Question

Question 4 (a) A 3,000 bit/second data terminal is connected to a modem with 25% raised-cosine roll-off pulse shaping is used. Calculate the transmission bandwidth Bt required at the modem output for each of the following schemes: (0) Binary amplitude-shift keying (ASK) transmission. [2 marks] (ii) Binary frequency-shift keying (FSK) transmission with a frequency deviation of +2,400 Hz around the carrier. [2 marks] (iii) 16-level quadrature amplitude modulation (QAM). [2 marks] (b) FSK transmission is used to transmit 750 bps digital signals over a telephone channel. The FSK signals are to fit into the range 500 to 3,000 Hz. The two carrier frequencies are taken to be 1,000 and 2,500 Hz. Assuming raised-cosine roll-off shaping, what roll-off factor is required? [4 marks] End of Assignment

Answer 1

@ Gilven Rh= 3,000 bps, d=250) 2= 0.25 () ASK B = 2R6 es Rectangular pulsy Br = 2 (RU/ Cltd) Rassed cosine pulsy By= R6 (148)] = 3k C1+025] = 3.75 kH3 Gig fik: [Br = Rb (ltd) of (fi-fe) I (finte) = 2400th - 3.75KHZ + 2.4K = 6.15 KHZ (1) 16-level QAM... Т-16 By = RbC1td) 3.75k logem 1 -0.97 lk logo16 Given © BW so 3 3.00 - 500 22500 Rb - 750 bps , BW= 2500 H3 f = 1,000 H3 = forf f = 2,500 Hz [BW = Rb (ltd) & (firfe) = 750 (1+2)+(1-fe) 2-5% 50,75k (1+) + 1500 = 2.5% = 0-75(italt lesk | =03330[= 33.347,