While GPS technology has been around since the early 1990s, it has recently begun to turn up in more and more consumer products. In particular, aftermarket car navigation applications have shown tremendous growth, with many companies bringing new products to market. Many of these are oriented towards Personal Digital Assistants (PDA) while others are stand-alone navigation devices that can be placed on the automobile dashboard. Both categories serve the same purpose: to allow drivers to navigate safely and efficiently to their destination.
Classically, GPS has been assumed to be an outdoor, open-sky technology. GPS was targeted at and used primarily in systems where the antenna could get a view of enough of the sky to allow it to acquire multiple satellites and develop a position fix. This had practical and often limiting implications for those applications. For example, to maximise the ability of a GPS antenna to «see” the sky, antennas were typically placed on the roof of the vehicle, requiring either a complex installation procedure or unsightly wires running from the antenna to the display device. Even in those situations, developing a position fix was difficult in areas where a large part of the sky was obscured, such as in forests with a lot of foliage coverings or in downtown areas where tall buildings block the satellite signals. Many of the original navigation systems installed by automobile manufacturers included other «dead reckoning” sensors such as gyros and odometer inputs to compensate for the places where no GPS fix was available. This again led to complex installations and made it difficult to find a robust aftermarket product. Today, thanks to more powerful GPS microchips and better navigation software, many of these issues have been mitigated enough to allow products that not only work well but are practical to install and use in an aftermarket environment. As a result, aftermarket navigation has emerged from a small niche to become one of the fastest-growing new segments of the consumer electronics market. However, it is important to remember that better GPS technology enabled these new applications; they didn’t just happen because the time was right. Specifically, products like SiRFXTrac or SiRFstarIII from SiRF Technology have dramatically improved the ability to track one’s position through tough signal environments with no special installation or outside antenna placement.
Case Study: aftermarket Car navigation
Look at the practical aspects of navigating in a car using a GPS-enabled device. There are many examples of products in this category, from car navigation units to GPS-enabled PDAs and GPS/Bluetooth peripherals that can be connected to a PDA or Smartphone. Neither the performance requirements nor the outdoor environment are different from those of the OEM car navigation applications of five years ago; the unit must still get an accurate position fix, once every second while navigating through city streets, under trees and beneath freeway overpasses. What has changed is the installation conditions needed to get to a viable product. Antennas on the roof are prohibited. At best, antennas are on the shelf beneath the windshield, at worst they could be down near the radio, as in the case of a PDA where it is nice to have the screen out of direct sunlight to allow easier viewing. In order to get the creative packaging of GPS into these new devices, it is often necessary to use a smaller, less efficient antenna. Many newer vehicles have metallised windscreens to keep the car interior cooler. Unfortunately, this also attenuates GPS signals, making the signals received at the antenna are much weaker. As GPS is integrated into devices with display screens or other wireless receivers, there is a possibility of interference or «noise” from those other devices which can make it more difficult for the receiver to get a clear reading of the signal. The combination of these problems means that to get a great user experience, the GPS technology has to be very good: it must overcome all of these installation conditions and still provide outstanding navigation performance in the tough environments that a driver will encounter. Fortunately, the latest GPS innovations provide the performance to overcome those difficult conditions.
What is important?
SiRF Technology has introduced two high-sensitivity products, starting with SiRFXTrac in 2003 and, more recently, the SiRFstarIII chipset introduced in 2004. Based on high-performance GPS engines and the proven navigation technology, these products provide two major advantages. First, they have significantly better tracking sensitivity, allowing receivers to continue to track the GPS satellite signals at very low signal strengths. Whether the GPS signal is obstructed by conditions outside the car (like trees) or inside the car (like interference from a display screen), this increased sensitivity will allow continuous position tracking in many more situations. In many cases, these products will allow the user to get a position fix even if there is no direct view of the sky at all, such as on the floor of a vehicle or even in some indoor environments. Second, they output very good navigation solutions, even while in low signal environments. Navigation is different from point location in that the receiver uses position fixes in combination with predictive algorithms to draw a smooth travel path that reflects «ground truth”. This is very difficult yet critical. As a receiver tries to track signals at lower signal strengths, it becomes more difficult to pick out high-quality signals from those that bounce off buildings or other obstructions. Consequently, the accuracy of the receiver falls, the position drifts or sometimes shows large position jumps. To be useful in these environments, the GPS technology must not only track satellites at low signal levels but must have the navigation capability to provide continuous, smooth position at those signal levels. This is obviously not an exhaustive list. Other considerations such as power consumption are also important in making a complete solution come together. However, if the basic navigation performance fails to meet the application’s needs, the receiver could require no power and still not be a good solution.
Choosing a GPS technology
Understanding the environment and the positioning needs of the application is critical in choosing a technology. Some important questions to address include: Is accurate navigation important to the application? For a turn-by-turn navigation system, this is crucial. Users expect their navigation system to match what they see outside. If your car is stopped at a corner, you expect the navigation system to show you at a corner, not halfway down the block. Turning directions must be given immediately, not three seconds after you pass the intersection. On the other hand, for a truck-tracking application, an occasional, approximate position may be good enough. What is the external environment? A GPS technology made for sailing or hiking environments may work well in outdoor situations, but fail miserably when much of the sky is blocked in downtown environments. A word of caution is appropriate here: consumers are harsh critics. They do not judge their experience with a GPS product based on the average condition; they judge it based on how it worked in the hardest conditions. If it fails in such situations, they have a negative impression. Experience has shown that successful products are those that are designed for extreme cases, not the average ones.
Extensive product tests
How will the GPS receiver be implemented? What antenna will be used? Is there likely to be interference from display screens or other wireless devices? Is there a user advantage to being able to place the device in the passenger compartment rather than near a windshield? The more difficult the implementation environment, the more the application will benefit from a high-sensitivity GPS technology. Unfortunately, product specifications will not always give a full picture. Most specification tests are static (that is the receiver isn’t moving) with powerful antennas sitting isolated on the roof of a building with a full 360-degree view of the horizon. That’s a far cry from the operating environment that many real-life GPS products see. Ultimately, test drives, history and real world user experiences determine which GPS products will provide the best user experience. Most leading GPS providers test their products under these conditions and can readily provide test data. Additionally, with the growth in GPS navigation, there are now some very good internet sites dedicated to testing GPS products and providing user forums for discussion of real-world performance issues.
Looking ahead
The fast growth of aftermarket GPS systems has been largely enabled by more robust GPS systems that not only meet the harsh GPS signal environments of the application but also overcome implementation challenges, allowing more practical implementations. It is a classic case of technical advances driving new applications which in turn trigger higher customer expectations, which once again will foster new technical advances. Looking forward, one can expect even better navigation on increasingly convenient devices. As devices become connected to a wireless network, the possibilities explode, with access to on-line content and peerto-peer connectivity. However, with progress comes complexity. It becomes more important than ever to understand the application environment and to choose the right GPS technology to provide an excellent user experience.
Source: http://www.epn-online.com/page/18334/gps-performance-drives-new-aftermarket-car-navigation-systems.html
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