UMTS is an advanced system. As it is noise- and power-limited, enhancement of the UL and DL performance can be obtained by the use of UL and DL remote amplifiers to overcome the passive losses from the base station (node B) to the antenna. This is the basic principle of an active DAS, which functions as distributed amplifiers in the system, offsetting the DL power and to some extend loading the base station with noise power on the uplink.
10.1.1 UMTS Radio Performance is All About Noise and Power Control
It is a fact that, in order to have optimum performance on a UMTS system, we need to insure:
- Strict power control: all mobiles use the same UL frequency, so all mobiles have to be controlled so that the received signal strength from them on the UL of the node B is kept at the same receive level (see Section 2.4.5). The offset of the node B DL power caused by a BDA, TMA or active DAS has to be considered in the node B setting.
- Noise load is controlled in the system: node B will measure the total UL noise (traffic) continuously, and use that measurement for admission control, to make sure that the overall system noise increase on the UL is kept below the desired threshold. The added UL noise from the active DAS, BDA or remote LNA has to be considered in the node B evaluation of noise/traffic increase.
- Delay of the DAS (synchronization window): delay in the external amplifier system has to be incorporated in the timing and cell size.
10.1.2 UMTS RF Parameter Reference ...