At NAB2007, Samsung demonstrated the Advanced-VSB (A-VSB) mobile TV delivery technology it has co-developed with Rohde & Schwarz, showing that it is possible for a broadcaster to transmit a mobile TV service with a .5Mb/s payload using just more than 2Mb/s of his 19.4Mb/s digital channel allocation. A-VSB is currently under consideration as an open standard for the delivery of video and audio to mobile devices.
As part of a series of demonstrations of A-VSB conducted throughout the duration of the show, KVMY, a Las Vegas-area Sinclair Broadcast Group station, transmitted two turbo-coded channel streams of programming with a Supplementary Reference Sequence (SRS) set to 10B to mobile receivers operating on a chartered bus being driven around the area of the Las Vegas Convention Center. The total useable payload of audio and video programming transmitted was 1Mb/s at half-rate turbo code (with a 0.19Mb/s overhead, for a total of 2.19Mb/s of channel capacity used). The station also transmitted programming created by Samsung specifically for the demonstration, which had a total payload of 0.5Mb/s at quarter-rate turbo code. The overhead was 0.19Mb/s, making the total channel capacity used also 2.19Mb/s. Because the 10B setting of the SRS uses 1.24Mb/s, the total capacity consumed by A-VSB during the demo was 5.62Mb/s.
Samsung also highlighted the A-VSB's Single Frequency Network (SFN) tool, which provides uniform signal strength through a service area and helps lessen echoes and other types of signal interference. The programming transmitted to the bus was retransmitted at a second frequency on a separate low-power SFN set up with the support of ION Media Networks, operating under an experimental license. The SFN had three transmitter sites, one on the Stratosphere tower of the Las Vegas strip, another on the Paris building on the south end and one inside the Las Vegas Convention Center at the ATSC's Digital TV Hot Spot.
While it is not necessary for a broadcaster to set up separate towers for an SFN, additional towers can help fill in any coverage gaps throughout a service area and equalize signal strength. For the demonstration, Samsung retransmitted the programming at a separate frequency to show the difference between an SFN-enabled picture and one that does not use SFN. In practice, a broadcaster could transmit the SFN on the same frequency as his main DTV channel.
In discussions with the press during and after the demonstration, Samsung executives noted that the 10B SRS setting was not the only possible setting for A-VSB. Depending on the number of mobile channel streams and level of performance a broadcaster wants, it is possible to set the SRS lower or higher, with the lowest setting being zero and the highest, 26B. Similarly, with A-VSB, a broadcaster can choose whatever number of turbo streams he desires.
According to John Godfrey, VP of government and public affairs for Samsung Information Systems America, the main goal of the demonstration was to show that broadcasters could deliver a high-quality mobile TV service without sacrificing a large portion of their allocated digital bandwidth. "You can set these things down at their minimum level and still have a flawless mobile service with a single stream of programming for a small video screen — about 5in or less — with plenty of bandwidth left for HD in the main stream."
Samsung has plans to make A-VSB evaluation kits (including prototype transmission and reception equipment) available on a limited basis to broadcasters and other partner companies in the third quarter of 2007. The company demonstrated an A-VSB-compatible prototype device at CES in January, an updated version of which it used as part of the NAB demonstration. That device incorporates a CMOS broadband RF integrated chip from MaxLinear, the MxL5005S, which provides a silicon-based alternative to large, discrete can tuners.
Harris and LG Electronics conducted a similar demonstration at NAB2007 of a competing mobile TV delivery technology, the Mobile-Pedestrian-Handheld (MPH) system. For this, a mobile one-channel stream was sent at about 560kb/s, with a 2.2Mb/s (half-rate) payload, and another at 300kb/s, with a 2.2Mb/s (quarter-rate) payload, to a bus being driven around the Las Vegas Convention Center.
For more information, visit www.samsung.com.
