R&S AFQ100A Operating Manual page 179

R&S AFQ100A
Interrupt-free measurement
In the case of continuously generated signals that contain whole-number multiples of the PRBS
sequence, the measurement occurs without interruption. Only the data and clock lines of the BERT
interface are used for the measurement. The length of the pseudo random sequence is 2 to the power
of the degree of the polynomial minus 1. For example, PRBS9 has a length of 511 (= 2
digits.
Restart function
The Restart function makes it possible to perform BER measurements with short signals or with signals
that are not continuously generated (and therefore do not contain any whole-number multiples of PRBS
sequences). An external signal at the BERT input halts the measurement and restarts it when the data
sequence begins, and the BER results of the relevant (sub)sequences are integrated.
start of PRBS generation
length of PRBS sequence
user data block
restart signal
Fig. 4-4 The length of the signal is too short for a complete PRBS sequence; PRBS generation is restarted by the Restart
signal when the signal begins anew.
Frames generated by the WinIQSIM2 software contain continuous PRBS data, i.e. the PRBS sequence
is continuously written to the user data fields. Consequently, if the instrument is used as a data source,
a restart is only necessary if (e.g. when using a waveform) the total length of the signal does not equal
a whole-number multiple of a PRBS sequence.
150 bits
a h user data
PRBS9 sequence
Fig. 4-5 TDMA signal generated by the WinIQSIM2 software with user data that contains the PRBS data sequence. The
PRBS sequence is continuously written to the user data fields.
1401.3084.32
restart of PRBS generation
user data block
150 bits
g a h user data
511 bits
Bit Error Rate Measurements - BERT Block
restart of PRBS generation
user data block
150 bits
g a h user data
4.68
9
-1) binary
150 bits
g a h user data g
E-3