Please consider risks involved for example in the following circumstances:

• A driverless car or other Intelligent Transport Systems (ITS) rely on navigation with poor integrity;
• A blind or mentally handicapped person cannot find his or her way safely in city traffic because the Personal Navigation (PN) guidance system is not capable of providing positions with accuracies that are verifiably better than one foot;
• Security guards, children, sick, elderly or outing people are trapped inside cave, elevator, house or cellar where all GPS navigation signals are totally blocked;
• A tornado, flash flood, wild animal or other environmental risk alert does not reach a person because his/her indoor mobile phone is not properly tracked due to obstructed GPS signals;
• A traveller is caught by blizzard, avalance or earth slide and the GPS receivers on spot cannot tell both the position and its accuracy for a focused rescue operation; or,
• An airline passenger forgets to switch his/her PC or mobile phone off and it starts to interfere with GPS navigation signals, fatally to aircraft navigation.

References are made to an expert's commentary of February 5, 1999 on the Final Report of the "GPS Risk Assessment Study" made by Johns Hopkins University (January 29, 1999) as well as to integrated GNSS and Loran-C navigation systems like EUROFIX.  

Fortunately, all computational (with the help of FKF) and hardware (through the massive volume production of mobile phones) obstacles will be removed from the path towards an everyman's hybrid navigation receiver of a superb operational reliability and accuracy. Most sophisticated receivers will exploit all available sources of positional information and not only the precise signals from the weak satellite transmitters of GPS, GLONASS or GNSS-2 (GALILEO EurosatNav) but also other phase-stable radio transmissions including most probably the robust Low Frequency (LF) radio signals from Loran-C chains as well as sensors of Inertial Navigation Systems (INS).  

These hybrid navigators (based on FKF and a sufficient number of redundant signals) will feature an adequate real-time verification (based e.g. on the MINQUE estimation theory ) of the actual positioning accuracies that may always vary significantly depending on local circumstances. Thus, a new standard - according to which each computed position is accompanied with its estimation accuracy - needs to be developed and adopted for all navigation receivers including personal mobile phones.  

Sor Etude No17
Sequence © Pierre R. Schwob - by permission. Original from the Classical MIDI Archives
* Last revised January 8, 2014.