a highway or railway network topology needs to deploy nodes along a long and narrow distance. Similarly, the external facilities on campus are too sparse for a mesh network. In these environments, the combination of a star topology can span a longer distance, making it more reliable and suitable.

Sub-GHz: Ideal for long-distance and Low-Power Communication

Wireless communication is inversely proportional to frequency. In terms of low power consumption, long-distance communication, or wall-crossing capabilities, sub-GHz RF is more advantageous. For many applications, 433MHz has become a global replacement for GHz (but Japan does not allow it to be used for wireless applications ). The Design Based on 868MHz and 915MHz can be used in the U.S. and European markets. There are many available frequencies that require no authorization or authorization. For system integrators, they can choose to optimize performance in certain regions or design systems in broad areas with public utilities. In this diversity, the sub-GHz band has less spectral interference than the GHz band. The band with less interference can improve the overall performance of the network and reduce the number of retransmission times during transmission.

Third parties and standard-based network protocol stacks can be used for sub-GHz RF, but many vendors still choose dedicated solutions to address their specific needs. Many wireless protocols face a problem. Interfaces must constantly activate "listeners" for communication in the network. Data transmission consumes more energy than data reception, but it is short-lived and has a long interval. Therefore, the average long-term energy consumption is usually lower. In many wireless protocols, the receiver does not know when the message will arrive. Therefore, you have to keep listening so that no data is lost. Therefore, even if there is no message, the receiver cannot completely disable energy consumption. This situation will limit the battery autonomy of the node and require regular replacement or charging of the battery.

Sub-GHz Transceiver, such as the Silicon Labs Si446x EZRadioPRO IC, supports the frequency range from 119MHz-1050MHz, the maximum link budget of 146dB, and only requires 50nA current consumption in sleep mode. To reduce the effect of multi-path fading, The EZRadioPRO chip supports dual antennas and integrates the antenna diversity logic algorithm in the chip. By combining frequency hopping and clock synchronization technology, system integrators can achieve a sub-GHz network that spans several kilometers between the Coordinator and the final node, at the same time, the end node can run with a single battery for more than 10 years. As a result, the system integrator can use a small number of coordinator to reliably cover a specific area and place the final node where the main power supply cannot be connected.