Coexisting Radio Frequency and Optical Wireless Directional Small Cells (CROWD Networks)

In this project we seek to use untapped optical wireless (OW) spectrum and the high areal spectral efficiency of directional small cells (DSCs) to augment existing RF small cells (RFSCs) to realize new levels of performance in future dense networks. In the proposed Coexisting RFSC and Optical Wireless DSC Network (CROWD), the optical DSC is used to offload high-speed downlink traffic from the RFSC while the RFSC provides coverage for highly mobile devices and devices without a reliable DSC connection. CROWD is intended to realize performance gains in wireless throughput, latency, and streaming performance. Outcomes of the work include: (1) analysis and simulation of heterogeneous CROWD networks under varying user traffic and mobility models, (2) a design framework and methodology for the creation and adoption of CROWD networks for future 5G systems, and (3) a functional proof-of-concept implementation in our existing testbed suitable for validation of the analytic and simulation results and as a blueprint for scale up.



Example of a CROWD network comprised of RF and Optical Wireless access points

The project is expected to realize a new operating point for hybrid, heterogeneous networking with RF and optical wireless physical layers. We anticipate discovering the critical intersection of cell size and handover properties (latencies, transition thresholds) for indoor mobile data consumption under realistic use cases. Although much work exists for RF small cells, WiFi characterization, or handover; the nature of providing seamless data delivery for a mixed mode of sub-meter cells with directional and omnidirectional network overlays is new territory anticipated for directional media such as visible light communication or LiFi. The work is expected to provide a framework for the analysis and study of future heterogeneous network behavior that is anticipated as the OW medium continues to expand toward THz speeds. The unique combination of skills of the research team supports achieving the proposed goals.

 The availability of spectrum for wireless communications has been identified as a critical enabler to growth in GDP; the proposed work seeks to exploit an alternative to the crowded RF arena to enable a new direction of research to realize untapped spectrum capacity. This capacity will permit the expanded capability of mobile wireless devices to continue to evolve, leading to enhances in many applications supporting quality of life, energy conservation, safety, and productivity that are derived directly from continuously-connected wireless devices.  We also anticipate influencing the development of the 5G agenda and adopted standards including the IEEE as the role of heterogeneous networks. The proposal includes educational activities that complement the proposed research, including mentoring female and under-represented students through the prestigious McNair fellowship, developing an interdisciplinary Massive Open Online Course (MOOC) as a high-school STEM attractor, and development of curriculum for several courses.

This project involves collaborators from Boston University, the New Jersey Institute of Technology, the University of Albany, and Chicago State University, focused on how future 5G systems will need to support and manage multiple communications media including existing RF-based WiFi, future mm-Wave, and wireless optical systems.



Myriad instances of handover between access technologies in a CROWD network


  1. Rahaim and T.D.C. Little, “Interference in IM/DD Optical Wireless Communication Networks,” Journal of Optical Communications and Networking, Vol. 9, No. 9, pp. D51-D63, 2017.
  2. M.B. Rahaim, T.D.C Little, H. Elgala and S. Govindasamy, “Ultra-Dense IoT Architecture using Hybrid CSMA with Sector Based Scheduling (CSMA/SS) via Visible Light Communications,” ACM MadCom, Proc. Intl. Conf. on Embedded Wireless Systems and Networks (EWSN), Uppsala, Sweden, Feb. 20-22, 2017.
  3. T.D.C. Little and M.B. Rahaim, “Driving Visible Light Communications Towards the Tipping Point for Broad Scale Adoption,” In Proceedings of ACM Workshop on Visible Light Communication Systems, Snowbird, UT, USA, October 2017 (VLCS’17), (Invited).
  4. R. Das, Z. Li, and A. Khreishah ”Integration of Asymmetric and Aggregated Li+WiFi Systems” Poster at NJIT REU Research Symposium, Newark NJ July 27, 2017
  5. J. Lopez, S. Shao, and A. Khreishah “Circular Retroreflector Based Visible Light Indoor PositioningPoster at NJIT REU Research Symposium, Newark NJ July 27, 2017
  6. S. Shao and A. Khreishah “Delay Analysis of Unsaturated Heterogeneous Omnidirectional-Directional Small Cell Wireless Networks: The Case of RF-VLC Coexistence,” in IEEE Transactions on Wireless Communication, Vol. 15 No. 12, Dec. 2016
  7. F. Hussein, H. Elgala, B. Fahs, M. Hella, “Experimental investigation of DCO-OFDM adaptive loading using Si PN-based receiver,” the IEEE Wireless and Optical Communication Conference (WOCC), pp. 1-5, April 7th 2017.
  8. S. Shao, A. Khreishah, and H. Elgala “Pixelated VLC-backscattering for Self-charging IoT Devices”, in IEEE Photonics Technology Letters, Vol. 29, No. 2, Jan. 2017, pp. 177-180