1. Amplitude Shift Keying (ASK)
Lecture 5:
Amplitude Shift Keying (ASK)
1nd semester
By: Adal ALashban

2. Outline - Analog conversion. - Modulation.
- Why we need digital modulation?
- Modulation of digital data.
- Types of digital-to-analog conversion.
- Aspects of digital-to-analog conversion.
- Bit rate and baud rate.
- Amplitude shift keying.

3. Introduction
- Digital data, more specifically, the binary data changes the properties of the carrier signal.
1- Amplitude
2- Frequency
3- Phase

4. Analog Conversion
- Digital-to-analog: conversion is the process of changing one of the characteristics of an analog signal based on the information in digital data (0 or 1).
- Analog-to-analog: low pass analog signal to band pass analog signal.

5. Modulation
- Definition: transforming the information to be transmitted into a format suitable for the used medium.
- The signals are transmitted as a sine wave which has three parameters: amplitude, frequency and phase shift.
- These parameters can be varied in accordance with data or another modulating signal.
- Two types of modulation:
1- Digital modulation: digital data (0, 1) is translated into an analog signal (baseband signal).
2- Analog modulation: the center frequency of the baseband signal generated by digital modulation is shifted up to the radio carrier.

6. Why we Need Digital Modulation?
- Digital modulation is required if digital data has to be transmitted over a medium that only allows analog transmission (modems in wired networks).
- Digital signals, i.e. 0/1, can be sent over wires using voltages.
- Wireless must use analogue sine waves.
- This translation is performed by digital modulation:
- Digital data is translated into an analog signal (baseband).
- Shift Keying is the translation process.
- Amplitude, Freq., Phase Shift Keying (ASK/FSK/PSK).

7. Modulation of Digital Data
Digital /Analog converter
Analog /Digital converter

8. Types of Digital to Analog Conversion
- A sine wave is represented by three characteristics: Amplitude, Frequency and Phase.
- We can change one of these characteristics to represent digital data.

9. Aspects of Digital to Analog Conversion
- Carrier Signal or carrier frequency:
- A high frequency signal that acts as a basis for the information signal.
- Digital information then modulates the carrier signal by modifying one or more of its characteristics (Amplitude, frequency or phase).
- This kind of modification is called modulation or shift keying, and the information signal is called modulated signal.

10. Carrier Signal
ASK modulated signal

11. Bit Rate and Baud Rate
- Bit rate: is the number of bits per second (bps ).
- Baud rate (Nbaud): is the number of signal units per second (baud/s).
A signal unit (one baud) is composed of 1 or more bits

12. Amplitude Shift Keying (ASK)
- In ASK the amplitude of the carrier signal is varied to represent binary 1 or 0.
- Both frequency and phase remain constant while the amplitude changes.
- The peak amplitude of the signal during each bit duration is constant, and its value depends on the bit (0 or 1).
ASK-Modulated signal

13. Digital Modulation; Amplitude Shift Keying (ASK)
- 0 and 1 represented by different amplitudes.
i.e. a basic sine wave.
- Problem: susceptible to interference.
- Constant amplitude is hard to achieve.
- ASK is used for optical transmissions such as infra-red and fiber (simple + high performance).
- In optical  light on = 1 light off = 0

14. Binary ASK (BASK) or On Off Keying (OOK)
- Although we can have several levels (kinds) of signal elements, each with a different amplitude, ASK is normally implemented using only two levels. This is referred to as binary amplitude shift keying.
- We can think of a carrier signal as an ON or OFF switch. In the modulated signal, logic 0 is represented by the absence of a carrier, thus giving OFF/ON keying operation and hence the name given OOK.

15. On Off Keying (OOK)

16. ASK Generation

17. Demodulator or Detector
- The demodulator determines the amplitude of the received signal and maps it back to the symbol it represents, thus recovering the original data.

18. Pros and Cons
- Pros:
ASK transmitter and receiver are simple to design.
ASK needs less bandwidth than FSK.
- Cons:
ASK transmission can be easily corrupted by noise.
- Application:
Early telephone modem (AFSK).
ASK is used to transmit digital data over optical fiber.

19. Any Questions ?