MULTIPLEXING TYPESMULTIPLEXING TYPES

Frequency Division MultiplexingFrequency Division Multiplexing

Time Division MultiplexingTime Division Multiplexing

Wavelength Division MultiplexingWavelength Division Multiplexing

Categories of multiplexing

FDM

Is the process of translating individual speech circuits (300-3400Hz) into pre assigned slots within the bandwith of transmission medium. and, the preassigned slots are always available to each user

FDM

FDM process

FDM demultiplexing example

Example 1

TDMTDM

The process where a transmission medium is shared by a number of circuits in time domain by establishing a sequence of time slots during which individual channels can be transmitted…Thus the entire bandwidth is periodically available to each channel

TDM

TDM frames

PCM PROCESSESPCM PROCESSES

FilteringFiltering SamplingSampling QuantizationQuantization EncodingEncoding Line codingLine coding

SAMPLINGSAMPLING

SAMPLING THEOREMSAMPLING THEOREM

“ “ If a band limited signal is sampled at regular If a band limited signal is sampled at regular intervals of time and at a rate equal to or more intervals of time and at a rate equal to or more than twice the highest signal frequency in the than twice the highest signal frequency in the band, then the sample contains all the band, then the sample contains all the information of the original signal”information of the original signal”

Fs= >2fHFs= >2fH

PULSE CODE MODULATIONPULSE CODE MODULATION

• Voice Frequency range 0- 4 KhzVoice Frequency range 0- 4 Khz• Sampling the Voice Signal @ 8 Khz Sampling the Voice Signal @ 8 Khz

(Double the Max. Frequency as per (Double the Max. Frequency as per sampling theorem) i.e. 8000s/secsampling theorem) i.e. 8000s/sec

• Sampling time period Ts=1sec/8000Sampling time period Ts=1sec/8000• Ts= 125 microsecTs= 125 microsec• Time available for sampling each channel, Time available for sampling each channel,

when we have N total channels=125/Nwhen we have N total channels=125/N• In PCM, Time frame=125microsec ;time In PCM, Time frame=125microsec ;time

available per chl=125/32 =3.9microsec. available per chl=125/32 =3.9microsec.

QUANTIZINGQUANTIZING

The process of measuring the numerical The process of measuring the numerical values of the samples and giving them a values of the samples and giving them a table value in a suitable scaletable value in a suitable scale

The finite number of amplitude intervals is The finite number of amplitude intervals is called the ‘quantizing interval’ like called the ‘quantizing interval’ like quantizing interval no.1 is 10-20mV; 2 is quantizing interval no.1 is 10-20mV; 2 is 20-30mV etc. in a case of 1V signal.20-30mV etc. in a case of 1V signal.

Linear quantizing is where the quantizing Linear quantizing is where the quantizing intervals are of the same sizeintervals are of the same size

QUANTIZING LEVELSQUANTIZING LEVELS

QUANTIZING (one side)QUANTIZING (one side)

QUANTIZINGQUANTIZING

Quantization intervals are coded in binary Quantization intervals are coded in binary form, and so the quantization intervals will be form, and so the quantization intervals will be in powers of 2. in powers of 2.

In PCM, 8 bit code is used and so we have 256 In PCM, 8 bit code is used and so we have 256 intervals for quantizing (128 levels in the intervals for quantizing (128 levels in the positive direction and 128 levels in negative positive direction and 128 levels in negative direction)direction)

QUANTIZING (both sides)QUANTIZING (both sides)

QUANTIZATION DISTORTIONQUANTIZATION DISTORTION

The deviation between the amplitude of The deviation between the amplitude of samples at the transmitter and receiving endssamples at the transmitter and receiving ends

In linear quantization, the distortion is more In linear quantization, the distortion is more and to decrease the distortion, the no. of steps and to decrease the distortion, the no. of steps in the given amplitude range has to be in the given amplitude range has to be increased.increased.

Due to BW limitations, more quantum levels in Due to BW limitations, more quantum levels in small amplitude region are planned results to small amplitude region are planned results to Non linear (uniform) quantization Non linear (uniform) quantization

COMPANDINGCOMPANDING

Is the process where non uniform quantization Is the process where non uniform quantization is achieved using segmented quantizationis achieved using segmented quantization

In companding, to specify the location of In companding, to specify the location of sample value, the following are necessary…sample value, the following are necessary…sign of the sample, the segment no., the sign of the sample, the segment no., the quantum level within the segment.quantum level within the segment.

SEGMENTATIONSEGMENTATION

PCM ENCODINGPCM ENCODING

FRAME STRUCTUREFRAME STRUCTURE

In PCM we have 32 Ts and Ts 0 (FAW) In PCM we have 32 Ts and Ts 0 (FAW) carries the synchronization signals and FAW carries the synchronization signals and FAW digit value is X 0 0 1 1 0 1 1 . FAW digit value is X 0 0 1 1 0 1 1 . FAW transmitted in alternate frame. In FAW unused transmitted in alternate frame. In FAW unused frames, supervisory and alarm signals are frames, supervisory and alarm signals are transmittedtransmitted

Ts 16 carries the signalling information (for 2 Ts 16 carries the signalling information (for 2 channels)channels)

FAW/ALARM DIGIT CODESFAW/ALARM DIGIT CODES

FRAME STRUCTUREFRAME STRUCTURE

For carrying the signalling for all 30 chls and For carrying the signalling for all 30 chls and for carrying sync. Data for all frames, in PCM for carrying sync. Data for all frames, in PCM 16 frame pattern is used and it is known as 16 frame pattern is used and it is known as multi framemulti frame

Duration of multi frame is 2msecs.Duration of multi frame is 2msecs.

PCM StandardsPCM Standards THERE ARE TWO STANDARDS OF PCM THERE ARE TWO STANDARDS OF PCM

NAMELY NAMELY 1) THE EUROPEAN 2 ) THE AMERICAN.1) THE EUROPEAN 2 ) THE AMERICAN. THEY DIFFER SLIGHTLY IN THE DETAIL OF THEY DIFFER SLIGHTLY IN THE DETAIL OF

THEIR WORKING BUT THE PRINCIPLES ARE THEIR WORKING BUT THE PRINCIPLES ARE THE SAME.THE SAME.

EUROPEAN PCM = 30 CHANNELSEUROPEAN PCM = 30 CHANNELS NORTH AMERICAN PCM = 24 CHANNELSNORTH AMERICAN PCM = 24 CHANNELS JAPANESE PCM = 24 CHANNELSJAPANESE PCM = 24 CHANNELS IN INDIA WE FOLLOW THE EUROPEAN PCM IN INDIA WE FOLLOW THE EUROPEAN PCM

OF 30 CHANNELS SYSTEM WORKING.OF 30 CHANNELS SYSTEM WORKING.

EUROPEAN PDH HIERARCHY WITH BIT RATESEUROPEAN PDH HIERARCHY WITH BIT RATES

1920+/- 15 ppm139.264 Mbps140 Mbps

480+/- 20 ppm34.368 Mbps34 Mbps

120+/- 30 ppm8.448 Mbps8 Mbps

30+/- 50 ppm2.048 Mbps2 Mbps

CHANNELSPARTS PER MILLION

BIT RATEMUX

Dig. Hier based on 24chl PCMDig. Hier based on 24chl PCM

MULTIPLEXING OF ASYNCHRONOUS SIGNALMULTIPLEXING OF ASYNCHRONOUS SIGNAL

in order to move multiple ASYNCHRONOUS 2 mbps data in order to move multiple ASYNCHRONOUS 2 mbps data streams from one place to another, they are combined streams from one place to another, they are combined together or “multiplexed” in groups of four.together or “multiplexed” in groups of four.

this is done by taking 1 bit/word from stream #1, followed this is done by taking 1 bit/word from stream #1, followed by 1 bit/word from #2, then #3, then #4.by 1 bit/word from #2, then #3, then #4.

the transmitting multiplexer also adds additional bits in the transmitting multiplexer also adds additional bits in order to EQUAL or synchronise the bits in the order to EQUAL or synchronise the bits in the multiplexer and the process adopted for such multiplexer and the process adopted for such synchronization is called “justification” bits or synchronization is called “justification” bits or

“ “ pulse stuffing ”pulse stuffing ”

JUSTIFICATION TYPESJUSTIFICATION TYPES

Positive justification: Common Positive justification: Common synchronization bit rate offered at each synchronization bit rate offered at each tributary is higher than the bit rate of tributary is higher than the bit rate of individual tributary.individual tributary.

Positive-negative justificationPositive-negative justification Negative justificationNegative justification

DIGITAL MUX CONCEPTSDIGITAL MUX CONCEPTS

• BYTE INTERLEAVINGBYTE INTERLEAVING• WORD / BYTE / BLOCK INTERLEAVING:WORD / BYTE / BLOCK INTERLEAVING:• IF THE CHANNEL TIME SLOT IS LONG ENOUGH IF THE CHANNEL TIME SLOT IS LONG ENOUGH

TO ACCOMMODATE A GROUP OF BITS THEN THE TO ACCOMMODATE A GROUP OF BITS THEN THE MULTIPLEXED SIGNAL IS CALLED A “ BYTE MULTIPLEXED SIGNAL IS CALLED A “ BYTE INTERLEAVED OR WORD INTERLEAVED SIGNAL”.INTERLEAVED OR WORD INTERLEAVED SIGNAL”.

D4D3D2D1C4C3C2C1B4B3B2B1A4A3A2A1

DIGITAL MUX CONCEPTSDIGITAL MUX CONCEPTS BIT INTERLEAVINGBIT INTERLEAVING::

ALTERNATELY EACH CHANNEL CODE CAN BE ALTERNATELY EACH CHANNEL CODE CAN BE SCANNED ONE DIGIT AT A TIME. THE SCANNED ONE DIGIT AT A TIME. THE MULTIPLEXED SIGNAL IS CALLED A “BIT MULTIPLEXED SIGNAL IS CALLED A “BIT INTERLEAVED SIGNAL”.INTERLEAVED SIGNAL”.

““BIT INTERLEAVING” IS USED IN HIGHER BIT INTERLEAVING” IS USED IN HIGHER ORDER MULTIPLEXING.ORDER MULTIPLEXING.

D4C4B4A4D3C3B3A3D2C2B2A2D1C1B1A1

Encoded FDM USA&canadaEncoded FDM USA&canada

Encoded TDM JapaneseEncoded TDM Japanese

Dig Hier based on 30chl PCM-Dig Hier based on 30chl PCM-Encoded TDM EuropeanEncoded TDM European