Random Receiver Orientation Effect on Channel Gain in LiFi Systems

Light-Fidelity (LiFi) has been considered as a complementary technology to radio frequency (RF) communications. The reliability of a LiFi channel highly depends on the availability and alignment of line-of-sight (LOS) links. In this study, we investigate the effect of receiver orientation including both polar and azimuth angles on the LOS channel gain in a LiFi system. The optimum tilt angle is calculated, which depends on both the user's location and direction. The probability density function (PDF) of signal-to-noise ratio (SNR) is derived for on-off keying (OOK) modulation. Using the derived PDF of SNR, the bit-error ratio (BER) of OOK in an additive-white Gaussian noise (AWGN) channel with random orientation of the receiver is evaluated. It is shown that the effect of random orientation is negligible if the optimum tilt angle is chosen. Finally, we assess the effect of random orientation on the Shannon-Hartley upper bound capacity.