Ramesh Kumar lama

 System noise temperature  Radio maps of sky  Sample link analysis  Link Budget details  Receiver figure of merit  Received isotropic power  Satellite repeater  Non linear Repeater Amplifier  Trade offs  Conclusion

 Link budget calculation  Only few key terms are introduced.  The goal of this link analysis is to determine whether or not the required error probability is met by examining the actually received and comparing it with required to met the system specification

 The receiving antenna gain and system temperature are often grouped together as  Separated specification leads to result with over specified system than the necessary.  Recognition of such over specification resulted in specifying the antenna and receiver front end as a single front of merit parameter such that cost effective trade-offs between the antenna design and receiver design might be employed.

 The received isotropic power In terms of Ratio With the implementation loss The received isotropic power

 Retransmits the messages they receive. ◦ Regenerative repeater  Regenerates, that is, demodulates and reconstitutes the digital information embedded in the received waveforms before retransmission  Designed to operate with only one or very few modulation formats  Link analysis treats the uplink and down link as two separated point to point analyses.  To calculate the bit error performance of regenerative satellite repeater link, it is necessary to determine to determine separately the bit error probability on the uplink and downlink.

 Overall bit error performance is approximated using the individual uplink and downlink bit error probabilities  Overall probability that a bit is correct is  Overall probability that a bit is in error is

◦ Only amplifies and retransmits. ◦ Can be used with many modulation formats ◦ overall SNR is dependent on the uplink SNR ◦ shares the repeater downlink power in proportion to the uplink power from each of the various uplink signal and noise

 The total satellite downlink EIRPs  The total power received at jth earth terminal with bandwidth W

 Power to noise ratio for signal i received at jth terminal  Over all power to noise ratio Uplink repeater noise degrades the overall SNR in two ways  It steals the downlink EIRP and contributes to total system noise  When the link is said to be uplink limited and most downlink EIRPs is wastefully allocated to uplink noise power.

 Power limitation in most satellite communication systems.  Inefficiencies associated with linear amplification stage are expensive.  Major undesirable effects of repeater nonlinearities a.Intermodulation noise b.Traveling wave tubes c.Phase variation d.Suppression of week signals

 Of the many analyses that support a developing communication system, the link budget stands out in its ability to provide overall system insight.  By examining the link budget, once can learn many things about the overall system design and performance.  For example from the link margin, one learns whether the system will meet its requirements comfortably, marginally or not at all.