Ultra KaSat: Completed Link Budget and Impact of Rain Fade on Link Budget

Completed Link Budget

Ultra KaSat is a new high throughput satellite dedicated to deliver broadband access to rural and suburban areas in France. BroadNet is an ISP located in Paris, has negotiated a deal with Ultra KaSat and found suitable installers for the equipment which it intends to deploy in areas that do not have good service quality via ADSL. 
 
Potential users of the service have asked the ISP to explain the quality of service that they should expect from the Ka-Band system as they have heard that it does not work when it is raining. Not being too familiar with satellite systems, but having a basic knowledge of engineering, the ISP found a link budget outline for the forward downlink to the user terminal as he understood that this was the most critical part of the system performance, as up-path power control can handle the up-path of the forward link and the use of a large hub antenna makes the return link of less importance. 
 
Despite his engineering ability the ISP was unable to complete the forward downlink link budget and he decided to ask for your help as you have been educated in satellite system performance. 
 
He has asked you to produce the following:- 
 
1. A completed link budget based upon his initial one given in Table 1; 
2. An indication of the level of rain fading that would be experienced at his test site in centre of the coverage area, Saint-Éloi, Limousin; 
3. The overall impact of this rain fade on the link budget (ITU-R Recommendation p.618 applies); 
4. Assess the co-channel interference; 
5. Suggestions as to ways in which the situation regarding rain impairments may be improved. 
 
Thus, you must prepare this material with full justification of the approach and parameters used in a report to BroadNet.

Provide a completed link budget based upon the initial one given in Table 1 along with material to justify the approaches adopted;  

2. Explain and exemplify the overall impact of this rain fade on the link budget and Calculate the highest modcod the test terminal can operate;
3. Find the actual outage probability for the test site;
4. If the satellite transmitting EIRP increases by 3 dB, what would you expect to be the impact on the data rate? Suggest to BroadNet some ways in which the situation regarding rain impairments may be improved. The above material should be presented in one document with a number of sections covering the points above. The submission should not be longer than 25 pages in total and the major elements should be clearly defined. Link budget calculations should be in an appendix.

To provide highly accurate analysis of a multi-beam satellite using advanced computational electromagnetic modelling methods such as Physical Optics, GTD or UTD would result in high levels of complexity and lengthy simulation run times. For system simulation studies this is often overcome by adopting as simpler antenna model based upon the illumination of a circular aperture which can provide results equivalent to those obtained using a single feed reflector antenna. This appendix provides background to such an approach which has been adopted for this study.
 
There is a need to taper the field distribution over the circular aperture in order to reduce sidelobe levels. Parabolic tapers to zero at the edge generally result in unacceptably low efficiency. Consequently, an alternative that uses a parabolic taper to a pedestal value at the edge is more appropriate and the antenna performance can be determined analytically for integer taper values and by numerical integration for non-integer values. Parabolic Taper on a Pedestal Aperture Distribution One of the earliest and most comprehensive references to this model is Sciambi, [RD-1] and a more recent and useful reference is due to Stutzman [RD-2]. We develop the model here base.