Study On Receiver Of High Data Rate Ultraviolet Communication System

Ultraviolet(UV) communication system which has the potential advantages of good security, high powerful anti-jamming, capability of non-line of sight(NLOS), low power, miniaturized transververs and high power densities is a new type optical communication system. Since 1960`s, UV communication system has generally matured and has been applied in US Army. But the data rate of UV communication system is no more than several kilo bits per second which is the bottlenecks of its wide application. Motivated by rapid advantage in deep UV light emmiting diodes (LEDs), filters and solar-blind photomultiplier tubes (PMTs), a high data rate UV communication system has been recently built and utilized for evaluation of NLOS UV links in outdoor environments according to certain literature. Compared with the UV communication system based on low pressure mercury vapor arc discharge lamp(hereinafter the term UV communication system based on low pressure mercury vapor arc discharge lamp will be used as low data rate UV communication system), the new one is much smaller in size, more flexibility and has much lower power comsumption. Besides, the most important thing is, the data rate has been improved of more quantity level.Unique UV atmospheric propagation characristics is the theoretical basis. This paper presents the effects of atmospheric absorption, scattering and turbulent diffution on UV communication system. According to these approaches, a singal scattering model based on ellipsoidal coordinates and a multiple scattering model based on Monte Calo simulation have been establelished. As a result, the latter can put a favorable construction on high data rate UV communication system.Taking Pulse position modulation (PPM) to drive LED arrays can enhance the ability of UV communication system to oppose disturbulance. PPM can also reduce the average power spectrum of light source and improve stability of system which is very suitable for high data rate UV communication system.In order to improve the data rate, one have accomplished some hardware designs of receiver base on low data rate UV communication system and sovled some key problems as follows: using deep LEDs which are modulated through pulse position modulation to substitude low pressure mercury vapor lamp; taking solar blind PMT together with filter as the detector; designing optic-electric convertion circuit and signal pretreatment circuit which transform the signal into standard CMOS level signal; taking FPGA development board as the PPM demodulation platform, during FPGA design, it is frame synchronization clock revovering that is the difficulty and the key stone.Experiments indicate that the high data rate UV communication system built by this paper is well on its way. Especially the data rate can be improved to 115.2Kbit/s within an area of interior distance. Besides, the high data rate UV communication system which has laid a good foundation of its utility is much smaller in size, more flexibility and has much lower power comsumption.