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THE MANCHESTER METROPOLITAN UNIVERSITY
FACULTY OF SCIENCE AND ENGINEERING
DEPARTMENT OF ENGINEERING AND TECHNOLOGY
SESSION 2004/
Examination for the BEng (HONS) ELECTRICAL AND ELECTRONIC ENGINEERING BEng (HONS) COMMUNICATION AND ELECTRONIC ENGINEERING BEng (HONS) COMPUTER AND ELECTRONIC ENGINEERING YEAR/STAGE TWO
UNIT 64EE2105 : COMPUTER SYSTEMS AND COMMUNICATION
ENGINEERING
Monday 23 May 2005
2:00 pm to 4:00 pm
Instructions to Candidates
Answer THREE questions.
All questions carry equal marks.
S008 25/08/
Answer THREE questions.
- (a) (i) Explain how bit synchronization can be obtained in a serial data communications link. [6]
(ii) Show in a diagram how the data sequence 00101 would be encoded using both NRZ and Manchester encoding schemes. [4]
(b) A communication system is shown in block diagram form below:
N 2
S 2 S^3 Receiver Amplifier gain Grx
Physical channel gain Gchannel
Transmitter Amplifier gain Gtx
S 1
N 1 N^3
The following signal and noise powers were measured at various points in the system and the results are given in the Table below (N.B. note the units carefully):
Measured signal power Measured noise power S 1 = 0.02 W Not needed S 2 = 50 W (^) N 2 = 2 μW S 3 = 0.01 W N 3 = 1 mW
(i) Calculate the dB gain of both the transmitter and channel stages (i.e. Gtx, and Gchannel ). [4]
(ii) Given that the receiver gain Grx is 50dB, calculate the signal gain of the complete system. [2]
(iii) Calculate the change in the Signal to Noise ratio across the physical channel. [4]
S008 25/08/2005 continued
- (a) Describe with the aid of suitable diagrams the following types of electromagnetic propagation used in free space radio communication systems:
(i) Ground (surface) wave; (ii) Space (direct) wave. [6]
(b) Explain the basic principle of operation of an optical fibre communication system. State TWO intrinsic advantages that optical fibre has compared with metallic conductors such as twisted pair wire. [8]
(c) Assume that the initial considerations in an optical fibre system are the choice of source and fibre. Given that the choice is between:
(i) an LED or (ii) a laser diode source;
together with
(i) 1 mm core diameter multimode step-index plastic fibre; (ii) 62.5 micron core diameter multimode graded-index glass fibre or (iii) single mode step-index glass fibre.
State, giving reasons for your choice in each case, which source/fibre combination would be most suitable for:
(A) a high datarate (> 500 Mbit/s) , long distance (>10km) communications system; (B) a medium datarate (around10 Mbit/s) , medium distance (around 2 km) communications system; (C) a short distance (around 20m) visible light guide for demonstration purposes. [6]
S008 25/08/2005 continued
- (a) State the TWO most significant causes of power loss when propagating a signal across a free space microwave link. [2]
(b) A microwave frequency communications link operates via a satellite that behaves effectively as a frequency converter with a gain of 100 dB (excluding the aerials) and has a common receive/transmit aerial with 30 dB gain.
The satellite is in earth orbit at a distance of 41,000 km from both the transmitting and receiving earth stations. The system operates with an uplink frequency of 6GHz and a downlink frequency of 3.75GHz.
The transmitting and receiving earth stations both have an aerial with 50dB gain, and the signal power at the earth station (i.e. prior to the transmitting aerial gain) is 500W.
(You may assume that the Aerial Receiving Aperture = A = G λ 2 / 4 π and the speed of propagation of the wave is c = 3 x 10^8 m/s )
Determine:
(i) the power density in (W/m^2 ) incident on the satellite receiving aerial. [6]
(ii) the Effective Isotropic radiated power (EIRP) in Watts radiated from the satellite transmitting aerial. [6]
(iii) the Signal to Noise ratio in dB at the earth station (i.e. after the aerial has amplified the incoming signal) if the combined noise power at this point in the system is 1μW. [6]
END
S008 25/08/
