What is FFT in OFDM?
Implementation of OFDM deals with application of Fast Fourier Transform (FFT) to modulation and demodulation processes to generate carriers orthogonal to each other. In conventional system, IFFT (Inverse Fast Fourier Transform) is used at transmitter side and FFT is used in receiver side.
Why FFT is used in OFDM transmitter?
At the receiver, we need to separate the components and demodulate them. So FFT is applied to transfer them back to the frequency domain where the same parallel symbols are obtained (which is called de-multiplexing). After that, a parallel-to-series block makes them a single bit stream again.
What are the main basis of OFDM system?
OFDM is based on the well-known technique of Frequency Division Multiplexing (FDM). In FDM different streams of information are mapped onto separate parallel frequency channels. Each FDM channel is separated from the others by a frequency guard band to reduce interference between adjacent channels.
Why do we use FFT and IFFT in OFDM?
FFT and IFFT are both two linear transformations on signals and are the reverse of each other. Hence applying FFT on a signal x followed by IFFT will reproduce x. The question becomes then why we use IFFT at transmitter and not FFT. Remember that signals need to be modulated by say N-QAM of the orthogonal subcarriers.
Which three types of QAM does OFDM support for wireless use?
Uses of OFDM This standard uses 64 subcarriers spaced by 312 kHz, which can be modulated with several different QAM variations: Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 16QAM or 64QAM. Mobile wireless systems employ OFDM to achieve high bandwidth channels.
What is OFDM system?
OFDM is a subset of frequency division multiplexing in which a single channel utilizes multiple sub-carriers on adjacent frequencies. In addition the sub-carriers in an OFDM system are overlapping to maximize spectral efficiency. Ordinarily, overlapping adjacent channels can interfere with one another.
Which standard uses OFDM process?
Orthogonal frequency division multiplexing (OFDM) is a modulation technique that is used in several applications ranging from cellular systems (3GLTE, WiMAX), wireless local area networks (LANs), digital audio radio, underwater communications, and even optical light modulation.
What is the difference between OFDM and OFDMA?
OFDMA stands for orthogonal frequency division multiplexing access. It is an extension of OFDM. The difference is that OFDMA is multi-user where OFDM is single-user. It has 3x higher throughput than single-user OFDM for short packets of data or multiple endpoints.
How is OFDM typically realized at the transmitter?
The inverse fast Fourier transform can therefore be used to realise the basic OFDM signal at the transmitter and the FFT can be used to recover (de-multiplex) the symbols at the receiver.