The Federal Communications Committee (FCC) is in the process of updating one of its key public safety initiatives, the E911 requirements, and one major area targeted for improvement is location accuracy. The current E911 Phase II requirements, which date from the 1990s, allow US Wireless Operators to meet the requirements even though location accuracy goals are not met in all local areas.
Passing E911 location requirements in rural locations, like North Dakota, is not very challenging because the A-GPS technology built into most mobile devices works well in open and sparsely-populated places. Urban locations such as New York City present quite a different challenge, since most current mobile devices will not meet E911 location accuracy requirements in urban environments where tall buildings and indoor usage are common. Current requirements allow US Operators to average out location accuracy over their entire national footprint, so the good performance in places like North Dakota cancels out the much poorer performance in more challenging places like New York City.
An FCC order released at the end of 2007 (FCC-07-166A1) stated that US Operators must be able to meet E911 requirements at the PSAP level by September 11, 2012. A PSAP (Public Safety Answering Point) is a regional call center for handling 911 emergency calls. Although this order was later challenged by industry bodies, it appears that the issue remains a priority for the FCC. While industry negotiations may result in a relaxation of the requirement from PSAP level to the county level, this would still raise the bar significantly in counties with large urban areas. If and when the FCC does put a location accuracy order in place, wireless operators will need to ensure that E911 Phase II requirements can at least be met in every county in the United States.
US operators today are only required to pass the FCC E911 Location requirement at the national-level, making it difficult to guarantee if the emergency location services will work in more challenging locations such as urban cities.
So will US Operators be able to meet these new requirements using existing A-GPS technology in devices? What are the alternatives?
Hybrid Location Solutions
It seems unlikely that current location technology (predominantly A-GPS) deployed in the majority of today’s mobile devices will be good enough to meet stricter E911 Phase II location requirements at the county level. High-end (and therefore expensive) GPS receivers coupled with advanced (most likely large) antennas may help, but "expensive" and "large" are not normally a good match for cost-sensitive consumer mobile devices.
As a result, there is a growing momentum to include other complimentary location technologies such as A-GLONASS, WiFi, RF Pattern Matching, Cellular Network Positioning, and Embedded Sensors. Each technology has its individual limitations, so it is highly unlikely that one single technology will be sufficient in the future; instead, a blend of location technologies – often called hybrid location technology – will likely be used to deliver the required levels of performance in all locations.
Here is a summary of location technologies along with their advantages and disadvantages:
|
Location Technology |
Advantage |
Disadvantage |
|
A-GPS Assistance data is provided over the cellular network to make the position calculation faster and more reliable – user location can take less than 20 seconds, with accuracies approaching 5 meters in open sky conditions. |
1 Good accuracy in open spaces 2 Fast Time-to-First Fix (TTFF) |
3 Poor accuracy indoors and in urban environments |
|
A-GPS + A-GLONASS GLONASS is a navigation satellite system, similar in concept to GPS, owned by Russia. Devices that use both GPS and GLONASS can take advantage of almost twice the number of usable satellites in the sky for much better location performance in challenging environments. Assistance data can be sent over the cellular network, similar to A-GPS |
4 Better performance in urban environments 5 Fast TTFF |
6 Poor performance indoors |
|
WiFi Positioning Nearly all smartphones today support Wi-Fi, a technology which can also be used for positioning, using comprehensive databases of access point locations. Triangulation or pattern-matching algorithms can be used to achieve good location performance, enabling indoor navigation applications in environments such as shopping malls. |
7 Good performance indoors and in urban environments (the more APs the better) 8 Fast TTFF 9 Uses existing receivers on device |
10 Poor performance in suburban and rural areas (where limited WiFi Access Points are present); non-standards based technology. |
|
RF Pattern Matching An RF “signature” is used to statistically determine location. This technology relies on existing receivers and measurement capability in devices, making it a software-only solution. Although this technology shows great potential, it is not yet widely deployed. |
11 Good theoretical performance 12 ##Uses existing receivers on device |
13 Accuracy is still in the process of being proven |
|
Cellular Network Positioning Cell Identification (Cell-ID), the simplest location technology, locates a user based on the cell they are using, though the accuracy of this technique varies widely. Cellular network triangulation, either signal strength-based or time-based, can be used to improve accuracy and time-based methods, such as Time Difference of Arrival, are common. |
14 Available everywhere 15 Very fast TTFF 16 Uses existing receivers on device |
17 Relatively low accuracy |
|
Embedded Sensors Inertial sensors, such as accelerometers and gyroscopes, can be used to supplement other location technologies. Once a location is known, dead reckoning algorithms can help track the location of devices without external references. This is very useful when driving through tunnels and passing through subway systems. |
18 Very good augmentation technology (helps make other technologies more accurate) |
19 Requires another location technology in order to work 20 Adds cost to device |
Industry Trends
Through its work with LBS technology leaders, it is clear to Spirent that hybrid location technology is becoming mainstream. It is still too early to tell which technologies will be the most important for augmenting the existing A-GPS and Cellular Triangulation positioning implementations, but both A-GLONASS and WiFi Positioning are beginning to gain traction, at least in the US market.
Another related trend is a move towards enabling technologies such as SUPL 2.0, a Secure User Plane protocol for passing location information between mobile devices and network positioning entities. SUPL 1.0 is a protocol commonly used in UMTS networks for sending GPS assistance data, thus enabling all the benefits of A-GPS. SUPL 2.0 adds many enhancements that make it more suitable for hybrid location technologies. In fact, SUPL 2.0 can support all of the technologies previously discussed in this article, which poses the question if it could be the leading candidate for enabling E911 Phase II service, overcoming the shortcomings of SUPL 1.0.
Commercial Location Services
Mandatory support for E911 Phase II has been a strong driver of location technology development in the United States. It should be noted that, in addition to helping mobile devices meet stricter E911 requirements, hybrid location technology can also enable better performance of commercial LBS applications. The ability to get fast and accurate location fixes any place in the world is fundamental to the growth and monetization of LBS applications. Although E911 requirements in the US may again be a driver for technology development and adoption, operators in other parts of the world are also looking at hybrid location technology to drive their commercial location-based services growth. Several leading device and technology vendors, including Apple, Nokia and Google, have already incorporated the benefits of apply hybrid location in their devices and applications.
Summary
The likely requirement to enhance E911 location accuracy in the coming years, coupled with the strong commercial drivers for better location accuracy, leads Spirent to believe a that major progress will be made in the development and deployment of hybrid location technology over the next couple years. Safety and security will improve as a result and the goal of anytime, anywhere commercial location services will finally become a reality.
About the Author
Brock Butler is currently director of product management at Spirent and responsible for UMTS location test product segment. After joining Spirent in 1999 as a development engineer, Brock progressed to a group manager, then product manager for one of Spirent’s key UMTS test products. He has been a part of the Spirent team which has made major contributions to development of the LBS standards in the 3GPP.