Frame synchronization: Difference between revisions

Revision as of 02:34, 24 September 2013

Revision as of 17:44, 3 December 2013

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{{context|date=February 2013}}

{{expert-subject|1=Video|date=February 2013}}

'''Frame synchronization''' is the process of synchronizing display pixel scanning to a synchronization source. When several systems are connected, a syncsynchronization signal is fed from a master system to the other systems in the network, and the displays are synchronized with each other.

While receiving a stream of [[data frame|framed]] [[data]], '''frame synchronization''' or '''framing''' is the process by which 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]]

The transmitter and the receiver must agree ahead of time on which frame [[synchronization]] scheme they will use.

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==

===Television===

{{further|Time base corrector}}

A '''frame synchronizer''' is a device used in [[live television]] [[television production|production]] to match the timing of an incoming [[video]] source to the timing of an existing video system. They are often used to "time in" consumer video equipment to a professional system but can be used to stabilize any video. The frame synchronizer essentially takes a picture of each [[Film frame|frame]] of incoming video and then immediately outputs it with the correct synchronization signals to match an existing video system. A [[genlock]] signal is required to provide a means for video synchronizing with the house reference.

===Telemetry===

[[Image:PCM Stream.jpg|frame|none|PCM Streamstream 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: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]]

The frame syncronisationsynchronization 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 (Subsub-Frameframe 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.

==See also==

* [[Asynchronous start-stop]]

* [[Phase synchronization]]

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==References==

{{Reflist}}

{{FS1037C MS188}}

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

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]