1 DCS MANUFACTURERS MEETING NOVEMBER 9, 2006 Peter Woolner Mitretek Systems Link Budgets

2 It is a theoretical calculation of end-to-end performance for a communications path under a specific set of conditions. Sometimes the conditions are stated; most often at least some of them are implied or assumed. Every link budget implies everything not included is irrelevant. –Sometimes this is true What Is a Link Budget

3 Why is a Link Budget Important A link budget is used to predict performance before the link is established. –Show in advance if it will be acceptable –Show if one option is better than another –Provide a criterion to evaluate actual performance

4 Link Budget Components A satellite link budget should include the following parts: 1.UPLINK 2.DOWNLINK 3.COMBINE 1 AND 2 4.DEFINE PERFORMANCE LIMIT(S) 5.COMPARE CALCULATED AND DESIRED PERFORMANCE

5 EXAMPLE PART 1 ParameterValue in dB Uplink transmit EIRP48.0 Net uplink losses Satellite receive G/T-17.0 Boltzmann’s constant(-198.6) Uplink receive C/N

6 EXAMPLE PART 2 ParameterValue in dB Downlink transmit EIRP22.5 Net downlink losses Satellite receive G/T15.0 Boltzmann’s constant(-198.6) Downlink receive C/N

7 EXAMPLE PART 3 ParameterValue in dB Uplink receive C/N Downlink receive C/N Combined C/N Data rate in dB (1200 bps)30.8 Calculated link E B /N

8 EXAMPLE PARTS 4 & 5 ParameterValue in dB Calculated link E B /N Required E B /N Operating margin2.6

9 LINK BUDGET EVALUATION The basic question is: Is the operating margin large enough? –It must be positive to account for the items listed in the budget –It also must cover the variations caused by everything that was not explicitly included Therefore a more useful question is: What was not included in the budget that might be a significant factor?

10 EVALUATION (continued) Some factors I consider important are: –Satellite non-linearity (NPR) –Satellite transmit power for your signal –Interference (including CDMA if implemented) –Allowance for future (worse) conditions –Lifetime of the system under evaluation –How closely can it be maintained at the parameters used in the budget