Editor’s Note: Welcome to our weekly Reality Check column. We’ve gathered a group of visionaries and veterans in the mobile industry to give their insights into the marketplace.
Today, most people think that the 911 system in the United States works well. In an emergency situation, a person can dial 911 on any type of phone, and first responders arrive at the scene of the crisis in a timely manner. Unfortunately, that was not always the case.
Take the unfortunate death of Jennifer Koon in 1993 as an example. Jennifer, a sophomore in college, was on her way home from work when she drove into a shopping plaza to get cash at an ATM. She was planning on going to a weekend concert with a friend, but she never got there. A stranger abducted Jennifer in the parking lot. She was driven to an unknown site and ultimately murdered. Police later found her body in an alley.
Before Jennifer was killed, she managed to dial 911 on her cell phone. At the time, however, the technology to locate a wireless 911 caller did not exist. As a result, the call-taker was unable to automatically locate her and send the necessary first responders to her location. According to Jennifer’s father, a New York State Assemblyman, “All [that the 911 call center] could do was listen to the last 20 minutes of my daughter’s life,” he said. While no one knows for sure whether an accurate location fix may have saved Jennifer’s life, it served as a catalyst to ensure that when 911 calls are made from cellphones are accurately located.
These days, when someone dials 911 from their cellphone, the caller’s location is sent to the call-taker fielding the call. The Federal Communications Commission enacted the Enhanced 911 (E-911) Phase II mandate in 2005, which required that all wireless operators must deploy technology to locate wireless 9111 calls. Since then, the 911 system has improved significantly. The Phase II mandate enabled the Public Safety Answering Points that answer 911 calls to receive precise location information, giving them the ability to more quickly identify and locate people in need of immediate assistance, even if the person cannot communicate over the phone. Now, emergencies can be handled much differently.
Take this hotel-robbery-gone-wrong, for instance. One night, in Chester County, Pennsylvania, a hotel manager’s shift was interrupted by two armed robbers who entered the hotel. The men subdued the manager, and then tied his hands and ankles. At one point during the altercation, the manager tried to set off the hotel’s silent alarm, but it did not work. Fortunately, the manager was able to dial 911 on his cellphone and dropped the phone onto the floor to avoid it being seen by the robbers.
Though the hotel manager was unable to speak on the cellphone, the 911 call-taker heard the commotion in the background, and quickly assessed that it was an emergency situation and that someone needed help. Unable to ask the person on the line any questions regarding the location of the emergency, the call-taker was still able to determine the location of the cellphone in order to direct the emergency response teams to the scene of the crime.
Of the many calls that are made to 911, those where a caller is unable to communicate are among the most challenging for emergency responders. When a 911 caller cannot ask for help or identify the location of the emergency, it is solely in the 911 call-taker’s hands to assess the nature of the situation and send the proper emergency response team in a timely manner. Fortunately, when a person dials 911 on their cellphone today, the person can be quickly and accurately located, even when they are unable to speak, which is vitally important, since often in emergency situations, seconds can sometimes mean the difference between life and death.
While much progress has been made, there remain certain environments and conditions that present challenges for particular location techniques. For instance, 911 calls that are made in dense urban areas with tall buildings, as well as indoors, are difficult for location technologies that require a clear line-of-sight with at least three GPS satellites.
Currently, there are two different location technologies that are employed by U.S. wireless carriers for to locate wireless 911 calls: U-TDOA (Uplink Time Difference of Arrival) and A-GPS (Assisted GPS).
The network-based technology, U-TDOA, determines a cellphone’s location by comparing the times at which its signal reaches multiple cell towers. This process is called multilateration. Because U-TDOA is network-based, no additional hardware or software needs to be installed into a cellphone, which means it can accurately locate any cell phone in any environment.
The handset-based technology, A-GPS, uses orbiting GPS satellites to locate cell phones. Assistance data from cell towers improves the time-to-first-fix of a GPS calculation. However, to provide a location, GPS requires a clear line-of-sight with the orbiting GPS satellites. This means that GPS is susceptible to failure when a cellphone is indoors, especially within buildings constructed of concrete and steel. In fact, even when a cellphone is outdoors, but surrounded by tall buildings, an “urban canyon” effect is created, and the signals are blocked by the buildings and the cellphone cannot be located.
Generally, A-GPS works well in rural and remote areas, and U-TDOA excels in suburban and urban environments. These complementary characteristics lend themselves to a hybrid location approach, whereby the two technologies are combined to increase effectiveness and provide the most exact location possible for wireless 911 calls in all environments.
What does the future hold for 9-1-1 calls and determining location anywhere at any time? There remains a need for a location technology that delivers high performance, even in challenging environments, such as indoors or in cities with tall buildings, and this need cannot be satisfied by A-GPS alone. A U-TDOA and A-GPS hybrid location solution has already been successfully tested on a city-wide scale. If deployed, it would ultimately lead to an improved public safety system for all U.S. citizens.
