Can you hear me now?
Engineers put emergency communication channels to the testMarch 8, 2010
After the wind and water from Hurricane Katrina pounded New Orleans in 2005, first responders struggled to communicate with one another. The storm ravaged cellular phone and emergency communication lines, plunging the handicapped city into more chaos.
For those in the communications industry, it’s no surprise that communication failures occur simultaneously with massive natural disasters such as Katrina or the earthquake in Haiti. There hasn’t been any rigorous testing of channels dedicated to emergency communications.
To help address the problem, David Matolak, a professor of electrical engineering and computer science at Ohio University, and two of his graduate students, Qiong Wu and Qian Zhang, spent 11 weeks last summer examining several wireless channels designated for emergency communication. The researchers were guests of the National Institute of Standards and Technology (NIST), an office within the U.S. Department of Commerce.
David Matolak, far right, tests emergency communication channels with Jeremy May of Colorado State University (left) and Kate Remley of NIST (center).
“We’re hoping we can help develop the infrastructure to help emergency service personnel respond to the events, no matter the cause,” Matolak says.
Certain frequency bands (at 470, 750, 900, 1800, 4900 MHz) are dedicated to emergency communication, allowing firefighters, police officers, and paramedics to talk or send data or video without interruption. Too many users on a system can lead to dropped calls or, worse yet, an inability to get through at all. Cell phone companies constantly test and retest their signals and channels, but this isn’t the case for emergency channels.
Working out of NIST’s Boulder, Colorado, field office, Matolak and his students measured the characteristics of wireless communication channels. Emergency communication radios often use signals from towers much like broadcast stations and cell phones. Many emergency service organizations place the towers close to their headquarters. These buildings are generally located in the center of towns and at lower heights than phone or broadcast towers.
“We found that the channel characteristics of the emergency communication frequency bands are similar to those of cellular channels, but often worse because the antennas are not elevated and cannot transmit with lots of power,” he says.
To evaluate the signals, Matolak, Wu, Zhang, and their NIST colleagues set up a mobile transmitter cart in several locations—on busy street corners in downtown Denver, in open spaces, and in buildings. The cart transmitted a signal, and the researchers recorded its characteristics with a companion receiver.
Depending on the received signal characteristics, the researchers could determine whether or not the channel in that area was good. In urban areas, signals often bounce off a building or vehicle before reaching the receiver. This can cause what is known as distortion, which for a voice signal can sound like an echo, a voice that fades, or a tinny noise. And these noises make it difficult to hear clearly and accurately, a must in emergency situations. Distortion can similarly cause problems with video or data transmissions.
Ohio University graduate students Qiong Wu and Qian Zhang (center left, right) participated in the study in downtown Denver with Jeremy May (left) and Bert Coursey of the Department of Homeland Security.
After compiling the measurements, Matolak and his colleagues constructed channel models for manufacturers or researchers to test other equipment and signals.
“I think, ideally, the models that we develop will be used by manufacturers who are designing equipment for use in the urban environment for first responders—and these models will have an impact,” he says.
First responders use wireless radios to communicate. Oftentimes they wear the radios on their uniforms, and the devices must be small and light. They also must be durable enough to withstand being dropped or exposed to fire. Knowing more about emergency wireless channels will help designers choose the best technology to enable seamless communication of these devices.
“It will help designers make better systems so the first responders can communicate better, do their jobs better, and maybe save more lives,” Matolak says.
Designers and industry groups have already started to notice. The 3GPP—otherwise known as the Third Generation Partnership Project, an industry group dedicated to advancing consumer third-generation wireless communication—has expressed interest in Matolak’s model—a validation of the work, he says.
This story will appear in the Spring/Summer 2010 issue of Perspectives magazine.
By Meghan Holohan