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 1.1: The circuit used to generate the ASK waveform

Figure 2

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 2.1: The circuit used to generate Sample-and-hold output

Figure 4

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 3.1: The circuit used to generate BPSK output

Figure 6

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 4.1: The circuit used to generate FSK output

Figure 8

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 5.1: The circuit used to generate ‘Natural-sampled’ waveform

Figure 10

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 6.1: The circuit used to generate ‘flat-top sampling’

Figure 12

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 7.1: The circuit used to generate two channel PAM-TDM

Figure 14

Figure 7.2: The two message signals to be time division multiplexed.

Figure 15

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 8.1: The block diagram used to generate QPSK output

Figure 17

Figure 8.2: The binary inputs to the BPSK modulators of figure 1 (the signals b₁(t) and b₂(t))

Figure 18

Figure 8.3: The two inputs to the adder of figure 1 (the signals s₁(t) and s₂(t))

Figure 19

Figure 8.4: The two BPSK waveforms along with the corresponding QPSK waveform

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