HowStuffWorks "How Silicon Makes a Solar Cell"

HowStuffWorks "How Silicon Makes a Solar Cell"

THEORY BEHIND GENERATION OF OFDM SUB-CARRIERS

                In my previous post I briefly explained the advantages of OFDM. But you may think how we can generate such closely aligned frequency spectrum. You may think that it would need several precise oscillators to    generate such orthogonal sub carriers. Your worry was true once in the past. That is why the OFDM (theory of which was proved in early 1960's) was out of the picture until late 1990's. But thanks to the rapid development of the Digital Signal Processors (DSP), OFDM became a feasible and practical technique in telecommunication in late 1990's. In this post I am trying to explain you the Discrete Algorithm which is behind this wonderful multiplexing scheme. In other words it is this algorithm which brought the DSPs into the OFDM.

INTRODUCTION TO OFDM

In order to avoid the frequency selective fading Frequency Division Multiplexing (FDM) is better when compared with the single carrier modulation schemes. Thus in FDM, frequency spectrum is divided into sub bands and each sub band carries data with low data rates. Hence when the signal is effected by frequency selective fading, only one sub band will be effected which results in minimal loss of data. But still FDM cannot overcome the multipath propagation. This is a tipical problem in domestic power line.

Orthogonal Frequency Division Multiplexing (OFDM) overcomes the fading due to multipath propagation using ‘cyclic prefix’. In OFDM the frequency spectrum is divided into subcarriers and each subcarrier is orthogonal to each other. This effectively reduces also the Inter Symbol Interferences (ISI).

The orthogonal property of the OFDM carriers is as shown below,

Figure: Orthogonal property of OFDM signals

Why I'm here..

It is the duty of every human being to share their knowledge. As a final year undergraduate of Engineering I thought that it's my time to do that job.
Insha Allah, I will present my understandings in the best way so that you will get them.
I'll be meeting you shortly with the best of the posts..Insha Allah.