Chapter 4
105
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. The absolute power at the
specified offset is also provided in dBm, or dBm/Hz.
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 measurement analyzes the total power levels within the defined
carrier bandwidth and at given frequency offsets on both sides of the
carrier frequency.
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.
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. 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
(Power Spectral Density reference) is selected, the results
are displayed as relative power in dB, and as absolute power in
dBm/Hz.
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