How do i generate a mapping qpsk?

cant found what function apply for [I,Q] = mappingqpsk

clear all, close cll, clc;

%-------------------------------------------------------------------------%
%                    Create bits to transmit                              %           
%-------------------------------------------------------------------------%

load('bitstream.mat')

%-------------------------------------------------------------------------%
%                         Map bits for transmition                        %           
%-------------------------------------------------------------------------%

[I,Q] = mappingqpsk('bitstream');   
figure(1)
subplot(2,1,1)
stem(I)
title('IQ')
legend('I')
subplot(2,1,2)
stem(Q,'r')
legend('Q')

Answer 1

[Pulkit]

According to my understanding you are trying to map input bitstreams to QPSK symbols, but you were unable to find function to do so in MATLAB.

The ‘QPSKModulator’ function from the communication toolbox could be used to achieve this functionality. The following example code might help you.

%Creating Bitstream
bitstream=[0,1,1,1,1,1,0,1]'

bitstream = 8×1

0 1 1 1 1 1 0 1

%Create QPSK Modulator system object
hMod = comm.QPSKModulator('BitInput',true)

hMod = 
  comm.QPSKModulator with properties:

       PhaseOffset: 0.7854
          BitInput: true
     SymbolMapping: 'Gray'
    OutputDataType: 'double'

%Modulating input bitstream  
modOut = step(hMod, bitstream)

modOut = 
  -0.7071 + 0.7071i
  -0.7071 - 0.7071i
  -0.7071 - 0.7071i
  -0.7071 + 0.7071i

%Seperating real and Imag from Complex type
I=real(modOut)

I = 4×1

-0.7071 -0.7071 -0.7071 -0.7071

Q=imag(modOut)

Q = 4×1

0.7071 -0.7071 -0.7071 0.7071

Please refer to this documentation link for more information regarding constellation used by 'QPSKModulator' function to map input bitstreams to QPSK symbols.

https://www.mathworks.com/help/comm/ref/comm.qpskmodulator-system-object.html

or

Type the following command into the MATLAB command window to get more insight.

help comm.QPSKModulator