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ece4305_lab2 - ECE4305 Software-Dened Radio Systems and...

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ECE4305: Software-Defined Radio Systems and Analysis Lab 2: Basic SDR Implementation of a Transmitter and a Receiver D-Term 2010 Objective This laboratory will provide a theoretical foundation for various modulation schemes and their ro- bustness to error. You will also be introduced to Simulink as a development tool for communications systems. This laboratory will implement a bare bones communication system in Simulink. This laboratory assumes a knowledge of MATLAB but little or no knowledge of Simulink. Contents 1 Theoretical Preparation 2 1.1 Digital Modulation Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.1 Pulse Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.2 Quadrature Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1.3 Phase Shift Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Power Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Probability of Bit Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3.1 Error Bounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 Software Implementation 9 2.1 Repetition Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2 Interleaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3 BER Calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.4 Receiver Implementation over an Ideal Channel . . . . . . . . . . . . . . . . . . . . . 10 3 GNU Radio Experiments 12 3.1 Python . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3.2 GNU Radio Companion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.2.1 GRC FFT Tutorial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.2.2 GRC Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2.3 More GRC Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.2.4 Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.3 Further Exploration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4 Analysis & Synthesis 23 5 Lab Report Instructions 24 References 25 1
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1 Theoretical Preparation This theory will give an understanding of several basic digital modulation schemes that form the foundation of modern communications. You will learn to analyze the power efficiency of various schemes and access a modulation schemes robustness to error. 1.1 Digital Modulation Schemes In analog modulation schemes, the message signal is modulated against a continuous wave. In digital modulation, the message signal is modulated against a pattern of bits, or symbols. This introduces the symbol, or baud rate, as a bandwidth consideration. 1.1.1 Pulse Amplitude Modulation Pulse amplitude modulation (PAM) constructs symbols with varying amplitudes. The most basic form of PAM is a series of rectangular waves with varying amplitudes. Figure 1: 4-PAM captured on a scope. For more information about pulse amplitude modulation, please refer to Section 5.2 of the course textbook [6]. 1.1.2 Quadrature Amplitude Modulation Like PAM, quadrature amplitude modulation (QAM) implies some sort of amplitude modulation. Unlike PAM, QAM modulation schemes use at least two phases. Recall the discussion of complex baseband and how 4-QAM is represented. S i ( t ) = I i ( t ) cos (2 πf c t ) + Q i ( t ) sin (2 πf c t ) (1) 2
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The two phases are orthogonal to each other, meaning you can essentially double your date rate “for free.” Rectangular QAM can be thought of as two orthogonal PAM signals being transmitted simultaneously. Mathematically, this may be represented as MPAM + MPAM = M-QAM. QAM constellations could also take the form of nested circles (called circular QAM), or any other geometric pattern that involves orthogonal modulators. Which geometric pattern you choose is the result of how easy the signal constellation is to transmit and how robust the constellation is to bit error.
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