Simulate White Gaussian Noise and Compression with LabVIEW Modulation Toolkit

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Various forms of distortion and noise are often introduced into Communications Systems due to the non-linearity of the components as well as interference from natural phenomena. This VI seeks to simulate Additive White Gaussian Noise (AWGN) and Compression. A single tone signal is generated along with the options in introduce compression and AWGN. The resulting signal is then visualized from three different viewpoints: Constellation Diagram, RF Time-Domain, and Frequency Domain. Additive White Gaussian Noise (AWGN) is most often introduced from a natural source such as thermal vibrations and black body radiation. It is commonly used to model satellite communication systems. While not a good model for surface systems due to multipath, terrain blocking, and interference etc, AWGN is often used to simulate background noise in a system. It can also be used to simulate jitter and resulting timing errors in serial communications.

Compression distortions are usually caused by non-linearity within the physical device being used for communication.

This following demonstration will simulate a single tone and the effect of introducing Additive White Gaussian Noise and Compression. These are common sources of interference seen in today’s communication systems.

1. First, open the “Comm System with Compression.vi” and run the program. Notice that there are several parameters available for controlling the simulation. We will start with the main option tabs. These are to the left of the interface and include AWGN, Modulation, and Distortion. Within these tabs you have the ability to configure the generated signal, along with the simulated interference.
   
   
2. The AWGN tab allows you to control whether or not you are taking AWGN into account in the system. You have the option of increasing or decreasing ratio of Energy per Bit (E_b) to the Spectral Noise Density (N₀).
3. The modulation tab allows you to increase or decrease the magnitude of the system. The modulation type can also be set to the following options: 4, 8, 16, 32, 64, 128, and 256 - Quadrature Amplitude Modulation (QAM). You also have the option of modeling the system as linear or non-linear. We will look at how you can customize the distortions from non-linearity in the next step. You also have the reset option for your signal in this tab.
4. The Distortion tab allows you to customize the five coefficients responsible for simulating non-linearity distortion.

Next we will look at the tabulated options on the right side of the interface. These options concern the different ways you can view the system being simulated. There is also a configuration tab which allows you to set the symbol rate of the system.

1. The first tab allows you to view the system via a constellation diagram. This displays the signal in terms of a two-dimensional scatter diagram. It displays the possible symbol in a given digital modulation in the complex plain. You will also be able to see the error vector magnitude (EVM) with the given modulation scheme.
   
   
2. The next tab allows you to view the signal in the RF time-domain.
   
   
3. You also have the option of viewing the signal in the frequency domain via a Fast Fourier Transform (FFT).
   
   
4. The fourth tab allows you to view the non-linearity of the model based upon the distortion coefficients set in the previous section of the program.
   
   
5. The final tab allows you to control the Symbol rate in Hz between the range of 1MHz and 10 MHz. It is important to note that this setting can only be changed when the program is not running.