OFDM

» It stands for Orthogonal Frequency Division Multiplexing.

» It is used for data transmission over radio broadcast channel and wireless communication channel.

» For finite length of channel

    
The channel order l is known at the transmitter while h(k) are still unknown.The partial channel information,the particular transmission techniques is known as orthogonal frequency division modulation can be implemented at transmitter where T is symbol duration and sampling period.

is frequency response of channel h(kT).

ORTHOGONALITY:

The peak of each signal concides with through of other signals.

Principle:

Basic Idea: Channel bandwidth divided into multiple subchannels to reduce ISI and frequency selective fading.

Multicarrier Transmission: Subcarriers are orthogonal to each other in frequency domain.

Time Domain Spreading: Spreading is achieved in time domain by repeating the same information in a OFDM symbol on two different jb bands .

Frequency Domain Spreading: Spreading is achieve by choosing congugate symmetric input for input to IFFT.

Theory: The baseband OFDM signal can be written as .

Cont....