lab2 - ECE4305 Software-Defined Radio Systems and Analysis...

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ECE4305: Software-Defined Radio Systems and Analysis Laboratory 2: Basic SDR Implementation of a Transmitter and a Receiver C-Term 2011 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 3 1.1 Digital Modulation Schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1 Pulse Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.2 Quadrature Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1.3 Phase Shift Keying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Power Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Probability of Bit Error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.1 Error Bounding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.4 Suggested Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.5 Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 Software Implementation 10 2.1 Repetition Coding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2 Interleaving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.3 BER Calculator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.4 Receiver Implementation over an Ideal Channel . . . . . . . . . . . . . . . . . . . . . 11 3 USRP2 Hardware Implementation 13 3.1 Differential Binary Phase-Shift Keying . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.1.1 Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 3.1.2 Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.1.3 Using Callback Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.2 Differential Quadrature Phase-Shift Keying . . . . . . . . . . . . . . . . . . . . . . . . 16 3.3 USRP2 In-phase/Quadrature Representation . . . . . . . . . . . . . . . . . . . . . . . 17 3.3.1 Observing In-phase and Quadrature Data . . . . . . . . . . . . . . . . . . . . 17 3.3.2 Mathematical Derivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1
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4 Open-ended Design Problem: Frame Synchronization 21 4.1 Frame Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.2 Barker Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.3 Simulink Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.3.1 Basic Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.3.2 Application of the Basic Idea . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 4.3.3 Incorporating USRPs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.4 Hints for Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4.5 Hints for Debugging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5 Lab Report Preparation & Submission Instructions 26 References 27 2
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1 Theoretical Preparation This section will provide an understanding of several basic digital modulation schemes that form the basis of modern communications. You will learn to analyze the power efficiency of various schemes and analyze mathematically the error robustness of these modulation schemes. 1.1 Digital Modulation Schemes In analog modulation schemes, the message signal modulates a continuous wave. Conversely, digital modulation involves having the message signal modulated against a pattern of bits and transforming them into symbols. As we will see, this can be accomplished by uniquely manipulating the amplitude and phase information of a signal during each symbol period T . 1.1.1 Pulse Amplitude Modulation Pulse amplitude modulation (PAM) is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. Demodulation is performed by detecting the amplitude level of the carrier at every symbol period. Pulse amplitude modulation (PAM) constructs symbols with varying amplitudes. The most basic form of PAM is a series of rectangular pulses with varying amplitudes. Figure 1: A two bit modulator (PAM-4) will take two bits at a time and will map the signal amplitude to one of four possible levels, for example 3 volts, 1 volt, 1 volt, and 3 volts.
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