# OpenStax_CNX

You are here: Home » Content » Digital Transmitter: Frequency Shift Keying Prelab Exercise

## Navigation

### Recently Viewed

This feature requires Javascript to be enabled.

# Digital Transmitter: Frequency Shift Keying Prelab Exercise

Module by: Matthew Berry. E-mail the author

Summary: Students fill in missing lines of code to create a Matlab simulation of a four-symbol frequency shift keying (FSK) transmitter. Students are encouraged to change the symbol period and observe the change in the transmitted signal's spectrum.

## Prelab: Matlab Preparation

We have made considerable use of Matlab in previous labs to design filters and determine frequency responses of systems. Matlab is also very useful as a simulation tool.

Use the following Matlab code skeleton to simulate your system and fill in the incomplete portions. Note that the code is not complete and will not execute properly as written. How does the spectrum of the transmitted signal change with T symb T symb ?



1    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
2    % Matlab code skeleton for Digital Transmitter
3
4    close all;clear;
5
6    % Generate random bits
7    bits_per_symbol=2;
8    num_symbols=64;
9    numbits=bits_per_symbol*num_symbols;
10    bits=rand(1,numbits)>0.5;
11
12    Tsymb=32;           % samples per symbol
13
14
15    % These are the 4 frequencies to choose from
16    % Note that 32 samples per symbol does not correspond to
17    % an integer number of periods at these frequencies
18    omega1 =  9*pi/32;
19    omega2 = 13*pi/32;
20    omega3 = 17*pi/32;
21    omega4 = 21*pi/32;
22
23
24    %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
25    % Transmitter section
26
27    % Initialize transmit sequence
28    index=1;			% Initialize bit index
29    n=1;				% Initialize sample index
30    phi=0;				% Initialize phase offset
31
32    % Generate 64 32-sample symbols
33    while (n<=num_symbols*Tsymb)
34
35      if (bits(index:index+1) == [0 0])
36         sig(n:n+Tsymb-1) = sin(omega1*[0:Tsymb-1]+phi);
37         phi = omega1*Tsymb+phi;	% Calculate phase offset for next symbol
38         phi = mod(phi, 2*pi);	% Restrict phi to [0,2*pi)
39
40     % -----------> Insert code here <-------------%
41
42      end % end if-else statements
43
44      index=index+2; % increment bit counter so we look at next 2 bits
45
46      n=n+Tsymb;
47    end   % end while
48
49
50    % Show transmitted signal and its spectrum
51    % ---------------> Insert code here <-----------------%



## Content actions

PDF | EPUB (?)

### What is an EPUB file?

EPUB is an electronic book format that can be read on a variety of mobile devices.

### Downloading to a reading device

For detailed instructions on how to download this content's EPUB to your specific device, click the "(?)" link.

| More downloads ...

### Add module to:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

#### Definition of a lens

##### Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

##### What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

##### Who can create a lens?

Any individual member, a community, or a respected organization.

##### What are tags?

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks