As is well known, Xiaomi’s smart kit includes a 4-piece set, which uses an industrial grade ZigBee RF chip based on NXP – JN5168- for networking communication, including body sensors, door and window sensors, wireless switches, and multifunctional gateways. The multifunctional gateway is connected to Xiaomi Cloud and other smart devices through Wi Fi technology.

In the above figure, DTCC901B 61430001-FU, we can see that Xiaomi’s multifunctional gateway integrates ZigBee chip JN5168 and Wi Fi module into a small circuit board. This ZigBee solution is the same as the ZigBee module of ZM5168 launched by Guangzhou Zhiyuan Electronics. We found out through checking the product introduction of ZM5168 that the ZigBee channel used by this chip is a global free channel of 2.4GHz. The Zigbee protocol 802.15.4 standard divides the 2.4 GHz ISM frequency band into 16 channels, each with a bandwidth of 2 MHz. The Zigbee spectrum list is shown below

The standard operating frequency range for Wi Fi in 802.11b/g is 2.4GHz (2.4GHz-2.4888GHz), divided into 14 channels with a bandwidth of 22MHz each. The Wi Fi spectrum list is as follows:

We can see from the spectrum of ZigBee and Wi Fi that their operating frequencies conflict with each other. In previous studies, we have known that the presence of Wi Fi interference leads to a packet loss rate of up to 58% in ZigBee networks. From the parameters of transmission power, CSMA mechanism backoff time, and data frame interval, it can be seen that Wi Fi nodes have overwhelming advantages in obtaining channels, which seriously affects the communication performance of ZigBee networks.
So, how does DTCC901B 61430001-FU achieve the coexistence of ZigBee and Wi Fi, similar to the smart gateway of Xiaomi Smart Home Package that works together with WiFi? This is an urgent problem that needs to be solved, and it is an important factor that directly affects whether ZigBee network can be popularized in smart homes. In response to this issue, the editor puts forward several personal opinions for everyone’s 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 intelligent gateway should be kept as far away from the Wi Fi router as possible, reducing the interference of the router’s Wi Fi signal on ZigBee signal through the attenuation of electromagnetic waves transmitted in the air.
Solution 2: Method 1 only physically solves the interference of Wi Fi signals on ZigBee networks. However, in practical applications, the distance between smart gateways and routers is uncontrollable or determined by user habits and home layout. Therefore, we can only achieve automatic avoidance of Wi Fi signal interference on ZigBee networks through ZigBee’s anti-interference algorithm.
This article proposes a communication mechanism algorithm called MuZi Mulit Channel ZigBee, which automatically avoids the interference of Wi Fi signals on ZigBee networks.
Firstly, through ZigBee’s CCA (Channel Idle Assessment) mechanism, interference detection is initiated to evaluate the level of interference in the surrounding area. If it is believed that the Wi Fi interference in the surrounding area reaches a certain level, which will have a greater impact on link performance, the channel switching process is initiated. The FastZigbee protocol built-in in the ZigBee module of ZM5168 has a unique interference detection algorithm.
Secondly, during channel switching and signal switching, in order to avoid excessive signal switching, we need to minimize the number of signals from the target network as much as possible. Therefore, a neighbor channel table is maintained at each node, with each table entry marked as<Ngh, Ch>, where Ngh is the address ID of the neighboring node and Ch is the current working channel of Ngh. Whenever a channel switches, it notifies its neighboring nodes of its selected target channel.
Finally, it is necessary to maintain the connectivity of the entire network and rebuild the channel table of adjacent nodes after ensuring successful switching of adjacent nodes.
For more information on the coexistence of ZigBee and Wi Fi, you can consult Guangzhou Zhiyuan Electronics’ ZigBee product ZM5168 series.