Communications Toolbox 
Syntax
y = dmod(x,Fc,Fd,Fs,'
method
/nomap
'
...); y = dmod(x,Fc,Fd,Fs,'
ask
'
,M); y = dmod(x,Fc,Fd,Fs,'
fsk
'
,M,tone); y = dmod(x,Fc,Fd,Fs,'
msk
'
); y = dmod(x,Fc,Fd,Fs,'
psk
'
,M); y = dmod(x,Fc,Fd,Fs,'
qask
'
,M); y = dmod(x,Fc,Fd,Fs,'
qask/arb
'
,inphase,quadr); y = dmod(x,Fc,Fd,Fs,'
qask/cir
'
,numsig,amp,phs); y = dmod(x,Fc,Fd,[Fs initphase],...); [y,t] = dmod(...);
Optional Inputs
Input 
Default Value 
tone 
Fd 
amp 
[1:length(numsig)] 
phs 
numsig*0 
Description
The function dmod
performs digital passband modulation and some related tasks. The corresponding demodulation function is ddemod
. The table below lists the modulation schemes that dmod
supports.
To Avoid the Mapping Process
Ordinarily, the dmod
function first maps the digital message signal to an analog signal and then modulates the analog signal. The generic syntax
uses the nomap
flag to tell dmod
that the digital message has already been mapped to an analog signal x
whose sampling rate is Fs
. As a result, dmod
skips its usual mapping step. You can use the modmap
function to perform the mapping step. In this generic syntax, method
is one of the seven values listed in the table above and the other variables are as in the next section.
To Modulate a Digital Signal (General Information)
The generic syntax y = dmod(x,Fc,Fd,Fs,...)
modulates the digital message signal that x
represents. x
is a matrix of nonnegative integers. If x
is a vector of length n, then y
is a vector of length n*Fs/Fd
. Otherwise, if x
is nbym, then y
is (n*Fs/Fd
)bym and each column of x
is processed separately.
Fc
is the carrier frequency in hertz. The sampling rates in hertz of x
and y
, respectively, are Fd
and Fs
. (Thus 1/Fd
represents the time interval between two consecutive samples in x
, and similarly for y
.) The ratio Fs/Fd
must be a positive integer. For best results, use values such that Fs
> Fc
> Fd
. The initial phase of the carrier signal is zero.
The generic syntax y = dmod(x,Fc,Fd,[Fs initphase],...)
is the same, except that the fourth input argument is a twoelement vector instead of a scalar. The first entry, Fs
, is the sampling rate as described in the paragraph above. The second entry, initphase
, is the initial phase of the carrier signal, measured in radians.
To Modulate a Digital Signal (Specific Syntax Information)
y = dmod(x,Fc,Fd,Fs,
performs '
ask
'
,M)
M
ary amplitude shift keying modulation. Each entry of x
must be in the range [0, M
1]. The maximum value of the modulated signal is 1.
y = dmod(x,Fc,Fd,Fs,
performs '
fsk
'
,M,tone)
M
ary frequency shift keying modulation. Each entry of x
must be in the range [0, M
1]. The optional argument tone
is the separation between successive frequencies in the modulated signal y
. The default value of tone
is Fd
. The maximum value of y
is 1.
y = dmod(x,Fc,Fd,Fs,
performs minimum shift keying modulation. Each entry of '
msk
'
)
x
is either 0 or 1. The maximum value of y
is 1.
y = dmod(x,Fc,Fd,Fs,
performs '
psk
'
,M)
M
ary phase shift keying modulation. Each entry of x
must be in the range [0, M
1]. The maximum value of y
is 1.
y = dmod(x,Fc,Fd,Fs,
performs '
qask
'
,M)
M
ary quadrature amplitude shift keying modulation with a square signal constellation. The table below shows the maximum value of y
for several small values of M.
M 
Maximum Value of y 
M 
Maximum Value of y 
2 
1 
32 
5 
4 
1 
64 
7 
8 
3 
128 
11 
16 
3 
256 
15 
Note
To see how symbols are mapped to the constellation points, generate a square constellation plot using qaskenco (M) .

y = dmod(x,Fc,Fd,Fs,
performs quadrature amplitude shift keying modulation, with a signal constellation that you define using the vectors '
qask/arb
'
,inphase,quadr)
inphase
and quadr
. The constellation point for the kth message has inphase component inphase
(k+1) and quadrature component quadr
(k+1).
y = dmod(x,Fc,Fd,Fs,
performs quadrature amplitude shift keying modulation with a circular signal constellation. '
qask/cir
'
,numsig,amp,phs)
numsig
, amp
, and phs
are vectors of the same length. The entries in numsig
and amp
must be positive. If k is an integer in the range [1, length(numsig)
], then amp
(k) is the radius of the kth circle, numsig
(k) is the number of constellation points on the kth circle, and phs
(k) is the phase of the first constellation point plotted on the kth circle. All points on the kth circle are evenly spaced. If you omit phs
, then its default value is numsig*0
. If you omit amp
, then its default value is [1:length(numsig)]
.
Note
To see how symbols are mapped to the constellation points, generate a labeled circle constellation plot using apkconst (numsig,amp,phs,'n') .

[y,t] = dmod(...)
returns the computation time in t
. t
is a vector whose length is the number of rows of y
.
Examples
An example on the reference page for ddemod
uses dmod
. Also, the code below shows the waveforms used to communicate the digits 0 and 1 using 4ASK modulation. Notice that the dmod
command has two output arguments. The second output, t
, is used to scale the horizontal axis in the plot.
Fc = 20; Fd = 10; Fs = 50; M = 4; % Use 4ASK modulation. x = ones(Fd,1)*[0 1]; x=x(:); % Modulate, keeping track of time. [y,t] = dmod(x,Fc,Fd,Fs,'ask',M); plot(t,y) % Plot signal versus time.
See Also
ddemod
, dmodce
, ddemodce
, amod
, amodce
dftmtx  dmodce 