Transmission Techniques for Multi User MIMO VLC Systems Using Flip-OFDM

Abstract

Flip Orthogonal Frequency Division Multiplexing (flip-OFDM) is one of the unipolar forms of OFDM used in Visible Light Communication (VLC) systems. This paper analyzed the multi user VLC systems to transfer flip-OFDM based signal using different form of Multiple Input Multiple Output (MIMO) transmission techniques. These transmission techniques are Repetitive Coding (RC), Spatial Modulation (SM), generalized spatial modulation (Generalized SM) and spatial multiplexing (SMP). Multi User Interference (MUI) at the transmitter has been bypassed using precoding process of Block Diagonalization (BD). The performance analysis of proposed system is carried out with the help of simulation. A comparative study for RC, SM, generalized SM and SMP for multi user VLC system is performed with regard to Bit Error Rate (BER) performance. These transmission techniques are compared with and without the use of flip-OFDM. Furthermore, we also analyzed the Peak-to-Average Power Ratio (PAPR) of flip-OFDM signal. Simulation results showed that the generalized SM outperforms RC, SMP, SM approximately by 9dB, 5dB, 2dB Signal-to-Noise RATIO (SNR), respectively without flip-OFDM and, 8.5dB, 7dB, 3.3dB SNR respectively with flip-OFDM to obtain a BER of 10−6. We also analyzed the MIMO transmission techniques with regards to transmission efficiency. It is found that SMP offers better transmission efficiency with lower modulation order. To obtain the spectral efficiency of 8 bits per channel use (bpcu), RC, SM, generalized SM and SMP needs modulation order M = 256, 64, 8 and 4, respectively. Hence SMP is power efficient.