| Wireless optical communication is an emerging communication technology that uses light as the carrier and the atmosphere as the transmission medium.Wireless optical communication is divided into line-of-sight communication and non-line-of-sight communication according to the communication method.At present,the mainstream infrared optical communication is line-of-sight communication,while ultraviolet optical communication transmits signals through atmospheric scattering,which can realize non-line-of-sight communication.It has the advantages of high confidentiality,flexibility,and all-weather work.It can be applied to complex terrain,the occasion of confidential communication.Research on non-line-of-sight ultraviolet communication has been carried out for many years at home and abroad,but it is currently limited to theoretical research,and there are problems such as high system error rate and narrow bandwidth.In this paper,the key technologies such as UV atmospheric transmission characteristics,modulation technology and diversity reception technology are researched,simulated and tested for the problems of non-line-of-sight UV optical communication.Firstly,the UV absorption and scattering mechanism is analyzed,a modified UV multiple scattering model is established,the system pulse spreading is studied under different geometrical conditions,then the path loss under different transmitting and receiving elevation angles and communication distance is analyzed,and finally the channel loss under different aerosol particle concentration is simulated and analyzed.The results show that:1)The increase of the transmitting and receiving elevation angle leads to the increase of the system pulse spreading,in which the transmitting elevation angle has more influence on the pulse spreading.When the receiving elevation angle is 10°,the pulse response width of the transmitting elevation angle of 90°is 14 times that of the transmitting elevation angle of 10°.The smaller the transmitting and receiving elevation angle,the greater the effect of the receiving field of view on the pulse spreading.2)Appropriate reduction of the transmitting and receiving elevation angle can reduce the path loss of UV light transmission in the atmosphere,the path loss of both transmitting and receiving elevation angle of 20°is about 4d B lower than that of both 40°.3)The lower the visibility in the short distance,the lower the path loss of atmospheric transmission than in clear weather,so in short-range non-visible UV communication in the short-range non-visual UV communication,the increase of haze particle concentration in the atmosphere can reduce the channel loss.Then,in view of the narrow bandwidth and low transmission rate of non-line-of-sight ultraviolet light communication,the performance of modulated light source and modulation technology is analyzed,for the research of modulation technique,the simulation system under the noise of the poisson distribution,baton,PPM modulation technology under the communication distance,the relationship between the transmission rate and bit error rate,and the communication system performance under different modulation modes is analyzed.The weak signal detection technology of the receiver is studied,and the performance analysis model of the non-line-of-sight ultraviolet communication system based on diversity reception is established.The communication performance of the ultraviolet communication system under single receiving detector and double receiving detector is analyzed.The results show that the bit error rate of non-line-of-sight ultraviolet communication is reduced by about two orders of magnitude by using the same gain merging technique.The experimental results show that the BER of the non-visual UV communication system is less than 10-7 at a communication distance of 18 m and a communication rate of 1Mbps.The experiments and analysis basically meet the pre-requirements and lay the foundation for further research on the non-visual UV communication system and engineering applications. |
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