Physical Layer Secure Communication Using Orbital Angular Momentum Transmitter and a Single-Antenna Receiver

Orbital angular momentum (OAM) for radio communications has the potential of simultaneously transmitting multiple signals at the same frequency and time resources. This multiplies the achievable channel capacity at a given bandwidth by increasing the available number of simultaneous data streams. One downside of OAM radio communication is the requirement of multimode radio frequency (RF) hardware at both ends of a link, i.e., the transmitter and the receiver. This is not always practically viable, especially as we move toward low-profile receivers in future communication devices. In this work, we present a novel method of OAM-based radio communication with enhanced physical layer security that requires only a single-antenna receiver. We first present the system architecture, then we design and realize a Rotman lens-based circular antenna array transmitter operating at 5.8 GHz. We then experimentally verify the capability of the hardware to create multiple modes. As a proof-of-concept, we propose a communication system that simultaneously uses modes 0 and +1 of the OAM beamformer and in doing so show how a single-antenna receiver can be used for data recovery. We first identify a general analog modulation expression and use the proposed system to transmit digitally modulated data stream to a single-antenna-equipped receiver. A precommunication training sequence is required to realize the proposed approach. The experimental results verify the simulated predictions.