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Difference between Manchester and Differential Manchester encoding

This page compares Manchester vs Differential Manchester and mentions difference between Manchester encoding and Differential Manchester encoding with their advantages and disadvantages.

Introduction:
There are various line coding techniques to convert data elements to signal elements. These include Unipolar (NRZ), Polar (NRZ, RZ, Biphase), Bipolar (AMI, Pseudoternary) , Multilevel (2B1Q, 8B6T, 4D-PAM5) and Multitransition (MLT-3). Biphase line coding include Manchester and Differential Manchester encoding. Refer Unipolar vs Polar vs Bipolar coding for difference between these types.

Manchester Encoding

• Transition is used at the middle of each bit period.
• Transition is used as clock edge and data mapping both.
- Low to High represents 1
- High to Low represents 0
• Used by IEEE 802.3 specification for Ethernet LAN (Short distances)

Manchester Encoding

Differential Manchester Encoding

• Dedicated mid-bit transition used only for clocking
• Data representation is mapped as per bit start time instant.
- No transition at start of a bit period represents as 1
- Transition at start of a bit period represents as 0 (Inverts on 0's - Opposite of NRZI)
• Example : Differential encoding
• Used by IEEE 802.5 specification for Token Ring LAN

Differential Manchester Encoding

Advantages of Manchester and Differential Manchester (Biphase) Encoding

Both Manchester and differential manchester fall under Biphase encoding type. Following are the advantages of Biphase encoding techniques.
➨It provides guaranteed mid bit transitions. Hence it offers synchronization facility at receiver. It is called self clocking codes.
➨As they are bipolar signals, ideally no DC components are present.
➨It provides error detection by detecting absence of expected transitions.

Disadvantages of Biphase encoding

Following are the disadvantages of Biphase encoding techniques.
➨It maps at least one transition per bit time and possibly two bits. Its modulation or signal rate is two times that of NRZ. Hence it requires more bandwidth.
➨It is used over shorter distances (in LANs).


Line coding techniques

Difference between Unipolar Polar and Bipolar coding    RZ vs NRZ vs Manchester coding    RZ vs NRZ pulse shapes    Advantages and disadvantages of NRZ encoding    RZ encoding    2B1Q coding    8B6T coding    4D PAM5 coding    MLT-3 coding    4B/5B encoding    8B/10B encoding    R8ZS scrambling    HDB3 scrambling   

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