# I need to insert an underwater acoustic channel model to an existing code that compared between OFDM and GFDM

The acoustic channel model that I have will output the channel impulse response. However, my signal is modulated in frequency domain (by doing fft). Hence, I want to obtain a frequency response of the CIR. Question :

1. Can I perform FFT on the CIR which give me frequency response and then just multiply my signal with it?

2. If that is correct, is the diagonal of the multiplication will be my signal after passing through the channel?

 H=fft(h,sys.N);    %sys.N = total data symbols h= CIR
Sig =H.*tf_ofdm;   %tf_ofdm = input signal
Signal=diag(output);  %output signal


I am doing FFT with the total data symbols because the CIR has random size every time it is being used.

• Not really. UWA channels are doubly selective. Which means, there will be inter-carrier interference (ICI). They also introduce time dilation/compression because they are wide-band, which needs to be accounted for. What channel model you are using? – BlackMath Sep 6 at 8:42
• @BlackMath , I am using the model shared by Rafael. The code is at here: github.com/rafaelschaves/uwa-channel-simulator – sterstar Sep 6 at 8:51
• I meant the mathematical model. Have you derived the channel output mathematically? – BlackMath Sep 6 at 12:48

I modeled the the acoustic channel noise in matlab:

    % On the Relationship Between Capacity and Distance in an
% Underwater Acoustic Communication Channel

Turbulence=17-(30*log10(f));
Noise_Turbulence=  power(10,(Turbulence*0.1));

Shipping=40+(20*(s-0.5))+(26*log10(f))-(60*log10((f)+0.03));
Noise_Shipping= power(10,(Shipping*0.1));

Wind=50+(7.5*(power(w,0.5)))+(20*log10(f))-(40*log10((f)+0.4));
Noise_Wind=power(10,(Wind*0.1));

Thermal=-15+(20*log10(f));
Noise_Thermal= power(10,(Thermal*0.1));

Noise=Noise_Turbulence+Noise_Shipping+Noise_Wind+Noise_Thermal;
Ambient_Noise=10*log10(Noise); %the values will be converted into dB

• Perhaps do you have the acoustic channel with Doppler effect? – sterstar Oct 16 at 14:17
• i am regenerating the result of the paper i refer in my code. I gor attenuation, Power spectral density graph, Figure3 SNR of paper results are not showing up correctly My y axis values are half. – Hashim Khan Oct 16 at 16:50