Question

QUESTION 3 Briefly explain the following Analog Pulse Modulation (APM): (i) Pulse Amplitude Modulation (PAM) Pulse Width Modulation (PWM) (iii) Pulse Position Modulation (PPM) (2 marks) (2 marks) (2 marks) b) There are several digital modulations techniques used to modulate digital signal. For a binary data 10111011, sketch the output waveform if the following modulator is used: Amplitude Shift Keying (ASK) (2 marks) Frequency Shift Keying(FSK) (2 marks) (iii) Phase Shift Keying (PSK) (2 marks) Assume the carrier is a sinusoidal signal. An 8 kHz audio signal with peak to peak voltage of 25 V is transmitted by using a Pulse Code Modulation (PCM) system and the quantization level used is 512. The signal is sampled at a rate of 15% higher than the minimum sampling frequency. Determine: The minimum sampling frequency, (2 marks) The sampling frequency used, (2 marks) The number of bits for every sample, (2 marks) (iv) The resolution step (1 marks) (v) The maximum quantization error, and (1 marks) (vi) The transmission bit rate. (1 marks) How the quantization error can be reduced? State an effect of reducing the quantization error (4 marks) [Total Marks:25]
Communication System

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Answer 1

(a) 6 Analog pulse modulation technique are mainly classified into false Amplitude Mooduktion CPAMI Pulse width modulation (PWM) / Pulse duration modulation CP dan DM) and Pulse Position Modulation (PPM), i Pulse amplitude Modulation (PAM) : Pulse amplitude Modulation is an analog modulating scheme in which the amplitude of the pulse carorien varies proportional to the instantaneous amplitude of the message signale The pulse amplitude modulated signal, will follow the amplitude of the original signal, as the signal traces out the path of the whole ware. In natural PAM, a signal sampled at the Nyquist kate is rescoustaucked, by Passing it through an efficient low pass filter (LPF) with exact cutoff facequency The following figures explain the pulse Amplitude Modulations 0 Modulating Signal Carrier Pulse train

th Natural PAM Though the PAM signal is passed through an LPF it comingt gecoreze the signal without distogtion Hence to avoid this hase, flat top sampling is as shown in the following figurer done. Flat - Top PAM Flat-top sampling is the process in which sampled signal can be represented in pulses for which the amplitude of the signal cannot be changed with respect to the analog signal to be sampled. The tops of amplitude demain flat. This process simplifies the coccit design. ii) Pulse Width Modulation (PWM) & Pulse Width Modulation (PWM) on Pulse Duration Modulation (PDM) or Pulse Time Moduktion (PTM) is an analog modulating scheme in which the duration or width a time of the Pulse cancies vancies Popcational to the instantaneous amplitude of the message signal.

in this o The width of the pulse varies method, but the amplituse of the signal remain constant Amplitude limiters are used to make the amplitude of the signal constant. These circuit clip off the amplitude, to desired level and hence the noise is limited to a The following figures explain the types of Pulse Width Modulations.

Carrier Pulse Modulating Signal 11 1 (b) (C)

There are three variations of PWM. They are The leading edge of the pulse being constant, the trailing edge varies according to the message signale - The trailing edge of the pulse being constant, the leading edge saues according to the message siguale - The center of the pulse being constant, the leading edge and the trailing edge varies according to the message signate These three types are shown in the above given figure with timing slots. iiPulse Position Modulation (ppm) Pulse position modulation scheme in which the amplitude and width of the pulses are kept constant, while the position of each pulse, with reference to the position of a reference pulse, Varcies according to the instante neous sampled value of the message signale The transmitter has to send synchronizing pulses Con simply sync pulses) to keep the transmitter and seceives in Synchronisk. These sync pulses help maintain the position of the pulses. The following figures explain the Pulse Position Modulation

Amplitude Time Amplitude Time Periodic sequential Pulse train Amplitude IPWM signal Time Amplitude b Time PIPM signal Pule position modulation is done in accordance with the pulse width modulated signal. Each training of the puse width modulation modulated signal becomes the starting point for pulses in PPM signale Hence the position of these pulses is propeational to the width to the PWM pulses

(b) binary data = 10 11 10 11 1 } 1 1 M o i, Ask FSK НАДМУДДДДЛТУЛДЛАЛ ii) PSK
beacuase of time limit i could solve this much you can ask last question separately.

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