M-PAM Joint Optimal Waveform Design for Multiuser VLC Systems Over ISI Channels

Visible light communication is a candidate technique to provide high-speed data transmissions. This paper proposes a joint optimal waveform design algorithm for visible light communication systems using M-ary pulse amplitude modulation to support multiple users. Transmitted waveforms and minimum mean squared error filters are jointly optimized to minimize the intersymbol and multiple access interferences. Based on different channel conditions, the designed waveforms and modulation constellation sizes can be adaptively adjusted to guarantee the highest bit rates. Channel uncertainty is also considered in this paper. Compared with optical code division multiple access and time division multiple access, the algorithm proposed can provide higher bit rates. In addition, the proposed algorithm can flexibly adjust the illumination level by changing the optimization constraints. An offline waveform design algorithm is then proposed to diminish the optimization computation time. A waveform lookup table can be established offline in advance, and the proper waveforms can be selected from the table based on the actual channel gains in real time. The performance of the offline algorithm can be estimated by using the channel uncertainty model.