8VSB

8VSB nyaéta métodeuvestigial sideband modulation 8 hambalan nu dipaké keur siaran terestrial (standar televisi digital ATSC) di Amérika Sarikat, Kanada, katut nagara séjénna.

 Lobana data anu bisa di pigawé (Throughput) 
Dina saluran 6 MHz (megahertz) nu dipaké keur siaran ATSC, 8VSB mawa 19.39 Mbit/det data nu kapaké, sok sanajan bit rate nu sanyatana dikirimna leuwih gedéna ogé alatan ditambahkeunnana kode forward error correction. Dalapan hambalan sinyal dipilih maké enkoder trellis. Aya ogé modulasi 2VSB, 4VSB, jeung 16VSB nu sawanda. 16VSB dipaké keur kabel digital ATSC, tapi quadrature amplitude modulation (QAM) geus jadi standar industri sacara de facto.

 Kauntungan nyimpen daya
Kauntungan utama 8VSB keur nu siaran nyaéta alatan téhnik ieu ngabutuhkeun leuwih saeutik daya pikeun nedunan hiji wewengkon nu sabanding jeung sistim NTSC nu aya saméméhna, tur dilaporkeun yén leuwih hadé tinimbang sisim alternatif pangilaharna, COFDM. Sababaraha stasion bisa ngarungkup aréa anu sarua nalika ngatransmisikeun dina kakuatan radiasi éféktif anu sarua jeung 10% tina kakuatan siaran analog.  Sedengkeun NTSC jeung lolobana sistem télevisi analog séjén ogé ngagunakeun téhnik sideband vestigial, sideband anu teu dipiharep bisa leuwih éféktif diayak dina transmisi ATSC 8VSB.  8VSB menggunakan hiji saringan Nyquist pikeun ngahontal ieu hal, sanajan saringan oge ngabalukarkeun transmisi jadi leuwih "gandéng". 

Panarima kudu nyokot  sampel sinyal anu katarima dina interval anu 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 ayana efek Doppler. Koréksi kasalahan Reed-Solomon téh hiji sistem primér anu dipaké pikeun ngajaga integritas data.

Dina usum panas 2005, ATSC medalkeun standar keur ngaronjatkeun VSB, atawa E-VSB  . Ku ayana ieu, bisa narima DTV dina panarima handheld nu dayana saeutik kalayan anteneu nu leuwih leutik kawas DVB-H di Éropa.

 Disputes over ATSC's use 
For some period of time, there had been a continuing lobby for changing the modulation for ATSC to COFDM, the way DVB-T is transmitted in Europe, and ISDB-T in Japan.  However, the FCC has 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., September 30, 1999.  As a result, it denied in 2000 a petition for rulemaking from Sinclair Broadcast Group requesting 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 to FCC tuner mandates, effectively ending this debate.

 8VSB vs COFDM 
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 30 feet (9 m) 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   lacking 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.Receiver Anomaly Retest

The debate over 8VSB versus COFDM modulation is still ongoing. Proponents of COFDM argue that it resists multipath far better than 8VSB. éarly 8VSB DTV (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, and MPH.

 Bifurcation of digital transmission systems 
The United States is also notable for créating a separate transmission system for digital radio.  An in-band on-channel (IBOC) system developed by iBiquity will be used instéad of the Eureka 147 Digital Audio Broadcast system that has been selected in Europe.  This is partially because the L band normally 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 as Digital Radio Mondiale.

Rujukan

Tempo oge
Tuner ATSC

 Tumbu luar
 What exactly is 8-VSB anyway? 

Kategori:Mode modulasi radio
Kategori:Televisi digital