Satellite Communication Networking

Chapter 26

    The first beneficiary of satellite communication system was the military forces for they can communicate each group during operations. They used also this for agriculture, forestry, geology, and even environmental science. For agriculture they used satellite communication in order to determine the productive from non productive yields. All this improves yield and prevents the waste of valuable chemicals. This practice is well established in America. They also used satellite communication networking for infrared vision, satellite based navigation, such as GPS.

        The process begins at an earth station,, an installation design to transmit and receives signal from a satellite in orbit around the earth. Then the earth station send an information via high powered, high frequency range signal to satellite and receives and retransmit the signals back to earth where they are receive by other earth stations in the coverage area of the satellite. This scenario is also mentioned during our national tour in Subic satellite station. The area that receives the signal of useful strength from the satellite is called satellite footprint.  Then the transmission process from the earth station to the satellite is called the uplink and the system from the satellite to the earth station is called downlink.     

       

        The satellite frequency has three common uses, the C-band, Ku-band, and the Ka-band. C-band and Ku-band are the most common frequency spectrums used by today’s satellite. The frequency and the wavelength are inversely proportional to each other. If the frequency increases the wavelength will decrease. For the design of antenna, consider the frequency and wavelength. The wavelength increases, larger antenna are required to receive the signal.

         Majority of satellite in orbit around the earth are positioned at a point of 22,300 miles above the earth’s equator in Geosynchronous Earth Orbit or GEO. This satellite can maintain an orbit with a period of rotation around the earth with exactly equal to 24 hours. The reason of this is that the satellite revolve at the same rotational speed of the earth, they appear stationary from the earth surface. That’s why the antenna that they are using doesn’t need to move after they have been properly aimed at a target satellite in the sky.

         Medium Earth Orbit is an innovation of communication. It gives rise to the new orbits and totally new system design. It has been proposed that the orbit distance of about 8,000 miles. The signals travel from MEO satellite travel a shorter distance which translates to improve signal strength at the receiving end. If the signal travels in a shorter distance the delay was reduced and it accommodates the needs of the system faster. That why it is better to use a MEO for satellite purposes.

      Low Earth Orbit or LEO is divided into 3 categories. First is called little LEO, second is big LEO, third is mega LEO. LEOs will orbit at a distance of 500 to 1000 miles above the earth. They consider this as a short distance, that’s why it can’t cause any delay for transmission. It could take .05 seconds and further reduces the need for sensitivity for the receiving equipment. The little LEO will operate in the 800 MHz range, big LEO will operate in the two GHz or above range, then the mega LEO will operate in the 20 to 30 GHz range. The mega LEO has a higher frequency associated that’s why it is capable of carrying more capacity and much capability for real time. If we say real time it means that it operates always at the present time.