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44-494: In 2004, the main ATSC standard was amended to support Enhanced ATSC (A/112); this transmission mode is backwardly compatible with the original 8-Bit Vestigal Sideband modulation scheme, but provides much better error correction. ATSC-M/H for mobile TV has been approved and added to some stations, though it is known that it uses MPEG-4 instead of MPEG-2 for encoding, and behaves as an MPEG-4-encoded subchannel, inheriting 8VSB from

88-408: A carrier by a real-valued data sequence results in a sum and a difference frequency, resulting in two symmetrical carrier side-bands. The symmetry means that one of the sidebands is redundant, so removing one sideband still allows for demodulation. As filters with zero transition bandwidth cannot be realized, the filtering implemented leaves a vestige of the redundant sideband, hence the name "VSB". In

132-442: A clock signal. If the clock phases drift apart, the demodulated I and Q signals bleed into each other, yielding crosstalk . In this context, the clock signal is called a "phase reference". Clock synchronization is typically achieved by transmitting a burst subcarrier or a pilot signal . The phase reference for NTSC , for example, is included within its colorburst signal. Analog QAM is used in: Applying Euler's formula to

176-1107: A further update to the status of its standards, with the following as Finalized: A/321 (System Discovery and Signaling); A/322 Physical Layer Protocl (COFDM); A/326 (Field Test Plan [Recommended Practice]); A/330 (Link Layer Protocol); A/333 (Service Usage Reporting); A/334 (Audio Watermark Emission); A/335 (Video Watermark Emission); A/336 (Content Recovery in Redistribution Scenarios [ATSC 3.0 over Cable and Satellite]); A/342 Part 1 (Audio Common Elements); A/342 Part 2 (Audio: Dolby AC-4 System); A/342 Part 3 (Audio MPEG-H System); and A/343 (Captions and Subtitles). The following are Proposed Standards: A/325 (Lab Performance Test Plan [Recommended Practice]); A/332 (Service Announcement); A/338 (Companion Device); A/341 (Video - H.265/HEVC). The following are Candidate Standards: A/300 (ATSC 3.0 System); A/324 (Scheduler/Studio-to-Transmitter Link); A/331 (Signalling, Delivery, Sync Error Protection); A/337 (Application Signalling); A/344 (Interactive Content); A/360 (Security and Service Protection). The following

220-472: A future transition to COFDM. However, with the development of ATSC 3.0 , an updated version of the American digital television standard designed for mobile reception and better single frequency network performance, the ATSC has decided to make the switch to OFDM with LDPC error correction (essentially COFDM). As a result, ATSC 3.0 will be incompatible with all current ATSC 1.0 receivers, and viewers will need

264-465: 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 a petition for rulemaking from Sinclair Broadcast Group requesting that broadcasters be allowed to choose between 8VSB or COFDM as is most appropriate for their area of coverage. The FCC report also acknowledged that COFDM would "generally be expected to perform better in situations where there

308-417: A higher order QAM constellation (higher data rate and mode) in hostile RF / microwave QAM application environments, such as in broadcasting or telecommunications , multipath interference typically increases. There is a spreading of the spots in the constellation, decreasing the separation between adjacent states, making it difficult for the receiver to decode the signal appropriately. In other words, there

352-495: A higher-order constellation, it is possible to transmit more bits per symbol . However, if the mean energy of the constellation is to remain the same (by way of making a fair comparison), the points must be closer together and are thus more susceptible to noise and other corruption; this results in a higher bit error rate and so higher-order QAM can deliver more data less reliably than lower-order QAM, for constant mean constellation energy. Using higher-order QAM without increasing

396-793: A new TV with a compatible tuner or a converter box. Unlike the previous digital TV transition which was mandated by the FCC, the "transition" to ATSC 3.0 will be completely voluntary. Additionally, the FCC has required that broadcasters who decided to make the switch to ATSC 3.0 continue to make their main channel available through a simulcast agreement with another in-market station (with a similar coverage area) through at least 2022. Sinclair announced an intention to bring ATSC 3.0 to 40 cities by 2020. 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,

440-434: A signal the same distance. In less populated areas, 8VSB may outperform COFDM because of this. However, in some urban areas, as well as for mobile use, COFDM may offer better reception than 8VSB. Several "enhanced" VSB systems were in development, most notably E-VSB , A-VSB , and MPH . The deficiencies in 8VSB in regards to multipath reception can be dealt with by using additional forward error-correcting codes which decreases

484-533: 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 −

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528-427: A three-path interferometer . In a QAM signal, one carrier lags the other by 90°, and its amplitude modulation is customarily referred to as the in-phase component , denoted by I ( t ). The other modulating function is the quadrature component , Q ( t ). So the composite waveform is mathematically modeled as: where f c is the carrier frequency.  At the receiver, a coherent demodulator multiplies

572-586: A transmitter monitor [2] Archived 2007-09-27 at the Wayback Machine 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. [3] The debate over 8VSB versus COFDM modulation is still ongoing. Proponents of COFDM argue that it resists multipath far better than 8VSB. This

616-521: A vestigial sideband technique, the unwanted sideband is filtered much more effectively in ATSC 8VSB transmissions. 8VSB uses a Nyquist filter to achieve this. Reed–Solomon error correction is the primary system used to retain data integrity. In summer of 2005, the ATSC published standards for Enhanced VSB, or E-VSB [1] . Using forward error correction , the E-VSB standard will allow DTV reception on low power handheld receivers with smaller antennas in much

660-483: Is ADSL technology for copper twisted pairs, whose constellation size goes up to 32768-QAM (in ADSL terminology this is referred to as bit-loading, or bit per tone, 32768-QAM being equivalent to 15 bits per tone). Ultra-high capacity microwave backhaul systems also use 1024-QAM. With 1024-QAM, adaptive coding and modulation (ACM) and XPIC , vendors can obtain gigabit capacity in a single 56 MHz channel. In moving to

704-617: Is a Draft Standard: A/323 (Physical Layer Uplink/Downlink). 8VSB 8VSB is the modulation method used for broadcast in the ATSC digital television standard . ATSC and 8VSB modulation is used primarily in North America ; in contrast, the DVB-T standard uses COFDM . A modulation method specifies how the radio signal fluctuates to convey information. ATSC and DVB-T specify the modulation used for over-the-air digital television; by comparison, QAM

748-413: Is dynamic multipath," such as mobile operation or in the presence of trees that are moving in high winds. However, with the introduction of 5th Generation demodulators in 2005 and subsequent improvements in generations 6 and 7, the equalization span is now about −60 to +75 microseconds (a 135 microsecond spread) and has virtually eliminated multipath, both static and dynamic, in 8VSB reception. In comparison,

792-408: Is important property of the modulation for receiving HDTV in e.g. moving vehicles that is not possible with 8VSB. Early 8VSB DTV (digital television) receivers often had difficulty receiving a signal in urban environments. Newer 8VSB receivers, however, are better at dealing with multipath, but a moving receiver can still not receive the signal. Moreover, 8VSB modulation requires less power to transmit

836-484: Is the modulation method used for cable . The specifications for a cable-ready television, then, might state that it supports 8VSB (for broadcast TV) and QAM (for cable TV). 8VSB is an 8-level vestigial sideband modulation . In essence, it converts a binary stream into an octal representation by amplitude-shift keying a sinusoidal carrier to one of eight levels. 8VSB is capable of transmitting three bits (2 =8) per symbol ; in ATSC, each symbol includes two bits from

880-465: Is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. It conveys two analog message signals, or two digital bit streams , by changing ( modulating ) the amplitudes of two carrier waves , using the amplitude-shift keying (ASK) digital modulation scheme or amplitude modulation (AM) analog modulation scheme. The two carrier waves are of

924-424: Is used extensively as a modulation scheme for digital communications systems , such as in 802.11 Wi-Fi standards. Arbitrarily high spectral efficiencies can be achieved with QAM by setting a suitable constellation size, limited only by the noise level and linearity of the communications channel.   QAM is being used in optical fiber systems as bit rates increase; QAM16 and QAM64 can be optically emulated with

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968-457: Is used for Freeview-HD. Communication systems designed to achieve very high levels of spectral efficiency usually employ very dense QAM constellations. For example, current Homeplug AV2 500-Mbit/s powerline Ethernet devices use 1024-QAM and 4096-QAM, as well as future devices using ITU-T G.hn standard for networking over existing home wiring ( coaxial cable , phone lines and power lines ); 4096-QAM provides 12 bits/symbol. Another example

1012-468: The MPEG transport stream which are trellis modulated to produce a three-bit figure. The resulting signal is then band-pass filtered with a Nyquist filter to remove redundancies in the side lobes, and then shifted up to the broadcast frequency. Vestigial sideband modulation (VSB) is a modulation method which attempts to eliminate the spectral redundancy of pulse-amplitude modulation (PAM) signals. Modulating

1056-615: The demodulator must now correctly detect both phase and amplitude , rather than just phase. 64-QAM and 256-QAM are often used in digital cable television and cable modem applications. In the United States, 64-QAM and 256-QAM are the mandated modulation schemes for digital cable (see QAM tuner ) as standardised by the SCTE in the standard ANSI/SCTE 07 2013 . In the UK, 64-QAM is used for digital terrestrial television ( Freeview ) whilst 256-QAM

1100-429: The 6 MHz ( megahertz ) channel used for broadcast ATSC, 8VSB carries a symbol rate of 10.76 megabaud , a gross bit rate of 32 Mbit/s , and a net bit rate of 19.39 Mbit/s of usable data. The net bit rate is lower due to the addition of forward error correction codes. The eight signal levels are selected with the use of a trellis encoder . There are also similar modulations 2VSB , 4VSB , and 16VSB . 16VSB

1144-513: The 8VSB scheme from its inception, and its improved demodulators have had no effect on its innate payload capacity . 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 will be challenging. Most analog terrestrial transmissions in the US were turned off in June 2009, and 8VSB tuners are common to all new TVs, further complicating

1188-414: The 90° phase shift that enables their individual demodulations. As in many digital modulation schemes, the constellation diagram is useful for QAM. In QAM, the constellation points are usually arranged in a square grid with equal vertical and horizontal spacing, although other configurations are possible (e.g. a hexagonal or triangular grid). In digital telecommunications the data is usually binary , so

1232-787: The Link Layer Protocol Standard (A/330) was elevated from Candidate to final standard, along with the Audio Watermark Emission Standard (A/334) and Video Watermark Emission Standard (A/335). ATSC Technology Group 3 (TG3) members have also begun voting on elevating the following Candidate Standards to Proposed Standard status (the final step before becoming an approved standard): Service Announcement (A/322), Service Usage Reporting (A/333) and Captions and Subtitles (A/343). TG3 members also are voting to elevate Security (A/360) to Candidate Standard status, joining Schedule and Studio-to-Transmitter Link Standard (A/324), which

1276-432: The advantage is the lower peak to average power ratio needed compared to COFDM. An 8VSB transmitter needs to have a peak power capability of 6 dB (four times) its average power. 8VSB is also more resistant to impulse noise. Some stations can cover the same area while transmitting at an effective radiated power of approximately 25% of analog broadcast power. While NTSC and most other analog television systems also use

1320-465: The bit error rate requires a higher signal-to-noise ratio (SNR) by increasing signal energy, reducing noise, or both. If data rates beyond those offered by 8- PSK are required, it is more usual to move to QAM since it achieves a greater distance between adjacent points in the I-Q plane by distributing the points more evenly. The complicating factor is that the points are no longer all the same amplitude and so

1364-431: The carrier frequency, which is known as the narrowband assumption . Phase modulation (analog PM) and phase-shift keying (digital PSK) can be regarded as a special case of QAM, where the amplitude of the transmitted signal is a constant, but its phase varies. This can also be extended to frequency modulation (FM) and frequency-shift keying (FSK), for these can be regarded as a special case of phase modulation . QAM

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1408-458: The equalization span in COFDM is −100 to +100 microseconds (200 microsecond spread), but the application of this much guard band space for COFDM substantially reduces its useful payload. In fact, much of Europe has adopted 1280×720p as its HD standard for DVB-T1 because of its reduced payload capacity . The introduction of DVB-T2 is meant to increase the ability of terrestrial transmissions to carry 1920×1080p content. 1920×1080i has always been part of

1452-461: The in-phase component can be received independently of the quadrature component.  Similarly, we can multiply s c ( t ) by a sine wave and then low-pass filter to extract Q ( t ). The addition of two sinusoids is a linear operation that creates no new frequency components. So the bandwidth of the composite signal is comparable to the bandwidth of the DSB (double-sideband) components. Effectively,

1496-430: The number of points in the grid is typically a power of 2 (2, 4, 8, …), corresponding to the number of bits per symbol. The simplest and most commonly used QAM constellations consist of points arranged in a square, i.e. 16-QAM, 64-QAM and 256-QAM (even powers of two). Non-square constellations, such as Cross-QAM, can offer greater efficiency but are rarely used because of the cost of increased modem complexity. By moving to

1540-407: The received signal separately with both a cosine and sine signal to produce the received estimates of I ( t ) and Q ( t ) . For example: Using standard trigonometric identities , we can write this as: Low-pass filtering r ( t ) removes the high frequency terms (containing 4π f c t ), leaving only the I ( t ) term. This filtered signal is unaffected by Q ( t ), showing that

1584-541: The remainder of the channel. ATSC 3.0 is a non-backwards-compatible version of ATSC being developed (as of May 18, 2016) that uses OFDM instead of 8VSB and a much newer video codec (instead of ATSC 1 and 2's MPEG-2 ). On March 28, 2016, the Bootstrap component of ATSC 3.0 (System Discovery and Signalling) was upgraded from candidate standard to finalized standard. On May 4, 2016, the Audio Codec component of ATSC 3.0

1628-399: The same frequency and are out of phase with each other by 90°, a condition known as orthogonality or quadrature . The transmitted signal is created by adding the two carrier waves together. At the receiver, the two waves can be coherently separated (demodulated) because of their orthogonality. Another key property is that the modulations are low-frequency/low-bandwidth waveforms compared to

1672-726: The same way DVB-H does in Europe, but still using 8VSB transmission. 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

1716-507: The sinusoids in Eq.1 , the positive-frequency portion of s c (or analytic representation ) is: where F {\displaystyle {\mathcal {F}}} denotes the Fourier transform, and ︿ I and ︿ Q are the transforms of I ( t ) and Q ( t ). This result represents the sum of two DSB-SC signals with the same center frequency. The factor of i (= e ) represents

1760-422: The spectral redundancy of DSB enables a doubling of the information capacity using this technique. This comes at the expense of demodulation complexity. In particular, a DSB signal has zero-crossings at a regular frequency, which makes it easy to recover the phase of the carrier sinusoid. It is said to be self-clocking . But the sender and receiver of a quadrature-modulated signal must share a clock or otherwise send

1804-451: The useful bit rate, such as that used by ATSC-M/H for Mobile/Handheld reception. ATSC 3.0 , the next major television standard in the United States, will use COFDM. The vast majority of U.S. TV stations use COFDM for their studio to transmitter links and news gathering operations . These are point-to-point communication links and not broadcast transmissions. Quadrature amplitude modulation Quadrature amplitude modulation ( QAM )

List of ATSC standards - Misplaced Pages Continue

1848-534: Was elevated to candidate standard, with two finalists remaining: Dolby AC-4 and MPEG-H Audio Alliance format from Fraunhofer IIS , Qualcomm and Technicolor SA . A third entry from DTS named DTS:X (a successor to DTS-HD ) was withdrawn before the standard was upgraded to candidate status. On September 8, 2016, the Physical Layer Download ( OFDM ) component of ATSC 3.0 was upgraded from candidate standard to finalized standard. On October 5, 2016,

1892-443: Was notably intended to be used for ATSC digital cable , but quadrature amplitude modulation (QAM) has become the de facto industry standard instead as it is cheap and readily available. A significant advantage of 8VSB for broadcasters is that it requires much less power to cover an area comparable to that of the earlier NTSC system, and it is reportedly better at this than the most common alternative system, COFDM . Part of

1936-693: Was recently elevated. On March 30, 2016, A/324 (Schedule and Studio-to-Transmitter Link) was upgraded from Proposed to Candidate Standard. On January 3, 2017, ATSC announced the updated status of its standards, in time for its debut at the Consumer Electronics Show in Las Vegas . As a result, this update, Captions and Subtitles (A/343) was upgraded from Candidate to Finalized Standard; Security (A-360), Lab Performance Test Plan (A-325) and Field Test Plan (A-326) were upgraded to Candidate Standard from "Under Consideration". By March 7, 2017, ATSC announced

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