脉冲展宽对紫外光通信误码率的影响

Influence of pulse broadening on bit error rate of ultraviolet communication

紫外激光散射通信会引起严重的脉冲展宽效应,由此导致的码间串扰会引起通信误码率。利用紫外光传输模型计算接收信号的时域分布;对"1"码和"0"码包络的概率密度分布按照"11"、"10"、"01"和"00"组合进行卷积,得到在采样时刻两侧相邻码元串扰量的概率密度函数。在引起误码临界值到采样时刻串扰量范围内,对概率密度函数进行积分可得上述4种情况的串扰引起误码的概率。仿真结果表明:距离5 km的直视通信符号速率须小于9.25×107Baud;距离1 km的非直视通信在收发端仰角同为20°、30°和40°时,对应的符号速率须小于4.0×107Baud、6.0×106Baud和3.6×105Baud。因此,若紫外激光用于低速无线光通信领域可忽略码间串扰的影响。

Pulse broadening caused by ultraviolet scattering communication may result in intersymbol interference（ ISI） which can result in bit-error-rate（ BER）. It is studied the influence of pulse broadening on bit error rate of ultraviolet communication. Firstly,time domain distribution of received signal is calculated by ultraviolet transmission model. Secondly,probability density distributions of different combinations of code ‘1 ＇and code ‘0 ＇are convolved according to the rules of‘11＇,‘10＇,‘01＇and‘00＇respectively,and then probability density distributions of ISI quantity caused by adjacent codes at both sides are obtained at sampling time. BER of the 4 cases caused by ISI is computed by an integral of ISI quantity probability density distributions within the bounds of ISI quantity at sampling time and critical value of ISI which causes BER. Simulation results show that the symbol rate should be lower than 1. 36 ×108Baud by LOS communication at a distance 5 km. By NLOS communication at distance 1 km,when elevations of transmitter and receiver are 20°,30° and 40° respectively,its corresponding symbol rates should be lower than 4. 0 ×10^7Baud,6. 0 × 10^6 Baud and 3. 6 × 10^5 Baud. As a result,BER caused by ISI can be ignored when ultraviolet is used for low speed wireless optical communication.