digital communications Data transmission and data reception or, more broadly, data communication or digital communications is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point o ...

, a chip is a pulse of a

direct-sequence spread spectrum In telecommunications, direct-sequence spread spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference. The direct-sequence modulation makes the transmitted signal wider in bandwidth than ...

(DSSS) code, such as a pseudo-random noise (PN) code sequence used in direct-sequence

code-division multiple access Code-division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communicatio ...

(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

bit The bit is the most basic unit of information in computing and digital communications. The name is a portmanteau of binary digit. The bit represents a logical state with one of two possible values. These values are most commonly represented a ...

s) 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. 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 In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in ' ...

, meaning that one

symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...

is represented by multiple chips. The ratio is known as the spreading factor (SF) or processing gain: :

\mbox = \frac

Orthogonal variable spreading factor

Orthogonal variable spreading factor (OVSF) is an implementation of

(CDMA) where before each signal is transmitted, the 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 In mathematics, orthogonality is the generalization of the geometric notion of '' perpendicularity''. By extension, orthogonality is also used to refer to the separation of specific features of a system. The term also has specialized meanings in ...

to each other. These codes are derived from an OVSF code tree, and each user is given a different code. An OVSF code tree is a complete

binary tree In computer science, a binary tree is a k-ary k = 2 tree data structure in which each node has at most two children, which are referred to as the ' and the '. A recursive definition using just set theory notions is that a (non-empty) binar ...

that reflects the construction of

Hadamard matrices In mathematics, a Hadamard matrix, named after the French mathematician Jacques Hadamard, is a square matrix whose entries are either +1 or −1 and whose rows are mutually orthogonal. In geometric terms, this means that each pair of rows i ...

References

External links

CDMA basics
{{Wireless-stub

Orthogonal variable spreading factor

See also

References

External links