The significant feature of the PCPC structure is the improvement of correlator output magnitude because it prevents the quantization effect on carrier phase ambiguity. The improvement becomes more critical significant when very few bits ADC are used.
The proposed PCPC structure is implemented in 1-bit SGR and successfully track PRN’s both in static mode and dynamic mode. Regarding the implementation of the FLL, it’s worth to mention that the phase offset effect of local carrier table must be considered in order to attain correct fequency variation. The effect is induced because the beginning phase of a pre-established carrier table is always zero while the local carrier of the following interval may have a nonzero beginning phase.
The proposed NB-DPD is developed based on digital approach which intuitively derives the carrier phase difference using the time delay between received signal and local reference signal. The derivations of the probability properties of the NB-DPD estimator are provided as in section 4.3. A series of simulation are performed to
verify th various
hase-angle cases. puter simulation
s in section 5.1.
rom the simulation results, the Monte Carlo simulation results are consistent with the nalytical results no matter what the SNR is. Note that the variance and the estimate rror reduce as the number of samples increases. For the SNR= -20dB case, when the umber of sample, N, is 17328, the maximum variance is 0.008 and the mzximum stimate error is around 7°. When the number of samples increases to 4 times, i.e., N = 9312, then the maximum variance and estimate error reduce to 0.0025 and 4.1°
spectively. It’s also noted that the variance reduces as the SNR increases. When
=69312, and SNR= -30dB, -20dB, and -10dB, the maximum variances are 0.019, .0024, and 0.00034 respectively. As for the maximum estimate error, we note that it lways occurs at
the analytical results when SNR= -10dB, -20dB, and -30dB wi p The analytical results are indeed verified by com a
F a e n e 6 re N 0
a θ =17°, 73°, 108°, 163° by 4.1° for SNR above -20dB.
he NB-DPD is based on binary symmetrical probability model considering both oiseless (P01 = P10 = 0) and noisy environments. It is equivalent to DPD in noiseless ase and thus inherits high accuracy properties of DPD in high SNR cases. The
R is, T
n c
NB-DPD performs generally better than the DPD in noisy cases. The lower the SN
the greater the improvement. Moreover, the NB-DPD works almost as well as rctangent-phase discriminator (APD) in low SNR environments and thus can be pplied to GNSS receivers.
he NB-DPD is implemented in a one-bit software-defined GPS receiver using PCPC tructure. The experimental results demonstrate the feasibility of the proposed scheme.
is worth to mention that PCPC structure can be applied to phase discriminators hose range is between
a a
T s It
w −π and π (compared with arctangent −π/2~π/2).
ence NB-DPD works well in PCPC structure.
he SGR, whose tracking loop is implemented with the PCPC structure and the B-DPD discriminator, is tested in receiving both the real GPS signals and the imulated high-dynamic GPS signals as shown in section 5.2. From the experiment
sults, the SGR can successfully track four satellite signals with good tracking quality, nd extract the ephemeras data and obtain user position.
s we consider high dynamic environments, e.g., LEO satellite with altitude 350 km, from a PS satellite are 46 kHz and 90 Hz/sec, respectively.[26] From our experimental sults, the SGR remains tracking when Doppler shift and Doppler rate achieve 42.6kHz and 643 Hz/sec (12.5g), respectively. Note that this verified capability is limited by the current available data and the greater tolerance is expected when the associated data is available in the future. Hence our algorithm and structure can be well applied in SGR for high dynamic environments.
From the comparison of the in-phase correlator outputs and the estimated frequency when the discriminator NB-DPD and APD are used in both static and dynamic modes as shown in Figure 5.2-2, Figure 5.2-4, and Figure 5.2-5. It’s noted that the SGR tracking performance as implemented with NB-DPD is almost same as with APD using less computation.
Finally, the progress of modern digital technology and the efficient computations of NB-DPD make it very attractive in real-time digital processing receivers.
H
T N s re a
A
the maximum Doppler shift and Doppler rate induced by a L1 carrier emitted G
re
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