lec8

CE-462 FALL 2010SATELLITE COMMUNICATIONSLecture 8Link Design (Part 4)

Institute of Space Technology

9/16/2009Institute of Space Technology*Downlink Design


9/16/2009Institute of Space Technology*Numerical Example 1 (1):Noise Temperature


9/16/2009Institute of Space Technology*Numerical Example 2 (1):Lossy Elements


04-Nov-2010Institute of Space Technology*Note:When system noise temperature is low, each 0.1 dB of attenuation ahead of RF amplifier will add approx. 6.6 K (290(1-1/100.01))


Carrier power to noise power spectral density ratio at Rx input04-Nov-2010Institute of Space Technology*Carrier power: C = PRNoise power spectral density: No = kT

or,C/No = (transmitter EIRP) (1/path loss) x (composite receiving gain/noise temperature) x (1/k)C/No = (EIRP)(1/L)(G/T)(1/k)


9/16/2009Institute of Space Technology*Numerical Example 3: (1)Link Budget: DBS-TV


Numerical Example 3: (2)Link Budget: DBS-TVIF filter designed to approximate root raised cosine (RRC) transfer function Noise BW of all RRC filters is always equal to the symbol rate of the digital txn.In DBS-TV system, QPSK signal with symbol rate = 20 Msps is assumedAntenna noise temperature = 35KLNA noise temp = 110K04-Nov-2010Institute of Space Technology*


9/16/2009Institute of Space Technology*Numerical Example 3: (3)Link Budget: DBS-TV


Selection of C/N marginsC/N margins used in DBS-TV systems are usually quiet small to avoid the need for large receiving antennaThe selection of C/N margins is a design tradeoff between:the outage level that customers can be expected to tolerate, the max allowable diameter for a receiving dish antenna, and the power o/p from the satellite transponders04-Nov-2010Institute of Space Technology*


Reduction in C/N due to increase in sky noise temperatureTotal path attenuation:

Sky noise temperature:

Coupling coefficient, of 90 to 95% is usedAntenna noise temperature:

System noise temp:

04-Nov-2010Institute of Space Technology*


Increase in noise power:

Received power reduced by attenuation:

Resulting downlink (C/N) in rain:

04-Nov-2010Institute of Space Technology*


9/16/2009Institute of Space Technology*Numerical Example 4: (1)Intelsat IV A Downlink Antenna Beams


9/16/2009Institute of Space Technology*Numerical Example 4: (2)Intelsat IV A Downlink


9/16/2009Institute of Space Technology*Note: Link Budgets and Multiple Access


*

lec8

Documents

system noise temperature

usedantenna noise temperature

klna noise temp

power op

link budget

downlink cn

power spectral density

prnoise power spectral