Mapping QPSK Gray (DVB-S)
| Dibits (b0 b1) |
I |
Q |
Phase |
Symbole |
| 00 |
+1/√2 ≈ +0.707 |
+1/√2 ≈ +0.707 |
+45° (π/4) |
↗ |
| 01 |
+1/√2 ≈ +0.707 |
−1/√2 ≈ −0.707 |
−45° (−π/4) |
↘ |
| 10 |
−1/√2 ≈ −0.707 |
+1/√2 ≈ +0.707 |
+135° (3π/4) |
↖ |
| 11 |
−1/√2 ≈ −0.707 |
−1/√2 ≈ −0.707 |
−135° (5π/4) |
↙ |
Constellation QPSK
Q (Quadrature)
│
10 │ 00
(↖) │ (↗)
● │ ●
-0.707,+0.707 │ +0.707,+0.707
│
─────────────────────┼─────────────────────► I (In-phase)
│
-0.707,-0.707 │ +0.707,-0.707
● │ ●
(↙) │ (↘)
11 │ 01
│
Mapping Gray: les symboles adjacents (horizontalement ou verticalement)
ne diffèrent que d'1 bit → une erreur de symbole = 1 bit erroné en moyenne
Normalisation: |I|² + |Q|² = 1 (puissance unitaire)
→ I, Q = ±1/√2 ≈ ±0.7071067811865476
Paramètres
| Paramètre | Valeur | Description |
|---|
| Modulation | QPSK | 4-PSK, 4 états de phase |
| Bits/symbole | 2 | Efficacité spectrale 2 bps/Hz |
| Mapping | Gray | Adjacent = 1 bit différent |
| Amplitude | 1/√2 | Puissance normalisée = 1 |
| Phases | ±45°, ±135° | 4 quadrants |