Implementation Of A Modulation System Capable Of Pi/4-QPSK And GMSK Using Software Defined Radio

Software-Defined Radio (SDR) defines radio communication functions using software on a general, open hardware platform that possesses scalability itself, which not only relieves communication systems from the constraints of hardware elements but also enables seamless connection between kinds of wireless communication systems and supports flexible services.Software Defined Radios become to true as a result of fruitful researches in this domain and great progresses achieved by hardware devices in recent more than a decade, and now are found in more and more communication systems. This thesis focuses on application of SDR to a transmitter. To streamline the application, at first some relevant issues are reviewed such as functional model of SDR and hardware platform architecture, which can help us get a good understanding into SDR and facilitate conceiving and developing projects. The flexibility and scalability of a SDR are decided basically by its hardware platform architecture. A good architecture can minimize the coupling between its components and enable plug-and-play, consequently makes a system employing SDR capable of upgrade, scalability and more cost-efficient. And, it also helps us fully exploit exclusive advantages of SDR. This thesis also discusses, from a mathematical perspective, the models of transmitters including unichannel, multichannel and channelized transmitters. A modified real signal model of channelized transmitter is presented that employs multiphase filters and Discrete Fourier Transform to maximize computing efficiency, which can mean much in a radio communication system that requires real-time processing. Then two typical digital modulation schemes, pi/4-QPSK and GMSK, are examined respectively with their conventional implementations. A linear approximation of the non-linear GMSK is proposed to help GMSK to be readily accommodated into a SDR. Finally, this thesis elaborates the construction of the transmitter using SDR that comprises mainly a DSP along with a programmable digital up-converter. The transmitter is capable, when coupled with appropriate software, of digital modulation schemes such as pi-QPSK, GMSK and so forth, and supervised by a personal computer.