What actually is the advantage of upsampling ?

[zeerum]

matlab question

hi
we were given a code about simulation of bpsk. in that code signal was upsampled. and then during pulse shaping by root raised cosine filter, it was multiplied by squareroot of upsampling factor as follows


x=round(rand(1,16000)); %generating random data
xk=(-1).^x; %generating BPSK symbols

x_input=upsample(xk,100);
b=sqrt(100)*firrcos(255,0.01,1,2,'rolloff','sqrt');



i want to know what actually is the advantage of upsampling( inserting extra zeroes between samples) and why was firrcos multiplied by sqrt(100)?

please explain on basic level as i am beginner to all of this.
thx

 

[mahdithdn]

matlab question

Hi,

1- Pulse shaping filter reduce side lob level and interference to other channel frequencies, but we have two choice for implementing Raise Cosine filter, (a) using analog filter after D/C converter, or (b) using upsampling for practical possibility of digital implementation.

2- sqrt(100) is because after upsampling signal power decrease 100 times and for canceling this effect we should multiple output by sqrt(100).

Regards

 

[zeerum]

Re: matlab question

thnx mahdithdn
that was great help
see these are conceptual querries which hardly get answered during lectures
so can u refer any book or material that would help me?

 

[mahdithdn]

matlab question

Hi zeerum

about upsampling you can refer to Discrete-Time Signal Processing by Allen Oppenheim. but I'm not able to suggest any book about discrete implementation of digital modulation, maybe the best advise is using Matlab communication toolbox and studying well-known book Digital Communication by Praokis (or a simpler book by Haykin).

Regards