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

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

Multiple Access Methods f1f1 f2f2 BW – bandwidth How can we service all three without interference?

Communications - Access Schemes FDMA – Frequency Division Multiple Access f1f1 f2f2 BW – bandwidth Multiple Access Methods TDMA – Time Division Multiple Access CDMA - Code Division Multiple Access Sharing same frequency bandwidth

Introduction to Space Systems and Spacecraft Design Space Systems Design 5 Communications - Access Schemes Customer A Customer B Customer C CBA f1f1 f2f2 CBA CBA Frequency Time FDMA TDMA CDMA f1f1 f2f2 Frequency CBA Division by freq. bands All three share same freq. & time Division by time

6 Code Division Multiple Access Introduction to Communications Introduction to Space Systems and Spacecraft Design Space Systems Design Baseband Data B Multiply Mixer X / Amplifier Code B Divide Baseband Data B Code B f 1 -f 2 Baseband Data A Multiply Mixer X / Amplifier Code A Divide Baseband Data A Code A f 1 -f 2 Baseband Data C Multiply Mixer X / Amplifier Code C Divide Baseband Data C Code C f 1 -f 2 Multiple channels over same freq. band

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

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

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

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

Introduction to Space Systems and Spacecraft Design Space Systems Design 11 Communications - Access Schemes Process signal received Baseband Data A/B Multiply Mixer X / Amplifier Code A/B Divide Baseband Data A/B f 1 -f 2 Code A/B

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

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

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

Introduction to Space Systems and Spacecraft Design Space Systems Design 15 Data Communications System Move 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 Communications - Access Schemes

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

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

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

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