BBU725U_Exp2

EXPERIMENT TWO:DIRECT SEQUENCE SPREAD

SPECTRUM TECHNIQUES

Abstract.This experiment is designed to learn the fundamentals of the direct

sequence spread spectrum and code division multiple address techniques.

1.Details of the experiment

A direct sequence spread spectrum modulator and demodulator is shown in Fig.(1),where a pseudorandom sequence generator generates the spreading se-quence.A m-sequence generator is usually adopted as the pseudorandom sequence

'

)(t Figure 1.Direct sequence spread spectrum system

generator,which is a linear feedback shift register’s (LFSR)output.A polynomial p (x )is used to describe the connections of the linear feedback shift registers.For example,the polynomial p (x )= n k =0c k x k is corresponding to the LFSR of the Fig.(2),where c k =1denotes a connection.

In this experiment,the following items need to be done.

(1)Write a program to generate the m sequence with p (x )=1+x 5+x 7+x 8+

x 9+x 13+x 15.

(2)Draw the autocorrelation of the generated m-sequence.

(3)Build up a simulation system of the Fig.(1)with the data rate 1bit/s,

spreading gain 64and the carrier frequency 128Hz.

Date :October 29,2008.

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2EXPERIMENTS OF WIRELESS NETWORK 310c n Figure 2.Linear feedback shift register