## Differential data encoding

An alternative and more frequently used method of coping with phase ambiguity in the carrier recovery process is to use differential encoding and decoding of the input and received data stream. This process is termed Differentially Encoded Phase Shift Keying (DEPSK). The challenge is to come up with an encoding/decoding scheme that will give the same decoded output regardless of whether the received data is inverted. Shown here is such an encoder based on an exclusive-or gate. This circuit operates by translating the input data into a coded data stream where a logic 1 at the input is coded as a change of logic state from the previous coded bit, and a logic 0 at the input as no change of state from the previous coded bit. Implementation of the 1-bit delay block can be achieved very simply using a clocked shift register. This encoding process is very efficient as it does not introduce any extra data bits and hence does not affect the throughput of the data modem. |

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