Indoor GNSS Never Looked Better!

The world of indoor location continues to evolve, with a number of variations on when and under what circumstances you might be able to wander around your local mall getting directions to your favorite ice-cream store on your iPhone. Some malls are mapped, some are not, some (most) have Wi-Fi hot-spots and Bluetooth beacons, some may be in areas where outdoor directional beacon are being tested and their signals penetrate indoors. But the thing they have in common is that most seem to lose GPS/GNSS signals once you get a few tens of meters away from the front entrance.

Some companies have managed to make indoor location in your mall work with a combination of GPS, plus all the RF signals that can be received, plus using inertial and/or magnetic sensors in your mobile phone, and sometimes also with detailed indoor map-matching — but no-one seems to do this in a simple, consistent, reproducible way for any store wanting to ensure you arrive at their door, or for a telecommunication industry wishing to standardize how it works for E911 and then field it everywhere.

So I’ve actually been looking for an indoor location outfit who might have found a consistent solution that can work from place to place — by that I mean from mall to mall, city to city, country to country, even continent to continent, and every time after first set-up — and I suspect that I may have now found one.

The team at iPosi in Denver is still working on their solution, but they have run some pretty convincing demonstrations in some very challenging locations, so they may have found an inside edge that could take them many places (sorry, about that pun).

While iPosi’s headquarters are is in Denver, the company also has labs in Boulder and offices in Dallas. It hasn’t been around too long — since 2011 — but it has been busy filing patents for the key technologies that drive their location technology. Of 40 total patents in the pipeline, five have been granted or allowed, 15 are pending, and 20 more are in development. With only six employees, iPosi is a small outfit, but it also gets design assistance from a European design center for other GNSS signal designs.

One of the key GNSS elements the iPosi team has going for them is an in-house developed GPS receiver with a sensitivity of -175 dBm. If you could get any sort of a signal deep inside a building, it’s possible that they might be able to receive it. But, for sure, anything you would receive deep inside would be just multipath – right? There are other pieces to this story however.

The iPosi system design is based on mobile phone “small-cell” installations. The world now has around 100 million multi-floor buildings with an average of eight floors each, and most buildings present some level of attenuation for external mobile phone cell-tower signals — never mind GPS signals. Most of us should be familiar with having to leave meetings to get “bars.” holding the phone up against a window, walking around to catch reflected indoor signals, and eventually having to leave the building and be with a group of other people who are doing the same thing – looking for a clear cell-phone signal to make a call. In the Northern U.S. and Canada in the winter, this can even be hazardous to your health!

So small cells behave as basically indoor “repeaters” of mobile phone signals. iPosi believes that an average of four of these repeaters are needed to broadcast sufficient signal on each average building floor. So iPosi embeds each small cell with one of its high-sensitivity receivers. Once positioned indoors, and over time, the receivers self-locate inside the building. Currently, installation of small cells can be somewhat cumbersome and time consuming, but non-GPS small cells can be located during installation using traditional indoor surveying techniques — such as laser-based measurements. Either that, or no measurements are made at all, and no device location information is associated with a device.

Small-cell setup.

With each small cell equipped with a high-sensitivity receiver — with especially clever algorithms to differentiate and interpret multipath over time — each device goes to work transmitting repeater mobile-phone signals and eventually self-locates. Contained within these signals are each small-cell location, plus a timing message that allows any standards-compliant handset to calculate range to each transmitter and to perform an OTDOA (Observed Time Difference Of Arrival) position fix.

If the small-cell location at install is also fed into the GIS database for the building and, more importantly, for the local area, the E911 “dispatchable address” for that building has GPS-level accuracy. And first responders will also have numerous other small-cell location aids within the building.

Another detail is that the iPosi receiver uses A-GNSS (including ephemeris) data, so it only needs small snapshots of signal to deduce position. This means very low power consumption for positioning at the small cell, which is good because small cells are mostly battery powered.

So, does it work? In FCC E911 demonstrations at the Omni Hotel in San Francisco, iPosi consistently located to within 50 meters horizontally and a few meters vertically.

• Masonry, turn-of-20th-century construction
• Approximately 15 floors, similar to surrounding
• Test site: ninth floor hotel room
• Horizontal error = 38 m, Vertical error = 9.5 m

There were several other tests in representative converted apartments, a modern four-story steel and concrete building, and inside a university auditorium. But the one that really caught my attention was the test iPosi ran in the basement of an engineering center.

Engineering center, lower basement 3.5 m below grade.

That’s 3.5 meters below grade! The iPosi receiver measurement system was able to determine that some of the signals were actually received directly from a GPS satellite — unbelievable! That’s through concrete and stone down to 3.5 meters below grade with a simple patch antenna!

Most of your average mall locations are not as location-hazardous as this basement test. Its possible that finding your way to the closest indoor ice-cream store could soon be child’s play, which will be especially helpful for the kids with smartphones.

iPosi is working with some of the key equipment suppliers in the industry. It’s quite likely that some of its evaluation sites could soon evolve into operational indoor location facilities. And iPosi’s argument is that its indoor location solution is truly scalable or can be readily standardized — as the telecom companies apparently would love for all indoor location technology to be — so the iPosi solution can readily transition across borders and countries, and roll out could be greatly simplified.

Tony Murfin

Hard to say if this will be the winning indoor location solution, but in the end the market will decide if it really is a scalable, simple solution, and if it will succeed — right?

Tony Murfin
GNSS Aerospace
tmurfin@gpsworld.com