Satellite Communications Payload and Systems Design

DURATION: FOUR DAYS
COURSE NO.: 3025

The new millennium promises a significant expansion of satellite communications systems and technology, particularly in digital broadband and the Internet. Developed for practicing communications systems and subsystems engineers, this updated course provides a practical understanding of how modern satellite payloads (repeater and antennas) and systems are designed and assembled to meet the most demanding service requirements of the private and government sectors. The lectures are broken down into major areas of investigation so that participants can focus on elements of a communications satellite payload and the overall system. The course begins from a systems engineering standpoint by identifying the requirements for the satellite payload and end-to-end system using current applications in digital video and broadband media, voice communication, mobile services, and interactive data. Requirements of the satellite payload are derived and defined down to major building blocks—the repeater and its components, and the antenna system—and design principles and performance budgets are reviewed for each element, such as receivers, multiplexers, power amplifiers, analog and digital processors, reflector and feeds, phased array antennas, and repeater performance budgeting. Critical analysis concepts such as loss budgeting, group delay, intermodulation distortion, digital impairments, and adjacent channel interference are covered for the subsystem and system designer. Following this, the ground segment and overall system are investigated, including requirements for major earth stations and user terminals to deliver one-way receive services such as DTH TV and data or two-way interactive services using VSAT and mobile communications technologies. The course concludes by considering a practical methodology for evaluating and optimizing the performance of the overall system. Throughout the course, emphasis is on design principles using classical mathematical techniques, along with modern software tools for personal computers. Examples and practical exercises are used extensively, and participants are encouraged to bring along their particular design problems for consideration in class.

COURSE MATERIALS:
The text, Introduction to Satellite Communication, 2nd ed., B. Elbert (Artech House, 1999) and detailed lecture notes and exercises are distributed on the first day of the course.

1. Communications Engineering Principles.
   

   Service Requirements for Communications Satellites: Satellite architectures; generic capabilities of GEO and non-GEO satellites; service requirements for Bent Pipe Satellites; digital TV (direct-to-home satellite broadcasting and DVB systems); telephony (single channel and multichannel services); data/VSAT Networks (star and mesh networks); performance of the Internet Protocol over satellite links; mobile services (CDMA and TDMA); digital audio broadcast (CD-quality radio, mobile data broadcasting); and service requirements for digital processing satellites. Systems Engineering to Meet Service Requirements: End-to-end link budget analysis; link budget tools (Excel and Satmaster Pro); network design methodology; analytical system analysis approaches; digital signal processing approaches; collecting and quantifying traffic requirements; defining the network topology and architecture; performing space segment versus ground segment trades. Payload Design for Optimum Performance: RF system analysis for the satellite payload; basic concepts (EIRP, SFD, and G/T); overview of transmission impairments; analog impairments (baseband intermodulation, differential phase and gain, crosstalk); digital impairments (Bit Error Rate [BER], Eb/No, eye opening, Intersymbol Interference); modeling repeaters (SPW, SystemView, and other tools); antenna concepts; co-polarized directivity and gain; cross-polarization; estimating antenna gain (gain-area product); computer modeling of antennas.

2. Payload Design and Integration.
   

   Repeater Design: Transponder design requirements; frequency translation and phase noise; frequency and polarization re-use; low noise amplification; power amplification (linear and limiter mode operation); traditional bent-pipe payload architectures; LNAs/downconverters/ receivers; input filters and multiplexers; passive microwave hardware; beam and channel switching/routing; high-efficiency power amplifiers; (TWTA, linearized TWTA, SSPA); output filters and multiplexers; processing payloads; digital processor technology; A/D and D/A conversion; demodulation-remodulation processing; multiplexing and packet switching. Antenna Configurations and Their Performance Characteristics: Fixed reflector and multiple feeds, movable and reconfigurable antennas, shaped reflectors, array antennas (horn, dipole, and waveguide lense). Estimating and Budgeting Payload Performance: Gain/loss budgets; Saturation Flux Density (SFD); system noise and its effect on G/T; EIRP optimization; budgeting for stability; repeater gain stability; antenna thermal effects; spacecraft pointing; G/T stability; EIRP stability; budgeting for channel characteristics and impacts to baseband signals; gain flatness (amplitude ripple); group delay and its impairment to digital services; phase shift vs. frequency; group delay ripple; out-of-band rejection (adjacent channel and external); amplitude linearity (C/3IM and NPR).

3. Earth Station and Overall System Engineering.
   

   Ground Segment Selection and Optimization: Classification of ground stations; RF analysis of ground segment requirements; transponder utilization principles; providing adequate uplink and downlink margin; selection of the appropriate antenna size; earth station internal tradeoffs (RF power and EIRP, receiver noise and G/T). Earth Stations and User Terminals: Developing the top-level specification; RF specifications; baseband specifications; detailed block diagram; EIRP and G/T budgeting; gain budgeting; system noise temperature; selecting RF and baseband equipment; antenna systems (center fed and offset parabolic, Cassegrain, tracking systems); transmitter systems (KPA, TWTA, SSPA, redundancy switching); low noise amplification (LNA, LNB, LNC); baseband systems selection and sizing; user terminal technology: modem, multiplexing, compression/decompression; interface to external devices: TV, telephone, PC, terrestrial networks. Systems Engineering Tools and Techniques: Performance comparison of multiple access systems: FDMA, TDMA, and CDMA; analytical models of network performance; equalization techniques; satellite sizing; transponder capacity planning; satellite system simulation (Satellite Toolkit); lessons learned in a real project.