We've been framed!

Communications News, Jan, 1998 by Glen Southworth

Serious research in the area of video bandwidth compression started more than 40 years ago. Although most of the efforts were directed toward conventional moving image television, a practical and easy compression technique was developed: freeze a single frame from an ordinary television camera and then process that still image in a form that could be transmitted at a low data rate. This process created a versatile form of television facsimile.

The key advantage of singleframe television is that it cad be sent and received over widely available narrow bandwidth circuits, such as ordinary telephone lines. These lines can be used for one- or two-way transmission for visual communications. The exploding phenomenon of the World Wide Web probably owes a major portion of its ancestry to slow-scan television technology.

But how do you transmit video if there is no telephone line or AC power available?

This is an important concern for remote-location observations -- detecting intruders in unattended areas such as pipeline pumping stations, for instance, or providing two-way visual communications for climbing expeditions.

Depending on circumstances, transmission modes include conventional high-frequency radio, once widely used by amateur radio operators, and portable satellite communications equipment such as that used by the Peace Climb group on Mount Everest. In special cases still images may be piggy backed on microwave transmissions. But there is another transmission mode that is gaining popularity and reaping benefits for users: cellular telephone.

Dr. David Swift, a professor of sociology at the University of Hawaii, pioneered its use for still-frame transmission nearly 10 years ago. Because a typical school classroom did not have telephone connections, Swift experimented with the cellular phone as a means of bringing special learning experiences to his students.

Today there are more than a dozen suppliers of remote monitoring systems. Systems range from simple one-way units to elaborate two-way computer-based setups. Capabilities can include remote control of cameras and other peripherals, operation in near real time, ability to handle many cameras at multiple locations, site and time identification, picture storage on a hard disk for high-quality and rapid retrieval, and image enhancement.

In the medical profession, a number of radiologists have found a new degree of freedom by connecting still-image equipment to their car phones. A page alerts them to return to the car, turn on the equipment, and then interpret X-rays or other images transmitted by cell phone.

The two-way information transfer by cellular phone can be very useful for unattended remote image viewing. A transmitting system may sit in a quiet standby mode and save battery power while the solar cell is not providing energy. When needed, the equipment can be requested to turn on and send a single picture or sequence, or perform an action such as switching between two or more cameras. On command, other types of data -- temperature, humidity, ground vibration, wind velocity, water level, or sound -- may be transmitted after being collected by a sensor.

Environmental protection and on-site power are essential requirements for an unattended remote video installation. One advantage of cellular is that its size and power requirements for still-image transmission system are normally substantially less than that for conventional real-time equipment. Cellular does require a good antenna location and reasonable proximity to the nearest relay receiving station, since cell phone transmission power is typically on the order of a few watts or less. A weak signal may produce a noisy image or fail completely.

A basic cell phone system typically has two components: a transmitter and its power and antenna system. The transmitter houses the following components in a sealed weatherproof box: solid state television camera, frame grabber, data formatter, cellular telephone, and battery. External components include an antenna and a solar panel for battery recharging.

With a cell phone RF output of sixtenths of a watt, a small 7-amp/hour battery can provide approximately 100 hours of standby operation or 14 hours of transmission time before requiring recharging. Use of a directional antenna can substantially extend operating range for a given amount of power.

Receiving equipment may be a compact AC-powered device that connects directly to a dial-up phone line. Functionally, it provides reconversion of the slowscan signal to conventional television standards for viewing on an ordinary video monitor or videotaping for later review. Alternately, a PC can be used as the basis of a more flexible receiving system.