HP 83206A, User Manual

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S:\HP83206A\USRGUIDE\MANUAL\meas.fm
Chapter 4, Making Measurements
WER (DTC or DCCH)
How the Test Set
measures WER
WER is measured in the DIGITAL MEASUREMENT screen.
When the Test Set is in Active state (the Active annunciator is on), the Test Set is
emulating a base station, but is not communicating with a mobile.
Selecting Dig Meas while in Active state signals the Test Set to bring up a traffic
channel. The data is then transmitted and received over that channel.
The mobile must be in loopback mode. For WER, the mobile demodulates the
data, convolutionally decodes it, corrects errors, and then re-transmits the data.
(This is different from loopback BER, where the mobile demodulates the data
then immediately retransmits it without performing any error correction.)
A word in TDMA is anything that has a CRC calculated on it, such as a speech
block, a FACCH, or a SACCH message. Speech and FACCH words are both
interleaved over two timeslots. SACCH words are spread over 12 timeslots. The
Test Set assembles blocks of data and computes the CRC which is sent to the
mobile. The mobile loops the data back to the Test Set after convolutional
decoding and error correction. The Test Set checks to see if the received CRC
matches the CRC that was sent. If the CRCs do not match, the whole word is
considered an error.
DCCH WER is measured differently than DTC WER. For DCCH WER, the
mobile reads the DCCH bursts, including the CRC and the shared channel
feedback (SCF) in the DCCH data stream. Then, instead of looping back all the
DCCH data, the mobile sends back the CRC and SCF to the Test Set. The Test Set
checks to see if the CRC and SCF match what was sent.