Dec. 14, 2001

Laser experiment links Lab to Mt. Diablo


Lab scientists and engineers will conduct communications experiments between Mount Diablo and the Laboratory to develop a wireless means of transmitting large quantities of data.

The experiments are being conducted as part of the Laboratory’s Secure Air-optic Transport and Routing Network, or SATRN program. SATRN is an NAI Laboratory Directed Research and Development strategic initiative, geared toward developing advanced technologies for long-range laser communications.
Proliferation detection, counterproliferation, arms control, counterterrorism and warfighting all require the timely and secure communication of information in situations where fiber-optic cable is physically or economically impractical.

"With the global proliferation of information technologies, commercially available satellite imagery and advanced weapons systems, the U.S. must focus on developing ways to best gather and distribute information on a global scale in near real-time, to maintain its technological edge," said Tony Ruggiero, principal investigator and SATRN project leader. "In the 21st century, the decision-maker will be forced to assimilate and act on information in a shorter time than ever before."

This assimilation of information is increasingly difficult as tactical and strategic reconnaissance and surveillance assets become more sophisticated and develop greater capabilities, requiring the transmission of ever more massive quantities of data, Ruggiero said. "Communication bottlenecks between command centers and tactical and strategic assets make the present information transport system slow, incomplete and unresponsive. A new generation of long-range, covert, high-capacity data links is required to remedy this situation and provide near-real-time data transport. Lasers have the potential to fulfill this need."

Laser communication consists of an optical system in which information is encoded on a laser beam and transmitted to a receiver. Functionally similar to radiofrequency or microwave communications, lasers use the optical part of the electromagnetic spectrum.

Ruggiero emphasized that the laser beams used for communication are not visible or harmful in any way. "The actual power transmitted is 100 times less than a standard household light bulb. But since it is highly directional, it can be transmitted over long distances. "

Systems for transmitting data using lasers over short distances of 100 to 500 meters — between buildings, for example — are well established. The challenge of the SATRN project is to extend that range to tens of kilometers while maintaining a high "availability," the percentage of time the link is accessible at an acceptably low "bit-error-rate," or the number of errors per bit of information transmitted.

Lab scientists will need to study the effects of atmospheric conditions on air-optic laser communications over long distances. Also, such beams cannot pass through opaque objects. A bird flying through the beam path would result in a data transmission error. The bird would be completely unharmed and unaware of any contact with the laser beam.

"One of the things we’re doing is developing error coding techniques to correct for this situation," Ruggiero said.

Another advantage is that laser communication is not affected by electromagnetic interference from other forms of wireless communication such as radio or microwave. Neither does it have any effect on these other wireless communications.

Mount Diablo was chosen because it’s the highest point in the Bay Area that provides a clear line of site to the Laboratory and because researchers will be able to set up equipment at an existing U.S. Navy communications facility there. The Lab has received permission from the Navy and advised appropriate regulatory and governmental agencies of the experiments while DOE is in the process of obtaining approval to modify the existing license agreement. The experiments, which will be conducted at different times of day, pose no danger to park users. Beams will be transmitted and received from an elevated platform in the Navy facility.
Researchers will conduct as many as 20 experiments over a two-year period with each experiment lasting three to five days, according to Ruggiero. On experiment days, data will be collected on and off throughout the day to sample changing atmospheric turbulence and weather conditions.

"We want to conduct the experiments at different times of the year to test the performance of the laser communication system in a variety of air turbulence and weather conditions."

He notes that there’s a good deal of commercial interest in this area of communication research. "It is an extension of work being done by major telecommunication companies to address the so called ‘last mile problem’ to longer ranges, mobile platforms and rapidly deployable communication infrastructures," Ruggiero said. "Data-centric networks play a key role in future visions of tele-medicine, tele-maintenance, emergency response, natural disaster prediction and warning, military planning, and intelligence gathering."