bert presentation

8/2/2019 BERT Presentation

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Prepared By,

Darshita Patel.(08BECR029)

Kosha Mistry. (08BECR020)


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INTRODUCTION

Whatis Bit Error Rate? Why bit error rate is used?

Noise and BER Eb/N0 and BER

Graph of BER Vs Eb/N0

BER Measurement

Applications of Bit Error Rate Measuring Instrument


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What is Bit Error Rate?

In digital transmission, BER is the percentage of bits

with errors divided by the total number of bits that

have been transmitted, received or processed over agiven time period.

The rate is typically expressed as 10 to the negative

power.


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Why bit error rate is used?

In digital communication,

when a signal passes through channel or link, it is

corrupted by noise. And errors are produced in it. Tofind and count the errors, we use Bit Error Rate

Measuring Instrument.


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Its definition is simply:

BER = Errors / Total Number of Bits


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Graph of BER Vs Eb

/N0


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BER Measurement

While the basic concept of BER measurement is simple,

send a data stream through the system and compare theoutput to the inputits execution is not trivial. Over an

infinitely long period of time, we can assume that a Data

transmission is a random process


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Block Diagram of Bit Error Rate Test Set

PN Generator Modulator RFTransmitterRF receiver Demodulator Error detector

ChannelNoise


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Why we use PN sequence? Pseudorandom Sequences are Used For Testing

The data generator creates a pseudorandom data

sequence as a test pattern.

Pseudorandom sequences are useful because theysimulate signals with a wide-range of frequency

components and because they are easy to implement

using shift-registers and logic gates. A simple four-stage

pseudo-random sequence generator is shown below. Toinitiate sequence generation, the four stages must be

prepared with any value other than '0000'. Seeding the

shift-register with all zeroes causes the circuit to always

generate zero bits.


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Pseudorandom data sequences are obviously not truly random. A bit error rate

tester could not use truly random data because it wouldn't know what data to compare

with. Instead, pseudorandom sequences are used, which have many of the sameproperties as truly random data, but repeat after a known quantity of bits. The properties

of a maximal length pseudorandom data sequence are listed.

Balance Property - The number of 1's and the number of 0's differ by at most one.

Run Property - Among the runs of 1's and 0's in the period, approximately 1/2 the runs

of each type are of length one, 1/4 are of length 2, 1/8 are of length 3, and so on.

Correlation Property - If the period of the sequence is compared term by term withany cyclic shift of itself, the number of agreements differs from the number of

disagreements by not more than one count.

Maximal Length - When implementing the data generator using an N-stage linear

feedback shift register, the number of bits in one period is equal to 2N-1. This also

means that every possible n-bit value is generated, except the n-zeroes case. A

maximal length pseudorandom sequence will have at most n-1 zeroes in a row, and

n ones in a row .


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Generating PN sequence


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1 1 1 1

0 1 1 1


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Details of Error detector

Ex-OR comparator Counter DisplayData with error

SynchronizedPN generator


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How to synchronize PN generator?


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Applications of Bit Error Rate

Measuring Instrument Satellite communication

different modulation techniques

wireless communication

Telecommunication

Radio communications systems


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