The biphasic (also biphase) coding schemes stand out for their unique approach to representing bits. They are characterized by the fact that each bit isn't represented by a single voltage level, but rather by a change in the signal level at the midpoint of each bit period. This means that each bit is represented by two signal changes (between a positive and a negative voltage), hence the name 'biphasic'. In this page, we'll cover the first scheme of this encoding family: Manchester.
The Manchester scheme keeps somewhat of a resemblance to the unipolar-non-return-to-zero level scheme, since the form of the transition that occurs at the middle of the interval (from low to high voltage and vice-versa) depends only on the current bit being transmitted -that is, it doesn't consider the "history" of the signal-. In this scheme, a bit 0 is represented by a transition from a high voltage to a lower one, while a bit 1 is represented by a transition from a low voltage to a higher one.
This encoding scheme has its own set of advantages and disadvantages. One of the main advantages is that it provides better synchronization compared to the unipolar schemes. This is because the frequent transitions in the Manchester encoding help the receiver to easily identify the timing of the bits. On the other hand, it must be noted that it requires a more complex encoding and decoding process than the unipolar schemes. Another drawback is that the bandwidth requirement is twice as much, since each bit is represented by two signal changes instead of one.
Coming up is a set of examples of the Manchester scheme.
