RELIABILITY

As discussed earlier, Forward Error Correction is required only on the downlink because of the high data rate and the corresponding high bandwidth which increases the noise in the channel. For the uplink, the bandwidth is only 775 Hz and ECC is not necessary because of negligible noise allowed in the frequency band.

A bit error rate of 10^-6 is acceptable for HDTV applications. For this requirement, a rate 2/3 convolution code is chosen which has a BER of less than 10^-6for a received SNR of 2 dB at the Earth station.

We propose to use the TC1000 (manufactured by Turbo Concept) which has a flexible coding rate and would deliver reliable data at our receiver on Earth. The cost of the TC1000 is $15000 and has a power requirement of less than 1 W. To find more about the TC1000, click HERE.

OUTAGES (RAIN ATTENUATION)

The X-band frequencies chosen for the design have negligible channel defects like rain, clouds, etc. The calculations for the rain attenuation margin are given below.

Allen telescope array is in Hat Creek, California at latitude of 40.8174 degrees N and 121.472 degrees W. This lies in the D region of the rain map.

Approximate look angle= 45 degrees. Rain storm height = 1 km,

Max operating frequency= 9.1 GHz (X band).

Consider horizontal polarization to account for the maximum possible rain attenuation.

At 9.1 GHz

α = 1.3, k = 0.0075

§ (dB/km) = k. R^α

R (rain rate) = 42 mm/hr (for the worst case scenario of rain, 0.001% of time).

§= 0.8 dB/km.

L_EFF= 1km/sin(45)

Rain Attenuation = § * L_EFF = 1.2 dB (for the worst case)

A rain attenuation margin of 1.2 dB is selected and used for link design.