Enhanced Performance of Visible Light Communication Using Three-dimensional Spatial Multi-user Holographic Multiplexing

Visible light communication (VLC) has recently emerged as a promising solution for 6G, offering high speed, efficient spectrum usage, and resistance to electromagnetic interference. In order to fully exploit the extensive coverage capabilities of VLC, multi-user communication scenarios have garnered significant attention. However, existing techniques, such as light beam shaping using Spatial Light Modulators (SLMs), are limited by uncontrollable focusing planes and positioning errors, which result in signal attenuation and communication interruption. Digital holography, another approach, is hindered by factors like dependence on physical lenses and high crosstalk for multiplate imaging. Moreover, varying lens types result in differing reconstructed image sizes, posing challenges for accurate holographic imaging. To address these issues, this paper proposes a Random Multiplate Hologram (RMPH) technique that employs high-dimensional orthogonal random vectors to achieve depth-multiplexed multi-user holography. This method effectively mitigates crosstalk between holograms, accurately controls users' three-dimensional positions and reception ranges, enhances system robustness, and increases signal acceptance probability (AP) when positioning errors are taken into account. The RMPH approach can accurately control the size and position of targets at different depths and achieve over 90% signal reception probability for users with varying reception ranges at distinct positions in simulations. Experimental results indicate that the RMPH method exhibits a power variation of only approximately 1 dB, compared to the multi-Fresnel lens (MF) method's power variation of up to 10.9 dB. Furthermore, the RMPH method demonstrates superior localization and communication capabilities, achieving an 9.40 dB power improvement at the edge of the receiving range compared to other methods. Moreover, the RMPH method helps to reduce cross-interference among different depths. Compared to the MPH method, the RMPH method shows an improvement of more than 4 dB in the received optical power when conducting forward and backward displacement. To the best of our knowledge, this is the first-time high-quality communications have been provided simultaneously to users at different 3D locations when a single transmitter is available. This outcome underscores the feasibility of future multi-user communication in the realm of visible light communication, leveraging the proposed RMPH method.