NCO相位截断对频域抗干扰性能影响分析

频域抗干扰易于工程实现、窄带干扰抑制性能好,是目前全球卫星导航系统(Global Navigation Satellite System,GNSS)抗干扰接收机中广泛采用的抗干扰算法。频域抗干扰接收机普遍采用数控振荡器(numerically controlled oscillator, NCO)生成本振信号。由于硬件约束,通常需要对NCO进行相位截断。而NCO相位截断是否合理对抗干扰性能影响较大。针对该问题,从NCO相位截断导致的本振杂散着手,从理论上分析其对混频和频域抗干扰环节的影响。在此基础上,给出一种NCO查找表地址位宽的理论计算模型,使得接收机的载噪比损耗接近无NCO相位截断的频域抗干扰接收机。仿真表明,抑制带宽大于100kHz、干信比小于80dBc的窄带干扰时,计算的NCO查找表地址位宽不超过10bit。无NCO相位截断的频域抗干扰接收机相比,采用NCO混频的抗干扰接收机的载噪比损耗最多增加0.6dB。

NCO phase truncation effect on performance of frequency domain adaptive filtering

Because of easy realization and excellent performance in suppressing narrow band interference, frequency anti-jamming is widely employed in current GNSS (Global Navigation Satellite System) anti-jamming receiver. Numerically controlled oscillator (NCO) is usually adopted in frequency domain anti-jamming receiver. Constrained by hardware, NCO phase truncation is needed. But, whether NCO phase is truncated reasonably influences anti-jamming performance greatly. Aiming at the problem, firstly analyze local oscillator spur caused by NCO phase truncation. Then, its effect on mixing and frequency domain anti-jamming is analyzed theoretically. Besides, a theoretical computing module of NCO look-up table width is brought forward. Thus, carrier noise loss approximates that of receiver with non-truncated phase NCO. Simulations show that NCO look-up table width computed by that module is no more than 10 bit, when suppressing narrow band interference whose band is above 100 kHz and Jam-signal-Ratio is below 80 dBc. When adopting that width, Carrier noise loss of receiver with NCO phase truncation increases 0.6 dB at most, compared to that of receiver with non-truncated phase NCO.