1. Line Coding and Binary Keying Modulation

2. Some Characteristics of Line Coding
Signal level and Data Level 1
Amplitude
Time
(a) Two signal level and two data level
(b) Three signal level and two data level

3. Bit Rate and Pulse rate
If a pulse carries only 1 bit, the pulse rate and the bit rate are the same. If the pulse carries more than 1 bit, then the bit rate is greater than the pulse rate. In general we have the following formula, in which L is the number of data levels of the signal..

4. DC component Amplitude 1 Time (a) Signal with DC components1
Amplitude
Time
(a) Signal with DC components
(b) Signal without DC components

5. Synchronization
In order to correctly interpret the signals received from the sender, the receiver's bit intervals must correspond exactly to the sender's bit intervals. If the receiver clock is faster or slower, the bit intervals are not matched and the receiver might interpret the signals dif­ferently than the sender intended.
A self-synchronizing digital signal includes timing information in the data being transmitted. This can be achieved if there are transitions in the signal that alert the receiver to the beginning, middle, or end of the pulse. If the receiver's clock is out of synchronization, these alerting points can reset the clock.

6. 1
Amplitude
Time
Sent
Received

7. Line Coding
Polar
Bipolar
Unipolar

8. Unipolar
Time
Amplitude
(a) Logic 0 1
(b) Logic 1
(c) Timing diagram

9. Differential Manchester
Polar RZ
NRZ
Polar
Manchester
Differential Manchester

10. Nonreturn to Zero-Level(NRZ-L)
Time
Amplitude
(a) Logic 0 1
(b) Logic 1
(c) Timing diagram

11. Nonreturn to Zero-Invert(NRZ-I)
Time
Amplitude 1
Logic 0 - No Transition from current state
Logic 1- Transition from current state to different state

12. This transition is used for synchronization
Return to Zero (RZ)
Time 1
Amplitude
(b) Logic 1
(a) Logic 0
(c) Timing diagram
This transition is used for synchronization

13. Manchester Encoding Time Amplitude (b) Logic 1 (a) Logic 0
(a) Logic 0
(c) Timing Diagram

14. Differential Manchester Encoding
Time
Amplitude 1
Logic 0 - Transition from current state to different state
Logic 1- Continuation of current state i.e. no transition

15. Logic 1- Levels are positive and negative alternately
Bipolar
Time
Amplitude 1
Logic 0 – Level Zero
Logic 1- Levels are positive and negative alternately

16. Two binary, one quaternary (2B1Q)00
Time
Amplitude 1 3 -1 -3 01 10 11

17. Multiline transmission, three level (MLT-3)
Time
Amplitude 1

18. Block Coding 010111010101 ... 01011110 m Bit Division 0101 1101 1110
m Bits
0101
1101
1110
m Bit to n Bit
Substitution
n Bits
01101
10101
011011
Line
coding
Digital signal

19. 4B/5B encoding
With a 4-bit block, we can have 16 (=24) different groups. With a 5-bit code, there are 32 (=25) possible codes. This means that we can map some of the 5-bit groups to the 4-bit groups. Some of the 5-bit codes are not used. We can apply a strategy or a policy to choose only the 5-bit codes that help us in synchronization and error detection.
0000
0001
0010
1000
1111
4-bit Blocks
00000
00011
00010
10000
11011
5-bit Blocks
11111

20. To achieve synchronization, we can use the 5-bit codes in such a way that, for example, we do not have more than three consecutive 0s or 1s. Block coding can definitely help in error detection. Because only a subset of the 5-bit codes is used, if one or more of the bits in the block is changed in such a way that one of the unused codes is received, the receiver can easily detect the error.
The selection of the 5-bit code is such that each code contains no more than one leading 0 and no more than two trailing 0s. Therefore, when these 5-bit codes are sent

21. Data Sequence
Encoded Sequence
0000
11110
Q (Quit)
00000
0001
01001
I (Idle)
11111
0010
10100
H (Halt)
00100
0011
10101
J ( start delimiter)
11000
0100
01010
K ( start delimiter)
10001
0101
01011
T (end delimiter)
01101
0110
01110
S(Set)
11001
0111
10010
R(Reset)
00111
1000
10011
1001
1010
10110
1011
10111
1100
11010
1101
11011
1110
11100
1111
11101

22. Digital to Analog Modulation
Types of methods
Amplitude shift keying (ASK): some audio modem, optical fiber, printer
Frequency shift keying (FSK): Computer Modem, HF and VHF radio
Amplitude shift keying (PSK): Mobile, Satellite (microwave) etc
Digital to Analog Modulation
FSK
QAM
PSK
ASK
Bit rate is the number of bits transmitted per second. Baud rate is the number of signal elements transmitted per second. Baud rate is less than or equal to the bit rate

23. ASK The carrier with unity amplitude
1 Baud
1 Bit 1
Bit rate: 6
Baud rate: 6
1 Sec
Time
Amplitude
The carrier with unity amplitude
Mathematically ASK waveform can be written as

24. The bandwidth which needs to be transmitted depends on the requirements of the application. Where there is a need to recover recognizably square pulses at the receiver (to operate a printer), it may be necessary to include at least the third harmonic sideband pair
This leads to the criterion

26. Example
The standard symbol speed of 66 words per minute used by many automatic teletype machines. This corresponds to 50 baud (symbol rate) per second which need an f0=25 Hz. Thus its 3rd harmonic BW is 75Hz or 120 Hz with guard band.
But where all that is needed is to be able to decide whether a one or a zero was received and an exact bit shape is not required.

27. FSK Where s2(t) is the complement of s1(t) so that s2(t)=1- s1(t)
1 Baud
1 Bit 1
Bit rate: 6
Baud rate: 6
1 Sec
Time
Amplitude
Where s2(t) is the complement of s1(t) so that s2(t)=1- s1(t)

28. PSK PSK has advantages over both ASK and FSK.
It has the same BW as ASK which is of course less than that of FSK.
It is less susceptible to noise corruption than FSK and of course very much better than ASK
BW reduced by multilevel scheme.

29. Which is same spectrum as ASK

30. Constellation Diagram Dibits (2 Bits) 10 Dibit Phase 00 0o 01 90o 11
Tribit Phase
000 0o
001 45o
010 90o o o o o o
000
Constellation Diagram
001
010
011
100
101
110
111

31. 4PSK 1 Baud 2 Bits 00 11 01 10 Bit rate: 12 Baud rate: 6 1 Sec Time
Amplitude

32. 4QAM 00 01 10 11
000
001
010
011
100
101
110
111
4-QAM
1 Amplitude, 4 Phases
8-QAM
2 Amplitudes, 4 Phases

33. 8QAM
000
001
011
010
110
111
101
100 1
Baud
3 Bits
Bit rate: 24
Baud rate: 08
1 Sec
Time
Amplitude

34. 16 QAM 3 Amplitudes 12 Phases 2 Amplitudes 8 Phases 4 Amplitudes