Frame synchronization: Difference between revisions

Revision as of 21:21, 27 April 2017

Revision as of 04:00, 30 April 2017

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{{context|date=February 2013}}

In [[telecommunication]], frame synchronization or '''framing''' is the process by which, while receiving a stream of [[Frame_(networking)|framed]] [[data]], incoming frame alignment signals (i.e., a distinctive [[bit]] sequences or [[syncword]]s) are identified (that is, distinguished from data bits), permitting the data bits within the frame to be extracted for decoding or retransmission.

== Framing ==

If the transmission is temporarily interrupted, or a [[bit slip]] event occurs, the receiver must re-synchronize.

[[Image:Frame Synced Stream.jpg|frame|none|Frame synchronized PCM stream — telemetry application]]

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Common frame synchronization schemes are:

;Framing bit: A common practice in [[telecommunication]]s, for example in [[T-carrier]], is to insert, in a dedicated [[Time-division multiplexing|time slot]] within the frame, a noninformation bit or '''framing bit''' that is used for synchronization of the incoming data with the receiver. In a [[bit stream]], framing bits indicate the beginning or end of a frame. They occur at specified positions in the frame, do not carry information, and are usually repetitive.

;Syncword framing: Some systems use a special [[syncword]] at the beginning of every frame.

;CRC-based framing: Some telecommunications hardware uses [[CRC-based framing]].

==Frame synchronizer==

[[Image:PCM Stream.jpg|frame|none|PCM stream prior to frame synchronization]]

In [[telemetry]] applications, a ''frame synchronizer'' is used to frame-align a serial pulse code-modulated ([[Pulse-code modulation|PCM]]) binary stream.

[[Image:Commutation.jpg|frame|none|Different types of commutation within a frame synchronized PCM stream]]

The frame synchronizer immediately follows the bit synchronizer in most telemetry applications. Without frame synchronization, [[Decommutator|decommutation]] is impossible.

[[Image:Frame Synced Stream.jpg|frame|none|Frame-synchronized PCM stream]]

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==External links==

* [http://www.ulyssix.com Telemetry Ground Station Processing Electronics telemetry link]

[[Category:Data transmission]]