Visible light communication (VLC) is an optical wireless communication technology that uses visible light emitting diodes (LEDs) as a communication source. Since the LEDs are also used for illumination, the cross-section emission effects of the LEDs need to be analyzed as they apply to indoor VLC channels. In order to evaluate the illumination and communication performance according to the emission cross-section pattern a simple LED model with a quasi-elliptic emission cross-section is proposed and compared to a circular LED model. The spatial distributions of the received optical power and root mean square delay spread are analyzed through calculation and comparison. The LEDs with a quasi-elliptic emission cross-section provide less fluctuation in the illumination and optical power distribution at the receiving plane. However, the RMS delay spread increases and subsequently the maximum data rate decreases for the quasi-elliptic emission cross-section LEDs. The single transmitter VLC system is found to support at least 17 and 24 Mb/s for circular and quasi-elliptic emission cross-section LEDs for the entire receiving plane, respectively. The four-transmitter VLC system is found to support at least at 30 and 33 Mb/s for circular and quasi-elliptic emission cross-section LEDs for the entire receiving plane, respectively.
Recently, the visible light communication (VLC) is considered as a future emerging technology in the telecommunication and lighting industry, as defined in the IEEE 802.15.7 standard. In the meantime, the ANSI E1.45 standard was made to provide VLC data transmissions from a VLC data server to a lighting device that is equipped with a VLC transmitter in lighting control networks. However, the ANSI E1.45 scheme cannot provide reliable transmissions of VLC data, and thus a lost data, if any, cannot be recovered. To overcome such limitation, timer-based VLC data transmission schemes have been studied by applying the retransmission scheme of Internet. However, these schemes still have limitation that the lost VLC data cannot be recovered immediately. Hence, in this study, the authors propose new reliable transmission schemes for VLC data over lighting control networks. The proposed schemes are classified into the packet-based (PRVS) and fragmentbased (FRVS) schemes. From performance analysis by simulation, the authors see that the FRVS gives the best transmission throughput among the four candidate schemes. In addition, it is shown that the proposed reliable transmission scheme can effectively perform the error recovery operation in the networks with packet losses, compared to the ANSI E1.45 scheme.
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