Indoor Wireless Communications

9RF Equipment and Distribution Systems

When designing an indoor radio system, one of the most important parameters to consider is to provide enough coverage in the building, as part of the requirements stated in Chapter 3. This is applicable to UMTS and LTE systems as well, although the design rules may change. This signal needs to be distributed across the building in the most suitable, efficient and economical way, ensuring the highest quality-of-service for all users.

In the early days of cellular radio, coverage inside a building used to be achieved by placing a macrocellular base station sufficiently close to it and downtilting the antennas to rely on outdoor-to-indoor penetration of the signal. This approach may still be applicable for small buildings in rural and suburban areas, and this is of course the easiest way to achieve in-building coverage. However, this method is limited only to buildings with sufficient LOS conditions with the serving cell, which do not attenuate the signal excessively. The RF signal is attenuated as it penetrates through the building and is affected by constructive and destructive rays adding together, or multipath propagation. Building penetration losses are often sufficiently large and thus produce unacceptable coverage in many areas. As well as providing poor coverage in many situations, this approach also imposes a further constraint on the amount of channels that can be allocated to the building – capacity from the external cell is taken ...