Ultraviolet communication has very good non-line-of-sight transmission and privacy. Traditional ultraviolet communication systems are too large to be practical. Based on ultraviolet light-emitting diode (UV LED ), an ultraviolet light communication system was designed. The optical path design, clock recovery, channel coding and other aspects were studied. The duplex transmission protocol was designed, and 4.8Kb/ was realized with smaller resources. s transmission of information. The system can be used for two-way secure transmission of close-range voice and data.
As a new communication means, UV communication has the most outstanding advantages: it is not easy to be detected and intercepted, and can be used for non-line-of-sight communication through scattering. It is very suitable for short-distance anti-jamming and occlusion communication environments.
Foreign countries began to study ultraviolet light communication in the 1960s, and completed many aspects of research from basic principles to practical systems. In 2000, GTE of the United States successfully developed a new concealed ultraviolet-light wireless simplex communication system based on mercury lamps for the US military. The communication rate of the system is 4.8Kb/s and the bit error rate can reach 106. In 2002, the US Department of Defense's Advanced Research Projects Agency (DARPA) launched the Semiconductor Ultraviolet Systems (SUVOS) program, whose core mission was to manufacture ultraviolet light-emitting diodes (UV LEDs). Under the impetus of the program, UV LEDs have been successfully developed and mass production has begun.
The University of California, Riverside and the Massachusetts Institute of Technology used UV LEDs to construct a simplex communication test system and studied the characteristics of the UV transmission channel.
Since 2000, the company has been tracking UV-light communication technology. Chongqing University, Beijing Institute of Technology, National Defense Science and Technology University and other units have completed the development of prototypes of UV-based simplex communication systems with a transmission rate of up to 9.6 Kb/s. But so far, the UV light source used in these systems in China is still a low-pressure mercury lamp or a xenon lamp, which is large in size and power consumption, and is difficult to be miniaturized and portable. Another outstanding problem is that these systems at home and abroad can only perform simplex communication, which limits the practicability of the system to some extent.
In this paper, a dual-UV optical communication system based on UV LED is studied and designed, which can be used for two-way confidential transmission of air and short-distance voice and data.
1. Characteristics of ultraviolet light communication
Ultraviolet communication has the following characteristics:
(1) The wavelength is 200 to 280 nm. This band is open and is not subject to the Radio Regulatory Commission and does not require frequency application when in use.
(2) Ultraviolet light of 200~280nm belongs to the day blind segment. The sunlight of this wavelength is absorbed by atmospheric molecules and suspended particles, and the signal intensity decays exponentially. The energy when it reaches the surface is very weak. Therefore, the background noise of ultraviolet light communication is very small.
(3) Due to the influence of atmospheric attenuation, ultraviolet light is suitable for short-range communication within a range of 1 km. After this range is exceeded, it will be difficult to detect, and there is little possibility of interference and interception. Therefore, the confidentiality of ultraviolet communication is very high.
(4) The ultraviolet light source illuminates the space of the receiver by the space, diffuses into the field of view of the receiver through the tiny particles diffused in the atmosphere, and is received by the receiver. Therefore, UV light can be used for non-line of sight communication (NLOS) and is suitable for use in occluded scenes.
Due to the above characteristics, the ultraviolet communication system can be widely used in tactical mobile communication and secure communication.
2. Design of duplex UV communication system
The current ultraviolet communication system is one-way communication, and the modulation method uses a conventional OOK (on-off) and PPM (pulse position modulation) mode. If you want to achieve two-way communication, one solution is to adopt frequency division multiplexing. The transmitting and receiving parties occupy a different wavelength in the range of 200~280nm. The other solution is to adopt time division multiplexing, and the transmitting and receiving sides share one wavelength. But take up different time slices. Due to the limited wavelength range of the day blind segment, the system capacity of the former solution is difficult to increase. This article takes the second option.
2.1 system composition
The core component of the system is UV? LED and UV detectors, in addition to a programmable logic array (FPGA), external voice compression codec chip and USB interface chip, respectively, to support the transmission of voice and data, as shown in Figure 1.
Figure 1 Block diagram of the UV communication system
Nife Battery,48V 800Ah Nife Battery,Ni-Fe Battery 700~1200Ah,Ni-Fe Battery 700~1200Ah
Henan Xintaihang Power Source Co.,Ltd , https://www.taihangbattery.com