The autonomous, and yet connected,  wireless world requires sensing and high-data-rate communications, accurate localization and ranging, and resiliency against interference and eavesdropping. These constitute our group main themes of the research that can be categorized as: 1) Next generation of high data rate communications and sensing, 6G and beyond, 2) Joint communication, localization, and security designs for the next generation of dense wireless sensor network (WSN) and IoT.

Thrust 1: Next generation of high data rate communications and sensing, 6G and beyond, [1-7]: The exploding demand for the next generation of cellular network, 6G and beyond, necessitates multiple-element transceivers such as scalable beamforming array, over 100 GHz, in order to provide the required high data rate communication as well as the high-resolution imaging. Intelligent and scalable millimeter-wave (MMW) and THz antenna arrays require heterogeneous integration with different technologies and components including: III-V compound material for efficient power generation above 100 GHz, photonic integrated circuits (ICs), micro-electromechanical (MEMS) or other passive filters to cancel out malicious attacks such as interference, microprocessors, etc, into a higher-level system-in-package (SiP). Therefore, future wideband and high-frequency scalable arrays need power-efficient and compact integration through novel architectures and innovations from transistor and circuit level up to package, system, and protocol level. In this research thrust we are trying to solve the major challenges for future heterogeneous integration of wideband scalable arrays include: 1) Interconnects and power delivery network, 2) Phase noise and frequency synchronization between tiles/dies, 3) Efficient wideband modulation, 4) Compact and low-cost antenna and IC array packaging, 5) Transmitter efficiency, heating distribution and mechanical stability, 6) Resiliency and interference cancellation.

Thrust 2: Communications, Localization, and Physical Layer Security Compatible with Machine Learning-Aided Protocols for the Next Generation of Dense IoT Networks [8-12]: The next generation of the wireless world, 5G, 6G and beyond, will also have over one trillion IoT devices connected. In order to have everything automated and connected, it is essential to develop novel solutions across three thrusts: 1) security protocols for detecting and overcoming malicious attacks such as jamming and eavesdropping, 2) accurate localization and ranging under severe multipath and in dense environments, and 3) efficient and low error rate communications under collisions in multi-node systems. On the security front, the main challenges for hardware implementation of physical layer security (PLS) protocols in IoT and sensor networks are underlying assumptions on synchronization, accurate localization, and beam alignment between reader and the IoT sensor nodes as well as information leakage in side-lobes with current directional antenna approaches. Furthermore, accurate localization and ranging become increasingly challenging as the number of connected nodes increases, mainly due to the rich scattering indoor environments leading to severe fading. In order to mitigate the multipath effect and to estimate the fading points, low-power and low-cost wideband or multiband localization techniques are required for future efficient miniaturized IoT nodes. In addition, joint localization and multi-node communications are desired for future low-latency and intelligent WSN. Therefore, collisions might occur whenever multiple IoT nodes intend to communicate to a reader at the same time. The current collision recovery protocols essentially try to avoid collisions and are constrained by the number of IoT nodes and the multi-path effects. Therefore, alternative protocols for collision recovery of two or more tags can potentially lead to a significant improvement in the overall throughput of the system. The aforementioned challenges for future intelligent WSN necessitate innovation and novelty from circuit level to the protocols and algorithms level, which is the main focus of our group research.

[1] Ebrahimi, M. Bagheri, P. Wu and J. F. Buckwalter, “An E-band, Scalable 2×2 Phased-array Transceiver using High Isolation Injection Locked Oscillators in 90nm SiGe BiCMOS,” 2016 IEEE Radio Frequency Integrated Circuits Symposium (RFIC), San Francisco, CA, 2016, pp. 178‒181.

[2] Ebrahimi, P. Wu, M. Bagheri and J. F. Buckwalter, “A 71–86-GHz Phased Array Transceiver Using Wideband Injection-Locked Oscillator Phase Shifters,” IEEE Transactions on Microwave Theory and Techniques (TMTT), vol. 65, no. 2, pp. 346‒361, Feb. 2017.

[3] Ebrahimi and J. F. Buckwalter, “Robustness of Injection-locked Oscillators to CMOS Process Tolerances” in International Conference on Theory and Application in Nonlinear Dynamics, Springer Press Publication, 2016. (invited book chapter).

[4] Ebrahimi and J. F. Buckwalter, “A 71–86 GHz Bidirectional Image Selection Transceiver Architecture,” IEEE Radio Frequency Integrated Circuits Symposium (RFIC), Honolulu, HI, 2017, pp. 384‒387.

[5] Ebrahimi and J. F. Buckwalter, “A High-Fractional-Bandwidth, Millimeter-Wave Bidirectional Image-Selection Architecture with Narrowband LO Tuning Requirements,” in IEEE Journal of Solid-State Circuits, (JSSC), vol. 53, no. 8, pp. 2164‒2176, Aug. 2018.

[6] Ebrahimi, K. Sarabandi, J. F. Buckwalter, “A 71-76 / 81-86 GHz, E-band, Phased Array Transceiver Module With Image Selection Weaver Architecture for Low EVM Variation” 2020 IEEE Radio Frequency Integrated Circuits Symposium (RFIC), 2020, pp. 95-98.

[7] Shah Zaib Aslam and Ebrahimi, “Compact Heterogeneous Integration for Next Generation High Frequency Scalable Array with Miniaturized and Efficient Power Delivery Network,” submitted to IEEE Transactions on Microwave Theory and Techniques. (Link: ).

  • [8] Ebrahimi, H. Mahdavifar “A Novel Approach to Secure Communication in Physical Layer via Coupled Dynamical Systems,” in Proceeding IEEE GLOBECOM 2018, Abu Dhabi, UAE, 2018.
  • [9] Mahdavifar and N. Ebrahimi, “Secret Key Generation via Pulse-Coupled Synchronization,” in 2019 IEEE International Symposium on Information Theory (ISIT), Paris, France, 2019, pp. 3037-3041.
  • [10] Ebrahimi, B. Yektakhah, K. Sarabandi, H. Kim, D. Wentzloff, D. Blaauw, “A Novel Physical Layer Security Technique Using Master-Slave Full Duplex Communication,” in proceeding of 2019 IEEE MTT-S International Microwave Symposium (IMS), Boston, MA, USA, 2019, pp. 1096-1099.
  • [11] Ebrahimi, H. -S. Kim and D. Blaauw, “Physical Layer Secret Key Generation Using Joint Interference and Phase Shift Keying Modulation,” in IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 5, pp. 2673-2685, May 2021.
  • [12] Payman Pahlavan and Ebrahimi, “Dual-band Harmonic and Subharmonic Frequency Generation Circuitry for Joint Communication and Localization Applications Under Severe Multipath Environment,” submitted to IEEE Transactions on Microwave Theory and Techniques. (Link: ).