WCDMA breathing effect and Coverage - Capacity trade off

In WCDMA, the relation between coverage and capacity referred to as “breathing effect”.  The load of WCDMA network has a greater effect on it's coverage. The load of WCDMA network impacts on own system in two ways, depending on which link (uplink and downlink) has been taken into account.  For uplink as more user added to the network, higher interference or noise will be detected at the Node B end.  This effect called rise over thermal. That’s why UE need to transmit at higher power to overcome this effect.

Rise Over Thermal (dB)

When the loading of the system increases the Ec/No degrades, but the RSCP remains constant. Degrading Ec/No is an indication of increased other cell interference which demands the increase of downlink traffic power. Power being a limited resource, the requirement of higher transmit power may not be available, thus the coverage not being met in loaded condition; this scenarios called “coverage and capacity trade-off” for the downlink in a WCDMA systems.

Coverage and Capacity Trade Off