STV0196 datasheet(20/23 Pages) STMICROELECTRONICS

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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 ; consequently there 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 or respondin 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(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).

ANNEXE 1 : C/n ESTIMATION (continued)

STV0196B

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