Bit Error Rate (BER)
WHY?
Bit error rate is a measure of the RF sensitivity of the
mobile in a digital channel. BER corresponds to an
"analog" sensitivity figure refered to a defined sig-
nal/noise ratio.
Requirement
Make the general test preparations.
The mobile must be in test mode.
HOW?
Press
{BER}
in the basic test mask. This calls up the RX
BER test mask, the entries from the basic test mask
being transfered into the entry and scroll fields of the
RX BER mask.
Change the entries as necessary.
Put the mobile into test mode and enter on it the same
transmission parameters shown in the RX BER mask
(channel number, slot number, rate, DVCC).
Enter in the Number field how often the BER test is to
be performed (number of bursts evaluated). The higher
the figure, the more dependable is the test result.
Start the test with
{RUN}
and look for the test result. You
can change RF level during a test (range of interest:
approx. –105 to –120 dBm).
End the test with
{STOP}
and repeat it if necessary with
different transmission parameters.
{RETURN} takes you back to the basic test mask.
Test Results
D
To measure BER, test set sends bit patterns. Mobile receives
them and sends them back unaltered. Test set calculates BER
by comparing transmitted bit patterns to those returned by
mobile. Five test bit patterns are available, so these are
repeated from sixth measurement.
RESULt6 BER Test result is BER averaged over number of bursts evaluated
(Number field). According to IS-55 standard, BER must
not exceed 3% at RF level of –110 dBm. Results display is
suppressed for BER figures of >40%; it does not appear again
until BER is <10% (hysteresis).
Fig. 10.25: RX BER test mask. Bit error rate
is ratio of number of errored bits received to
total number of bits received during period of
observation. In this example mobile has BER
of > 5% at -114 dBm receive level. ATT again
draws your attention to compensation of
cable attenuation in test setup (see "General
Preparations").
IS-136 MS Bit Error Rate (BER)
10-42
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