Advanced Mobile Satellite Services

Advanced Mobile Satellite Services

Advanced Mobile Satellite Services

P. Martinraj

UG scholar, Department of Aeronautical,

Parisutham Institute of Technology &science, Thanjavur-Tamil Nadu-India,

N. Praveen

UG scholar, Department of Aeronautical,

Parisutham Institute of Technology &science, Thanjavur-Tamil Nadu-India,

Abstract:-Mobile satellite services provide two-way voice and data communication to global users who are on the go or in remote locations; terminals range in size from handheld to laptop- size units. Terminals can also be mounted in a vehicle, with communications maintained while the vehicle is moving. MSS operates at L-band- low enough frequency spectrum to avoid the rain fade associated with higherbandwidth Ku-band and Ka band fixed satellite systems.Mobile satellite system fulfill the dream of communication anywhere. Satellite communication has now a days become very import due to its applications.This research paper includes explanation about various types of satellites and their orbits how the satellite phones can be used to communicate.

Keywords:- Mobile satellite system, GPS, satellite phones, frequency bands.

are transmitted to the satellite, their storing can also be done in the satellite until the satellite comes into range of a receiving earth station. Not like a geostationary system, the whole of the Earths surface can be covered by a single satellite. However, when the satellite is not in view there can be time gaps in coverage of given geographical locations. Thus by increasing the number of satellites there will be increase inthe coverage of the system by decreasing the time gaps when a satellite is not in view of a given location. Some of the applications are:

1. In military sector, providing robust and secure communications network

2. To provide communication when the terrestrial systems fail due to disaster and also to communicate

   A.History

   1. INTRODUCTION

      family and friends during disaster.

3. World travellers can use a satellite phone to keep in

In a 1945 Wireless World article the English science fiction writer Arthur C. Clarke (19172008) described in detail the possible use of communications satellites for mass communications. Satellite launching logistics, possible orbits and ways of the creation of a network of world-revolving satellites was examined by Clarke while pointing to the advantages of high-speed global communications. Three geostationary satellites would provide coverage over the whole earths surface was proposed by C. Clarke. The idea of the earth satellite vehicle was given by US military when Secretary of Defence, James Forrestal, made a public announcement on December 29, 1948 that his office was coordinating that project between the various services.

B. Mobile Satellite System

Mobile Satellite communications systems use satellites that are either static or revolving. The satellite remains in a fixed position with a geostationary system with respect to a given geographical location (the satellite is actually in a fixed orbit and moves in a consistent relationship to the Earth). The satellite can receive and transmit messages to any transmitter or transceiver with this type of system that is within the fixed geographical area visible to the satellite at all times. Based on geostationary satellites a communication system may have more than one satellite to cover a greater part of the Earths surface. An orbiting communications satellite moves in an orbit so that it passes above a given geographical location at periodic time intervals. It means that earth bound transmitters come into the satellites range at these periodic time intervals and transmit or receive only while the satellite is in range or visible.Until the satellite is in range the transmitter can store messages. When messages

touch with family without having to send lovedones a

new telephone number for each destination. 4) Used by govt. and govt. agencies to transfer information before any disaster

1. TECHNICAL DETAILS

   1. Types of Communication Satellites (a)Geostationary Satellite:

      They are launched 36000 km above earth. This type of satellites seems to be stationary with respect to earth. With this type of system the satellite can, at all times, receive and transmit messages to any transmitter or transceiver that is within the fixed geographical area visible to the satellite. A communication system based on geostationary satellites may have more than one satellite to cover a greater percentage of the Earths surface (2-3 satellites) 2.1.2 Non Geostationary Satellites: They are not stationary they revolve in a circular orbit around the earth with a constant velocity. It means that it is such a system where earth bound transmitters or transceivers come into the satellites range at some periodic time intervals and transmit or receive only while the satellite is in range or visible. Unlike a geostationary system, a single satellite can feasibly cover the whole of the Earths surface. However, there may be evolution of time gaps while covering when the satellite is not in view of given geographical locations. They are of 3 types

      1. High Earth Orbit (HEO)

      2. Medium Earth Orbit (MEO)

      3. Low Earth Orbit (LEO)

         Out of these LEO is used the most in mobile satellite communication .It is launched 500-200kmabove earth.

   2. Satellite Phones

      A satellite telephone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. Functionality like voice, short messaging service and low- bandwidth internet access are supported through most systems. It depends on the architecture of a particular system, that what will be the coverage. It may be entire Earth, or only specific regions. The size and weight of the early satellite phone handsets is comparable to that of a late1980s or early-1990s cell phone, but usually with a large retractable antenna. Now a days the satellite phonesare same in size to a regular mobile phone while some prototype satellite phones have no distinguishable difference from an ordinary Smartphone. These satellite phones are mainly used by those living in poor

   3. How Does the Communication Takes Place

   There can be many types of mobile satellite communication .That can be satellite phone to cellular phone or there can be satellite phone to satellite phone communication. They can be described in brief as follows: (a)From Satellite Phone To Cellular Phone

   • The caller enters the number she wishes to dial and presses the send key. The phone than do some processing and eventually find the nearest orbiting satellite and sends the call information to it.

   • Gateway: The point to which the satellite relays the call to the nearest ground receiver. The gateway do the work to patch the calls through. If a call to India originates in America, the gateway wont be able to patch the call through the existing phone network. Than the gateway will transmit the call to the near most satellite, which will help to pass the call along till it reaches one that can help linking to the receiver. It depends on the location of the caller (transmitter) and receiver that how many times it may happen.

   • The call comes from the satellite and is received by receiver's network. The format of the call has to be manipulated so that it may be received on a standard phone or cell phone. Once the received call is converted and the connection established the call is said to be connected.

   • The same goes in reverse when someone is calling a satellite phone (say Globalstar phone) from a cellular phone or landline .Calls are transferred to one of the Globalstar gateways then that gateway sends the call up to a relay satellite then back down to the Globalstar satellite phone user. Globalstar calls this their bent pipe technology.

2. FREQUENCY BANDS

   Table 1.1 below presents the frequency bands available for satellite communications. It is observed that increasing bandwidth is available in the higher-frequency bands. Generally, the higher the frequency, the greater the effect of transmission impairments.

   Table 1.1 Frequency Bands for Satellite Communications

   Band	Frequency Range	Total bandwidth	General Applications
   L*	1 to 2 GHZ	1 GHZ	Mobile satellite services
   S*	2 to 4 GHZ	2 GHZ	MSS, NASA, deep space research
   C	4 to 8 GHZ	4 GHZ	Fixed satellite services
   X	8 to 12.5 GHZ	4.5 GHZ	FSS, Military, terrestrial earth exploration and meteorological satellites
   Ku	12.5 to 18 GHZ	5.5 GHZ	FSS, broadcast satellite service (BSS)
   K	18 to 26.5 GHZ	8.5 GHZ	BSS, FSS
   Ka	26.5 to 40 GHZ	13.5 GHZ	FSS

   The mobile satellite service (MSS) is allocated frequencies in the L and S-bands. In these bands, compared to higher frequencies, there is a greater degree of refraction and greater penetration of physical obstacles, such as foliage and non-metallic structures. These are desirable characteristics for mobile satellite service. Also the same bands are heavily being used for terrestrial applications. Therefore, there is intense competition among the various microwave services for L and S-band capacity.

   Benefits of mobile satellite system over terrestrial system.

   There are many advantages that mobile satellite communication has over terrestrial wireless communication systems, such merits are enumerated below.

   • The area of coverage is a good advantage in satellite base communication which far exceeds that of terrestrial system.

   • The speed to deliver new services to the market is a merit of satellite communication over that of terrestrial systems.

   • Satellite – to – satellite communication links can be designed with great precision because the conditions between communicating satellites are more time invariant than those between two terrestrial wireless antennas.

   • Transmission cost is independent of distance, within the satellites area of coverage. In terrestrial wireless system more cost will be incurred to cover as much area as satellite does.

   • Broadcast, multicast and point to point applications are already accommodated in satellite communication systems.

   • Very high bandwidths or data rates are available to satellite communication users.

   • The quality of transmission is normally high in satellite communication than terrestrial although satellite links are subject to short-term outages or degradation.

3. Advantages of Mobile Satellite Communication

   • The designing of satellite-to-satellite communication links with great precision can be done because the conditions between communicating satellites are more time invariant than those between two terrestrial wireless antennas.

   • Within the satellites area of coverage transmission cost is not dependent on distance. In terrestrial wireless system more cost will be incurred to cover as much area as satellite does.

   • The transmission quality is generally high in satellite communication than terrestrial although satellite links are subject to short-term outages or degradation.

   • Without using relay with high capacity is capable of transmitting signal long distances

   • Point to multipoint Installation of satellite circuit is rapid.

4. FUTURE SCOPE

   • It has great scope in future.

   • Light weight and cheaper satellites are being made.

   • Smaller and cheaper mobile terminals are being made.

   • New techniques to reduce propagation delays are being found.

   • Inventions are leading to an era of publically using it.

5. CONCLUSION

Observation This type of communication is very useful in military communication .It has a very incredible role before and after any disasters .It is also very helpful for the travellers. Although it is very important and helpful, it suffers from some disadvantages. There are large propagation delays, Repairing and maintenance after launching is difficult, high cost and high risks on launching

.Moreover the terminals are very costly, so that everybody cannot afford it. It promises a new era of GLOBAL CONNECTIVITY.

REFERENCES

[1] Michael J. Miller, satellite communications, vol-3,1997 [2] "Is US Building A New Moon" , May 1949, Popular Science

[3] Stojce Demov Llcev, Global Mobile Satellite Communications, 3rd edition ,p1-5

[4] Ramjee Prasad, Advanced Mobile Communication Systems, vol1, 1991 http://www.globalcomsatphone.com

[5] http://www.superco.gov

[6] http://www.globalsatellitecommunications.com