Pn Sequence Generator USING MAT LAB

8/8/2019 Pn Sequence Generator USING MAT LAB

1/13

PN SEQUENCE GENERATOR

USING MAT LAB

BY

S.Dileep

07891A0426


2/13

WHAT IS PN SEQUENCE GENERATOR?

Pseudo random Noise sequence generator is a

circuit which generates pseudo random noise

sequences.

A pseudo- noise sequence is a binary sequence

with a noise like wave form that usually

generated by means of a Linear feedback shift

registers.


3/13

BLOCK DIAGRAM OF LINEAR FEEDBACK SHIFT

REGISTER


4/13

WHAT IS LINEAR FEEDBACK SHIFT

REGISTER?

A Feedback shift register consists of an ordinary shift

register made up of m Flip-Flops .

The flip-flops in the shift register are regulated by a single

timing clock.

At each pulse of the clock, the state of each flip-flop isshifted to the next one i.e. the contents of the register is

shifted right by one position at each clock cycle.

The feedback from the left most register are XOR- ed

together, to give a random sequence.

But this binary sequence is not totally random, because itdoes repeat after many cycles, thats why it is so called as

pseudo random noise sequence generator.


5/13

SHIFT REGISTER

LENGTH:

This is often referred to as the degree, and in general, the

longer the shift register, the longer the duration of the pn

sequence before it repeats.

The combination of taps and their location is often referred

to as a polynomial, and expressed as:

P(x)=1+x^2+x^3

Where the leading 1 represents x^0, which is the output of

the last register, x^2 is the output of register stage 3 and

x^3 the output of XOR.

A maximal sequence for a shift register of length L is

referred as m-sequence, and is defined as:

L=2^m-1.


6/13

PN SEQUENCE


7/13

APPLICATIONS :

These pn sequence generators are widely usedin Cmos testing process as to generate test

patterns.

And also used to generate spreading codes in

CDMA,FDMA and PCM.


8/13

PROPERTIES:

In each period of a maximal length sequence, the number

of 1s is always one more than the number of 0s.This

property is called as the Balance property.

Example:

101000111101001 Among the runs of 1s and of 0s in each period of a

maximal-length sequence, one half the runs of each kind

are of length one, one fourth are of a length two, one-

eighth are of length three, and so on as long as these

fractions represent meaningful numbers of runs. This

property is called the Run property.


9/13

The autocorrelation function of a maximal-length sequence

is periodic and binary value. This property is called ascorrelation property.


10/13

PN sequences have single autocorrelation peak, thisfeature permits the transmission to be

asynchronous.


11/13

ADVANTAGES ANDDISADVANTAGES :

The sequences generated by

an LFSR can be nearly

random with long periods,which aids in making the

spread signal appear noise

like.

Easy of implementation.

Output of lfsr is periodic.

For any given size of LFSR, a

maximum of different unique

m-sequences can be generated

.

Cross correlation properties

are good for more than two

users. Thats why we go forgold sequences.

Advantages: Disadvantages:


12/13


13/13

TTHANKHANKYYOUOU

Pn Sequence Generator USING MAT LAB

Documents

Transcript of Pn Sequence Generator USING MAT LAB