Communications - Access Schemes

1. Communications - Access Schemes Introduction to Space Systems and Spacecraft Design Space Systems Design

2. Communications - Access Schemes Got link with Satellite Have assigned frequency & BW How do we work with multiple ground stations to use the satellite service? 2 Introduction to Space Systems and Spacecraft Design Space Systems Design

3. Multiple Access Methods BW – bandwidth f1 f2 How can we service all three without interference?

4. Communications - Access Schemes BW – bandwidth f1 f2 Multiple Access Methods FDMA – Frequency Division Multiple Access TDMA – Time Division Multiple Access CDMA - Code Division Multiple Access Sharing same frequency bandwidth

5. Communications - Access Schemes A B C Customer A FDMA Customer B Customer C Division by freq. bands f1 f2 Frequency TDMA A B C A B C Division by time Time CDMA A B C All three share same freq. & time f1 f2 Frequency 5 Introduction to Space Systems and Spacecraft Design Space Systems Design

6. Introduction to Communications Code Division Multiple Access Multiply Mixer Multiply Mixer Multiply Mixer f1-f2 f1-f2 f1-f2 Divide Divide Divide Baseband Data A Baseband Data C Baseband Data B Baseband Data A Baseband Data B Baseband Data C Amplifier Amplifier Amplifier Amplifier Amplifier Amplifier Code A Code C Code B / X / X X / Code B Code C Code A Multiple channels over same freq. band 6 Introduction to Space Systems and Spacecraft Design Space Systems Design

7. Communications - Access Schemes 7 Introduction to Space Systems and Spacecraft Design Space Systems Design

8. Communications - Access Schemes 8 Introduction to Space Systems and Spacecraft Design Space Systems Design

9. Communications - Access Schemes 9 Introduction to Space Systems and Spacecraft Design Space Systems Design

10. Communications - Access Schemes Transmit this signal 10 Introduction to Space Systems and Spacecraft Design Space Systems Design

11. Communications - Access Schemes Process signal received Multiply Mixer f1-f2 Divide Baseband Data A/B Baseband Data A/B Amplifier Amplifier Code A/B X / Code A/B 11 Introduction to Space Systems and Spacecraft Design Space Systems Design

12. Communications - Access Schemes Process signal received 12 Introduction to Space Systems and Spacecraft Design Space Systems Design

13. Communications - Access Schemes 13 Introduction to Space Systems and Spacecraft Design Space Systems Design

14. Communications - Access Schemes 14 Introduction to Space Systems and Spacecraft Design Space Systems Design

15. Communications - Access Schemes Communications System Move Data Data Convert to Baseband Data # bits for ADC Sample rate Choose a frequency for carrier to send on fc availability of equipment? can use band? Choose a modulation scheme (BPSK, QPSK, FSK, AFSK ----) How much power can you get from Tx to Rx? How much BER can your tolerate? Need to use FEC? Do link equations ---- got enough margin? Choose equipment antennas polarization 15 Introduction to Space Systems and Spacecraft Design Space Systems Design

16. Communications - Access Schemes Other Communication Considerations 1. Contact time with satellite (distance between gs & sat) LEO GEO Molnyia 2. Doppler shift on signals to and from satellite Satellite To Satellite ? when approaching ? when leaving V From Satellite fr > fc when approaching fr <fc when leaving Ground Station 16 Introduction to Space Systems and Spacecraft Design Space Systems Design

17. Communications - Access Schemes How do you calculate doppler shift? fr = freq. at Tr at gs fc = carrier freq. at Tx on sat fr = fc fr < fc fr > fc 17 Introduction to Space Systems and Spacecraft Design Space Systems Design

18. Communications - Access Schemes Communications Design Guidelines for University Satellites 18 Introduction to Space Systems and Spacecraft Design Space Systems Design

19. Communications - Access Schemes Questions? 19 Introduction to Space Systems and Spacecraft Design Space Systems Design