Application of the TDD Underlay Concept to Home NodeB Scenario

This paper presents a spectrum sharing approach which exploits the clustered distribution of users as would be expected in a typical home with several communicating devices (also known as a femto-cell) or in public places such as airports, malls, etc. From each cluster, a mobile station (MS), known as a gateway mobile (GM), acts as a relay between the other users of the cluster and the base station (BS) of the associated cell. The system makes use of frequency division duplexing (FDD) for communication between the BS and the GM. Traffic is assumed to be asymmetric in favour of downlink (DL) due to current trends in user traffic requirements. The unused resources in the uplink band are then used for communication within the cluster using time division duplexing (TDD underlay). This model is compared against one in which the same user distribution is assumed but the GM concept is not made use of, i.e., an FDD system. Based on the results, it has been shown that the proposed enhancements lead to a significant increase in system spectral efficiency through the use of intra-cluster communication.