Urban Positioning on a Smartphone
I have been drooling over this article for a while. In fact if you search 'gnss smartphones' this article comes up 3-6 times in several GPS/GIS websites.
Location information technology improves all the time. The biggest shortcoming will always be line of sight. You just cannot receive radio signals if you have a mass between you and the transmitter. This principal has always made field work a pain. Most improvements to the technology has been to change the number of transmitters. For example, network location was a significant improvement because there are far more cell towers out there now and so you have more options then ever.
Another option is to improve how the multipath signals are processed. That is what this article talks about. The process uses a 3D model of a city and the 'shadow' GPS signals to recreate a location. The process will not completely fix issues users have in dense urban environments, but it does dramatically improve the areas that you can receive signals. It is not uncommon to be on one side of a street with perfectly adequate signal, but virtually no signal on the other side. This process might allow you to receive signal on both sides.
The prospect of having a 3D model of every city you work in is a little daunting, but memory gets cheaper every day. Processing times are getting faster every day so this technology paired with sensor fusion might make urban or dense canopy survey restriction a thing of the past.