8/6/2019 Practica N2 PAM

http://slidepdf.com/reader/full/practica-n2-pam 1/4

UCSP - Facultad de Ingeniería – Ing. Telecomunicaciones 2011-1

Comunicaciones Digitales

PRIMERA UNIDAD

2Guía de Prácticas

 Pulse Amplitude Modulation (PAM)

Grupo: ___________ Fecha:________________Horario:____________ 

Alumno(s):

Nota:

 ___________________________________________________ 

 ___________________________________________________ 

1. Objetivos

• Entender la formación de pulso utilizando filtros formadores.

• Delimitación del ancho de banda.

• Eliminación de ruido utilizando filtros formadores.

2. Contenido teórico

Un sistema de comunicaciones digitales está compuesto básicamente por los elementos

mostrados en la Fig. 1.

1

8/6/2019 Practica N2 PAM

http://slidepdf.com/reader/full/practica-n2-pam 2/4

UCSP - Facultad de Ingeniería – Ing. Telecomunicaciones 2011-1

Comunicaciones Digitales

Figura 1. Esquema de bloques un sistema transmisor digital.

Como se muestra, el canal es un elemento infaltable que sirve para poder enviar las formas de

onda hacia desde el receptor hacia el transmisor. Sin embargo, este introduce distorsiones a la

señal y así producen cambios que se traducen en el receptor como errores (bits que cambian

de valor).

1. Waveform simulation

a. Draw a plot of BER vs. Eb/N0

 – EbNodB = 0:8

 – Compare with ideal

 – Plot using semilogy

 – NumErr =10, blocks of data bits of length 1e4

 – Suggested structure:

Define variables

for number of EbNo

define variables count errors and trx. bitswhile ne<NumErr 

transmit and receive a block of bits count errors and num of bits (save or 

accumulate)end

2. Generate 20 symbols BPSK 

 – Define a raised cosine pulse with 4 samples per symbol and 0.5 of roll off:

rcosine.

 – Use function upsample to fill with 3 zeros between symbols.

 – Use functions filter and conv to obtain the waveform (check the differences)

 – Obtain the symbols using downsample

2

8/6/2019 Practica N2 PAM

http://slidepdf.com/reader/full/practica-n2-pam 3/4

UCSP - Facultad de Ingeniería – Ing. Telecomunicaciones 2011-1

Comunicaciones Digitales

• Use plot(symbols,'o') to see the symbols

• Where are the symbols? Have they suffered any delay?

La Convolucion atrasa la señal

3. Generate 20 symbols using the square root raised cosine

• Use eyediagram and see the ISI in transmission

• Extract the symbols with downsample and use plot(symbols,'o') to see the ISI

 – Pass this signal with its adapted filter ???????• Use eyediagram and see now there is no ISI

 – Obtain the symbols using downsample

• Use plot(symbols,'o') to see the symbols• Calculate the delay, how many trailing zeros are needed to avoid losing any symbol

when filter is used?

4. Why adapted filters are used?

 – Generate 1000 BPSK symbols with raised cosine and with square root raised cosine.

 – Generate noise with a SNR = 3 dB for each

• Both signals have different powers??????? – Obtain symbols from the raised cosine plus noise signal, ???????

• Discard transient symbols at beginning and end• Obtain bits and calculate the number of errors

 – Pass the root raised cosine signal plus noise through the adapted filter, obtain

symbols, ???????• Discard transient symbols at beginning and end.

• Obtain bits and calculate the number of errors

5. Spectrum of signals

 – Represent the spectrum of the raised cosine pulse shaped signal generated before.hs=spectrum.welch;

psd(hs,signal) – Check if the signal is bandlimited as expected

Draw a BER plot for BPSK with pulse shaping and adapted filter 

 – EbNodB = 0:8; Ms = 4 (samples per symbol)

IV. Equipos y materiales

Laboratorio: Señales y Datos

3

8/6/2019 Practica N2 PAM

http://slidepdf.com/reader/full/practica-n2-pam 4/4

UCSP - Facultad de Ingeniería – Ing. Telecomunicaciones 2011-1

Comunicaciones Digitales

Equipos y dispositivos:

•

PC.

Software:

• MATLAB

Materiales y fungibles:

V. Actividades

Desarrollar en MATLAB los códigos necesarios para llevar a cabo esta práctica.

Resultados:

Mostrar los resultados obtenidos

 

clear all

close all

clc

for i=0:8;

 b=randint(1,10^2);

M=b*2-1;

Eb_N0(i+1)=10^(i/10);

VarN=(1*4)/(2*Eb_N0(i+1)*1);

 N=sqrt(VarN)*randn(1,10^2);

R=b+N;

dmap=(R>=0);s=sum(abs(dmap-b));

BER(i+1)=s/(10^2);

end

n=0:8;

stem(n,BER)

4