Direct-sequence spread spectrum: Difference between revisions

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{{Short description|Modulation technique to reduce signal interference}}

{{Use mdy dates|date = March 2019}}

{{Modulation techniques}}

{{Multiplex_techniques}}

In [[telecommunicationtelecommunications]]s, '''direct-sequence spread spectrum''' ('''DSSS''') is a [[spread-spectrum]] [[modulation]] technique primarily used to reduce overall signal [[Interference (communication)|interference]]. The direct-sequence modulation makes the transmitted signal wider in bandwidth than the information bandwidth.

After the despreading or removal of the direct-sequence modulation in the receiver, the information bandwidth is restored, while the unintentional and intentional interference is substantially reduced.<ref name="ref 1">{{cite book| title=Principles of Spread-Spectrum Communication Systems, 4th ed.| year=2018|last1=Torrieri|first1=Don}}</ref>

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==Transmission method==

Direct-sequence spread-spectrum transmissions multiply the datasymbol sequence being transmitted bywith a pseudorandom spreading sequence that has a much higher bit rate than the original datamessage rate. TheUsually, resultingsequences transmittedare signalchosen resemblessuch bandlimitedthat the resulting spectrum is spectrally [[white noise|white]],. like an audio recordingKnowledge of "static".the same However, this noise-like signalsequence is used to exactly reconstruct the original data at the receiving end,. byThis multiplyingis itcommonly implemented by the sameelement-wise spreadingmultiplication sequencewith (becausethe {{nowrap|1spreading ×sequence, 1followed {{=}}by 1}},summation andover {{nowrap|−1a ×message −1symbol {{=}} 1}})period. This process, known as ''despreading'', is mathematically a [[correlation]] of the transmitted spreading sequence with the spreading sequence. thatIn thean receiverAWGN already knowschannel, the transmitterdespreaded is using. After the despreading, thesignal's [[signal-to-noise ratio]] is approximately increased by the spreading factor, which is the ratio of the spreading-sequence rate to the data rate.

While a transmitted DSSS signal occupies a much wider bandwidth than athe simpledirect modulation of the original signal would require, its frequency spectrum can be somewhat restricted for spectrum economy by a conventional analog bandpass filter to give a roughly bell-shaped envelope centered on the [[carrierPulse frequency]]. In contrast, [[frequencyshaping|pulse-hoppingshape spread spectrumfiltering]] pseudorandomly retunes the carrier and requires a uniform frequency response since any bandwidth shaping would cause amplitude modulation of the signal by the hopping code.

If an undesired transmitter transmits on the same channel but with a different spreading sequence (or no sequence at all), the despreading process reduces the power of that signal. This effect is the basis for the [[code-division multiple access]] (CDMA) propertymethod of DSSSmulti-user medium access, which allows multiple transmitters to share the same channel within the limits of the [[cross-correlation]] properties of their spreading sequences.

==Benefits==

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* [[IEEE 802.15.4]] (used, e.g., as PHY and MAC layer for [[Zigbee]], or, as the physical layer for [[WirelessHART]])

* [[Radio-controlled model]] Automotive, Aeronautical and Marine vehicles

* Spread spectrum [[radar]] for covertness and resistance to [[Radar jamming and deception|jamming]] and [[Spoofing attack|spoofing]]

==See also==

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==References==

{{reflist}}

* [httphttps://ieeexplore.ieee.org/xpldocument/login.jsp?tp=&arnumber=1095547&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D1095547/ The Origins of Spread-Spectrum Communications]

* {{FS1037C}}

* [[NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management]]

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{{cdma}}

[[Category:Computer network technology]]

[[Category:Quantized radio modulation modes]]

[[Category:Wireless networking]]