2.4GWLAN Network Interference Analysis

As one of the most significant infrastructure of a smart city, WLAN has been widely used and deployed. However, with the further deployment of WLAN, the interference arisen from WLAN should not be ignored. The interference not only decrease the data transmission and make network congested, but also lead to serious consequences in those industrial control systems, which have the same frequency band with WLAN.Currently, most WLAN devices work in 2.4 GHz frequency band. In this frequency band, there are three kinds of serious interference, which are the interference between different WLANs, the interference between WLAN and the TD-LTE network and the interference between WLAN and metro CBTC system. In the paper, we mainly focus on these three interference. By analyzing causes of the interference problems, the related solutions are presented. For the interference between WLANs, the solution is to interleave the channels to decrease the interference in the identical and adjacent frequency. The results demonstrate that the interference can be effectively avoided, when the channel interval is bigger than 5.And, the deployment of WLAN working in 5.8 GHz frequency can improve the network handling capacity and decrease interference between networks. For the interference between WLAN and TD-LTE network, the solution is to increase the antenna insulation degree and the performance of the combiner and filter, so that the spurious-emission interference, blocking interference and inter-modulation interference can be improved. It turns out that when the antenna’s horizontal spacing is bigger than 4m, vertical spacing is bigger than 0.4m and signal to noise ratio is bigger than 25 d B, the mutual interference can be ignored. For the interference between WLAN and metro CBTC system, the solution is distributing the working channels reasonably, controlling the number of interference sources, controlling the transmitting power from the interference source, increasing the system redundancy and improving the channel detection threshold.In order to solve the above three problems, relevant testing projects have been performed. The test data has been obtained, through computer simulation, building of simulation scenes and the actual measuring. Based on the analysis of these test data,the anti-interference methods have been proposed. Finally, feasible suggestions of WLAN’s deployment and management working in 5GHz and 5.8GHz have beenpresented.