EAGER: SARE: Directional Modulation Non-Contiguous OFDM Retrodirective Communication for Secure IoT

In the upcoming era of the Internet-of-Things (IoT), billions of physical devices will be networked together and enable emerging concepts, such as smart homes and smart cities, leading to new paradigms for connected human societies. As such, devices such as intelligent sensors and controllers—often operating on small-capacity batteries and running applications on ultra-low-power processors—will need to be able to communicate with each other, while being connected to the internet cloud. In this scenario, IoT gateways serve as an essential component in bridging IoT devices and the internet. As the IoT gateways will need to deal with critical tasks at the edge IoT devices, it is essential to ensure secure communication links between the gateway and the devices against any spoofing attacks by adversarial entities. Since end-to-end encrypted sessions between the edge devices and the gateway cannot be relied upon for secure communications due to the high computational resource demand and battery burden of such cryptographic strategies, there is an urgent need to develop physical-layer (PHY) secure communication schemes. To this end, this project develops a directional modulation non-contiguous orthogonal frequency division multiplexing (NC-OFDM) retrodirective communication scheme that will have a profound impact in securing IoT applications. The outcome of this project will enable a highly secure PHY communication scheme among the IoT devices and gateways against malicious spoofing attacks. Furthermore, the unique combination of NC-OFDM and directional modulation retrodirective array will make such attacks very unlikely to succeed even with sophisticated machine learning (ML) techniques. In addition, the educational plan of the project aims to broaden participation of graduate, undergraduate and high school students, including underrepresented minority groups, in relevant research on microwave and antenna technologies, signal processing and ML, and wireless communications. In terms of technical details, the research project addresses a critical security issue in IoT applications that are susceptible to malicious spoofing attacks via an innovative PHY solution combining NC-OFDM transmission and a directional modulation retrodirective array. As compared with traditional OFDM transmissions, NC-OFDM transmissions take place over a subset of active subcarriers to either avoid incumbent transmissions or for strategic considerations. As such, NC-OFDM transmissions have low probability of exploitation characteristics against classic attacks based on cyclostationary analysis. On the other hand, retrodirective antenna arrays are well known to be able to respond to an interrogator by sending signals back to the interrogator location without a priori knowledge, which is particularly useful in a multipath-rich environment. By incorporating the directional modulation technique, the antenna array will corrupt the information by distorting the digital modulation’s constellation diagrams in all unwanted transmitting directions. One way to realize the directional modulation functionality is to use time-modulated antenna arrays, in which the aliasing effects resulting from the time-modulation frequency are used to distort the signals in the undesired directions. Furthermore, the unique integration of NC-OFDM and directional modulation enabled by a time-modulated retrodirective antenna array whose modulation frequency is the NC-OFDM subcarrier can potentially lead to an unprecedented level of PHY hardware security against spoofing attacks by an adversary, even when the adversary is equipped with sophisticated ML-based attack techniques. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.