Internet of Things Smart Home-zigbee wireless sensor network and application analysis

Internet of Things Smart Home-zigbee wireless sensor network and application analysis

Since mankind has entered the information age, information in nature comes from sensors. With the development of technology, people are no longer satisfied with the original single, independent sensor system. In many cases, we need to aggregate information from different regions to achieve a comprehensive judgment of the situation on the spot.

On the farm, we need to understand the irrigation conditions of the crops, soil air quality to ensure the healthy growth of crops; in the mining area, we need to know the gas concentration, the location of the miners and the temperature and humidity of the underground mines, and the dust concentration to ensure the safety of workers; In large buildings, we need to understand the influence of environmental humidity and wind speed on each location of the building and its own aging degree, and maintain the structural health of the building in a timely manner. Usually, in these cases, the sensors used to collect the data are placed at a distance of thousands of kilometers, and continuous data detection needs to be carried out over a period of months or even years, and the staff cannot perform frequent maintenance. At this time, long-distance wiring, data aggregation, remote configuration of sensors, long-term power supply of the system, and signal security are all issues that engineers need to consider.

With the development of wireless sensor network technology, these bottlenecks have been resolved one by one. In a wireless sensor network, each node can independently collect and summarize data. Depending on the scale of the application, the number of nodes can reach tens of thousands, monitoring various signals over a range of tens of square kilometers.

So, what exactly is a wireless sensor network?

Wireless sensor network technology

A wireless sensor network is a sensor network composed of independently distributed nodes and gateways. Sensor nodes placed in different locations continuously collect external physical information, such as temperature, sound, vibration, etc. Nodes that are independent of each other communicate through the wireless network. Each node of the wireless sensor network can achieve collection, simple data processing, and can also receive data from other nodes, and finally send the data to the gateway. Engineers can obtain data from the gateway, view historical data records or perform analysis. Generally, the hardware structure of a typical wireless sensor network node includes: sensor interface, ADC, microprocessor, power supply, and wireless transceiver.

The wireless sensor network was born in the 1970s and was first used in projects funded by the US military. After nearly 30 years of development, the application of wireless sensor networks has gradually turned to civilian use. It has appeared in forest and river environmental monitoring, in the intelligent application of the built environment, and in some industrial environments where wired sensors cannot be placed. Figure. In 1999 and 2003, American Business Week and MIT Technology Review Magazine successively rated them as the 20 most influential technologies in the 21st century and the 10 new technologies that changed the world.

As a technology developed for applications, the selection of wireless sensor networks in the project must consider practicality. To build a typical wireless sensor network, the following four important factors must be considered: network selection, topology, power consumption, and compatibility.

The choice of wireless network

Wireless technology is the most critical part of wireless sensor networks. In the typical application of wireless sensor networks, the acquisition nodes are usually placed far apart, and sometimes the acquisition nodes located outdoors cannot be connected to the power grid, so when selecting a wireless network, the bandwidth, transmission distance and power consumption are three Main considerations.

At the beginning of the birth of wireless sensor network technology, existing wireless protocols are difficult to meet the requirements of low power consumption, low cost, and high fault tolerance. At this time ZigBee technology came into being. Over the past 10 years of development, ZigBee has proved to be the most suitable wireless technology for wireless sensor networks: it has a bandwidth of 250kbps and a transmission distance of up to 1km. And the power consumption is smaller, the use of ordinary AA batteries can support the device to work continuously for up to several years.

The following figure lists the performance comparison of wireless protocols such as Cellular, Bluetooth, Wi-FI, and ZigBee. ZigBee protocol wins with its low power consumption and long-distance transmission capability. It is suitable for unattended for several years. Monitoring applications.

Comparison of wireless protocols such as ZigBee and cellular networks (Cellular), Bluetooth, Wi-FI

Network topology

For wireless sensor networks with more than tens of nodes, choosing a suitable network structure can not only extend the transmission distance of the network but also ensure the stability of signal transmission. Star is the simplest network topology. Each node has a channel leading directly to the gateway, but its transmission distance is limited. Using a tree topology can solve this problem. After adding routing nodes, data on distant nodes can be transmitted to the gateway through the routing nodes. However, the tree topology still has reliability problems. Once the routing node has a problem, all the paths from this node to the gateway will be cut off. Therefore, for wireless networks with high reliability requirements, it is recommended to select a mesh topology structure.

Network topology: star, tree and mesh topology

Take the wireless sensor network of National Instruments (hereinafter referred to as NI) as an example. Every node in NI's wireless sensor network can be configured as a routing node. Depending on the needs of the application, engineers can choose a tree topology or mesh topology. As shown in the figure below, under the mesh topology, node 4 has two channels to the gateway. Once node 1 fails and is damaged, data can also be transmitted back to the gateway through node 2 to avoid data loss.

NI wireless sensor network in mesh topology

System power consumption

Wireless sensor networks are usually placed outdoors and cannot be wired for long distances, which involves two problems, one is signal transmission, and the other is power supply of equipment. The signal transmission problem can be solved by choosing a wireless network; and for the power supply problem of the device, you must consider the external power supply, such as a battery or a small power generation device. Due to the limited amount of power that the battery can supply, in order to meet the requirements of long-term use of the device, the energy consumption of the wireless sensor network node must be strictly controlled. In the hardware structure of wireless sensor network nodes, wireless transceivers and microprocessors are large energy consumers. Therefore, on the one hand, users should choose ZigBee technology to ensure the low power consumption of the wireless transceiver. At the same time, on the premise of ensuring the performance of the processor, they should also choose the processor with the sleep function and the lowest energy consumption.