Que.21 What is VSAT technology?
Answer:
- VSAT is a technology, used to define two-way satellite communications. Besides system use small dish antennas that vary from 75 centimeters to 1.5 meters in diameter. VSAT terminal access satellites in orbit to transfer data from one earth station to other or to access the Internet. The VSAT network is managed by the hub.
- Typical data rates of VSAT are 56 kbps to 4 Mbps. VSAT access satellites in geosynchronous orbit to relay data from remote earth stations to other terminals or master earth stations also called hubs.
- VSAT is most commonly used to transmit narrowband data such as RFID data, and point of-sale transactions such as credit card or broadband data for communication to remote locations.
- The first commercial VSAT was a C band of 6 GHz using the spread spectrum technology. nowadays VSAT has mostly been used in Ku band 12 to 14 gigahertz for providing portable network connectivity data or telephony applications.
Que.22 what are the advantages of the VSAT network?
Answer:
- Advantages of VSAT network:
- VSAT network provides fast data transmission.
- The user retains complete control of communication within the network.
- High availability and excellent data transmission quality were provided by the VSAT network.
- VSAT networks also give the highest performance among all communication.
- VSAT can be installed anywhere irrespective of terrestrial communication infrastructure.
- VSAT networks are easily installed and maintenance is easy.
- VSAT is used in wide applications such as telephony fax television high-speed data communication services Internet access satellite news gathering and digital audio broadcasting.
Que.23 What is GPS technology?
Answer:
- Global Positioning System GPS is used in navigation for ships and aircraft and in surveying.
- GPS segment consists of 24 orbiting satellites in medium earth orbit (MEO) at a nominal altitude of 22,200 kilometers with an orbital inclination of 55 degrees that provides navigation and timing information to military and civil users worldwide. The system also consists of a worldwide satellite control network and GPS receivers unit that acquires the satellite’s signal and translates them into the position information.
- Clusters of 4 groups of satellites are called constellations, with each constellation separated by 60 degrees in longitude.
- The satellite carries station-keeping fuel and is maintained in the required orbits by occasional station-keeping maneuvers just like GEO satellites.
- The orbits of 24 GPS satellites ensure that at anytime anywhere in the world a GPS receiver can pick up signals from at least 4 satellites up to 10 satellites may be visible sometimes and more than 4 satellites are visible nearly all the time first they provide a direct read out to the present positioning of GPS receiver with a typical accuracy of 30 meters.
- A large number of GPS receivers can operate simultaneously because all that a GPS receiver has to do is to locate itself to receive signals from 4 GPS satellites.
Que.24 What are the Applications of GPS technology?
Answer:
GPS provides:
- 24 hours, worldwide services.
- Extremely accurate 3-dimensional location information that is providing latitude longitude and altitude readings.
- Extremely accurate velocity information.
- Precise timing services.
- A worldwide common grid that is easily converted to any local grid.
- Continuous real-time information.
- Accessibility to an unlimited number of worldwide users.
- Civilian users support at a slightly less accurate level.
Que.25 Why the medium earth orbit of high 2000 kilometers to 8000 kilometers are not suggestible for satellite communication?
Answer: Satellites are not placed between the height of 2000 kilometers to 8000 kilometers because the VAN Allen radiation belt lies between these levels. This belt generates radiation continuously which can harm the electronic components which are used in satellites for satellite communication.
Que.26 What kind of satellites are placed in (LEO) low earth orbit?
Answer: Satellites in lower earth orbit are placed at heights of 2000 to 8000 kilometers above the earth’s surface. The time period is of 95 to 120 minutes. And these require a large number of satellites to cover the entire earth approximately 66 satellites are required to cover the entire earth. These satellites are mainly used in remote sensing and providing mobile communication.
Que.27 Why frequencies of 6/4 GHz are most widely used for satellite communication?
Answer:
- 6/4 GHz frequency of the microwave is mostly used for satellite communication because of the following reasons:
- Absorption by rain attenuation is very low below 11 GHz.
- There is no change of polarisation when the wave passes through the ionosphere at this frequency.
- RF components are readily available at this frequency band.
- Sky noise is also low at 4 gigahertz and therefore signals to noise ratio at the receiving antenna is not much deteriorated.
Que.28 What is the Link budget? How the link budget of satellite communication is calculated?
Answer:
- The analysis of losses and gains of a connecting link between transmitter and receiver is known as the Link budget.
- The link budget calculation accounts for several factors in satellite communication such as absorption by the medium through which satellite signal propagates, various kind of noise sources, and various design considerations of the earth station. The main factor to control the design of the link is the frequency of uplink and the frequency of downlink.
Que.29 What are the Disadvantages associated with a satellite placed in Geostationary orbit?
Answer:
- The main disadvantage of Geostationary orbit is, that we have a round trip delay of 0.5 seconds.
- Another disadvantage is that it has poor coverage beyond 75 degrees to 80 degrees North and South of the equator.
- The losses suffered by signal to go to a geostationary satellite and for a signal to come back is high, so high-power transmitters are required for geostationary satellites.
Que.30 What are the different kinds of sensors used for satellite communication?
Answer:
- The different kinds of sensors used for satellite communications are :
- Sun sensor: sun sensors are used to keep the satellite aligned towards the sun to receive the maximum energy from the sun. Solar panels are used to capture the radiations from the sun and then convert them into electrical energy that acts as a power backup for the various electronic components used in satellite communication.
Gyroscope: It is used to keep the satellite aligned in its own orbit, as the orientation of the satellite changes with time due to the effect of the gravitational force of the Sun, Moon, and Earth. This sensor determines the orientation of satellites in their orbit.
- Various other sensors are current sensors voltage sensors And temperature sensors to keep the current-voltage and temperature to a set value.
- GPS sensors are used for tracking the satellite’s position before a satellite is placed in its orbit.
Que.31 What are the different types of losses that occur in satellite communication?
Answer: The different types of losses that occurred in satellite communication are:
- Attenuation in the atmosphere and I know sphere.
- Losses associated with transmitting antenna
- Losses associated with receiving antenna
- Other losses include attenuation due to rain, earth station back of losses, feeder losses and polarisation mismatch losses etc.
Que.32 What is G/T ratio in satellite communication? How this ratio can be improved?
Answer:
- G/T ratio is the ratio of antenna gain (G) of the ground station to the input noise temperature (T). It is also known as a figure of merit and it is denoted by M. where M= Antenna gain of earth station/ total input noise temperature.
- For a given satellite and signal transmission the only parameter of the earth station that affects the channel-to-noise ratio is G&T.
Methods of improvement of G/T ratio:
- To improve the figure of merit G is increased and T is decreased.
- The gain of the antenna (G) can be increased by using a large aperture antenna.
- Total input noise temperature T is decreased by keeping the noise figure to a minimum value by proper design of the component.
Que.33 What is satellite communication?
Answer: Satellite communication is a method of transmitting and receiving data using artificial satellites orbiting the earth. Satellite communication systems use a network of satellites to transmit data between two or more locations on the earth’s surface, allowing for communication over long distances without the need for terrestrial infrastructure.
Que.34 How does satellite communication work?
Answer: Satellite communication systems typically consist of a network of artificial satellites orbiting the earth, ground-based transmitter and receiver stations, and terminal equipment for transmitting and receiving data. The satellites in the network are positioned at a specific altitude above the earth’s surface and are equipped with antennas for transmitting and receiving data. The ground-based transmitter and receiver stations, also known as earth stations, are used to send and receive data to and from the satellites. The terminal equipment, such as satellite phones or satellite modems, is used by end users to transmit and receive data to and from the satellite network.
Que.35 What are the advantages of satellite communication?
Answer:
- There are several advantages to using satellite communication, including:
- Wide coverage area: Satellite communication systems can cover a wide area, including remote or underserved regions that may not have access to terrestrial communication infrastructure.
- Reliability: Satellite communication systems are generally reliable, as they are not affected by terrestrial infrastructure failures or natural disasters such as earthquakes or hurricanes.
- High bandwidth: Satellite communication systems can provide high bandwidth and data rates, allowing for the transmission of large amounts of data in real-time.
- Flexibility: Satellite communication systems can be easily deployed and are flexible, allowing for the rapid deployment of communication capabilities in emergency situations or in areas where terrestrial infrastructure is not available.
Que.36 What are the limitations of satellite communication?
Answer:
- There are several limitations to satellite communication, including:
- Cost: Satellite communication systems can be expensive to set up and maintain, as they require the deployment and maintenance of satellites and ground-based infrastructure.
- Latency: Satellite communication systems may have higher latency compared to terrestrial communication systems, as the signal must travel to and from the satellite, which is orbiting at a high altitude above the earth’s surface.
- Signal strength: Satellite signals may be weaker than terrestrial signals, as they must travel through the atmosphere, which can cause signal degradation.
- Interference: Satellite signals may be susceptible to interference from other sources, such as other satellites or terrestrial communication systems.
Que.37 What are some applications of satellite communication?
Answer:
- Satellite communication systems are used in a wide range of applications, including:
- Television and radio broadcasting
- Internet connectivity
- Mobile phone communication
- Military and government communication
- Navigation and positioning
- Remote sensing and environmental monitoring
- Disaster recovery and emergency communication
Que.38 How do satellite communication systems ensure secure communication?
Answer:
Satellite communication systems use various methods to ensure secure communication, including:
- Encryption: Satellite communication systems may use encryption to protect the data being transmitted from unauthorized access.
- Frequency hopping: Satellite communication systems may use frequency hopping to randomly change the frequency on which the data is transmitted, making it difficult for unauthorized parties to intercept the signal.
- Spread spectrum: Satellite communication systems may use spread spectrum technology to spread the data across a wide frequency band, making it more difficult for unauthorized parties to intercept the signal.
- Antenna diversity: Satellite communication systems may use multiple antennas at the transmitter and receiver to improve the signal-to-noise ratio and reduce the effects of interference.
Que.39 How do satellite communication systems handle multiple users?
Answer: Satellite communication systems may use various methods to handle multiple users, including:
- Frequency division multiple access (FDMA): In FDMA, different users are assigned different frequencies to use for their communication.
- Time division multiple access (TDMA): In TDMA, different users are assigned different time slots to use for their communication.
- Code division multiple access (CDMA): In CDMA, different users are assigned different codes to use for their communication.
Que.40 How do satellite communication systems maintain their orbits?
Answer: Satellite communication systems maintain their orbits using various methods, including:
- Station keeping: Satellite communication systems may use thrusters to make small adjustments to their orbits to maintain their position.
- Gravity gradient stabilization: Satellite communication systems may use the earth’s gravity to maintain their position in orbit.
- Solar pressure: Satellite communication systems may use the pressure from sunlight to maintain their position in orbit.
