How is 2.4G ZigBee compatible with Wi-Fi?[Copy link]
As we all know, Xiaomi's smart set includes 4 sets of human body sensors, door and window sensors, wireless switches and multi-function gateways, which use an industrial-grade ZigBee RF chip based on NXP--JN5168 for networking communication. The multi-function gateway is connected to Xiaomi Cloud and other smart devices through Wi-Fi technology.
In the above picture, we can see that Xiaomi's multi-function gateway integrates the ZigBee chip JN5168 and the Wi-Fi module into a small circuit board. This ZigBee solution is the same as the ZigBee module ZM5168 launched by Guangzhou Zhiyuan Electronics. We know from the product introduction of ZM5168 that the ZigBee channel used by this chip is the global free channel 2.4GHz. The Zigbee protocol 802.15.4 standard divides the 2.4 GHz ISM band into 16 channels, each with a bandwidth of 2 MHz. The ZigBee spectrum list is as follows
The standard operating frequency band of Wi-Fi in 802.11b/g is 2.4GHz (2.4GHz-2.4888GHz), which is divided into 14 channels, each with a bandwidth of 22MHz. The Wi-Fi spectrum list is as follows:
From the spectrum of ZigBee and Wi-Fi when they are working, we can see that their working frequencies conflict with each other. In previous studies, we know that the existence of Wi-Fi interference causes the ZigBee network packet loss rate to be as high as 58%. From the parameters such as the transmission power, the backoff time of the CSMA mechanism, and the data frame interval, it can be seen that the Wi-Fi node has an overwhelming advantage in acquiring channels, which has a serious impact on the communication performance of the ZigBee network. So, how do smart gateways like Xiaomi Smart Home Set Gateway, which work with WiFi and ZigBee, achieve the coexistence of ZigBee and Wi-Fi? This is an urgent problem to be solved, and it is an important factor that directly affects whether the ZigBee network can be popularized in smart homes. In response to this problem, the editor puts forward some personal opinions for your reference. Solution 1: The ZigBee network and Wi-Fi in the smart gateway adopt a time-sharing communication mechanism to avoid conflicts. And during communication, the smart gateway is kept as far away from the Wi-Fi router as possible, and the interference of the router Wi-Fi signal to the ZigBee signal is reduced by the attenuation of electromagnetic waves when transmitted in the air. Solution 2: Method 1 is to physically solve the interference of Wi-Fi signals to the ZigBee network, but in actual applications, the distance between the smart gateway and the router is uncontrollable, or it is determined by the user's usage habits and home layout. Then we can only use ZigBee's anti-interference algorithm to automatically avoid the interference of Wi-Fi signals to the ZigBee network. Here, a communication mechanism algorithm called MuZi—Multi-channel ZigBee is proposed to automatically avoid the interference of Wi-Fi signals on ZigBee networks. First, through ZigBee's CCA (channel free assessment) mechanism, interference detection is started to evaluate the interference level in the surrounding range. If it is considered that the surrounding Wi-Fi interference has reached a certain level and will have a greater impact on link performance, the channel switching process is started. The FastZigbee protocol built into the ZigBee module of ZM5168 has a unique interference detection algorithm built in. Secondly, when switching channels and signals, in order to avoid excessive signal switching, we need to minimize the number of target signals in the entire network as much as possible. Therefore, a neighbor channel table is maintained at each node, and each entry is recorded as, where Ngh is the neighbor node address ID and Ch is the current working channel of Ngh. Whenever the channel switches, it notifies its neighbor nodes of its selected target channel. Finally, the connectivity of the entire network needs to be maintained. After ensuring that the neighbor node switches successfully, the neighbor node channel table is rebuilt.
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