Optimization of the Receiving Orientation Angle for Zero-Forcing Precoding in VLC

• Published in: IEEE communications letters Vol. 25; no. 3; pp. 921 - 925
• Main Authors: Morales-Cespedes, Maximo, Haas, Harald, Armada, Ana Garcia
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Complexity theory; Line of sight communication; multiuser multiple-input single-output; optical channel; Optimization; Orientation; Performance degradation; Photodetectors; Photometers; Precoding; Radio frequency; Receiving; Scattering; Simulation; Visible light communication; Visible light communications; zero forcing
• ISSN: 1089-7798; 1558-2558
• DOI: 10.1109/LCOMM.2020.3038027

We study the performance of linear zero-forcing (ZF) precoding in multiuser multiple-input single-output visible light communications (VLC) when we are able to select the receiving orientation angle (ROA) of each user. For radio-frequency communications, the non-line-of-sight rich scattering environment usually ensures the linear independence among user's channels. However, this condition is less likely to happen in VLC systems, degrading the performance of ZF precoding. In this work, we propose a variable ROA (vROA) photodetector able to modify its orientation vector in order to generate semi-orthogonal channel responses among users. We derive the algorithm for determining the orientation of the vROA photodetector of each user, obtaining optimal and suboptimal solutions with high and low complexity, respectively. Simulation results show that the performance of ZF precoding is improved considerably by managing the users ROA.