| Wireless "Solar blind" ultraviolet can realize non-line-of-sight communication through the scattering of atmospheric particles,which has the advantages of good security,strong anti-interference ability and high secrecy.However,the attenuation of wireless ultraviolet transmission is serious and the transmission power is limited.MIMO technology can use diversity reception technology at the receiver so that the effects of signal scattering and energy attenuation are reduced.Meanwhile,wireless UV MIMO communication technology can meet the need of close covert communication in complex environment,suppress atmospheric turbulence,improve the error performance of wireless ultraviolet communication system and solve the problem of helicopter safely landing in complex and low altitude environment.The space-time coding method of wireless ultraviolet MIMO system can effectively obtain higher diversity gain and coding gain,achieve higher spatial reuse and angle multiplexing,suppress the signal fading in the turbulent channel and improve the frequency spectrum utilization and reliability of wireless UV communication system.Therefore,the scheme of bit complementary orthogonal space-time code in wireless UV MIMO channel is mainly studied,and the performance of low altitude wireless ultraviolet MIMO link under the condition of weak turbulence is also analyzed.The specific work is as follows:(1)The related concepts of wireless ultraviolet communication network,MIMO technology and current research situation in this field at home and abroad is briefly introduced.Meanwhile,the theory of wireless ultraviolet MIMO communication system is also analyzed.(2)According to the characteristics of approximate line of sight communication in the process of Wireless ultraviolet MIMO leading helicopter to land,line of sight and approximate line of sight communication link model of the wireless ultraviolet MIMO system is studied.Bit error performance of the two link model MIMO systems under the weak turbulence condition is simulated and analyzed.After calculating and analyzing the simulation results,we find that bit error rate of 4×4 system is improved by about 16.9dB and 26.3dB respectively compared with single input and single output system in two links.The result indicated that MIMO system can suppress turbulence and improve the resisting attenuation ability.Meanwhile,BER performance is much better than that of single input single output system.(3)Combining the wireless UV MIMO technology with the bit complement orthogonal space time coding,it analyzes bit error rate of the two communication modes(line of sight and non line of sight communication link model)in the wireless ultraviolet MIMO communication system under the weak turbulence condition.When the binary bit number is N=10000,the Monte Carlo method is used to simulate the error performance of the wireless ultraviolet MIMO system(using the coded 2×1 and 2×2 systems)in LOS and NLOS links.After calculating and analyzing the simulation results,we find that bit error rate of 2×2 system in these two links is improved by about 8dB and 7.8dB respectively relative to single input and single output system.2×2 system needs the least transmission power,the farther transmission distance,the bigger data transmission rate and the lower bit error rate.The result indicated that adopting Space-Time Coding of MIMO technology through increasing detectors can achieve high spatial multiplexing and angle multiplexing,obtain high diversity gain and coding gain,which is beneficial to improve the performance of the system.In conclusion,this paper combines the MIMO technology with space-time coding which is applied to wireless UV communication.It can reduce the bit error rate effectively,suppress channel fading and improve the frequency spectrum utilization by the scheme.Therefore,it has wide application foreground. |
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