RF CURRENT



Welcome to RF Current, a weekly electronic newsletter focusing on Broadcast technical and F.C.C. related issues. This newsletter is part of The RF Page @ www.transmitter.com, a web site devoted to TV Broadcast RF engineering. For more information see the What is... guide to the R.F. Page site.

Issues are dated each Monday, although recently I've needed an extra day or two to complete each issue. Articles may be posted earlier if time permits or if there is a major, breaking story.

<<< Back to August 16 - Issue 178

August 23, 1999 - Issue 179 Delayed Final Edition

DTV - Motorola and Nxtwave Claim Solution to ATSC 8-VSB Indoor Reception Problems (Aug. 24)
As reported in the July 19issue of RF Current, demonstrations by Sinclair Broadcasting showed current generation ATSC 8-VSB receivers failed to work reliably, if at all, when using indoor antennas. As word of the demonstrations spread, broadcasters called for manufacturers to show improved 8-VSB receivers or allow the use of the DVB-T COFDM transmission standard. Products announcemented by Motorola and Nxtwave, if they deliver what they promise, may be the last minute reprieve 8-VSB supporters have been hoping for.

Motorola issued a press release - New Digital Receiver Technology from Motorola Enhances 8-VSB Reception, Solves Multipath Problems - on Monday describing the MCT2100 demodulator and forward error correction (FEC) chip. The release said
"Broadcasters expressed concern recently when third-party test results showed that multipath reflections interfered with DTV reception. Addressing this issue, Motorola, in collaboration with TV pioneer Sarnoff Corporation, has created a revolutionary digital signal processing architecture known as the MCT2100 demodulator and forward error correction (FEC) chip. The chip uses advanced proprietary algorithms and unique equalization architecture, providing excellent signal reception even for the most extreme static and dynamic multipath signal ensembles."
The release goes on to say that the MCT2100, in an environment with static multipath, can correct for echos (ghosts) up to 41 microseconds delayed from the main signal. The chip uses a full equalizer design, providing better performance than spare equalizer techniques. The chip uses 8-VSB technology licensed from Sarnoff Corporation on a non-exclusive basis. Glenn Reitmeir, VP for DTV and Web Media at Sarnoff, said ""The MCT 2100 is a major step forward in implementing the perfect pictures and reliable data transmission that the creators of the ATSC standard intended for DTV and HDTV."

The Motorola MCT2100 chip shows up in earlier Motorola documents. A May 21, 1999 product sheet describes the features of the MCT2100, including a "High performance robust complex equalizer". Fast acquistion time is also mentioned, with a comment that the MCT2100 "uses a unique implementation of novel algorithms to meet all of these requirements and much more."

Doug Lung, publisher of RF Current, asked Frank Eory, at Motorola's Digital TV Operations division in Chandler, Arizona, if any tests had been done to see what amount of multipath the MCT2100 was able to handle, under both best case and worst case scenarios. Mr. Eory answered:
"Static echoes with amplitudes up to 0.1 dB below the desired signal have been tested and show several dB's of SNR margin over threshold of visibility (TOV), which is approximately 15.5 dB. The precise delay or phase of the echo (which creates spectral notches over 20 dB) is not an issue unless it is carefully arranged to create a deep notch at the VSB pilot carrier frequency. In the event that such a static echo occurs in the real world, it would require a one time antenna re-orientation to get the deep notch away from the pilot."
What does this mean in a real world situation, like the Sinclair demonstrations? Eory answered:
"Dynamic echo ensembles with phase changes of 10 Hz have been tested using a lab emulation of the Sinclair 'Lombard Street' measurements. After the success of that test, the largest echo (measured at -8 dB by Sinclair/Oak Technology) was increased to -6 dB, still at 10 Hz phase variation. SNR margin above TOV was maintained for this 'Lombard Street Plus' ensemble. In this dynamic multipath test, 15 dB notches ripple through the spectrum, so we also see the pilot amplitude changing by 15 dB. This is not an issue for pilot tracking, since the pilot is visible with some regularity and no antenna adjustment is required.

"A lab emulation of the Sinclair 'Harbor Apartment' ensemble was tested <-4 dB largest echo and several smaller echoes out to 23 microseconds). 10 Hz phase changes were applied and again, several dB's of margin over TOV were measured."

These results indicate that with the proper demodulator technology, 8-VSB should perform as well as COFDM when using indoor antennas in an environment with significant amounts of multipath. Eory cautioned, however, that multipath performance is not as simple as "X dB echo" or "Y Hz dynamic phase changes". He said "The performance is a complex function of the entire echo ensemble and we are still characterizing this performance space of echo amplitudes and dynamic phase changes."

Motorola said samples of the chip will be provided to major OEMs in September. Production of the MCT2100 will begin in the fourth quarter of this year and substantial volumes should be available in early 2000. In high volumes, the price is quoted at under 20 dollars. Eory said TV sets containing the chip should reach the market by second quarter 2000, but products such as set-top boxes or receiver cards for PC using the chip could appear as early as first quarter 2000.

Another chip manufacturer licensing the Sarnoff 8-VSB technology is NxtWave Communications in Irvine, California. The same day Motorola announced the improvements in the MCT2100, Nxtwave had a notice on their web site urging readers to check back August 24th for an important announcement. That announcement was NxtWave Communications - Breakthrough Receiver Chip Makes Mobile and Indoor Reception of Broadcast Digital Television Possible. The press release described the NXT2000 multimode VSB/QAM receiver chip, Matt Miller, president and CEO of NxtWave Communications, said "With the NXT2000 we?ve cracked the code for indoor and mobile reception, shown that VSB is a robust and commercially viable standard, and paved the way for mass market deployment of error-free digital TV." The NXT2000 is able to acquire an 8-VSB DTV signal in 50 milliseconds or less, allowing channel surfing, and includes a built in signal quality indicator to make it easier to align receive antennas. The advanced equalizer in the NXT2000 is able to handle multipath with delays from minus 4.5 microseconds to plus 44.5 microseconds.

The Technology Page on the NxtWave web site says "We have made algorithmic breakthroughs in blind adaptive equalization which enable consumers to receive video and data in an entirely new and innovative way. NxtWave's exclusive technology gives our manufacturing customers (and ultimately consumers) significant cost and performance advantages." NxtWave said its chip uses "Blind Adaptive Equalization" to enable the chip to work in difficult indoor and mobile reception environments. A NXT2000 Datasheet is available as an Adobe Acrobat PDF file. More specific details on the NXT2000 should be available here once RF Current is able to contact NxtWave.

If the Motorola and NxtWave chips peform in the real world, the ATSC 8-VSB standard will be off the ropes and back in the ring, in the nick of time. Given the vast difference in performance between what these chips promise and what current generation ATSC receivers offer, it appears the early adopters of terrestrial DTV technology will want to upgrade, regardless of whether the 8-VSB standard continues or broadcasting moves to COFDM. We will all be watching for the first real world tests of these new devices.

DTV - Study Outlines ATSC 8-VSB Field Tests, Lists Target DTV Receiver Performance Standards (Aug. 20)
ATSC placed a 24-page technical paper Preliminary DTV Field Test Results and Their Effects on VSB Receiver Design on its web site this week. The paper, written by Gary Sgrignoli at Zenith, is published in the August 1999 IEEE Transactions on Consumer Electronics. The paper summarizes the results of 8-VSB reception tests at 2,682 outdoor sites and 242 indoor sites. The paper includes background information on the VSB digital transmission system and outlines how the field tests were conducted. The methodology used for indoor testing, which in many ways is more complex, is also discussed.

The paper includes detailed test results from the Charlotte ACATS tests as well as tests at Raleigh NC (WRAL), Chicago IL (WGN), San Jose CA (KICU), New York (WCBS), Washington DC (WHD and WETA) and Seattle WA (KOMO and KING). The results are interesting. The outdoor tests included some obstructed sites. One way to see how the 8-VSB system performed is to compare the number of sites with having service with the number of sites have greater than the minimum required field strength. These numbers were within five percent except at WGN Chicago, WCBS New York, WHD Washington DC and both KOMO and KING in Seattle, WA. The paper summarizes the results at the various sites. At KICU, tests were done comparing circular polarization with horizontal only polarization. No improvement was found when horizontal receive antennas were used. WCBS had a total service availability of 80 percent. This is not as bad as it sounds, since 25 percent of the sites were in the "concrete canyons" of New York and 25.3 percent of the sites were obstructed. Obstructions were a problem in Seattle, where around 40 percent of the test sites were obstructed. Tests also uncovered sites with strong signals where no reception was possible due to strong, sometimes dynamic, multipath. This was similar to what was found in Washington DC

Indoor reception results are included for the ACATS Charlotte NC tests and tests in Washington DC, Raleigh and Chicago. The results varied widely, from raw service availability less than 41 percent in Washington DC to over 80 percent in Raleigh and 100 percent in Chicago. The wide difference in transmitter antenna height above average terrain, from less than 600 feet in Washington DC to over 1200 feet in Chicago and Raleigh may explain some of the variation, although sufficient signal level was present at more than 80 percent of the locations for all signals except WETA in Washington DC.

Table 9, Target DTV Receiver Performance Parameters, should attract interest from broadcasters and set manufacturers alike. It may help form the basis of either a voluntary or mandated 8-VSB receiver performance standard. The paper notes that these field tests were done using either the Grand Alliance prototype receiver or a second generation IC based receiver. The performance of these receivers may not be the same as that of consumer receivers. The paper describes key DTV receiver subsystem parameters, including antenna/downlead, DTV tuner noise figure, overload capability, phase noise, AGC, equalization/ghost canceling and synchronization.

The last three parameters are particularly important for DTV reception with indoor antennas. The paper reports that "Field tests have shown a need for faster AGC capability with 5-10 dB signal fades occurring more often that some would have expected. Since airplane flutter and large trucks may cause fast signal fluctuations that must be tracked by the AGC, the speed of the gain control circuit should be faster than 75 Hz.". With regard to the equalization/ghost canceling, the paper says:
"Certainly, equalizers must deal with large ghosts in excess of 50%. Complex, dynamic multipath is the most serious challenge to the DTV receiver performance, especially on UHF frequencies. Good static performance on strong ghosts (>50%) can be achieved by using the known VSB binary frame sync as a training signal. However, dynamic conditions are common in the field, requiring the use of data-directed methods during these conditions. Since data-directed equalization uses sliced data to determine its tap coefficients, white noise threshold can be affected by as much as a couple of dB when using conventional methods. In order to have good white noise performance, the equalizer could use the frame sync in static multipath cases and then switch to the data-directed in cases where the multipath is dynamic (beyond a certain speed). The switch must be accurate and fast to minimize burst error effects. Newer techniques are being developed that will allow data-directed equalization to reach almost the same level of performance as using the frame sync as a training signal, thereby removing the need for switching between frame-sync and data-directed modes."
Receiver synchronization loops should lock down to a signal-to-noise ratio of 0 dB. Gary Sgrignoli, the paper's author, suggests "a 'tuning meter' available to the viewer for antenna adjustment is desired."

New chip designs appear to be able meet the target multipath D/U parameters of less than 4 dB for quasi-static multipath, less than 7 dB for dynamic multipath (1 microsecond at less than 5 Hz rate) and less than 10 dB for dynamic multipath at a 10 Hz rate. The paper ends with the comment: "Professional VSB demodulators continue to provide a moving target of performance specifications for DTV receivers, providing information to consumer receiver designers on possible system and circuit improvements. DTV receiver implementation will continue to improve as second and third generation units become available on the market at the turn of the millenium."

DTV - RCA Thomson Introduces HDTV/DTV Products (Aug. 19)
Thomson Consumer Electronics announced it was introducing a new line of RCA and PROSCAN brand digital TV products "that deliver lifelike picture performance and theatre-quality sound at a fraction of the cost of high-definition digital TV sets." Products include digital high resolution monitors, with 52 and 62 inch rear projection digital monitors being added to the company's existing 32 and 35 inch direct view monitors. These monitors have a conventional 4:3 aspect ratio. Two new set-top receivers were mentioned in the announcement - the long awaited RCA DTC100 and the PROSCAN PSHD105, both with a suggested retail price under 650 US dollars. The receivers can be connected to a Thomson-brand digital high-resolution monitor through an RGB component S-VGA interface. Refer to the Thomson press release Thomson to Deliver Low-Cost Digital Television with Wide Variety of Digital Solutions for more information.

Thomson also announced true HDTV receivers in the 8000 dollar price range. The Thomson Press Release - America's Most Advanced Digital Television Receivers Ship to Retailers in New York, California and Indiana said the new HDTV models "offer robust reception", but did not elaborate.

DIGITAL TELEVISION STATION APPLICATIONS - See ap990818.txt for more information
Call (DT) Ch. Licensee Location ERP (kW) HAAT (m) Antenna
KUTP 26 United Television Phoenix AZ 67 517 Dielectric TFU-20DSC-R CT150


DIGITAL TELEVISION STATION APPLICATIONS - See ap990817.txt for more information
Call (DT) Ch. Licensee Location ERP (kW) HAAT (m) Antenna
WHO 19 The New York Times Des Moines IA 550 609 Dielectric TFU-30GTH-R04
WEAU 39 WEAU Licensee Eau Claire WI 988.4 583.2 Dielectric TFU-30DSC-R03


OTHER Items of Interest

Next >>>> August 30 - Issue 180


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Last modified August 25, 1999 by Doug Lung dlung@transmitter.com
Copyright 1999 H. Douglas Lung