In a typical STB design for IPTV, the most common input is an Ethernet cable
from the home broadband router or gateway from the cable-TV or DSL provider
(Fig. 3). The MPEG4/H.264 compressed
video in the IP packets is passed to a DSP that performs its magic decompression
and FEC decoding.
Separate video and audio outputs drive their respective DACs. Other video inputs
can come from a tuner, NTSC, or other source. Note that HDMI and DVI interfaces
are provided for DVDs and other devices. IR, UART, modem, and power-line-modem
(PLM) interfaces are provided as needed.
The compression and decompression process lies at the heart of all these designs.
The Motion Picture Experts Group (MPEG) standards are widely used: the older
MPEG2 for ATSC HDTV and satellite TV, and the newer and more efficient MPEG4
and H.264 ITU standard for IPTV and mobile TV (see "Video Processing Brings
New Meaning To Motion," Sept. 1, 2006, p. 48, ED Online 13291).
The key problem with IPTV is getting the broadband connection to the STB. The
cable or DSL modem usually resides at the PC location well away from the TV
sets. One solution, the digital media adapter (DMA), transfers audio and video
signals to the TV sets. This device implements a major home network solution
and may well provide a hard drive for audio and video downloads.
Many homes already have a home network, mostly wireless, so multiple PCs can
share the high-speed Internet connection. Homes adopting IPTV will need a change
or upgrade. Most current wireless networks aren't fast enough to support IPTV.
And since the incoming broadband line comes into a router or gateway connected
to the PC, you'll need networking to get the TV signals to the TV sets.
Recent surveys indicate that the average home has 4.3 TV sets. A better than
average home network is the only hope for IPTV to be successful. Wireless in
the form of 802.11a/b/g isn't fast enough and has limited range or spotty coverage,
especially as it goes through walls.
Ultra-Wideband (UWB) is supposed to fulfill this need for speed with its 480-Mbit/s
rate, but only over very short distances. Anything longer than 10 m will be
a challenge, especially through walls. Wi-Fi 802.11n multiple-input/ multiple-output
(MIMO) upgrades to your Wi-Fi network may be a better choice, but it's yet to
be proved. Apple's iTV STB contains an 802.11 wireless network that lays early
claim to solving the problem of streaming video to TV sets.
Two newer technologies may emerge as the home network of choice for broadband
and DTV. MoCA (Multimedia over Coax Alliance) uses the cable-TV wiring available
in most homes today. HomePNA 3 combines both installed cable-TV coax and twisted-pair
telephone wiring.
HomePNA 3, which can connect virtually any device (PC, TV, VoIP phone, etc.)
using existing wiring, can deliver up to 240 MHz of bandwidth. Developed under
the sponsorship of the Home Phoneline Networking Alliance, this system was recently
adopted by AT&T's Uverse IPTV system for home networking. Coppergate Communications
makes a chip set for implementing the HomePNA 3 networking solution in set-top
boxes for the AT&T U-verse system.
For more, see "Digital TV: Issues And Impacts" at www.electronicdesign.com,
Drill Deeper 14016.