Direct-sequence spread spectrum: Difference between revisions

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Revision as of 15:13, 30 November 2019

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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>

With DSSS, the message bits are are modulated by a pseudorandom bit sequence known as a spreading sequence. Each spreading-sequence bit, which is known as a chip, has a much shorter duration (larger bandwidth) than the original message bits. The modulation of the message bits scrambles and spreads the pieces of data, and thereby results in a bandwidth size nearly identical to that of the spreading sequence. The smaller the chip duration, the larger the bandwidth of the resulting DSSS signal; more bandwidth multiplexed to the message signal results in better resistance against interference.<ref name="ref 1">{{cite book| title=Principles of Spread-Spectrum Communication Systems, 4th ed.| year=2018|last1=Torrieri|first1=Don}}</ref><ref name="ref 2">{{cite book| title=Principles of Mobile Communication, 4th ed.| year=2017|last1=Stuber|first1=Gordon L.}}</ref>

Some practical and effective uses of DSSS include the [[Code Division Multiple Access]] (CDMA) method, the [[IEEE 802.11#802.11b|IEEE 802.11b]] specification used in [[Wi-Fi]] networks, and the [[Global Positioning System]].<ref name="ref 3">{{cite book|title=Wireless Communications Principles and Practice, 2nd ed.| year=2010|last1=Rappaport|first1=Theodore}}</ref><ref name="ref 4">{{cite book| title=Global Positioning System: Signals, Measurements, and Performance, rev. 2nd ed.| year=2012|last1=Pratep|first1=Misra|last2=Enge|first2=Per}}</ref>