EE5550 Radio and Optical Communication Systems

1.a)Satellite communication systems play an important part in broadcast networks. Discuss various sub systems that needs to be considered at the design stage for such a satellite system.

b)A microwave link is to be designed to function as a high capacity communication link with the following features and hardware:

Operating frequency: 4.5 GHz with 50 MHz bandwidth  

Transmit power: 7 W

Transmitter - receiver separation - 50 km

Tx Antenna: gain = 8 dBi

Rx Antenna: aperture area = 0.5 m2,   efficiency = 87%,

Low-noise RF amplifier (LNA): gain = 8 dB, Noise Temperature = 54 K

Antenna – LNA cable loss: 0.9 dB

Range of required signal to noise ratio to meet specified quality of service: 36.2 to 36.4 dB  (Ambient Temperature = 290 K, Velocity of light  = 3.0x108 m/s, Boltzmann’s constant,  k = 1.38x10-23 J/K) Determine the required components and their characteristics for the receiver design and clearly state all assumptions that you will make.

Discuss the dominant noise in RF transmitter designs and techniques to reduce such noise.

Recent advances in technology have aided the development of a class of miniaturized satellites called SmallSats  that typically weigh less than 500 kg. CubeSats are key members of this family. Discuss challenges with antennas designs for cubeSats and formulate possible antenna architectures for this type of satellite.

Discuss the application of CDMA techniques including the advantages and disadvantages for satellite networks and critically compare the systems in Table 3 in terms of revenue and performance with appropriate justification.  

Energy per bit to noise spectral density ratio 10.4 dB 9.2 dB

Spectral efficiency (bits/s/Hz) X 2

Available satellite transponder bandwidth (MHz) 200 250

Table 3

Equation 3a can be used to aid the analysis:

BN : Equivalent noise bandwidth of receiver

Eb/No: Energy per bit to noise spectral density ratio

b)A satellite communication system employs 100 MHz transponder bandwidth, 80 dB carrier to Noise ratio and a single antenna beam on its downlink. Synthesize possible solutions to double the capacity of the downlink employing the same bandwidth, carrier to noise ratio per link, and quality of service, operating over the same band.

4.a)A number of factors in Fig. 4 increase the noise level within a fibre optic communication line (shown as straight lines). Name each of these factors and briefly explain their origin.

b)With the aid of schematics, explain how an erbium doped fibre amplifier (EDFA) is used to boost power in a point-to-point fibre optic communication system.  Consider the following point-to-point optical system: receiver sensitivity of -34 dBm, multi mode fibre with a loss of 0.21 dB/km, patch leads with a loss of 2.63 dBm at each end of the   22 km fibre and source and receiver connector loss of 0.62 dBm each. Assume a 6.3 dBm power margin at the receiver is needed.  If we launch with power Ptx = -19 dBm would there be sufficient power to drive this optical system?

5.a) With the aid of schematics, explain the technique that Avalanche Photo Diodes (APD) use to increase performance in a opto-electronic receiver.

b) Your job is to create an optical fibre system that will run through a village and provide connection to all its residents. There are 60 houses in the village. You are using a bus topology with the following characteristics:  PT = 1 mW, minimum value of Pn = 0.1mW, C = 5% and  is a further 5%. Would your system sufficiently cover all the houses in that village?