Direct-sequence spread spectrum

<h2 id="transmission-method">Transmission method</h2>
<p>Direct-sequence spread-spectrum transmissions multiply the symbol sequence being transmitted with a spreading sequence that has a higher rate than the original message rate. Usually, sequences are chosen such that the resulting spectrum is spectrally <a href="/facts/White_noise/wJ0SR21n">white</a>.  Knowledge of the same sequence is used to reconstruct the original data at the receiving end. This is commonly implemented by the element-wise multiplication with the spreading sequence, followed by summation over a message symbol period. This process, <i>despreading</i>, is mathematically a <a href="/facts/Correlation/egkluAEm">correlation</a> of the transmitted spreading sequence with the spreading sequence. In an AWGN channel, the despreaded signal's <a href="/facts/Signal-to-noise_ratio/qohClhyG">signal-to-noise ratio</a> is increased by the spreading factor, which is the ratio of the spreading-sequence rate to the data rate.
</p><p>While a transmitted DSSS signal occupies a wider bandwidth than the direct modulation of the original signal would require, its spectrum can be restricted by conventional <a href="/facts/Pulse_shaping/GrhYVMUJ">pulse-shape filtering</a>.
</p><p>If an undesired transmitter transmits on the same channel but with a different spreading sequence, the despreading process reduces the power of that signal. This effect is the basis for the <a href="/facts/Code-division_multiple_access/o2RLKE4M">code-division multiple access</a> (CDMA) method of multi-user medium access, which allows multiple transmitters to share the same channel within the limits of the <a href="/facts/Cross-correlation/Fs1hY3br">cross-correlation</a> properties of their spreading sequences.
</p>
<h2 id="benefits">Benefits</h2>
<ul><li>Resistance to unintended or intended <a href="/facts/Radio_jamming/j4xyPQsQ">jamming</a></li>
<li>Sharing of a single channel among multiple users</li>
<li>Reduced signal/background-noise level hampers <a href="/facts/Signals_intelligence/Iwzvw6AW">interception</a></li>
<li>Determination of relative timing between transmitter and receiver</li></ul>
<h2 id="uses">Uses</h2>
<ul><li>The United States <a href="/facts/GPS/DKVLnzF3">GPS</a>, European <a href="/facts/Galileo_positioning_system/sPyWl594">Galileo</a> and Russian <a href="/facts/GLONASS/sLh1vQ6p">GLONASS</a> <a href="/facts/Satellite_navigation/lVgPlF5v">satellite navigation</a> systems; earlier GLONASS used DSSS with a single spreading sequence in conjunction with <a href="/facts/FDMA/mQTBIpzA">FDMA</a>, while later GLONASS used DSSS to achieve <a href="/facts/CDMA/o2RLKE4M">CDMA</a> with multiple spreading sequences.</li>
<li>DS-CDMA (Direct-Sequence Code Division Multiple Access) is a <a href="/facts/Multiple_access/CdCGxpcu">multiple access</a> scheme based on DSSS, by spreading the signals from/to different users with different codes.  It is the most widely used type of <a href="/facts/CDMA/o2RLKE4M">CDMA</a>.</li>
<li><a href="/facts/Cordless_telephone/Y6PEsMk7">Cordless phones</a> operating in the 900 MHz, 2.4 GHz and 5.8 GHz <a href="/facts/Band_(radio)/AP2frA1C">bands</a></li>
<li><a href="/facts/IEEE_802.11b/WcN5bIIS">IEEE 802.11b</a> 2.4 GHz <a href="/facts/Wi-Fi/u94quCsx">Wi-Fi</a>, and its predecessor <a href="/facts/802.11-1999/VtAWQ3bQ">802.11-1999</a>. (Their successor <a href="/facts/802.11g/DYaeYj0q">802.11g</a> uses both <a href="/facts/Orthogonal_frequency-division_multiplexing/YhPkx5ql">OFDM</a> and DSSS)</li>
<li><a href="/facts/Automatic_meter_reading/8X2ANTxP">Automatic meter reading</a></li>
<li><a href="/facts/IEEE_802.15.4/PH0j6uVX">IEEE 802.15.4</a> (used, e.g., as PHY and MAC layer for <a href="/facts/Zigbee/SG0GxpjI">Zigbee</a>, or, as the physical layer for <a href="/facts/WirelessHART/V4LHoKfl">WirelessHART</a>)</li>
<li><a href="/facts/Radio-controlled_model/wPPuCk5b">Radio-controlled model</a> Automotive, Aeronautical and Marine vehicles</li>
<li>Spread spectrum <a href="/facts/Radar/jk9BTbFA">radar</a> for covertness and resistance to <a href="/facts/Radar_jamming_and_deception/sGoEJ6Bv">jamming</a> and <a href="/facts/Spoofing_attack/hyBGUakY">spoofing</a></li></ul>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Complementary_code_keying/PBzKhIsl">Complementary code keying</a></li>
<li><a href="/facts/Frequency-hopping_spread_spectrum/hJS6o3xy">Frequency-hopping spread spectrum</a></li>
<li><a href="/facts/Linear-feedback_shift_register/22pktBbX">Linear-feedback shift register</a></li>
<li><a href="/facts/Orthogonal_frequency-division_multiplexing/YhPkx5ql">Orthogonal frequency-division multiplexing</a></li></ul>

<ul><li><a href="https://ieeexplore.ieee.org/document/1095547/">The Origins of Spread-Spectrum Communications</a></li>
<li> This article incorporates <a href="/facts/Copyright_status_of_works_by_the_federal_government_of_the_United_States/Q1jvr96g">public domain material</a> from <a href="https://web.archive.org/web/20220122224547/https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm"><i>Federal Standard 1037C</i></a>. <a href="/facts/General_Services_Administration/Np3opv9x">General Services Administration</a>. Archived from <a href="https://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm">the original</a> on January 22, 2022.</li>
<li><a href="/facts/NTIA_Manual_of_Regulations_and_Procedures_for_Federal_Radio_Frequency_Management/NU3jouvb">NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management</a></li></ul>
<h2 id="external-links">External links</h2>
<ul><li><a href="http://www.marcus-spectrum.com/page4/SSHist.html">Civil Spread Spectrum History </a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>Torrieri, Don (2018). Principles of Spread-Spectrum Communication Systems, 4th ed. <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>"Espacenet - Bibliographic data". worldwide.espacenet.com. Retrieved December 2, 2020. <a href="https://worldwide.espacenet.com/publicationDetails/biblio?FT=D&date=19460806&DB=worldwide.espacenet.com&locale=en_EP&CC=US&NR=2405500A&KC=A&ND=7" target="_blank">https://worldwide.espacenet.com/publicationDetails/biblio?FT=D&date=19460806&DB=worldwide.espacenet.com&locale=en_EP&CC=US&NR=2405500A&KC=A&ND=7</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Torrieri, Don (2018). Principles of Spread-Spectrum Communication Systems, 4th ed. <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Stuber, Gordon L. (2017). Principles of Mobile Communication, 4th ed. <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Rappaport, Theodore (2002). Wireless Communications Principles and Practice, 2nd ed. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Pratep, Misra; Enge, Per (2012). Global Positioning System: Signals, Measurements, and Performance, rev. 2nd ed. <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
</ol>

Direct-sequence spread spectrum open-in-new

Direct-sequence spread spectrum