In this paper, three kinds of 32-QAM
constellation shaping schemes are proposed and demonstrated in an SC-FDE based VLC system, where two special circular constellations, named Circular (4, 11, 17) and Circular (1, 5, 11, 15), and a triangular constellation are designed based on the Shannon's criterion.
It fluctuated around [10.sup.-6], whereas it fluctuated at [10.sup.-2] and [10.sup.-0.5] during heavy rain under 16-QAM and 32-QAM, respectively.
These problems occurred for 33 min and 47 min during the rainy periods under the 16-QAM and 32-QAM schemes, respectively.
The major rain effect occurred for 23 min/day under QPSK, whereas it reached 27, 36, and 38 min/day under the 8-PSK, 16-QAM, and 32-QAM schemes, as shown in Figure 10(b).
The amount of losses was not significant, and the PER occurred only under the 32-QAM scheme, as shown in Figure 11.
The ERS output shows that trees significantly affect PER performance under the 32-QAM scheme, as shown in Figure 12.
Complete blocking of transmission data occurred when the car was under the bridge even for small crossing period under the 32-QAM and 16-QAM schemes, whereas a higher PER was reached under the 8-PSK modulation scheme.
The required SNRs of the different modulation levels (BPSK, 4-QAM, 8-QAM, 16-QAM, 32-QAM
, 64-QAM, 128-QAM and 256-QAM) under the target BER are calculated based on .