Pseudo-Noise (PN) Ranging Systems - CCSDS

CCSDS INFORMATIONAL REPORT CONCERNING PSEUDO-NOISE RANGING SYSTEMS
2.8.3.4 TM BER
In the absence of ranging, the telemetry symbol error probability is
P
id , TM
( e)
1
=
2
erfc
Ranging introduces interference, as shown in figure 2-30: in the absence of noise and
ranging, the detector input only takes the two values ±0.7, while in the presence of ranging 4
levels appear, and the lowest level in absolute value (i.e., 0.5) is more frequent for code T2B
(left) than T4B (right). Table 2-17 lists the losses of the telemetry system at PTM(e)=10 -4 ,
mTM=1.25 rad, mRG=0.7, and it is possible to observe that code T4B generates a smaller loss,
and that pulse h ( ) produces less interference than pulse (t)
. Figure 2-31 shows the
sin t
telemetry losses due to the ranging signal as function of mRG, when mTM=1.25 rad: the loss
increases with mRG, and the best case is that with code T4B and h sin ( t)
. Further simulations
were run in order to measure the losses when a non-integer ratio exists between the chip rate
and the TM symbol rate; figure 2-32 shows the cases of RTM=500 ks/s and Rc=1.7 Mc/s or
1.9 Mc/s: the differences between the cases h ( ) and (t)
is much reduced, and pulse
hsq (t)
is now to be preferred, while code T2B again introduces a higher loss on the telemetry
system than code T4B. In conclusion, the ranging signal worsens the telemetry system
performance and code T2B has a greater impact than code T4B; the measured losses are
below 1 dB, but the exact loss depends on the chosen parameters.
Figure 2-30: Samples at the Input of the Zero-Threshold Detector of the Telemetry
Receiver; Case of Pulse hsq(t), mTM=1.25 rad, mRG=0.7 rad, Codes T2B
(Left) and T4B (Right), No Noise
CCSDS 414.0-G-1 Page 2-71 March 2010
sin t
E
TM , d
N
0
.
h sq
h sq