21-05-2012, 03:10 PM
Laser Satellite Communication Network
Vibration Effect and Possible Solutions
[attachment=22585]
INTRODUCTION
Communication from any place to another on earth is
an attractive goal. One method to achieve this aim is by
networking satellites together to cover the globe (Fig. 1).
In this method, the information is transferred from the
ground to the nearest satellite above and then propagates
between the satellites to the satellite above the destination.
This last satellite then transmits the information down
to the destination. The idea of a satellite communication
network is no longer science fiction. Today, a number
of serious consortiums develop satellite communication
networks. The objective of these communication projects is
to service personal communication users almost everywhere
on earth. The intersatellite links (ISL’s) in those projects use
microwave radiation as the carrier. The use of optical ISL’s
has some advantages over the use of microwave ISL’s: 1)
smaller size and weight of the terminal, 2) less transmitter
power, 3) higher immunity to interference, 4) larger data.
SATELLITE COMMUNICATION
NETWORKS—PRESENT STATUS
Today, there are a number of serious consortiums developing
satellite communication networks [1]–[5], [26].
The objective of these communication projects is to service
personal communication users almost everywhere on earth.
The amount of money invested worldwide in those projects
is assumed to be tens of billions of U.S. dollars. The
incentive for this huge investment is the expectation of a
growing need for personal communication services (PCS’s)
unlimited by the coverage of cellular systems. There are
two trends for network development: a) using ISL’s (space
switch) and b) using a ground station for each hop (ground
switch). Using ISL’s almost eliminates the dependence on
ground stations. This has some advantages:
COMPARISON BETWEEN MICROWAVE
AND OPTICAL ISL’S
Comparisons between the microwave and laser technologies
involve many considerations [5]–[7], [25]. In Table
2, we present some of the possible criteria for satellite
communication segments. The important factors for satellite
communication are mass, size, data rate, and power consumption.
The optical link is better than the microwave link
according to such factors. The main disadvantage of optical
links is the lack of knowledge, subsystems, and experience
from previous projects (technologies without history). Some
researchers made quantitative comparisons between RF
(23 and 60 GHz) and optical links for various satellite
communication scenarios at data rates of 25 and 360 Mb/s.
The results of the comparison for present technology.
THE VIBRATION STATISTICS MODEL
Due to noise in the tracking system and mechanical
vibrations, described in the previous two sections, the
satellite transmitter beam to the receiver satellite vibrates.
This degrades the communication system performance. The
statistical model of the transmitter vibrations derives from
the sources of the vibrations. The two simple models
popularly used as statistical models are Rayleigh and normal
probability density distribution functions (pdf’s). The
Rayleigh model is used mostly when the tracking noise is
the dominant noise. To use this model, we assume that the
SNR of the tracking system is large and that the azimuth and
elevation tracking processes are independent and identically
distributed so that the radial pointing error angle model is
Rayleigh distributed with pdf [15]
DISCUSSION AND SUMMARY
This paper deals with the effects of transmitter pointing
direction vibration and possible solutions to those effects
for satellite optical communication networks. Real-time
applications such as video conferencing, medical imaging,
and multimedia from any point on earth to any other point
can become a reality if optical communication networks are
implemented. This review points out that even low values
of vibration amplitudes in each satellite can dramatically
decrease the performance of the network.
Vibration Effect and Possible Solutions
[attachment=22585]
INTRODUCTION
Communication from any place to another on earth is
an attractive goal. One method to achieve this aim is by
networking satellites together to cover the globe (Fig. 1).
In this method, the information is transferred from the
ground to the nearest satellite above and then propagates
between the satellites to the satellite above the destination.
This last satellite then transmits the information down
to the destination. The idea of a satellite communication
network is no longer science fiction. Today, a number
of serious consortiums develop satellite communication
networks. The objective of these communication projects is
to service personal communication users almost everywhere
on earth. The intersatellite links (ISL’s) in those projects use
microwave radiation as the carrier. The use of optical ISL’s
has some advantages over the use of microwave ISL’s: 1)
smaller size and weight of the terminal, 2) less transmitter
power, 3) higher immunity to interference, 4) larger data.
SATELLITE COMMUNICATION
NETWORKS—PRESENT STATUS
Today, there are a number of serious consortiums developing
satellite communication networks [1]–[5], [26].
The objective of these communication projects is to service
personal communication users almost everywhere on earth.
The amount of money invested worldwide in those projects
is assumed to be tens of billions of U.S. dollars. The
incentive for this huge investment is the expectation of a
growing need for personal communication services (PCS’s)
unlimited by the coverage of cellular systems. There are
two trends for network development: a) using ISL’s (space
switch) and b) using a ground station for each hop (ground
switch). Using ISL’s almost eliminates the dependence on
ground stations. This has some advantages:
COMPARISON BETWEEN MICROWAVE
AND OPTICAL ISL’S
Comparisons between the microwave and laser technologies
involve many considerations [5]–[7], [25]. In Table
2, we present some of the possible criteria for satellite
communication segments. The important factors for satellite
communication are mass, size, data rate, and power consumption.
The optical link is better than the microwave link
according to such factors. The main disadvantage of optical
links is the lack of knowledge, subsystems, and experience
from previous projects (technologies without history). Some
researchers made quantitative comparisons between RF
(23 and 60 GHz) and optical links for various satellite
communication scenarios at data rates of 25 and 360 Mb/s.
The results of the comparison for present technology.
THE VIBRATION STATISTICS MODEL
Due to noise in the tracking system and mechanical
vibrations, described in the previous two sections, the
satellite transmitter beam to the receiver satellite vibrates.
This degrades the communication system performance. The
statistical model of the transmitter vibrations derives from
the sources of the vibrations. The two simple models
popularly used as statistical models are Rayleigh and normal
probability density distribution functions (pdf’s). The
Rayleigh model is used mostly when the tracking noise is
the dominant noise. To use this model, we assume that the
SNR of the tracking system is large and that the azimuth and
elevation tracking processes are independent and identically
distributed so that the radial pointing error angle model is
Rayleigh distributed with pdf [15]
DISCUSSION AND SUMMARY
This paper deals with the effects of transmitter pointing
direction vibration and possible solutions to those effects
for satellite optical communication networks. Real-time
applications such as video conferencing, medical imaging,
and multimedia from any point on earth to any other point
can become a reality if optical communication networks are
implemented. This review points out that even low values
of vibration amplitudes in each satellite can dramatically
decrease the performance of the network.