| Visible light communication(VLC)technology is a green lighting technology that utilizes the new Light Emitting Diode(LED)to provide lighting and communication at the same time.With its advantages of high confidentiality,no electromagnetic interference and no current radio wave method,it is particularly suitable for the new indoor lighting communication scheme.However,because non-transparent objects will block the transmission of visible light,and the use of visible light for uplink communication will cause certain visual interference to people,and limit its use scene.At the same time,from the level of communication system,the isolated visible light communication system does not share information at the level of information,and the application level is disjoined,which makes it unable to maintain correlation and mutual assistance with the outside world.In view of the above shortcomings,it is necessary to introduce a widely existing backbone network to connect with it,which can not only assume the role of uplink but also solve the problem of "information isolate island".As a ubiquitous network with the widest coverage and the largest number of users in the world and no radiation,power lines play an important role in the layout of smart power grids.While providing LED with electric drive lighting,it can not only break through the possibility of transmission between non-transparent objects,but also save the cost of secondary wiring.It can also use power line transmission data as uplink to introduce the external backbone network.This paper relies on the cascading technology of power line communication and visible light communication,and selects Orthogonal Frequency Division Multiplexing(OFDM)technology adapted to the respective channels on two different transmission channels to resist the ubiquitous communication media.Physical layer effects such as multipath effects and impedance fading,and only OFDM modulation mode is used to effectively avoid signal reprocessing in the secondary modulation process and reduce the redundancy of the cascaded communication system.First,the communication cascade scheme of OFDM modulation is studied by establishing the reference model of power line and visible light.The signal frame structure is designed according to the frequency band range of the power line OFDM sub-carrier,and the DC offset OFDM visible light modulation transmission scheme is selected in the direct VLC link of Intensity Modulation/Direct Detection(IMDD).Secondly,the matlab and Optisystem platforms have verified the fitting degree of the reference model in typical indoor application scenarios.Based on this basis,the realization principle of the communication drive circuit at all levels is analyzed,and the power line coupling module and the visible light transceiver module suitable for cascade communication are designed.Finally,a PLC-VLC cascaded communication system platform was designed and built,and experimental tests were carried out.The overall output sampling scheme of the DAC/ADC with a sampling rate of 400KSa/s was realized.The results show that,in a laboratory environment,the system uses a single 5m power line as the uplink,a 1W single lamp bead as the lighting source,and the visible light transmitting and receiving end can achieve stable communication on the power line with visible light downstream within a range of 20cm.The transmission error rate of the power line system and the visible light system can reach the order of 10-4. |
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