Research On The Key Technology Of Wireless Communication With Laser Based On Acoustic-Optic Modulation

Wireless communication means that both sides of terminals through wireless technology to transmit text, voice or other datas. The wireless communication, which based on laser, is more and more be favored by researchers at home and abroad, because of its advantages such that wide frequency band, strong resistance to electromagnetic interference, and no apply for frequency. The main research content of this paper is laser wireless communication. Based on hardware such as laser, acousto-optic modulator,photomultiplier tubers, and programmable logic devices, this paper designed and set up a complete set of laser wireless communication system, and realized the communication experiment on the mode of simplex, duplex and retro-reflected.This paper analyzes the principle of laser transmission, the transmission model and the working way of laser communication. The final solution plans to use the semiconductor laser as the communication light source, use the visual model and acousto-optic modulation to set up the platform structures, and do the experiment.In order to guarantee the smooth of the communication system, this paper tested the key devices at first. The internal and external modulation of the laser, the control way of the acousto-optic modulator, and the simple communication system all be tested. The results show that the laser can be use to do optical communication, which internal modulation frequency can reach 30 KHz and external modulation frequency can reach5 MHz at most. And the acousto-optic can be used by three ways to control,at last this paper choose to input TTL level to realize the digital modulation.Simplex communication mode is widely used and the system is easy to be built.This paper builds the complete simplex communication system at first, with 2FSK modulation way and acouto-optic external modulation. The result of the simplex communication experiment shows that the system can transfer numbers and letters at the transmission rate of 115.2 kbit/s, and the maximum carrier is 0.7MHz.In order to expand the application fields of free space optical communication, a communication system of Modulating Retro-reflector is designed, which is based on simplex communication system. This system works by using FPGA development board to send TTL signal to control the AOM, and adopting quaternary modulation mode which is combined 2FSK and 2PWM modulation method to realize the reverse modulation laser communication indoor. Besides that we have encrypted the serialsignal through the encryption way of CRC and transposition, also added a new improved hamming coding for error correction. The results shows that the MRR laser communication system is achieved whose transfer rate is 230.4 kbit/s, high frequency carrier is 1 MHz,and the bit error rate is less than 10-6.To improve the hardware can do the duplex communication, which can realize the information feedback with instructions. The paper use the modulation method which has combined the external and internal modulation, and choose the different modulation mode to send and receive information. At last the communication system realized time-division duplex communication which the downlink transmission rate is about30kbit/s, and the uplink rate can reach 3 Mbit/s.