Brief Analysis of ZigBee Wireless Network Design and Application (1)

The ZigBee protocol is a global open standard to provide low-power wireless connections for many applications with test and control functions. ZigBee enhances the functions of 802.15.4 with flexible and scalable network topology, easy-to-install comprehensive settings, smart routing technology, and anti-DDoS capability. ZigBee also has strict security measures and can coexist with other wireless technologies such as Bluetooth and WiFi in the same work environment.

The wireless transmission distance of ZigBee is closely related to the working environment. When the standard wireless control module outputs 0 dBm power, the outdoor working distance can reach 450 meters. However, in the room, due to the absorption, reflection, diffraction, and standing wave effects of the wall and other objects, the distance is greatly shortened; the working distance of the output power module is approximately 10 times greater than that of the 15dBm power module. In addition, the network and cluster tree topology can further increase the working distance.

Communication security and reliability

Due to Wireless Interference and poor sending/receiving conditions, ZigBee uses multiple technologies to ensure the reliability of communication. First, the ZigBee network uses the encoding mechanism during wireless transmission. In the GHz band, orthogonal phase-shift keying (PSK) modulation technology is used, and the four-bit data symbol is transformed into a 32-bit chip sequence. Even if there are other wireless signals in the same channel at the same time, ZigBee messages can completely reach the destination.

Second, its transmission adopts a carrier listening and multi-point access solution with conflict avoidance. To put it simply, a node needs to listen on the channel before sending it to check whether it is smooth. If the channel is working, the node listens again after delay, and then continues until the channel starts to send messages. Second, after the message arrives at the destination, the receiving device sends a confirmation signal to indicate that the message has been received. If the sender does not receive a confirmation signal, it will send the original message again within a certain interval.

ZigBee provides a "security toolbox" to provide high security. The main measures include:

◆ Access control table: Only predefined "friendly" nodes can be added to the network;

◆ 128-bit AES-based encryption technology: a high-security key-based encryption system. Some wireless controllers also provide hardware confidentiality functions.

◆ Message update Timer: rejects timeout messages to prevent external message intrusion from attacking the network.