In view of the problem of a sharp fall on network performance due to network interference caused by channel overlapping aroused by ISM (Industrial Scientific Medical) band shared between WiFi and ZigBee, and severe spectrum underutilization induced by the current CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) mechanism, a subcarrier-nulling 2×2 noncoherent antenna MIMO (Multi-Input Multi-Output) PHY (Physical Layer) model was proposed in this paper. In this model, to avoid co-channel interference, a WiFi transmitter needs to detect ZigBee signals appearing in its adopted channel before data transmission, and if any, this transmitter will null the subcarriers within the spectrum occupied by ZigBees, and take advantage of the rest subcarriers to transmit its packets. The receiver needs to identify the subcarriers used by the transmitter, and finish the follow-up work. By this means, interference will be eliminated by signal spectrum separation, thus achieving the goal of heterogeneous network coexistence and making parallel data transmission available. The experiments were run on the test bed composed of GNURadio/USRP platform and ZigBee nodes, and the experiment results show that subcarrier-nulling enabled 2×2 noncoherent antenna MIMO to gain 50%-70% throughput of that in the full bandwidth scenario, and during parallel data transmission ZigBee’s valid received packets ratio is at least 90%.
