Achievable Rate Region of the Zero-Forcing Precoder in a 2 X 2 MU-MISO Broadcast VLC Channel with Per-LED Peak Power Constraint and Dimming Control

摘要

In this paper, we consider the 2 X 2 multi-user multiple-input-single-output(MU-MISO) broadcast visible light communication (VLC) channel with two lightemitting diodes (LEDs) at the transmitter and a single photo diode (PD) at eachof the two users. We propose an achievable rate region of the Zero-Forcing (ZF)precoder in this 2 X 2 MU-MISO VLC channel under a per-LED peak and averagepower constraint, where the average optical power emitted from each LED isfixed for constant lighting, but is controllable (referred to as dimmingcontrol in IEEE 802.15.7 standard on VLC). We analytically characterize theproposed rate region boundary and show that it is Pareto-optimal. Furtheranalysis reveals that the largest rate region is achieved when the fixedper-LED average optical power is half of the allowed per-LED peak opticalpower. We also propose a novel transceiver architecture where the channelencoder and dimming control are separated which greatly simplifies thecomplexity of the transceiver. A case study of an indoor VLC channel with theproposed transceiver reveals that the achievable information rates aresensitive to the placement of the LEDs and the PDs. An interesting observationis that for a given placement of LEDs in a 5 m X 5 m X 3 m room, even with asubstantial displacement of the users from their optimum placement, reductionin the achievable rates is not significant. This observation could therefore beused to define "coverage zones" within a room where the reduction in theinformation rates to the two users is within an acceptable tolerance limit.