Frame synchronization: Difference between revisions

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While receiving a stream of [[data frame|framed]] [[data]], '''frame synchronization''' is the process by which incoming frame alignment signals, ''(i.e.'', distinctive [[bit]] sequences (/a [[syncword]]), are identified, ''(i.e.'', distinguished from data bits,) permitting the data bits within the frame to be extracted for decoding or retransmission. This is sometimes referred to as "''framing"''.

== Framing ==

[[Image:Frame Synced Stream.jpg|frame|none|Frame Synchronized PCM Stream -- Telemetry Application]]

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

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The most 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 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]].

* '''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==

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===Telemetry===

[[Image:Frame SyncedPCM Stream.jpg|frame|none|Frame Synchronized PCM Stream prior to frame synchronization]]

In [[telemetry]] applications, a '''frame synchronizer''' is used to frame align a serial pulse code modulated ([[PCM]]) (Pulse Code Modulated)binary stream. [[Image:PCM Stream.jpg|frame|none|PCM Stream prior to Frame Synchronization]]

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

In [[telemetry]] applications, a '''frame synchronizer''' is used to frame align a serial [[PCM]] (Pulse Code Modulated)binary stream. [[Image:PCM Stream.jpg|frame|none|PCM Stream prior to Frame Synchronization]]

The Frameframe Synchronizersynchronizer immediately follows the Bitbit Synchronizersynchronizer in most telemetry applications. Without frame synchronization [[Decommutator|decommutation]] is impossible.

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

The Frame Synchronizer immediately follows the Bit Synchronizer in most telemetry applications. Without frame synchronization [[Decommutator|decommutation]] is impossible.

The Frameframe Syncsyncronisation Patternpattern is a known binary pattern which repeats at a regular interval within the PCM stream. The frame synchronizer recognizes this pattern and aligns the data into Minorminor Framesframes or Sub Framessub-frames. Typically the frame sync pattern is followed by a counter (Sub-Frame ID) which dictates which minor or sub frame in the series is being transmitted. This becomes increasingly important in the decommutation stage where all data is deciphered as to what attribute was sampled. Different commutations require a constant awareness of which section of the major frame is being decoded.

[[Image:Frame Synced Stream.jpg|frame|none|Frame Synchronized PCM Stream]]

The Frame Sync Pattern is a known binary pattern which repeats at a regular interval within the PCM stream. The frame synchronizer recognizes this pattern and aligns the data into Minor Frames or Sub Frames. Typically the frame sync pattern is followed by a counter (Sub-Frame ID) which dictates which minor or sub frame in the series is being transmitted. This becomes increasingly important in the decommutation stage where all data is deciphered as to what attribute was sampled. Different commutations require a constant awareness of which section of the major frame is being decoded.

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

==See also==

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* [[Self-synchronizing code]]

* [[Superframe]]

* [[GenlockGenerator locking]]

==References==

{{FS1037C MS188}}

;===Scientific Articles:articles===

* J. L. Massey. "Optimum frame synchronization ". IEEE trans. comm., com-20(2):115-119, April 1972.

* R Scholtz. "Frame synchronization techniques", IEEE Transactions on Communications, 1980.

* P. Robertson. "Optimal Frame Synchronization for Continuous and Packet Data Transmission", PhD Dissertation,

R Scholtz. "Frame synchronization techniques", IEEE Transactions on Communications, 1980

P. Robertson. "Optimal Frame Synchronization for Continuous and Packet Data Transmission", PhD Dissertation,

1995, Fortschrittberichte VDI Reihe 10, Nr. 376 [http://www.kn-s.dlr.de/People/Robertson/Papers/diss.pdf PDF]

==External links==

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

* [http://www.algolith.com/products/broadcast/frame-synchronization/index.html Algolith Frame Synchronizer Solutions]

[[Category:Data transmission]]