  Optical wireless communication (OWC) systems have been the subject of a
significant amount of interest as they can be used in sixth generation (6G)
wireless communication to provide high data rates and support multiple users
simultaneously. This paper investigates the impact of receiver orientation on
resource allocation in optical wireless systems, using a wavelength division
multiple access (WDMA) scheme. Three different systems that have different
receiver orientations are examined in this work. Each of these systems
considers 8 simultaneous users in two scenarios. WDMA is utilised to support
multiple users and is based on four wavelengths offered by Red, Yellow, Green
and Blue (RYGB) LDs for each AP. An angle diversity receiver (ADR) is used in
each system with different orientations. The optimised resource allocations in
terms of wavelengths and access point (AP) is obtained by using a mixed-integer
linear programming (MILP) model. The channel bandwidth and SINR are determined
in the two scenarios in all systems. The results show that a change in the
orientation of the receiver can affect the level of channel bandwidth and SINR.
However, SINRs in both scenarios for all users are above the threshold (15.6
dB). The SINR obtained can support t data rate of 5.7 Gbps in both scenarios in
all systems.
