EG4217/EG7217 Advanced Communications Coursework 4

Task 1

ITUdryair.m, sat_dist.m and freespace.m

The programme ITUdryair.m calculates the loss due to absorption by oxygen.                  The programme sat_dist calculates the distance from a satellite to the ground-station.

A communications satellite orbits at a height of 500 km above the earth.  It transmits a signal with an EIRP of 100W at a carrier frequency of 52 GHz to a ground-station at sea-level with a gain of 30 dBi.  The threshold value for the received signal is – 130 dBW.

The air pressure measured at the ground-station is 1013 hPa and at 12 km height, it is measured as 150 hPa.  The temperature at the ground-station is 17O C.

a.     Calculate the scale height for oxygen pressure.

b.    Use ITUdryair.m and this scale height to calculate the oxygen loss when the satellite is overhead.

c.     Divide by the loss in part (b) by a vector containing the sines of elevation angles               [5,10,15, …,90] degrees to get the loss for these elevations and plot the loss as a function the elevation angle.

d.    Calculate the distance of the satellite from the ground station for this same range of elevation angles

e.     Add free-space loss to the oxygen loss to get the total loss as a function the elevation angle

f.      Use the link-budget to calculate the minimum elevation angle at which the signal from the satellite can be received.

Task 2

SAMrain.m

This function calculates the loss associated with rain; the formerfor 0.01% of the time

A geostationary satellite has an elevation of 20O from Leicester, which has an altitude of 62 m       above mean sea-level and it has approximately the same elevation as seen from a few miles away in Buxton, Derbyshire, which has an altitude of 330 m.  Use the approximate latitude of 53O N for  both stations and calculate how much better or worse the signal would be in Buxton, compared   to Leicester, for the worst 52 minutes of a typical year.  The satellite’s carrier signal has a                frequency of 35 GHz.

Task 3

ITUrainattenuation.m

From document ITU-R P837, find the rain rate in mm/hour for the rainiest 0.01% of the time in Kolkata (Calcutta), India.

A geostationary TV satellite has an elevation of 64O, as seen from Kolkata, which is at sea-level.  A 15 GHz TV signal is received by a large antenna and distributed to subscribers.  In dry weather,    the signal-to-noise ratio at the subscribers’ homes is 10 dB, which is sufficient to ensure a good    TV signal.  However, the operators are worried that if it goes below 5dB, viewers will complain.    How many hours per year would you expect to see this level of degradation? (To help you answer this question, use the inbuilt Matlab command p=logspace(-1,-3,10) to create a range of                      percentages.  These percentages may be input to ITUrainattenuation.m as the last input parameter. Then use the loglog command to plot rain attenuation against p on a log-log graph.)

What other effect (that is not taken into consideration in the Matlab programme) might make this value inaccurate?