1. Data Communication, NUML-Islamabad
Chapter 5. Multiplexing
Data Communication, NUML-Islamabad

2. 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).
Data Communication, NUML-Islamabad

3. Data Communication, NUML-Islamabad
Audio Channel
4-kHz Bandwidth
Data Communication, NUML-Islamabad

4. 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.
Data Communication, NUML-Islamabad

5. Data Communication, NUML-Islamabad
5.2.1 FDM Hierarchy
BASIC GROUP: 12-Channels- 60 to 108 kHz. fc f 1 f
108-4n
112-4n
116-4n n 2 f 12
Basic Group
Voice circuit
G1 ( kHz) 11 10 9 8 7 6 4 3 60
108
frequency (kHz)
Data Communication, NUML-Islamabad

6. Data Communication, NUML-Islamabad
60-Channel Supergroup 60
108 1
420
480
528
360
312 2
468
576
408 fc 3
516
624
456 4
564
672
504 5
612
720
552
f kHz G1 G2 G3 G4 G5
Super Group
SG ( kHz)
Combining 5 groups of 12 ch into 60-ch supergroup
Frequency range:
312 to 552 kHz
Data Communication, NUML-Islamabad

7. Data Communication, NUML-Islamabad
960-Channel Mastergroup
1116
1364
1612
1860
2108
2356
2604
2852
3100
3348
SUPERGROUP CARIER FREQUENCIES
4340
4092
3844
3596 1 2 3 4 5 6 7 8 9 10 11 12 13 14
f ( kHz)
SG1
SG2
SG3
SG16
MASTER-GROUP
kHz
Figure supergroups assembly for 960 telephony channels
Data Communication, NUML-Islamabad

8. Data Communication, NUML-Islamabad
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 channels long-haul FDM hierarchy
Data Communication, NUML-Islamabad

9. Data Communication, NUML-Islamabad
FDM Bandwidths
Type of baseband Bandwidth
_________
Voice kHz
Audio channel 4 kHz
Video 4 MHz
Television channel 6 MHz
Multiplexed voice:
12 channels 48 kHz
24 channels 96 kHz channels 144 kHz 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 MHz
1,200 channels MHz
1,260 channels MHz
1,800 channels MHz
2,700 channels MHz
Data Communication, NUML-Islamabad

10. Data Communication, NUML-Islamabad
RF Carriers
Radio channels: 4GHz, 6GHz 1 2 N
Number of multiplexed channels:
Maximum up to 2700 telephone channels or
television signal. RX TX
Figure Multiplexed channels for RF propagation
Data Communication, NUML-Islamabad

11. 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.
Data Communication, NUML-Islamabad

12. Data Communication, NUML-Islamabad
Pulse Insertion
f1(t) T
(a) One PAM signal
f2(t) TX
(c) Two PAM signals
(a) Second PAM signal
Tx :Time spacing between adjacent samples
Tx= T/n
n: number of input signals
Data Communication, NUML-Islamabad

13. Data Communication, NUML-Islamabad
Example
Ch3
Ch4
Ch5
Ch6
Ch2
Ch1 t
Multiplexed
PAM waveform
Data Communication, NUML-Islamabad

14. Data Communication, NUML-Islamabad
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.
Data Communication, NUML-Islamabad

15. Digital Multiplexing Techniques
1) BIT-BY-BIT Basis: Known as bit or digit interleaving
2) WORD-BY-WORD Basis: Known as byte or word interleaving).
Figure Digital multiplexing
Data Communication, NUML-Islamabad

16. 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 = 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 Mbit/s.
Data Communication, NUML-Islamabad

17. Data Communication, NUML-Islamabad
T1 System
Multiplexes 24 digital telephone channels of 64 kbit/s into a Mbit/s (= 64 kbps x 24 channels).
Aggregate Transmission Rate: (24channels x 8bit/channel + 1bit) / 125 µs = Mbit/s
Data Communication, NUML-Islamabad

18. PCM Frame Structure – E1 Format1 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
Time slot
F S Channel no.
Figure Mbps frame structure – E1
Bit no.
64 kbps
Data Communication, NUML-Islamabad

19. PCM Hierarchy Data Rates
Channels
Ist Order
MUX
(30x1=30ch) 1 2 30
2nd Order
(30X4=120 ch) 3 4
3rd Order
(120x4=480 ch)
4th Order
(480x4=1920 ch)
2.048 Mb/s
8.448 Mb/s
Mb/s
Mb/s
Figure PCM hierarchies (a) E-hierarchy levels (b) T-hierarchy levels (c) E-System multiplexing hierarchy levels showing data rates
Data Communication, NUML-Islamabad

20. Data Communication, NUML-Islamabad
2048k
(30 Ch)*
8448k
(120 Ch) x4
34 386k
(480 Ch) k
(1920) Ch k
(7680) Ch
Europe　（CEPT）
1544k
(24 Ch)
6312k
(96 Ch) x5
32 064k
97 728k
(1440 Ch) x3
397200k
(5760 Ch)
Japan x7
44 736k
(672 Ch)
North America
Data Communication, NUML-Islamabad