QPSK Constellation
00
45°
01
135°
11
225°
10
315°
Quadrature Phase Shift Keying - 2 bits per symbol
Symbol Mapping: Each pair of bits (dibit) maps to one of 4 phases: 45°, 135°, 225°, 315°.
Spectral Efficiency: 2 bits per symbol = double the bit rate of BPSK for same bandwidth!
Gray Coding: Adjacent symbols differ by only 1 bit, minimizing errors from noise.
I/Q Representation: s(t) = I·cos(ωt) - Q·sin(ωt) where I,Q ∈ {-1, +1}.
Applications: Wi-Fi, LTE, DVB-S, cable modems, satellite links.