Technical data

Chapter 3 109
1xEV-DO Analyzer and Over Air Test
Interpretation of 1xEV-DO Tx and Over Air Analyzer Measurement
Results
1xEV-DO Analyzer and Over Air
Test
Interpretation of 1xEV-DO Tx and Over Air Analyzer
Measurement Results
This section contains expected result values and possible causes of error if the
expected results are not met.
Frequency Error
The standards specify very tight Frequency Error performance. In the PCS bands,
the 0.05 parts-per-million specification translates to only 99 Hz at a carrier
frequency of 1980 MHz or 40 Hz at 850 MHz cellular frequencies. Frequency Error
shows up as uncorrelated power that adds to the noise floor or shows up in other
Walsh codes.
If a particular site loses its reference to GPS time, its reference signals will begin to
drift over time. Access Terminals already using the site can remain on the air
because they derive their timing from the signals transmitted by the access network.
However, access terminals using other sites/sectors may be prevented from using
the site because they are confused by the error in frequency. This creates what is
known as the “island cell effect”. By itself, the cell is still functional. To the rest of
the system, it's inaccessible.
This island cell effect can be caused by a failure in the site's GPS receiver and
timebase distribution network. Using the test set's Internal GPS receiver provides an
independent time reference that will allow you to determine if this cell site is out of
sync with the rest of the network.
PN Offset
Verify that the PN Offset is correct. If you are in Manual mode, the PN Offset will
display the value you entered. Make sure the Time Offset is small (less than 3 µs). If
the Time Offset is greater than expected, see the section on Time Offset below. If
you are in Auto mode, the test set will tune to the PN Offset with the smallest
amount of Time Offset. If an incorrect PN Offset is displayed, the Time Offset will
likely be very small.
Time Offset
Time Offset is a measure of the time of the arrival of the pilot signal from the access
network with respect to GPS time. It is expressed in microseconds.
The 1xEV-DO standards specify a maximum time offset of 10 µs. Generally 5 µs is
a recommended maximum, although many access network manufacturers specify