Approximately 70-80 per cent of mobile traffic comes from inside buildings. It is especially true in urban environments where high data levels are the priority of the mobile users. Only serving macro base station within a few hundred meters of the building will provide appropriate degree of RF signal to enable indoor voice / data services for mobile 3 G network. Just a few buildings fall into that category of real estate. As every indoor mobile phone can be serviced by more than one macro cells (base stations), soft transfer in 3 G network would further increase the traffic load on the network. To provide mobile network networks such as HSPA (High Speed Packet Access) or EVDO (Evolution-Data Optimized) indoor high-speed networks, the only option is an indoor distributed antenna system (DAS). Check more info here.
DAS is used for balanced propagation of the RF signal inside a building with ample power to provide 3 G voice and data services. DAS can be used to isolate the indoor network from the outdoor macro cells that serve to eliminate the soft mobile indoor phone transfer. This would lower the traffic load and increase the 3 G network speed. Indoor DAS can also provide insulation between serving and non-serving outdoor network cells for HSPA high speed data service. This means less co-channel interference in the serving cell of the HSPA and results in higher data rate for the service of HSPA. To conquer the building with an indoor coverage, it is possible to place directional antennas at the edge and corners of the building and point towards the building’s centre. The total indoor area is dominated by the indoor cell, while minimizing leakage to the macro network at the same time.
DAS distributes a single dominant RF signal inside the building by breaking the signal from the base station inside to several indoor antennas to cover the entire building. DAS is classifiable as passive or aggressive. Passive DAS distributes the RF signal through passive components. Coax wire, splitters, terminators, attenuators, circulators, couplers and filters (duplexer, diplexer or triplexer) are such passive elements. Planning DAS includes calculating the maximum loss in the systems from the base station to each antenna and doing the link budget for the particular area covered by each antenna.