SRS-based user proximity detection in LTE small cells

Heterogeneous Networks (HetNets) consist of two layers of base stations: a coverage layer that consists of conventional macro base stations and a capacity layer of low-power base stations, variously called small, pico etc. To maximize spectrum reuse in the capacity layer, dense small cell deployment is necessary. However, with a large number of small cells, user´s battery consumption increases due to the increased number of measurements to be performed in order to achieve high offloading gain. In addition, small cells also need to transmit reference signals which consumes power and also contributes to interference in the macro-cell. These problems can be mitigated by network-based user detection algorithms and user-based small cell discovery algorithms. In this paper, we propose an efficient network-based user proximity detection method that determines a user´s presence by listening to its uplink transmissions like Sounding Reference Signals (SRS) transmissions, or Physical Random Access CHannel (PRACH) transmissions that are used for random access. This can be used to take handover decisions as well as to control the ON-OFF periods of the small cell.