4.6 Other Hybrid DAS Solutions
Often it can be effective to combine different type of DAS designs in a project, using passive DAS in one part of the building close to the base station, and active DAS in other more distant areas.
It is also possible to combine DAS solutions with macro sectors; for example an outdoor macro site might also be connected to an indoor DAS in the same building, for example where the outdoor sites are located on the roof.
The combination of different concepts will often enable the radio planner to design the DAS as economically as possible, and at the same time maximize performance. Once again it is all about using more tools in the toolbox; do not always rely on only one type.
4.6.1 In-line BDA Solution
It is possible to add an in-line bidirectional amplifier (BDA) to a passive DAS in order to boost the performance of both the uplink and downlink on distant parts of the DAS, as shown in Figure 4.19. However it is a fact that all passive attenuation prior to the BDA, between the BDA and antenna, will seriously impact the noise figure on the system, limiting the uplink performance, which is especially a concern for 3G/UMTS/HSUPA indoor designs. Preferably the BDA should be installed as close as possible to the antenna. Refer to Section 7.2 for more details on how to optimize the BDA design.
As the name suggests, the BDA is a two-way amplifier ...