Pattern Synchronization - Agilent Technologies N4906B Serial BERT User Manual

Pattern Synchronization

Hardware-Generated Patterns
Memory-Based Patterns
Agilent N4906B Serial BERT, User's Guide, October 2005
Pattern Synchronization
The Serial BERT calculates bit error rates by comparing the received
data with the expected data patterns. To do this, it needs to know
where the start of the pattern is located in the data stream.
Introduction to Pattern Synchronization
Pattern synchronization (sync) refers to aligning the incoming data
pattern with the internal reference pattern. This is accomplished in
one of two ways:
For 2^n-1 PRBS patterns, bits from the incoming data pattern "seed"
the error detector's pattern generator, causing it to generate a
precisely aligned internal reference pattern.
For software-generated and user patterns, a 48-bit pattern from the
pattern is used as a detect word. Optimally, this detect word should be
unique within the entire pattern. The error detector searches for this
detect word within the incoming data stream, and uses the point in the
data stream as a reference, and compares all following bits with the
pattern. If the measured BER is better than the synchronization BER,
the error detector is synchronized.
There are thus three possible outcomes for a synchronization:
• Single instance of the detect word in the data stream
Expected
Pattern
Detect Word
48 bits
Incoming
Bit stream
Reference
Point
Detect Word
Correct Sync
48 bits
Detect Word
48 bits
Setting up the Error Detector
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