Pseudo-Noise (PN) Ranging Systems - CCSDS

CCSDS INFORMATIONAL REPORT CONCERNING PSEUDO-NOISE RANGING SYSTEMS
Table 2-8: Maximum Search versus Threshold Comparison Acquisition Procedure
T2B Acquisition
Time (s)
T4B Acquisition
Time (s)
Maximum Search Threshold Comparison
Ideal Processing
No Quantization
Ideal Processing
No Quantization
Ideal Processing
3-bit
Quantization
Ideal Processing
1-bit
Quantization
10.6 21.5 22.9 33.8
Loss (dB) 3.1 3.4 5.1
175.6 358.2 381.0 562.7
Loss (dB) 3.1 3.4 5.1
Clearly the impact due to one-bit quantization is around 2 dB when compared to the non-
quantized case while three-bit soft quantization reduces this loss down to 0.3 dB only.
2.5 ON-BOARD PN TRACKING JITTER
2.5.1 SQUARE-SQUARE MATCHED CASE
The PN ranging code resembles a square-wave with a few ‘errors’. Therefore the CTL can be
simply designed by modifying a DTTL according to figure 2-13. The filtered loop error is
added to the nominal chip rate and the result is used to control the NCO frequency. The
ranging signal clock component is coherently related to the transmitted carrier frequency;
therefore it is possible to apply an aided acquisition scheme for proper CTL synchronization.
With this approach, the chip rate is obtained by adding the nominal chip rate to the carrier
loop error scaled by the ratio of the ranging chip rate by the uplink carrier frequency. This
second term offers an estimation of the Doppler on the ranging signal and allows improving
the CTL acquisition performance because only the chip phase (not the frequency) must be
recovered. The CTL NCO output frequency is used to drive the shift registers which generate
the six code components in the Code Generator blocks.
The signal at the CTL input is derived from the carrier quadrature channel and it can be
expressed as:
where:
ts is the sampling interval;
A is the amplitude of the chip;
T = Tc is the chip period;
() i = r(
its
) = A∑
ak
⋅ p(
its
− kT −τ
) Ni
r +
k
CCSDS 414.0-G-1 Page 2-27 March 2010