PDH Basic

Access Network SupportAccess Network Support 1

Basic Transmission Basic Transmission SystemSystem


TropicsTropics

1. Transmission Network Topology2. Radio Wave Propagation3. Free Space Loss and Fade

Margin4. PDH Hierarchy5. Frequency Band and Channels

Spacing6. Transmission HOP and

Protection7. Transmission Antenna8. Modulation Technique etc.


Transmission SystemTransmission System

OXCOADM

OADMOADM

ILA

ILA

OTM

OTM

OTM

ADM

ADM

ADM

ADMAD

MTM

REGADM

ADM

ADM AD

M

ADM

PDH

BTS

BTSBTS V.28

STM-1

V.11G.703

SWS 1/0SWS 1/0

BackboneNetwork

MetropolitanNetwork

AccessNetwork

End-userNetwork

BTSBTS

BTS


Chain TopologyChain Topology

TX Point or BSC end

BTS End or Single Point

This type of network is suitable for long distant narrow transmission system like along roads.

Advantage: o Low concentration of equipment at TX point.o Frequency planning is easier.

Disadvantage: o High capacity requires near TX endo One link failure affects all sites after that link.o Extended bandwidth


Star TopologyStar Topology

TX Point or BSC end


This type of topology is suitable small surrounded network such as city urban area.

Advantage: o Independent link for BTSo One link failure do not affect many link.

Disadvantage: o Require Clear LOSo High concentration of equipment at TX point.o Difficult frequency planning.o Require large space for antennas mounting.


Tree TopologyTree Topology

TX Point or BSC end


This type of topology is suitable for small or medium surrounded network such as city urban area.

Advantage: o Independent link for BTSo Short hop distance and so require small antenna system.o Easy to find LOSo Frequency reuses is easier.

Disadvantage: o One link failure may affects many linko High concentration of equipment at TX point.

1+1 protection may be implemented for high capacity link.

1+1 hop for protection


Ring TopologyRing Topology

TX Point or BSC end


This type of topology is normally used in metropolitan area where high availability of network is required.

Advantage: o Traffic can be rerouted easily if any link fails.o Easy to monitor from Management System.

Disadvantage: o Every site must be connected with it’s two neighbors sites. o High bandwidth required.o MUX equipment is required for digital cross connection.


Radio wave propagationRadio wave propagation

Reflected

Refracted

Direct

Propagation Technique

Free space propagationRefractionReflection and scatteringDiffractionAbsorption


Power Level in a Fading free Power Level in a Fading free conditioncondition

PTX Output Power

PowerLevel

Distance

GTX

Antenna Gain

A = Free Space LossGas Absorption(Obstacle Loss)

GRX

Antenna Gain

PRX Input Power

BER Receiver Threshold


Free Space LossFree Space Loss

d

f

Basic Free space loss calculation

A [dB]= 92.4 + 20 log d + 20 log f

Where d = distance in km f = frequency in GHz

A = 92.4 + 20 log 30 + 20 log 15 = 145 dB


Fade MarginFade Margin

M = Fading margin

Receiver Threshold (BER=10-3, BER=10-6)

Distance

PTX Output Power

A = Free Space LossGas Absorption (Obstacle Loss)

PRX Input Power

PowerLevel

The performance of the system is affected by the path conditionsThe fading margin is designed in order to overcome the loss aroused due to fading condition.


Plesiochronous Digital Hierarchy Plesiochronous Digital Hierarchy (PDH)(PDH)

• One frame thus contains one octet of each of the carried channels.

• A frame is transmitted 8000 times each second, yielding a

8* 32 * 8000 = 2 048 000 bps or

2.048 Mbps• The corresponding T1 frame used

in USA contains 24 speech channels with 8-bit coding and 1 framing bit.

{(8*24)+1}*8000=1544000 bps or

1.544 Mbps

• A multi-frame is a series of consecutive frames (16 in Europe, 12 in USA).

A typical Plesiochronous Drop &

Insert


PDH StandardPDH Standard

400Mb/s

100Mb/s

32Mb/s

6.3Mb/s

Japan

274Mb/s

45Mb/s

6.3Mb/s

565Mb/s

139Mb/s

34Mb/s

8Mb/s

2 Mb/s 1.5Mb/s

North AmericaEurope

×4 ×4

×4

×4

×4

×4

×3

×5

×6

×7

×4

1.5Mb/s

NO Global Standard


PDH Hierarchy (European PDH Hierarchy (European Standard)Standard)

• The first PDH multiplex level is E1, containing (as noted before, 30 channels and 2 control channels), 2.048 Mbps.

• The second PDH multiplex level is E2, containing four E1multiplexes (120channels).– The bit rate is 8.448 Mbps, containing frames of 1056bits, (4 *256 bits for the multiplexes and 4 * 8 bits for justification and frame alignment).

• The third PDH multiplex level, E3 contains four E2 multiplexes (called tributaries), yielding 480 channels.

• The fourth PDH multiplex level, E4 contains four E3 multiplexes (1920 channels).

i) a = E1 = 2.048 Mbps ii) b = E2 = 8.448 Mbps iii) c = E3 = 34.368 Mbps iv) d = E4 = 139.264 Mbps


Limitations of PDHLimitations of PDH

140/34Mbit/s

34/140Mbit/s

/

Optical signal

/34/8Mbit/s 8/34Mbit/s

8/2Mbit/s 2/8Mbit/s

2Mbit/s

m

ultip

lex

mu

ltiple

x

mu

ltiple

x

de m

ultip

lex

de

mu

ltiple

x

de

mu

ltiple

x

op

tic

al

ele

ctric

al

ele

ctric

al

op

tica

lOptical signal

DDF

Lack of performance monitoring and managementLess FlexibilityWeak O&M features ----> no Overheads


SDH Global StandardSDH Global Standard

North American

European

Japan

STM-1

STM-4

STM-16

STM-64

PDH

Non Unified International

Interface

Unified International

Interface

SDH


SDH HierarchySDH Hierarchy

Level Speed (Mbps) Capacity (No of E1)

STM-1 155.520 63

STM-4 622.080 252

STM-16 2488.320 1008

STM-64 9953.280 4032


Frequency Sub-BandFrequency Sub-Band

21952.00 MHz21952.00 MHz

23002.00 MHz23002.00 MHz

TXTX RXRX

RXRX TXTX

Duplex (1050 MHz)

21.6 GHz 23.6 GHz

TX frequency of one end must be same of RX frequency of the other end.

Duplex Distance: Frequency range between TX and RX frequency Channel Spacing: Frequency range between two adjacent channels

Frequency Band used by Grameen Phone

7GHz, 8GHz, 11GHz, 15GHz, 23GHz, 38GHz


Channel Spacing and BandwidthChannel Spacing and Bandwidth

3.5 MHz 7 MHz

21953.75 MHz

4X2 Mbit/s (7 MHz)

2x2 Mbit/s (3.5 MHz)

3.5 MHz1.75 MHz

21952.00 MHz

7 MHz 14 MHz

8X2 Mbit/s (14 MHz)

21957.25 MHz

14 MHz 28 MHz

21964.25 MHz

16X2 Mbit/s (28 MHz)


Transmission HopTransmission Hop

Terminals

HOP = 2 Terminals (Tx+Rx)Terminal consists of

Indoor Unit: Traffic RelatedOutdoor Unit: Frequency RelatedCoaxial cable/ Waveguide: Interconnection


Hop ConfigurationHop Configuration

Unprotected terminal1 + 0

Protected terminal1 + 1


Protected SystemProtected System

TX RX

f1

f1

Hot Stand-by and Space Diversity


Protected System Cont….Protected System Cont….

f1 or (f1+ f2)

Single Antenna system HSB or WSB


Protected System Cont….Protected System Cont….

TX RX

f1

f2

WSB and Frequency Diversity

Alarm

No TX Switching, only RX switching


Transmission AntennaTransmission Antenna

Large antennaLow frequency

Advantage: Long range Interference suppression High Antenna Gain

Small antennaHigh frequencyAdvantage: Less wind load Less visibility Lower cost for the

antenna and the installation

Disadvantage: Low gain Vulnerable to

interference


Antenna Type (Performance)Antenna Type (Performance)

”Standard”

”High performance”

Absorbing material(high performance)

With radom


ModulationModulation

PSK: Phase is changed in modulator

QAM: Phase and Amplitude both are changed.


Modulation Cont….Modulation Cont….

C-QPSKC-QPSK

• QPSK four phases 0, 90,180 and 270 degrees.

• Two symbols per bit can be transmitted. Each symbol’s phase is compared relative to the previous symbol.

• If there is no phase shift (0 degrees), the bits “00” are represented. If there is a phase shift of 180 degrees, the bits “11” are represented.

Modulation: Technique how intelligent signal is transmitted over carrier signal


Modulation Cont….Modulation Cont….

Comparison of Different Modulation Techniques

Date post:	14-Oct-2014
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