18-10-2012, 05:27 PM
Mobile Computing
Mobile Computing .ppt (Size: 486 KB / Downloads: 80)
Spectrum and bandwidth
Electromagnetic signals are made up of many frequencies
Shown in the next example
The 2nd frequency is an integer multiple of the first frequency
When all of the frequency components of a signal are integer multiples of one frequency, the latter frequency is called fundamental frequency (f)
period of the resultant signal is equal to the period of the fundamental frequency
Period of s(t) is T=1/f
Fourier Analysis
Any signal is made up of components at various frequencies, in which each component is a sinusoid.
Adding enough sinusoidal signals with appropriate amplitude, frequency and phase, any electromagnetic signal can be constructed
Spectrum and bandwidth
It is the range of frequencies that a signal contains (among its components)
In the example, spectrum is from f to 3f
absolute bandwidth is the width of the spectrum
3f-f = 2f
Data Rate and bandwidth
There is a direct relationship between data rate (or signal carrying capacity) and bandwidth
Suppose we let a positive pulse represent 1 and negative pulse represent 0
Then the waveform (next slide) represents 1010..
Duration of each pulse is tbit = (1/2) (1/f)
Thus data rate is 1/ tbit = 2f bits/sec
As we add more and more frequencies the wave looks more like a square wave