Mobile TV Using Existing ATSC Technology
A paper from Triveni, “TV Broadcaster Connecting with the Mobile User,” presented by Richard Chernock at NAB2007 offers an easy way to implement a form of mobile DTV.
Triveni’s “Skyscraper” product was introduced several years ago and provides a way to transmit data in the ATSC signal. The data is received on specialized ATSC receivers and a computer running Triveni software. Triveni tested the system in a vehicle in New York City to see how well it would work in a mobile environment. In his presentation at NAB, Chernock said that a significant number of the files were received, although data on the testing wasn’t included in the paper printed in the 2007 NAB Broadcast Engineering Conference Proceedings.
The difference between this mobile connection and the one being developed as the ATSC M/H standard is that it isn’t real time. Triveni’s paper explains that real-time reception of video programming on the road is needed primarily for passengers in the car. Most driving is done alone, which diminishes the need for high-bandwidth real-time content.
| This screen shot was taken while viewing KCET-HD off-air in Terminal 2 at LAX.|
Although conventional ATSC reception may not work while the car is in motion or parked in an underground parking lot, during stops while driving or while parked on the street it often does work, especially with fifth generation demodulator chips. The Triveni paper lists several applications suitable for stored content. Updating traffic information requires only small files that can be updated every 5 to 10 minutes. Weather forecasts and localized “point of interest” information, with more graphics, take file sizes up to 500 KB that would be transmitted as less frequent intervals. Larger files, transmitted less frequently, could include audio podcasts for the driver and video programs for passengers.
Triveni’s Skyscraper Web page, (www.trivenidigital.com/products/skyscraper.asp
) shows the technology available now. Triveni software and a supported receiver are required, limiting widespread use of the technology.
I see one way to increase interest in ATSC file transmission. Rod Hewitt’s TSReader, a transport stream analyzer, decoder, recorder and stream manipulator for MPEG-2 systems, can receive the data streams using a wide variety of ATSC tuners. Combine the data routines in TSReader with Triveni software to manage the “receive, store and assemble” functions needed to handle intermittent reception on most off-the-shelf USB tuners. Then make it available for download on the Web at a reasonable cost, or even for free in an advertiser-supported environment, and thanks to inexpensive USB tuners from AutumnWave, DVICO, Hauppauge, Pinnacle and others, there would be an instant audience.
ATSC standards such A/90, A/95 and A/97 describe how to transmit data and software updates over the ATSC stream, (see www.atsc.org/standards.html
for copies of these standards and associated documents). Triveni isn’t the only company able to implement the standards. As I’ll describe later, an increasing number of USB ATSC chip sets now work under Linux, which could provide an inexpensive way to make this technology available in a wide variety of products.ATSC MOBILE/HAND-HELD STANDARD
My last RF Technology column described MPH and A-VSB demos at NAB. In June, 10 companies submitted proposals to ATSC. While some of these only considered data formats and content management, submissions by LG, Samsung, and Micronas involve transmission. The LG and Harris MPH proposal and the Samsung and Rohde and Schwarz A-VSB proposal have been widely discussed.
I’ve seen no public details about the Micronas submission. Rich Citta, the chief scientist at Micronas, developed high performance 8-VSB receiver technology at Linx before it was acquired by Micronas. Three years ago at NAB, Citta reported on the successful testing of a single-carrier mobile DTV transmission system. That system used a 4-VSB signal with half-rate coding. It will be interesting to see the technical details of the Micronas proposal. Detailed technical proposals were due at ATSC July 6.
One of many items ATSC will have to consider in evaluating the proposals is their compatibility with the existing ATSC transmission standard. A criticism of Samsung and Rohde and Schwarz’s A-VSB proposal is that it modifies the adaptation fields in the ATSC standard, which could preclude use of these fields for future ATSC enhancements on systems not using A-VSB.
LG and Harris said their MPH proposal does not change the adaptation headers or PSIP and does not disturb the error detection/correction of legacy DTV receivers. When this was written LG and Harris had released few technical details to the public on how the MPH system works, but their presentation at the NAB Mobile TV session emphasized compatibility with existing ATSC receivers. New service data is processed at the packet level and concatenated processing is used at the trellis level. While earlier statements indicated the system would only work with specialized Harris STL systems, the NAB presentation said no changes or additions are required to the STL.
In the NAB presentation, LG showed how MPH data is interleaved into Reed-Solomon frames along with cross-interleaved error-correction bytes. Data is sent in bursts interleaved over one or more frames. This allows the system to handle error bursts up to 15 ms or longer if inter-frame interleaving is used. The MPH proposal also includes added training signals, but these were not described at NAB.
Look for more details here on the proposed ATSC M/H formats as more information is made public.UPDATE ON PORTABLE ATSC RECEIVERS
In my recent reports on USB ATSC receivers, I noted that I hadn’t been able to get any of them to fully function under Linux. I’m pleased to report that I now have the DVICO FusionHDTV5 USB Gold tuner successfully displaying ATSC and open cable QAM on my Kaffeine media player with the Xine engine and the HVR-950 displaying ATSC and analog TV. I noticed on AVS Forum there has been some progress made in getting the AutumnWave OnAir Creator to work under Linux, but firmware remains an issue with the OnAir GT.
| This screen shows the signal strength and SNR indicator as well as the channel list in the Kaffeine |
Hauppauge’s HVR-950 USB ATSC tuner uses hardware similar to that in the Pinnacle HDTV Stick Pro, which I’ve described before. I found the hardware performance matched that of the Pinnacle HDTV Pro Stick. Ron Hewitt’s TSReader includes a driver for the HVR-950 and it works perfectly with it. For what it’s worth, TSReader will display the SNR from the HVR-950 to three decimal places! The HVR-950 has become my main over-the-air and analog cable USB tuner because it works so well with Kaffeine for viewing off-air ATSC DTV and with the TVTime program for viewing off-air or cable analog TV. Unfortunately, the HVR-950 doesn’t demodulate cable QAM signals and the FusionHDTV5 USB Gold tuner won’t display analog channels under Linux, so I have both receivers on my desk.
It is often easier to install devices in Linux than in Windows because the device drivers are included as “modules” in the Linux kernel and loaded as needed. However, in some cases, the kernel, the heart of the Linux system, may need to be updated to support DTV reception. I’ve had good luck with 2.6.21 and 2.6.22. I use Mepis (www.mepis.org
), which is based on the free Ubuntu Linux distribution and is easy to keep up-to-date.
Install DVB/ATSC support as modules. Download “v4l-experimental” and install it in the new kernel. You will need to compile the software, but for most systems under Linux that’s as easy as typing “make all” and “make install” in the v4l-experimental directory. You need to download the firmware for the FusionHDTV5, Pinnacle HD Pro Stick or the HVR-950 from the Internet. See the links for more information on installing v4l-experimental and firmware.
Scanning channels and building a channel list that Kaffeine or TVTime can use to tune the channels isn’t as easy under Linux as it is with the manufacturers’ programs under Windows. I won’t go into the details here, but you will need to run “scan” to scan ATSC channels and generate a list of local stations and then use “atsc-converter” to convert it to a file in Kaffeine format. Just type “scan” at a shell prompt for instructions. I do a scan in each city I visit and save the list under a file name with the city as an extension. This makes it easy to get up and running as I move around the country. The scan program requires a list of frequencies to search. For the U.S., cable, NTSC and ATSC frequency files are usually in /usr/share/dvb/atsc.
All of this is more difficult to describe than to do. The Linus TV Web site, (www.linuxtv.org
) is a good place to start. The Hauppauge and Pinnacle USB stick tuners, as well as some others, are covered in the EM2880 DevWiki at mcentral.de/wiki/index.php/Em2880
. “Luna6” has detailed instructions and tips for the HVR-950 at http://lunapark6.com/usb-hdtv-tuner-stick-for-windows-linux-hauppauge-wintv-hvr-950.html
. Also see www.penlug.org/twiki/bin/view/Main/DigitalTelevisionDVB
. While it says “DVB,” it covers ATSC reception on the pcHDTV HD3000. Drop me an e-mail if you run into problems. Getting one of these receivers working under Linux is a great way to learn how the chips inside the receivers function.
I should mention that AutumnWave responded to my request in a previous column for a larger signal strength display to make it easier to align antennas when using their tuners. The AutumnWave antenna aiming software even gives an aural indication of signal quality so you don’t even have to look at the laptop or PC screen to peak the antenna!
Comments and questions are welcome. E-mail me at firstname.lastname@example.org