Impact of Pilot Pollution on SHO Performance

Soft handovers are an essential part of a WCDMA network functionality. Taking full advantage of SHOs requires careful setting of parameters. In addition, state of the network affects the performance of SHO algorithm. Pilot pollution, i.e., too many hearable pilots, can make it difficult for SHO algorithm to perform properly, and DL transmit power as well as signalling capacity can be wasted for poor decisions and unnecessary active set updates. In addition to simulations, field measurements have been carried out in a pre-commercial WCDMA network, where also the effect of different downtilting scenarios has been studied. The behavior of SHO algorithm has been evaluated in pollution free and pilot polluted areas. The target of the paper is to show how pilot pollution disturbs a UE from making reasonable proposals for active set updates, how pilot pollution problem can be reduced, and network performance improved by increasing antenna downtilt.

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