8PSK

8PSK, or eight-phase shift keying, is a digital modulation scheme in which each symbol encodes three bits by selecting one of eight equally spaced phase states of a constant-amplitude carrier. The constellation consists of eight points on the unit circle, separated by 45 degrees, and Gray-coded mappings are commonly used to minimize bit errors between adjacent symbols.

Compared with QPSK, 8PSK provides higher spectral efficiency, delivering 3 bits per symbol rather than 2. This allows higher data throughput at the same symbol rate. However, for a given bit error rate, 8PSK generally requires a higher signal-to-noise ratio, because its decision regions are smaller and the scheme is more sensitive to phase noise, Doppler, and non-linearities in the transmission chain. In additive white Gaussian noise (AWGN) channels, the bit error rate of Gray-coded 8PSK is higher than that of QPSK at the same Eb/N0.

8PSK is used in systems that seek greater throughput without increasing bandwidth excessively, such as certain satellite communications and parts of the DVB-S2 standard, which supports multiple modulations including QPSK, 8PSK, and higher-order APSK schemes for different service requirements.

Implementation typically involves coherent demodulation with carrier phase recovery and symbol-by-symbol decision based on the closest constellation point. The constant-amplitude nature of PSK helps with power amplifier efficiency, but the scheme demands more stringent phase synchronization and linearity than QPSK.