[About 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.
Terrestrial Broadcasts
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/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.

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.

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
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.

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.

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