TCS - Uplink Design

UPLINK DESIGN

The details of the UPLINK DESIGN calculation are available in the EXCEL SHEET HERE.

For the uplink design (control channel), the communication is direct from the Earth to the Rover. This is because the control channel has a very small data rate of 1kbps and very little noise enters this channel because of the low bandwidth required. Forward Error Correction Methods are not necessary on the uplink.

At the rover antenna, the bit error rate of the received signal is expected to be less than 10^ (-6). The carrier to noise ratio for QPSK at this bit error rate is given by:

This gives a required C/N ratio of 22.595 at the rover antenna. The block diagram for the communication system is given next.

For the uplink a carrier frequency of 9.1 GHz is chosen. This X band frequency has negligible rain attenuation and has been allocated by the FCC for radiolocation. However, since we only require a bandwidth of 775 Hz for the control channel, we can request the FCC to use this frequency for a very short term usage without causing interference to other users.

The control signal has a bit rate of 1 kbps. Because the modulation scheme is QPSK, the symbol rate is therefore, 500 symbols/sec.

Bandwidth calculation

B_RF= R_S * (1+ α) = 500 * (1+0.55) = 775 Hz.

The table below summarizes the different parameters and their values for the uplink design. For detailed design calculation, CLICK HERE.

Parameter

Value

Comments

Earth to Rover frequency

9.1GHz

X band

Max Distance between Earth surface and moon

376295 km

Bandwidth

775 Hz

Control channel

Power transmitted from earth

16 dB

w/ antenna gain of 55.3 dBi

Power Received at rover

-141 dB

w/ antenna gain of 11.4 dBi

Actual SNR at the rover

32.1 dB

Minimum SNR at rover with 4 dB margin

26.6dB

At Yagi-Uda Antenna

Actual Link Margin achieved at rover

9.49 dB