Presented By

Md. Nazrul Islam ID: 143-15-4480Department : C.S.EDaffodil International University Dhaka Bangladesh

Presentation On

Analog Transmission And Error Detection

Contents

1. Analog Transmission 2. Digital to Analog Conversion3. Analog to Analog Conversion4. Error5. Error Detection6. Types of Error7. Checksum

Analog Transmission

What is analog transmission?

Type of analog transmission:1. Digital to analog conversion2. Analog to analog conversion

What is digital to analog conversion?

Type of digital to analog conversion:1.Amplitude shift keying2.Frequency shift keying3.Phase shift keying

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.

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.

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

ANALOG ANALOG CONVERSION

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

TYPES

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.

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.

Continued……(FM)

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.

Continued…..(PM)

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

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

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.

Rutvi Shah 21

Single bit Error

0 0 0 0 1 0 1 0 0 0 0 0 0 0 1 0

Burst Error0 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

CS244a Handout 13 22Winter 2008

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.

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

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.

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.

10.28

11 10

Advantage

Checksum mainly detects single-bit changes in data.

A checksum is mainly employed in data validation when implementing software.

THANK YOU