5.8 Co-existence Issues for GSM/UMTS
When deploying different radio systems and frequency bands using the same DAS for distribution, there are concerns that need special attention. You need to make sure that one system does not cause IM problems that will degrade the performance on its own or on other bands.
The problem rises exponentially with the power you feed to the DAS. The more power, the bigger the issue, mainly due to PIM (see Sections 4.3 and 5.7.3).
5.8.1 Spurious Emissions
A major source of co-existence problems is spurious emissions from the GSM transmitters (as shown in Figure 5.34). Therefore it is highly recommended always to use high-quality pass band filters on all transmitters, in a multioperator or multisystem DAS solution, when combining GSM and UMTS. Those filters will normally be a part of the base station, the combiner, but check the specifications of the base station to be sure.
Spurious emissions from GSM are restricted in the UL UMTS band (1920–1980 MHz) to a maximum measured in 100 kHz bandwidth (equivalent to in a 3.84 MHz channel). Any multioperator or multisystem DAS should be designed accordingly, in ...