| Summary: | 碩士 === 國立中正大學 === 通訊工程研究所 === 107 === Because manufacturing technology of light-emitting diodes (LEDs) has gradually matured, LED is popular recently. The novel communication system that uses visible light as medium to transmit signals is expected as complementary to current wireless communication technologies based on Radio Frequency (RF) system. In general, the energy emitted from Imaging Optics is considered with the intersection of the receiver location and the projection area. In this paper, each receiver is refined with smaller grid with uniform size. Accordingly, the receive energy only dependent to the irradiation and incident angles. The construction of the channel matrix based on this way takes into account not only the area of the receivers but also the angles from the imaging optics to the receivers. In this paper, the modified projection locations of the LED lamp on the receiver plane derived from the pinhole imaging are different from the center of the projection in the imaging visible light communication (VLC) system. Considering the refined method in [19] adjust the projection center, the construction of the channel matrix is more feasible in the simulation of the multiple-input multiple-output (MIMO) VLC system. The maximal gap of system performance between the previous and the new methods is almost 1 dB.
The existing VLC techniques consider spatial modulation (SM) and spatial multiplexing (SMP) in 4×4 Multiple-Input Multiple-Output (MIMO) schemes. With the development of camera resolution in smart phones (more than 12 million pixels), each pixel can be an optical receiver. Therefore, the massive MIMO techniques constructed in RF systems can be applied into the VLC system. In addition, this paper designs a scheme with more receivers up to 25 to receive more transmitted energy. Eventually, the transmission efficiency can be increased with more powerful modulation. The related gain becomes larger as the projected area increases. In summary, gain of the system with 25 receivers can be up to 5 dB (BER 10-2) compared with the system with 4 receivers.
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