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122 Chapter 4
Making Measurements
Making the Adjacent Channel Power (ACP) Measurement
Making the Adjacent Channel Power (ACP)
Measurement
Purpose
Adjacent Channel Power(ACP) is the power contained in a specified
frequency channel bandwidth relative to the total carrier power. It may
also be expressed as a ratio of power spectral densities between the
carrier and the specified offset frequency band.
As a composite measurement of out-of-channel emissions, ACP
combines both in-band and out-of-band specifications to provide useful
figures-of-merit for spectral regrowth and emissions produced by
components and circuit blocks without the rigor of performing a full
spectrum emissions mask measurement.
To maintain a quality call by avoiding channel interference, it is
important to measure and reduce any adjacent channel leakage power
transmitted from a mobile phone. The characteristics of adjacent
channel leakage power are mainly determined by the transmitter
design, particularly the low-pass filter.
Measurement Method
This ACP measurement analyzes the total power levels within the
defined carrier bandwidth and at given frequency offsets on both sides
of the carrier frequency.This measurement requires the user to specify
measurement bandwidths of the carrier channel and each of the offset
frequency pairs up to 5. Each pair may be defined with unique
measurement bandwidths.
It uses an integration bandwidth (IBW) method that performs a time
domain data acquisition and applies FFT to get a frequency domain
trace. In this process, the channel integration bandwidth is analyzed
using the automatically defined resolution bandwidth (RBW), which is
much narrower than the channel bandwidth. The measurement
computes an average power of the channel over a specified number of
data acquisitions, automatically compensating for resolution bandwidth
and noise bandwidth.
If
Total Pwr Ref is selected as the measurement type, the results are
displayed as relative power in dBc and as absolute power in dBm. If
PSD Ref (Power Spectral Density Reference) is selected, the results are
displayed as relative power in dB, and as absolute power in dBm/Hz.