Power Control

Power control is a major enhancement of CDMA2000 over IS-95, which
enables higher data rates. The primary power control enhancement is with
the fast-forward link power control.
As discovered through practical implementation issues, CDMA systems
are interference-limited, and reducing the interference results in an
improvement in system capacity.
Enabling better power control of both the forward and reverse links has
several advantages:
■ System capacity is enhanced or optimized.
■ Mobile battery life is extended.
■ Radio path impairments are properly or better compensated for.
■ Quality of Service (QoS) at various bit rates can be maintained.
Obviously, with any wireless system that is interference-limited, it is
important to ensure that all transmitters, whether mobile or located at a
base station, transmit at the lowest power level while maintaining a good
communication link.
To achieve this, CDMA2000 utilizes fast-response, closed-loop power control
on the reverse link. In summary, the BTS measures the reverse link from
the mobile and sends power control commands to increase or decrease the
mobile’s power level, which is similar to IS-95. It is important to note that the
mobile can also operate autonomously and make power corrections based on
the Frame Error (Erasure) Rate (FER) of the forward link. From that, it
infers what it needs to do for the reverse link in terms of power control.
Also, a refinement to the closed-loop power control is located on the
reverse link and that is where the base station performs an outer-loop
power control, which is a refinement process for the inner power control
process. Specifically, if the frame received from the mobile arrives without
error, the base station instructs the mobile to power down, while on the
other side if the frame arrives in error, the mobile is instructed to power up.
With CDMA2000, the use of power control on the forward channel is possible
with the introduction of the reverse pilot channel. The reverse pilot
channel for power control was introduced to help reduce the interference
caused by forward energy. Effectively, the mobile measures the received
power and compares it against a threshold that the mobile then feeds back
to the base station. Upon receipt of the power information, the mobile is
then instructed to power up or power down.

In addition, as with the reverse power link, an outer loop power control
process dynamically adjusts the target Energy per bit per Noise Ratio
(Eb/No). This is done by measuring the FER with a target FER, and if the
FER is greater than the target, it is instructed to power up. If it is below the
target FER, it is instructed to power down.