modify 'phased.FreeSpace' function or include other channel model

Recently, I'd like to implement Path loss exponent and distance estimation in a short-range wireless network, and plan to use phased.FreeSpace function and modify it to adapt lognormal path loss and shadowing model to derive path loss exponent and distance. Can any one has solutions to achieve this work?

[Vinayak]

Can you give us a little more detail as to how do you want to modify the "phased.freeSpace" function.

If you only want to modify the input parameters of the "phased.freeSpace function" in MATLAB according to the need, then you can refer to the documentation link below.

https://www.mathworks.com/help/phased/ref/phased.freespace-system-object.html

[Da-Ren Chen]

the matlab code is as follows:

f=2.4e9; %Transmitted signal frequency in Hertz

waveform = phased.RectangularWaveform('SampleRate',5e6,...

'PulseWidth',6e-7,'OutputFormat','Pulses',...

'NumPulses',1,'PRF',1e2);

target = phased.RadarTarget('Model','Nonfluctuating',...

'MeanRCS',1,'OperatingFrequency',5.88e9);

targetpos = phased.Platform('InitialPosition',[1; 1; 1],...

'Velocity',[0.5; 0.5; 0]);

antenna = phased.IsotropicAntennaElement(...

'FrequencyRange',[5e8 f]);

transmitter = phased.Transmitter('PeakPower',1e-3,'Gain',0,...

'InUseOutputPort',true);

transpos = phased.Platform('InitialPosition',[1;1;0.1],...

'Velocity',[0;0;0]);

radiator = phased.Radiator('OperatingFrequency',f,'Sensor',antenna);

collector = phased.Collector('OperatingFrequency',f,'Sensor',antenna);

channel = phased.FreeSpace('SampleRate',waveform.SampleRate,...

'OperatingFrequency',f,'TwoWayPropagation',false);

receiver = phased.ReceiverPreamp('Gain',0,'LossFactor',3,...

'SampleRate',5e6,'NoiseFigure',5,...

'EnableInputPort',true,'SeedSource','Property','Seed',1e3);

I would like to change the channel using phased.FreeSpace() which is based on the custom lognormal pathloss and shadowing, not just freesapace model.

thanks!

[Da-Ren Chen]

the custom lognormal pathloss and shadowing function is as follows:

function [PL,Pr_dBm] = logNormalShadowing(Pt_dBm,Gt_dBi,Gr_dBi,f,d0,d,L,sigma,n)

%Pt_dBm = Transmitted power in dBm

%Gt_dBi = Gain of the Transmitted antenna in dBi

%Gr_dBi = Gain of the Receiver antenna in dBi

%f = frequency of transmitted signal in Hertz

%d0 = reference distance of receiver from the transmitter in meters

%d = array of distances at which the loss needs to be calculated

%L = Other System Losses, for no Loss case L=1

%sigma = Standard deviation of log Normal distribution (in dB)

%n = path loss exponent

%Pr_dBm = Received power in dBm

%PL = path loss due to log normal shadowing

lambda=3*10^8/f; %Wavelength in meters 計算出波長，單位為公尺

K = 20*log10(lambda/(4*pi)) - 10*n*log10(d0) - 10*log10(L);%path-loss factor

X = sigma*randn(1,numel(d)); %normal random variable

PL = Gt_dBi + Gr_dBi + K -10*n*log10(d/d0) - X ;%PL(d) including antennas gains

Pr_dBm = Pt_dBm + PL; %Receieved power in dBm at d meters

end

Answer 1

[Anshuman]

Hi,

Yes, it is possible to modify the 'phased.FreeSpace' function in MATLAB to accommodate the lognormal path loss and shadowing models, and use it to estimate the path loss exponent and distance in a short-range wireless network. Here are the steps that you can follow:

1. Create a custom function in MATLAB that takes the input parameters required for the lognormal path loss and shadowing models, such as the frequency, antenna heights, and shadowing standard deviation, and returns the path loss exponent and distance between the transmitter and receiver.
2. Use the 'phased.FreeSpace' function as a template for your custom function. Create a copy of the 'phased.FreeSpace' function and rename it to a descriptive name, such as 'pathLossEstimator'.
3. Modify the copied function to include the lognormal path loss and shadowing models. You can add additional input parameters and processing steps as needed to implement these models. For example, you could add an input parameter for shadowing standard deviation and use it to compute the received power with a lognormal distribution.
4. Test your custom function with simulated or measured data to verify its accuracy and compare it with the 'phased.FreeSpace' model. You can also use different statistical methods to improve the accuracy of your model.

Here is the sample code implementation:

function [PL_exp, d] = pathLossEstimator(pt, freq, ht, hr, shadowingStdDev, Pr)
    c = physconst('LightSpeed');
    lambda = c/freq;
    a = ((4*pi*ht*hr)/lambda)^2;

    % Compute path loss exponent
    Pr_ref = pt*getFreeSpaceLoss(freq, ht, hr);
    PL_exp = log10(Pr_ref/Pr)/(10*log10(d_ref/d));

    % Compute distance
    Pr_lognormal = Pr_ref/(d^PL_exp);
    Pr_shadowing = Pr_lognormal + shadowingStdDev*randn();
    Pr_real = abs(Pr_shadowing);
    d = sqrt((pt*Pr_real*a)/(4*pi*Pr_ref));

end

Note that this is just an example implementation and that there might be various factors to consider while optimizing the models based on different scenarios.

Hope it helps!

[Da-Ren Chen]

the custome lognormal pathloss and shadowing is listed below:

function [PL,Pr_dBm] = logNormalShadowing(Pt_dBm,Gt_dBi,Gr_dBi,f,d0,d,L,sigma,n)

%Pt_dBm = Transmitted power in dBm

%Gt_dBi = Gain of the Transmitted antenna in dBi

%Gr_dBi = Gain of the Receiver antenna in dBi

%f = frequency of transmitted signal in Hertz

%d0 = reference distance of receiver from the transmitter in meters

%d = array of distances at which the loss needs to be calculated

%L = Other System Losses, for no Loss case L=1

%sigma = Standard deviation of log Normal distribution (in dB)

%n = path loss exponent

%Pr_dBm = Received power in dBm

%PL = path loss due to log normal shadowing

lambda=3*10^8/f; %Wavelength in meters 計算出波長，單位為公尺

K = 20*log10(lambda/(4*pi)) - 10*n*log10(d0) - 10*log10(L);%path-loss factor

X = sigma*randn(1,numel(d)); %normal random variable

PL = Gt_dBi + Gr_dBi + K -10*n*log10(d/d0) - X ;%PL(d) including antennas gains

Pr_dBm = Pt_dBm + PL; %Receieved power in dBm at d meters

end

in the second step you provided, how can I get the original 'phased.FreeSpace' function? and how to replace it with the proposed lognormal pathloss and shadowing function? or modified it?

Thanks!

[Da-Ren Chen]

the matlab code is as follows:

f=2.4e9; %Transmitted signal frequency in Hertz

waveform = phased.RectangularWaveform('SampleRate',5e6,...

'PulseWidth',6e-7,'OutputFormat','Pulses',...

'NumPulses',1,'PRF',1e2);

target = phased.RadarTarget('Model','Nonfluctuating',...

'MeanRCS',1,'OperatingFrequency',5.88e9);

targetpos = phased.Platform('InitialPosition',[1; 1; 1],...

'Velocity',[0.5; 0.5; 0]);

antenna = phased.IsotropicAntennaElement(...

'FrequencyRange',[5e8 f]);

transmitter = phased.Transmitter('PeakPower',1e-3,'Gain',0,...

'InUseOutputPort',true);

transpos = phased.Platform('InitialPosition',[1;1;0.1],...

'Velocity',[0;0;0]);

radiator = phased.Radiator('OperatingFrequency',f,'Sensor',antenna);

collector = phased.Collector('OperatingFrequency',f,'Sensor',antenna);

channel = phased.FreeSpace('SampleRate',waveform.SampleRate,...

'OperatingFrequency',f,'TwoWayPropagation',false);

receiver = phased.ReceiverPreamp('Gain',0,'LossFactor',3,...

'SampleRate',5e6,'NoiseFigure',5,...

'EnableInputPort',true,'SeedSource','Property','Seed',1e3);

I would like to change the channel using phased.FreeSpace() which is based on the custom lognormal pathloss and shadowing, not just freesapace model.

thanks!