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In [[digital communications]], a '''chip''' is a pulse of a [[direct-sequence spread spectrum]] (DSSS) code, such as a pseudo-noise code sequence used in direct-sequence [[code division multiple access]] (CDMA) [[channel access]] techniques.

In a binary direct-sequence system, each chip is typically a rectangular pulse of +1 or –1 amplitude, which is multiplied by a data sequence (similarly +1 or –1 representing the message bits) and by a carrier waveform to make the transmitted signal. The chips are therefore just the bit sequence out of the code generator; they are called chips to avoid confusing them with message bits.<ref>{{cite book | title = Satellite Communications Systems | author = Gérard Maral and Michel Bousquet | publisher = John Wiley and Sons | year = 2002 | isbn = 0-471-49654-5 | url = http://books.google.com/books?id=RlIX7Pbjtg8C&pg=PA306&dq=chip+message+bit+direct-sequence&lr=&as_brr=3&ei=JvasSKOaNo_-sQOGlbGQBA&sig=ACfU3U35lRdkKat8qlb20VB624RyNj90dQ }}</ref>

The [[chip rate]] of a code is the number of pulses per second (chips per second) at which the code is transmitted (or received). The chip rate is larger than the [[symbol rate]], meaning that one [[symbol (data)|symbol]] is represented by multiple chips. The ratio is known as the ''spreading factor'' (SF) or processing gain:
:<math>\ \mbox{SF} = \frac{\mbox{chip rate}}{\mbox{symbol rate}}</math>

== Orthogonal variable spreading factor ==
[[File:Drzewo ciagow ortogonalnych.png|thumb|280px|OVSF code tree]]
'''Orthogonal variable spreading factor''' ('''OVSF''') is an implementation of [[Code division multiple access]] (CDMA) where before each signal is transmitted, the [[Spread spectrum|signal is spread over a wide spectrum range]] through the use of a user's code. Users' codes are carefully chosen to be mutually [[orthogonal]] to each other.

These codes are derived from an OVSF code tree, and each user is given a different, unique code. An OVSF code tree is a complete [[binary tree]] that reflects the construction of [[Hadamard matrix|Hadamard matrices]].

==References==

{{reflist}}

== External links ==

* [http://www.umtsworld.com/technology/cdmabasics.htm CDMA basics]

{{cdma}}

{{Wireless-stub}}

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