Manchester Encoding: The normal binary logics of one and zero are no more used to send data from one station to other station. The reason of not using plain binary signal is they cause ambiguities resulting in false interpretation of sent data. The major culprit is zero, where even no data is sent the receiver can assume it as zero. So to clear out the ambiguity or to ensure proper interpretation of data, a coding technique called Manchester coding is employed in IEEE802.3 standards. There are two of Manchester coding, they are simple Manchester coding and differential Manchester coding. Summary
Each bit is transmitted in a fixed time (the "period").
A 0 is expressed by a low-to-high transition, a 1 by high-to-low transition (according to G.E. Thomas' convention -- in the IEEE 802.3 convention, the reverse is true). The transitions which signify 0 or 1 occur at the midpoint of a period. Transitions at the start of a period are overhead and don't signify data. Manchester code always has a transition at the middle of each bit period and may (depending on the information to be transmitted) have a transition at the start of the period also. The direction of the mid-bit transition indicates the data. Transitions at the period boundaries do not carry information. They exist only to place the signal in the correct state to allow the mid-bit transition. Although this allows the signal to be self-clocking, it doubles the bandwidth requirement compared to NRZ coding schemes (or see also NRZI). In the Thomas convention, the result is that the first half of a bit period matches the information bit and the second half is its complement. If a Manchester encoded signal is inverted in communication, it is transformed from one convention to the other. This ambiguity can be overcome by using differential Manchester encoding.
Differential Manchester Encoding Shown in above figure is a variation of basic Manchester encoding. A '1' bit is indicated by making the first half of...
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