Line code: Difference between revisions

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Revision as of 21:46, 23 April 2020

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== Transmission and storage ==

[[File:Binary Line Code Waveforms.png|framedthumb|centerupright=2.4|An arbitrary bit pattern in various binary line code formats]]

After line coding, the signal is put through a physical communication channel, either a [[transmission medium]] or [[data storage medium]].<ref name="paulsen">Karl Paulsen. [http://www.tvtechnology.com/media-servers/0150/coding-for-magnetic-storage-mediums/186738 "Coding for Magnetic Storage Mediums"] {{Webarchive|url=https://web.archive.org/web/20140521215946/http://www.tvtechnology.com/media-servers/0150/coding-for-magnetic-storage-mediums/186738 |date=2014-05-21 }}.2007.</ref><ref>{{citation|author1=Abdullatif Glass |author2=Nidhal Abdulaziz |author3=and Eesa Bastaki |url=http://ro.uow.edu.au/cgi/viewcontent.cgi?article=1285&context=dubaipapers|title=Slope line coding for telecommunication networks|year=2007|p=1537|journal=IEEE International Conference on Signal Processing and Communication|publisher=IEEE|___location=Dubai|quote=Line codes ... facilitates the transmission of data over telecommunication and computer networks and its storage in multimedia systems.}}</ref> The most common physical channels are:

* the line-coded signal can directly be put on a [[transmission line]], in the form of variations of the voltage or current (often using [[differential signaling]]).

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* the line-coded signal can be converted to magnetized spots on a [[hard drive]] or [[tape drive]].

* the line-coded signal can be converted to pits on an [[optical disc]].

Each line code has advantages and disadvantages. Line codes are chosen to meet one or more of the following criteria:

* Minimize transmission hardware

* Facilitate synchronization

* Ease error detection and correction

* Achieve a target [[spectral density]]

* Eliminate a [[DC component]]

Some of the more common binary line codes include:

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! Signal !! Comments !! 1 state !! 0 state

|-

| NRZ–L || [[Non-return-to-zero]] level. This is the standard positive <br>logic signal format used in digital circuits.

| forces a high level

| forces a low level

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| stays low for the entire period

|-

| Biphase–L || Manchester. Two consecutive bits of the same type <br>force a transition at the beginning of a bit period.

| forces a negative transition in the middle of the bit

| forces a positive transition in the middle of the bit

|-

| Biphase–M || Variant of Differential Manchester. There is always a <br>transition halfway between the conditioned transitions.

| forces a transition

| keeps level constant

|-

| Biphase–S || Differential Manchester used in Token Ring. There is always <br>a transition halfway between the conditioned transitions.

| keeps level constant

| forces a transition

|-

| Differential <br>Manchester <br>(Alternative)|| Need a Clock, always a transition in the middle <br>of the clock period

| is represented by no transition.

| is represented by a transition at the <br>beginning of the clock period.

|-

| Bipolar || The positive and negative pulses alternate.

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| keeps a zero level during bit period

|}

[[File:Binary Line Code Waveforms.png|framed|center|An arbitrary bit pattern in various binary line code formats]]

Each line code has advantages and disadvantages. Line codes are chosen to meet one or more of the following criteria:

* Minimize transmission hardware

* Facilitate synchronization

* Ease error detection and correction

* Achieve a target [[spectral density]]

* Eliminate a [[DC component]]

== Disparity ==