Antenna and Excitation Signal Shared Joint OAM Spatial Field Digital Modulation System

As a special form of index modulation (IM), spatial field digital modulation (SFDM) encodes information in the spatial distribution of electromagnetic (EM) field, achieving high energy efficiency, low hardware complexity, and physical layer security features. In this paper, a joint spatial field digital modulation (JSFDM) system is proposed to transmit SFDM signals and bandpass modulation signals simultaneously. The JSFDM system contains two independent links: an SFDM link and a bandpass modulation link, which share antenna resources and excitation signals without requiring coordinated operation. The architecture of the proposed JSFDM system is similar to space modulation (SM) systems. As a contrast, such JSFDM system eliminates the need for joint design, joint demodulation, or time synchronization between two links. Hence, the JSFDM system could be regarded as a simple combination of the original SFDM system and the bandpass modulation system. Based on IEEE 802.11n protocol, we design and build its prototype using a multi-mode orbital angular momentum (OAM) antenna for practical verification. Numerical simulations and experimental measurements demonstrate its feasibility, and reveal the determinants that influence the bit error rate (BER) performance. The proposed JSFDM scheme could be seamlessly integrated with the existing digital bandpass modulation communication protocols, thus establishing an additional SFDM link over current commercial wireless communication systems.