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

Introduction to Space Systems and Spacecraft Design Space Systems Design 2 Communications - Access Schemes

Introduction to Space Systems and Spacecraft Design Space Systems Design 3 Communications - Access Schemes

Introduction to Space Systems and Spacecraft Design Space Systems Design 4 Communications - Access Schemes

Introduction to Space Systems and Spacecraft Design Space Systems Design 5 Communications - Access Schemes

Introduction to Space Systems and Spacecraft Design Space Systems Design 6 Communications - Access Schemes

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 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 ----) 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 10 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 11 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 12 How can you improve quality before transmitting signal – accuracy 1. Increase number of bits in ADC/DAC what is max? 2. Increase sample rate what is max? How can you improve quality of transmitted signal ---- accuracy 1. Increase power to reduce BER 2. Choose modulation with good BER 3. Further improvement ---- use error encoding? What about the transmitted signal? 1. What is transmission rate R? 2. What is the bandwidth that you need BW? Consideration in Design of Comm System Communications - Access Schemes

Introduction to Space Systems and Spacecraft Design Space Systems Design 13 Communications Design Guidelines for University Satellites Communications - Access Schemes

Introduction to Space Systems and Spacecraft Design Space Systems Design 14 Communications - Access Schemes Use of Link Equation Spread Sheet

Introduction to Space Systems and Spacecraft Design Space Systems Design 15 Communications - Access Schemes Questions?