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TH E MANCH ESTER M ETR O PO LITAN UNIVER SITY
FACULTY O F SCIENCE AND ENGINEER ING
D EPA R TMENT O F ENGINEER ING AND TECH NO LO GY
SESSIO N 2001/
Exam ination for th e BEng (H O NS) ELECTR ICA LAND ELECTR O NIC ENGINEER ING BEng (H O NS) CO MMUNICA TIO N AND ELECTR O NIC ENGINEER ING BEng (H O NS) CO MPUTER A ND ELECTR O NIC ENGINEER ING BEng (H O NS) ELECTR O NIC ENGINEER ING W ITH M A NA GEMENT BEng (H O NS) ELECTR O NIC ENGINEER ING (PA R T-TIME) YEA R TW O
UNIT 64EE2071 : CO M M U NICATIO N ENGINEER ING
Th ursday 23 May 2002
9 .30 am to 11.30 am
Instructions to Candidates
A nsw er TH R EE questions. ALL questions carry equalm ark s.
A supplem entary answ er sh eet for part of Question 3.is provided. If used you m ust attach it to your answ er book.
- (a) State w h at is m eant by th e term ‘m odulation’and outline th e m ain reasons for its use in com m unication system s. [6]
(b ) Explain w ith th e aid of a suitab le diagram h ow a frequency m odulated (FM) w aveform can b e produced and sh ow w ith th e aid of a sk etch w h at an FM w aveform w illlook lik e in th e tim e dom ain. [6]
(c) In an FM transm itter th e m odulated output signalis ch anging b e tw een 9 0.010 MH z and 89 .09 0 MH z at a rate of 5000 tim es per second.
D e term ine:
(i) th e carrier frequency; (ii) th e m odulating (intelligence) frequency; (iii) th e FM signalb andw idth. [5]
A noth er possib le com m unication tech nique for b roadcast transm ission of an audio signalis A m plitude Modulation (A M ). State any advantages and disadvantages FM h as for th is application w h en com pared w ith A M. [3]
- (a) A 1k H z sinusoidalsignalvaries betw een m axim um and m inim um am plitudes of + 1 Volt and –1 Volt (th e am plitude versus tim e w aveform for th is signalis sh ow n in th e top b ox on th e supplem entalansw er sh eet). Th is analog signalis sam pled 10 tim es over one period, by a 0 to + 1 Volt pulsed w aveform w ith a 20% duty cycle.
O n th e supplem entary answ er sh eet provid e d , sh ow , in b oxes A and B respectively,
(i) th e pulse sam pling w aveform and (ii) the Pulse Amplitude Modulated (PAM) waveform which results from the sampling process [6]
(b ) Explain h ow th e PA M w aveform could be quantised using 8 different levels to produce a Quantised Pulse A m plitude Modulated (QPA M ) w aveform. Th en evaluate th e m axim um quantisation error in volts and th en draw th e resulting Q PAM w aveform in b ox C on th e supplem entary answ er sh eet. [8]
(c) State h ow m any bits w ould b e required if th e resulting Q PAM signalw ere to b e turned into a b inary code sequence. H ence com plete th e coding Tab le Q 3 on th e supplem entary A nsw er sh eet. [6]
- Explain b riefly w h at is m eant by th e follow ing term s:
(a) Bandw idth (b ) Ch annelCapacity (c) Baudrate [6]
W ith th e aid of suitab le diagram s explain th e operation of th e follow ing digital m odulation sch em es:
(i) A m plitude sh ift k eying (A SK ).
(ii) Ph ase sh ift k eying (PSK ) [6]
Explain w h y it is considered better to use com b ined m ulti-levelA SK -PSK m odulation sch em es for use in m odem s operating over teleph one lines. [3]
A com b ined A SK -PSK m odulation sch em e is used to encode 3 b its into sym b ols according to th e follow ing tab le:
relative ph ase bit sym b ol am plitude sh ift m eaning value
1 45 0 0 0 "0" 1 135 0 0 1 "1" 1 225 0 1 0 "2" 1 315 0 1 1 "3" 2 45 1 0 0 "4" 2 135 1 0 1 "5" 2 225 1 1 0 "6" 2 315 1 1 1 "7"
Sk etch th e constellation diagram for th is m odulation sch em e, clearly indicating sym b olvalues in th e diagram. [5]
