There is fierce competition between Distributed Antenna Systems (DAS) and small cells vendors for coverage and capacity in the $8.5 billion enterprise in-building wireless systems market with each vendor having distinct strengths and weaknesses, according to ABI Research. These systems centralize the baseband function like DAS but use Cloud RAN (CRAN) techniques to distribute signals over dedicated fiber to remote radio heads in the building.
Modern DAS systems challenge small cells by building on their inherent advantages of neutral host, and macrocell parity and adding features such as traffic steering and multiple network convergence (for example Wi-Fi or public safety) on the same in-building backhaul. They also challenge small cells by tackling one of the main drawbacks: cost per sq. foot of installation and OPEX needed for system cooling and operation. However, small cells do not immediately provide a neutral host capability and are complex to configure and virtualize since the baseband, unlike DAS, is distributed in each small cell which must coordinate with its neighbour to mitigate interference. Hybrid systems are a recent development where the best of DAS and small cells merge. ABI Research believes that it is innovations such as these that are laying the groundwork for in-building 5G.
More information on this can be seen in one of their Reports - DAS Rises to the Small Cell Challenge