LRT

 Source Code
Table of Contents

Home Page

System Overview

Link Budget

Communications Design

Cost Analysis

References

Source Code
All code was simulated using Matlab. 

Link Budget

%Point mapping

%Far side of the moon observatory : 1

%Satellite at lagrange point L2 : 2

%Satellite in lunar orbit : 3

%Earth station DSN: 4

 

%Path 1: Moon->Sat@L2 :

%Pr2=Pt1+Gt1+Gr2-20*log10(R1to2)-20*log10(4*pi/lambda)

%Path 2: Sat@L2->Sat@LunarOrbit :

%Pr3=Pt2+Gt2+Gr3-20*log10(R2to3)-20*log10(4*pi/lambda)

%Path 3: Sat@LunarOrbit->DSN EarthStation

%Pr4=Pt3+Gt3+Gr4-20*log10(R3to4)-20*log10(4*pi/lambda)

%Planetary Constants and system settings

Mearth=5.9736e24;

Rearth=6371e3;

Mmoon=7.349e22;

Rmoon=1738e3;

Dearth2moon=384400e3;

OrbitHeight=Rmoon+100e3; %1838e3

k=1.3607e-23; %Boltzman's constant

G=6.672e-11;

Tsys_moon=20;

Tsys_sat=20;

Tsys_earth=298;

BW=8.16e9;

EoNo_256QAM_turbocode=14;

rain_fade=1;

data_rate=6.4e10;

SNR_Recv=EoNo_256QAM_turbocode+10*log10(data_rate/BW);

 

%Carrier Freq

fc=19.48e9;

%=.0154m

lambda=3e8/fc;

%Antenna Gains

%=95.2772 dB

Gt1=10*log10(.9*(4*pi/lambda^2)*(pi*150^2));

%=58.9224 dB

Gt2_linear=.75*(4*pi/lambda^2)*(pi*2.5^2);

Gt2=10*log10(.75*(4*pi/lambda^2)*(pi*2.5^2));

Gr2=Gt2;

Gt3=Gt2;

Gr3=Gt2;

%=76.5532 dB

Gr4=10*log10(.94*(4*pi/lambda^2)*(pi*17^2));

%Distance from Moon observatory to Satellite at lagrangian point L2

%=6.1528e7 m

R1to2=Dearth2moon*(Mmoon/(3*Mearth))^(1/3);

%Distance from Satellite at lagrangian point L2 to Satellite in lunar orbit

%=6.1556e7 m

R2to3=sqrt(R1to2^2+OrbitHeight^2);

%Distance from Satellite in lunar orbit to Earth station

%=3.8440e8 m

R3to4=sqrt(Dearth2moon^2+OrbitHeight^2);

%0.1862

HPBW_needed=2*atan(100e3/R2to3);

%0.1961

HPBW_actual=sqrt(30000/Gt2_linear);

 

%Power of noise at the moon observatory

%=-116.5352 dB

PNmoon=10*log10(k*Tsys_moon*BW);

%Power of noise at the satellites

%=-116.5352 dB

PNsat=10*log10(k*Tsys_sat*BW);

%Power of noise at the earth station

%=-104.8033 dB

PNearth=10*log10(k*Tsys_earth*BW);

 

Pr2=EoNo_256QAM_turbocode+PNsat+10*log10(data_rate/BW);

Pt1=Pr2-Gt1-Gr2+20*log10(R1to2)+20*log10(4*pi/lambda)+rain_fade;

 

Pr3=EoNo_256QAM_turbocode+PNsat+10*log10(data_rate/BW);

Pt2=Pr3-Gt2-Gr3+20*log10(R2to3)+20*log10(4*pi/lambda)+rain_fade;

Pr4=EoNo_256QAM_turbocode+PNearth+10*log10(data_rate/BW);

Pt3=Pr4-Gt3-Gr4+20*log10(R3to4)+20*log10(4*pi/lambda)+rain_fade;

 

Pt1_Watts=10^(Pt1/10)

Pt2_Watts=10^(Pt2/10)

Pt3_Watts=10^(Pt3/10)

Total_power_Watts=Pt1_Watts+Pt2_Watts+Pt3_Watts

 

Channel Budget

%Typical Radio astronomy intensity level for brightest source (W/Hz*m^2)

multiplier=10^-23;

BW=3e9;

Rsat_moon=150;

Tsys_moon=20;

k=1.3607e-23; %Boltzman's constant

fmax=4e9;

Nyquist_rate=2*fmax;

code_rate=6/8;

QAM=256;

QAM_rate=log2(QAM);

rolloff=.02;

%Power of noise at the moon observatory

%=-120.8809 dB

PNmoon=10*log10(k*Tsys_moon*BW)

signal_power_req=10*log10(multiplier*BW*(pi*Rsat_moon^2)*.9)

SNR_req=abs(signal_power_req-PNmoon)

quantization=ceil(SNR_req/6)

data_rate=Nyquist_rate*quantization

coded_data_rate=data_rate/code_rate

symbol_rate=coded_data_rate/QAM_rate

BW_transmit=(1+rolloff)*symbol_rate

 

Pulse Shaping

f0 = 8.16e9/4; % pulse signal frequency

alpha = 0.02; % roll-off factor

period=1/f0;

Tb=period/2;

Rb=1/Tb;

t1 = -15/f0; % first sample

t2 = -t1; % second sample

N = 1024; % number of time-domain samples

t = linspace(t1,t2,N/2); % creates a time-domain axis

f = (-N/2:N/2-1)/(t2-t1); % creates a frequency-domain axis

x = (sin(2*pi*f0*t)./(2*pi*f0*t)).*(cos(2*pi*alpha*t*f0)./(1-(2*alpha*f0*t).^2)); % raised cosine

subplot(2,1,1)

plot(t,x)

xlabel('time (in sec)'), ylabel('amplitude')

X = fft(x,N);

XX = abs(fftshift(X))*(t2-t1)/N; % shifts/scales FFT output for plotting

XX_new = 20*log10(XX/max(XX));

subplot(2,1,2)

plot(f,XX_new), axis([-5e9 5e9 -100 10]), grid on

xlabel('Frequency (Hz)'), ylabel('power (dB)')