Satellite Link Design Considerations
Satellite links are used to deliver long distance telecommunications voice/data services, broadband internet services, television broadcast and communications with remote and hard to reach locations. Satellite link consists of an uplink and a downlink. Uplink connects transmit earth station to satellite and downlink connects satellite to the receive earth station. Signal quality in the uplink depends on how strong the signal is transmitted from the source earth station and how the satellite receives it. On the downlink side, signal quality depends on how strong the satellite retransmits the signal and how the earth station receives it.
Earth stations are categorized by the size of the earth station antenna. Large earth station has antenna with 10 to 30 meters in diameter. Small earth station has antenna with diameter between 1 to 10 meters. VSAT (Very Small Aperture Terminal) earth station has antenna with 0.3 to 1 meter in diameter. There are three earth station system parameters need to be considered when designing satellite links. The first one is transmitter EIRP (Effective Isotropic Radiated Power) which is equal to Pt (transmitter output power) × Gt (transmit antenna gain). EIRP measures the signal power sends out from the transmit earth station. The second parameter is the earth station Figure of Merit which is equal to G (receive antenna gain) ÷ T (system noise temperature). G/T measures the sensitivity of the receiving system and the quality of the received signal. The third parameter is the earth station system noise temperature which measures the amount of noise power generated by the receive earth station.
The main objective of satellite link design is to maximize link data rate while minimizing the BER (Bit Error Rate) at the receiver subjects to the constraint of received power and channel bandwidth. The BER of a satellite link is a function of Eb/No (energy per bit noise density ratio) in the information channel. A satellite communications system designer must attempt to ensure a minimum Eb/No in the receiver channels to satisfy the link BER criteria which also meet the constraints on satellite transmit power and RF bandwidth. In digital transmission, Eb/No in a baseband channel depends on C/N (carrier to noise ratio) of the receiver, the type of modulation used in the baseband channel and the channel bandwidth. Hence, the main concern in design and analysis of satellite link is to calculate and evaluate the link C/N in which C is the received carrier power in the earth station/satellite and N is the noise plus interference (caused by earth stations of adjacent satellite) power in the receiver.
Loss due to rain is the most important impairment to the transmission of satellite signal. Rain attenuation is a function of rain rate at earth station location and satellite link carrier frequency. Average value of rain rate (mm/hr) of a country can be obtained from the department of Meteorology of that country. Rain effects become severe at wavelength approach the rain drop size. If the satellite link is to maintain during rainfall, then extra transmit power is needed to overcome the maximum attenuation induced by the rain. Hence accurate assessment of expected rain loss needs to be made when evaluating link parameters.
The earth station antenna look angle (azimuth & elevation) can be calculated using the longitude of the geosynchronous satellite plus the latitude and longitude of the earth station. The deviation of the earth station antenna pointing direction from the antenna electric axis is termed the antenna pointing error. This error reduces the gain of the earth station antenna because the antenna gain is maximum when measured at its electric axis. Hence, antenna point loss needs to be evaluated in satellite link design and it applies to both transmit and receive antennas.
Questions and Answers
Article Tags:
satellite
,uplink
,downlink
,earth station
,antenna
,ber
,rain attenuation
,point error
,c n
,vsat
,eirp
,figure of merit
,noise temperature
,television
,broadcast
,communications
,g t
Video calling is a technological advancement that has made communication way easier for many people. In this way, you get to speak with a person from a hundred or so miles away through the Internet.
Mobile has made the switch from a voice- and messaging-centric technology to become a predominantly data channel. It's happened so fast that wireless networks are barely able to keep up, and growth will continue to compound for the foreseeable future. Wireless carriers & mobile operators are employing a variety of tools to help their networks handle data more efficiently and quickly, but none is as significant as the transition to fourth-generation technology, 4G Long Term Evolution (LTE).
Estonia has emerged as one of the world's most dynamic and modern free market economies. Its flat tax system and tax exemption rules for undistributed company profits have attracted vast amounts of foreign investment capital. The requirement to balance the country's annual budget is written into the constitution which means that the national debt is a mere 6% of GDP.
While i shifted my architecture practice to Birmingham, I wanted being entirely up-to-date tough furniture along with gear I selected for that brand-new office. For this reason My partner and i took the time to be on the world wide web along with understand about hosted pbx.
There are many businesses that still a new traditional phone because it is routine to possess a number where your visitors as well as sellers can get to anyone with a central business office.
Optical Fiber is used to transmit microwave signals for cable television in RFoG (Radio Frequency over Glass) Network. Radio-over-fiber technology can transmit microwave signals for cellular radio, WLAN and microwave antenna remoting.
Cable television networks have grown from the coaxial cable networks for TV broadcast delivery to a broadband hybrid fiber coax (HFC) networks which can carry voice, data and multimedia services. DOCSIS and PacketCable standards were developed to enhance the speed, QoS and capability of the cable TV networks to deliver VOIP, packetized and real time network services.
MIMO wireless system uses multiple antennas at the transmitter and receiver to send and receive data. Examples of MIMO systems are IEEE 802.11n WLAN and 4G cellular networks such as WiMAX and LTE. MIMO techniques can significantly increase the capacity and range of wireless systems.
An optical transport network (OTN) is an All Optical Network (AON) where optical connections, known as lightpaths, are used for data transmission. Lightpaths are used to provide wavelength services such as low latency broadband data service, dedicated private lines and virtual private networks.
Discuss this Article
