Using sigstrength() for raytracing propagation model

I'm trying to run a ray tracing simulation for a simple ground reflection scenario. I have an STL file with a "floor" that is 1m wide (in y-direction) and 25m long (in the x-direction). I place a transmitter at the location [0.1;0.5;3]. I place 1000 receivers collinear with the transmitter, and at the same height:

clear all;clc;close all;
stlFile = '25m1m_floor.stl';
viewer = siteviewer('SceneModel',stlFile); % Required to link STL for ray tracing

tx = txsite('cartesian', 'AntennaPosition', [0.1;0.5;3], 'TransmitterFrequency', 900e6, 'TransmitterPower', 0.001);

numPointsX = 1000;numPointsY = 1;
x = linspace(0.1, 25, numPointsX); y = linspace(0.5, 0.5, numPointsY); [X, Y] = meshgrid(x, y);
Z = 3 * ones(size(X)); 

for j = 1:numPointsX
    for i = 1:numPointsY
        rxs(i,j) = rxsite('cartesian', 'AntennaPosition', [X(i,j); Y(i,j); Z(i,j)], 'CoordinateSystem', 'cartesian');
    end
end


%To display the tx and rx in siteviewer
%{

show(tx,"ShowAntennaHeight",false);


for i = 1:numel(rxs)
    show(rxs(i),"ShowAntennaHeight",false);
end
%}

pm = propagationModel('raytracing', 'Method', 'sbr', 'MaxNumReflections', 1,...
    'SurfaceMaterial', 'concrete', 'CoordinateSystem', 'cartesian');

ss(1,:) = sigstrength(rxs,tx,pm);



packetLength = 33;
txPower = 0.01;
for j = 1:numPointsX
    for i = 1:numPointsY
        rx = rxs(i,j);
        rays_out = raytrace(tx, rx, pm);
        rays = rays_out{:};
        [RSS(i,j), rxPower(i,j)] = calcRSSRays(rays,packetLength,txPower);
    end
end

figure;plot(x,RSS);
hold;plot(x,ss);


function [RSS,rxPower] = calcRSSRays(rays,packetLength,txPower)

    data = randi([0 3], packetLength, 1); 
    txPacket = sqrt(txPower)*pskmod(data, 4, pi/4);
    
    rxPacket = zeros(1, packetLength);
    
    pathGains = -[rays.PathLoss];
    phaseShifts = [rays.PhaseShift];
    
    pathGainsLinear = 10.^(pathGains / 10); 
    
    for s = 1:packetLength
        E_ray = sqrt(pathGainsLinear) .* exp(-1j .* phaseShifts); 
        E_total = sum(E_ray * txPacket(s),"all"); 
        rxPacket(s) = E_total;
    end
    rxPower = mean(abs(rxPacket).^2); 
    RSS = 10 * log10(rxPower./txPower); 
    

end

The transmitter frequency is 900Mhz so the wavelength is around 0.33m. I've specified MaxNumReflections as 1, which I think should capture the ground reflection, and when I plot for one tx-rx pair, I can see that:

Since the tx and rx are all at the same height, I think I should get an RSS profile which decays with distance according to the power rule (i.e. 1/d^2), but with undulations where the ground reflected path interferes constructively and destructively with the line of sight ray.

However, when I plot the output from the sigstrength() function, there are no undulations. I've also tried calculating RSS from a packet-level simulation that I wrote, taking the rays output from the raytrace function - I think this is correct, because I do see the interference pattern in it:

Does anyone know if I've made a mistake in the ray-tracing/use of sigstrength()? Or is any further calculation required on it?

Or is this something to ask Mathworks support?

NOTE 1: Question editor doesn't recognize .stl file extension for upload, so I've changed the extension to .txt. Extension needs to be changed to .stl to run it.

NOTE 2: I posted this question earlier, but I've come up with a better version of the simulation, so I've deleted that one before any answers/comments were posted on it.

Answer 1

[Imran Khan]

Asked Mathworks support, sigstrength() power calculation has been reworked after version 2022Ra to incorporate phase calculations - now output of sigstrength() and packet-level simulation is identical.