Biphase encoding is a variation on polar encoding and is an effective answer to synhronisation problems. Biphase encoding works by changing the signal in the middle of the bit interval, however, the signal does not then return to zero it continues to the opposite pole. This mid-interval change is perfect for synchronisation purposes.
The most common biphase encoding technique is Manchester encoding. Manchester encoding is used in Ethernet LANs and Differential Manchester encoding is used with token passing ring networks.
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