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lab1_s11 - Spring 2011 UCSB ECE 146B Communications II Lab...

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UCSB Spring 2011 ECE146B: CommunicationsII Lab 1: Introduction to linear modulation Assigned: March 29, 2011 Due: April 15, 2011 (at the beginning of the lab session) Reading: Chapter 4 We will use the labs to gradually develop a reasonably complete matlab simulator for a linearly modu- lated system. Thus, later labs will build on earlier ones. Background Figure 1 shows block diagrams corresponding to a typical DSP-centric realization of a communication transceiver employing linear modulation. In the labs, we model the core components of such a system using the complex baseband representation, as shown in Figure 2. Given the equivalence of passband and complex baseband, we are only skipping modeling of finite precision effects due to digital-to-analog conversion (DAC) and analog-to-digital conversion (ADC). These effects can easily be incorporated into Matlab models such as those we will develop, but are beyond the scope of the current set of labs. demodulation) Transmit filter (implemented at rate 4/T) I Q Digital streams rate 4/T Analog I Q Dnconverter ADC ADC filter (implemented at rate 4/T) DSP for receiver functions (includes coarse analog passband filtering) Upconverter Two-dimensional symbols rate 1/T I Q Digital streams rate 4/T DAC DAC I Q waveforms baseband Analog symbols Estimated waveforms baseband Passband Channel Receive (synchronization, equalization, Figure 1: Typical DSP-centric transceiver realization. Our model does not include the blocks shown in dashed lines. Finite precision effects such as DAC and ADC are not considered. The upconversion and downconversion operations are not modeled. The passband channel is modeled as an LTI system in complex baseband. A few points worth noting about the model of Figure 2: Choice of transmit filter: The PSD of the transmitted signal is proportional to | G TX ( f ) | 2 (see Chapter 4). The choice of transmit filter is made based on spectral constraints, as well as considerations such as sensitivity to receiver timing errors and intersymbol interference. Typically, the bandwidth employed is of the order of 1 T .
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