Telecommunications Technology AD DA Conversion

1
Telecommunications TechnologyA/D D/A Conversion

• Week 4

ICS 620
2
Overview

• Analog versus digital signals
• A/D D/A conversions
• Carrier Signaling formats
• dB

3
Unity Chart
100
10-3
10-6
10-9
10-12
10-15
1015
1012
109
106
103
1
000
000
000
000
000
000
000
000
000
000
000
000
milli-
micro-
nano-
pico-
femto-
alto-
kilo-
mega-
giga-
tera-
peta-
exa-
K
M
G
T
m
?
n
p
f
P
E
a
4
Analog versus digital signals

• Nature is analog
• Analog is frequency efficient
• Signals and noise
• As signals diminish, amplifiers are used
• Noise is amplified as well as signal
• Digital is more repeatable
• All we need is to detect and recreate

5
A/D Conversions
Filter
Sample
Quantize
Encode

• Sample
• Nyquist Rate
• Quantize
• Number of Levels
• Encode
• Pulse Code Modulation

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Sample

• Nyquist Rate
• How many samples are needed such that information
  is not lost

Analog Signal
Time
8
Sampling
One Possible Rate
Two times that Rate
9
Sampling - A better view
Basic Rate
Two times Basic Rate
10
Sampling - How Close Are We?
May be Okay?
Basic Rate
Two times Basic Rate
This is better.
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The Nyquist Rate

• For fidelity, the sampling rate must be at least
  two times the highest frequency of the information

Highest frequency
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Filter

• Limits the frequency of the signal for processing

Signal Power
Low Pass
Frequency
Raw Signal
Input Signal
Frequency
Frequency
15
Quantize

• Number of Levels
• A pure sample will be any of the infinite
  possible number of levels

16
Quantize

• It is impossible to transmit infinitely variable
  values through digital means (without an
  infinitely long number)
• So we limit the possible values

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Quantize
2.0
1.9
1.8
1.7
1.6
1.525
Assign to 1.5
1.5
1.4
1.385
Assign to 1.4
1.3
1.2
1.1
1.0
Sample 1
Sample 2
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Encode

• Assign a binary code representing the signal
  level value of the sample
• How do we determine what the number of levels
  will be?

One Possible Code
Volts
11010
An Example
11001
11000
10111
10110
10101
10100
10011
10010
10001
10000
19
Pulse Code Modulation

• The US digital voice standard
• Uses 8 bits to represent 255 levels (0 000 0000
  is not used)
• The MSB is the sign bit
• The next 3 bits define a segment or chord
• The 4 LSBs are the level in the chord

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Companding
127
111
95
79
Output
63
47
31
15
Input
21
Companding
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Expanded View
1111 1101 1011 1001 0111 0101 0011 0001
1110 1100 1010 1000 0110 0100 0010 0000
001
0
1111 1101 1011 1001 0111 0101 0011 0001
1110 1100 1010 1000 0110 0100 0010 0000
Output 0 000 1100
000
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Expanded View Again
1111 1101 1011 1001 0111 0101 0011 0001
1110 1100 1010 1000 0110 0100 0010 0000
001
0
1111 1101 1011 1001 0111 0101 0011 0001
1110 1100 1010 1000 0110 0100 0010 0000
Output 0 001 1101
000
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D/A Conversions

• Decode
• Low Pass Filter

25
Signal Formats

• Binary Formats
• Unipolar NRZ
• Unipolar RZ
• Polar NRZ
• Polar RZ
• Bipolar RZ -- Alternate Mark Inversion (AMI)

26
Binary Formats
Mark
Mark
Mark
Mark
Space
Space
Space
1
0
1
0
0
1
1
Unipolar NRZ
Unipolar RZ
Polar NRZ
Polar RZ
Bipolar RZ (AM I)
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Bits Per Second Vs Baud

• Bits per second is a measure of the information
  rate.
• Baud is a measure of the transfer rate in symbols
  per second
• Only for binary formats are the rates equal

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Asynchronous Vs Synchronous

• Asynchronous has no timing requirements
• Uses Start and Stop bits for reference
• Synchronous has timing
• Relies on the clock for reference
• Continuous bit stream

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Asynchronous Vs Synchronous
Asynchronous
Isochronous
1
2
3
4
5
6
7
8
9
10
11
12
Synchronous
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Multiplexing

• Using a channel to transmit more than one
  communication
• Common forms--FDM, TDM, WDM

Combined Comm Path
Mux
Mux
Individual Comm Paths
Individual Comm Paths
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Inverse-Multiplexing

• Using multiple channels to transmit information
  larger than a single channel
• E. G. 336Kbps video over 6 voice channels

Mux
Mux
Composite Comm Paths
Composite Comm Paths
Distributed Comm Path
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36
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Digital Trunk Hierarchy
38
Multiplexed Signal Formats

• Transmission
• T-1 -- 1.544 Mbps
• T-2 -- 6.312 Mbps
• T-3 -- 44.736 Mbps
• T-4 -- 274.176 Mbps
• E-1 -- 2.048 Mbps

39
Digital Trunk
T1 Mux (Chan Bank)
DS1
T2 Mux (M1-2)
24 DS0
T3 Mux (M2-3)
DS2
DS1
T4 Mux (M3-4)
DS1
DS2
DS2
DS3
DS1
DS2
DS3
1C Mux
DS2
DS4
48 DS0
DS1C
DS2
DS3
DS2
DS3
T3 Mux (M1-3)
Level Voice bps DS0 1
64k DS1 24 1.544M DS1c 48
3.152M DS2 96 6.312M DS3 672
44.736M DS4 4032 274.176M
DS3
28 DS1
DS3
North American Hierarchy
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Digital Trunk
E1 Mux
E1
E2 Mux
30 DS0
E4 Mux
E3
E1
E3 Mux
E2
E1
E2
E5 Mux
E3
E4
E1
E2
E3
E4
E3
E2
E5
E4
Level Voice bps DS0 1
64k E1 30 2.048M E2 120
8.448M E3 480 34.368M E4
1920 139.264M E5 7680 565.148M
E4
European Hierarchy
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T-Carrier Framing
Framing Bit
Channel 24
Channel 1
Channel 2
Info Bits
Info Bits
Info Bits
Signaling Bit (Sometimes)
Signaling Bit (Sometimes)
Signaling Bit (Sometimes)
DS0 is The D4 format of one time slot Baseband
digital signal 8bits at 8000 times/sec
42
T-Carrier Framing
Framing Bit
Channel 24
Channel 1
Channel 2
FB
FB
FB
CH1
CH2
CH23
CH24
CH1
CH2
CH23
CH24
Frame 5
Frame 6
A DS1 frame -- 24 voice (DS0) channels
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E-Carrier Framing
Channel 31
Channel 0
Channel 1
b0
b7
CH1
CH15
CH31
CH1
CH30
CH31
CH30
CH15
CH0
CH0
CH16
CH16
Channels 0 and 16 are the signaling channels.
An E-1 frame -- 30 voice (DS0) channels with two
signal channels
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T-Carrier Framing
Framing Bit
Channel 24
Channel 1
Channel 2
FB
FB
FB
CH1
CH2
CH23
CH24
CH1
CH2
CH23
CH24
Frame 5
Frame 6
F5
F6
F7
F8
F9
F10
F11
F12
F12
F1
Superframe
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T1 Framing
F1
0
0
0
1
1
0
1
1
1
0
0
1
0
1
0
0
0
1
1
0
1
1
1
0
0
1
0
Superframe Framing Word
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T1 Framing
F1
0
0
0
1
1
0
1
1
1
0
0
1
0
1
0
0
0
1
1
0
1
1
1
0
0
1
0
Superframe Framing Word
Extended Superframe
F13
F14
F15
F16
F17
F18
F19
F20
F21
F22
F23
F24
F5
F6
F7
F8
F9
F10
F11
F12
F24
F1
D
D
D
D
D
D
D
D
D
D
D
D
D
C4
C5
C6
C1
C2
C3
0
1
1
0
0
1
1
C bits CRC-6 bits D bits Data link bits
(Maint) 001011 6 bit framing pattern
47
T2 Framing
T1 a
T1 b
4 each T1 Frames
T1 c
T1 d
1 T2 Frame
125?s
available for bit stuffing
12bits
M1
C11
C12
C13
F0
F1
M2
C21
C22
C23
F0
F1
125 ? s
M3
C31
C32
C33
F0
F1
M4
C41
C42
C43
F0
F1
M1
C11
C12
C13
F0
F1
48
T2 Framing
Bit Interleaved
M1
48 Information Bits
Control Bit
49
Network Design Considerations for T-Carriers
50
Multiplexed Signal Formats

• One's Density Rule
• FCC -- limit 80 zeros with 12.5 density over a
  short interval
• Bellcore -- limit 15 zeros in row with a 12.5
  average density.
• And a CSU will require at least one "1" in each
  byte

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Multiplexed Signal Formats-contd

• Synchronization
• Zero Code Suppression (ZCS)
• Bipolar with 8 Zero Substitution (B8ZS)
• Cyclical Redundancy Check (CRC)

52
Normal Handling of Zeros
Framing Bit
Channel 24
Channel 1
Channel 2
FB
FB
FB
CH1
CH2
CH23
CH24
CH1
CH2
CH23
CH24
Frame 5
Frame 6
F5
F6
F7
F8
F9
F10
F11
F12
F12
F1
Superframe
Any occurrence of 8 Zeros will be replaced with 7
Zeros and a One.
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Zero Code Suppression (ZCS)

• ZCS is used in D4 and ESF by stuffing a 1
  into a string of zeros to provide a keep-awake
  signal to the distant end of the circuit.

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B8ZS

• Replaces any string of 8 zeros with a
  recognizable line code that alerts the distance
  end of the violation.

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B8ZS
0
0
0
0
1
0
1
0
0
0
0
Unipolar NRZ
AMI
B8ZS
AMI
B8ZS

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Multiplexed Signal Formats (cont'd)

• Fractional T-1
• Concept is to share network capacity
• Drop and insert technique
• Requires specialized channel bank

To Telco
Cust 1
Cust 2
Cust 3
Ch 1-5
Ch 6-17
Ch 17-24
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Amplification and Loss

• Signal Gain or Decrease
• System components
• Ratio of output to input
• Volts or Watts

System
Signal In
Signal Out
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Signal Strengths (dB)

• Power in decibels
• 10 log (power out / power in)

Example
System
25 Watts
5 Watts
Gain 10 x log ( 5 / 25 )
Gain 10 x log ( 0.2 )
Gain 10 x ( - 0.699 )
Gain - 6.99
Note Negative gain is a loss.
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dB Logarithms
n

• If 10 N

Then
Log n
10
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Summary

• Analog and digital signals
• Multiplexing
• Carrier Signaling Format
• Amplification Losses