microwave planning and design
TRANSCRIPT
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Slide No 1
Microwave Radio Planning and Link Design
CISCOM Training Center
Microwave Planning and Design
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Slide No 2
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
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Slide No 3
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
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Slide No 4
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)
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Slide No 5
Microwave Radio Planning and Link Design
PCM and E1 Overview
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Slide No 6
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
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Slide No 7
Microwave Radio Planning and Link Design
PCM Coder Block Diagram 64 kb/s
S/HS/H QuantizerQuantizerLPFLPF EncoderEncoder 64 kb/s PCM signal
Analog signal
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Slide No 8
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
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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
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Microwave Radio Planning and Link Design
E1 frame diagramTime Slot
0
Time Slot
1
Time Slot
2
Time Slot
31
Time Slot
30
Time Slot
29
………….
…………
Time Slot
16
…………
…………
125s
Si 0 0 1 1 0 1 1
Si 1 A Sn Sn Sn Sn Sn
Frame containing frame alignment signal (FAS)
Frame not containing frame alignment signal
1 2 3 4 5 6 7 8
Bits
Frame Alignment Signal (FAS) pattern - 0011011Si = Reserved for international use (Bit 1)Sn = Reserved for national useA = Remote (FAS Distant) Alarm- set to 1 to indicate alarm condition
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Slide No 11
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
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Slide No 12
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
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Slide No 13
Microwave Radio Planning and Link Design
Digital Multiplexing: PDH and SDHOverview
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Microwave Radio Planning and Link Design
European Digital Multiplexer Hierarchy
• Plesiochronous Digital Hierarchy (PDH)
• Synchronous Digital Hierarchy (SDH )
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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
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Microwave Radio Planning and Link Design
European PDH Multiplexing Structure
1
30
1 E1
4 x E1
16 x E1
4 x 34
Higher order multiplexing
2048 kbps
8448 kbps
34,368 kbps
139,264 kbps
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Microwave Radio Planning and Link Design
European PDH Multiplexing Structure-used
MUX DEMUX
Primary PCM Multiplexing
BTSMultiplexing
DataMultiplexing
MUX DEMUX
MUX DEMUX
MUX DEMUX
MUX DEMUX
1st order 2.048 Mbps
E1
2nd order 8.228 Mbps
E23rd order
34.368 MbpsE3
VF
Data
mobile
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Slide No 18
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
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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
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Slide No 20
Microwave Radio Planning and Link Design
SDH Bit Rates
155.52 Mbit/s
622.08 Mbit/s
2.48832 Gbit/s
STM-1
STM-4
STM-16
4
4
3
STM-0 51.84 Mbit/s
STM-64
4
9.995328 Gbit/s
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Microwave Radio Planning and Link Design
General Transport Module STM-N
RSOH
MSOH
PayloadAU pointer
1
9
5
3
N. 270 columns
N. 9 N. 261
SOH: Section OverheadAU: Administration UnitMSOH: Multiplexer Section OverheadRSOH: Repeater Section Overhead
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Microwave Radio Planning and Link Design
SDH Multiplexing Structure
C-4VC-4
C-12
C-3VC-3
VC-12TU-12
TU-3TUG-3
TUG-2
AUGAU-4 STM-Nx 1
x 1x 3
x 7 x 3
x N
C: ContainerVC: Virtual ContainerTU: Tributary UnitTUG: Tributary Container GroupAU: Administrative UnitAUG: Administrative Unit Group
Mapping Aligning Multiplexing
140 Mbps
2 Mbps
34 Mbps
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Slide No 23
Microwave Radio Planning and Link Design
From 2 Mbps to STM-1
STM-1VC-4
+ POH+ POH
VC-122 Mbits
(Justification)
+ SOH
SOH: Section Overhead
POH: Path Overhead
SDH MUX
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Slide No 24
Microwave Radio Planning and Link Design
Containers C
=
PDH Stream
Justification bits
Container
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Slide No 25
Microwave Radio Planning and Link Design
Virtual Containers VC
=
Container
Path overhead
Virtual Container
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Slide No 26
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
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Slide No 27
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.
– SurvivabilityWith 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 insertSDH 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.
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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.
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Microwave Radio Planning and Link Design
GSM Block Diagram (E1 links)
MSC1
MSC3MSC2
BSC1
BSC2
BTS
BTS
BTS
BTS
BTS
BTS
BTSBTS
SDH
PDH Abis
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Microwave Radio Planning and Link Design
Abis- Interface
• 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
BSC Abis-Interface
BTS
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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)
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Slide No 32
Microwave Radio Planning and Link Design
Digital Microwave systems Overview
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Microwave Radio Planning and Link Design
Digital Microwave system• Equipment
– E1– MUX– IF MODEM– Transceiver
In door
Out door TRU
– FeederFor In door
Co-axial transmission line
Waveguide transmission line
For Outdoor
IF between modem ODU Transceiver (TRU)
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Microwave Radio Planning and Link Design
MODEM- Digital Modulation• PSK
– 2 PSK– 4 PSK– 8 PSK
• QAM– 8 QAM– 16 QAM– 32 QAM– 64 QAM– 128 QAM
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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
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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
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Microwave Radio Planning and Link Design
RADIO EQUIPT Example: DART
Dish diameter: 30 cm
Antenna dish
Radio Equipment
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Microwave Radio Planning and Link Design
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Slide No 39
Microwave Radio Planning and Link Design
Radio Equipment Datasheet
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Microwave Radio Planning and Link Design
Microwave Allocation in Radio spectrum
3 k 30 k 300 k 3 M 30 M 300 M 3 G 30 G 300 G
VLF LF MF VHF
VHF Very low frequency
LF Low frequency
MF Medium frequency
HF High Frequency
VHF Very High Frequency
UHF Ultra High Frequency
SHF Super High Frequency
EHF Extremely High Frequency
UHF SHFHF EHF
• Microwave primarily is utilized in SHF band, and some small parts of UHF & EHF bands
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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
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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
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Microwave Radio Planning and Link Design
23 GHz Band - example
21224 22456
1232
11201120
22456 23576
Low High
2 x 2 (3.5 MHz) 4 x 2 (7 MHz) 8 x 2 (14 MHz) 16 x 2 (28 MHz)Possible Number of Channels
320 160 80 40
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Microwave Radio Planning and Link Design
Channel Spacing
1.75 MHz 3.5 MHz
3.5 MHz 7 MHz
7 MHz 14 MHz
14 MHz 28 MHz
2 E1
4 E1
8 E1
16 E1
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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.
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Slide No 46
Microwave Radio Planning and Link Design
Performance and availability objectives
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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 – radio wave propagation– hardware failure– Resetting time after repair– Frequency dependant interference problems
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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.
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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
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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.
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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
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Microwave Radio Planning and Link Design
ITU-T G.821 HRX Hypothetical Reference Connection
Local Grade
Medium Grade
Medium Grade
Local Grade
High Grade
T-reference point
T-reference point
1250 km 1250 km25,000 km
27,500 km
LE LEINT INT
40 %15 % 15 % 15 %15 %
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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
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Slide No 54
Microwave Radio Planning and Link Design
ITU-T G.821 performance & Availability Examples
BER 10-6
BER 10-3
DM
ES
SES
<10s >10s
SES
Available time (AT) Unavailable time (UAT)
DM
ESESESES
DM DM
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Slide No 55
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
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Slide No 56
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
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Slide No 57
Microwave Radio Planning and Link Design
G.821 Performance Objectives over HRX
Local Medium Medium LocalHigh
0.0150.015 0.0150.015
1.51.5 1.51.5
1.21.21.21.2
0.04
4
3.2
1250 km 1250 km25000 km
INT LE
SES 0.2% (0.1%+0.1% for High and Medium grade for adverse conditions0.05 0.05
DM 10 %
ES 8 %
ITU-T; G.821, F.697, F.696
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Slide No 58
Microwave Radio Planning and Link Design
P & A for HRPD – High Grade
High Grade2500
0054 %(0.004+0.05)
0.4 %
0.32 %
SES (Additional 0.05% for adverse propagation
conditions)
DM
ES
0.3 % UAT
Note: between 280 to 2500 all parameters are multiplied by (L/2500)
1/10 of HRX ITU-T; G.821, Rep 1052
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Slide No 59
Microwave Radio Planning and Link Design
P & A for HRDS – Medium Grade
– Used for national networks, between local exchange and international switching center
Performance and availability Objectives for HRDSPerformance parameter Percentage of any month
Class 1
280 km
Class 2
280 km
Class 3
50 km
Class 4
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 study
Under study
Under study
UAT 0.033 0.05 0.05 0.1
IT-T; G.821, F.696, Rep 1052
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Slide No 60
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.
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Slide No 61
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
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Slide No 62
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
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Slide No 63
Microwave Radio Planning and Link Design
HW Unavailability
• Unavailability of one equipment module – HW
where
MTTR is mean time to repair
MTBF is mean time between failures.
MTTR MTBF
MTTR N1
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Slide No 64
Microwave Radio Planning and Link Design
Calculation of Unavailability
• Unavailability of cascaded modules
N1N1 N3N3N2N2 NnNn
i
n
i
n
ii
n
iss NNiNAN
11111111
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Slide No 65
Microwave Radio Planning and Link Design
Calculation of Unavailability
• Unavailability of parallel modules
N1N1
N3N3
N2N2
NnNn
i
n
is NN
1
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Slide No 66
Microwave Radio Planning and Link Design
Improvement in Availability in n+1 protection• HW protection
• Unavailability of a n+1 redundant system
212
1 1!21!2
11
n
n NNn
n
nN
Can be approximated 21 2
1N
nNn
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Slide No 67
Microwave Radio Planning and Link Design
Improvement in Availability in Loop protection• HW and route protection
• Unavailability in a loop
Where,– J: Amount of hops in loop– K: Consecutive number of hop from the hub– N: Unavailability of the hop
J
kii
k
ii NNN
11
N6N5
N4
N3 N2
N1
N7
N=(N1+N2)(N3+N4+N5+N6+N7)
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Slide No 68
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
• 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
N
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Slide No 69
Microwave Radio Planning and Link Design
Topology Planning
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Slide No 70
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– 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
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Slide No 71
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
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Slide No 72
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
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Slide No 73
Microwave Radio Planning and Link Design
Topology Planning• Network topology is based on
– Traffic– Outage requirements
• Most frequently used topologies– Star– Daisy Chain– Loop
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Slide No 74
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)
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Slide No 75
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
– 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
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Slide No 76
Microwave Radio Planning and Link Design
Daisy Chain
• 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)
Application: along roads
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Slide No 77
Microwave Radio Planning and Link Design
Daisy Chain
• (grooming)
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Slide No 78
Microwave Radio Planning and Link Design
TreeApplication: 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
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Slide No 79
Microwave Radio Planning and Link Design
LoopBTSs 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
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Slide No 80
Microwave Radio Planning and Link Design
Topology Planning
• Define clusters
• Select reference node
• Chose Backbone
• Decide the topology
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Slide No 81
Microwave Radio Planning and Link Design
Diversity
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Slide No 82
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.
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Slide No 83
Microwave Radio Planning and Link Design
DiversityDiversity 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 where P refers to BER Diversity
nelSinglechan
P
PI
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Slide No 84
Microwave Radio Planning and Link Design
Diversity Improvement
10 –3
20
10 -4
10 -5
10 -6
10 -7
4030
Diversity improvement
factor
No diversity
diversity
Fade Depth
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Slide No 85
Microwave Radio Planning and Link Design
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
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Slide No 86
Microwave Radio Planning and Link Design
Space Diversity
Separate paths Tx Rx
Rx
S
1 1
1
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Slide No 87
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
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Slide No 88
Microwave Radio Planning and Link Design
Frequency diversityIt 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
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Slide No 89
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
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Slide No 90
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
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Slide No 91
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
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Slide No 92
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
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Slide No 93
Microwave Radio Planning and Link Design
Combined diversity
Combined space and frequency diversity
TX
TX
RX
RX
RX
RX
f1
f1
f2
S
f2
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Slide No 94
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
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Slide No 95
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.
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Slide No 96
Microwave Radio Planning and Link Design
Microwave Antennas
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Slide No 97
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
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Slide No 98
Microwave Radio Planning and Link Design
Antenna Gain•The gain of parabolic antenna referred to an isotropic radiator is given by:
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
)4
log(102 AGain
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Slide No 99
Microwave Radio Planning and Link Design
Antenna Gain-cont.• This figure shows the relation between the gain of microwave dish and frequency with different dishdiameters
• Can be approximated Gain = 17.8 + 20log (d.f) dBi
where,
d : Dish diameter (m) f : Frequency in GHz
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Slide No 100
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
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Slide No 101
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
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Slide No 102
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
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Slide No 103
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 GainBoth EIRP and Power expressed in dBWAntenna 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
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Slide No 104
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
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Slide No 105
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
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Slide No 106
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
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Slide No 107
Microwave Radio Planning and Link Design
Plane Reflectors
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Slide No 108
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
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Slide No 109
Microwave Radio Planning and Link Design
Back to back antennas
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Slide No 110
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
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Slide No 111
Microwave Radio Planning and Link Design
• 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
Cross Polarization
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Slide No 112
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
28 MHz
Vertical
Horizontal
1 2 3 4 5 6 7 8 1’ 2’ 3’ 4’ 5’ 6’ 7’ 8’
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Slide No 113
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
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Slide No 114
Microwave Radio Planning and Link Design
Antenna Datasheet
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Slide No 115
Microwave Radio Planning and Link Design
Digital Antenna pattern
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Slide No 116
Microwave Radio Planning and Link Design
Antenna Pattern
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Slide No 117
Microwave Radio Planning and Link Design
Radio Propagation
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Slide No 118
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)
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Slide No 119
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
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Slide No 120
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
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Slide No 121
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
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Slide No 122
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
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Slide No 123
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
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Slide No 124
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 fading
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Slide No 125
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
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Slide No 126
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
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Slide No 127
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
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Slide No 128
Microwave Radio Planning and Link Design
EM wave Reflection coefficient-cont.
Reflection loss (ρ)
-35
-5
-15
-15-25
5
0.2 0.80.60.4Total reflection coefficient (ρ)
Amax
Amin
• 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
The figure shows different
values of total reflection
coefficient, and the minimum
and maximum values
with respect to them
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Slide No 129
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
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Slide No 130
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
Reflected wave
Refracted wave
Medium 1
Medium 2
θi θr,n1
,n2
n2 > n1
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Slide No 131
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.
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Slide No 132
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 with atmosphere
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Slide No 133
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=1.33a
rK
e
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Slide No 134
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
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Slide No 135
Microwave Radio Planning and Link Design
Formation Of Ducts- Refraction and reflectionGround 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
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Slide No 136
Microwave Radio Planning and Link Design
Formation Of Ducts- Refraction and reflection
Earth
Elevated DUCT
Earth
Ground Based DUCT
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Slide No 137
Microwave Radio Planning and Link Design
Formation Of Ducts- Explanation Refraction and reflection
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Slide No 138
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
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Slide No 139
Microwave Radio Planning and Link Design
ITU-R DUCT Probability CONTOUR MAPS
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Slide No 140
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
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Slide No 141
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.
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Slide No 142
Microwave Radio Planning and Link Design
Diffraction lossPractical 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
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Slide No 143
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
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Slide No 144
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
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Slide No 145
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
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Slide No 146
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.
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Slide No 147
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.
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Slide No 148
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
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Slide No 149
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
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Slide No 150
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
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Slide No 151
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
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Slide No 152
Microwave Radio Planning and Link Design
Mutipath Fading
Frequency selective fading
Normal signal
Flat fading
P
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Slide No 153
Microwave Radio Planning and Link Design
Microwave Link Planning and Design
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Slide No 154
Microwave Radio Planning and Link Design
Hop Calculations (Design)
Free Space LossGas Absorption
Obstacle Loss
Rain fadingMultipath fading
Link BudgetFading prediction
Performance & Availability Objectives
Predictable Statistically Predictable
Always present and predictable Predictable
if present
Not always present but statistically
predictable
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Slide No 155
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
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Slide No 156
Microwave Radio Planning and Link Design
Path Profile Example• Path profiles are necessary to determine site locations and
antenna heights
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Slide No 157
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
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Slide No 158
Microwave Radio Planning and Link Design
Path Profile: Fresnel Zone Example
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Slide No 159
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
221
ddd
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Slide No 160
Microwave Radio Planning and Link Design
• First Fresnel zone radius
• 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)
– 2. F1 (radius)
fd
ddF
211 3.17
Fresnel Zone Equation
[m]
m102015
10103.17
m71015
553.17
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Slide No 161
Microwave Radio Planning and Link Design
Fresnel Zone Radii calculations“Table Tool”
4.0 10.0 15.0 20.0 30.0 40.0
7.0 9.2 12.7 13.3 15.0 17.3 18.613.0 10.3 13.6 12.1 13.6 13.8 14.215.0 10.1 14.2 11.3 13.4 12.4 13.118.0 9.2 15.2 10.6 13.8 11.6 13.023.0 7.7 17.1 9.6 14.7 10.9 13.426.0 6.7 19.6 8.6 16.0 10.1 14.138.0 5.1 23.9 7.3 18.1 9.1 15.2
Distance in kmFrequency GHz
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Slide No 162
Microwave Radio Planning and Link Design
Obstacle Loss: Fresnel Zone is not Cleared
Obstacle Loss
Knife Edge obstacle loss Smooth spherical obstacle loss
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Slide No 163
Microwave Radio Planning and Link Design
Knife Edge Losses
0 12 2060 dB
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Slide No 164
Microwave Radio Planning and Link Design
Smooth Spherical Earth Losses
10
20
30
dB
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Slide No 165
Microwave Radio Planning and Link Design
Line-Of-Sight Survey
• LOS Survey– To verify that the proposed network design is feasible considering
LOS constraints
LOS
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Slide No 166
Microwave Radio Planning and Link Design
Line-Of-Sight Survey- Flowchart
LOS Survey
LOS Report
Update the design
Network Design
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Slide No 167
Microwave Radio Planning and Link Design
LOS Survey EquipmentNecessary:
• Compass
• Maps : 50 k or better
• Digital Camera
• GPS Navigator
• Binoculars
• Hand-held communication equipment
• Signaling mirrors
Optional:
• Clinometer
• Altimeter
• Laptop
• Spectrum analyzer
• Antenna horn
• Low noise amplifier
• Theodolite
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Slide No 168
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
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Slide No 169
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
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Slide No 170
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.
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Slide No 171
Microwave Radio Planning and Link Design
LOS Survey Report• Site Data
– Name– Coordinates– Height– Address
• Proposed Tower Height• LOS Confirmation• Azimuth and Elevation• Path short description• Photographs
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Slide No 172
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.
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Slide No 173
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 (fading is ignored)
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Slide No 174
Microwave Radio Planning and Link Design
Link Budget (con’d)
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)
AFSLGLPP outin
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Slide No 175
Microwave Radio Planning and Link Design
Link Budget
Tx
Gt Gr
Rx
Output power
Received power
Antenna gain
Branching loss Feeder
lossAntenna
gain
Feeder loss
Branching loss
Free space loss + atmospheric atten.
Fade Margin
Receiver threshold
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Slide No 176
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(dB) = 92.4 + 20logf(GHz) + 20logD(km)
2244
c
fDDLp
where,
Lp = free space path loss
D = distance
f = frequency
λ = wavelength
c = velocity of light in free space (3*108 m/s)
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Slide No 177
Microwave Radio Planning and Link Design
Free Space Loss
Tx Rx
Lp
Link Budget Parameters
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Slide No 178
Microwave Radio Planning and Link Design
Link Budget Parameters
• Total Antenna Gain:
Ga = 20 log (Da) + 20 log (f) + 17.8
• Atmospheric attenuation occurs at higher frequencies , above 15 GHz due to atmospheric gases, and given by:
Where d is path link in km , a is specific attenuation in dB/km
Daf
dA aa
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Slide No 179
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 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
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Slide No 180
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
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Slide No 181
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, …
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Slide No 182
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– Ep: path inclination in mrad = d
hhEP
21
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Slide No 183
Microwave Radio Planning and Link Design
Flat Fading- cont. ITU-R P.530-7• The geoclimatic (K) depends on type of the path
– Inland linksPlains: 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
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Slide No 184
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
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
r
mB
sel WP
2
20103.4
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Slide No 185
Microwave Radio Planning and Link Design
Frequency Selective Fading ITU-R F.1093
4/30
1002.
1
P
e
5.1
507.0
dm
2/
2/
2010w
w
Bc
W
Where, Po: The fading occurrence factor
Where, d : Path length (km)
Where, Bc: Signature depth
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Slide No 186
Microwave Radio Planning and Link Design
Frequency Selective Fading ITU-R P.530-7
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)
NMr
MB
NMMr
MB
Msel
NMM
WWP,
220
,
220 101015.2
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Slide No 187
Microwave Radio Planning and Link Design
Space Diversity Improvement ITU-R P.453
Where,s : Vertical separation between antennas in m
f : Frequency in GHz
d : Path length
F : Fade Margin
: The difference in antenna gain between the two antenna in dB
Po : from the formula of flat fading
101001034.3
101
04.148.012.087.04 GMP
dfs o
eI
I
PP
I
PP selflatmp
mpdiv
G
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Slide No 188
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:
where
γR : Specific rain attenuation (dB/km)
deff : Effective path length, km
k and a are given in the table
effRR dA .
aR Rk
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Slide No 189
Microwave Radio Planning and Link Design
Usable path lengths with rain intensity example: 15 GHz
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Slide No 190
Microwave Radio Planning and Link Design
Rain zone contours (Americas)Rain zone contours (Far East)
Rain zone contours (Europe and Africa)
ITU-R presents the cumulative distribution of rain intensity for 15 different zone as shown below
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Slide No 191
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
) / 12 . 0 log( 172 . 0 29812 . 0 546 . 0 ( 628 . 1101 . 010
F ARP
%
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Slide No 192
Microwave Radio Planning and Link Design
Frequency Planning
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Slide No 193
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
For adjacent channel interference
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Slide No 194
Microwave Radio Planning and Link Design
Frequency PlanningFrequency 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
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Slide No 195
Microwave Radio Planning and Link Design
Frequency PlanningInterference• 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 discriminationNote: Rain has greater attenuation on horizontal polarization thus use horizontal
polarization for shorter hops
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Slide No 196
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
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Slide No 197
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
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Slide No 198
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
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Slide No 199
Microwave Radio Planning and Link Design
Channel Capacity and Separation
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
Channel separation
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Slide No 200
Microwave Radio Planning and Link Design
Co-channel Interference – Far
Tx/Rx Tx/Rx
Tx/Rx
Tx/Rx
Tx = f1
Rx = f2
Tx = f1
Rx = f2
Tx = f2
Rx = f1
Tx = f2
Rx = f1
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Slide No 201
Microwave Radio Planning and Link Design
Co-channel Interference – Near
Tx/Rx
Tx/Rx Tx = f1
Rx = f2
Tx = f2
Rx = f1
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Slide No 202
Microwave Radio Planning and Link Design
Adjacent Channel Interference
fRx fTx
Interference
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Slide No 203
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:
• A Rule of Thumb
Threshold Degradation < 3 dB
10/101log10 IRTe LCLTeTel LL
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Slide No 204
Microwave Radio Planning and Link Design
Threshold Degradation
Receiver threshold,
dBm -82
-84
-86
-88
-80-78-76
-72
-74
-70
14 191716 1815 2120 22 23
Signal to Interference ratio, dB
3dB
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Slide No 205
Microwave Radio Planning and Link Design
Channel plan
Tx=4ARx=4B
Tx=4BRx=4A
1A 7A6A5A4A2A 3A 7B6B5B4B3B2B1B
Low sub-band High sub-band
Duplex distance
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Slide No 206
Microwave Radio Planning and Link Design
High / Low Tx Channel Allocation
H
LH
H
L
H
LH
H/L
L
Near interference
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Slide No 207
Microwave Radio Planning and Link Design
High / Low Tx Channel Allocation
H
H/L
L
L
L
H
H H
H
L
Interference
New frequency
band
Rings with odd number of sites should be avoided
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Slide No 208
Microwave Radio Planning and Link Design
Channel Plan
7 Channels
28 MHz(17x2 Mbps)
f
1A 7A6A5A4A3A2A
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Slide No 209
Microwave Radio Planning and Link Design
Channel Plan
28 MHz(17x2 Mbps)
f14 MHz(8x2 Mbps)
11 Channels
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Slide No 210
Microwave Radio Planning and Link Design
Channel Plan
28 MHz(17x2 Mbps)
f14 MHz(8x2 Mbps)
15 Channels
7 MHz(4x2 Mbps)
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Slide No 211
Microwave Radio Planning and Link Design
Output Power
High output power
High output power
High output power
Interference
Only High output power
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Slide No 212
Microwave Radio Planning and Link Design
Output Power
Low output power
High output power
Low output power
No Interference
High and low output power
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Slide No 213
Microwave Radio Planning and Link Design
Interference
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Slide No 214
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
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Slide No 215
Microwave Radio Planning and Link Design
Noise in Digital SystemsNoise 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
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Slide No 216
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
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Slide No 217
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
• Noise Figure NF = 10 log(F) (dB)
outputat ratiopower S/N available
inputat ratiopower S/N availableF (unitless)
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Slide No 218
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 15-25 dB
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Slide No 219
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
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Slide No 220
Microwave Radio Planning and Link Design
Threshold Degradation
Receiver threshold,
dBm -82-84-86-88
-80-78-76
-72-74
-70
14 1917
16 1815 2120 22 23Signal to Interference ratio, dB
3dB
• A Rule of Thumb
Threshold Degradation < 3 dB given that the required signal to interferer is not violated
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Slide No 221
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 cross-
Polar interference XPI
dBE
ELogXPI
21
11.20
dBE
ELogXPD
12
11.20Where E11and E12 are
given in the next figure
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Slide No 222
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
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Slide No 223
Microwave Radio Planning and Link Design
Cross Polar Interference
E1
E2
E11
E22
E21
E12
Dual polarized system suffering from XPI
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Slide No 224
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
10/1101log10 LCLTeTel
RTeLL
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Slide No 225
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
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Slide No 226
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
Co-ordination area for off-key hole region
Key hole region
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Slide No 227
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
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Slide No 228
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.
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Slide No 229
Microwave Radio Planning and Link Design
Examples of Interference RF coupling• Examples
V
H
Cross Polarization Adjacent channel
f2
f1
f1
Front-to-Back
f1f1’
Over Shoot
f1 f1’ f1
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Slide No 230
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
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Slide No 231
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
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Slide No 232
Microwave Radio Planning and Link Design
Digital Map and Tools Overview
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Slide No 233
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
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Slide No 234
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)
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Slide No 235
Microwave Radio Planning and Link Design
Digital Maps - Vector Data (Linear)
• Succession of points describing:– Highway– Roads– Railways– Rivers– Borders– coastlines
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Slide No 236
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)