Multi-RAU pilots for ROF enabled distributed antenna systems

Future cellular systems require an aggressive frequency reuse in order to provide the expected data rates. For these systems, interference is a major issue to be addressed by the physical layer. Radio over fiber enabled distributed antenna systems can provide a competitive solution to mitigate interference. In this architecture, multiple non collocated remote antenna units (RAU) are transparently connected to a single central unit which performs coordination and joint processing. In downlink context, multi-RAU channel estimation is a key feature which allows the mobile station to combat interference using joint detection. However, pilot patterns in current cellular standards are designed for single cell scenarios and are not adapted to the DAS context. We propose here a generic capacity analysis framework to assess the impact of multi-RAU channel estimation on the link performance. This framework is then applied to highlight the enhancement provided by a proposed modification of LTE pilot patterns suitable to the DAS topology. We show that pilot coordination between neighbouring RAUs combined with interference cancellation on the terminal side provides a substantial gain to the downlink user throughput.