We wish to increase system capacity by maximizing the number of simultaneous
users we can accommodate in the WCDMA system. If each UE transmit power is adjusted so that the
SIR level at the NodeB is at minimal acceptable level (i.e., QoS), then capacity can be increased.
We will discuss three forms of power control, namely,
Open loop
Closed loop inner
Closed loop outer
The above forms of power control will be discussed with the uplink and downlink frame timing relationship
shown in Fig. 7.87. The uplink is transmitted To 1024 chips behind the downlink time slot.
3G WIDEBAND CDMA 413
FIGURE 7.87 Uplink and downlink time slot relationship with power control timing emphasis.
Time Slot
Measure
SIR
TPC
Downlink
Uplink
To
Time Slot Time Slot
Time Slot Time Slot Time Slot
The basic operations consist of measuring the received SIR and comparing this filtered value to a
target SIRTarget. The outcome of the comparison will be used to generate TPC commands to be inserted
into the transmit bit stream.
The first form of power control is called open loop. Here the measured received signal power from
the NodeB is used to determine the transmit power of the UE. In an effort to help the UE determine
a reliable initial transmit power, an equation is used by the UE.
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