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GPS作为当前最先进的卫星导航系统,已成为现代战场必不可少的战斗保障设施,能否对GPS实施有效干扰,是能否在未来战争中占据主动的关键之一。脉冲作为现代战场中的常见信号,易于产生且干扰能量集中,若参数设置适当,可在短时间内导致GPS接收机性能的恶化。
关于脉冲干扰影响直扩系统的研究目前多集中于对误码率的推导分析上,文献[1-3]通过建立仿真模型,分析了脉宽和脉冲重复周期对系统误码率的影响,但只以误码率作为干扰效果评估指标过于片面,未能充分揭示出脉冲信号的干扰机理,就GPS而言,也不具有针对性。文献[4-7]论述了脉冲干扰对GPS接收信号的影响,提出可通过计算GPS接收机的载噪比来评估干扰效果,这虽然相比文献[1-3]更能反映出脉冲干扰的作用本质,但未作数学理论推导,也未能仿真分析出不同的干扰参数选取对载噪比的影响,借鉴性不强。另外,干扰对接收机码跟踪性能的影响并不是完全依赖于载噪比[8]。文献[9-10]对干扰下的GPS接收机码跟踪误差进行了推导,但未见对脉冲干扰样式的分析,而且由于脉冲信号的离散谱线特性,其对同样具有离散谱线特征GPS信号码跟踪的影响,文献[9-10]中的结论已不再适用[11]。
本文在对脉冲干扰信号建模的基础上,根据GPS接收机的信号处理过程,分别推导了脉冲干扰下离散谱C/A码信号和连续谱M码信号的干扰等效载噪比和码跟踪误差,通过仿真分析并综合考虑接收机的自动增益控制(automatic gain control, AGC)和频域滤波等因素,对不同GPS扩频码的脉冲干扰参数取值范围进行了合理设置,在降低被接收机抗干扰手段抑制的同时,提升干扰效率。
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脉冲干扰是指将干扰能量集中在一个脉冲周期的某一段时间内发射的干扰样式。射频脉冲干扰信号可表示为:
$$J(t) = \sqrt {2{P_J}} p(t)\cos [2{\rm{ \mathsf{ π} }}({f_0} + {f_J})t + \varphi ]$$ (1) 式中,${f_0}$为期望信号中心频率;${P_J}$为干扰功率;${f_J}$为干扰频偏;$\varphi $为干扰相位;$p(t)$为基带脉冲信号,常见为矩形脉冲,其时域和频域的表达式分别为:
$$\left\{ \begin{array}{l} {p_{矩形}}(t) = \left\{ {\begin{array}{*{20}{c}} 1&{nT \le t \le \tau + nT}&{n = 0, 1, 2, \cdots }\\ 0&{其他}&{} \end{array}} \right.\\ {S_{矩形}}(f) = \frac{\tau }{T}\sum\limits_n^{} {{\rm{Sa}}(f{\rm{ \mathsf{ π} }}\tau )\delta \left( {f + \frac{n}{T}} \right)} \end{array} \right.$$ (2) 式中,$\tau $和$T$分别为脉宽和脉冲重复周期。
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压制干扰对GPS接收机捕获、载波跟踪和数据解调的影响可统一归结到对干扰等效载噪比的计算上,而对码跟踪的影响却不能单纯用干扰等效载噪比来表征,因此,兼顾采用干扰等效载噪比和码跟踪误差作为干扰效果的评估指标。由于$\tau $和$T$的取值没有一个相对固定的范围,且两者之间存在一定的依赖关系,还有可能对${f_J}$的最佳设置造成影响,因此,本文只分析不同脉冲干扰参数取值对离散谱C/A码信号和连续谱M码信号产生的干扰效果,以求揭示出脉冲干扰参数的影响本质,从而设置参数取值范围,提高干扰利用效率。
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脉冲干扰经过离散谱C/A码解扩解调后的频域形式为:
$$Z(f) = \sqrt {2{P_J}} [{S_{矩形}}(f)({S_{{\rm{C/A}}}}(f){{\rm{e}}^{{\rm{j2 \mathsf{ π} }}f\hat \tau }})\delta (f - {f_d} - {f_J})]$$ (3) 式中,${S_{{\rm{C/A}}}}(f)$为用来解扩的C/A码频谱;$\hat \tau $为码相位估计误差;${f_d}$为多普勒频移。将式(3)通过一个冲激响应$h(t) = {1 \mathord{\left/ {\vphantom {1 {{T_d}}}} \right. } {{T_d}}}$($ - {{{T_d}} \mathord{\left/ {\vphantom {{{T_d}} 2}} \right. } 2} \leqslant t \leqslant {{{T_d}} \mathord{\left/ {\vphantom {{{T_d}} 2}} \right. } 2}$)的低通滤波器后可得:
$$\begin{array}{l} Z{'}(f) = \sqrt {2{P_J}} \\ \left[ \sum\limits_n {\sum\limits_k {P_{矩形n} } {C_k}{\rm{Sa}}\left( {{\rm{ \mathsf{ π} }}\left( {f - {f_d} - \Delta {f_J} - \frac{l}{{{N_c}{T_c}}} + \frac{k}{{{N_c}{T_c}}} + \frac{n}{T}} \right){T_d}} \right){{\rm{e}}^{{{ - {\rm{j2 \mathsf{ π} }}k\hat \tau } \mathord{\left/ {\vphantom {{ - {\rm{j2 \mathsf{ π} }}k\hat \tau } {({N_c}{T_c})}}} \right. } {({N_c}{T_c})}}}}{{\rm{e}}^{{\rm{j}}(\varphi - \hat \theta )}}} \right] \end{array}$$ (4) 式中,$P_{矩形n}$和${C_k}$分别为$S_{矩形}$和${S_{{\rm{C/A}}}}(f)$各离散谱线的傅里叶系数;${N_c}$为C/A码码长;${T_c}$为C/A码码宽;$l$为最靠近${f_J}$的C/A码谱线序号;$\Delta {f_J}$为${f_J}$与第$l$条C/A码谱线的频差($\left| {\Delta {f_J}} \right| < {1 \mathord{\left/ {\vphantom {1 {(2{N_c}{T_c})}}} \right. } {(2{N_c}{T_c})}}$);${T_d}$为相关积分时间;$\hat \theta $为本地载波的相位估计。鉴于C/A码周期为1 ms,因此,可将$T$分为$T \ll 1{\rm{ ms}}$、$T \gg 1{\rm{ ms}}$和$T = 1{\rm{ ms}}$这3种情况进行干扰效能讨论[5]。
当$T \ll 1{\rm{ ms}}$时,相关器输出的干扰等效载噪比为:
$${\left( {\frac{C}{{{N_J}}}} \right)_{{\rm{C/A}}}} = \frac{{{P_s}{{[{R_0}(\hat \tau )]}^2}}}{{{P_J}{{\left[ {\left| {{P_{矩形0}}{C_l}} \right|{\rm{Sa}}({\rm{ \mathsf{ π} }}({f_d} + \Delta {f_J}){T_d})} \right]}^2}}}$$ (5) 式中,${R_0}( \bullet )$为伪码带限自相关函数。设${f_d} = 0$,${f_J}$与C/A码的第$l$条谱线重合,当$T \ll 1{\rm{ ms}}$时,相关器输出处的干扰分量为常数,将式(4)变换到时域可表示为:
$$z' = \sqrt {2{P_J}} \left| {{P_{矩形0}}{C_l}} \right|{{\rm{e}}^{{\rm{j}}( - 2{\rm{ \mathsf{ π} }}\hat \tau {l \mathord{\left/ {\vphantom {l {({N_c}{T_c})}}} \right. } {({N_c}{T_c})}} + \varphi - \hat \theta - {\alpha _l})}}$$ (6) 式中,${\alpha _l} = {\rm{angle}}({C_l})$。经过非相干超前减滞后功率(noncoherent early-late processing, NELP)处理后可得到:
$$\begin{array}{l} {D_{{\rm{NELP}}}} = \overbrace {2{P_s}\left[ {{R_0}^2\left( {\hat \tau + \frac{{d{T_c}}}{2}} \right) - {R_0}^2\left( {\hat \tau - \frac{{d{T_c}}}{2}} \right)} \right]}^{信号分量} + \\ \overbrace {4{P_s}X\left[ \begin{array}{l} {R_0}^2\left( {\hat \tau + \frac{{d{T_c}}}{2}} \right)\cos ( - 2{\rm{ \mathsf{ π} }}\hat \tau {l \mathord{\left/ {\vphantom {l {({N_c}{T_c})}}} \right. } {({N_c}{T_c})}} - {{{\rm{ \mathsf{ π} }}dl} \mathord{\left/ {\vphantom {{{\rm{ \mathsf{ π} }}dl} {{N_c}}}} \right. } {{N_c}}} + \varphi - \theta - {\alpha _l}) - \\ {R_0}^2\left( {\hat \tau - \frac{{d{T_c}}}{2}} \right)\cos ( - 2{\rm{ \mathsf{ π} }}\hat \tau {l \mathord{\left/ {\vphantom {l {({N_c}{T_c})}}} \right. } {({N_c}{T_c})}} + {{{\rm{ \mathsf{ π} }}dl} \mathord{\left/ {\vphantom {{{\rm{ \mathsf{ π} }}dl} {{N_c}}}} \right. } {{N_c}}} + \varphi - \theta - {\alpha _l}) \end{array} \right]}^{干扰分量} \end{array}$$ (7) 式中,$d$为早迟码间距(码片);$\theta $为载波相位;$X = \sqrt {{{{P_J}} \mathord{\left/ {\vphantom {{{P_J}} {{P_s}}}} \right. } {{P_s}}}} \left| {{P_{矩形0}}{C_l}} \right|$。由于$\varphi $和$\theta $都在$[0, 2{\rm{ \mathsf{ π} }}]$间独立随机取值,因此,$ - 2{\rm{ \mathsf{ π} }}\hat \tau {l \mathord{\left/ {\vphantom {l {({N_c}{T_c})}}} \right. } {({N_c}{T_c})}} + \varphi - \theta - {\alpha _l}$的主值也任意分布在$[0, 2{\rm{ \mathsf{ π} }}]$之间,令其等于$\phi $。根据码跟踪环的鉴相过程,可得:
$$ {\hat \tau _{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}}(l) = \frac{{X\sin (\phi )\sin ({{{\rm{ \mathsf{ π} }}dl} \mathord{\left/ {\vphantom {{{\rm{ \mathsf{ π} }}dl} {{N_c}}}} \right. } {{N_c}}})\sum\limits_{k = - 1{\rm{ }}023}^{1{\rm{ }}023} {{{\left| {{C_k}} \right|}^2}\cos ({\rm{ \mathsf{ π} }}fd{T_c})\delta \left( {f + \frac{k}{{{N_c}{T_c}}}} \right)} }}{{2{\rm{ \mathsf{ π} }}\sum\limits_{k = - 1{\rm{ }}023}^{1{\rm{ }}023} {f{{\left| {{C_k}} \right|}^2}\sin ({\rm{ \mathsf{ π} }}fd{T_c})\delta \left( {f + \frac{k}{{{N_c}{T_c}}}} \right)} \cdot \left[ {\sum\limits_{k = - 1{\rm{ }}023}^{1{\rm{ }}023} {{{\left| {{C_k}} \right|}^2}\cos ({\rm{ \mathsf{ π} }}fd{T_c})\delta \left( {f + \frac{k}{{{N_c}{T_c}}}} \right)} + X\cos (\phi )\cos ({{{\rm{ \mathsf{ π} }}dl} \mathord{\left/ {\vphantom {{{\rm{ \mathsf{ π} }}dl} {{N_c}}}} \right. } {{N_c}}})} \right]}} $$ (8) 式(8)中由于$\phi $的存在,可考虑干扰影响最严重时的情况,求解${{\partial {{\hat \tau }_{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}}} \mathord{\left/ {\vphantom {{\partial {{\hat \tau }_{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}}} {\partial \phi }}} \right. } {\partial \phi }} = 0$并证明${{{\partial ^2}{{\hat \tau }_{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}}} \mathord{\left/ {\vphantom {{{\partial ^2}{{\hat \tau }_{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}}} {\partial {\phi ^2}}}} \right. } {\partial {\phi ^2}}}$在${{\partial {{\hat \tau }_{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}}} \mathord{\left/ {\vphantom {{\partial {{\hat \tau }_{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}}} {\partial \phi }}} \right. } {\partial \phi }} = 0$的点不为零,即可得到$\hat \tau _{{\rm{NEL}}{{\rm{P}}_{({\rm{C/A}})}}}^{\max }$:
$$\begin{gathered} \hat \tau _{{\rm{NEL}}{{\rm{P}}_{\left( {{\rm{C/A}}} \right)}}}^{\max }(l) = \\ \frac{{X\sin ({{{\rm{ \mathsf{ π} }}dl} \mathord{\left/ {\vphantom {{{\rm{ \mathsf{ π} }}dl} {{N_c}}}} \right. } {{N_c}}})\sum\limits_{k = - 1{\rm{ }}023}^{1{\rm{ }}023} {{{\left| {{C_k}} \right|}^2}\cos ({\rm{ \mathsf{ π} }}fd{T_c})\delta \left( {f + \frac{k}{{{N_c}{T_c}}}} \right)} }}{{2{\rm{ \mathsf{ π} }}\sum\limits_{k = - 1{\rm{ }}023}^{1{\rm{ }}023} {f{{\left| {{C_k}} \right|}^2}\sin ({\rm{ \mathsf{ π} }}fd{T_c})\delta \left( {f + \frac{k}{{{N_c}{T_c}}}} \right)} \cdot \sqrt {{{\left[ {\sum\limits_{k = - 1{\rm{ }}023}^{1{\rm{ }}023} {{{\left| {{C_k}} \right|}^2}\cos ({\rm{ \mathsf{ π} }}fd{T_c})\delta \left( {f + \frac{k}{{{N_c}{T_c}}}} \right)} } \right]}^2} - {X^2}{{\cos }^2}({{{\rm{ \mathsf{ π} }}dl} \mathord{\left/ {\vphantom {{{\rm{ \mathsf{ π} }}dl} {{N_c}}}} \right. } {{N_c}}})} }} \\ \end{gathered} $$ (9) 由式(5)和式(9)可以看出,此时只有$n = 0$($0 < \left| {{P_{矩形0}}} \right| < 1$)的中心干扰谱线进入到接收机的中频带宽内,干扰效果较差。
当$T \gg 1{\rm{ ms}}$时,相关器输出的干扰等效载噪比为:
$$\begin{array}{c} {\left( {\frac{C}{{{N_J}}}} \right)_{{\rm{C/A}}}} = \\ \frac{{{P_s}{{[{R_0}(\hat \tau )]}^2}}}{{{P_J}{{\sum\limits_{n = - M}^M {\left[ {\left| {{P_{矩形n}}{C_l}} \right|{\rm{Sa}}\left( {{\rm{ \mathsf{ π} }}\left( {\frac{n}{T} - {f_d} - \mathit{\Delta }{f_J}} \right){T_d}} \right)} \right]} }^2}}} \end{array}$$ (10) $M$的大小由$T$和${T_d}$共同确定,同理可得:
$$ \begin{array}{c} z' = \sqrt {2{P_J}} \times \\ \left( {\sum\limits_{n = - M}^M {\left| {{P_{矩形n}}} \right|{\rm{Sa}}\left( {\frac{{{\rm{ \mathsf{ π} }}n{T_d}}}{T}} \right)} {{\rm{e}}^{ - {\rm{j}}{\beta _{矩形n}}}}} \right)\left| {{C_l}} \right|{{\rm{e}}^{{\rm{j}}( - 2{\rm{ \mathsf{ π} }}\hat \tau {l \mathord{\left/ {\vphantom {l {({N_c}{T_c})}}} \right. } {({N_c}{T_c})}} + \varphi - \hat \theta - {\alpha _l})}} \end{array} $$ (11) 式中,${\beta _{矩形n}} = {\rm{angle}}({P_{矩形n}})$。对比式(11)和式(6)容易发现,式(9)对此种情况同样适用。由于$P_{矩形n}$为实数,因此,主瓣内的谱线相位为零,而脉冲干扰的能量主要就集中在主瓣内,则此时$X$为:
$$X = \sqrt {{{{P_J}} \mathord{\left/ {\vphantom {{{P_J}} {{P_s}}}} \right. } {{P_s}}}} \left( {{P_{矩形0}} + 2\sum\limits_{n = 1}^M {{P_{矩形n}}{\rm{Sa}}\left( {\frac{{{\rm{ \mathsf{ π} }}n{T_d}}}{T}} \right)} } \right)\left| {{C_l}} \right|$$ (12) 由式(10)和式(12)可以看出,$T \gg 1{\rm{ ms}}$时有包含脉冲干扰中心谱线在内的多条谱线会对C/A码信号产生作用。另外,由于式(10)和式(12)都只与$\left| {{C_l}} \right|$有关,因此,$T \gg 1{\rm{ ms}}$时的脉冲干扰${f_J}$设置与单频干扰类似。
当$T = 1{\rm{ ms}}$时,相关器输出的干扰等效载噪比为:
$${\left( {\frac{C}{{{N_J}}}} \right)_{{\rm{C/A}}}} = \frac{{{P_s}{{[{R_0}(\hat \tau )]}^2}}}{{{P_J}\sum\limits_{n = - M}^M {{{\left[ {\left| {{P_{矩形n}}{C_{l - n}}} \right|{\rm{Sa}}({\rm{ \mathsf{ π} }}({f_d} + \Delta {f_J}){T_d})} \right]}^2}} }}$$ (13) 该情况下对应的式(4)的时域形式为:
$$z' = A\sqrt {2{P_J}} {{\rm{e}}^{{\rm{j}}\left( { - 2{\rm{ \mathsf{ π} }}\hat \tau {l \mathord{\left/ {\vphantom {l {\left( {{N_c}{T_c}} \right)}}} \right. } {\left( {{N_c}{T_c}} \right)}} + \varphi - \hat \theta + B} \right)}}$$ (14) 式中,
$$ \left\{ \begin{array}{l} A = {\rm{abs}}\left( {\sum\limits_{n = - M}^M {{P_{矩形n}}\left| {{C_{l - n}}} \right|{{\rm{e}}^{ - {\rm{j}}{\varphi _{l - n}}}}} } \right)\\ B = {\rm{angle}}\left( {\sum\limits_{n = - M}^M {{P_{矩形n}}\left| {{C_{l - n}}} \right|{{\rm{e}}^{ - {\rm{j}}{\varphi _{l - n}}}}} } \right) \end{array} \right. $$ (15) 这种情况下主瓣内的所有干扰谱线不再受${T_d}$的限制而都能产生作用。由于式(13)和式(15)的计算涉及到${C_{l - n}}$和${C_{l + n}}$,因此,${f_J}$的设置与单频干扰有所差异。
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由于M码周期长、码速率快,其频谱近乎连续,可通过计算$\int_{{\rm{ }} - \infty }^{{\rm{ }}\infty } {{G_{矩形}}(f){G_{\rm{M}}}(f){\rm{d}}f} $($G(f)$为功率谱密度函数)得到脉冲干扰下M码信号的干扰等效载噪比:
$$ {\left( {\frac{C}{{{N_J}}}} \right)_{\rm{M}}} = \frac{{{P_s}{{[{R_0}(\hat \tau )]}^2}}}{{{P_J}\left[ {\sum\limits_{n = \left\lceil {{{ - T} \mathord{\left/ {\vphantom {{ - T} \tau }} \right. } \tau }} \right\rceil }^{\left\lfloor {{T \mathord{\left/ {\vphantom {T \tau }} \right. } \tau }} \right\rfloor } {P_{_{矩形n}}^2{T_{c1}}{\rm{S}}{{\rm{a}}^2}\left( {{\rm{ \mathsf{ π} }}\left( {{f_J} - \frac{n}{T}} \right){T_{c1}}} \right){{\tan }^2}\left( {\frac{{{\rm{ \mathsf{ π} }}\left( {{f_J} - \frac{n}{T}} \right)}}{{2{f_s}}}} \right)} } \right]}} $$ (16) 式中,${T_{c1}}$和${f_s}$分别为M码的码宽和副载频;$\left\lfloor \bullet \right\rfloor $和$\left\lceil \bullet \right\rceil $分别表示向下和向上取整。可以看出,式(16)与$T = 1{\rm{ ms}}$脉冲干扰下的C/A码信号情况类似,即${T_d}$对$T$的取值没有影响,$T$越大,产生作用的干扰项和信号项越多。当脉冲间隔$T - \tau $远远超过GPS接收机的最大导航数据更新周期时(飞行器一般为1 000 ms[12]),接收机可通过AGC电路对占空比很小的突发强脉冲进行检测和接收信号消零[13],在剩余时间内,接收机还是能够正常工作(除非造成接收机前端饱和),因此,可将$T \leqslant 1{\rm{ }}000{\rm{ ms}}$作为对M码信号脉冲干扰$T$取值的约束条件。
由于M码信号频谱近乎连续,对于脉冲干扰可看作是由${{2T} \mathord{\left/ {\vphantom {{2T} \tau }} \right. } \tau }$个相互独立的窄带干扰的合成,而每一个窄带干扰满足相关输出干扰分量服从零均值高斯分布的假设[9-10],因此,脉冲干扰下M码信号NELP处理码跟踪误差为:
$$ \begin{array}{l} {{\hat \tau }_{{\rm{NEL}}{{\rm{P}}_{({\rm{M}})}}}} = \frac{{\sqrt {{B_n}} }}{{2{\rm{ \mathsf{ π} }}\int_{ - {\beta _r}/2}^{{\beta _r}/2} {f{G_{\rm{M}}}(f)\sin ({\rm{ \mathsf{ π} }}fd{T_{c1}}){\rm{d}}f} }}\\ \sqrt {\begin{array}{*{20}{c}} {\left( {\frac{{{P_J}}}{{{P_s}}}\sum\limits_{n = \left\lceil { - T/\tau } \right\rceil }^{\left\lfloor {T/\tau } \right\rfloor } {P_{矩形n}^2{G_{\rm{M}}}\left( {{f_J} - \frac{n}{T}} \right){{\sin }^2}\left( {{\rm{ \mathsf{ π} }}\left( {{f_J} - \frac{n}{T}} \right)d{T_{c1}}} \right)} } \right) \times }\\ {\left( {1 + \frac{{\sum\limits_{n = \left\lceil { - T/\tau } \right\rceil }^{\left\lfloor {T/\tau } \right\rfloor } {P_{矩形n}^2{G_{\rm{M}}}\left( {{f_J} - \frac{n}{T}} \right){{\cos }^2}\left( {{\rm{ \mathsf{ π} }}\left( {{f_J} - \frac{n}{T}} \right)d{T_{c1}}} \right)} }}{{{T_d}\frac{{{P_s}}}{{{P_J}}}{{\left( {\int_{ - {\beta _r}/2}^{{\beta _r}/2} {{G_{\rm{M}}}(f)\cos ({\rm{ \mathsf{ π} }}fd{T_{c1}}){\rm{d}}f} } \right)}^2}}}} \right)} \end{array}} \end{array} $$ (17) 式中,${B_n}$为码环噪声带宽;${\beta _r}$为接收机前端等效预相关带宽;${T_d}$为相关积分时间。
Effect Analysis of Pulse Jamming against GPS
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摘要: 脉冲干扰广泛存在于现代战场电磁环境中。为了提升脉冲干扰在导航对抗中的应用效率,根据GPS接收机工作过程,以干扰等效载噪比和码跟踪误差作为干扰效果评估指标,对脉冲干扰参数影响下的离散谱特征C/A码信号和连续谱特征M码信号的干扰效果评估指标分别进行了理论推导和仿真分析。为确保干扰效果,对于C/A码信号,脉冲干扰频偏可根据C/A码PRN#信息预先计算比较得到,脉冲重复周期设置为1 ms,脉宽在0.01~0.05 ms取值;对于M码信号,脉冲干扰频偏可依据单频干扰频偏设置预先计算平均得到,通过减小脉冲重复周期和提高脉冲幅度来保证干扰效果,在脉冲重复周期固定时,占空比在0.002~0.005取值。该结论揭示了脉冲干扰对GPS信号的影响本质,对提高干扰利用效率具有借鉴意义。Abstract: Pulse jamming is widely used in electromagnetic environment of modern battlefield. In order to improve pulse jamming application efficiency in navigation countermeasure, the theoretical derivation and numerical simulation about jamming effect evaluation indexes of discrete spectrum C/A code signal and continuous spectrum M code signal are performed respectively under the influence of pulse jamming parameters, which are based on the process of GPS receiver and evaluated by indexes of jamming efficient carrier-to-noise ratio and code tracking error. To ensure effect of jamming, for the C/A code signal, pulse jamming frequency offset can be preset after calculating and comparing by acquiring PRN number information of C/A code, pulse repetition period can be set to 1ms and pulse duration can take value between 0.01~0.05 ms, but for the M code signal, the jamming frequency offset can be preset after calculating and averaging according to the method of acquiring single frequency jamming frequency offset, the jamming effect can be ensured by decreasing pulse repetition interval and increasing pulse amplitude, when the pulse repetition interval is fixed, pulse duty cycle can take value between 0.002~0.005. The conclusion reveals the influence essence of pulse jamming to GPS signal, which is significant for improving pulse jamming application efficiency.
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