On the performance of beam-tracking antennas for downlink layer separation in multi-layer CDMA cellular systems

The separation of two-layers in multi-layer cellular systems when a single frequency band is used is a challenging task. The novel solution proposed in this paper for a CDMA system is based on the implementation of beam-tracking antennas at the macrocells to address the high cross-layer interference, which is the main limiting factor for small cells. We evaluated the downlink performance of embedded hotspots in mixed service (voice and data) macrocell network. The macrocell to hotspot interference and the system capacity for different macrocell base station beamwidths is obtained and is compared with a conventional 3-sectored system. It is illustrated that both macrocell and hotspot capacity increase by using beam-tracking antennas at the macrocell base stations, and it is also shown that there is a trade-off between increasing throughput at the macrocell itself, and increasing the extra capacity achieved at the hotspot.