#### Example 5.6

## Differential PSK (DPSK)

Differential PSK (DPSK) is based on the same 'change of state' encoding/decoding methodology as used in DEPSK, but improves upon it by incorporating the differential decoding task as part of the data demodulation task, and at the same time does away with the need for a 'carrier recovery' mechanism. |

The differential encoding block and PSK modulator is common to both DPSK and DEPSK, but the receiver operates by comparing the phase of the current incoming carrier symbol with that of the previous carrier symbol. In this process, it rolls 'coherent detection' and 'differential decoding' into one operation. Clearly, this detection process is much simpler than that required for true coherent PSK and consequently DPSK is widely used in wired and radio modems for medium-rate signalling (up to 4800 bps). DPSK, however, has a slightly poorer noise immunity than PSK since the phase reference for DPSK is now a noisy delayed version of the input signal rather than potentially a well-filtered, virtually noiseless reference from a carrier recovery process.