Focus on Research
Penn State Intercom......November 1, 2001

Reliable, wireless, infrared local
area networks demonstrated

By Barbara Hale
Public Information RESEARCH_Kavehrad

University engineers have shown that broadband, wireless, indoor, local area communication networks that rely on non-line-of-sight infrared signal transmission can offer low error rates as well as safe, low -- below one watt -- power levels.

Mohsen Kavehrad, professor of electrical engineering and holder of the W. L. Weiss (AMERITECH) chair, said, "Line-of-sight or point-to-point infrared signal transmission, which is used, for example, in television remote controls, is highly efficient at low power levels but suffers from the need for alignment between the transmitter and receiver. If someone 'shadows' or blocks the remote control beam while you're trying to change the channel, the signal can't get through.

"On the other hand, non-line-of-sight transmission, which uses a broad diffuse beam, suffers less from shadowing but usually forfeits the power efficiency, broadband and low error rate values that infrared transmission can offer."

Now, Kavehrad and his colleagues at the Center for Information and Communications Technology Research have developed a new link design that uses a multi-beam transmitter with a narrow field of view receiver. The system has a bit-error rate of only one error per billion bits and uses milliwatt-transmitted power levels. Svetla Jikova, research associate, collaborated with Kavehrad on writing a paper on their work.

Kavehrad said, "This error rate is unmatched considering the offered transmission capacity."

To use the Penn State signaling scheme, for example, to form a local area network for a group of computers in a room, each machine is equipped with a low-power infrared source and a holographic beam splitter. The original low- power beam is separated into several na rrow beams, which strike the ceiling and walls at points that form an invisible grid throughout the entire volume of the room. Because the beams also are reflected at each of the strike points, they can be used to send or receive information.

Since the beams created by the splitter are narrow, narrow field-of-view receivers are used. Using a narrow field- of-view receiver makes it easier to filter out noise. In addition, receivers consisting of more than one element can ensure continued coverage when some of the transmitter beams are blocked.

Kavehrad noted, "Others have attempted to develop local area networks with radio frequencies. However, indoors, radio frequencies can pose a radiation hazard.

"Infrared signals, on the other hand, pose no such hazard, especially at the low powers used by our system. However, since the sun is an infrared emitter, as well as fluorescent and incandescent bulbs, light coming in through windows or from artificial lighting can add background noise to the system. This noise, to some extent, can be filtered at the receivers."

The University team developed a framework for computer simulation under which properties of room, transmitter and receiver are quantified. Using the simulation results, they showed that the system has a bit-error rate of only one error per billion bits in 99 percent of the coverage area at bit rates up to a few hundred megabits per second. In addition, the system uses transmitted power levels well below one watt.

The system is being patented by the University.  


Barbara Hale can be reached at

X-ray emissions detected
from elusive cosmic objects

A type of celestial object that has long stumped astronomers has been found to emit X-rays, thus proving a theory of how the objects form.

A team of astronomers including Steven Pravdo of NASA's Jet Propulsion Laboratory in Pasadena, Calif.; Eric D. Feigelson, Gordon Garmire, Yoshitomo Maeda and Yohko Tsuboi at Penn State; and John Bally at the University of Colorado, have concluded that these objects, called Herbig Haro objects, are produced by high-velocity shocks.

Herbig Haro objects are found in regions where new stars are forming. They are nebulae, or dust-and-gas clouds. They form when high-velocity gas emitted from young stars collides with clouds of interstellar material. The collision heats the gas in the surrounding nebula to sufficiently high temperatures to produce X-rays. Observations for the past 20 years showed no evidence of
X-ray emission from these objects.

For more of this story, check

Aging, disabled inmates
require special care

By Vicki Fong
Public Information

With stricter sentencing policies, states are facing a growing prison population of aging inmates. In addition, there are younger, disabled inmates who need long-term health care assistance.

A University study examines ad-hoc and planned strategies used by one state's correctional system to deal with these needs, and suggests ways to deal with inmates' long-term care needs at prisons nationwide.

"Longer mandatory sentences and more life sentences without the possibility of parole have significantly helped to boost the prison population over two decades," said study co-author Cynthia Massie Mara, associate professor of health care administration and policy at Penn State Harrisburg. "It's inevitable that as this larger population ages within the prisons, they will require greater long-term care. Also, more prisoners, including younger ones, require daily living assistance due to physical disabilities from injuries or from diseases such as AIDS or hepatitis C."

Mara and Christopher K. McKenna, associate professor of management science at Penn State Harrisburg, conducted the study, which is the first comprehensive research of long-term care in a prison system.

The researchers surveyed corrections health care administrators of all 25 state correctional institutions (SCIs) in Pennsylvania. They found that 22 SCIs reported having at least one inmate needing assistance, and that 1.8 percent of Pennsylvania's total state inmate population requires daily living help. Inmates ranging from 18 to 89 years of age were reported as having at least one daily living impairment, but nearly 24 percent of inmates 65 years and older are affected. Within the total group, the percentage of women inmates needing assistance is 1.88 percent.

The study identified several models or strategies being used to provide long-term care, but the strategies were mainly developed ad-hoc, or as needed, rather than from a comprehensive plan.

The researchers said that the care of infirm, aging inmates who need long-term care can cost up to $70,000 a year per person, according to general estimates. Across the nation, policymakers and planners in various state corrections departments should conduct comprehensive assessments of their populations and existing facilities, the team suggested.

"First, states should identify inmates who currently need long-term care and inmates who are likely to require care in the future," Mara said. "Other issues include staff and training needs, inmates helping other inmates, safety of older inmates, women inmates who need long-term care, modification of jobs for inmates who need assistance, release planning, hospice care, buildings and grounds and cost of care."  


Vicki Fong can be reached at