Tutorial (1) Wireless Communications 3rd year Communications
In a microwave system a fixed Rx is received a simple reflected wave
0.1 cos o (t - ) in addition to the LOS wave 0.3 cos o t
- Find an expression for overall received signal.
- At which carrier frequencies the received signal components are constructed
if the delay value due to the reflected path is 5 nano-second.
- Sketch the received signal amplitude vs carrier frequency for frequencies
from 100 MHz to 1 GHz.
(1) If the transmit power is 1 W and carrier frequency is 2.4 GHz and the receiver
is at a distance of 1.6 Km from the transmitter. Assume that the Tx and Rx
antenna gains are 1.6
(i) Find receive power in dB in the free space of a signal
(ii) What is the path loss in dB.
(2) If a transmitter produces 50 watts of power, express the transmit power in
units of (a) dBm and (b) dBW. If 50 watts is applied to a unity gain antenna
with a 900 MHz carrier frequency, find the received power in dB at a free
space distance of 100 meters from the antenna. What is the P r(10 Km)?
Assume unity gain for the receiver antenna.
(3) The noise figure of a cell phone receiver is specified as 16 dB. What is the
equivalent noise temperature? Assume that reliable detection of a 30 kHz FM
signal by this receiver requires an SNR of 13 dB. What is the receiver
sensitivity in dBm.
(4) A satellite receiving system employs a 5 m parabolic antenna operating at 12
GHz. The antenna noise temperature is 100 K, and the receiver front-end
noise temperature is 120 K. Calculate [G/T].
(5) A satellite transmits with an EIRP of 46 dBW. Calculate the received carrier-
to-noise ratio if the bandwidth is 35MHz and the receiver has a G/T of 25
dB/K. Assume the distance between the earth and the satellite is 35,786 km.
(6) In a satellite link transmitting video signal the required S/N ratio is 45.7 dB.
Determine the required G/T of the receiver if the transmitter is FM with the
following characteristics: EIRP is 54 dBw, slant range 38,000 Km, rainfall
attenuation 0.1 dB/Km, carrier frequency 6.954 GHz, other losses 5 dB.
Assume suitably the additional data required.
(7) A satellite carrying a 9.8 GHz continuous-wave beacon transmitter is located
in geosynchronous orbit 37,586 km from an earth station. The beacon’s output
power is 0.3 W and feeds an antenna of 19 dB gain toward the earth station.
The antenna is 3.65 m in diameter with an aperture efficiency of 62.5%.
(i) Calculate the satellite EIRP.
(ii) Calculate the receiving antenna gain.
(iii) Calculate the path loss.
(iv) Calculate the received power.
If the overall system noise of the earth station is 1189 K, calculate
(v) The earth station G/T.
(vi) The received noise power in a 115 MHz noise bandwidth.
(vii) The receiver carrier-to-noise ratio in the above noise bandwidth.
(9) For link to be maintained between a geosatellite and an earth station about
35,786 km apart, calculate the carrier power (in dB) necessary giving the
following antenna characteristics:
- 60% efficiency.
- 2.5 cm wavelength.
- 1.3 m diameter transmitting dish.
- 1.0 m diameter receiving dish.
To ensure high service quality, it is suggested that the carrier power at the
receiver input must be at least -116 dBW.
(10) A QPSK signal is transmitted by satellite. Raised-cosine filtering is used, for
which the rolloff factor is 0.2 and a bit error rate (BER) of 10-5 is required.
For the satellite downlink, the losses amount to 200 dB, the receiving earth-
station G/T ratio is 32 dBK-1, and the transponder bandwidth is 36 MHz.
Calculate
(a) the bit rate which can be accommodated, and
(b) the EIRP required.
(11) A BPSK signal with bit rate 60 Mb/s is transmitted by satellite at downlink
carrier of 3.7 GHz from a parabolic antenna of 6 m. The satellite transmitter
generates an output power 8 kW. If the downlink total losses to the receiving
earth station is 240 dB and the transponder bandwidth is 36 MHz calculate:
i- the required carrier to noise density ratio (C/N o) if a BER of 10-6 is
considered.
ii- the satellite EIRP required ( in dB)
iii- the receiving ES Figure of Merit (G/T)r
vi- the carrier to noise power ratio (C/N) for downlink.
( Hint: Pe = ½ exp(-Eb/No) )
