Analog Transmission And Error Detection

2. Presented By
Md. Nazrul Islam
ID: 143-15-4480
Department : C.S.E
Daffodil International University
Dhaka Bangladesh

3. Presentation On
Analog Transmission And Error
Detection

4. Contents
1. Analog Transmission
2. Digital to Analog Conversion
3. Analog to Analog Conversion
4. Error
5. Error Detection
6. Types of Error
7. Checksum

5. Analog Transmission

6. What is analog transmission?
Type of analog transmission:
1. Digital to analog conversion
2. Analog to analog conversion

7. What is digital to analog conversion?
Type of digital to analog conversion:
1.Amplitude shift keying
2.Frequency shift keying
3.Phase shift keying

8. Amplitude shift keying (ASK) : Amplitude-shift
keying (ASK) is a form of amplitude modulation that
represents digital data as variations in the amplitude
of a carrier wave.

9. Frequency shift keying : Frequency shift keying
(FSK) is a frequency modulation scheme in which digital
information is transmitted through discrete frequency
changes of a carrier signal.

10. Phase shift keying : Phase shift keying (PSK) is a
digital modulation scheme that conveys data by
changing (modulating) the phase of a reference signal.

11. ANALOG  ANALOG CONVERSION
• Analog signals are modified to represent analog data.
• Also known as Analog Modulation.
• Required when BANDPASS is used.

12. TYPES

13. Amplitude Modulation
• In AM transmission, the carrier signal is modulated so that its amplitude
varies with the changing amplitudes of the modulating signal. The
frequency and phase of the carrier remain the same. Only the amplitude
changes to follow variations in the information. The following figure
shows how this concept works. The modulating signal is the envelope of
the carrier.

14. Frequency Modulation
• In FM transmission, the frequency of the carrier signal is
modulated to follow the changing voltage level (amplitude)
of the modulating signal. The peak amplitude and phase of
the carrier signal remain constant, but as the amplitude of
the information signal changes, the frequency of the carrier
changes correspondingly.
• The following figure shows the relationships of the
modulating signal, the carrier signal, and the resultant FM
signal. FM is normally implemented by using a voltage-
controlled oscillator as with FSK. The frequency of the
oscillator changes according to the input voltage which is the
amplitude of the modulating signal.

15. Continued……(FM)

16. Phase Modulation
• In PM transmission, the phase of the carrier signal is modulated to
follow the changing voltage level (amplitude) of the modulating
signal. The peak amplitude and frequency of the carrier signal remain
constant, but as the amplitude of the information signal changes, the
phase of the carrier changes correspondingly. It is proved
mathematically that PM is the same as FM with one difference.
• In FM, the instantaneous change in the carrier frequency is
proportional to the amplitude of the modulating signal; in PM the
instantaneous change in the carrier frequency is proportional to the
derivative of the amplitude of the modulating signal. The following
figure shows the relationships of the modulating signal, the carrier
signal, and the resultant PM signal.

17. Continued…..(PM)

18. Errors
A bit error occurs when a source sends a bit, b, and the destination
receives NOT b.
The error can take place on the link , in a switch or router along the path,
or in the source or destination (e.g. failed hardware, or bit errors in
memories).
1. . .bi be  

19. Rutvi Shah 19
1 0 0 1 1 1 0 0 1 0 1
1 0 0 1 0 1 0 0 1 0 1
Sent
Received
Error

20. Rutvi Shah 20
TYPES OF ERRORS
• Single bit error :-
- Only one bit in the data unit has changed.
• Burst error :-
- It means that two or more bits in the data unit has changed.

21. Rutvi Shah 21
Single bit Error
0 0 0 0 1 0 1 0 0 0 0 0 0 0 1 0
Burst Error
0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1
0 1 0 1 1 1 0 1 0 1 0 0 0 0 1 1
0 changed to 1
Received Sent
Sent
Received
Bits corrupted by Burst Error

22. Winter 2008 CS244a Handout 13 22
Detecting and Correcting Errors
• When we transmit a message, we typically append a checksum to the
message.
• The checksum is calculated by performing a function over all the bits
in the message.

23. A checksum is a simple type of redundancy check that is
used to detect errors in data.

24. Sender site:
1. The message is divided into 16-bit words.
2. The value of the checksum word is set to 0.
3. All words including the checksum are
added using one’s complement addition.
4. The sum is complemented and becomes the
checksum.
5. The checksum is sent with the data.

26. Receiver site
1. The message (including checksum) is
divided into 16-bit words.
2. All words are added using one’s complement addition.
3. The sum is complemented and becomes the
new checksum.
4. If the value of checksum is 0, the message
is accepted; otherwise, it is rejected.

28. 10.28
1
1 1
0

29. Advantage
Checksum mainly detects single-bit changes in data.
A checksum is mainly employed in data validation when
implementing software.

31. THANK YOU