Unambiguous Processing Techniques of Binary Offset Carrier Modulated Signals - Global Navigation Satellite Systems: Signal,Theory and Applications - page 57

2

M − i

⎛ ⎞

(7)

ξ = ⎜

⎟ i

M

⎝ ⎠

For M = , the gap between

the largest side peak and the main peak is only 2.5 dB. With increase of M , the difference
between the maximum side peak and the main peak decreases, while the false acquisition
probability increase.

M = , side peaks are 6 dB weaker than the main peak. But for 2 6

(a)

(b)
Fig. 2. (a) The Statistic in Acquisition Stage and (b) The Discriminator Curve in Tracking
Stage of BOC(2 n , n ) Signal

It can be seen from Figure 2(b) that when using a traditional narrow early-minus-late
(NEML) tracking loop (Van Dierendonck et al., 1992) with the early-late separation ∆, the
discriminator characteristic curve of BOC( m , n ) signal has a smaller linear domain than the
one of the BPSK-R( n ) signal. Besides, the discriminator characteristic curve of a BOC( m , n )
signal has 2 M - 2 stable false lock points which are due to the side peaks of the
autocorrelation function. If a false acquisition occurs, in tracking stage, the code tracking
loop will initially lock on a false lock point. Even if there is no false acquisition, the false lock
can result from high noise, jitter, or short loss of lock.

Figure 3 shows an example of false lock caused by the excessive initial code delay bias in
BOC(2 n , n ) signal tracking. The C / N 0 in this example is 45 dB-Hz, and the predetection
integration time is 1 ms, with the early-late separation 0.1 chips. It can be seen that with the