Design and Implementation of a Software Defined Radio Receiver for AM Band
Type of DegreeThesis
Electrical and Computer Engineering
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Since the mid-1990s, the radio industry has actively focused on implementing more and more radio functions in the digital domain. This has been furthered by availability of high speed, high performance data converters and faster digital processors. In 1993, Joe Mitola, III coined the term 'Software Radio (SR)' for a radio system that uses DSP primitives to perform signal manipulation instead of the traditional analog hardware. Such a system is more robust, compact, power-efficient and highly reconfigurable. An ideal Software Radio system consists of a transmitting/receiving antenna, high speed data converter and a powerful digital processor. However, the state of current technology is such that this can only be partially achieved. Due to speed and performance limitations of existing data converters and digital processors, it is customary to use an RF front-end between the antenna and the data converter. Such a system is then termed as a Software-Defined Radio (SDR). This thesis deals with the design and implementation of a low-cost SDR receiver which bandpass samples AM Intermediate Frequency (IF) and demodulates it in real-time using quadrature demodulation. The system uses an AM/FM trainer kit to obtain an AM IF, a high speed PCI-based data acquisition (DAQ) card for analog-to-digital (A/D) conversion, MATLAB to perform signal processing in the digital domain and a sound card to produce the demodulated analog signal. A Graphical User Interface (GUI) is developed which allows the user to start/stop the program, select a suitable bandpass sampling frequency and view the time and frequency domain representation of the demodulated signal. This work also discusses bandpass sampling and quadrature demodulation followed by a rigid mathematical analysis to point out advantages and disadvantages of the two techniques.