We can receive high-quality video feeds from almost anywhere in the Western world. So it's easy to assume that such links are standard and ordinary. For much of the world, however, this situation is not the case. The news-reporting path to your TV from remote lands, such as Afghanistan, which lacks a wideband or cellular infrastructure, requires the careful merger of data-handling geostationary satellites and portable earth-bound terminals.
Even with this combination, the video quality is not at conventional broadcast levels, but it is amazing that it happens at all. The feed is restricted to a relatively modest "talking-head" news presentation with low frame rate and somewhat static image. This modest technology replaces the traditional still picture above audio-the technology that news organizations were once restricted to for broadcasting.
As with most such developments, the apparent simplicity hides a complex system operating at various levels. In the case of these remote, live-from-the-field video feeds, the most common user terminal equipment is 7E Communications Ltd's (www.7e.com) Talking Head. The company deployed this model in 2000 and has sold about 200, mostly to news organizations, according to The Wall Street Journal and The Economist.
The fully self-contained, less-than-$20,000 Talking Head system fits into a briefcase and weighs less than 5 kg (11 lbs), including video camera, signal-processing system, RF circuits, and satellite antenna. It provides live audio and video transmission and a return audio-only cue path so that a reporter can simultaneously hear instructions from the home studio. It includes requisite video- and audio-compression circuits, providing G.711, G.722, and G.728 audio coding and ITU H.320 video functions using H.261 and H.263 video coding. Motion Media Technology (www.motion-media.com) developed the compression algorithms, which provide a balance among factors such as picture resolution, motion smoothness, and object detail. It also provides audio functions, such as echo cancellation, which requires a multiprocessor-DSP architecture. Picture resolution is 352 x 288 pixels at 15 frames/sec and 176 x 144 pixels at 30 frames/sec.
The unit accepts NTSC or PAL video with standard 75V, 1V p-p input through a BNC .25-in. phone-socket input. It also accepts line-level, high-impedance microphones with balanced and unbalanced inputs, as well as a low-impedance balanced input, using a combination of standard phono and standard three-pin XLR connectors; the design also includes a small audio-mixing console. An operator sets up and monitors transmissions using the system's 6.4-inch-diagonal LCD.
Power consumption, a critical factor, is less than 20W. You can operate this unit from a 10.8 to 14.4V dc supply or from 9 to 25V if you don't use the integral display, through a 90 to 264V ac, 47- to 400-Hz ac adapter, or from a BP-90A video-camera battery.
Aim high to reach. Although the Talking Head system is both complex and compact, it doesn't by itself provide a link to your studio. The vendor designed the system for use with the Inmarsat-B satellite network, providing connectivity and linkup via the Euro-ISDN (Integrated Services Digital Network) standard at 64 kbps for a single channel and 128 kbps with dual channels, under ISDN basic rate (2B+D). It also provides for the 56- or 112-kbps North American ISDN arrangement.
Behind the system's abilities lies the Inmarsat (International Marine Satellite, (www.inmarsat.com) system. Inmarsat's founders established it as a global consortium more than 20 years ago to provide reliable wireless links to ships at sea, which have no convenient nearby cellular base stations. In 1999, developers reestablished Inmarsat as a private company with a similar mission and charter but with the added goal of providing links to remote, land-based users.
The Inmarsat system comprises four geostationary satellites, plus a spare, assigning one satellite each to the Indian Ocean, the eastern Atlantic Ocean, the western Atlantic Ocean, and the Pacific Ocean. Although earlier Inmarsat satellites aimed at analog and voice communications, the latest series, Inmarsat-B, targets digital communications, including Group 3 facsimile, 64- and 56-kbps ISDN, and a basic 9.6-kbps data connection. The satellites each provide both broad footprint coverage and seven steerable spot beams so that Inmarsat can focus the satellites' coverage on areas of highest user concentration and traffic. In contrast, the Iridium system used 66 low-orbit satellites to maintain worldwide coverage. Iridium's relatively low orbits allowed for much lower power transmitters but had far more complex system-management issues due to the satellites' short orbital periods.
The user-terminal antenna for Inmarsat measures just 80 cm (32 in.) across. Ship-mounted versions of the unit must be on a stabilized platform to maintain aim as the ship rolls. For ground-based reporters, this feature is unnecessary, but careful initial aim is vital. The antenna folds into the Talking Head carrying case when not in use.
Similar to the Talking Head terminal, Inmarsat also operates land Earth stations, which link to their satellites and control the system operation and resources. Land Earth stations are the connections between the Inmarsat system and conventional communication networks to bring a user's signal to the television studio-in the case of news coverage-or to any other user.
What does it cost to reach out and touch someone when you are using the Inmarsat channel to provide a basic video and audio report from a place such as Afghanistan? Plan on spending $7 for each minute you are on the air. Keep in mind that you get a relatively low-resolution, low-frame-rate image with moderate-quality audio-not full-motion, high-frame-rate video. This option may be a lot better than the voice-only alternatives, however.