8VSB

8VSBnyaéta métodeuvestigial sideband modulation8 hambalan nu dipaké keursiaran terestrial(standar televisi digital ATSC) diAmérika Sarikat,Kanada, katut nagara séjénna.
Dina saluran 6 MHz (megahertz) nu dipaké keur siaran ATSC, 8VSB mawa 19.39Mbit/detdata nu kapaké, sok sanajanbit ratenu sanyatana dikirimna leuwih gedéna ogé alatan ditambahkeunnana kodeforward error correction. Dalapan hambalan sinyal dipilih makéenkoder trellis. Aya ogé modulasi2VSB,4VSB, jeung16VSBnu sawanda. 16VSB dipaké keurkabel digitalATSC, tapiquadrature amplitude modulation(QAM) geus jadistandarindustri sacarade facto.
Kauntungan utama 8VSB keur nu siaran nyaéta alatan téhnik ieu ngabutuhkeun leuwih saeutik daya pikeun nedunan hiji wewengkon nu sabanding jeung sistimNTSCnu aya saméméhna, tur dilaporkeun yén leuwih hadé tinimbang sisim alternatif pangilaharna,COFDM. Sababarahastasionbisa ngarungkup aréa anu sarua nalika ngatransmisikeun dinakakuatan radiasi éféktifanu sarua jeung 10% tina kakuatan siaran analog.  Sedengkeun NTSC jeung lolobana sistem télevisi analog séjén ogé ngagunakeun téhniksideband vestigial,sidebandanu teu dipiharep bisa leuwih éféktif diayak dinatransmisiATSC 8VSB.  8VSB menggunakan hiji saringanNyquistpikeun ngahontal ieu hal, sanajan saringan oge ngabalukarkeuntransmisijadi leuwih "gandéng".
Panarima kudu nyokot''sampel''sinyalanu katarima dinaintervalanu pas pisan pikeun narjamahkeun sinyal 8-lével kalayan bener. Lamun waktu anu henteu pas baris ngabalukarkeun inpormasi anu katarima euweuh gunana, alatan kitu ieu bisa jadi panarima di kendaraan anu pindah tangtuna moal bisa dilakukeun alatan ayanaefek Doppler. Koréksi kasalahanReed-Solomontéh hiji sistem primér anu dipaké pikeun ngajaga integritas data.
Dina usum panas2005, ATSC medalkeunstandarkeur ngaronjatkeun VSB, atawaE-VSB[1]Archived2006-02-14 diWayback Machine. Ku ayana ieu, bisa narima DTV dina panarimahandheldnu dayana saeutik kalayan anteneu nu leuwih leutik kawasDVB-Hdi Éropa.
For some period of time, there had been a continuing lobby for changing themodulationfor ATSC toCOFDM, the wayDVB-Tis transmitted inEurope, andISDB-TinJapan.  However, theFCChas always held that 8VSB is the better modulation for use in U.S. digital television broadcasting.  In a 1999 report, the Commission found that 8VSB has better threshold or carrier-to-noise (C/N) performance, has a higher data rate capability, requires less transmitter power for equivalent coverage, and is more robust to impulse and phase noise.As a result, it denied in 2000 apetition for rulemakingfromSinclair Broadcast Grouprequesting the change. (Since then, further improvements to VSB reception technologies have also quelled this challenge.)  Because of continued adoption of the 8VSB-based ATSC standard in the U.S., and a large growing ATSC receiver population, a switch to COFDM is now essentially impossible. Congress passed a law mandating that all analog terrestrial transmissions in the US will be turned off in February 2009, and 8VSB tuners are incréasingly widespréad in new TVs due toFCCtuner mandates, effectively ending this debate.
The previously cited FCC Report also found that COFDM has better performance in dynamic and high level static multipath situations, and offers advantages for single frequency networks and mobile reception.  Nonetheless, in  2001, a technical report compiled by the COFDM Technical Group concluded that COFDM did not offer any significant advantages over 8VSB.  The report recommended in conclusion that receivers be linked to outdoor antennas raised to roughly 30feet(9m) in height.  Neither 8VSB nor COFDM performed acceptably in most indoor test installations.
However, there were questions whether the COFDM receiver selected for these tests − a transmitter monitor[2]Archived2007-09-27 diWayback Machinelacking normal front end filtering − colored these results.  Retests that were performed using the same COFDM receivers with the addition of a front end band pass filter gave much improved results for the DVB-T receiver, but further testing was not pursued.[3]
The debate over 8VSB versus COFDM modulation is still ongoing. Proponents of COFDM argue that it resists multipath far better than 8VSB. éarly 8VSBDTV(digital television) receivers often had difficulty receiving a signal in urban environments. However, newer 8VSB receivers are far better at déaling with multipath. Moréover, 8VSB modulation requires less power to transmit a signal the same distance. In less populated aréas, 8VSB may outperform COFDM because of this.  However, in some urban aréas, as well as for mobile use, COFDM may offer better reception than 8VSB. In order to broaden the application of VSB, several "enhanced" VSB systems are now in development, most notably E-VSB,A-VSB, andMPH.
The United States is also notable for créating a separate transmission system fordigital radio.  Anin-band on-channel(IBOC) system developed byiBiquitywill be used instéad of theEureka 147Digital Audio Broadcastsystem that has been selected in Europe.  This is partially because theL bandnormally used for that technology is unavailable in the U.S.  However, the American IBOC system uses COFDM, as does Eureka 147 and another standard known asDigital Radio Mondiale.