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Microwave Radio Planning and Link Design
CISCOM Training Center
Microwave Planning and Design
Slide No 1
Microwave Radio Planning and Link Design
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
PCM and E1 Overview
Slide No 5
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
PCM Coder Block Diagram 64 kb/s
Analog
signal
Slide No 7
LPF
S/H
Quantizer
Encoder
64 kb/s
PCM signal
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
•
•
•
•
•
•
•
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
Microwave Radio Planning and Link Design
E1 frame diagram
Time Slot
Time Slot
Time Slot
…………
Time Slot
………….
Time Slot
Time Slot
Time Slot
0
1
2
…………
16
…………
29
30
31
125s
Bits
1
2
3
Frame containing
frame alignment
signal (FAS)
Si
0
0
1
Frame not containing
frame alignment
signal
Si
A
Sn
1
4
5
6
7
8
1
0
1
1
Sn
Sn
Sn
Sn
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
Microwave Radio Planning and Link Design
E1 Transmission Media
• Symmetrical pair: Balanced, 120 ohm
• Co-axial: Unbalanced, 75ohm
• Fiber optic
• Microwave
• Satellite
• Other wireless radio
• Wireless Optical
Slide No 11
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Digital Multiplexing: PDH and SDH
Overview
Slide No 13
Microwave Radio Planning and Link Design
European Digital Multiplexer Hierarchy
• Plesiochronous Digital Hierarchy (PDH)
• Synchronous Digital Hierarchy (SDH )
Slide No 14
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
European PDH Multiplexing Structure
Higher order multiplexing
4 x 34
16 x E1
4 x E1
139,264 kbps
1
1 E1
8448 kbps
30
2048 kbps
Slide No 16
34,368 kbps
Microwave Radio Planning and Link Design
European PDH Multiplexing Structure-used
1st order
2.048 Mbps
E1
VF
Primary PCM
Multiplexing
Data
MUX
DEMUX
MUX
DEMUX
Data Multiplexing
BTS
MUX
DEMUX
mobile Multiplexing
MUX
DEMUX
Slide No 17
2nd order
8.228 Mbps
E2
3rd order
34.368 Mbps
E3
MUX
DEMUX
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Slide No 20
51.84 Mbit/s
Microwave Radio Planning and Link Design
General Transport Module STM-N
N. 270 columns
N. 9
1
3
5
RSOH
AU pointer
MSOH
9
Slide No 21
N. 261
Payload
SOH: Section Overhead
AU: Administration Unit
MSOH: Multiplexer Section
Overhead
RSOH: Repeater Section
Overhead
Microwave Radio Planning and Link Design
SDH Multiplexing Structure
C-4
VC-4
x 3 TUG-3
x7
AU-4
x1
Mapping
Aligning
Multiplexing
Slide No 22
x1
TUG-2
AUG
xN
x3
STM-N
TU-3
VC-3
C-3
TU-12
VC-12
C-12
140 Mbps
C: Container
VC: Virtual Container
TU: Tributary Unit
TUG: Tributary Container Group
AU: Administrative Unit
AUG: Administrative Unit Group
34 Mbps
2 Mbps
Microwave Radio Planning and Link Design
From 2 Mbps to STM-1
(Justification)
2 Mbits
+ POH
SOH: Section Overhead
POH: Path Overhead
Slide No 23
STM-1
VC-4
VC-12
SDH
MUX
+ POH
+ SOH
Microwave Radio Planning and Link Design
Containers C
Justification bits
=
PDH
Stream
Slide No 24
Container
Microwave Radio Planning and Link Design
Virtual Containers VC
Path overhead
=
Container
Slide No 25
Virtual
Container
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
GSM Block Diagram (E1 links)
MSC1
BTS
SDH
MSC2
MSC3
BTS
BSC1
PDH
Abis
BTS
BTS
BTS
BTS
Slide No 29
BSC2
BTS
BTS
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Digital Microwave systems Overview
Slide No 32
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
• PSK
MODEM- Digital Modulation
– 2 PSK
– 4 PSK
– 8 PSK
• QAM
– 8 QAM
– 16 QAM
– 32 QAM
– 64 QAM
– 128 QAM
Slide No 34
Microwave Radio Planning and Link Design
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 Radio Planning and Link Design
Microwave Equipment Specification
• Operating Frequency
• Modulation
• Capacity
• Bandwidth
• Output power
• Receiver Thresholds @ BER’s 10-6 and 10-3
• MTBF
• FKTB
Slide No 36
Microwave Radio Planning and Link Design
RADIO EQUIPT Example: DART
Radio
Equipment
Antenna
dish
Dish diameter: 30 cm
Slide No 37
Microwave Radio Planning and Link Design
Slide No 38
Microwave Radio Planning and Link Design
Radio Equipment Datasheet
Slide No 39
Microwave Radio Planning and Link Design
Microwave Allocation in Radio spectrum
VLF LF MF
3k
30 k
300 k
HF VHF UHF SHF EHF
3M
• Microwave primarily is
utilized in SHF band, and
some small parts of UHF &
EHF bands
Slide No 40
30 M
300 M
3G
30 G
300 G
VHF
Very low frequency
LF
Low frequency
MF
Medium frequency
High Frequency
Very High Frequency
Ultra High Frequency
Super High Frequency
Extremely High Frequency
HF
VHF
UHF
SHF
EHF
Microwave Radio Planning and Link Design
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 Radio Planning and Link Design
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
– 8 x 2 Mbps with a bandwidth of 14 MHz
– 16 x 2 Mbps with a bandwidth of 28 MHz
Slide No 42
Microwave Radio Planning and Link Design
23 GHz Band - example
1232
1120
21224
22456
Low
2 x 2 (3.5 MHz)
320
Slide No 43
1120
22456
23576
High
Possible Number of Channels
4 x 2 (7 MHz)
8 x 2 (14 MHz)
160
80
16 x 2 (28 MHz)
40
Microwave Radio Planning and Link Design
Channel Spacing
1.75 MHz
3.5 MHz
2 E1
3.5 MHz
4 E1
8 E1
16 E1
Slide No 44
7 MHz
14 MHz
7 MHz
14 MHz
28 MHz
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Performance and availability objectives
Slide No 46
Microwave Radio Planning and Link Design
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
–
–
–
–
Slide No 47
radio wave propagation
hardware failure
Resetting time after repair
Frequency dependant interference problems
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
•
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
Microwave Radio Planning and Link Design
ITU-T G.821 HRX Hypothetical Reference Connection
27,500 km
1250 km
25,000 km
1250 km
T-reference
point
T-reference
point
INT
LE
15 %
Local
Grade
Slide No 52
15 %
Medium
Grade
LE
INT
40 %
15 %
High
Grade
Medium
Grade
15 %
Local
Grade
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
ITU-T G.821 performance & Availability
Examples
BER 10-6
BER 10-3
<10s
>10s
DM SES DM
ES
ES
ES
Available time (AT)
Slide No 54
DM
SES
DM
ES
ES
Unavailable time (UAT)
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
0.015
0.015
0.04
0.015
0.015
0.05
0.05
1.5
1.5
4
1.5
1.5
1.2
1.2
3.2
1.2
1.2
INT
Slide No 57
LE
SES 0.2%
(0.1%+0.1% for
High and Medium
grade for adverse
conditions
DM 10 %
ES 8 %
Microwave Radio Planning and Link Design
P & A for HRPD – High Grade
1/10 of HRX
2500
High Grade
0054 %
(0.004+0.05)
0.4 %
0.32 %
0.3 %
ITU-T; G.821, Rep 1052
SES
(Additional 0.05% for
adverse propagation
conditions)
DM
ES
UAT
Note: between 280 to 2500 all parameters are multiplied by (L/2500)
Slide No 58
Microwave Radio Planning and Link Design
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
SES
DM 10 %
Errored Seconds ES 8 %
RBER
UAT
Slide No 59
Percentage of any month
Class 1
Class 2
Class 3
280 km
280 km
50 km
0.006
0.0075
0.002
0.045
0.2
0.2
0.036
0.16
0.16
5.6x10-10
Under
Under
study
study
0.033
0.05
0.05
Class 4
50 km
0.005
0.5
0.4
Under
study
0.1
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Calculation of Unavailability
• Unavailability of cascaded modules
N1
N2
N3
Nn
n
 n

N s  1  As  1   1  N i   1  1   Ni    N i
i 1
 i 1  i 1
n
Slide No 64
Microwave Radio Planning and Link Design
Calculation of Unavailability
• Unavailability of parallel modules
N1
n
N s   Ni
i 1
N2
N3
Nn
Slide No 65
Microwave Radio Planning and Link Design
Improvement in Availability in n+1 protection
• HW protection
• Unavailability of a n+1 redundant system
N n 1 
 2

1
n  1
n 1 2

 N 1  N 
n  2! n  1  2 ! 
Can be approximated
Slide No 66
N n 1 
n 1 2
N
2
Microwave Radio Planning and Link Design
Improvement in Availability in Loop protection
• HW and route protection
• Unavailability in a loop
N=(N1+N2)(N3+N4+N5+N6+N7)



N    N i   N i 
 i 1  i  k 1 
k
N1
N4
N5
Where,
– J: Amount of hops in loop
– K: Consecutive number of hop from the hub
– N: Unavailability of the hop
Slide No 67
N2
N3
J
N6
N7
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Topology Planning
Slide No 69
Microwave Radio Planning and Link Design
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
–
–
–
–
Slide No 70
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Topology Planning
• Network topology is based on
– Traffic
– Outage requirements
• Most frequently used topologies
– Star
– Daisy Chain
– Loop
Slide No 73
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
–
–
–
–
–
Slide No 75
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Daisy Chain
• (grooming)
Slide No 77
Microwave Radio Planning and Link Design
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
– Expansions might require upgrading or rearrangement
Slide No 78
Microwave Radio Planning and Link Design
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 loop
Slide No 79
Microwave Radio Planning and Link Design
Topology Planning
• Define clusters
• Select reference node
• Chose Backbone
• Decide the topology
Slide No 80
Microwave Radio Planning and Link Design
Diversity
Slide No 81
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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:
Improvement factor
Slide No 83
I
PSinglechannel
PDiversity
where P refers to BER
Microwave Radio Planning and Link Design
Diversity Improvement
10 –3
No
diversity
10 -4
10 -5
diversity
Diversity
improvement
factor
10 -6
10 -7
20
Slide No 84
30
40
Fade Depth
Microwave Radio Planning and Link Design
• Space diversity
Single 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
Microwave Radio Planning and Link Design
Space Diversity
Tx 1
Separate paths
Rx 1
S
Rx 1
Slide No 86
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Slide No 88
systems
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Combined diversity
Combined space and frequency diversity
TX
RX
f1
TX
f2
f1
f2
RX
S
RX
RX
Slide No 93
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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 Radio Planning and Link Design
Microwave Antennas
Slide No 96
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Antenna Gain
•The gain of parabolic antenna referred to an isotropic
radiator is given by:
Gain  10 log(  A 
4

2
)
where:
– = aperture efficiency (typical values : 0.5-0.6)
–  = 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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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:
3dB = ± 35. /D in degrees
– The 10dB deflection angle is found approximately by:
10dB = 60. /D in degrees
Slide No 102
Microwave Radio Planning and Link Design
•
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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( /2 )) in dB
where :
– AR is the physical reflector area in m2
– F is the radio frequency in GHz
–  is the angle in space at the passive
repeater in degrees
Slide No 106
Microwave Radio Planning and Link Design
Plane Reflectors
Slide No 107
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Back to back antennas
Slide No 109
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
•
•
•
•
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
Microwave Radio Planning and Link Design
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
28 MHz
Slide No 112
3
4
5
6
7
8
1’
2’
3’
4’
5’
6’
7’
8’
Microwave Radio Planning and Link Design
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
10dB = 60. /D in degrees
Slide No 113
Microwave Radio Planning and Link Design
Antenna
Datasheet
Slide No 114
Microwave Radio Planning and Link Design
Digital Antenna
pattern
Slide No 115
Microwave Radio Planning and Link Design
Antenna Pattern
Slide No 116
Microwave Radio Planning and Link Design
Radio Propagation
Slide No 117
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Slide No 124
fading
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
The figure shows different
values of total reflection
coefficient, and the minimum
and maximum values
with respect to them
Slide No 128
loss (ρ)
5
-5
-15
-15
-25
-35
Amax
Amin
0.4
0.6
0.2
0.8
Total reflection coefficient (ρ)
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
EM wave Refraction and Ray bending
• Refraction cause ray bending in the atmosphere
• In free space, the radio wave follows straight line
no atmosphere
Slide No 132
with atmosphere
Microwave Radio Planning and Link Design
EM wave Refraction: K-Factor
• K is a value to indicate wave bending
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Formation Of Ducts- Refraction and reflection
Elevated DUCT
Earth
Slide No 136
Ground Based DUCT
Earth
Microwave Radio Planning and Link Design
Formation Of Ducts- Explanation
Refraction and reflection
Slide No 137
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
ITU-R DUCT Probability CONTOUR MAPS
Slide No 139
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Mutipath Fading
P
Flat fading
Slide No 152
Normal
signal
Frequency
selective
fading
Microwave Radio Planning and Link Design
Microwave Link Planning and Design
Slide No 153
Microwave Radio Planning and Link Design
Hop Calculations (Design)
Predictable
Statistically Predictable
Free Space Loss
Gas Absorption
Always present
and predictable
Rain fading
Multipath fading
Obstacle Loss
Predictable
if present
Link Budget
Performance &
Availability Objectives
Slide No 154
Not always present
but statistically
predictable
Fading prediction
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Path Profile Example
• Path profiles are necessary to determine site locations and
antenna heights
Slide No 156
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Path Profile: Fresnel Zone Example
Slide No 158
Microwave Radio Planning and Link Design
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
d1  d 2  d 
Slide No 159

2
Microwave Radio Planning and Link Design
Fresnel Zone Equation
•
First Fresnel zone radius
F1  17.3 
•
•
d1  d 2
d f
[m]
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:
– 1. F1 (radius) 17.3 
55
 7m
15  10
– 2. F1 (radius)  17.3 
10  10
 10m
15  20
Slide No 160
Microwave Radio Planning and Link Design
Fresnel Zone Radii calculations
“Table Tool”
Frequency
GHz
7.0
13.0
15.0
18.0
23.0
26.0
38.0
Slide No 161
4.0
9.2
10.3
10.1
9.2
7.7
6.7
5.1
10.0
12.7
13.6
14.2
15.2
17.1
19.6
23.9
Distance
15.0
13.3
12.1
11.3
10.6
9.6
8.6
7.3
in km
20.0
15.0
13.6
13.4
13.8
14.7
16.0
18.1
30.0
17.3
13.8
12.4
11.6
10.9
10.1
9.1
40.0
18.6
14.2
13.1
13.0
13.4
14.1
15.2
Microwave Radio Planning and Link Design
Obstacle Loss: Fresnel Zone is not Cleared
Obstacle Loss
Knife Edge obstacle loss
Slide No 162
Smooth spherical obstacle loss
Microwave Radio Planning and Link Design
Knife Edge Losses
0
Slide No 163
0
6
12
20 dB
Microwave Radio Planning and Link Design
Smooth Spherical Earth Losses
30
20
10
dB
Slide No 164
Microwave Radio Planning and Link Design
Line-Of-Sight Survey
LOS
• LOS Survey
– To verify that the proposed network design is feasible considering
LOS constraints
Slide No 165
Microwave Radio Planning and Link Design
Line-Of-Sight Survey- Flowchart
Network Design
Update the
design
LOS Survey
LOS Report
Slide No 166
Microwave Radio Planning and Link Design
LOS Survey Equipment
Necessary:
• Compass
• Maps : 50 k or better
• Digital Camera
• GPS Navigator
• Binoculars
• Hand-held communication
equipment
• Signaling mirrors
Slide No 167
Optional:
• Clinometer
• Altimeter
• Laptop
• Spectrum analyzer
• Antenna horn
• Low noise amplifier
• Theodolite
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
• Site Data
– Name
– Coordinates
– Height
– Address
LOS Survey Report
• Proposed Tower Height
• LOS Confirmation
• Azimuth and Elevation
• Path short description
• Photographs
Slide No 171
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Slide No 173
(fading is ignored)
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
Link Budget
Gt
Gr
Rx
Tx
Output
power
Antenna
gain
Branching
Feeder
loss
loss
Free space loss +
atmospheric atten.
Feeder
Received
loss
power
Antenna
Branching
gain
loss
Fade
Margin
Receiver threshold
Slide No 175
Microwave Radio Planning and Link Design
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
Lp
 4 D 
 




2
 4  fD 
 

c


2
where,
Lp = free space path loss
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
Microwave Radio Planning and Link Design
Link Budget Parameters
Free Space Loss
Lp
Tx
Slide No 177
Rx
Microwave Radio Planning and Link Design
Link Budget Parameters
• Total Antenna Gain:
Ga = 20 log (Da) + 20 log (f) + 17.8
f
Da
• Atmospheric attenuation occurs at higher frequencies ,
above 15 GHz due to atmospheric gases, and given by:
Aa   a  d
Where d is path link in km , a is specific attenuation in dB/km
Slide No 178
Microwave Radio Planning and Link Design
Link Budget Parameters
• Rx Level: Signal strength at the receiving antenna
PRx= PTx-LBRL-+GTx-LFS-Lobs+GRx - LTx feeder – LRx feeder
Where,
PRx : received power level
PTx : transmitted power level
LBRL : branching loss
LFS : free space loss
LTx feeder : Tx feeder loss
Slide No 179
GTx :Tx gain
Lobs :Diffraction loss
GRx :Rx gain
LRx feeder : Rx feeder loss
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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
Microwave Radio Planning and Link Design
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: path inclination in mrad = E P  1
d
Slide No 182
Microwave Radio Planning and Link Design
•
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
Microwave Radio Planning and Link Design
Frequency Selective Fading ITU-R F.1093
• Result from surface reflections or introduced by
atmospheric anomalies such as strong ducting gradients
Psel  4.3  10

B
20
 m2
  W 
r
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
Microwave Radio Planning and Link Design
Frequency Selective Fading ITU-R F.1093
  1 e
3/ 4 

P


 .2 0  

 100  

Where,
Po: The fading occurrence factor
1.5
d 
 m  0.7   
 50 
w/ 2
W

 Bc
10 20
w / 2
Slide No 185
Where,
d : Path length (km)
Where,
Bc: Signature depth
Microwave Radio Planning and Link Design
Frequency Selective Fading ITU-R P.530-7
BNM
B
2
2

 M



Psel  2.15    WM  10 20  M  WNM  10 20  M

 r ,M
 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
Microwave Radio Planning and Link Design
Space Diversity Improvement ITU-R P.453
P mp
Where,
div

P mp
I

P flat  P sel
I


  3 . 34 10  4  s 0 .87  f  0 .12 d 0 .48  Po

100

I  1  e


 1 . 04





M  G
  10 10


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
Microwave Radio Planning and Link Design
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 (R0.01)
The attenuation due to the rain in .01% of the time for a given path
may be found by:
AR   R .d eff
where
γR : Specific rain attenuation (dB/km)
deff : Effective path length, km
 R  k  Ra
k and a are given in the table
Slide No 188
Microwave Radio Planning and Link Design
Usable path lengths with rain intensity
example: 15 GHz
Slide No 189
Microwave Radio Planning and Link Design
ITU-R presents the cumulative distribution of rain
intensity for 15 different zone as shown below
Rain zone contours (Far
East)
Slide No 190
Rain zone contours
(Europe and Africa)
Rain zone contours (Americas)
Microwave Radio Planning and Link Design
Rain Fading ITU-R P.530
•
The relation between fading margin and unavailability for the path
is given by:
%
Where
– AR0.01 : Rain attenuation exceeded 0.01% of the time
– F: Fade margin
Slide No 191
Microwave Radio Planning and Link Design
Frequency Planning
Slide No 192
Microwave Radio Planning and Link Design
Frequency planning
• Objective of frequency planning
– Efficient use of available frequency band
– Keep interference level as low as possible
• Frequency plan must consider interference
– C/I Objectives
• Note: the requirements depends on
– Equipment
– Frequency
– Bandwidth
Slide No 193
For adjacent channel interference
Microwave Radio Planning and Link Design
Frequency Planning
Frequency Allocation
• From operator’s point of view, it is best to get a block of
frequencies or several adjacent channels from each
frequency band
– Installation and maintenance of microwave radio is less complicated
– Interference analysis is only needed between operators own hops
• It is recommended to assign the available channels or
•
frequency block to certain capacities so that 2X2, 4X2,
8X2, 16X2 will not interleave.
Normally in 18-38 GHz, four hops using the same channel
can arrive at star if they are at 90 degrees angle from each
other
Slide No 194
Microwave Radio Planning and Link Design
Frequency Planning
Interference
• Interference needs more concern at star points because several
microwave radios transmit and receive are close to each other
• Don’t use higher transmitter output power than required
• Frequency planning in star points is trivial if multiple channels are
used (inefficient use of channels)
• Re use same channel (efficient use of channels)
– All stations at star transmit either high or low, while high-low alteration must be
applied in chains.
– Good angle separation
– Cross polarization gives extra discrimination
Note: Rain has greater attenuation on horizontal polarization thus use horizontal
polarization for shorter hops
Slide No 195
Microwave Radio Planning and Link Design
Frequency Planning
• The radio spectrum is allocated to various services by
•
ITU’s Administrative Radio Conference (WARC)
ITU-R is responsible for providing RF channel
arrangement
– Alternated channel arrangement
– Co-channel arrangement
– Interleaved arrangement
Slide No 196
Microwave Radio Planning and Link Design
Alternated Channel arrangement
• Every channel will have opposite polarization to the
•
adjacent channels
This arrangement is used(neglecting co-polar adjacent
interference) if the below rule holds
XPDmin+(NFD –3)>(C/I)min
NFD=adj. Ch. Received power / adj. Ch. Power received after BB filter
• Advantage:
Easily filfilled by standard antenna to radio equipment
• Disadvantage:
Limited spectrum effective
Slide No 197
Microwave Radio Planning and Link Design
Co-channel arrangement
• In this arrangement every radio channel is utilized twice
for independent traffic on opposite polarization for the
same path
• The following demand must be fulfilled
[10log(1/(1/10^((XPD + XIF)/10) +1/10^((NFD-3)/10)))] > (C/I)
Where,
NFD :Net Filter discriminator
XIF :is XPD improvement factor
Slide No 198
Microwave Radio Planning and Link Design
Channel Capacity and Separation
Channel separation
Slide No 199
Capacity
Channel Separation
2 X 2 Mbps
3.5 MHz
4 X 2 Mbps
7 MHz
8 X 2 Mbps
14 MHz
16 X 2 Mbps
28 MHz
Microwave Radio Planning and Link Design
Co-channel Interference – Far
Tx/Rx
Tx = f1
Rx = f2
Tx/Rx
Tx = f2
Rx = f1
Tx/Rx
Tx = f1
Rx = f2
Slide No 200
Tx = f2
Rx = f1
Tx/Rx
Microwave Radio Planning and Link Design
Co-channel Interference – Near
Tx = f1
Tx/Rx Rx = f
2
Tx/Rx
Tx = f2
Rx = f1
Slide No 201
Microwave Radio Planning and Link Design
Adjacent Channel Interference
fRx
fTx
Interference
Slide No 202
Microwave Radio Planning and Link Design
Receiver Threshold Degradation
•
•
Presence of interfering signals will give a receiver threshold
degradation
The degraded receiver threshold level LTel is calculated from:

LTel  LTe  10 log 1  10
•
  LTe  C R  LI  / 10 
A Rule of Thumb
Threshold Degradation < 3 dB
Slide No 203

Microwave Radio Planning and Link Design
Threshold Degradation
Receiver
threshold,
dBm
-70
-72
-74
-76
-78
-80
-82
-84
-86
-88
3dB
14 15 16 17 18 19 20 21 22 23
Signal to Interference ratio, dB
Slide No 204
Microwave Radio Planning and Link Design
Channel plan
Low sub-band
High sub-band
1A 2A 3A 4A 5A 6A 7A
1B 2B 3B 4B 5B 6B 7B
Duplex distance
Tx=4A
Rx=4B
Slide No 205
Tx=4B
Rx=4A
Microwave Radio Planning and Link Design
High / Low Tx Channel Allocation
L
H
H
L
H
H
H
L
L
Near interference
H/L
Slide No 206
Microwave Radio Planning and Link Design
High / Low Tx Channel Allocation
Rings with odd number of sites should be avoided
H
H
L
L
H/L
Interference
Slide No 207
H
L
L
H
New
frequency
band
H
Microwave Radio Planning and Link Design
Channel Plan
7 Channels
1A
2A
28 MHz
(17x2 Mbps)
Slide No 208
3A
4A
5A
6A
7A
f
Microwave Radio Planning and Link Design
Channel Plan
11 Channels
28 MHz
(17x2 Mbps)
Slide No 209
14 MHz
(8x2 Mbps)
f
Microwave Radio Planning and Link Design
Channel Plan
15 Channels
28 MHz
(17x2 Mbps)
Slide No 210
14 MHz
(8x2 Mbps)
7 MHz
(4x2 Mbps)
f
Microwave Radio Planning and Link Design
Output Power
Only High output power
High output
power
High output
power
High output
power
Interference
Slide No 211
Microwave Radio Planning and Link Design
Output Power
High and low output power
Low output
power
High output
power
Low output
power
No Interference
Slide No 212
Microwave Radio Planning and Link Design
Interference
Slide No 213
Microwave Radio Planning and Link Design
Digital Systems and BER
• Performance of digital transmission system can be
•
evaluated by BER, Bit Error Rate
Telephony BER degradation versus audible degradation:
– 10-6: Noise not audible
– 10-5: Barely audible
– 10-4: audible, understandable
– 10-3: disturbing
– More than 10-3: sync loss, link loss
•
Data and in particular multimedia media application
require a very low BER
Slide No 214
Microwave Radio Planning and Link Design
Noise in Digital Systems
Noise can originate from a variety of sources, and many of
these sources are man-made so they can be eliminated
• Thermal noise
• Noise Factor and Noise Figure
• S/N Ratio
• Receiver Thresholds
Slide No 215
Microwave Radio Planning and Link Design
White Noise in Digital Systems
• Thermal noise is generated from random motion of
•
electrons due to thermal energy
Pn=KTB (W) where :
– k=Boltzmann’s constant
– T=temperature in Kelvin
– B=bandwidth of noise spectrum
• Typical values are : T=300 K , b= 6MHz , -106 dBm
Slide No 216
Microwave Radio Planning and Link Design
Noise Factor and Noise Figure
• Noise Factor and Noise Figure are figures of merit used to
•
•
indicate how much the S/N deteriorates as a signal passes
through a circuit or series of circuits.
Noise factor:
– Is defined in terms of signal to noise ratio
available S/N power ratio at input
(unitless)
F
available S/N power ratio at output
Noise Figure
NF = 10 log(F) (dB)
Slide No 217
Microwave Radio Planning and Link Design
Noise in Digital Systems
• Signal to interference ratio defines the minimum
difference between the signal and the interferer levels. It
depends on bandwidth, modulation and manufacturer.
• Usually for digital system signal to interference ratio 1525 dB
Slide No 218
Microwave Radio Planning and Link Design
Receiver Thresholds
• Threshold (10-3): Received level at BER 10-3
• Threshold (10-6): Received level at BER 10-6
Threshold = White noise + Noise figure + S/N
Threshold
S/N
NF
White noise
Slide No 219
Microwave Radio Planning and Link Design
Threshold Degradation
•
A Rule of Thumb
Threshold Degradation < 3 dB
given that the required signal
to interferer is not violated
-70
-72
-74
-76
Receiver -78
threshold, -80
-82
dBm
-84
-86
-88
3dB
14 15 16 1 18 19 20 21 22 23
Signal to Interference
ratio, dB
7
Slide No 220
Microwave Radio Planning and Link Design
Cross Polar Interference XPI
• Both multi path- and rain fading can result in severe
•
degradation of XPD level
Cross Polar interference Cancellers (XPIC) in the receiver
remove the unwanted signal that has leaked from the
opposite polarization into the wanted one
The quantitative
Description of crossPolar interference XPI
E11
dB
XPI  20.Log
E21
E11
XPD  20.Log
dB
E12
Slide No 221
Where E11and E12 are
given in the next figure
Microwave Radio Planning and Link Design
Cross Polar Interference
• Depolarization Causes
– Scattering or reflection from land or water surfaces
– Reflection from an atmospheric layer
– Tropospherical turbulence
Slide No 222
Microwave Radio Planning and Link Design
Cross Polar Interference
E1
E11
E21
E2
E12
E22
Dual polarized system suffering from XPI
Slide No 223
Microwave Radio Planning and Link Design
Ways to include interference in
performance calculation
• The interference calculation are performed by calculation
•
•
the interference level and determining the receiver
threshold degradation
Start from allowed interference level at the input of the
disturbed receiver and then comparing it with level of the
interfering signal
The degradation receiver threshold level

LTel  LTe  10 log 1  10 LTe CR  L1 /10 
Slide No 224

Microwave Radio Planning and Link Design
Interfering waves propagation mechanisms
• Long-term interference mechanisms:
– Diffraction
– Troposcatter
– Line-of-site
• Short-term interference mechanisms:
– Ducting: layer refraction/reflection
– Hydrometeor scatter
Slide No 225
Microwave Radio Planning and Link Design
Selecting Interfering Stations
•
•
Before performing interference calculation the possible interfering
station must be selected in the area of interference
Co-ordination area are the area around given station where possible
co-channel interference from near site are situated
Key hole
region
Co-ordination area for offkey hole region
Slide No 226
Microwave Radio Planning and Link Design
Propagation in Interference Calculations
•
•
•
Select interfering site by calculating coordination area
Select minimum interference levels
Predict interferer signal level
–
–
–
–
–
–
Decide whether an average year or worst –month prediction is required
Assemble the basic input data
Derive the annual or worst-month radio meteorological data from maps
Analyze the path profile, and classify the path according to the path geometry
Identify which individual propagation models need to be invoked
Calculate the individual propagation predictions using each of the models
identified in the previous step
– Combine the individual predictions to give the overall statistics
Slide No 227
Microwave Radio Planning and Link Design
Interference Calculation
• Undesirable RF coupling between radio channels
– Cross polarization: occurred in channels operating on opposite
polarization
– Adjacent channel:the channel filter at the receiver and the width of
the transmitted spectrum determined the interference level
– Front to back:The interference level is mainly a function of the
antenna front-to-back ratio
– Over shoot:If the paths are aligned , interference due to overshoot
is critical. Use of opposite polarization or change of radio channels
is recommended.
Slide No 228
Microwave Radio Planning and Link Design
Examples of Interference RF coupling
• Examples
V
H
f2
f1
f1
Cross Polarization
f1 ’
f1
Front-to-Back
Slide No 229
Adjacent channel
f1
f1 ’
Over Shoot
f1
Microwave Radio Planning and Link Design
Interference Calculations- cont.
• Preconditions
– Network diagram: drawn to scale and angle, includes all radio-relay
circuits within the frequency band concerned
– Network data : antenna types and radiation patterns, transmitter
output power
– RL equipment interference data, normally given as diagrams
•
•
•
•
Digital to digital interference diagrams
Digital to analog interference diagrams
Analog to digital interference diagrams
Adjacent-channel attenuation as a function of channel spacing
– Antenna radiation patterns: for all types of antennas used in the
network
Slide No 230
Microwave Radio Planning and Link Design
Interference Calculations- cont.
• Interference evaluation on digital network
– It is necessary to check each antenna discrimination in the nodal
stations for all disturbances
– In the beginning, only the most critical interference path has to be
examined
– As a start, standard performance antennas are used, and no level
adjustments are made to reduce interference problems, this case is
worst case
– Co-polar operation
– Cross-polar operation
Slide No 231
Microwave Radio Planning and Link Design
Digital Map and Tools Overview
Slide No 232
Microwave Radio Planning and Link Design
Digital Maps
• Digitized Geographical data is needed
• Maps sampling (examples)
– Urban: 20 to 50m
– Suburban: 50-100m
– Open: 100m
Slide No 233
Microwave Radio Planning and Link Design
Digital Maps-Geographical Databases
• The choice of the geographical databases depends on the
•
propagation model used
A compromise has to be reached between:
– Cost
– Accuracy
– Calculation speed
– The chosen configuration
• Geographical databases types are:
– Vector data (Linear)
– Altitude
– Clutter (land use data)
Slide No 234
Microwave Radio Planning and Link Design
Digital Maps - Vector Data (Linear)
• Succession of points describing:
– Highway
– Roads
– Railways
– Rivers
– Borders
– coastlines
Slide No 235
Microwave Radio Planning and Link Design
Digital Maps - Altitude
• One altitude value per each pixel
• Each point of the pixel is assumed at the same altitude
• Two categories of altitude databases
– Digital Terrain Model (DTM)
– Digital Evaluation Model (DEM)
Slide No 236