chapter 5. multiplexing

Data Communication, NUML-Islamabad

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Chapter 5. Multiplexing


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Definition of Multiplexing

• Transmission of information (either voice or data) from more than one source to more than one destination on the same transmission medium (facility).”

• Or multiplexing is sending of number of separate signals together, over the same cable or bearer, simultaneously and without interference.

• TYPES: • 1) frequency division multiplexing (FDM) • 2) time division multiplexing (TDM).


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Audio Channel

• 4-kHz Bandwidth


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5.2 Frequency-Division Multiplexing

• SUBCARRIERS: First modulating messages onto several subcarriers and forming a composite baseband signal that consists of the sum of these modulated subcarriers, and

• MAIN CARRIER: This composite signal may then be modulated onto the main carrier.

• FREQUENCY ALLOCATION: In FDM, each channel of system is assigned a discrete portion of transmitted frequency. Thus many narrow bandwidth channels can be accommodated by a single wide bandwidth transmission system.


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5.2.1 FDM Hierarchy• BASIC GROUP: 12-Channels- 60 to 108 kHz. fc

0 4 f

1

104 108 112

1

0 4 f 108-4n

112-4n

116-4n

n

108-4n

112-4n

n

0 4 f 100 104 112

2

100 104

2

104 108

1

0 4 f 60 64 68

12

60 64

12

Basic GroupVoice

circuit

1

2

12

G1 (60-108 kHz)

12

11

10

9 8 7 6 7 4 3 2 1

60

108 frequency (kHz)

fc

fc

fc


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60-Channel Supergroup

• Combining 5 groups of 12 ch into 60-ch supergroup

• Frequency range:

312 to 552 kHz

0 60 108

1

420

480

528

360

312

1

360

312

0 60 108

2

468

528

576

408

360

2

408

360

fc

0 60 108

3

516

576

624

456

408

3

456

408

fc

0 60 108

4

564

624

672

504

456

4

504

456

fc

0 60 108

5

612

672

720

552

504

5

552

504

fc

312 360 408 456 504

1 2 3 4

552

5

f kHz

G1

G2

G3

G4

G5

Super Group SG (312-552 kHz)


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960-Channel Mastergroup

1116 1364 1612 1860 2108 2356 2604 2852 3100 3348

SUPERGROUP CARIER FREQUENCIES

4340409238443596

Figure 5.2.1-3 16-supergroups assembly for 960 telephony channels

SG1

SG2

SG3

SG16

MASTER-GROUP

60-4028 kHz

564 804812 1052

1060 1300 1308

1548

1556 17961804 2044

2052 22922300 2540

2548 27882796 3036

3 4 5 6 7 8 9 10 11 12

f ( kHz)

1 2

13

14 15 16

3044 32843292 3532

3540 37803788 4028

312 55260 300


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FDM Hierarchy

Basic Group

(12 ch)Voice circuit

1

2

12

G1

G2

G3

G4

G5

Supergroup

SG1

SG2

SG3

SG16

Mastergroup 960 ch

12 ch/group

(12 ch/group X 5 groups = 60 ch) (60 ch/SG

X 16 SG = 960 ch)

Figure 5.2.1-4 960-channels long-haul FDM hierarchy


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FDM Bandwidths• Type of baseband Bandwidth• _________• Voice 3.4 kHz• Audio channel 4 kHz• Video 4 MHz• Television channel 6 MHz• Multiplexed voice:• 12 channels 48 kHz• 24 channels 96 kHz

36 channels 144 kHz60 channels 240 kHz

• 120 channels 480 kHz• 240 channels 960 kHz• 300 channels 1.2 MHz• 600 channels 2.4 MHz• 900 channels 3.6 MHz• 960 channels 3.84 MHz• 1,200 channels 4.80 MHz• 1,260 channels 5.04 MHz• 1,800 channels 7.20 MHz• 2,700 channels 10.8 MHz


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RF Carriers

TXRX

1

2

N

Figure 5.2.1-5 Multiplexed channels for RF propagation

Radio channels: 4GHz, 6GHz

Number of multiplexed channels: -Maximum up to 2700 telephone channels or -television signal.


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5.3 Time-Division Multiplexing

• Definition: TDM is time interleaving of samples from several sources so that information from these sources can be transmitted serially over a single communication channel.


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Pulse Insertionf1(t)

T

(a) One PAM signal

f1(t) f2(t)

TTX

(c) Two PAM signals

f2(t)

T

TX(a) Second PAM signal

Tx :Time spacing between adjacent samples

Tx= T/n

n: number of input signals


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Example

Ch3

Ch4

Ch5

Ch6

Ch2

Ch1t

Multiplexed PAM waveform

1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5

6


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Digital Multiplexing

• Forming High-Bit-Rate Signal: Several low-bit-rate signals can be multiplexed, or combined, to form one high-bit-rate signal to be transmitted over a high-frequency medium.

• Diverse Nature Signals: Signals from various incoming channels may be of such diverse nature as a digitized voice signal (PCM), computer output, telemetry data, a digital facsimile, and so on.


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Digital Multiplexing Techniques1) BIT-BY-BIT Basis: Known as bit or digit interleaving 2) WORD-BY-WORD Basis: Known as byte or word interleaving).

Figure 5.4-1 Digital multiplexing


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5.5 PCM Hierarchies – E1 System

• CAPACITY: • No. of Time Slots: 32• 1) No. of digital telephone channels: 30 of 64 kbit/s • 2) plus one for synchronization/transmission of alarms • 3) and other one for signalling.

• TRANSMISSION RATE: • 32channels x 8bit/channel/125 µs =2.048 Mbit/s• (32 TS x 64 kbps = 2.0248 Mbit/s)

• USAGE:E1 circuits are used to connect medium and large companies.

• E3 lines are used between exchanges countries, and have transmission speed of 34.368 Mbit/s.


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T1 System

• Multiplexes 24 digital telephone channels of 64 kbit/s into a 1.544 Mbit/s (= 64 kbps x 24 channels).

• Aggregate Transmission Rate: (24channels x 8bit/channel + 1bit) / 125 µs = 1.544 Mbit/s


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PCM Frame Structure – E1 Format

0 1 2 3 4 5 6 7 8 9 10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

1 2 3 4 5 6 7 8 Bit no.

F 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 S 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Channel no.

Time slot

1 frame = 125s

64 kbps

Figure 5.5-1 2.048 Mbps frame structure – E1


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PCM Hierarchy Data Rates

Channels

Ist OrderMUX

(30x1=30ch)

1

2

30

2nd OrderMUX

(30X4=120 ch)

1

2

3

4

3rd OrderMUX

(120x4=480 ch)

1

2

3

4

4th OrderMUX

(480x4=1920 ch)

1

2

3

4

2.048 Mb/s 8.448 Mb/s 34.368 Mb/s 139.268 Mb/s

Figure 5.5.1-2 PCM hierarchies (a) E-hierarchy levels (b) T-hierarchy levels (c) E-System multiplexing hierarchy levels showing data rates


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2048k(30 Ch)*

8448k(120 Ch)

8448k(120 Ch)

x4

34 386k(480 Ch)

34 386k(480 Ch)

139 268k(1920) Ch

139 268k(1920) Ch

x4

x4

564 264k(7680) Ch

564 264k(7680) Ch

x4

Europe　（ CEPT）

1544k(24 Ch)

6312k(96 Ch)

6312k(96 Ch)x

4

x5

32 064k(480 Ch)

32 064k(480 Ch)

97 728k(1440 Ch)

97 728k(1440 Ch)

x3

397200k(5760 Ch)

397200k(5760 Ch)

x4

Japan

x7

44 736k(672 Ch)

44 736k(672 Ch)

North America

chapter 5. multiplexing

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