Faculty of Engineering Sciences
Electronics and Communications Department
Fall 2013
ELE 466
Communication Systems
Sheet(5)
PCM
Dr. Amr Abouel Magd Ahmed
Eng : Ahmed Al Wakeel
2012 – 2013
Sheet ( 5 )
(1)
A television signal (video and audio) has a bandwidth of 4.5 MHz. This signal is
sampled, quantized, and binary coded to obtain a PCM signal.
(a) Determine the sampling rate if the signal is to be sampled at a rate 20% above the
Nyquist rate.
(b) If the samples are quantized into 1024 levels, determine the number of binary
pulses required to encode each sample.
(c) Determine the binary pulse rate (bits per second) of the binary-coded signal, and
the minimum bandwidth required to transmit this signal.
Sol.
(2)
Given the data stream 1110010100, sketch the transmitted sequence of pulses for each of
the following line codes:
(a) Unipolar nonreturn-to-zero.
(b) Polar nonreturn-to-zero.
(c) Unipolar return-to-zero.
(d) Bipolar return-to-zero.
(e) Manchester code.
(f) Differential code. (start with zero)
Sol.
(3)
Given the sine wave signal, sketch the transmitted sequence of pulses for each of the
following:
(a) PAM (pulse amplitude modulation).
(b) PPM (pulse position modulation).
(c) PWM (pulse width modulation).
(4)
Sketch the waveform of binary FSK signal in response to the input binary sequence
110010101001, rest frequency 70 MHz and an input bit rate of 20 Mbps and modulation
index 0.5.
(5)
For a BPSK modulator with a carrier frequency of 50 MHz and an input bit rate of 10
Mbps, determine the maximum and minimum upper and lower side frequencies, draw the
output spectrum, determine the minimum Nyquist bandwidth and calculate the baud.
(6)
An audio signal of bandwidth 4 kHz is sampled at a rate 25% above the Nyquist rate and
quantized. The quantization error is not to exceed 0.1% of the signal peak amplitude. The
resulting quantized samples are now coded and transmitted by 4-ary pulses.
(a) Determine the minimum number of 4-ary pulses required to encode each sample.
(b) Determine the minimum transmission bandwidth required to transmit this data.
Sol.
(7)
Binary data is transmitted over a certain channel at a rate of Rb bit/s. To reduce the
transmission bandwidth, it is decided to transmit this data using 8-ary multi amplitude
signaling.
(a) By what factor is the bandwidth reduced.
(b) By what factor is the transmitted power increased, assuming the minimum
separation between pulse amplitudes to be the same in both cases.
Hint: Take the pulse amplitudes to be ±A/2, ±3A/2, ±5A/2 and ±7A/2 so that the
minimum separation between various amplitude levels is A (the same as in the binary
case pulses ±A/2). Assume all the eight levels equally likely.
Sol.
(8)
In multiamplitude scheme with M = 16. Determine the minimum transmission bandwidth
required to transmit data at a rate of 12000 bits/sec.