A Model for Dynamic Behavior of Ranging Errors in TOA-Based Indoor Geolocation Systems

In TOA based indoor geolocation systems ranging error is a function of the bandwidth of the system and the availability of the direct path between the transmitter and the receiver. With a detected direct path (DDP) condition and UWB transmission, precise range estimates are feasible while in undetected direct path (UDP) conditions large ranging errors occur which can not be cured with the increase of the transmission power or bandwidth. This paper uses Markov chain and the results of measurement calibrated ray tracing with 500 MHz bandwidth in a typical office environment to introduce a novel model for the behavior of the ranging errors observed by a randomly moving mobile terminal in an indoor area. The model divides the behavior of the ranging error into three categories. The first is DDP where the errors are usually small and mainly caused by multipath. The second category, natural UDP (NUDP), is caused by path-loss and exhibits medium ranging errors. The third category, shadowed UDP (SUDP), is caused by objects blocking the direct path and demonstrates very large ranging errors. Parameters of the Markov model are calculated from the results of wideband channel characteristics for different locations of a mobile. Results of the simulated errors from the modeling and the actual errors from the channel profile show close agreement.