BA 371 VB.Net Assignment 2: Can You Hear Me Now?

The article Antennas Get Smart by M. Cooper (Scientific American, July 2003, pp. 48-55; available through OSU Libraries and the EBSCOhost database) describes how the signals of two or more transmitters operating at the same wavelength cause an interference pattern that includes both dead (zero signal) zones and zones that receive very strong signals.

In summary, if two transmitters are separated by a distance which equals half the wavelength at which they transmit (assume that both transmit at the identical wavelength), then antennas located in-line with the transmitters will not detect any signal, while antennas located perpendicular to the halfway point in the transmitter array will receive double the signal strength (see the picture below). The reason for this is that when an antenna is in-line with the transmitters the signals from the transmitters arrive 1/2 a wavelength out of phase and hence, cancel each other out. Conversely, when the distance between the antenna and the first transmitter equals the distance between the antenna and the second transmitter, the signals from both transmitters arrive simultaneously and hence, add up.

Similarly, when the distance between the transmitters becomes large compared to the wavelength at which they are broadcasting, a very complex interference pattern with a multitude of weak and strong signal zones results (see pictures below).


Signal strength at 1/2 wavelength separation of transmitters.

Signal strength at .5(m) wavelength.

For this assignment you must program a GUI that allows your user to locate two transmitters at arbitrary locations in a rectangular area, and which allows specification of the wavelength at which the transmitters are operating. After entering these data, the program computes the signal strength everywhere in the rectangular area.

Please carefully read all the matarial on this page and pay careful attention to the requirements stated below.

Click here for a demo version.

Requirements and allowances:

• Make sure that you understand the nature of the problem and the math relating to how two signals add up (read the relevant section in the SciAm paper!). If you don't understand the problem it is hard to write a program for it.
• Your program needs to accommodate only two transmitters.
• You should assume that the signals from the transmitters do not attenuate; i.e., signal strength does not diminish with distance.
• For the rectangular area, assume an isotropic, featureless plane across which the signals propagate. Ignore any signal blockage or reflection by the transmitters (assume that both the transmitters are points; i.e., they have no size).
  
• Your program must have a graphical, forms-based interface for specifying the locations of the transmitters, the broadcasting wavelength, and must indicate the dimensions of the rectangular area.
• Your program MUST be object-oriented. With this we mean to say that you MUST include a transmitter class. Transmitter objects of which your program creates two, privately(!!) store their X and Y coordinates.
• Each 'point' in the surrounding, rectangular area MUST be modeled as an object of the class antenna. Like a transmitter, an antenna has private(!!) positional information. Based on this information and the positional information of the transmitter, the antenna can compute its signal strength (this computation must be done by the antenna object itself!!).
• To compute signal strength S at a specific point (antenna) use the following (or equivalent) computation:

S = 1 + sin((π/2) + (abs(d₁ - d₂)/W * 2π))

where:

• W = wavelength.
• d₁ = distance from the antenna to the first transmitter.
• d₂ = distance from the antenna to the second transmitter.
• Scale the signal strength (between 0 (no signal) and 2.0 (double signal strength)) to the associated gray color ranging from RGB=0;0;0 (black) for signal strength 0 to RGB=255;255;255 (white) for signal strength 2.0.

• Make your program robust so that it catches and handles input errors; e.g., it should not accept negative wavelengths or nonnumeric positional information.

A few hints:

• For your signal strength map canvas, use a PictureBox object from the VB.Net Toolbox.

• To color a point in the rectangular area use a so-called Pen object.

• To set the color of the pen object, set its color attribute in RGB.
  
• The following code example shows you how you can set up a nested loop that visits all positions on your picture box and colors them according to signal strength. Notice how this assumes that you have a PictureBox1 object, an Antenna object called MyPhone and a pen object called RectanglePen. Also note that to color the 'pixel' we simply color a rectangle with width and height = 1.

  
          RectanglePen = New Drawing.Pen(Color.Black, 1)
  
          PBwidth = PictureBox1.Width   'Tells the for loop when to stop
          PBheight = PictureBox1.Height 'Tells the nested for loop when to stop
  
          For Xpos = 0 To PBwidth Step 1  'Loops through all X coordinates
              For Ypos = 0 To PBheight Step 1 'Loops through all Y coordinates at each X
                  MyPhone = New Antenna(Xpos, Ypos)   'Constructs a new antenna object at the coordinates
  
                  'Get the signal strength from the antenna object
                  SignalStrength = MyPhone.getSignalStrength(Trans1, Trans2)
  
                  'Convert the signal strength into an RGB color with 100% strength equal to RGB 255,255,255
                  ColorStrength = CInt(255.0 * (SignalStrength / 2.0))
  
                  'Set the pen color based on the signal strength
                  RectanglePen.Color = System.Drawing.Color.FromArgb(ColorStrength, ColorStrength, ColorStrength)
  
                  'Draws the rectangle at the given coordinates
                  PictureBox1.CreateGraphics.DrawRectangle(RectanglePen, Xpos, PBheight - Ypos, 1, 1)
              Next Ypos
          Next Xpos
          RectanglePen.Dispose()  'Disposes the pen object before creating a new one with a new color and a new size
  

• Note that when you move the program's window around on your screen while the program is running, or when you position another window on top of your program window and then remove it again, your canvas might not repaint itself properly. Although this can be fixed (notice that the demo program does not have this problem), this behavior is perfectly acceptable for this assignment.