Technical data

Chapter 7 215
CDMA Analyzer
Interpretation of CDMA Tx Analyzer Measurement Results
CDMA Analyzer
A phone moving outward toward the limit of its cell will need to acquire the
adjacent cell in order to hand off. If the time offset of the target cell is too far from
that of the current site, the handoff may not happen.
The dependence of the phone on correct system time limits the physical distance to a
target cell's antenna. Each PN Offset is 52.08 µs; if the propagation delay is too
long, the received PN Offset may be different from the value designated on the Sync
channel. This difference can confuse the phone, causing the handoff to fail.
Another cause of timing error is a bad GPS receiver or timing distribution network
within the base station. To test your base station's GPS and timing distribution
system, you can use the internal GPS receiver to generate an accurate timing
reference for the test set to use while performing base station tests.
Channel Power
When making channel power measurements, make sure you have accounted for the
loss of the test cable and high power attenuator you are using. If you do not know
the loss of your test cable and high power attenuator configuration, perform an
insertion loss measurement and enter the insertion loss as the RF In Loss value. For
more information see “Two Port Insertion Loss” on page 123.
If the channel power is lower than expected, verify you have a good connection to
the RF output of the base station. Also, verify the cable you are using to connect to
the base station is not faulty. A low channel power may also indicate a bad power
amplifier.
Inaccurate channel power (high or low) may indicate an incorrect power setting at
the base station.
Estimated Rho
The CDMA base station standard specifies that Rho must be greater than 0.912.
Typical values for a healthy base station are greater than 0.94.
Rho failures can indicate problems in:
• Compression in linear amplifiers
• Magnitude and phase errors in the IQ modulator
• Phase non-linearity (group delay)
• Spurious signals in the transmission path
• Carrier feedthrough
Because the uncorrelated power appears as interference to the phones, poor Rho
performance will affect the sector's capacity. The added interference can require that