STV0196B
ANNEXE 1 : C/n ESTIMATION (continued)
A.2 - Scaling and Correction versus Puncture Rate
Scaling
This simple operation is recommended to easily
compare data which have been recorded under
different sensitivity conditions. To do so, the result
S of the C/N indication is multiplied by a coefficient
so that the scaled value would correspond to a
measure done with the highest counting period
(SN = 11).
Remark : Scaling is not done for results which have
beenrecordedafterchangingthe AGCreferencelevel.
Scaling operation : Scaled_value = (S) x (factor)
factor = 64 when C/N estimation is done with SN = 00
factor = 16 when C/N estimation is done with SN = 01
factor = 4 when C/N estimation is done with SN = 10
factor = 1 when C/N estimation is done with SN = 11
Correction versus puncture rate
This correction is not required when a reference
look-up table have been memorized for each pos-
sible puncture rate. When required, the correction
is done with respect to the puncture rate PRref of
the reference look-up table :
Scorrected
=
(S)
⋅
PRcurrent
PRref
PR current : the puncture currently identified with
the bits 0,1,2 of VSTATUS register.
A.3 - Comparing with the look-up table
In the application the read value Srs (scaled and
corrected) will seldom exactly match a value of the
look-up table ; consequentlythere will be the need
for some interpolation.
To make it simple, a linear interpolation is preferred,
with such a solution a good precision can be
achieved when the look-up table is built with a small
step for the C/N (or Eb/No).
Interpolation
Generally Ssr will be between two values of the
reference look-up table : V(Min.) ≤ Ssr ≤ V(Max.),
with V(Min.) corresponding C/N(Max.) and V(Max.)
c orre sp on din g t o C / N(Min.) (w it h t yp i ca l ly
(C/N(Max.)) - (C/N(Min.)) = 0.5dB).
The calculated C/N corresponding to Ssr is :
C/N
=
C/N(Max.)
−
C/N(Max.)
−
C/N(Min.)
⋅
V(Min.) − Ssr
V(Min.) − V(Max.)
in above calculation C/N (or Eb/No) are given in
algebraic value (not in dB).
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