1. We leveraged the unique physical-layer features among heterogeneous wireless communication technologies for parallel and concurrent communication to significantly improve spectrum efficiency in the unlicensed band. We use the coexistence of three popular and representative IoT techniques (i.e., WiFi, Bluetooth, and ZigBee) as an example to illustrate our proposed research ideas. The proposed techniques have the potential to improve the spectrum efficiency in other frequency bands where heterogeneous wireless communication technologies coexist.

2. We developed physical-layer authentication techniques, in which each IoT device superimposes some unforgeable information onto physical-layer signals for the IoT gateway to detect and verify before demodulating and decoding the signals. Working for both uplink and downlink transmissions, our techniques can dramatically improve the resilience of the IoT system to illegitimate traffic.

3. We developed incentive-compatible and differentially private mechanisms for the gateway service provider to select mobile users for filling network-coverage holes. Our techniques aim to provide the best possible incentives for mobile users, minimize the overall cost of the gateway service provider for fulfilling network-coverage tasks, and also provide differential location privacy to mobile users.