Link Budget in WCDMA / UMTS

Link budget planning is part of the network planning process, which helps to dimension the required coverage, capacity and quality of service requirement in the network. UMTS WCDMA macro cell coverage is uplink limited, because mobiles power level is limited to (voice terminal 125mW). Downlink direction limits the available capacity of the cell, as BTS transmission power (typically 20-40W) has to be divided to all users. In a network environment both coverage and capacity are interlinked by interference. So by improving one side of the equation would decrease the other side. System is loosely balanced by design. The object of the link budget design is to calculate maximum cell size under given criteria:

Type of service (data type and speed)
Type of environment (terrain, building penetration)
Behavior and type of mobile (speed, max power level)
System configuration (BTS antennas, BTS power, cable losses, handover gain)
Required coverage probability