Collect useful sentences in Papers (5)

Alternative technologies are sought for such difficult environments

Indoor positioning technologies can be classified into three categories: technologies based on signals of opportunity, technologies based on pre-deployed infrastucture, and others.

The signals-of-opportunity are signals (radio frequency - RF - signals are the most common) that are not intended for positioning and navigation, such as signals of WiFi, television and FM radio. Since these signals are designed for other purposes, and given the reality of the harsh signal propagation environment, using them for positioning to achieve high accuracy is a very difficult, if not impossible, task [1, 2].

The low cost and wide coverage of such methods are the main advantages. "fingerprinting"

There are many positioning technologies that require the deployment of infrastructure, such as positioning systems using infrared, ultrasound and ultra wide band [3-5], as well as bespoke RF-based systems.

Deploying new infrastructure is costly, and hence the coverage is often very limited - typically using "hot spot" mode. 

A significant advantage of this type of system is that the artificially generated magnetic field is not affected by most obstacles, hence multipath or non-line-of-sight errors are avoided.

Using the geomagnetic field for outdoor navigation is not new.

An obvious advantage of using the magnetic field for positioning is that no infrastructure needs to be pre-deployed, which makes such a system cost effective.

many animals use the geomagnetic field naturally to navigate their way around the Earth [18]


Reference:

Li, B., Gallagher, T., Dempster, A. G., & Rizos, C. (2012, November). How feasible is the use of magnetic field alone for indoor positioning?. In Indoor Positioning and Indoor Navigation (IPIN), 2012 International Conference on (pp. 1-9). IEEE.