Page 204 - 卫星导航2021年第1-2合期

Wang et al. Satell Navig (2021) 2:4 Page 4 of 9

Fig. 4 Schematic diagram of using pilot-channel signal authentication (NCO, Numerically Controlled Oscillator)

the high-order components are fltered out. When the (14)
tracking loop is stable, the I and Q channel signals are V t = σ n −2 ln P fa
(assuming there are no frequency diference and initial where σ n is the standard deviation of the noise, and P fa is
phase diference between the received IF signal and the false alarm probability. If V i is higher than V t , the authen-
replicated signal) tication successes, otherwise fails.

√
i p (t) = s IF (t) 2 cos(ω o t + ϕ o,p ) 2. Only data channel used for authentication

= P r2 Q out + n i,p + ···
√ (12) Te schematic diagram is shown in Fig. 5. Te dashed
q p (t) = s IF (t) 2 sin(ω o t + ϕ o,p )
box in the fgure is the identity authentication module,

= P r1 I out + n q,p + ··· and the rest is the traditional tracking loop. After mixing
the IF signal with the locally generated carriers, the high-
where ω o is the frequency of the local carrier, ϕ o,p is the order components are fltered out. When the tracking
initial phase of the local carrier, and n i,p , n q,p are the loop is stable, the I and Q channel signals are (assuming
noises of the I and Q channels, respectively. there are no frequency diference and initial phase dif-
Equation (9) tells that the authentication is not afected ference between the received IF signal and the replicated
by the data bits. First, the Q channel signal in Eq. (12) is signal)
correlated and integrated with the pilot channel spread-
√
ing code c p and the phase hopping sequence c(k) . Te i d (t) = s IF (t) 2 cos(ω o t + ϕ o,d )
higher-order components will be cleared after the flter
in the authentication module. Ten, to further improve = P r1 I out + n i,d + ··· (15)
√
C N , a coherent accumulation for the length of T coh is q d (t) = s IF (t) 2 sin(ω o t + ϕ o,d )

0
carried out, and the normalized detection value V i is
= − P r2 Q out + n q,d + ···

V i =− P r1 (ϕ PH · π/180) (13)
when θ is small, sin θ ≈ θ . Te threshold value V t is