Global positioning system (GPS) functionality is quickly becoming a major market driver for consumer electronics applications, emerging as a primary differentiator in next-generation systems. The ability to accurately determine one's position crosses automotive applications to personal navigation devices (PNDs) to cellular handsets. Additionally, while there are many advanced GPS services under development, such as location-based advertising, the base function of locating users relative to a map is more than enough to propel GPS into mainstream devices if it can be delivered without significantly adding to the overall cost and processor load.
To provide the performance and accuracy consumers expect at a price they are willing to pay, however, developers need to become familiar with a number of key technologies that make implementing GPS in consumer electronics devices possible--most specifically, the new Galileo satellite network. Through the availability of additional satellite signals, PNDs will be able to acquire and lock positions faster and more accurately than GPS-only devices, especially in urban environments where location-based services are most in demand and GPS accuracy is insufficient.
Galileo is a parallel global positioning network of satellites being developed and implemented under the auspices of the European Union. Galileo was designed to work with GPS rather than compete with it. Galileo satellites will transmit signals in a number of bands, one of which--the L1 band--uses the same frequency as GPS. The L1 band will be spaced between GPS satellites with complementary orbits, thereby increasing the number of signals that can be acquired from any particular location. This will have a significant impact on accuracy in urban canyons. At least four satellites are required to get a decent lock on position. A Galileo/GPS-based PND would allow satellites from both systems to be used at the same time, so that many more satellites would be available. In fact, with this level of accuracy, PNDs would be able to determine which side of the street pedestrians are walking on.
GPS, which is over 30 years old, is run by the U.S. Department of Defense and was not originally designed to serve the commercial market. In effect, Galileo complements GPS. Galileo will provide greater accuracy than GPS (± 4 meters, compared with ±10 meters for commercial applications) because of the greater number of signals available. It will not be controlled by a single government agency that can black out services or change satellite accuracy without warning.
At this time, one Galileo test satellite has been deployed (Giovea), which has proven the all-important transmission mechanisms of the technology. As deployment progresses, 27 Galileo satellites will be launched into orbit. Given today's lengthy product development cycles, many OEMs are already beginning to consider implementing Galileo/GPS-based architectures and seeding the market with them so that once the Galileo system is available, consumers will be able to take immediate advantage of it. Ideally, these devices will operate using GPS alone until Galileo is launched, at which time devices can be upgraded to acquire Galileo signals. Even if OEMs do not plan on upgrading devices already deployed, designing architectures capable of supporting both systems today avoids time-to-market delays and lost opportunity when Galileo becomes available.
Because GPS and Galileo use the same frequency band (and center frequency of 1.575 GHz), it is possible to utilize one radio that operates with both systems (i.e., a dual radio). Slight differences in signal acquisition, however, will need to be implemented in a configurable fashion. Specifically, Galileo signals utilize a 4-MHz bandwidth, compared with 2 MHz for GPS, and will implement a different coding scheme. From a baseband perspective, these modulation schemes can both be demodulated using correlators, so a single baseband processor can be utilized where a single flexible correlator block can be independently configured to demodulate both Galileo and GPS signals simultaneously.