Technical data

216 Chapter 7
CDMA Analyzer
Interpretation of CDMA Tx Analyzer Measurement Results
CDMA Analyzer
the signal on traffic channels be raised to overcome the interference. This may, in
turn, be seen as further interference. At some point, the site will have to shed calls in
order to supply the remaining calls with enough signal versus the interference in the
system.
Carrier Feedthrough
A good carrier feedthrough level is less than -25 dB. The IS-97 standard does not
specify carrier feedthrough; however, this measurement provides an additional tool
to troubleshoot the base station's transmitter.
In the frequency domain, carrier feedthrough can show up as an uncorrelated energy
spike that can be seen on the spectrum analyzer by closely spanning into the top of
the CDMA signal. The effects of carrier feedthrough can also show up as higher
noise levels on the Code Domain Power screen. The inactive Walsh codes will be
pushing the -27 dB specification for noise. Carrier feedthrough can be caused by the
lack of isolation across the mixer and cavity of the transmitter's I/Q modulator.
Shielding can help reduce carrier feedthrough.
Noise Floor
A good noise floor value is between -40 dB and -45 dB for modern base stations. If
the noise floor is above these values (for example, -20 dB), the modulator may be
the source of the added noise. Another possibility is a problem with the base
station's channel card. The channel card generates the individual Walsh codes.
Pilot Power
If the measured value of pilot power is more than +/-0.5 dB different from the
intended setting, it may indicate the following:
• There has been a change made to the digital gain setting of the pilot channel.
• The base station power amplifier has a problem.
Delta Page Power
If the measured value of Delta Page Power is more than +/-0.5 dB different from the
intended setting, it may indicate that the digital gain setting for the Paging Channel
has been changed.
Delta Sync Power
If the measured value of Delta Sync Power is more than +/- 0.5 dB different from
the intended setting, it may indicate that the digital gain setting for the sync channel
has been changed.