Good day im trying to plot a graph of the effect of distance of separation between the TX/RX and the receive signal strength, using Friis's free space equation. I am having an issue with the graph when my pr is in db unit.

My code:

clc;

close all;

clear all;

d=1:0.1:20 ;

f=2100000000;

Wavelength=(3*10^8/f).^2;

PT=50.12;

PR=(Wavelength./(4*pi*d).^2)*PT ;

PR1=10*log(PR/(10*10.^-3)) ;

subplot(2,1,1); 

plot(d,PR);

xlabel('x--> D (distance in Km)'); 

ylabel('y--> PR (path loss)'); 

title('Distance of separation between the TX/RX and the receive signal strength'); 

grid on

subplot(2,1,2); 

plot(d,PR1);

xlabel('x--> D (distance in Meter)'); 

ylabel('y--> PR (Path loss in dB)'); 

title('Distance of separation between the TX/RX and the receive signal strength'); 

grid on;

[Yashlin Naidoo]

My pr linear value when converted to dbm doesnt correspond to the graph value.

[Stephan]

Hi,

sorry i guess my answer didnt help - deleted it. What exactly is the difference between your result from calculation and the plot? Are you sure the unit of the second x-values is m instead of km?

Best regards

Stephan

Answer 1

[Wick]

You're plotting exactly what you're asking for. However, I don't think you're asking what you think you're asking. Your definition of PR1 doesn't appear to reference P0. It's a fixed scalar of 0.01;

PR1=10*log(PR/(10*10.^-3)) ;

did you intend to divide by 0.01? That's what 10*10.^-3 evaluates to. I would have expected PT there. Perhaps you intended 0.001? That's just '1e-3' in MATLAB notation (without the quotes).

Edit: Also, in MATLAB, log is the natural log (base e) usually written as ln. If you want the base 10 log the command is log10. dB is usually defined in base 10.

Answer 2

[John Barber]

You probably already have an answer but try this....

Power Transmitted Vs. Distance

clc; clear; close all;
%%%%%% Pt(dBm) Vs Distance (m) MATLAB Code %%%%%
%%% desined By Braden Gustitis & John Barber %%%
%%%%%%%%% Senior Design Project ENGR 402 %%%%%%% 
%%%%%% Used PTx Vs Distance calculator to validate MATLAB results %%%%%%
%%%%%%     https://www.radiolabs.com/stations/wifi_calc.html      %%%%%%
C=3.0e8;        % Speed of light
f0 = 2.4e9;     % Frequency
Lambda = C/f0;  % Wavelength
Gr = 2;         % Receiver gain (estimated)
Gt = 2;         % Transmitter gain (estimated)
Pt = 80:-5:0;      % Tx power from 80 dBm to 0 dBm
i = 1:length(Pt);
%%%%%%%%%%%%%%% Per ScreenBeam   %%%%%%%%%%%%%%
%%%%%%%%%%%% Power Received levels %%%%%%%%%%%%
PrR = -67;          % P Rx Reliable     -67 dBm
PrG = -60;          % P Rx Good         -60 dBm
PrE = -50;          % P Rx Excellent    -50 dBm
%%%%%%%%%%% Pt - 
LfsR = Pt-PrR;       % difference between PTx & PRx ==> Pt - PrR  Reliable    
LfsG = Pt-PrG;       % difference between PTx & PRx ==> Pt - PrG  Good
LfsE = Pt-PrE;       % difference between PTx & PRx ==> Pt - PrE  Exellent
% XR, XG, XE to simplify exponent in below equation
XR = LfsR + Gr + Gt;        
XG = LfsG + Gr + Gt;
XE = LfsE + Gr + Gt;
% Freespace Pathloss equation modified to output distance
RR = (Lambda .* 10 .^ ((XR)/20)) ./ (4 .* pi);   % Reliable  ~ -67 dBm
RG = (Lambda .* 10 .^ ((XG)/20)) ./ (4 .* pi);   % Good      ~ -60 dBm
RE = (Lambda .* 10 .^ ((XE)/20)) ./ (4 .* pi);   % Excellent ~ -50 dBm
figure
plot(RR,Pt(i), 'DisplayName', 'Pr = -67dBm "Reliable"')
title('R(Pt) of 2.4 GHz')
xlabel('Distance in meters')
ylabel('Pt in dBm')
xlim([0 5000]);         % change to adjust distance
grid on
hold on
plot(RG, Pt(i), 'DisplayName', 'Pr = -60dBm "Good"')
plot(RE, Pt(i), 'DisplayName', 'Pr = -50dBm "Exellent"')
legend(Location="northwest")
legend(fontsize=14)
legend show
hold off