GPS World, July 2013

SURVEY GOVERNMENT Mobile Computing GPS Product Design Challenges Small low cost GPS devices have proliferated in the marketplace and the drivers and applications that support them at a consumer level are available to make GPS acquisition seem cheap and easy Where it starts crossing over into an area of challenge is how to put a more accurate professional grade GPS into a device while meeting demands to keep it less expensive sleeker and smaller for the user According to Trimble Mobile Computing Solutions director of engineering Cary Keist If you want to improve performance better than 2 4 meters not just in open sky but especially under multi path you have to invest in a good antenna an antenna larger than anything thats going to fit into a sleek thin phone And it will have to be pointed to the sky and it will have to have a good ground plane That all takes up room Theres no way around that fact Were seeing competitor products that are rugged and claim GPS capability and are thin but they only offer 10 meter capability which isnt good enough or 2 4 meters in open sky but as soon as you walk up to a building your accuracy is destroyed Alternatively Keist explained you end up with products that have a big snout Some have gone the opposite direction with a big antenna that makes it bulky Weve tried to split the difference Were introducing a Juno T41 handheld with a small extended snout for more advanced 1 2 meter performance even in multi path environments Not the same accuracy as the GeoExplorer 6000 but way better than many others Tablets The tablet form factor has a double problem in housing professional level accuracy antennas an antenna has to point to the sky in addition to being of sufficient size Sky pointing requires a tablet to be vertical but many applications designed for the tablet require it to be flat for work So far this has meant that tablets have been fitted with appendages that can rise at an angle New technologies are under investigation but none has appeared on the market yet Eventually antennas will shrink along with every other technology that prizes miniaturization but it comes down to physics GPS signals are weak to begin with Given the satellite system and the current signals the larger the area of the antenna the more reliable your signal is going to be Theres no easy path right now to have an antenna be very tiny and very accurate Innovation over the next few years will try to find clever ways to put as much antenna as you can in as small a form factor as is possible Keist said Fragility GPS receivers and antennas are not especially delicate they can be made to handle temperature extremes shock and vibration Where it does get a difficult for the makers of rugged handhelds is that as products become larger and weigh more greater countermeasures are required to keep them rugged The heavier the object is the more damage it will sustain when dropped onto concrete Manufacturers add plastic casings around the handheld form to cushion the shock of the landing That in turn adds more weight Its like rocket science for every added pound of weight on the rocket you have to add a half pound of rocket fuel then you have to add more rocket fuel to boost the half pound of rocket fuel weight that was added to push the rocket and so on In building rugged handhelds that are dropped manufacturers calculate this in reverse GPS receivers are going to be relatively heavy in comparison to any consumer device Antennas are large with an awkward shape so to have them survive the drop and vibration tests you have to do a good job of packaging within a rugged device housing to keep it as small as you can without adding mass or building a shape that would be susceptible to breaking Keist said You have to invest in clever design and modeling and trying to keep the cost low So its not technically impossible but if you do it right the design process is expensive and requires rigorous modeling and testing GPS World July 2013 www gpsworld com 36