Small-Cell Assisted Group Paging for Massive MTC in LTE Networks: Design and Analysis

Long-Term Evolution cellular networks are the main enabler for the massive Machine-Type Communications service and therefore must handle a large number of Machine-Type Devices (MTDs). To control the number of devices allowed to contend on the Physical Random Access Channel (PRACH), the group paging scheme that divides the MTDs into smaller groups and lets the network sequentially trigger the groups has been studied. However, as the number of PRACH preambles is limited, a group's size must be kept relatively small compared to the MTD population. This paper exploits the possibility that a significant portion of the MTDs is also covered by densely deployed small-cells such that a Small-cell Base Station (SBS) may act as a representative for its MTDs during the preamble transmission step to reduce the load on PRACH. Once the SBS succeeds, its MTDs then contend locally to send their own signaling messages on the corresponding reserved uplink resources. Computer simulations show that the manageable group size can be significantly increased at a reasonable cost on the Physical Uplink Shared Channel. A theoretical model to quickly predict the effect of the ratio of MTDs that are under the coverage of the SBSs is also derived and verified.