1. Fundamentals of Microwave & Satellite Technologies
Telekomunikasi Dasar

2. Historical Perspective
Founded during WWII
Used for long-haul telecommunications
Displaced by fiber optic networks
Still viable for right-of-way bypass and geographic obstruction avoidance

3. Microwave Spectrum Range is approximately 1 GHz to 40 GHz
Total of all usable frequencies under 1 GHz gives a reference on the capacity of in the microwave range

4. Microwave Impairments
Equipment, antenna, and waveguide failures
Fading and distortion from multipath reflections
Absorption from rain, fog, and other atmospheric conditions
Interference from other frequencies

5. Microwave Engineering Considerations
Free space & atmospheric attenuation
Reflections
Diffractions
Rain attenuation
Skin affect
Line of Sight (LOS)
Fading
Range
Interference

6. Free Space & Atmospheric Attenuation
Free space & atmospheric attenuation is defined by the loss the signal undergoes traveling through the atmosphere.
Changes in air density and absorption by atmospheric particles.

7. Reflections
Reflections can occur as the microwave signal traverses a body of water or fog bank; cause multipath conditions

8. Diffraction
Diffraction is the result of variations in the terrain the signal crosses

9. Rain Attenuation
Raindrop absorption or scattering of the microwave signal can cause signal loss in transmissions.

10. Skin Affect
Skin Affect is the concept that high frequency energy travels only on the outside skin of a conductor and does not penetrate into it any great distance. Skin Affect determines the properties of microwave signals.

11. Line of Sight Fresnel Zone Clearance
Fresnel Zone Clearance is the minimum clearance over obstacles that the signal needs to be sent over. Reflection or path bending will occur if the clearance is not sufficient.

12. LOS & FZC-cont’d
Fresnel Zone D2 D1
D1 X D2
F x D
72.2
secret formula

13. Caused by multi-path reflections and heavy rains
Microwave Fading
Normal Signal
Reflective Path
Caused by multi-path reflections and heavy rains

14. Range
The distance a signal travels and its increase in frequency are inversely proportional
Repeaters extend range
Back-to-back antennas
Reflectors

15. Range-cont’d
High frequencies are repeated/received at or below one mile
Lower frequencies can travel up to 100 miles but miles is the typical placement for repeaters

16. Interference Adjacent Channel Interference Overreach
digital not greatly affected
Overreach
caused by signal feeding past a repeater to the receiving antenna at the next station in the route. Eliminated by zigzag path alignment or alternate frequency use between adjacent stations

17. Components of a Microwave System
Digital Modem
Radio Frequency (RF) Unit
Antenna

18. Digital Modem
The digital modem modulates the information signal (intermediate frequency or IF).

19. RF Unit
IF is fed to the RF unit which is mounted as close physically to the antenna as possible (direct connect is optimal).

20. Antenna
The antenna is a passive device that radiates the modulated signal. It is fed by direct connect of the RF unit, coaxial cable, or waveguides at higher frequencies.

21. Waveguides
Waveguides are hollow channels of low-loss material used to direct the signal from the RF unit to the antenna.

22. Modulation Methods
Primarily modulated today with digital FM or AM signals
Digital signal remains quiet until failure threshold bit error rate renders it unusable

23. Bit Error Rate (BER)
The BER is a performance measure of microwave signaling throughput
10 or one error per million transmitted bits of information
Data fail over is at 10; voice traffic can withstand this error rate -6 -3

24. Diversity
Space Diversity
Frequency Diversity
Hot Standby
PRI

25. Space Diversity
Normal Signal
Faded Signal
Transmitter
Receiver

26. Space Diversity-cont’d
Space Diversity protects against multi-path fading by automatic switch over to another antenna place below the primary antenna. This is done at the BER failure point or signal strength attenuation point to the secondary antenna that is receiving the transmitted signal at a stronger power rating.

27. Frequency Diversity Transmitter Receiver Rx Frequency #1 Active Tx
Protect Tx
Frequency #2
Transmitter
Receiver

28. Frequency Diversity-cont’d
Frequency Diversity uses separate frequencies (dual transmit and receive systems); it monitors primary for fail over and switches to standby. Interference usually affects only one range of frequencies. Not allowed in non-carrier applications because of spectrum scarcity.

29. Hot Standby* failure switch Transmitter Receiver
Active Rx #1
System Tx
Primary #1
Standby Rx #2
System Tx
Standby #2
failure switch
Transmitter
Receiver
*Hot standby is designed for equipment failure only

30. PRI (Primary Rate Interface)
PRI is an ISDN service providing user with 23,64 kbps for channel message and 1,64 kbps data channel for control & signalling. PRI is ISDN E1 interface.
System Transmission Facilities
System Receiver Facilities
Connect to PRI interface & PSTN
Connect to PRI interface & PSTN
Transmitter
Receiver
To PSTN
To PSTN

31. Percent Availability equals:
Availability Formula
Percent Availability equals:
1 – (outage hours/8760 hours per year)
Private microwaves have 99.99% availability

32. Microwave Path Analysis
Transmitter output power
Antenna gain
proportional to the physical characteristics of the antenna (diameter)
Free space gain
Antenna alignment factor
Unfaded received signal level

33. Microwave Radio Applications

38. Satellite Communications

39. Satellite-Related Terms
Earth Stations – antenna systems on or near earth
Uplink – transmission from an earth station to a satellite
Downlink – transmission from a satellite to an earth station
Transponder – electronics in the satellite that convert uplink signals to downlink signals

40. Ways to Categorize Communications Satellites
Coverage area
Global, regional, national
Service type
Fixed service satellite (FSS)
Broadcast service satellite (BSS)
Mobile service satellite (MSS)
General usage
Commercial, military, amateur, experimental

41. Classification of Satellite Orbits
Circular or elliptical orbit
Circular with center at earth’s center
Elliptical with one foci at earth’s center
Orbit around earth in different planes
Equatorial orbit above earth’s equator
Polar orbit passes over both poles
Other orbits referred to as inclined orbits
Altitude of satellites
Geostationary orbit (GEO)
Medium earth orbit (MEO)
Low earth orbit (LEO)

42. Geometry Terms
Elevation angle - the angle from the horizontal to the point on the center of the main beam of the antenna when the antenna is pointed directly at the satellite
Minimum elevation angle
Coverage angle - the measure of the portion of the earth's surface visible to the satellite

43. Minimum Elevation Angle
Reasons affecting minimum elevation angle of earth station’s antenna (>0o)
Buildings, trees, and other terrestrial objects block the line of sight
Atmospheric attenuation is greater at low elevation angles
Electrical noise generated by the earth's heat near its surface adversely affects reception

44. GEO Orbit Advantages of the the GEO orbit
No problem with frequency changes
Tracking of the satellite is simplified
High coverage area
Disadvantages of the GEO orbit
Weak signal after traveling over 35,000 km
Polar regions are poorly served
Signal sending delay is substantial
GEO : Geosynchronous equatorial orbit

45. LEO Satellite Characteristics
Circular/slightly elliptical orbit under 2000 km
Orbit period ranges from 1.5 to 2 hours
Diameter of coverage is about 8000 km
Round-trip signal propagation delay less than 20 ms
Maximum satellite visible time up to 20 min
System must cope with large Doppler shifts
Atmospheric drag results in orbital deterioration
LEO : Low earth orbit

46. LEO Categories Little LEOs Big LEOs Frequencies below 1 GHz
5MHz of bandwidth
Data rates up to 10 kbps
Aimed at paging, tracking, and low-rate messaging
Big LEOs
Frequencies above 1 GHz
Support data rates up to a few megabits per sec
Offer same services as little LEOs in addition to voice and positioning services

47. MEO Satellite Characteristics
Circular orbit at an altitude in the range of 5000 to 12,000 km
Orbit period of 6 hours
Diameter of coverage is 10,000 to 15,000 km
Round trip signal propagation delay less than 50 ms
Maximum satellite visible time is a few hours
MEO : Medium Earth Orbit

48. SOURCE: WASHINGTON UNIV.
Satellite Systems
GEO (22,300 mi., equatorial)
high bandwidth, power, latency
MEO
LEO (400 mi.)
low power, latency
more satellites
small footprint
V-SAT (Very Small Aperture
Terminal)
private WAN
SATELLITE MAP
GEO
M EO
LEO
SOURCE: WASHINGTON UNIV.

49. Geostationary Orbit
SOURCE: BILL LUTHER, FCC

50. GPS Satellite Constellation
Global Positioning System
Operated by USAF
28 satellites
6 orbital planes at a height of 20,200 km
Positioned so a minimum of 5 satellites are visible at all times
Receiver measures distance to satellite
SOURCE: NAVSTAR

51. Frequency Bands Available for Satellite Communications

52. Satellite Link Performance Factors
Distance between earth station antenna and satellite antenna
For downlink, terrestrial distance between earth station antenna and “aim point” of satellite
Displayed as a satellite footprint (Figure 9.6)
Atmospheric attenuation
Affected by oxygen, water, angle of elevation, and higher frequencies

53. Satellite Footprint

54. Satellite Network Configurations

55. Capacity Allocation Strategies
Frequency division multiple access (FDMA)
Time division multiple access (TDMA)
Code division multiple access (CDMA)

56. Frequency-Division Multiplexing
Alternative uses of channels in point-to-point configuration
1200 voice-frequency (VF) voice channels
One 50-Mbps data stream
16 channels of Mbps each
400 channels of 64 kbps each
600 channels of 40 kbps each
One analog video signal
Six to nine digital video signals

57. Frequency-Division Multiple Access
Factors which limit the number of subchannels provided within a satellite channel via FDMA
Thermal noise
Intermodulation noise
Crosstalk

58. Forms of FDMA Fixed-assignment multiple access (FAMA)
The assignment of capacity is distributed in a fixed manner among multiple stations
Demand may fluctuate
Results in the significant underuse of capacity
Demand-assignment multiple access (DAMA)
Capacity assignment is changed as needed to respond optimally to demand changes among the multiple stations

59. FAMA-FDMA FAMA – logical links between stations are preassigned
FAMA – multiple stations access the satellite by using different frequency bands
Uses considerable bandwidth

60. DAMA-FDMA
Single channel per carrier (SCPC) – bandwidth divided into individual VF channels
Attractive for remote areas with few user stations near each site
Suffers from inefficiency of fixed assignment
DAMA – set of subchannels in a channel is treated as a pool of available links
For full-duplex between two earth stations, a pair of subchannels is dynamically assigned on demand
Demand assignment performed in a distributed fashion by earth station using CSC

61. Reasons for Increasing Use of TDM Techniques
Cost of digital components continues to drop
Advantages of digital components
Use of error correction
Increased efficiency of TDM
Lack of intermodulation noise

62. FAMA-TDMA Operation
Transmission in the form of repetitive sequence of frames
Each frame is divided into a number of time slots
Each slot is dedicated to a particular transmitter
Earth stations take turns using uplink channel
Sends data in assigned time slot
Satellite repeats incoming transmissions
Broadcast to all stations
Stations must know which slot to use for transmission and which to use for reception

63. FAMA-TDMA Uplink

64. FAMA-TDMA Downlink