One of the main targets of the fifth generation (5G) mobile communication systems and beyond is providing high data rate wireless transmissions and ubiquitous coverage to users. To support increasing subscriber populations in indoor environments, indoor wireless communication systems are required, but frequency spectrum allocations are limited and requires reuse of the limited spectrum. In order to design efficient and reliable indoor communication systems, a thorough understanding of the reuse distance is vital. This paper investigates a number of important issues associated with indoor radio propagation and frequency reuse planning in multi-storey buildings employing indoor distributed antenna system (DAS), where distributed remote antenna units (RAUs) supported by a central unit (CU) communicate with mobile equipment (MEs). In the DAS, co-channel interference caused by frequency reuse is a restraining factor as the frequency reuse distances are generally smaller. The effect of different reuse distances, penetration losses, pathloss exponents, and co-channel interference on spectral efficiency is analysed and performance evaluated over a wide range of potential ME locations.