User's Manual Part 2

Tech-X Flex
®
(NG2) Tech-X Flex User Guide - Firmware v06.50
8-17
Intro
Overview
Wi-Fi
Ethernet
System
IP/Video
MoCA
RF
Specs
Pre-FEC
Post-FEC
(Pre- and post-
FEC BER - Bit
error ratio)
The ratio of errored bits to total bits, before and after the unit
applies forward error correction (FEC) with Viterbi and Reed-
Solomon algorithms. The two measurements are intended to
show the signal as it exists on the wire and the signal after a
typical receiver applies FEC, the latter of which more
accurately represents the signal that will be decoded and
processed.
Because BER is calculated from sampled bits, the precision
increases with the sample size. Therefore, tests that run
repeated measurements can keep a cumulative data set and
continue to increase the precision of the BER calculation.
BER measurements may be presented in scientific notation.
For example, a measurement of 1.2e-5 equals 1.2 x 10
-5
or
0.000012, which is equivalent to 12 errored bits per 1,000,000
(1 million) transmitted.
FEC operates using redundant information that is intentionally
transmitted with a digital signal that provides two primary
functions:
• A means of determining when bit errors occur, similar to a
checksum
• A limited ability to reconstruct the original bitstream in the
event of bit errors
Ideally, the post-FEC ratio should be very small, such as zero
to one error per billion bits transmitted (1.0e-9). Small
increases in bit errors can have a rapidly deteriorating effect on
digital video quality, depending on where the errors occur.
Important note about BER and configured thresholds: The
“lower” a BER threshold, the longer it takes the unit to
accumulate enough sample data to accurately display a BER
calculation and indicate threshold violations. For example, if a
BER threshold is set to 1.0e-9, the unit technically requires a
sample set of at least a billion bits to properly detect a
threshold violation and therefore may introduce significant
delay with the presentation of the result.
Measurement Description
Preliminary issue - Limited distribution only!