Over the past ten years several organizations within the wireless telecommunications industry have invested significant time and resources in studying wireless location technologies. Of the technologies that have been investigated to date all have proven to have certain strengths and weaknesses. As of yet no single location technology has been identified that provides optimal performance across all environments. As a result, it is desirable to have a set of complementary technologies that together can provide acceptable performance across all reasonable circumstances. In significant live field deployments to date location technologies based on uplink time difference of arrival (U-TDOA) techniques have proven to provide excellent performance in urban, suburban and indoor environments. The U-TDOA technologies do not require modifications to handsets, so performance for existing mobile stations has proven to be excellent in these same environments. In some rural environments where cell site densities and coverage are very limited the performance of U-TDOA has proven to degrade without the assistance of other location methods. The A-GPS and E-OTD location technologies currently supported in the GERAN standard have significant capabilities. They also have weaknesses that can be mitigated by complementing them with U-TDOA. For example, in urban and indoor environments where reception of GPS signals becomes very difficult and sometimes impossible the performance of A-GPS technologies degrades significantly. In these same urban and indoor environments U-TDOA technologies have proven to perform well because the SNR of uplink channels remains high and cell site densities are most dense. Additionally, in urban and dense suburban environments where higher accuracies become more valuable but the effects of multipath become more significant, the performance of E-OTD technologies is limited by their inability to mitigate the effects of multipath. In these same urban and dense suburban environments U-TDOA technologies have proven to perform well due to their ability to utilize advanced super-resolution techniques to mitigate the effects of multipath. Finally, U-TDOA is able to cover 100% of existing mobile stations today, while A-GPS and E-OTD location methods depend on the subscriber purchasing new location capable mobile stations. It is desirable to have support for U-TDOA in the GERAN standards in order to facilitate a location technology that complements the current standardized A-GPS and E-OTD technologies. Products that support all of these technologies will provide a more robust location solution that will enable the widest and most valuable set of applications and services. By standardizing U-TDOA this technology will be able to achieve significant performance improvements through integration with the network infrastructure making it a very viable and attractive technology for manufacturers and operators.

The following document describes how the Uplink Time Difference Of Arrival (U-TDOA) location method works in GSM and GPRS environments.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

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