In this slide,some topics data communication are discussed. They are in the title. Every topic has been described easily and graphically.

1. W E L C O M E
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2. P r e s e n t a t i o n
O n
Phase Modulation , Error, Hamming
Distance , GSM
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3. L e t ’ s S t a r t o u r
P r e s e n t a t i o n
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4. CONTENTS
ConclusionError & GSM
Hamming
Distance
Phase
Modulation

5. Phase Modulation

6. Phase Modulation

7. Phase Modulation

8. Phase Modulation
 PM Bandwidth :

9. Error
 What is Error :
Networks must be able to transfer data from one device to another with acceptable
accuracy. For most applications, a system must guarantee that the data received are
identical to the data transmitted. Any time data are transmitted from one node to the
next, they can become corrupted in passage. Many factors can alter one or more bits of
a message. Some applications require a mechanism for detecting and correcting errors.
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10. Error
 What is Error :
Data can be corrupted during transmission. Some applications require that errors be
detected and corrected.
Some applications can tolerate a small level of error. For example, random errors in
audio or video transmissions may be tolerable, but when we transfer text, we expect a
very high level of accuracy.
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11. Types
 Whenever bits flow from one point to another, they are subject to unpredictable
changes because of interference. This interference can change the shape of the
signal. In a single-bit error, a 0 is changed to a 1 or a 1 to a O. In a burst error,
multiple bits are changed. For example, a 11100 s burst of impulse noise on a
transmission with a data rate of 1200 bps might change all or some ofthe12 bits
of information.

12. Single-Bit Error
The term single-bit error means that only 1 bit of a given data unit (such as a byte,
character, or packet) is changed from 1 to 0 or from 0 to 1.
In a single-bit error, only 1 bit in the data unit has changed.
To understand the impact of the change, imagine that each group of8 bits is an
ASCII character with a 0 bit added to the left. 00000010 was sent, meaning start of
text, but 00001010 was received, meaning linefeed.

13. Single-Bit Error
Single-bit errors are the least likely type of error in serial data transmission. To
understand why, imagine data sent at 1Mbps. This means that each bit lasts only
1/1,000,000 s, or 1s. For a single-bit error to occur, the noise must have a duration
of only 1s , which is very rare; noise normally lasts much longer than this.

14. Burst Error
The term burst error means that 2 or more bits in the data unit have changed from
1to 0 or from 0 to 1.
A burst error means that 2 or more bits in the data unit have changed.
In this case, 0100010001000011 was sent, but 0101110101100011 was received.
Note that a burst error does not necessarily mean that the errors occur in
consecutive bits. The length of the burst is measured from the first corrupted bit to
the last corrupted bit. Some bits in between may not have been corrupted.

15. Burst Error
A burst error is more likely to occur than a single-bit error. The duration of noise is
normally longer than the duration of 1 bit, which means that when noise affects
data, it affects a set of bits. The number of bits affected depends on the data rate
and duration of noise. For example, if we are sending data at I kbps, noise can
affect 10 bits; if we are sending data at I Mbps, the same noise can affect 10,000
bits.

16. GSM
 The Global System for Mobile Communication (GSM) is a European standard
that was developed to provide a common second-generation technology for all
Europe. The aim was to replace a number of incompatible first-generation
technologies.
 Bands GSM uses two bands for duplex communication. Each band is 25 MHz in
width, shifted toward 900 MHz, as shown in Figure . Each band is divided into
124 channels of200 kHz separated by guard bands.

17. GSM
 Transmission Figure 16.8 shows a GSM
system. Each voice channel is digitized
and compressed to a 13-kbps digital
signal. Each slot carries 156.25 bits (see
Figure ). Eight slots share a frame
(TDMA). Twenty-six frames also share a
multiframe (TDMA). We can calculate
the bit rate of each channel as follows:

18. Hamming Distance
The Hamming distance between two words is the number of differences between
corresponding bits.
One of the central concepts in coding for error control is the idea of the Hamming
distance. The Hamming distance between two words is the number of differences
between the corresponding bits. We show the Hamming distance between two
words x and y as d(x, y)

19. Hamming Distance
The Hamming distance can easily be found if we apply the XOR operation (ffi) on
the two words and count the number of Is in the result. Note that the Hamming
distance is a value greater than zero.

20. Minimum Hamming Distance
The minimum Hamming distance is the smallest Hamming distance between all
possible pairs in a set of words.
Although the concept of the Hamming distance is the central point in dealing with
error detection and correction codes, the measurement that is used for designing a
code is the minimum Hamming distance. In a set of words, the minimum Hamming
distance is the smallest Hamming distance between all possible pairs. We use d
min to define the minimum Hamming distance in a coding scheme. To find this
value, we find the Hamming distances between all words and select the smallest
one.

21. Conclusion
 Phase modulation is similar in practice to frequency modulation (FM). ... But PM
and FM are not exactly equivalent, especially in analog applications. When an FM
receiver is used to demodulate a PM signal, or when an FM signal is intercepted by
a receiver designed for PM, the audio is distorted.
 The Hamming distance is used to define some essential notions in coding theory,
such as error detecting and error correcting codes.

22. Conclusion
 GSM (Global System for Mobile communication) is a digital mobile telephony
system that is widely used in Europe and other parts of the world. GSM uses a
variation of time division multiple access (TDMA) and is the most widely used of the
three digital wireless telephony technologies (TDMA, GSM, and CDMA).
 Error coding is used for fault tolerant computing in computer memory, magnetic
and optical data storage media, satellite and deep space communications,
network communications, cellular telephone networks, and almost any other form
of digital data communication

23. Reference
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24. T H A N K Y O U !
F o r H a v i n g P a t i e n t .
A n y Q u e s t i o n s ?