1. Introduction to Information Technologies
Fall 2004
Lektion 4
Forts kapitel 4: Digital transmission.
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2. Introduction to Information Technologies
Fall 2004
Chapter 4
Digital Baseband Transmission
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3. Introduction to Information Technologies
Fall 2004
Figure DC component
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4. Introduction to Information Technologies
Fall 2004
Figure Lack of synchronization
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5. Introduction to Information Technologies
Fall 2004
Example 3
In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps?
Solution
At 1 Kbps:
1000 bits sent 1001 bits received1 extra bps
At 1 Mbps:
1,000,000 bits sent 1,001,000 bits received1000 extra bps
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6. Introduction to Information Technologies
Fall 2004
Figure Lack of synchronization
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7. Introduction to Information Technologies
Fall 2004
Example 3
In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps?
Solution
At 1 Kbps:
1000 bits sent 1001 bits received1 extra bps
At 1 Mbps:
1,000,000 bits sent 1,001,000 bits received1000 extra bps
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8. Introduction to Information Technologies
Fall 2004
Figure Line coding schemes
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9. Introduction to Information Technologies
Fall 2004
Note:
Unipolar encoding uses only one voltage level.
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10. Introduction to Information Technologies
Fall 2004
Figure Unipolar encoding
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11. Introduction to Information Technologies
Fall 2004
Note:
Polar encoding uses two voltage levels (positive and negative).
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12. Introduction to Information Technologies
Fall 2004
Figure Types of polar encoding
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13. Introduction to Information Technologies
Fall 2004
Note:
In NRZ-L the level of the signal is dependent upon the state of the bit.
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14. Introduction to Information Technologies
Fall 2004
Note:
In NRZ-I the signal is inverted if a 1 is encountered.
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15. Introduction to Information Technologies
Fall 2004
Figure NRZ-L and NRZ-I encoding
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16. Introduction to Information Technologies
Fall 2004
Figure RZ encoding
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17. Introduction to Information Technologies
Fall 2004
Note:
A good encoded digital signal must contain a provision for synchronization.
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18. Introduction to Information Technologies
Fall 2004
Figure Manchester encoding
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19. Introduction to Information Technologies
Fall 2004
Note:
In Manchester encoding, the transition at the middle of the bit is used for both synchronization and bit representation.
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20. Introduction to Information Technologies
Fall 2004
Figure Differential Manchester encoding
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21. Introduction to Information Technologies
Fall 2004
Note:
In differential Manchester encoding, the transition at the middle of the bit is used only for synchronization. The bit representation is defined by the inversion or noninversion at the beginning of the bit.
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22. Introduction to Information Technologies
Fall 2004
Note:
In bipolar encoding, we use three levels: positive, zero, and negative.
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23. Introduction to Information Technologies
Fall 2004
Figure Bipolar AMI encoding
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24. Introduction to Information Technologies
Fall 2004
Figure Mulilevel pulse amplitude modulation (PAM)
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25. Introduction to Information Technologies
Fall 2004
Figure Mulilevel PAM
A signal has M data levels with a pulse duration of T
PulseRate fs = 1 / T pulses/s
Bit Rate R = fs x log2 M
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26. Introduction to Information Technologies
Fall 2004
Example
A signal has four data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows:
Pulse Rate = = 1000 pulses/s
Bit Rate = PulseRate x log2 L = 1000 x log2 4 = 2000 bps
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27. Introduction to Information Technologies
Fall 2004
Figure Data transmission and modes
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28. Introduction to Information Technologies
Fall 2004
Figure Parallel transmission
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29. Introduction to Information Technologies
Fall 2004
Figure Serial transmission
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30. Introduction to Information Technologies
Fall 2004
Note
In asynchronous transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte. There may be a gap between each byte.
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31. Introduction to Information Technologies
Fall 2004
Note
Asynchronous here means “asynchronous at the byte level,”
but the bits are still synchronized; their durations are the same.
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32. Introduction to Information Technologies
Fall 2004
Figure Asynchronous transmission
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33. Exempel på asynkron serie-kommunikation: RS232C (”com-porten”)
Introduction to Information Technologies
Fall 2004
Exempel på asynkron serie-kommunikation: RS232C (”com-porten”)
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34. Introduction to Information Technologies
Fall 2004
Note
In synchronous transmission, we send bits one after another without start or stop bits or gaps. It is the responsibility of the receiver to group the bits.
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35. Introduction to Information Technologies
Fall 2004
Figure Synchronous transmission
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