MATLAB R2024b: Quadrature Amplitude Modulation-Demodulation

This article is describing most properties a user should know before using the QAM function on MATLAB R2024b, but with terms changing.

The syntax for QAM modulation

Inside the round brackets ( ), user must set certain arguments. There are three classifications of the arguments: input arguments, name-value arguments, and output arguments.

qammod(input_arguments, name_value_arguments, output_arguments)

The following are going to describe in detail about each arguments.

Input arguments

X — input signal**

Input signal must be either binary values or integers in the range [0, (M-1)]

That means it will be easy if a user set the input signal already in binary digits (bits) whether using randi, but it becomes a more complex challenge when the input is multimedia such as: text file, RGB image, grayscale image, audio file, or many other extensions of file. If using one of the multimedia, the user must convert the value of the file to the acceptable input types.

Supported data types for QAM modulation on MATLAB R2024b are double | single | fi(S,WL,0) | int8 | int16 | uint8 | uint16.

Note: Binary inputs of QAM modulation, the number of rows must be an integer multiple of log2(M).

M — modulation order**

Is a positive integer powers of two. This value represents how many points in the QAM modulation diagram constellation. More points of order so higher data rate supported but more vulnerable to any interference.

Modulation order mathematically is the number of groups of bits can be processed in a symbol. For example, 16-QAM with 4 modulation order can process 4 bits in each symbol, 64-QAM with 6 mod order processes 6 bits for each symbol, and so on.

To determine which modulation order in QAM schemes, a user may calculate by two ways: by logarithmic =>> log2(M) which M is the modulation order, M = 16 | 64 | 256 or more. Or by power of number, M = 2^k which k is the number of bits per symbol.

symOrder — symbol order**

to map binary data to specific constellation points on a constellation diagram.

On MATLAB R2024b, there are three mapping options available: ‘gray’ | ‘binary’ | vector.

‘gray’ syntax is the default value that uses Gray-coded ordering, differs adjacent bit patterns on a constellation point by only one bit.

‘binary’ syntax uses binary-coded ordering.

vector syntax uses custom symbol ordering.

Example in Story

A wireless engineering student wants to modulate an … what the input signal is, how many number of bits per symbol is, the output, the name-value. State all the arguments either in a default value.

Glossarium

symbol = groups of bits, in any M-QAM orders.

MSB = Most Significant Bit means a bit which is having the greatest effect on the number and is at the left-most bit, e.g. ‘0011 1010’ the MSB is ‘0011’ and the LSB is ‘1010’ by placing location.

LSB = Least Significant Bit, the opposite meaning of the MSB.