Indoor GPS — New or Not New
Underground / indoor GPS repeater maintains your position
Posted Feb 21st 2007 10:32AM by Darren Murph
Filed under: GPS
Sure, there’s a number of uber-sensitive GPS receivers out there that claim to maintain your position whilst under a bridge, in a tunnel, or cramped up in some thick-walled office building, but a recent patent application is looking to implement a repeater system to ensure the best possible geo-location data regardless of your surroundings. Rather than utilizing a WiFi / GPS hybrid method to keep track of objects, the GPS repeater system would require multiple GPS antennae to be setup atop buildings and other obstructions, which would be wired to an indoor RF repeater system that directional receivers could tap into. The indoor segment would not only repeat the signals, but it would reportedly amplify them as well to ensure a solid connection. ,,, read the rest of the Engadget article here, there’s a lot of useful comments in the comments as well as the occasional Luddite or two who don’t “get” it.
To lay a little groundwork, Indoor or underground GPS is not practical using just the standard GPS architecture. GPS signals do not penetrate structures very well, and those that do are subject to what is called multi-path errors … literally they bounce off walls, floors and ceilings and confuse the GPS receiver as it is trying to calculate the delays from the in-range satellites.
There are some GPS chips which allege to work better inside. Most of these are made by Qualcomm and/or Qualcomm patents and are properly called “assisted” GPS. They make use of cell phone signals and tower trilateration/multilateration to help cancel out some of the erroneous GPS positions so that the receiver can concentrate on the “good” signals.
They work, but have varying degrees of success … mainly dependent upon cell coverage in the area of intended use. They will do absolutely nothing for you in areas with weak or no cell coverage … which includes the vast majority of the world’s surface.
Another method that has been around for years is simple re-radiation. This involves a GPS receiver on the roof, a cable connection to a transmitter inside and the rebroadcasting of the received satellite signals inside the confined space. This causes multi-path issues also but the rebroadcast can include a correction signal which will mitigate part of the problem.
To do the job really right this patent sketch above shows a system that will rebroadcast more than one satellite’s signal inside in a manner that let’s the indoor receiver essential receive the original signal without multipathing. It should provide a better solution than what is on the market, but time will tell.
The real amusement for me in this issue was once again how the Internet geek community which alleges to be so smart about gadgets in many cases knows nothing about any gadget that doesn’t have a C:> prompt. But in fairness some smart folks do come out of the woodwork on occasion, but they sure don’t run the sites,