Pseudo-Noise (PN) Ranging Systems - CCSDS

CCSDS INFORMATIONAL REPORT CONCERNING PSEUDO-NOISE RANGING SYSTEMS
sequence; e.g., the ranging sequence might be the sequence resulting from some sort of
voting by the chips of all the probing sequences at the same chip time. A correlation (i.e.,
chip-by-chip multiplication followed by a summation) of the received ranging sequence is
made with a model of each probing sequence and its distinct cyclic shifts to determine which
cyclic shift is ‘in-phase’ with the received sequence over the portion of the received sequence
where the correlation is performed. The probing sequences must have the property that, when
all these ‘in-phase’ decisions are correctly made, they determine the delay (modulo the
ranging sequence period L) in chips of the received ranging sequence relative to its
corresponding model (local replica).
There are two important quality measures for probing sequences:
– acquisition time;
– spectral properties.
Acquisition time refers to the time required to carry out the correlations for the probing
sequences and their cyclic shifts and should be as small as possible. Because it is the
presence in the ranging sequence of a component proportional to a probing sequence that
determines the effectiveness of correlating with that probing sequence, the spectra of the
probing-sequence waveforms should be such that they are not substantially attenuated by the
filtering at the transmitter of the ranging sequence as may be required to avoid interference
between the ranging signal and other TT&C signal components (e.g., telemetry signals).
The two important quality parameters of the ranging measurement are
– its random-noise variation;
– its ambiguity resolution.
The first task of the receiver (after the phase demodulation of the received phase-modulated
signal) is to lock onto the range clock. The clock tracking jitter (due to thermal noise)
determines the standard deviation of the measurement error in meters.
After locking onto the range clock, the receiver correlates in some manner a model of the
ranging sequence with the received ranging sequence to determine the integer number of
chips, modulo the period L in chips of the ranging sequence, that the signal has been delayed
in its round trip from the Earth station. The (one-way) ambiguity due to the period of the
ranging sequence in meters is
For example, with L = 1,009,470 chips and
km.
1 c ⋅ L
U = c ⋅ L ⋅Tc
=
2 4 f
CCSDS 414.0-G-1 Page 2-2 March 2010
RC
6
f RC = 10 Hz, U ≈ 75,710,000 m or about 75,710
In the analysis for the evaluation of the acquisition time for the different ranging sequences,
one of the main reference parameters is the chip SNR 2E / N where C 0 E is the received chip
C