The road to MDTV

The NAB 2011 show is history. Visitors and exhibitors are home or headed home, ready to share stories of this year’s event with peers and bosses. If you were fortunate enough to visit the show, welcome home. Hopefully, you got more out of the event than you expected and your experience was safe and successful. Clearly, NAB 2011 provided much to discuss and explore in future “Transition to Digital” newsletters for some time to come.

Before delving into technical issues, let’s start with a simple question. Why is the industry so excited about mobile DTV, which is also known as ATSC M/H, A/153, and most recently MDTV? Of course, the answer is money. Everyone wants a new revenue stream to make more money, and many see mobile DTV as a fresh new opportunity to do just that. Besides, we all have new DTV transmitters and HDTV equipment to pay for with revenue streams that, except for the Internet, haven’t changed much for decades. It’s not just broadcasters that sense money in mobile DTV business, it’s also content providers, consumer electronics manufacturers and, if all goes as planned and hoped, advertisers will love it.

Halfway there
A few years ago, the local CBS affiliate I was with hired a high-profile group of branding consultants to work with department heads to identify and establish a station brand. Without revealing the many details the station’s owners paid a small fortune for us to learn, it all boiled down to this: Who are we, and what do viewers in our market expect from us? We began by identifying what made us different from the other 499 local and national channels on cable and satellite, and what we do better than they do. Fast-forward past several months of focus groups, internal research and day-long meetings, and the answer became glaringly apparent. It was local news.

Many entities from Hollywood to Hoboken are eager to produce mobile DTV content, but local news content is already being produced in stations, and we broadcasters know that’s what the local audience wants. In terms of the physical requirements for the production of mobile DTV content, about all that local news broadcasters need to do is some repurposing and more live updates.

Unfortunately, broadcasters aren’t the only ones who have recognized that local markets want local news and that mobile electronics are wildly popular. Fortunately, broadcasters have the biggest and most powerful wireless digital pipeline. At least that’s how it is for now, but that’s another story for a future tutorial.

Not your father’s mobile TV
Mobile DTV is new, but mobile TV is not. Sony sold the first Watchman in 1982, but the first truly mobile TV was the Sinclair Microvision Pocket TV Receiver, introduced in 1966. Sony’s Watchman, incidentally, was dropped in 2000. As analog TV went away, so did handheld pocket TVs. Aside from the obvious, the difference between the analog pocket TVs of yesteryear and the new mobile DTV technology is programming. Your Watchman received the same programming on the same channel as your TV at home. Mobile DTVs can receive a dedicated digital subchannel specifically designed and programmed for a mobile audience.

With the advent of wireless digital RF transmission (DTV, cellular and WiMax), nearly all the technology is in place for the delivery of mobile content. LCD-type screens and a wide array of portable and mobile digital devices with video screens — such as smart phones, notebooks, navigation devices, the Amazon Kindle and similar products — provide the display technology for mobile DTV viewing and are being rapidly adopted by a growing number of consumers.

Thanks to the whirlwind growth of the handheld and mobile display market, the economy of scale for displays has already kicked in. The only missing mobile DTV element at the consumer level yet to achieve the economy of scale is the ATSC receiver. You can safely bet the next generation of handheld digital devices will integrate ATSC receivers. Samsung and LG Electronics are already designing and making mobile DTV receiver/demodulator chips. As of today, mobile DTV receivers are more in the prototype, one-off or modular phase, but it won’t take long for convenient, self-contained products to flood the market, perhaps as early as the 2011 holiday season.

Local news stations are producing local news content 24/7. Digital RF transmission systems are in place, display technology is widespread and inexpensive, and receivers are on the way. There are only two more steps toward mobile DTV’s success. The biggest and final step is advertising, and we’ll let the sales department, agencies and advertisers deal with that. One interesting fact to bear in mind about mobile DTV is that it doesn’t have to be a free service. What station manager or owner hasn’t dreamed of charging viewers subscriptions like cable and satellite providers do? Mobile DTV allows it.

The last step we engineers need to be concerned about regarding producing a product the sales department can sell is upgrading the station, transmitter plant and antenna to meet the special requirements of mobile DTV.
Examining the details of the technology it takes for a station to make DTV work in the real world was the topic of many formal and informal meetings and discussions at NAB 2011. If there is a common denominator, it is that mobile DTV still has a few wrinkles to iron out.

Bits and pieces
The basic equipment stations need to begin broadcasting mobile DTV services include an audio and video program encoder, an IP encapsulator to encapsulate Internet data in the ATSC stream, a multiplexer to combine the conventional ATSC program stream and the mobile DTV stream, and an electronic service guide (ESG) server. While DTV transmission systems are mobile DTV-ready, ATSC exciters must be replaced or enabled for mobile DTV. Sometimes the procedure can be as simple as a software upgrade.

Mobile DTV transmission can require less than 1MB/s of the 19.4MB/s ATSC 8VSB stream, so it is highly likely your station has the bandwidth to carry the service. The actual bandwidth allocated to mobile DTV within ATSC standards can be from zero to about 14Mb/s. In that broad range, mobile DTV can be scaled to provide myriad services beyond a single A/V presentation.

Each facility and transmitter plant is different. Check with the manufacturers of your transmitter, STL and traffic software system (for the electronic service guide) for compatibility and necessary upgrades.

One other element that appears to be critical to mobile DTV success is the DTV transmission antenna’s propagation characteristics. Because viewers of mobile DTV are likely to be in motion, polarization and robustness of the ATSC RF signal becomes more critical. When DTV signals bounce off and around metallic structures such as buildings, bridges and water towers, the polarization tends to rotate, which can cross-polarize the signals at the receiver. Horizontally polarized transmission seems to cause the most problems for mobile DTV reception. Circular polarization appears to work best, although more work and experimentation is still being done to determine more solutions and recommendations on this issue.

In addition, mobile DTV viewers are likely to be in locations not necessarily highly populated with fixed DTV receivers. In these locations, such as downtown or in shopping malls, antenna characteristics such as gain and beam tilt become more critical. In the most generic terms, less gain and a little beam tilt may improve mobile coverage, but this can vary greatly by market and local topography.

Although mobile DTV technology appears to be slightly ahead of its business models, it’s still a work in progress, and it looks like there could be a few bumps in the visible road ahead for both. We engineers will leave the business models to the brain trusts, but like any new broadcast technology, mobile DTV will require our special attention, experimentation and patience as products and content develop and markets expand. Ultimately, broadcast engineers will make it work. Isn’t that what broadcast engineering is all about?