Question 1: What factors should be considered when choosing a digital encoder (line codes)? Briefly illustrate five of those factors. Use sketches and additional text to explain the following encoding techniques: NRZ-L, Bipolar-AMI, Manchester, HDB3, B8ZS and 4B/5B. Your explanation of each technique should comprise the encoding rule, advantages and disadvantages. No mathematical equations are necessary.
Question 2: A modified NRZ code known as enhanced-NRZ (E-NRZ) operates on 7-bit words; inverting bits 2,3,6 and 7; and adding one parity bit to each word. The parity bit is selected to make the total number of 1s in the 8-bit word an odd count. What are the advantages of E-NRZ over NRZ? Are there any disadvantages?
Question 3: Why should a modem be used to transmit binary data via a PSTN?
(A) Use sketches and additional text to explain the given modulation methods.
(a) Amplitude shift keying.
(b) Frequency shift keying.
(B) Discuss the factors that influence the choice of carrier frequency and the bandwidth used by the demodulator section of a modem.
Question 4: Data is to be transmitted using a modem at 9600 bps. Determine the minimum bandwidth of the system with the following modulation methods (a) FSK (b) ASK. Use the excess bandwidth factor r = 0:5. Compare ASK and BFSK in terms of transmission bandwidth
for a constant data rate.
Question 5: Find the Nyquist rate for the following signals:
(a) x(t) = 5 sin 3000πt cos 4000πt
(b) x(t) = (sin 500πt)/(πt)(c) x(t) = [(sin 300πt)/(πt)]2
The binary channel with bit rate 36000 bps is available for PCM voice transmission. Find out appropriate values of the sampling rate, the number of quantizing levels, and the binary digits, supposing a maximum frequency of 3.2 kHz.
Question 6: An analog information signal, whose maximum frequency is 6000Hz, is to be transmitted by using a PCM system. The quantization error should not exceed the ±1 % of the peak-to-peak analog signal.
(a) Determine the minimum number of bits per sample or bits per PCM word that must be used in this system?
(b) Determine the minimum required sampling rate, and what is the resulting bit rate?
(c) Determine the PCM pulse or symbol transmission rate?
Question 7: A PCM system uses 8 bits per sample and the analog signal is limited to 4.3 kHz. The PCM data is transmitted using (a) BFSK and (b) ASK. Determine the bandwidth required for transmission in each case. Assume that r = 0:55.
Question 8:
(a) Consider a sinusoidal signal m(t) = Acos(2πfmt) applied to a delta modulator with step size Δ. Find out the range of the step size so that slope overload will be avoided. Suppose that delta modulation (DM) system is designed to operate at 3 times the Nyquist rate of the input signal. The quantizing step size is 250 mV. Find out the maximum amplitude of a 1-kHz input sinusoid for which the delta modulator doesn't show slope overload.