Editing Linear-feedback shift register (section)

=== Uses in digital broadcasting and communications ===

==== Scrambling ====
{{Main | Scrambler}}
To prevent short repeating sequences (e.g., runs of 0s or 1s) from forming spectral lines that may complicate symbol tracking at the
receiver or interfere with other transmissions, the data bit sequence is combined with the output of a linear-feedback register before modulation and transmission. This scrambling is removed at the receiver after demodulation. When the LFSR runs at the same [[bit rate]] as the transmitted symbol stream, this technique is referred to as [[scrambler|scrambling]]. When the LFSR runs considerably faster than the symbol stream, the LFSR-generated bit sequence is called ''chipping code''. The chipping code is combined with the data using [[exclusive or]] before transmitting using [[binary phase-shift keying]] or a similar modulation method. The resulting signal has a higher bandwidth than the data, and therefore this is a method of [[spread-spectrum]] communication. When used only for the spread-spectrum property, this technique is called [[direct-sequence spread spectrum]]; when used to distinguish several signals transmitted in the same channel at the same time and frequency, it is called [[code-division multiple access]].

Neither scheme should be confused with [[encryption]] or [[encipherment]]; scrambling and spreading with LFSRs do ''not'' protect the information from eavesdropping. They are instead used to produce equivalent streams that possess convenient engineering properties to allow robust and efficient modulation and demodulation.

Digital broadcasting systems that use linear-feedback registers:
* [[ATSC standards|ATSC Standards]] (digital TV transmission system – North America)
* [[Digital Audio Broadcasting|DAB]] ([[Digital Audio Broadcasting]] system – for radio)
* [[DVB-T]] (digital TV transmission system – Europe, Australia, parts of Asia)
* [[NICAM]] (digital audio system for television)

Other digital communications systems using LFSRs:
* Intelsat business service (IBS)
* Intermediate data rate (IDR)
* [[HDMI]] 2.0
* [[Serial digital interface|SDI]] (Serial Digital Interface transmission)
* Data transfer over [[Public switched telephone network|PSTN]] (according to the [[ITU-T]] V-series recommendations)
* [[Code-division multiple access|CDMA]] (Code Division Multiple Access) cellular telephony
* [[Fast Ethernet#100BASE-T2|100BASE-T2 "fast" Ethernet]] scrambles bits using an LFSR
* [[Gigabit Ethernet#1000BASE-T|1000BASE-T Ethernet]], the most common form of Gigabit Ethernet, scrambles bits using an LFSR
* [[PCI Express]]
* [[SATA]]<ref>Section 9.5 of the SATA Specification, revision 2.6</ref>
* [[Serial Attached SCSI]] (SAS/SPL)
* [[USB 3.0]]
* [[IEEE 802.11a-1999|IEEE 802.11a]] scrambles bits using an LFSR
* [[Bluetooth Low Energy]] Link Layer is making use of LFSR (referred to as whitening)
* [[Satellite navigation|Satellite navigation systems]] such as [[Global Positioning System|GPS]] and [[GLONASS]]. All current systems use LFSR outputs to generate some or all of their ranging codes (as the chipping code for CDMA or DSSS) or to modulate the carrier without data (like GPS&nbsp;L2&nbsp;CL ranging code). GLONASS also uses [[frequency-division multiple access]] combined with DSSS.

==== Other uses ====
LFSRs are also used in [[radio jamming]] systems to generate pseudo-random noise to raise the noise floor of a target communication system.

The German time signal [[DCF77]], in addition to amplitude keying, employs [[phase-shift keying]] driven by a 9-stage LFSR to increase the accuracy of received time and the robustness of the data stream in the presence of noise.<ref name="phasemod">{{cite conference |url=https://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_4/4.4_zeit_und_frequenz/pdf/5_1988_Hetzel_-_Proc_EFTF_88.pdf |title=Time dissemination via the LF transmitter DCF77 using a pseudo-random phase-shift keying of the carrier |first=P. |last=Hetzel |date=16 March 1988 |conference=2nd European Frequency and Time Forum |location=Neuchâtel |pages=351–364 |access-date=11 October 2011}}</ref>