Cellular based location technologies for UMTS: a comparison between IPDL and TA-IPDL

The paper describes and compares two variations of the observed time difference of arrival (OTDOA) location method as applied to UMTS. Both use idle periods in the base station, where most or all traffic is switched off for a short period. The two configurations differ in that in one (TA-IPDL), the idle periods are deliberately time aligned across base stations, whereas in IPDL the idle periods are deliberately offset. This has impacts on performance, complexity and signalling. A network simulator is described, along with the methodology used to assess the performance of the two techniques, and the details of their implementation. This includes discussion of both the time of arrival determination algorithm, and the fixing algorithm. A comprehensive set of results is then provided for a wide range of conditions, including different cell sizes and propagation environments, as well as indoor coverage. The results show that time alignment can be used to improve positioning performance not only in interference limited conditions, but also inside buildings as well as in the non-homogeneous network layouts which are likely to be typical in early deployments