As we all know, Xiaomi's smart set contains 4 sets, human body sensor, door and window sensor, wireless switch and multi-function gateway are based on NXP's industrial grade ZigBee RF chip - JN5168 for networking communication. The multi-function gateway is connected to Xiaomi cloud and other smart devices through Wi-Fi technology.
In the figure below, we can see that Xiaomi's multi-function gateway integrates the ZigBee chip JN5168 and Wi-Fi modules into a small circuit board. This ZigBee solution is the same solution as the ZigBee module of ZM5168 launched by Guangzhou Zhiyuan Electronics. We know 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 with a bandwidth of 2 MHz per channel. The ZigBee spectrum list is shown below.
Wi-Fi's standard operating band for 802.11b/g is 2.4GHz (2.4GHz-2.4888GHz), divided into 14 channels, each with a bandwidth of 22MHz. The Wi-Fi spectrum list is as follows:
From the spectrum when working with ZigBee and Wi-Fi, we can see that the frequency of their work is conflicting. In previous studies, we know that the existence of Wi-Fi interference causes the packet loss rate of the ZigBee network to be as high as 58%. From the parameters of the transmit power, the backoff time of the CSMA mechanism, and the data frame interval, Wi-Fi can be seen. Nodes have an overwhelming advantage in acquiring channels and thus have a severe impact on the communication performance of ZigBee networks.
So, how does an intelligent gateway like the Xiaomi Smart Home Suite Gateway that works with WiFi and ZigBee together realize the coexistence of ZigBee and Wi-Fi? This is an urgent problem to be solved and directly affects whether the ZigBee network can be intelligent. An important factor in the popularity of the home . In response to this question, Xiao Bian put forward some personal opinions for your reference.
Solution 1: The ZigBee network and Wi-Fi in the intelligent gateway adopt a time-sharing communication mechanism to avoid conflicts. In the communication, the intelligent gateway is kept away from the Wi-Fi router as far as possible, and the interference of the Wi-Fi signal of the router to the ZigBee signal is reduced by the attenuation of the electromagnetic wave transmitted in the air.
Solution 2: One method is to physically solve the interference of the Wi-Fi signal to the ZigBee network, but in practical applications, the distance between the intelligent gateway and the router is uncontrollable, or is determined by the user's usage habits and family layout. Then, we can only automatically avoid the interference of Wi-Fi signals on the ZigBee network through ZigBee's anti-interference algorithm.
Here, a small article proposes a MuZi-Mulit Channel Zigbee (multi-channel ZigBee) communication mechanism algorithm to automatically avoid the interference of Wi-Fi signals on the ZigBee network.
First, through ZigBee's CCA (Channel Idle Evaluation) mechanism, interference detection is initiated, and the interference level in the surrounding range is evaluated. If the surrounding Wi-Fi interference is considered to be a certain degree, the link performance will be greatly affected. The channel switching process is initiated. The ZZ5168 ZigBee module's built-in FastZigbee protocol has a built-in interference detection algorithm.
Secondly, when performing channel switching and signal switching, in order to avoid excessive signal switching, we need to minimize the number of signals of the target of the entire network. Therefore, each node maintains a neighbor channel table, and each entry is recorded as Ngh is the adjacent node address ID, and Ch is the current working channel of Ngh. Whenever a channel switches, it notifies its neighboring nodes of its selected target channel.
Finally, the connectivity of the entire network needs to be maintained. After ensuring the success of the neighboring node handover, the adjacent node channel table is reconstructed.
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