52528672 microwave-planning-and-design

Microwave Radio Planning and Link Design

CISCOM Training Center

Microwave Planning and Design

Slide No 1


Course Contents
• PCM and E1 TDM Overview
• Digital Multiplexing: PDH and SDH Overview
• Digital Microwave Systems Overview
• Microwave links Performance and Quality Objectives
• Topology and Capacity Planning
• Diversity
• Microwave Antennas

Slide No 2


Course Contents (con’d)
• Radio Propagation
• Microwave Link Planning and Design
– Path Profile
– LOS Survey
– Link Budget
– Performance Prediction
• Frequency Planning
• Interference
• Digital map and tools overview

Slide No 3


Planning Objectives
• MW Radio Planning Objectives
– Selection of suitable radio component
– Communication quality and availability
– Link Design
– Preliminary site location and path profile, LOS survey
– Channel capacity
– Topology
– Radio frequency allocation (planning)

Slide No 4


PCM and E1 Overview

Slide No 5


Voice channel digitizing and TDM
• Transmission:
– Voice
– Data
• Voice is an analog signal and needs to be digitized before
transmitted digitally
• PCM, Pulse Code Modulation is the most used technique
• The European implementation of PCM includes time
division multiplexing of 30 64 kb/s voice channels and 2
64kb/s for synchronization and signaling in basic digital
channel called E1
• E1 rate is 2.048 Mb/s = 32 x 64 kb/s

Slide No 6


PCM Coder Block Diagram 64 kb/s

Analog 64 kb/s
signal
LPF
LPF S/H
S/H Quantizer
Quantizer Encoder
Encoder
PCM signal

Slide No 7


E1 History
• First use was for telephony (voice) in 1960’s with PCM
and TDM of 30 digital PCM voice channels which called
E1
• E1 is known as PCM-30 also
• E1 was developed slightly after T1 (1.55 Mbps) was
developed in America (hence T1 is slower)
• T1 is the North America implementation of PCM and
TDM
• T1 is PCM-24 system

Slide No 8


E1 Frame
• 30 time division multiplexed (TDM) voice channels, each running at
64Kbps (known as E1)
• E1 rate is 2.048 Mbps containing thirty two 64 kbps time slots,
– 30 for voice,
– One for Signaling (TS16)
– One for Frame Synchronization (TS0)
• E1 (2M) Frame rate is the same PCM sampling rate = 8kHz, Frame
duration is 1/8 kHz = 125 μs (Every 125 us a new frame is sent)
• Time slot Duration is 125 μs/32 = 3.9 μs
• One time slot contains 8 bits
• A timeslot can be thought of as a link running at 8000 X 8 = 64 kbps
• E1 Rate:
64 X 32 = 2048000 bits/second
Slide No 9


E1 frame diagram
Time Slot Time Slot Time Slot ………… Time Slot …………. Time Slot Time Slot Time Slot
0 1 2 ………… 16 ………… 29 30 31

125µs

Bits

1 2 3 4 5 6 7 8
Frame containing
frame alignment Si 0 0 1 1 0 1 1
signal (FAS)

Frame not containing
frame alignment Si 1 A Sn Sn Sn Sn Sn
signal

Frame Alignment Signal (FAS) pattern - 0011011
Si = Reserved for international use (Bit 1)
Sn = Reserved for national use
A = Remote (FAS Distant) Alarm- set to 1 to indicate alarm condition

Slide No 10


E1 Transmission Media

• Symmetrical pair: Balanced, 120 ohm
• Co-axial: Unbalanced, 75ohm
• Fiber optic
• Microwave
• Satellite
• Other wireless radio
• Wireless Optical

Slide No 11


GSM coding and TDM in terrestrial E1
• As we know PCM channel is 64Kb/s
• Bit rate for one voice GSM channel is 16Kb/s between
BTS and BSC (terrestrial)
• One GSM E1 is 120 GSM voice channels
• The PCM-to-GSM TRAU (transcoder) reduces no of E1’s
by 4
• Each GSM radio carries 8 TCHs in the air, this equivalent
to 8x16Kb/s=2x64Kb/s between BTS and BSC.
• Each GSM radio has 2 time slots in the GSM E1.
• Example: 3/3/3 site require 9x2=18 E1 time slots for
traffic and time slot(s) for radio signaling links
Slide No 12


Digital Multiplexing: PDH and SDH
Overview

Slide No 13


European Digital Multiplexer Hierarchy
• Plesiochronous Digital Hierarchy (PDH)

• Synchronous Digital Hierarchy (SDH )

Slide No 14


PDH Multiplexing

• Based on a 2.048Mbit/s (E1) bearer
• Increasing traffic demands that more and more of these
basic E1 bearers be multiplexed together to provide
increased capacity
• Once multiplexed, there is no simple way an individual E1
bearer can be identified in a PDH hierarchy

Slide No 15


European PDH Multiplexing Structure
Higher order multiplexing
4 x 34

16 x E1

4 x E1
139,264 kbps
1 1 E1
34,368 kbps

8448 kbps
30
2048 kbps

Slide No 16


European PDH Multiplexing Structure-used
1st order 2nd order
2.048 Mbps 8.228 Mbps
E1 E2
MUX 3rd order
DEMUX 34.368 Mbps
Primary PCM E3
VF Multiplexing
MUX
DEMUX
Data MUX
Data Multiplexing
DEMUX
MUX
DEMUX
BTS
mobile Multiplexing
MUX
DEMUX
Slide No 17


PDH Problems
• Inflexible and expensive because of asynchronous
multiplexing
• Limited network management and maintenance support
capabilities
• High capacity growth
• Sensitive to network failure
• Difficulty in verifying network status
• Increased cost for O&M

Slide No 18


SDH

• Synchronous and based on byte interleaving
• provides the capability to send data at multi-gigabit rates over
fiber-optics links.
• SDH is based on an STM-1 (155.52Mbit/s) rate
• SDH supports the transmission of all PDH payloads, other than
8Mbit/s

Slide No 19


SDH Bit Rates
STM-64 9.995328 Gbit/s

4

STM-16 2.48832 Gbit/s

4

STM-4 622.08 Mbit/s
4

STM-1 155.52 Mbit/s
3

STM-0 51.84 Mbit/s

Slide No 20


General Transport Module STM-N
N. 270 columns

N. 9 N. 261

1
SOH: Section Overhead
3 RSOH AU: Administration Unit
AU pointer MSOH: Multiplexer Section
5
Payload Overhead
RSOH: Repeater Section
MSOH Overhead

9

Slide No 21


SDH Multiplexing Structure
140 Mbps
VC-4 C-4

TU-3 34 Mbps
x 3 TUG-3 x1 VC-3 C-3

2 Mbps
x7 TUG-2 TU-12 VC-12 C-12
x3
C: Container
AU-4 AUG STM-N VC: Virtual Container
x1 xN TU: Tributary Unit
Mapping TUG: Tributary Container Group
Aligning AU: Administrative Unit
Multiplexing AUG: Administrative Unit Group

Slide No 22


From 2 Mbps to STM-1

(Justification)

2 Mbits VC-12 VC-4 STM-1

+ POH SDH + POH + SOH
MUX

SOH: Section Overhead
POH: Path Overhead
Slide No 23


Containers C

Justification bits

= Container

PDH
Stream

Slide No 24


Virtual Containers VC

Path overhead

= Virtual
Container
Container

Slide No 25


SDH Advantages
• Cost efficient and flexible networking
• Built in capacity for advanced network management and
maintenance capabilities
• Simplified multiplexing and demultiplexing
• Low rate tributes visible within the high speed signal.
Enables direct access to these signals
• Cost efficient allocation of bandwidth
• Fault isolation and Management
• Byte interleaved and multiplexed

Slide No 26


SDH Benefits over PDH
• SDH transmission systems have many benefits over PDH:
– Software Control
allows extensive use of intelligent network management software for high
flexibility, fast and easy re-configurability, and efficient network
management.

– Survivability
With SDH, ring networks become practicable and their use enables
automatic reconfiguration and traffic rerouting when a link is damaged.
End-to-end monitoring will allow full management and maintenance of
the whole network.

– Efficient drop and insert
SDH allows simple and efficient cross-connect without full hierarchical
multiplexing or de-multiplexing. A single E1 2.048Mbit/s tail can be
dropped or inserted with relative ease even on Gbit/s links.
Slide No 27


SDH Benefits over PDH- con’d
– Standardization
enables the interconnection of equipment from different suppliers
through support of common digital and optical standards and
interfaces.

– Robustness and resilience of installed networks is increased.

– Equipment size and operating costs
reduced by removing the need for banks of multiplexers and de-
multiplexers. Follow-on maintenance costs are also reduced.

– Backwards compatibly
will enable SDH links to support PDH traffic.
Slide No 28


GSM Block Diagram (E1 links)

MSC1
BTS
SDH

MSC2 BTS
MSC3 BSC1
PDH
Abis
BTS
BTS
BTS BSC2 BTS

BTS
BTS

Slide No 29


Abis- Interface

BSC Abis-Interface
BTS

• Connects between the BSC and the BTS
• Has not been standardized
• Primary functions carried over this interface are:
Traffic channel transmission, terrestrial channel management, and radio
channel management
• On Abis-Interface, two types of information
Traffic information
Signalling information
Slide No 30


Abis- Interface
• Traffic Information
– The traffic on the physical layer needs ¼ TS (Time Slot)
on the E1 with bit rate = 16 Kb/s
– 4 channels exist within one TS
• Signalling Information
– Different rates on the physical layer: 16 Kb/s, 32 Kb/s,
and 64 Kb/s
– The protocol used over the Abis-Interface is LAPD
protocol (Link Access Protocol for the ISDN D-channel)
– The signalling link between the BSC and the BTS is
called RSL (Radio Signalling Link)

Slide No 31


Digital Microwave systems Overview

Slide No 32


Digital Microwave system
• Equipment
– E1
– MUX
– IF MODEM
– Transceiver
In door
Out door TRU
– Feeder
For In door
Co-axial transmission line
Waveguide transmission line
For Outdoor
IF between modem ODU Transceiver (TRU)

Slide No 33


MODEM- Digital Modulation
• PSK
– 2 PSK
– 4 PSK
– 8 PSK
• QAM
– 8 QAM
– 16 QAM
– 32 QAM
– 64 QAM
– 128 QAM

Slide No 34


Protecting MW Links
• Microwave links are protected against
– Hardware failure
– Multipath Fading
– Rain Fading

• Protection Schemes
– 1 + 1 configuration
– Diversity
– Ring

Slide No 35


Microwave Equipment Specification
• Operating Frequency
• Modulation
• Capacity
• Bandwidth
• Output power
• Receiver Thresholds @ BER’s 10-6 and 10-3
• MTBF
• FKTB

Slide No 36


RADIO EQUIPT Example: DART

Radio
Equipment Antenna
dish
Dish diameter: 30 cm

Slide No 37


Slide No 38


Radio Equipment Datasheet

Slide No 39


Microwave Allocation in Radio spectrum

VLF LF MF HF VHF UHF SHF EHF
3k 30 k 300 k 3M 30 M 300 M 3G 30 G 300 G

VHF Very low frequency
• Microwave primarily is LF Low frequency
utilized in SHF band, and MF Medium frequency
some small parts of UHF & HF High Frequency
EHF bands VHF Very High Frequency
UHF Ultra High Frequency
SHF Super High Frequency
EHF Extremely High Frequency

Slide No 40


Microwave Bands
• Some Frequency bands used in microwave are
– 2 GHz
– 7 GHz
– 13 GHz
– 18 GHz
– 23 GHz
– 26 GHz
– 38 GHz
• The usage of frequency bands will depend mainly on the
budget calculation results and the path length

Slide No 41


Microwave Capacities

• Capacities available for microwave links are
– 1 x 2 Mbps with a bandwidth of 1.75 MHz
– 2 x 2 Mbps with a bandwidth of 3.5 MHz
– 4 x 2 Mbps with a bandwidth of 7 MHz

Slide No 42


23 GHz Band - example
1232
1120 1120
21224 22456 22456 23576
Low High

Possible Number of Channels
2 x 2 (3.5 MHz) 4 x 2 (7 MHz) 8 x 2 (14 MHz) 16 x 2 (28 MHz)
320 160 80 40

Slide No 43


Channel Spacing

1.75 MHz 3.5 MHz
2 E1
3.5 MHz 7 MHz
4 E1

7 MHz 14 MHz
8 E1

14 MHz 28 MHz
16 E1

Slide No 44


International Regulatory Bodies
• ITU-T
Is to fulfil the purposes of the Union relating to telecommunication
standardization by studying technical, operating and tariff questions
and adopting Recommendations on them with a view to
standardizing telecommunications on a world-wide basis.
• ITU-R
plays a vital role in the management of the radio-frequency spectrum
and satellite orbits, finite natural resources which are increasingly in
demand from a large number of services such as fixed, mobile,
broadcasting, amateur, space research, meteorology, global
positioning systems, environmental monitoring and, last but not
least, those communication services that ensure safety of life at sea
and in the skies.

Slide No 45


Performance and availability objectives

Slide No 46


Performance Objectives and availability objectives
• Dimensioning of network connection is based on the
required availability objective and performance
• Dimension a network must meet the standard
requirements recommendations by ITU
• The performance objectives are separated from
availability objectives
• Factors to be considered
– radio wave propagation
– hardware failure
– Resetting time after repair
– Frequency dependant interference problems

Slide No 47


ITU-T Recs for Transmission in GSM Net

• All BTS, BSC and MSC connections in GSM network are
defined as multiples of the primary rate if 2 Mbps,

• ITU-T Rec G.821 applies as the overall standard for
GSM network.

• ITU-T Rec G.826 applies for SDH.

Slide No 48


The ITU-T Recs (Standards)
• The ITU-T target standard are based on two
recommendations:
– ITU-T Recommendation G.821,intended for digital connection with
a bit rate of 64 kBit/s. Even used for digital connection with bit rates
higher than 64kBit/s. G.821 will successively be replaced by G.826.
– ITU- T Recommendation G.826, used for digital connection with bit
rates of or higher than 2,048 kBit/s (European standard) or 1,544
kBit/s (USA standard).
• The main difference between G.826 and G.821 is that
G.826 uses Blocks instead of bits in G.821

Slide No 49


ITU-T G.821 some definitions
• HRX : hypothetical Reference Connection
– This a model for long international connection, 27,500 km
– Includes transmission systems, multiplexing equipment and switching

• HRDP: Hypothetical Reference Digital Path
– The HRDP for high grade digital relay systems is 2500 km
– Doesn’t include switching

• HRDS: Hypothetical Reference Digital Section
– It represents section lengths likely to be encountered in real networks
– Doesn't include digital equipments, such as multiplexers/demultiplexers.

Slide No 50


ITU-T G.821 some definitions (con’d)
• SES : Severely Errored Seconds
– A bit error rate (BER) of 10-3 is measured with an integration time of 1 second.

• DM : Degraded Minutes
– A bit error rate (BER) of 10-6 is measured with an integration time of 1 minute.

• ES : Errored Seconds
– Is the second that contains at least one error

• RBER: Residual Bit Error Rate
– The RBER on a system is found by taking BER measurements for one month
using a 15 min integration time, discarding the 50 % of 15 min intervals which
contain the worst BER measurements, and taking the worst of the remaining
measurements
Slide No 51


ITU-T G.821 HRX Hypothetical Reference Connection

27,500 km

1250 km 25,000 km 1250 km

T-reference T-reference
point point

LE INT INT LE

15 % 15 % 40 % 15 % 15 %
Local Medium Local
High Medium
Grade Grade Grade
Grade Grade

Slide No 52


ITU-T G.821 some definitions

• The system is considered unavailable when one or both of the
following conditions occur for more than 10 consecutive seconds
– The digital signal is interrupted
– The BER in each second is worse than 10 –3
• Unavailable Time (UAT)
– Begins when one or both of the above mentioned conditions occur for 10
consecutive seconds
• Available Time (AT)
– A period of available time begins with the first second of a period of 10
consecutive seconds of which each second has a bit error ratio (BER) better than
10-3

Slide No 53


ITU-T G.821 performance & Availability
Examples

BER 10-6

BER 10-3
<10s >10s

DM SES DM DM SES DM
ES ES ES ES ES

Available time (AT) Unavailable time (UAT)

Slide No 54


ITU-T G.821 Availability
• Route availability equals the sum of single link
availabilities forming the route.
• Unavailability might be due to
– Propagation effect
– Equipment effect

Note: Commonly used division is to allocate 2/3 of the allowed total
unavailability to equipment failure and 1/3 to propagation related
unavailability

Slide No 55


ITU-T G.821 Performance Objectives
• SES : Severely Errored Seconds
– BER should not exceed 10–3 for more than 0.2% of one second intervals in any
month
– The total allocation of 0.2% is divided as: 0.1% for the three classifications
– The remaining 0.1% is a block allowance to the high grade and the medium grade
portions
• DM : Degraded Minutes
– BER should not exceed 10–6 for more than 10% of one minute intervals in any
month
– The allocations of the 10% to the three classes
• ES : Errored Seconds
– Less than 8% of one second intervals should have errors
– The allocations of the 8% to the three classes

Slide No 56


G.821 Performance Objectives over HRX
ITU-T; G.821, F.697, F.696
1250 km 25000 km 1250 km
Local Medium High Medium Local SES 0.2% (0.1%
+0.1% for High and
0.015 0.015 0.04 0.015 0.015
Medium grade for
0.05 0.05 adverse conditions

1.5 1.5 4 1.5 1.5
DM 10 %

1.2 1.2 3.2 1.2 1.2 ES 8 %
INT LE

Slide No 57


P & A for HRPD – High Grade
1/10 of HRX ITU-T; G.821, Rep 1052
2500
High Grade
0054 % SES
(0.004+0.05) (Additional 0.05% for
adverse propagation
conditions)
0.4 % DM

ES
0.32 %

0.3 % UAT

Note: between 280 to 2500 all parameters are multiplied by (L/2500)
Slide No 58


P & A for HRDS – Medium Grade
IT-T; G.821, F.696, Rep 1052
– Used for national networks, between local exchange and
international switching center
Performance and availability Objectives for HRDS
Performance parameter Percentage of any month
Class 1 Class 2 Class 3 Class 4
280 km 280 km 50 km 50 km
SES 0.006 0.0075 0.002 0.005
DM 10 % 0.045 0.2 0.2 0.5
Errored Seconds ES 8 % 0.036 0.16 0.16 0.4
RBER 5.6x10-10 Under Under Under
study study study
UAT 0.033 0.05 0.05 0.1
Slide No 59


P & A for HRX – Local Grade
– The local grade portion of the HRX represents the part between the
subscriber and the local exchange
– Error performance objectives are:
BER shouldn’t exceed 10–3 for more than 0.015% of any month with
an integration time of 1 s
BER shouldn’t exceed 10-6 for more than 1.5% of any month with an
integration time of 1 min
The total errored seconds shouldn’t exceed 1.2% of any month
– Unavailability objectives for local grade circuits have not yet been
established by ITU-T or ITU-R.

Slide No 60


Performance Predictions
• System performance is determined by the probability for
the signal level to drop below the radio threshold level or
the received spectrum to be severely distorted

• The larger fade margin, the smaller probability for the
signal to drop below the receiver threshold level

Slide No 61


Availability
• The total unavailability of a radio path is the sum of the
probability of hardware failure and unavailability due to rain
• The unavailability due to hardware failure is considered for
both the go and return direction so the calculated value is
doubled
• The probability that electronic equipment fails in service is not
constant with time
• the high probability of hardware failure occurred during
burn-in and wear-out periods
• During life time the random failures have constant probability

Slide No 62


HW Unavailability

• Unavailability of one equipment module – HW
MTTR
N1 =
MTBF + MTTR

where

MTTR is mean time to repair

MTBF is mean time between failures.

Slide No 63


Calculation of Unavailability

• Unavailability of cascaded modules

N1
N1 N2
N2 N3
N3 Nn
Nn

n
 n
 n
N s = 1 − As = 1 − Π (1 − N i ) ≈ 1 − 1 − Σ Ni  = Σ N i
i =1  i =1  i =1

Slide No 64


Calculation of Unavailability

• Unavailability of parallel modules
N1
N1

N2
N2
n
N s = Π Ni
i =1 N3
N3

Nn
Nn

Slide No 65


Improvement in Availability in n+1 protection
• HW protection
• Unavailability of a n+1 redundant system

N n +1 =
1

( n + 1)  N 2 (1 − N ) ( n +1) −2
 2! ( ( n + 1) − 2 )! 
n 

n +1 2
Can be approximated N n +1 = N
2
Slide No 66


Improvement in Availability in Loop protection
• HW and route protection
• Unavailability in a loop N=(N1+N2)(N3+N4+N5+N6+N7)

N3 N2
 k
 J

N =  ∑ N i  ∑ N i  N1
 i =1  i = k +1  N4
N7
N5 N6

Where,
– J: Amount of hops in loop
– K: Consecutive number of hop from the hub
– N: Unavailability of the hop
Slide No 67


HRDS - Example
• HRDS: Medium grade class 3, 50 km. If the link is 5km
find UAT in % & s/d

N

• Solution:
– From table of HRDS, Medium grade class 3, 50 km >>UAT =
0.05%
– For 5 km >> UAT = (0.05%) * 5/50 = 0.005%
– UAT = (0.005/100) * 365.25*24= 0.438h/y = 26min/y = 4s/d

Slide No 68


Topology Planning

Slide No 69


Capacity and Topology planning
• Capacity demand per link results from transceiver capacity at those
BTS which are to be connected to the microwave link
• One transceiver reserves 2.5 time slots for traffic and signalling
• It is common to design for the higher capacity demand.
• For rapid traffic increase, the transmission network is dimensioned
to reserve the capacity of 6 transceivers
• The advantage to reserve capacity
– Flexibility in topology planning
– New BTS s can be added to existing transmission links
– New transceivers can be added without implementing new transmission links
– No need for changeover to new transmission links in fully operating network

Slide No 70


Transmission Capacity Planning-Traffic
Motorola-standards
• Bit rate for one voice PCM channel is 64Kb/s
• Bit rate for one voice GSM channel is 16Kb/s between
BTS and BSC
• Each GSM radio carries 8 TCHs in the air, this equivalent
to 8x16Kb/s=2x64Kb/s between BTS and BSC.
• Each GSM radio has 2 time slots in the GSM E1.
• Example: 3/3/3 site require 9x2=18 E1 time slots for
traffic and one time slot for RSL, total is 19 time slots

Slide No 71


Transmission Capacity Planning-Example
• Example: How Many Motorola micro-cells can be daisy
chained using one E1 at maximum?
• Solution:
– Motorola micro cell has 2 radios (omni-2)
– Each micrcell requires 2x2 time slots for traffic and 1 time slot for
rsl
– So each micro cell requires 5 time slots (64 kb/s time slots)
– Each E1 contains 31 time slots
– [31time slots] divided by [5 time slots/microcell] gives us the the
maximum no of daisy chained microcells
– So 6 microcells can be daisy chained at maximum
Slide No 72


Topology Planning
• Network topology is based on
– Traffic
– Outage requirements

• Most frequently used topologies
– Star
– Daisy Chain
– Loop

Slide No 73


Star
•Each station is connected with a separate link to the MW hub.
•Commonly used for leased line connections (needs low
availability)

Slide No 74


Star
• Advantages
– Easy to design
– Independent paths which mean link failure affects only one node
– Easy to configure and install
– Can be expanded easily

• Disadvantages
– Limited distance from BTS or hub to the BSC
– Inefficient use of frequency band
– Inefficient link capacity use as each BTS uses the 2 Mbps
– High concentration of equipment at nodal point
– Interference problem

Slide No 75


Daisy Chain

Application: along roads

• Advantages
– Efficient use of link capacity (if BTSs are chained to the same 2Mbps)
– Low concentration of equipment at nodal point

• Disadvantages
– Installation planning is essential as the BTSs close
– If the first link is lost, the traffic of the whole BTS chain is lost
– extended bandwidth (grooming)
Slide No 76


Daisy Chain

• (grooming)

Slide No 77


Tree
Application: Used for small or medium size network

• Advantages
– Efficient equipment utilization by grooming
– Short paths which require smaller antenna
– Frequency reuse

• Disadvantages
– Availability , one link failure affect many sites
Slide No 78
– Expansions might require upgrading or rearrangement


Loop
BTSs are connected onto two way multidrop chain

• Advantages
– Provide the most reliable means of transmission protection against microwave link
fading and equipment failure
– Flexibility y providing longer hops with the same antenna size, or alternatively,
smaller antenna dishes with the same hop length
• Disadvantages
– Installation planning; since all BTSs of a loop must be in place for loop protection
– More difficult to design and add capacity
– Skilled maintenance personnel is required to make cofiguration changes in the
Slide No 79
loop


Topology Planning

• Define clusters
• Select reference node
• Chose Backbone
• Decide the topology

Slide No 80


Diversity

Slide No 81


Diversity
• Diversity is a method used if project path is severely
influenced by fading due to multi path propagation
• The common protection of diversity techniques are:
– Space Diversity
– Frequency Diversity
– Combination of frequency and space Diversity
– Angle Diversity

Note: frequency diversity technique takes advantage because of the
frequency selectivity nature of the multi path depressive fading.

Slide No 82


Diversity
Diversity Improvement
• The degree of improvement afforded by all of diversity
techniques on the extents to witch the signals in the
diversity branches of the system are uncorrelated.
• The improvement of diversity relative to a single channel
given by:
PSinglechannel
Improvement factor I = where P refers to BER
PDiversity

Slide No 83


Diversity Improvement
10 –3
No
diversity
10 -4

10 -5 diversity

Diversity
10 -6
improvement
factor

10 -7

20 30 40 Fade Depth

Slide No 84


Single Diversity
• Space diversity
– Employs transmit antenna and two receiver antenna
– The two receivers enables the reception of signals via different
propagation paths
– It requires double antenna on each side of the hop, a unit for the
selection of the best signal and partially or fully duplicated
receivers

Note: whenever space diversity is used, angle diversity should also
be employed by tilting the antenna at different upwards angles

Slide No 85


Space Diversity

Separate paths
Tx 1 Rx 1

S

Rx 1

Slide No 86


Frequency diversity
• The same signal is transmitted simultaneously on two
different frequencies
• One antenna is required on either side of the hops, a unit
selecting the best signal and duplicate transmitters and
receivers
• A cost-effective technique
• Provides equipment protection , also gives protection
from multipath fading

Slide No 87


Frequency diversity
It is not recommended for 1+1 systems, because 50% of the
spectrum is utilized
For redundant N+1 systems this technique is efficient, because the
spectrum efficiency is better, but the improvement factor will be
reduced since there are more channel sharing the same diversity
channel
1+1 systems

Slide No 88


Hot standby configuration
• Tx and Rx operate at the same frequency, so there is no frequency
diversity could be expected
• This configuration gives no improvement of system performance,
but reduces the system outage due to equipment failures
• Used to give equipment diversity (protection) on paths where
propagation conditions are non-critical to system performance

Slide No 89


Hybrid diversity
• Is an arrangement where 1+1 system has two antennas at
one of the radio sites
• This system effect act as space diversity system, and
diversity improvement factor can be calculated as for
space diversity

Slide No 90


Angle diversity
• Angle diversity techniques are based upon differing angles of
arrival of radio signal at a receiving antenna, when the signals are a
result of Multipath propagation
• The angle diversity technique involves a receiving antenna with its
vertical pattern tilted purposely off the bore sight lines
• Angle diversity can be used is situations in witch adequate space
diversity is not possible or to reduce tower height

Slide No 91


Combined diversity
• In practical configuration a combination of space and
frequency diversity is used
• Different combination algorithms exist
• The simple method (conservative) to calculate the
improvement factor for combined diversity configuration
I = Isd + Isd

Slide No 92


Combined diversity
Combined space and frequency diversity

TX RX
f1

f2
TX RX
f1
S
f2 RX

RX

Slide No 93


Path Diversity
• Outage due to precipitation will not be reduced by use of
frequency,angle or space diversity.
• Rain attenuation is mainly a limiting factor at frequencies above
~10 GHz
• Systems operating at these high frequencies are used in urban areas
where the radio relay network may from a mix of star and mesh
configurations
• The area covered by an intense shower is normally much smaller
than the coverage of the entire network
• Re-Routing the signal via other paths

Slide No 94


Path Diversity

• The diversity gain (I.e. the difference between the attenuation
(dB) exceeded for a specific percentage of time on single link and
that simultaneously on two parallel links
– Tends to decrease as the path length increases from 12 km or a given percentage
of time, and for a given lateral path separation
– Is generally greater for a spacing of 8 km than for 4 km, though an increase to
12 km dose not provide further improvement
– Is not significantly dependent on frequency in the range 20 – 40 GHz, for a
given geometry, and
- Ranges from about 2.8 dB at 0.1% of the time to 0.4 dB at 0.001% of the time, for
a spacing of 8 km, and path lengths of about the same value for a 4 km spacing
are about 1.8 to 2.0 dB.

Slide No 95


Microwave Antennas

Slide No 96


Microwave Antennas
• The most commonly used type is parabolic antenna
• The performance of microwave system depends on the
antenna parameters
• Antenna parameters are:
– Gain
– Voltage Standing Wave Ratio (VSWR)
– Side and back lobe levels
– Beam width
– Discrimination of cross polarization
– Mechanical stability

Slide No 97


Antenna Gain
•The gain of parabolic antenna referred to an isotropic
radiator is given by:
4π
Gain ≈ 10 log(η × A × 2
)
λ
where:
η= aperture efficiency (typical values : 0.5-0.6)
λ = wavelength in meters
– A = aperture area in m2
Note : the previous formula valid only in the far field of the antenna, the
gain will be decreased in the near field, near field antenna gain is
obtained from manufacturer

Slide No 98


Antenna Gain-cont.
• This figure shows the relation
between the gain of microwave dish
and frequency with different dish
diameters

• Can be approximated
Gain = 17.8 + 20log (d.f) dBi
where,
d : Dish diameter (m)
f : Frequency in GHz

Slide No 99


VSWR
• VSWR resembles Voltage Standing Wave Ratio
• It is important in the case of high capacity systems with
stringent linearity objectives
• VSWR should be minimum in order to avoid intermodulation
interference
• Typical values of VSWR are from 1.06 to 1.15
• High performance antennas have VSWR from 1.04 to 1.06

Slide No 100


Side and Back lobe Levels
• The important parameters in frequency planning and
interference calculations are sidelobe and backlobes
• Low levels of side and backlobes make the use of
frequency spectrum more efficient
• The levels of side and backlobes are specified in the
radiation envelope patterns
• The front to back ratio gives an indication of backlobe
levels
• The front to back ratio increases with increasing of
frequency and antenna diameter

Slide No 101


Beam Width
• The half power beam width of antenna is defined as the
angular width of the main beam at –3dB point

– An approximate formula used to find the beam width is:
α3dB = ± 35. λ/D in degrees
– The 10dB deflection angle is found approximately by:
α10dB = 60. λ/D in degrees

Slide No 102


Antenna Characteristics – EIRP and ERP
• Effective Isotropic Radiated Power (EIRP)
– It is equal to the product of the power supplied to a transmitting antenna and the
antenna gain in a given direction relative to an isotropic radiator (expressed in
watts)
– EIRP = Power - Feeder Loss + Antenna Gain
Both EIRP and Power expressed in dBW
Antenna gain expressed in dBi
• Effective Radiated Power (ERP)
– The same as EIRP but is relative to a half-wave dipole instead of an isotropic
radiator
• EIRP = ERP + 2.14 dB
• Example
Transmitter Output Power = 4 Watts = 36 dBm, Transmission Line Loss = 2 dB, and
Antenna Gain = 10 dBd. Calculate the ERP
– Answer: ERP = 36 - 2 + 10 = 44 dBmd
Slide No 103


Passive Repeater
• Two types of passive repeaters :
– Plane reflectors
– Back to Back antennas
• The plane reflector reflects MW signals as the mirror
reflects light
– The laws of reflection are valid here
• The back to back antennas work just like an ordinary
repeater station, but without frequency transportation or
amplification of the signal

Slide No 104


Passive Repeater- cont.

• By using passive repeaters; the free space loss becomes:
AL= AFSA – GR + AFSB
where
– AFSA is the free space loss for the path site A to passive repeater
– AFSB is the free space loss for the path site B to passive repeater
– GR is the gain of the passive repeater

Slide No 105


Plane Reflectors
• More popular than back to back antennas due to :
– Efficiency is around 100%
– Can be produced with much larger dimensions than parabolic antennas
• The gain of plane reflectors is given by:
GR= 20 log( 139.5 . f2 .AR . cos( Ψ/2 )) in dB
where :
– AR is the physical reflector area in m2
– F is the radio frequency in GHz
Ψ is the angle in space at the passive
repeater in degrees

Slide No 106


Plane Reflectors

Slide No 107


Back to back Repeater
• Use of them is practical when reflection angle is large
• The Gain of back to back antennas is given by
GR= GA1 – AC + GA2 in dB
where :
– GA1: is the gain of one of the two antennas at the repeater in dB
– GA2: is the gain of the other antenna at the repeater in dB
– AC : is the coupling loss between antennas in dB

Slide No 108


Back to back antennas

Slide No 109


Antenna Characteristics - Polarization

• Co-Polarization
– The transmit and receive antennas have the same polarization
– Either horizontal or vertical (HH or VV)
• Cross-Polarization
– The transmit and receive antennas have different polarization
– Either HV or VH

Slide No 110


Cross Polarization
• Transmission of two separate traffic channels is performed on the
same radio frequency but on orthogonal polarization
• The polarization planes are horizontal and vertical
• The discrimination between the two polarization is called Cross
Polar Discrimination (XPD)
• Cross-Polarization Discrimination (XPD)
– the ratio between the power received in the orthogonal (cross polar) port to the
power received at the co-polar port when the antenna is excited with a wave
polarized as in the co-polar antenna element
• Good cross polarization allows full utilization of the frequency band

Slide No 111


Cross Polarization
• To ensure interference-free operation, the nominal value
of XPD the value is usually in the rang 30 – 40 dB
• Discrimination of cross polar signals is an important
parameter in frequency planning

Vertical

Horizontal
1 2 3 4 5 6 7 8 1’ 2’ 3’ 4’ 5’ 6’ 7’ 8’

28 MHz

Slide No 112


Mechanical Stability
• Limitations in sway / twist for the structure of the
structure (tower or mast) correspond to a maximum 10
dB signal attenuation due to antenna misalignment
• The maximum deflection angle may be estimated for a
given antenna diameter and frequency by using
α 10dB = 60. λ/D in degrees

Slide No 113


Antenna
Datasheet

Slide No 114


Digital Antenna
pattern

Slide No 115


Antenna Pattern

Slide No 116


Radio Propagation

Slide No 117


Electromagnetic (EM) Waves
• EM wave is a wave produced by the interaction of time varying
electric and magnetic field
• Electromagnetic fields are typically generated by alternating
current (AC) in electrical conductors
• The EM field composes of two fields (vectors)
– Electric vector E
– Magnetic vector H
• Electromagnetic waves can be
– Reflected and scattered
– Refracted
– Diffracted
– Absorbed (its energy)

Slide No 118


Electromagnetic Waves Properties
• E and H vectors are orthogonal
• In free space environment, the EM-wave propagates at
the speed of light (c)
• The distance between the wave crests is called the
wavelength (λ)
• The frequency ( f )is the number of times the wave
oscillates
• The relation that combines the EM-wave frequency and
wavelength with the speed of light is:
λ=c/f
Slide No 119


Radio Wave Propagation

• The propagation of radio wave is affected by :
– Frequency Effect
– Terrain Effect
– Atmospheric Effect
– Multipath Effect

All the above mentioned effects cause a degradation in
quality

Slide No 120


Frequency Effect

• Attenuation: Loss
• Propagation of radio depends on frequency band

• At frequencies above 6 GHz radio wave is more affected
by gas absorption and precipitation
– At frequencies close to 10 GHz the effects of precipitation begins to
dominate
– Gas absorption starts influencing at 22 GHz where the water vapour
shows characteristic peak
Slide No 121


Terrain effect
• Reflection and scattering
• The radio wave propagating near the surface of earth is
influenced by:
– Electrical characteristics of earth
– Topography of terrain including man-made structures

Slide No 122


Atmospheric effect
• Loss and refraction
• The gaseous constituents and temperature of the
atmosphere influence radio waves by:
– Absorbing its energy
– Variations in refractive index which cause the radio wave reflect,
refract and scatter

Slide No 123


Multipath effect
• Multipath effect occurs when many signals with different
amplitude and/or phase reach the receiver

• Multipath effect is caused by reflection and refraction

• Multipath propagation cause fading

Slide No 124


EM wave Reflection and scattering

• When electromagnetic waves incide on a surface it might
be reflected or scattered
• Rayleigh criterion used to determine whether the wave
will be scattered or reflected
• The reflected waves depend on the frequency, incidence
angle and electrical property of the surface

Slide No 125


EM wave Reflections

• Reflection of the radio beam from lakes and large surfaces
are more critical than reflection from terrain with
vegetation
• Generally, vertical polarization gives reduced reflection
especially at lower frequencies
• If there is a great risk from reflection ,space diversity
should be used

Slide No 126


EM wave Reflection coefficient (ρ)

• Reflection can be characterized by its total reflection
coefficient ρ
• ρ is the quotient between the reflected and incident field
• When ρ = 0 nothing will be reflected and when ρ =1 we
have specular reflection
• reflection coefficient decreases with frequency

Slide No 127


EM wave Reflection coefficient-cont.
• The resulting electromagnetic field at a receiver antenna is
composed of two components,the direct signal and the reflected
signal
• Since the angle between the both components varies between 0
and 180 the signal will pass through maximum and minimum
values respectively Reflection
loss (ρ)
The figure shows different 5 Amax
values of total reflection -5
-15 Amin
coefficient, and the minimum
-15
and maximum values
-25
with respect to them -35
0.2 0.4 0.6 0.8
Total reflection coefficient (ρ)
Slide No 128


EM wave Refraction

• Refraction occurs because radio waves travel with
different velocities in different medium according to their
electrical characteristics.

• Index of refraction of a medium is the ratio of the velocity
of radio waves in space to the velocity of radio waves in
that medium

Slide No 129


EM wave Refraction
• Radio wave is refracted toward the region with higher
index of refraction (denser medium)

Incident wave

n2 > n1 Reflected wave
Medium 1 ,n1 θi θr

Medium 2 ,n2

Refracted wave

Slide No 130


EM wave Refraction
• Refractivity depends on
– Pressure
– Temperature
– Humidity

• Refractive Gradient (dN/dh) represents refractive
variation with respect to height (h), related to the earth
radius.

Slide No 131


EM wave Refraction and Ray bending
• Refraction cause ray bending in the atmosphere
• In free space, the radio wave follows straight line

no atmosphere with atmosphere

Slide No 132


EM wave Refraction: K-Factor
• K is a value to indicate wave bending
a
K= e
r

re :is the effective radius of the ray due to refraction
a :is the earth radius = 6350 km

– For temperate regions :
dN/dh = - 40N units per Km,
K=4/3=1.33

Slide No 133


K-Factor and Path Profile Correction
• Path profile must be corrected by K-factor
• Radius of earth must be multiplied by K-factor, less
curvature of earth

Slide No 134


Formation Of Ducts- Refraction and reflection
Ground Based Duct: Refraction and reflection
• The atmosphere has very dense layer at the ground with a
thin layer on top of it.

Elevated Duct: Refraction only
• The atmosphere has a thick layer in some height above
ground.
• If both the transmitter and the receiver are within the
duct, multiple rays will reach the receiver
• If one is inside and the other is outside the duct, nearly no
energy will reach the receiver
Slide No 135


Formation Of Ducts- Refraction and reflection

Elevated DUCT Ground Based DUCT

Earth Earth

Slide No 136


Formation Of Ducts- Explanation
Refraction and reflection

Slide No 137


Ducting Probability- Refraction and reflection
• Duct probability percentage of time when dN/dh is less
than –100 N units/km per specified month
• ITU-R issues DUCT Probability CONTOUR MAPS
• The ducting probability follows seasonal variations
• This difference in ducting probability can be explained by
the difference in temperature and most of all by difference
in humidity
• From the map the equatorial regions are most vulnerable
to ducts

Slide No 138


ITU-R DUCT Probability CONTOUR MAPS

Slide No 139


Multipath Propagation - Refraction and reflection
• Multipath propagation occurs when there are more than
one ray reach the receiver
• Disadvantages:
– Signal strength changes rapidly over a short time and distance
– Multipath delays which causes time dispersion
– Random frequency modulation due to Doppler shifts
– Delay spread of the received signal
• Multipath transmission is the main cause of fading
• Fading is explained in later slides
Slide No 140


Diffraction
• Diffraction occurs and causes increase in transmission loss
when the size of obstacle between transmitter and
receiver is large compared to wavelength
• Diffraction effects are faster and more accentuated with
increased obstruction for frequencies above 1 GHz
• Transmission obstruction loss over irregular terrain is
complicated function of frequency, path geometry,
vegetation density and other less significant variable
• Practical methods are used to estimate the obstruction
losses.

Slide No 141


Diffraction loss
Practical methods are used to estimate the obstruction
losses
• Terrain Averaging: ITU-R P.530-7
– Diffraction loss in this method can be approximated for losses
greater than 15 dB
Ad = -20h/F1 + 10 (dB) : ITU-R P.530-7
Where, Ad : diffraction loss.
h: height difference between most significant blockage and
path trajectory.
F1: radius of first freznal zone

Slide No 142


Knife edge models
• Knife edge approximation is used when the obstruction is
sharp and inside the first freznal zone
– Single Knife edge
– Bullington
– Epostein-Peterson
– Japanese Atlas

Slide No 143


Absorption
• At frequency above 10
GHz the propagation of
radio waves through the
atmosphere of the earth is
strongly effected by
resonant absorption of
electromagnetic energy by
molecular water vapor and
oxygen

Slide No 144


Rain Attenuation
• When radio waves interact with raindrops the
electromagnetic wave will scatter
• The attenuation depends on frequency band, specially for
frequencies above 10 GHz
• The rain attenuation calculated by introducing reduction
factor and then effective path length
• The rain attenuation depends on the rain rate, which
obtained from long term measurement and very short
integration time
• The Earth is divided into 16 different rain zones

Slide No 145


Rain Attenuation
• Rain rate is measured to estimate attenuation because it is
hard to actually count the number of raindrops and
measure their individual sizes so
• Rainfall is measured in millimeters [mm], and rain
intensity in millimeters pr. hour [mm/h].
• Since the radio waves are a time varying electromagnetic
field, the incident field will induce a dipole moment in the
raindrop will therefore act as an antenna and re-radiate
the energy.
• A raindrop is an antenna with low directivity and some
energy will be re-radiated in arbitrary directions giving a
net loss of energy in the direction towards the receiver.
Slide No 146


Raindrop shape
• As the raindrops increase in size, they depart from the
spherical shape
• Raindrops are more extended in the horizontal direction and
consequently will attenuate horizontal polarized waves more
than the vertical polarized.
• This means that vertical polarization
is favorable at high frequencies
where outage due to rain is dominant.

Slide No 147


Fading

• The radio waves undergo variations while traveling in the
atmosphere due to atmospheric changes. The received
signal fades around nominal value.

• Multipath Fading is due to metrological conditions in the
space separating the transmitter and the receiver which
cause detrimental effects to the received signal

Slide No 148


Fade Margins
• Fade Margin is extra power

• Fade Margins will be explained in link design for the
following:
• Multipath Fading
– Flat Fading
– Selective Fading
• Rain Fading

Slide No 149


Mutipath Fading
• As the fading margin increased the probability of the
signal to drop below the receiver threshold is decreased

• Flat fading or non-selective occurs when all components
of the useful signal are affected equally
• Frequency selective fading occurs if some of the spectral
components are reduced causing distortion
• Total fading
Ptot =Pflat + Psel
Slide No 150


Mutipath Fading
• The impacts of multipath fading can be summarized as
follows:
– It reduces the signal-to-noise ratio and consequently increases the
bit-error-rate (BER)
– It reduces the carrier-to-interference (C/I) ratio and consequently
increases the BER
– It distorts the digital pulse waveform resulting in increased
intersymbol interference and BER
– It introduces crosstalk between the two orthogonal carriers, the I-rail
and the Q-rail, and consequently increases the BER

Slide No 151


Mutipath Fading

P
Flat fading Normal
signal Frequency
selective
fading

Slide No 152


Microwave Link Planning and Design

Slide No 153


Hop Calculations (Design)
Predictable Statistically Predictable

Free Space Loss
Gas Absorption Rain fading
Multipath fading
Obstacle Loss
Always present
and predictable Not always present
Predictable but statistically
if present predictable

Link Budget
Fading prediction
Performance &
Availability Objectives

Slide No 154


Path Profile

• Path profile is essentially a plot of the elevation of the
earth as function of the distance along the path between
the transmitter and receiver

• The purpose of path profile:
– To check the free line of sight
– To check the clearance of the path to avoid obstacle attenuation
– When determining the fading of received signal

Slide No 155


Path Profile Example
• Path profiles are necessary to determine site locations and
antenna heights

Slide No 156


Path Profile: Clearance of Path
• Design objective: Full clearance of direct line-of-sight and
and an ellipsoid zone surrounding the direct line-of-sight
• The ellipsoid zone is called the Fresnel Zone

Slide No 157


Path Profile: Fresnel Zone Example

Slide No 158


Fresnel Zone
• Fresnal Zone is defined as the zone shaped as ellipsoid
with its focal point at the antennas on both ends of the
path
• If there is no obstacle within first Fresnel zone ,the
obstacle attenuation can be ignored and the path is
cleared
• Equation of path of ellipsoid
λ
d1 + d 2 − d =
2

Slide No 159


Fresnel Zone Equation
• First Fresnel zone radius
d1 × d 2
F1 = 17.3 × [m]
d× f

• Fresnel zone – Exercise: Calculate the fresnel zone radius at mid
path for the following cases
– 1. f= 15GHz, K=4/3, d=10km
– 2. f = 15GHz, K=4/3, d=20km
• Solution:
= 17.3 ×
5×5
= 7m
– 1. F1 (radius) 15 × 10

10 × 10
= 17.3 × = 10m
– 2. F1 (radius) 15 × 20

Slide No 160


Fresnel Zone Radii calculations
“Table Tool”
Frequency Distance in km
GHz 4.0 10.0 15.0 20.0 30.0 40.0
7.0 9.2 12.7 13.3 15.0 17.3 18.6
13.0 10.3 13.6 12.1 13.6 13.8 14.2
15.0 10.1 14.2 11.3 13.4 12.4 13.1
18.0 9.2 15.2 10.6 13.8 11.6 13.0
23.0 7.7 17.1 9.6 14.7 10.9 13.4
26.0 6.7 19.6 8.6 16.0 10.1 14.1
38.0 5.1 23.9 7.3 18.1 9.1 15.2

Slide No 161


Obstacle Loss: Fresnel Zone is not Cleared
Obstacle Loss

Knife Edge obstacle loss Smooth spherical obstacle loss

Slide No 162


Knife Edge Losses

0 0 6 12 20 dB

Slide No 163


Smooth Spherical Earth Losses

30

20

10
dB

Slide No 164


Line-Of-Sight Survey

LOS

• LOS Survey
– To verify that the proposed network design is feasible considering
LOS constraints

Slide No 165


Line-Of-Sight Survey- Flowchart

Network Design

Update the
design LOS Survey

LOS Report

Slide No 166


LOS Survey Equipment
Necessary: Optional:
• Compass • Clinometer
• Maps : 50 k or better • Altimeter
• Digital Camera • Laptop
• GPS Navigator • Spectrum analyzer
• Binoculars • Antenna horn
• Hand-held communication • Low noise amplifier
equipment
• Signaling mirrors • Theodolite

Slide No 167


LOS Survey Procedure - Preparation
• Preparation
– Maps of 1:50k scale or better to be used and prepared
– List of hops to be surveyed
– Critical obstacles should be marked in order to verify LOS in the
field
– Organize transport and accommodation
– Organize access and authorization to the sites
– Prepare LOS survey form

Slide No 168


LOS Survey Procedure - Field
• Verification of sites positions and altitudes
• Confirmation of line-of-sight using
– GPS
– Compass
– Binocular
– And other methods in the next slide
• Take photographs
• Estimate required tower heights
• Path and propagation notes
Slide No 169


Other Methods of LOS Survey
• Mirrors
• Flash
• Balloon
• Portable MW Equipment
• Driving along the path and taking GPS and altitude
measurements for different points along it.

Slide No 170


LOS Survey Report
• Site Data
– Name
– Coordinates
– Height
– Address
• Proposed Tower Height
• LOS Confirmation
• Azimuth and Elevation
• Path short description
• Photographs
Slide No 171


Link Budget

• Includes all gains and losses as the signal passes from transmitter to
the receiver.

• It is used to calculate fade margin which is used to estimate the
performance of radio link system.

Slide No 172


Link Budget
• Link budget is the sum of all losses and gains of the signal
between the transmitter output and the receiver input.
• Items related to the link budget
– Transmitted power
– Received power
– Feeder loss
– Antenna gain
– Free space loss
– Attenuations
• Used to calculate received signal level (fading is ignored)
Slide No 173


Link Budget (con’d)

Pin = Pout − ∑ L + ∑ G − FSL − A

Where,
Pin = Received power (dBm)
Pout = Transmitted power (dBm)
L = Antenna feeder loss (dB)
G = Antenna gain (dBi)
FSL = Free space loss (dB) (between isotropic antennas)
A = Attenuations (dB)

Slide No 174


Link Budget
Gt Gr
Tx Rx

Output Antenna
power gain Free space loss +
atmospheric atten. Feeder
Branching Received
loss
loss Feeder power
Antenna
loss Branching
gain
loss
Fade
Margin

Receiver threshold
Slide No 175


Link Budget Parameters-Free Space Loss
• It is defined as the loss incurred by an electromagnetic wave as is
propagates in a straight line through the vacuum

 4π 
D
2
 4π 
fD
2 where,
Lp =  =  Lp = free space path loss
 λ   c 
D = distance
f = frequency
λ = wavelength
c = velocity of light in free space (3*108 m/s)

Lp(dB) = 92.4 + 20logf(GHz) + 20logD(km)

Slide No 176


Link Budget Parameters
Free Space Loss

Lp

Tx Rx

Slide No 177



• Total Antenna Gain: f Da
Ga = 20 log (Da) + 20 log (f) + 17.8

• Atmospheric attenuation occurs at higher frequencies ,
above 15 GHz due a = γ a × d
Ato atmospheric gases, and given by:

Where d is path link in km , γa is specific attenuation in dB/km
Slide No 178



• Rx Level: Signal strength at the receiving antenna
PRx= PTx-LBRL-+GTx-LFS-Lobs+GRx - LTx feeder – LRx feeder
Where, PRx : received power level GTx :Tx gain
PTx : transmitted power level Lobs :Diffraction loss
LBRL : branching loss GRx :Rx gain
LFS : free space loss LRx feeder : Rx feeder loss
LTx feeder : Tx feeder loss

Slide No 179


Fading

• Fading types
– Multipath Fading; Dominant cause of fading for f < 10 GHz
• Flat Fading
• Frequency Selective Fading
– Rain Fading; Dominant cause of fading for f > 10 GHz

Slide No 180


Fade Margin and Availability

• Is the difference between the nominal input level and receiver
threshold level
From Link Budget
FM = Received Power – Receiver threshold

• Fade margin is designed into the system so as to meet outage
objectives during fading conditions
• Typical value of Fade Margin is around 40 dB
• Availability is calculated from the Fade Margin value as in F.1093,
P.530-6, P.530-7, …
Slide No 181


Flat Fading ITU-R P.530-7
Pflat =Po . 10–F/10
where:
– F equals the fade margin
– Po the fading occurrence factor

Po = k. d3.6 . f0.89 .(1+|Ep|)-1.4
Where:
– k is geoclimatic factor
– d is path length in Km
– f is frequency in GHz h − h2
EP = 1
– Ep: path inclination in mrad = d

Slide No 182


Flat Fading- cont. ITU-R P.530-7
• The geoclimatic (K) depends on type of the path
– Inland links
Plains: low altitude 0 to 400m above mean sea level
Hills: low altitude 0 to 400m above mean sea level
Plains: Medium altitude 400 to 700m above mean sea level
Hills: Medium altitude 400 to 700m above mean sea level
Plains: High altitude more than 700m above mean sea level
Hills: High altitude more than 700m above mean sea level
Mountains: High altitude more than 700m above mean sea level
– Coastal links over/near large bodies of water
– Coastal links over/near medium-sized bodies of water
– Indistinct path definition
• To calculate K value, refer to formulas and tables in ITU-R P.530-7

Slide No 183


Frequency Selective Fading ITU-R F.1093
• Result from surface reflections or introduced by
atmospheric anomalies such as strong ducting gradients
B 2
− τm
Psel = 4.3 × 10 20 ×η × W ×
τr
Where,
η : Probability of of the occurrence of multipath fading
W: Signature width (GHz), equipment dependent
B : Signature depth (GHz), equipment dependent
τm: Mean value of echo delay
τr : Time delay used during measurements of the signature curves (reference delay)
ns. Normally 6.3 ns
Slide No 184


Frequency Selective Fading ITU-R F.1093
 3/ 4 
 −.2× P0  
 
  100  
η = 1− e   Where,
Po: The fading occurrence factor

1.5
d 
τ m = 0.7 ×   Where,
 50  d : Path length (km)

w/ 2 − Bc
W= ∫
−w/ 2
10 20 Where,
Bc: Signature depth

Slide No 185


Frequency Selective Fading ITU-R P.530-7
 B
− M τM 2 B
− NM τM 2 
Psel = 2.15 × η × WM × 10 20 × + WNM × 10 20 × 
 τ r ,M τ r , NM 
 

Where,
Wx: Signature width
Bx: Signature depth
τx: The reference delay used to obtain signature in
measurements
x: Denotes either Minimum phase (M) or Not Minimum phase (NM)
Slide No 186


Space Diversity Improvement ITU-R P.453
P Pflat +P
P div =
mp
mp
= sel

I I
 
 −3.34⋅10−4 ⋅s 0.87 ⋅ f −0.12 ⋅d 0.48 ⋅ Po


−1.04 


M − ∆G

I= 1 − e 100 
 ⋅10 10
 
 
Where,
s : Vertical separation between antennas in m
f : Frequency in GHz
d : Path length
F : Fade Margin
∆G : The difference in antenna gain between the two antenna in dB
Po : from the formula of flat fading
Slide No 187


Rain Attenuation ITU-R P.530
• Rain Intensity in mm/h
– The reference level is the rain intensity that is exceeded .01% of all the time (R 0.01)
• The attenuation due to the rain in .01% of the time for a given path
may be found by:
AR = γ R .d eff

where
γR : Specific rain attenuation (dB/km)
deff : Effective path length, km
γ R = k × Ra
k and a are given in the table
Slide No 188


Usable path lengths with rain intensity
example: 15 GHz

Slide No 189

52528672 microwave-planning-and-design

52528672 microwave-planning-and-design

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