Improving positioning in LTE through collaboration

This paper represents a preliminary study of cooperative positioning in Long Term Evolution (LTE) systems. Many applications, such as location-based services and Enhanced 911 (E911), require that the locations of users in a cellular system are available. The global navigation satellite system (GNSS) is the most accessible positioning systems which are widely used in cellphones. However, poor operation in indoor and dense environments leads us to use cellular localization as a backup solution. In cellular localization, the locations of users are determined via measurements obtained within the network without aid of any external sources (e.g., GNSS). Observed time difference of arrival (OTDOA) is a positioning technique introduced in Release 9 of the 3GPP LTE specification. In OTDOA technique, the User Equipment (UE) measures the time difference of signals between several eNodeBs (base stations in LTE) and uses a trilateration algorithm to find its location. In the current 3GPP LTE specification, the UE can only collect measurements from eNodeBs. Therefore, in many situations, the UE is not able to communicate to a sufficient number of eNodeBs and cannot find its location without ambiguity. In this paper, we propose a cooperative localization technique for LTE systems in which the UE communicates not only with eNodeBs but also with other UEs. It will be shown that cooperative localization can significantly improve the localizability in the network, meaning that more UEs can be localized. Cooperative localization also enhances the accuracy which is highly beneficial for some applications, especially E911. A series of computer simulations are conducted to show the benefits of cooperative localization where the 3GPP simulation parameters are assumed.