Saturday, September 25, 2010

Digital Communication Experiments

Summary: In this module, some digital communication experiments are performed using the NI-ELVIS workbench and the virtual exeriments available in the LanVIEW software.
EXPERIMENT NO: 1
ASK Generation
The method of generating the ASK waveform is given in figure 1.1, along with its corresponding output in figure 1.2.
Figure 1
Figure 1 (graphics1.png)
Figure 1.1: The circuit used to generate the ASK waveform
Figure 2
Figure 2 (graphics2.png)
Figure 1.2: The message signal with its ASK waveform
EXPERIMENT NO: 2
Sample-and-hold
The method of generating the sample and hold out is given in figure 2.1, along with its corresponding output in figure 2.2. Incidentally, LF-398 is a sample and hold IC.
Figure 3
Figure 3 (graphics3.png)
Figure 2.1: The circuit used to generate Sample-and-hold output
Figure 4
Figure 4 (graphics4.png)
Figure 2.2: The message signal with its corresponding Sample-and-hold output
EXPERIMENT NO: 3
BPSK
The ‘binary phase shift keying’ (BPSK), output can be obtained using the circuit of figure 3.1. An example output is contained in figure 3.2.
Figure 5
Figure 5 (graphics5.png)
Figure 3.1: The circuit used to generate BPSK output
Figure 6
Figure 6 (graphics6.png)
Figure 3.2: The binary message signal with its corresponding BPSK output
EXPERIMENT NO: 4
FSK
The ‘binary frequency shift keying’ (BFSK), output can be obtained using the circuit of figure 4.1. An example output is contained in figure 4.2.
Figure 7
Figure 7 (graphics7.png)
Figure 4.1: The circuit used to generate FSK output
Figure 8
Figure 8 (graphics8.png)
Figure 4.2: The binary message signal with its corresponding BFSK output
EXPERIMENT NO: 5
Natural sampling
The method of generating the ‘natural sampled’ signal is given in figure 5.1, while figure 5.2 has the output.
Figure 9
Figure 9 (graphics9.png)
Figure 5.1: The circuit used to generate ‘Natural-sampled’ waveform
Figure 10
Figure 10 (graphics10.png)
Figure 5.2: The message signal with its corresponding natural sampled output
EXPERIMENT NO: 6
Flat-top sampling
The method of generating the ‘flat-top-sampled’ signal is given in figure 6.1, while figure 6.2 has a typical input and corresponding output.
Figure 11
Figure 11 (graphics11.png)
Figure 6.1: The circuit used to generate ‘flat-top sampling’
Figure 12
Figure 12 (graphics12.png)
Figure 6.2: The message signal with its corresponding Flat-top sampled output
EXPERIMENT NO: 7
PAM-TDM
The method of generating the two channel pulse-amplitude-modulation time-division-multiplexed (PAM-TDM) output is given in figure 7.1, while a typical output is contained in figure 3, with figure 2 having the two message signals. A straight forward extension to include more analog channels is possible.
Figure 13
Figure 13 (graphics13.png)
Figure 7.1: The circuit used to generate two channel PAM-TDM
Figure 14
Figure 14 (graphics14.png)
Figure 7.2: The two message signals to be time division multiplexed.
Figure 15
Figure 15 (graphics15.png)
Figure 7.3: The carrier, and the corresponding PAM-TDM waveform
EXPERIMENT NO: 8
QPSK
The blocks used for the generation of quadrature phase shift keying (QPSK), output are given in figure 8.1, while the signals at various stages are contained in figures 8.2 through 8.4.
Figure 16
Figure 16 (graphics16.png)
Figure 8.1: The block diagram used to generate QPSK output
Figure 17
Figure 17 (graphics17.png)
Figure 8.2: The binary inputs to the BPSK modulators of figure 1 (the signals b1(t) and b2(t))
Figure 18
Figure 18 (graphics18.png)
Figure 8.3: The two inputs to the adder of figure 1 (the signals s1(t) and s2(t))
Figure 19
Figure 19 (graphics19.png)
Figure 8.4: The two BPSK waveforms along with the corresponding QPSK waveform

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