Visible light communication (VLC) needs to take into account both lighting and communication, so multi-light-source distribution is required, and optical multiple input multiple output (OMIMO) technology emerges. The traditional OMIMO system improves the channel capacity by activating all antennas to transmit information, resulting in strong co-channel interference between channels and poor information reliability. Optical spatial modulation (OSM), as a new type of OMIMO technology, activates one transmit antenna at every moment to avoid co-channel interference between channels. At the same time, since the transmitting antenna itself carries some bit information, the transmission rate of the system is improved. However, OSM must meet the requirement that the number of transmit antennas is an integral power of 2, and only one antenna is used at the same time, which limits its application. On the basis of the OSM system, the optical generalized spatial modulation (OGSM) system transmits information by activating multiple antennas. At the same time, all activated antennas can transmit the same or different data information, thereby further improving the transmission rate. But the antenna selection of OGSM is random, so we propose a VLC multiple input multiple output (MIMO) system scheme based on OGSM. The scheme improves the transmission rate by activating multiple transmitting antennas and combining with modulation methods such as multiple phase shift keying (MPSK) system; at the same time, a norm-based antenna selection algorithm is introduced, which greatly reduces the computation complexity.

In order to analyze the performance of OGSM system, we combine OGSM system with OMIMO system. At the transmitter, the number of activated transmit antennas is used to carry the constellation modulated transmission symbols to construct a constellation mapping table; at the same time, in order to improve the bit error performance, a norm-based antenna selection algorithm is introduced in combination with the channel characteristics. The system selects the sub-channel with the largest channel norm to transmit information in turn, and then selects the optimal antenna combination. At the receiving end, in order to obtain the antenna combination and modulation symbols, the maximum likelihood (ML) detection algorithm is used to obtain the Euclidean distance. The theoretical bit error rate (BER) of the OGSM system is analyzed through the segmented boundary theory. Furthermore, the spectral efficiency, transmission rate and complexity of the OGSM system under different conditions are analyzed (Table 2).

For reliability, we use a norm-based antenna selection algorithm to improve the bit error performance. When the number of active antennas N_a at the transmitting end is 2, the modulation method is binary phase shift keying (BPSK), and the transmission rate is 4 bpcu, it can be obtained that for the BER of 10^-4, using the norm-based antenna selection algorithm, and for 2, 3, and 4 receiving antennas, the average signal-to-noise ratio (SNR) is improved by 3.1 dB (Fig. 2). When the modulation method is BPSK, the number of active antennas N_a at the transmitting end is 2, and the number of receiving antennas N_r is 1 and 2 respectively, for the BER of 10^-4, the SNR of 4 receiving antennas scheme is reduced by 8.4 dB in comparison with the 3 receiving antennas scheme (Fig. 3). When the number of active antennas N_a at the transmitting end is 2, the number of receiving antennas N_r is 2, and the modulation methods are BPSK, 4-pulse amplitude modulation (4PAM), quadrate amplitude modulation (QAM), and quadrature phase shift keying (QPSK), for the BER of 10^-3, compared with BPSK, the transmission rates of the other three modulation methods are all increased by 2 bpcu, and the SNRs are increased by 0.7 dB, 3.2 dB, and 5.1 dB, respectively (Fig. 4). For effectiveness, with the increase of the modulation order and the number of activated transmit antennas, the transmission rate and spectral efficiency will increase (Table 2).

Aiming at the disadvantage that OSM can only activate one antenna at the same time, an OGSM scheme is proposed. This scheme significantly improves the transmission rate of the system by changing the transmitting antenna number from one to multiple and by using modulation methods such as MPSK. At the same time, using the norm-based antenna selection algorithm, the system gets better bit error performance than those using the traditional random antenna selection algorithm. The main conclusions include: by increasing the number of receiving antennas, the bit error performance will be improved; when the number of activated transmitting antennas is constant, by using different modulation methods, such as BPSK, QPSK, 4PAM, and QAM, with the increase of the modulation order, the transmission rate of the system will increase, but the bit error performance will be impaired.