Electronic addictions abound, due mainly to the surging popularity of gadgets like MP3 players and video games. In the face of this electronics mania, television remains a leading pastime. Even average viewers spend several hours a day watching the tube. But the type of viewing is changing. Instead of sitting in front of the latest LCD or plasma screen, viewers are on the go with their portable devices. New standards have been established, services are available, and hit shows soon will be arriving in the palm of your hand.
Most mobile TV will reside in cell phones. In fact, a high percentage of the more than a billion new phones sold per year will have mobile TV. Other formats will include embedded TV receivers in laptops and netbooks or USB dongles and mini-cards. Some devices will be dedicated to mobile TV. It could even show up in personal navigation devices and in-vehicle installations like current backseat DVD players. Some of these devices are available now in various formats and standards. But beginning in 2010, a parade of new products is expected to arrive.
THE SMALL SCREEN
Mobile TV screens are mostly LCDs, but we’ve seen a gradual adoption of newer organic LED (OLED) screens. Sizes range from a little over 2 in. to about 3.5 in. in cell phones with a variety of different formats (Table 1). The width measurement indicates the number of pixels per horizontal scan line, and the height measurement is the number of horizontal scan lines. Other formats are available as well.
Another related issue is frame rate, which is the total number of completely scanned frames or pictures that occur per second (fps). Movies are commonly 24 fps, while most fixed TV is 30 fps. Slower rates produce an annoying flicker, creating a jerky and unnatural picture. Mobile TV rates tend to be slower because faster rates severely impact bandwidth needs.
The minimum acceptable rate is about 15 fps, but you may see some mobile TV at 10 or 12 fps, while 15 to 20 fps is far better. To see how this affects the streaming of video to the screen, assume a QVGA screen with 320 × 240 = 76,800 pixels. Using 24-bit color per pixel and a 15-fps rate, the bit stream rate is:
76,800 × 24 × 15 = 27,648,000 bits/s
This will require a bandwidth of about 28 MHz minimum using basic binary phase-shift-keying (BPSK) modulation, which is impractical. That’s why video compression is employed.
Standard digital TV almost universally uses MPEG2 compression. Mobile TV, on the other hand, takes advantage of MPEG4 and similar H.264 compression methods. Compression ratios greater than 100 are possible. Typical compressed video data-stream rates are usually in the 128- to 768-kbit/s range. Commonly available cellular bandwidths permit 256- to 384- kbit/s rates for reasonable resolution and frame rate.
VIDEO IN A CELL PHONE
There are five basic ways to get video into a cell phone or other mobile device.
- Unicast: Video brought to your phone over the cellular network on a one-to-one basis
- Multicast: Using the cellular network to deliver video to multiple users simultaneously
- Over-the-air (OTA): Broadcast video wirelessly over a separate spectrum
- OTA download: Video downloaded wirelessly for storage and viewing later
- Offline download: Getting the video from the Internet via a PC and stored in the device for viewing at another time
The two most common forms are unicast and OTA broadcast.
Unicast delivers video over the existing cellular network, but at the expense of voice capacity. A common 3G basestation can typically handle an average of about 200 voice calls simultaneously. One lowresolution video stream (128 kbits/s) is the equivalent of about 10 calls, while higher resolution at 384 kbits/s would use as much bandwidth for 30 calls. So video very quickly consumes a basestation’s capacity, though it can be manageable if the resolution is low and video segments are short.
Increased-capacity basestations using 3.5G to 3.75G technology like HSPA help the situation, but they don’t completely solve the problem. Luckily, video isn’t widely used now. If every subscriber jumped on YouTube at the same time, the network would collapse and no voice calls would be possible. Clever management is needed to maintain some balance between voice and video.
Don’t forget that a significant and growing segment of that capacity goes to messaging and e-mail, not to mention Internet browsing. Juggling that combination is a major challenge. And now, with the Federal Communications Commission (FCC) on the verge of mandating net neutrality, carriers will not be able to restrict, subdivide, or otherwise manage their network capacity in a way that permits them to make even a modest profit. Politics and a lack of common sense rule these days.
The bottom line is that video uses too much of the available capacity and is far less profitable than any other service. Messaging is the most profitable use of the network, with voice second. Video is far less profitable unless the network operator charges as necessary to make it possible to provide that service. But in the end, there is still only so much capacity in a basestation.
Forthcoming Long-Term Evolution (LTE) basestations will be far more able to handle video, but they too have an upper limit. Analysis of the profitability issues and capacity, as well as capital expenditures and operating expenditures, have led carriers to minimize video offerings and price them as necessary to manage their capabilities. That’s opened up an opportunity for over-the air TV.
Over-the-air TV is a broadcast method that’s completely separate from the cellular network. Cellular carriers aren’t typically involved except in how they select the cell phones they sell with OTA TV capability.
In OTA TV, broadcast stations in each city or metro area transmit the video to separate TV receivers built into cell phones or other devices. OTA TV is like standard broadcast TV but designed to be more robust under mobile conditions. The broadcast stations transmit at very high power levels, so they cover a very large geographic area.
OTA TV comes in two versions—free and fee-based. Both are implemented around the world in some form, and more models are on the way. Japan and Korea lead the world in mobile handset TV adoption, followed by Europe. The U.S. is well behind but catching up with two standards: FLO TV, which is a fee-based service, and the soon-to-arrive simulcast of currently available ATSC digital TV.