MODEO AND DVB-H
The first " competing" system is Modeo. A subsidiary of Crown Castle International Corp., Modeo LLC owns, operates, and deploys over 10,000 cell sites in the U.S. and other countries. Modeo also is the name of the video service expected later this year. The company will develop its own unique programming and content that best fits the small screen and the battery limitations of handsets. Programs will be a mix of news, weather, sports, music, and short clips. The offerings also will include multiple music channels and podcasts. Modeo uses the well-established Digital Video Broadcast-Handset (DVB-H) standard. DVB-H is a mobile version of the DVB-Terrestrial standard developed by the European Telecommunications Standards Institute (ETSI). The standard (EN302 034) defines a digital mobile TV method that can be used in cell phones, PDAs, laptops, and even special handheld or vehicle-installed consumer TVs.
This broadcast system can use any available spectrum, most of which will fall in the 400-MHz to 2-GHz range. Frequencies below 700 MHz are generally preferred, since they produce the most reliable reception. Yet the Modeo system uses a 5-MHz segment of spectrum at 1.67 GHz, which was previously used for weather balloons. Crown Castle bought it at an FCC auction several years ago, and it's now available nationwide. Services using only one continuous piece of spectrum are called single-frequency networks (SFNs), as opposed to the usual paired spectrum (for frequency duplexing) employed in most cellular networks.
Modeo develops video content, stores it on a server, and then distributes it to the company's stations nationwide via a satellite system (Fig. 2). Each local area station has its own tall transmission tower, which is similar to other radio and TV broadcast towers. The individual towers are expected to cover a radius of up to 20 miles. However, each installation will be different, depending on terrain and other factors. In some cases, multiple local stations or repeaters may be needed to get reliable coverage over the desired area. The transmit sites use kilowatt-level transmitters to emit the signal out to handhelds using the DVB-H protocol.
The handsets are also connected to their native cellular provider using a 2.5G or 3G network. While the DVB-H broadcast doesn't need the cellular network to function, an uplink would make consumer response and feedback possible. A two-way connection can even make the video interactive. Besides, there must be a tie-in to a cellular carrier just to get the receiver chips inside the handsets, which are almost always specified and/or subsidized by the carrier that sells them. The cellular operators also probably will handle billing, which they're already equipped to do.
The primary DVB-H requirement was a system that can reliably receive a 15-Mbit/s data stream in 8 MHz of bandwidth. However, the standard also can accommodate versions in 5-, 6-, and 7-MHz bandwidths at lower rates. Also, DVB-H addresses the power-consumption problem many portable devices face through a feature called time slicing.
While the transmitter transmits continuously, the receiver gets bursts of data. The tuner's front end only turns on when it expects to gets its data. The single high-speed data stream is divided up into multiple time-multiplexed " channels." With 10 channels, a receiver need only be on for about one-tenth of the time. With the receiver off 90% of the time, great power savings accrue. DVBH handhelds should provide a viewing time of two-and-a-half to three hours.
DVB-H's real success is its use of the robust and flexible orthogonal frequency-division multiplexing (OFDM). Few other access and modulation methods provide better performance under the severe conditions a mobile handset experiences. Multipath is a given, as is higherthan-usual levels of manmade noise. Add to that the Doppler effects present when a handset or other receiver is in motion. Indoor reception is expected, too.
The DVB-H standard features three modes of OFDM—2K, 4K, and 8K. These figures represent the number of OFDM carriers. The 2K and 8K formats are common in DVB-T, while the 4K mode is new for DVB-H. Carrier modulation may be quadrature phase-shift keying (QPSK), 16QAM (quadrature amplitude multiplication), or 64QAM. The broadcaster selects the exact mode and modulation method for the spectrum and desired coverage. The receivers adapt themselves to the received signal.
DVB-H also offers multiprotocol encapsulation with forward error correction (MPE-FEC). The video data comes as IP datagrams that are encapsulated in MPE packets or sections. Each has a 12-byte header, the data payload, plus a 32-bit CRC. The video IP datagrams comprise the compressed video.
DVB-H is designed to use the MPEG-2 compression scheme. However, most new systems are expected to use the MPEG-4 Part 10 standard, which is the ITU's H.264 compression method and codec definition. Audio-compression formats such as Microsoft Windows Media Audio (WMA), MP3, and AAC are also supported.
Multiple data streams of video data are then time-multiplexed before transmission. The number of time slots or channels depends on the selected number of OFDM carriers and the final peak data speed. DVB-H is expected to support up to 10 video channels. The actual rate of each will be in the 100- to 300-kbit/s range. Because of the timeslicing feature, channel change time is expected to take 1 to 2 seconds, which is a bit slower than the average channel-surfing experience. A GPS-based clock at the transmitter will control the time slicing and demultiplexing.
Most DVB-H handsets will use LCD color screens in the 2- to 2.5-in. diagonal size with a 320- by 240-pixel quartervideo-graphics-array (QVGA) and up to 256k colors. Frame rate will be 30 fps for the highest quality, but 15 fps may be used in some cases.
Modeo LLC heavily tested the system in Pittsburgh last year. It's expected to go into operation later this year in selected U.S. cities, including New York City. A rollout to 30 major markets is planned for 2007. Check out the new Mobile DTV Alliance, which is the industry forum supporting and promoting DVBH in the U.S., at www.mdtvalliance.org.
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