Last week, the first on-the-road public demonstration of Advanced-VSB (A-VSB) left no doubt in this observer’s mind (and eyes) that the proposed ATSC transmission mode can provide broadcasters with DTV reception in moving vehicles at any legal speed.

Aldo Cugnini
Analyst

Riding in a specially equipped invitation-only demonstrator bus at the 2007 Consumer Electronics Show, a live demonstration showed rock-solid pictures even when our vehicle hit Las Vegas highway speeds. The technology, developed by Samsung and Rohde & Schwarz, is now being standardized by ATSC, with field testing under way and a completed open standard targeted for the first half of 2007.

Building on the current ATSC transmission standard to enhance DTV receivers’ ability to receive the main TV transport stream in dynamic environments, A-VSB enables broadcasters to include multiple streams with additional error correction and time diversity encoding for enhanced reception. In addition, A-VSB facilitates synchronization of multiple transmission towers, which should improve coverage with higher uniform signal strength throughout a service area, even in locations that normally would be shielded by obstacles such as hills or buildings.

The demonstration used QVGA video, coded using H.264 and transmitted at 600 kb/s. It was carried on Sinclair Broadcast Group’s KVMY (Henderson) on UHF channel 22. Side-by-side displays of conventional (VSB) and A-VSB video provided ample evidence of the viability of the new service. Sinclair’s Mark Aitken and Harvey Arnold came along for the ride, together with our Samsung host John Godfrey and other guests.

Aitken explained that with ATSC transmission apparently limited to fixed or low-speed portable applications, most broadcasters had given up on the idea of DTV reception in high-speed vehicles. With A-VSB however, such a limitation is now lifted, with simulations showing that artifact-free reception is possible at speeds of up to 170 mph.

Adding further drama to the demo, our hosts handed out a number of small handheld TVs - modified T-DMB units, purportedly with actual A-VSB silicon - tuned to the same DTV program. Despite highway speeds, and my attempts at disturbing the reception, the pictures were again unperturbed. Only when the two-rod antennae were completely collapsed and folded onto the unit was there an interruption of service.

The proposal, apparently a revision of one submitted to ATSC in 2001, incorporates three new elements: a Supplementary Reference Signal (SRS), a Scalable Turbo Stream (STS), and support for Single Frequency Networks (SFN). A-VSB receivers utilize the SRS in order to remain "locked in" to the transmission. This helps maintain reception of the main stream and any turbo stream(s) even with rapidly changing multi-path interference, such as when the signal is reflected from moving objects near the receiver or when the receiver itself is moving.

The SRS adds an additional equalizer training sequence to the Transport Stream Adaptation Field. (For more technical details, see next month’s Projection Monthly with Flat Panel Coverage.) A receiver equipped with this new equalizer can track rapid multipath fading, and thus supports mobile reception. SRS can be used alone, without the STS, offering a slight improvement in portable (stationary - not true mobile) service.

The last option - SFN - is possible by adding a new element that synchronizes the transport frame sequences to a GPS reference. With one, two, or all three options, A-VSB should be backward compatible with legacy digital TV receivers, which ignore the added information in the signal while continuing to receive the main TV stream (e.g., high definition TV programming.)

Samsung has not yet decided whether they will charge a license fee for their A-VSB Intellectual Property, but promises in any event to abide by the ATSC "RAND" (reasonable and non-discriminatory terms) policy.

The demo appears to bear out what Samsung research and field tests have shown - that A-VSB turbo streams are receivable even when the receiver is moving rapidly in a typical urban environment. Currently on a fast track, an official ATSC Standard could be released as early as this summer. Further work on a new STS System Information (SI) protocol is expected to take another year. In addition, because of the bitrate tradeoffs, ATSC plans to look at optimizing bit allocation for the new service - a challenge for sure, in that quality and service will certainly compete both technically and financially.

Samsung expects that with additional work on power management, plus miniaturization of antennas and tuners, A-VSB will enable both portable and mobile digital TV reception direct from local TV stations. There are already several service providers experimenting with mobile video - essentially to mobile telephone handsets. Given the different business model for broadcast TV - and different service providers - it will be interesting to see how a service using A-VSB competes with other emerging services based on MHP or MediaFlo.