How TV Phones Work


Nokia N92 phone. 
Nokia N92 phone. 
Photo courtesy © Nokia, 2005

­Widespread mobile television has been a long time coming. TV-enabled cell phones have been a­vailable in Korea since 2002. In that first incarnation, the TV signals were transmitted over a standard cellular network, meaning per-minute watching fees and unbelievable phone bills. In 2003, Samsung and Vodafone introduced phones in Korea and Japan that received local analog TV broadcasts for free. But the video was choppy, and it drained the phone battery.

The real "mobile TV revolution" is only beginning, as telecom companies release high-quality, DTV-enabled phones and simultaneously rush to build the broadcast networks to deliver the corresponding content. In this article, we'll find out what types of mobile TV are in the works and take a look at some of the phones that receive the signals.

The basic idea of the TV phone is pretty simple: It's a cell phone that acts as a TV receiver. If you've read How Television Works, you know that TV signals are just radio signals. Cell phones pick up radio signals all the time -- it's what they do. In the case of TV phones, they have the ability to receive radio signals in the TV-allocated frequency bands in addition to the bands allocated for cell-phone voice data. For instance, a TV phone in the United States might tune in to the 2110-to-2170-MHz band for a conversation and the 54-to-60-MHz band to pick up TV channel 2.

Radio spectrum Radio spectrum
Radio spectrum

Just like your home TV, a TV phone has the equipment to extract the audio and video content from radio signals and process them to display a TV show on its screen.

The concept is not earth-shattering, but delivering TV signals within a mobile framework poses some challenges. For one thing, streaming video requires fast transmission speeds. Previous "2G" GSM networks provided data-delivery speeds of 10 to 14 kilobits per second (Kbps), and "2.5G" networks offered 30 to 100 Kbps. At 10 Kbps, a TV show is really a slide show; and at 100 Kbps, it's pretty choppy. There's also the bandwidth issue. Television data takes up a lot more space than voice data, and delivering live TV to thousands of cell phones simultaneously can slow a network to a crawl. Finally, receiving, processing and displaying video content requires battery power, and cell phones don't have much juice to spare.

­ But technology advances are beginning to make TV phones a viable luxury. Fast "3G" networks (which provide broadband Internet access to cell phones and other mobile devices) provide data-transfer rates of 144 Kbps to 2 megabits per second (Mbps). 3G multicasting technology saves bandwidth by allowing multiple subscribers to access a single broadcast stream (as opposed to unicasting, which is a one-to-one transmission). And companies are implementing power-saving transmission techniques like time slicing, which transmits data in spaced intervals so the receiver can turn off in between transmissions.

While you can subscribe to a TV service plan right now (such as MobiTV, Sprint TV or SmartVideo) if you have the right phone, the standards for mobile TV broadcast and delivery methods are still in their infancy. In the next section, we'll take a look at the primary methods of mobile TV distribution.

TV phones are the way of the future, but click here see how telephones have evolved over time.­

Mobile TV Broadcasts

There are a lot of broadcast and delivery methods in use or in development. You can broadcast live TV to cell phones via satellite, terrestrial towers or WiFi networks. Here's a look at the basic techniques involved in each approach.

WiFi/WiMAX

This broadcast method streams live TV signals via the Internet. A Web-enabled smartphone with data capabilities can pick up the stream from any WiFi hotspot or WiMAX coverage area.

Sling Media's Slingbox uses this approach with a slight twist. Instead of broadcasting the TV signals directly from the content provider, the Slingbox hardware "placeshifts" the TV signals delivered to your home TV, streaming them via your home Internet connection to a mobile receiver like a Web-enabled cell phone or laptop.

Terrestrial

Land-based broadcasting methods send out analog or digital TV signals over the air from terrestrial base stations. A phone with a TV antenna and an analog or digital TV tuner (receiver) can pick up the signals.

There are a bunch of mobile-TV versions that utilize land broadcast, including analog broadcast TV, digital broadcast TV and 3G-network broadcasting. Standards like T-DMB (Terrestrial Digital Multimedia Broadcast), MBMS (Multimedia Broadcast and Multicast Services), MediaFLO (a proprietary Qualcomm technology) and DVB-H all utilize aspects of 3G technology.

DVB-H, or Digital Video Broadcasting - Handheld, is an adaptation of the DVB-Terrestrial standard used to broadcast over-the-air DTV to homes in Europe. DVB-H uses orthogonal frequency division multiplexing (OFDM) to make efficient use of available bandwidth. OFDM lets providers transmit more than one signal in one bandwidth space and spread data streams over multiple channels. It may sound like a clutter of data, but the system modulates different signals at different frequencies so the receiver can figure out which it's supposed to listen to and which it should ignore and can put together related signals coming from different channels. In the DVB-H setup, a content provider sends live video and audio streams through an encoder (it's typically H.264 encoding for video and AAC for audio), and the encoder forwards them to a 3G streaming server. The server sends the data to multiple broadcast towers that deliver the content to the coverage areas. The system uses the previously mentioned time slicing technique to reduce power requirements. The typical maximum transfer rate for a DVB-H system is 15 Mbps.

Satellite

Some standards rely on satellite broadcasting to deliver live TV to cell phones. They can broadcast from satellite to phone, from satellite to base station to phone or use both methods simultaneously.

Two systems that employ this approach are MBSAT and S-DMB. In the S-DMB (Satellite Digital Multimedia Broadcasting) system, a content server sends the live TV feed through an encoder (typically MPEG-4 for video and AAC for audio) and transmits the data to an S-DMB satellite in the frequency range of 13.824 to 13.883 GHz. The geostationary satellite rebroadcasts the signals directly to terrestrial repeaters at 12.214 to 12.239 GHz and directly to cell phones on the S-band, 2.630 to 2.655 GHz. The terrestrial repeaters fill in the gaps where satellite signals get disrupted, like in a city surrounded by tall buildings or in the subway. The dual broadcasts are coordinated so that if a subscriber happens to be within range of the satellite and a tower at the same time, he'll receive both broadcasts and end up with a stronger signal. An S-DMB system can reach data rates of 128 Kbps.

WiFi broadcasting is in use everywhere, and the S-DMB service has been up and running in Korea since mid-2005. DVB-H had its first commercial launch in June 2006 in Italy and is currently in trials around the world. In the next section, we'll check out some of the cell phones that are compatible with mobile-TV systems.

Mobile TV Reception

Toshiba V401T
Toshiba V401T
Photo courtesy Vodafone K.K.

When it comes to receiving TV signals, you're dealing with a TV tuner, which is a type of radio receiver. There are both analog and digital tuners, and it's the same technology that's in a stationary TV set.

The basic premise underlying a TV tuner is that content providers transmit TV signals in certain radio-frequency bands for certain channels. Just like an AM/FM radio tuner, the TV tuner listens to a specific frequency to pick up the radio waves transmitted to the antenna for a specific channel. It then extracts the video and audio signals from those radio waves.

To turn those signals into a TV show, the tuner sends them to an audio/video (A/V) processor, which decodes and reformats the information so the electronics in the display can create a picture out of it. (See How Television Works, How DTV Works and How Graphics Cards Work for complete information on this process.)

One analog-TV phone on the market is the Toshiba V401T. It picks up the same signals a rabbit-ear TV picks up, meaning watching TV on this phone doesn't cost anything. The V401T has a built-in analog TV tuner and antenna, an A/V processor and a 2.2-inch, 320x240-pixel QVGA display. It can generate 30 frames per second, which is standard TV motion, and you can watch up to one hour of TV on a single battery charge. Phones that receive analog TV typically don't offer as much viewing time as digital receivers partly because it takes more power to digitize the analog signals for the phone's digital display.

Nokia N92 phone Nokia N92 phone
Nokia N92 phone
Photo courtesy © Nokia, 2005

With the Nokia N92, you can watch up to four hours per charge. The N92 is a DVB-H receiver due for release by mid-2006. Under the hood is a TV antenna and DVB-H radio receiver -- essentially a digital TV tuner that listens to the radio bands between 470 and 702 MHz. The phone's audio/video processor displays 30 frames per second on a 2.8-inch QVGA screen with 16 million colors. One of the coolest features of Nokia's DVB-H phone is the swivel screen, which you can adjust for portrait or landscape TV-viewing modes. There's also an "Electronic Service Guide" that displays TV programming, among other things, and you can record up to 30 minutes of TV on the phone for later playback.

Samsung SCH-B250 Samsung SCH-B250
Samsung SCH-B250
Photo courtesy Samsung Electronics

The latest satellite-TV phone on the market is the Samsung SCH-B250 (only in Korea as of March 2006). It has a built-in S-DMB receiver with antenna and a hi-res QVGA screen. The screen is oriented horizontally and swivels for switching between portrait and landscape modes while the phone is still upright. It has a video-out jack for sending S-DMB content to an external display, and you can watch up to three hours of TV on a full charge.

The current availability of mobile-TV handsets is fairly limited because the content-delivery systems aren't deployed on a mass scale. But that's likely to change within the next six to 18 months, and with increased content delivery will come increased functionality on the receiving end.

The Future of Mobile Entertainment

LG V9000 LG V9000
LG V9000
Photo courtesy LG Electronics

In early 2006, LG unveiled the V9000 phone, a T-DMB receiver with the added bonus of virtual surround sound. LG's prototype SB130 is an S-DMB phone that can pause live TV like a DVR, recording up to an hour of programming using its onboard memory. Features like DVR functionality and surround sound point to the possibility that TV-enabled cell phones will become increasingly focused on providing a satisfying viewing experience, instead of just something to look at on the commuter train.

Along this line, as mobile-TV content becomes more readily available, we'll almost definitely see larger screens on TV phones. Some analysts are even predicting multiple phone displays -- one for cell-phone and Web functions and one dedicated to streaming video. If the technology is to gain a real foothold, and if high-end features like HDTV reception are to be viable options, battery life will have to increase. High-end TV phones will also offer advertisers a whole new content platform. Companies are already talking about embedding Web links in mobile-TV programming so users can click their way to a product in the middle of a show. This would probably necessitate the dual-display feature in order to be effective.

Even showing so much promise and industry enthusiasm, mobile TV has some obstacles to overcome both on the device side and the content side. To deliver the types and range of content that consumers really want, mobile-TV providers will have to license programming from the major TV networks. The licensing fees will probably end up raising the cost of any TV subscription service. Content providers will also face digital rights management (DRM) issues in delivering licensed content to users. They'll have to develop DRM schemes that limit what users can do with the copyrighted TV programming that's delivered to their cell phones. And if the uproar surrounding DTV, DVD, CD and MP3 DRM schemes is any indicator, it could get hairy. Still, you never know -- maybe everybody will just get along when it comes to mobile TV.

For more information on TV phones and related topics, check out the links on the next page.

Related HowStuffWorks Articles

More Great Links

Sources

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