Communications Toolbox |

**Modulating the Signal**

This part of the example modulates the data in the column vector `signal`

in two different ways. The `dmodce`

function performs both modulations and puts the results into the two-column matrix `modsignal`

.

The first call to `dmodce`

, which creates the first column of `modsignal`

, tells `dmodce`

to use QASK modulation on `M`

symbols. The string `'qask'`

indicates the QASK method as well as the default square constellation configuration. In this case, the configuration implements Gray code.

The second call to `dmodce`

, which creates the second column of `modsignal`

, tells `dmodce`

to use QASK modulation with a signal constellation whose configuration is represented in the vectors `inphase`

and `quadr`

. The variables `inphase`

and `quadr`

are length-`M`

vectors that list the in-phase and quadrature components, respectively, of the points in the signal constellation. The points are listed in sequence, to associate a message symbol of k with the (k+1)st elements in `inphase`

and `quadr`

. Whereas Gray code labels the constellation points in a special way, this configuration lists points in a sequence that is merely convenient for creating `inphase`

and `quadr`

.

These lines also illustrate some common ways to manipulate matrices in MATLAB. If you are not familiar with the colon notation in MATLAB or with functions like `ones`

and `zeros`

, then you should consult the MATLAB documentation set.

% Use M-ary QASK modulation with two different labeled % square constellations. modsignal(:,1) =

`dmodce`

(signal,Fd,Fs,'qask',M); inphase = [-3:2:3 -3:2:3]; quadr = [ones(1,4), -1*ones(1,4)]; modsignal(:,2) =`dmodce`

(signal,Fd,Fs,'qask/arb',inphase,quadr);

Creating the Signal | Adding Noise |