LTE Advanced: 3GPP Solution for IMT-Advanced

8.4 Interference Management

It is well-known that interference poses the main limitation in today's mobile communication systems, in particular for urban deployments where base station distances are typically on the order of less than a kilometer, and where all radio resources are reused in all cells. While this holds for both homogeneous and heterogeneous deployments, the fact that large and small cells in a HetNet use very different transmit powers raises particularly challenging interference issues, which will be discussed in this section.

Consider a simplified multi-layer setup with a large and small base station as depicted in Figure 8.8, and assume for now that both cells reuse all available radio resources (so-called co-channel deployment). The small base station will use a significantly lower downlink transmit power than the macro base station. As terminals by default connect to the cell from which they receive the strongest downlink signal, this means that the cell border will be much closer to the small base station than the macro (indicated through a bold line). If range extension is used, the cell border will be shifted towards the larger base station (thin line). The point where the uplink signals originating from a terminal are received equally strongly at both base stations, however, will be more or less in the middle between these (indicated through a dashed line and denoted as virtual uplink cell border). The fact that we have these different cell borders in uplink ...