Can anybody kindly explain how the Orthogonal Frequency Division Multiple Access works and its advantages in simple English, avoiding using “Fourier”? I am totally confused about many descriptions that using “Fourier” things to explain. (Or if anyone can make “Fourier” things clearer to understand...)
In wireless it is common practice to view signal in time domain or frequency domain. For example, in time domain a simple sinusoid signal with a frequency of one Hertz (one cycle per second and hence time period of one second) shows that at the time axis sine wave will repeat itself after one second . We can view the same signal in the frequency domain as well, where it will be just a delta function at One Hertz frequency (in the frequency domain, the x-axis represent frequency and in time domain x-axis represents time). Think of the Fourier as a Tardis machine, you punch in some numbers on this machine and it will take you to frequency world to display how the same thing exist there and of course, you can get back to time world again by reversing the process which brought you in frequency world at the first place. So it is easy to see that a never ending time domain signal of time period one second is just represented by one point in the frequency domain.
What is orthogonality? To explain this, let us talk about things in frequency domain only. As usual, the signals are represented in complex numbers or complex exponentials. We can view these complex exponentials or signals in two-dimensional coordinates form as well which is called vector representation of a signal. A cosine wave of magnitude one in represented by (1 + 0 * i) or in vector form [ 1; 0 ] and Sine wave of magnitude one is represented by ( 0 + 1i ) or in vector form [0;1 ]. Two signals are said to be orthogonal if the dot product of their vectors is equal to zero. Hence cosine and sine waves are orthogonal to each other. Which simply means that if we view those two signals in time domain, there will be a moment when Cosine will be at its peak but at the same time Sine wave will be zero.
OFDM exploit this property of orthogonality and put information bits on those orthogonal signals at one time. Since signals are orthogonal, the receiver just needs to know the frequency and exact phase to retrieve all the information (by sampling process). This process provides protection against inter-symbol interference (ISI), the major advantage of OFDM technique. Also OFDM provides huge advantage in frequency selective Fading because it breaks wide band spectrum (carrier) into small chunks of spectrums (subcarriers).
Hope it might help.