短周期PN序列水声直扩系统抗单频干扰能力的变化规律与试验验证

Variation law and experimental verification of anti-single-frequency interference ability of underwater acoustic DSSS system with short-period PN sequences

对无法定量分析短周期PN序列直扩系统抗单频干扰性能的问题,首先通过理论推导得到单频干扰经相关处理产生的干扰分量;然后,结合直扩系统对单频干扰的处理增益,针对水声系统扩频序列周期较短的现实情况,提出了周期性PN序列水声直扩系统抗单频干扰性能定量分析的理论表达式;最后,通过仿真和试验验证了理论表达式的正确性。结果表明:单频干扰经相关处理后得到的干扰序列呈直流或正弦分布;单频干扰对系统误码率的影响与信干比、干扰频偏、相位偏差以及扩频码本身结构有关,误码率随干扰相位偏差变化呈周期分布;在干扰频偏值为整数倍码元带宽的所有工况中,频偏为一倍码元带宽的单频干扰对系统影响最大;简明的理论表达式,对快速预报现实短码水声系统抗单频干扰性能的变化规律具有重要意义。

In order to solve the problem of being unable to quantitatively analyze the anti-single-frequency interference performance of the direct sequence spread spectrum(DSSS)communication system with a short-period PN sequence,firstly,the interference components produced by correlation processing of single frequency interference were derivated theoretically.Then,combined with the processing gain of DSSS system to single frequency interference,and in view of the fact that the spread spectrum sequence period of underwater acoustic system was short,a theoretical expression was put forward for quantitative analysis of the anti-single frequency interference performance of periodic PN sequence DSSS underwater acoustic system.Finally,the correctness of the theoretical expression was verified by simulations and experiments.The results reveal that the interference sequence formed by correlation processing of single frequency interference has a direct current(DC)or sinusoidal distribution;that the effect of single-frequency interference on the system bit error rate is affected by the signal-to-interference ratio,interference frequency offset,phase deviation,and the spreading code structure itself;that the bit error rate varies with the interference phase variation on a regular basis,i.e.,the single-frequency interference with a frequency offset of one time the symbol bandwidth has the greatest influence on the system in all working conditions where the interference frequency offset is an integer multiple of the symbol bandwidth.The concise theoretical expression is extremely useful for quickly predicting the variation law of the anti-single frequency interference performance of a short code underwater acoustic system.