Before revision:  These measurements are gathered today during highly expensive drive tests  and will be reported in the near future by users equipments thanks to the 3GPP MDT feature ( still costly in terms of battery consumption and signaling overhead ). In both cases , predicting the coverage on a location where no measurements are available remains a key and challenging task.
After revision:  These measurements are gathered today during highly expensive drive tests and will be reported in the near future by users equipments thanks to the 3GPP MDT feature ( still costly in terms of battery consumption and signaling overhead . Therefore , predicting the coverage on a location where no measurements are available remains a key and challenging task.