2. Satellite Link Budgets: Thinks 2 know
AJAL.A.J
professorajal@gmail.com
MOB: 8907305642
DEPARTMENT OF ECE
UNIVERSAL ENGINEERING COLLEGE,
THRISSUR- KERALA
INDIA
2
4. Satellite Link
The ultimate goal of satellite is to provide
satisfactory transmission relayed between earth
stations.
Satellite always use band pass channels.
5. Estimation
• You are planning for a tour.
• The estimate prepared = Rs 5,000 /• Back home after tour
Amount in wallet
= Rs 5,00 /You pat yourself on the back for a job well
done because you still have Rs 5,00 /- left
in your wallet
5
6. The only difference …
• We do something similar with
communication links , called creating a
link budget.
• The only difference is that
Traveler signal
Instead of Rs, it starts out with power
Rs power
6
7. At the end of the day …..
• It spends its power (or) attenuates as it
travels , be it wired or wireless
7
8. What Is a Link Budget
• 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
8
9. LINK BUDGET
A link budget is a relatively simple
addition and subtraction of gains and
losses within an RF link.
When these gains and losses of various
components are determined and summed, the
result is an estimation of end-to-end system
performance in the real world.
10. 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
10
11. LINK BUDGET CAN Minimize Bandwidth
Power
“Power limited” –
too much power
1:1
Bandwidth
“Bandwidth limited”
12. Link Budget Components
•
A satellite link budget should include the
following parts:
1.
2.
3.
4.
5.
UPLINK
DOWNLINK
COMBINE 1 AND 2
DEFINE PERFORMANCE LIMIT(S)
COMPARE CALCULATED AND DESIRED
PERFORMANCE
12
13. 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
13
14. EVALUATION (continued)
• Some factors we consider important are:
– Satellite non-linearity
– 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
14
15. LINK BUDGET
• Performance objectives for digital links
consist of:
• BER for normal operating conditions
• Link Availability, or percentage of time that
the link has a BER better than a specified
threshold level
19. Carrier Parameters
Forward Error Correction (FEC)
1/2 FEC:
1
E
2
E
3
E
4
E
5
5
6
E
E
6
E
7
E
7
3/4 FEC:
1
2
3
E
4
7/8 FEC:
1
2
X
3
4
5
6
7
E
E
Data Bit
Extra Bit
20. Why Optimal FEC Rates ?
– To achieve optimum use of power
and bandwidth
– To provide best possible availability
within system limitations
– Transmission Rate = Data Rate * 1/FEC
20
22. Earth Segment Parameters
Antenna Size
– What?
– Impact?
- Diameter
- Efficiency
- The larger the antenna diameter,
the higher the antenna gain
- The larger the antenna diameter,
the better the antenna G/T
