Technical data

Chapter 8 257
CDMA Over Air
Interpretation of CDMA Over Air Measurement Results
CDMA Over Air
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.
The Time Offset should be within the following limits:
• Less than +/- 10 µs if the receiving antenna is next to the base station, or
• Less than +/- 10 µs, plus 1 µs for every 300 meters (1000 feet) you are away
from the base station.
If the measured value of the Delay falls outside of the expected range, consider the
following problems:
• The GPS receiver is not working correctly, and the base station timing is
incorrect.
• The base station main oscillator is not working correctly, and the base station
timing is incorrect.
• The GPS receiver is not locked to the GPS satellites.
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. When measuring Rho
over-the-air, these values can only be achieved under very good conditions for
multipath power and pilot dominance. For example, a Multipath Power of < 0.1 dB
and a Pilot Dominance of > 15 dB is required to measure Rho of 0.912. For more on
the affects of pilot dominance and multipath power on Estimated Rho see “Criteria
for Making Valid CDMA Over Air Measurements” on page 221.
Verify that the Estimated Rho meets the following criteria:
• Greater than 0.8 if the Multipath Power and Pilot Dominance properties remain
at the defaults of 0.4 dB and 10 dB, respectively, or
• Greater than 0.912 if you have set the Multipath Power and Pilot Dominance
properties to 0.1 dB and 15 dB, respectively.