Compute Average Power of 256 QAM Signal in MATLAB

Compute the average power of a 256 QAM signal using a sliding window of 16 samples.

Initialization

Create a powermeter object with a sliding window of length 16 samples and a reference load of 50 ohms. Use this object to measure the average power of a 256 QAM signal in dBm units.

Visualize the average power of the signal using the timescope object.

FrameLength = 512;
Fs = 1000;
pm  = powermeter(16, 'Measurement', 'Average power', ...
                     'ReferenceLoad', 50, ...
                     'PowerUnits', 'dBm');
scope  = timescope('SampleRate',Fs,...
                   'TimeSpanSource','property',...
                   'TimeSpan',20,...
                   'YLabel','dBm',...
                   'YLimits',[0 50]);
title = 'Average power based on a sliding window of 16 samples';
scope.Title = title;

Compute the Average Power

Generate a sequence of pseudorandom integer values drawn uniformly from [0 255] using the randi function. Apply quadrature amplitude modulation (QAM) on this signal using the qammod function. Compute the average power of this signal using the powermeter object. View the computed average using the timescope object.

tic;
while (toc < 5)
 x = randi([0 255], FrameLength, 1);
 y = qammod(x, 256);
 averagePower = pm(y);
 scope(averagePower);
end