Design and construction of a modem for satellite use

Thesis (MScEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: In this thesis the design and testing of the baseband components of a modem intended for use as a telemetry and control link for a low earth orbit satellite is presented. This includes parts of the physical layer as well as a basic data-link layer. Binary phase-shift keying (BPSK) is used as the modulation scheme and is realised by making use of software defined radio on a standard x86 computer with digital to analogue and analogue to digital converters that use a universal serial bus (USB) connection. The data-link layer makes use of a basic framing scheme and provides bit synchronisation, an automatic repeat request (ARQ) system and Bose Chaudhuri Hocquenghem (BCH) forward error correction (FEC). The ARQ system ensures that data is delivered reliably and the FEC improves the system’s performance in noisy conditions. A prototype system was developed to test the performance of the individual layers as well as the system as a whole. For testing purposes the Linux Internet Protocol (IP) stack is used as higher network layers. Radio frequency hardware developed by Verschaeve [1] modulates the signal away from baseband, transmits it over the air and receives it.AFRIKAANSE OPSOMMING: In hierdie tesis word die ontwerp en toetsing van die basisband komponente van ‘n modem, bedoel vir gebruik op ‘n satelliet in ‘n lae-aarde wentelbaan, bespreek. Die ontwerp sluit dele van die fisiese vlak sowel as ‘n verbindingsvlak in. Binêre faseskuifsleuteling word gebruik as die modulasieskema en word verwesenlik deur gebruik te maak van sagteware gedefinieerde radio. Dit voer uit op ’n standaard x86 rekenaar wat deur middel van USB gekoppel is aan ’n digitaal-na-analoog- en ’n analoog-na-digitaal-omsetter. Die verbindingsvlak het ‘n eenvoudige ramingskema. Dit voorsien bis sinkronisasie, die hersending van verlore rame en Bose Chaudhuri Hocquenghem (BCH) voorwaartse foutverbetering. Die hersending van verlore rame verseker dat data betroubaar oorgedra kan word en foutverbetering verbeter die stelsel se vermoëns in ruiserige toestande. ‘n Prototipe stelsel is ontwikkel om die vermoëns van die individuele vlakke, sowel as die stelsel as ’n geheel, te toets. Tydens toetsing is die Linux Internet Protokol stapel gebruik vir die hoër netwerk vlakke. Radio komponente wat deur Verschaeve [1] ontwikkel was is gebruik om die sein uit te saai en te ontvang