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4.2 Digital Data, Digital Signal

Receiver needs to determine bit information from the signal level, for instance, by sampling the signal level at the middle if the time interval and comparing the value to a threshold.
                        ||
                        ||
 ||| |||  |- --| |-|-|| ||| -|| |||  -|
 ||| ||| ||| --| |||||| ||| ||| ||| --|
---------------------------------------
-- ||| ||| -|- --| |- ||  -|- ||| ||  |
     | ||                       - |
  -| --| --| --| --| --|--| --| --| --|
  || | | | | | | | | | || | | | | | | |
  || | | | | | | | | | || | | | | | | |
--  -- --- --- --  --  -- --- --- ---

Nonreturn-to-Zero-Level (NRZ-L) Signal Encoding

Positive and negative voltage levels for binary digits.

|   |   |  |   |   |   |   |  |   |   |   |
|0  |1  |0 | 0 | 1 |1  |0  |0 | 0 | 1 |1  |
|   |---|  |   |---|---|   |  |   |---|---|
|   |   |  |   |   |   |   |  |   |   |   |
|---|   |--|---|   |   |---|--|---|   |   |
|   |   |  |   |   |   |   |  |   |   |   |

spectral
density-
   1.4 --     ||-  NRZ  -L, NRZI
   1.2 ---|  --||| (differential) Manchester
   1.0 -- ||||| -||
   0.8 --  ||--  -|ABM8IZ,S, psHeDuBd3oternary
   0.6 --  ||  ||||-||||
   0.4 -- ||||||--|--  ||||
   0.2 -|--|--|--|-|--|--|--|--|-|--|
                                      normalized
         0.2   0.6   1.0  1.4   1.8    frequency

Nonreturn-to-Zero-Inverted (NRZI) Signal Encoding

NRZI is a differential encoding in which the signal is decoded by comparing the polarity of adjacent signal levels: 1 encoded by transition between levels and 0 encoded by a lack of transition.

|   |   |  |   |   |   |   |  |   |   |   |
|0  |1  |0 | 0 | 1 |1  |0  |0 | 0 | 1 |1  |
|   |---|--|---|   |---|---|--|---|   |---|
|   |   |  |   |   |   |   |  |   |   |   |
|---|   |  |   |---|   |   |  |   |---|   |
|   |   |  |   |   |   |   |  |   |   |   |

Similar advantages and disadvantages as NRZ-L.

Bipolar-AMI Signal Encoding

A multilevel binary approach in which binary 0 is represented by a lack of pulse, and a binary 1 is represented by a positive or a negative pulse. The binary 1 pulses must alternate in polarity.

|   |   |  |   |   |   |   |  |   |   |   |
|0  |1  |0 | 0 | 1 |1  |0  |0 | 0 | 1 |1  |
|   |---|  |   |   |---|   |  |   |   |---|
|---|   |--|---|   |   |---|--|---|   |   |
|   |   |  |   |---|   |   |  |   |---|   |
|   |   |  |   |   |   |   |  |   |   |   |

AMI stands for alternate mark inversion, whereas mark and space historical references to binary digits 1 and 0.

Pseudoternary Signal Encoding

A multilevel binary encoding that complements the bipolar-AMI encoding: binary 1 is represented by a lack of pulse, and a binary 0 is represented by a positive or a negative pulse. The binary 0 pulses must alternate in polarity.

|   |   |  |   |   |   |   |  |   |   |   |
|0  |1  |0 | 0 | 1 |1  |0  |0 | 0 | 1 |1  |
|---|   |  |---|   |   |   |--|   |   |   |
|   |---|  |   |---|---|   |  |   |---|---|
|   |   |--|   |   |   |---|  |---|   |   |
|   |   |  |   |   |   |   |  |   |   |   |

Manchester Signal Encoding

Manchester encoding is a biphase encoding in which the transition takes place in the middle of the bit period: a low-to-high transition for 1, and a high-to-low transition for 0.

|   |   |  |   |   |   |   |  |   |   |   |
|0  |1  |0 | 0 | 1 |1  |0  |0 | 0 | 1 |1  |
|-| | --|| |-| | --| --|-| |-||-| | --| --|
| | | | || | | | | | | | | | || | | | | | |
| --|-| ||-| --|-| |-| | --| -| --|-| |-| |
|   |   |  |   |   |   |   |  |   |   |   |

Differential Signal Encoding

A biphase encoding in which transition at the start of the bit period represents 0, and a lack of transition at the start of the bit represents 1. In addition, a transition occurs at the middle of each bit period just for the purpose of clocking.

|   |   |  |   |   |   |   |   |  |   |   |
|0  |1  |0 | 0 | 1 |1  |0  |0  |0 | 1 | 1 |
| --|-| |-||-| | --|-| |-| |-|||| | --|-| |
| | | | | || | | | | | | | | |||| | | | | |
|-| | --| -| --|-| | --| --| -||--|-| | --|
|   |   |  |   |   |   |   |   |  |   |   |

Bipolar with 8-zeros Substitution (B8ZS) Signal Encoding

The bipolar-AMI encoding supplemented with a scrambling scheme, which uses two code violations to ensure synchronization in runs of 0's.

| | | || | | | | | | | | | || | | | |
1 1 0 0|0|0|0|0|00 1 1 0 0 0|0|0|1|0|
|-| | || | | | | | |-| | | || | |-| |
| | |-||-|-|-|-|-|-| | |-|-||-|-| |-|
| |-| || | | | | | | |-| | || | | | |
| | | || | | | | | | | | | || | | | |

| | | || | | | | | | | | | || | | | |
1 1 0 0|0|0|0|0|00 1 1 0 0 0|0|0|1|0|
|-| | || | |-| |-| |-| | | || | |-| |
| | |-||-| | |-| | | | |-|-||-|-| |-|
| |-| || |-| | | |-| |-| | || | | | |
| | | || | | | | | | | | | || | | | |

High-Density Bipolar 3-Zeros (HDB3) Signal Encoding

The bipolar-AMI encoding supplemented with the following substitution scheme for `0000' runs.
Number of bipolar pulses (ones) since last substitution
Polarity of preceding pulse Odd even
-000-+00+
+000+-00-

| | | || | | | | | | | | | || | | | |
1 1 0 0|0|0|0|0|00 1 1 0 0 0|0|0|1|0|
|-| | || | | | | | |-| | | || | |-| |
| | |-||-|-|-|-|-|-| | |-|-||-|-| |-|
| |-| || | | | | | | |-| | || | | | |
| | | || | | | | | | | | | || | | | |

| | | || | | | | | | | | | || | | | |
1 1 0 0|0|0|0|0|00 1 1 0 0 0|0|0|1|0|
|-| | || | |-| | |-| |-| | || | |-| |
| | |-||-| | |-|-| | | | |-|| |-| |-|
| |-| || |-| | | | |-| |-| ||-| | | |
| | | || | | | | | | | | | || | | | |

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