Performance Characterization on Random Access in LTE-Based Two-Tier Small-Cell Networks

In Long-Term Evolution (LTE) random access (RA) systems, upon an access failure, the user equipment not only performs a backoff to randomly spread the retransmission attempt over a certain time period but also increases the transmission power for the retransmission, which is called a power ramping (PR) scheme. This paper analyzes the RA performance of LTE-based two-tier small-cell networks, in which the PR scheme may be a source of uplink cross-tier interference to the macrocell and small cells. To reduce cross-tier interference, we propose a scheme for partial sharing (PS) of orthogonal random access preambles (RAPs), in which small cells are allowed to use a subset of RAPs, whereas the macrocell uses the whole set of RAPs. We compare the PS scheme with a full-sharing scheme, in which the entire set of RAPs is shared by the macrocell and small cells. Our study characterizes the RA performances of LTE-based two-tier small-cell networks in terms of throughput, access delay, mean power consumption, and RAP-dropping probability and shows the benefits of the PS scheme and its trade-off between throughput and access delay of small cells.