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Bit Error Rate DemystifiedPresented by

Sunrise Telecom Broadband …a step ahead

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Introduction

Bit Error Rate (BER) is an important concept to understand in any digital transmission system since it is a major indicator of the health of the system.

As data is transmitted some of the bits may not be received correctly. The more bits that are incorrect, the more the signal will be affected.

Its important to know what portion of the bits are in error so you can determine how much margin the system has before failure.

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What is BER?

BER is defined as the ratio of the number of wrong bits over the number of total bits.

Sent Bits 1101101101

Received Bits 1100101101

BER = # of Wrong Bits

# of Total Bits=

1

10= 0.1

error

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What is BER?

BER is normally displayed in Scientific Notation. The more negative the exponent, the better the BER. Better than 1.0E-6 is needed after the FEC for the system to

operate.

Decimal Scientific Notation1 1.0E+00

0.1 1.0E-010.01 1.0E-020.001 1.0E-03

0.0001 1.0E-040.00001 1.0E-05

0.000001 1.0E-060.0000001 1.0E-07

0.00000001 1.0E-080.000000001 1.0E-09

Lower and

Better BER

Decimal Scientific Notation0.00001 1.0E-050.000009 9.0E-060.000008 8.0E-060.000007 7.0E-060.000006 6.0E-060.000005 5.0E-060.000004 4.0E-060.000003 3.0E-060.000002 2.0E-060.000001 1.0E-06

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Noise and Intermittents

Errors caused by noise or intermittent causes can have the same BER, but very different effects.

Errors that are spread out are due to noise problems Errors that are grouped are due to intermittent problems such

as ingress or loose connectors.

Spaced Errors 1101101011010011100

Burst Errors 1111101011101101101

This Example Shows the Same Error Rate But the Burst Errors are More

Difficult to Correct

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Pre and Post FEC BER

The Forward Error Correction (FEC) can correct errors up to a point, after which errors are passed on to the decoding circuitry.

It’s important to know the Pre and Post FEC BER to know how hard the FEC is working to correct errors. The harder it’s working, the closer the system is to failure.

Pre FEC BER (Before Correction)

Post FEC BER (After Correction)

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Error Seconds

To get an idea of whether the errors are caused by noise or intermittent problems, errors can be measured over a one second period.

If no errors are seen in a one second period, this is known as a Error Free Second.

If some errors are received in a one second period that can't be handle by the FEC and seen by the end-user, this is known as a Error Second.

If errors in a one second period that the FEC can't handle exceed  a set threshold, this is known as a Severely Errored Second.

A Severely Errored Second has a BER within that second of 1E-6 or worse at the output of the FEC.

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Error Second and Severely Errored Second Display

Error Seconds and Severely Errored Seconds Over the

Indicated Elapsed Time

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Conclusions

BER is a very important measurement for determining the health of digital systems.

Determining the PRE and POST FEC BER can tell you how hard the FEC is working giving an indication of system margin.

Error seconds or severely errored seconds can indicate intermittent errors.

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