北斗卫星导航B1I信号电文双向差分解调技术

BeiDou satellite navigation B1I signal message two-way differential demodulation technology

关键词:  双向差分解调  差分相移键控  导航电文  锁频环  卫星导航接收机  高轨航天器

Key words:  Two-way differential demodulation  Differential phase shift keying  Navigation message  Frequency-locked loop  Satellite navigation receiver  High-orbit spacecraft

摘要:

卫星导航系统在高轨航天器自主导航应用中，面临接收到的卫星信号微弱且动态变化大的问题。为此，导航接收机通常采用锁频环（FLL）跟踪卫星导航信号的载波。由于FLL只锁定信号载波频率而不锁定载波相位，需采用差分解调技术应对高轨航天器自主解调导航电文的要求。为进一步提升导航电文差分解调性能，在解析差分解调比特误码率传递规律的基础上，提出了前后双向差分递归解调的改进方法。以北斗卫星导航系统B1I信号为例，开展了蒙特卡罗模拟仿真测试。测试结果表明，相较于常规的单向差分递归解调，前后双向差分递归解调方法将电文译码性能提升了约0.5 dB。

Abstract:

In the application of autonomous navigation for high-orbit spacecraft, satellite navigation systems are challenged by weak and dynamically varying received satellite signals. Consequently, frequency-locked loop (FLL) are commonly used by navigation receivers to track the carrier frequency of satellite navigation signals. As the frequency-locked loop only locks on to the signal carrier frequency rather than the carrier phase, differential demodulation technology is necessary to meet the requirements of autonomous demodulation of navigation messages for high-orbit spacecraft. In order to further improve the performance of differential demodulation of navigation messages, an improved method of forward and backward two-way differential recursive demodulation is proposed based on the analysis of the transmission characteristics of the differential demo-dulation bit error rate. Taking the B1I signal of the BeiDou satellite navigation system as an example, a Monte Carlo simulation test is conducted. The results show that compared with the conventional one-way differential recursive demodulation, the proposed forward and backward two-way differential recursive demodulation method improves the message decoding performance by about 0.5 dB.