The current generation of the foot-mounted INS implementation (module) seen above is described in the paper
John-Olof Nilsson, Amit K Gupta, and Peter Händel. Foot-mounted inertial navigation made easy ‚ In proc. IPIN 2014, Oct. 28–30, 2014.
This paper is the best and most complete general description of the modules. Further, descriptions of various aspects of the modules is also found in the other publications in the Publications section.
From a user perspective, the module may be seen as a step measurement device. As illustrated above, it will measure the displacement and heading change over each step and send this to an application platform. Here they can be summed up to track the user.