OFDM


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OFDM

(Orthogonal Frequency Division Multiplexing) A digital transmission technique that uses a large number of carriers spaced apart at slightly different frequencies. First promoted in the early 1990s for wireless LANs, OFDM is used in many wireless applications including Wi-Fi, WiMAX, LTE, ultra-wideband (UMB), as well as digital radio and TV broadcasting in Europe and Japan. It is also used in land-based ADSL (see OFDMA).

Although frequency division multiplexing (FDM) implies multiple data streams, orthogonal FDM carries only one data stream broken up into multiple signals. Hundreds or thousands of carriers, known as "subcarriers," are used for a single data channel.

Lower Speeds - Easier Detection
The multiple subcarriers enable the receiver to more easily detect the signals in environments with multipath and other interference. In addition, each subcarrier can transmit a lower-speed signal, all of which are aggregated at the receiving side into the original high-speed signal. Lower speed signals are also more easily deciphered at the receiving end.

OFDM subcarriers can be modulated by any method, although QAM and QPSK are typically used (see QAM and PSK). Coded OFDM (COFDM) adds forward error correction. See carrier, bandwidth, CCK/OFDM and 8-VSB.
References in periodicals archive ?
The OFDM signals from both X and Y polarization Directions need to be converted from a RF signal to an optical signal through the RF to optical converter system (RTO), each consist of two mach-zehender modulators and a CW laser source, polarization splitter and combiner are used before and after this process.
The basic theory of conventional OFDM and WOFDM system share many similarities in terms of their functions [1,3,10].
Furthermore, the OS-clipping scheme used in the OFDM-OQAM system even shows better performance than the OFDM system with the conventional clipping scheme.
The system design environment provides flexible OFDM models for quickly constructing the necessary signals.
Figure 3 shows block diagram of a MIMO OFDM system with 2 transmit and 2 receive antennas according to which simulation is done.
The OFDM Forum is a market development association comprised of hardware manufacturers, software firms, telecommunications companies and other users interested in Orthogonal Frequency Division Multiplexing (OFDM) technology in wireless applications.
flash-OFDM can be likened to putting time-division multiple access on top of OFDM, yielding all the benefits of both technologies in terms of robustness under mobility and channel-delay spreads, interference averaging from other cells, and orthogonality inside the cell.
Microsoft has also indicated its support for the forum's goal of delivering a single OFDM standard.
OFDM signal is made up of unfiltered QAM subcarriers which mean following a sinc function, the edges of spectrum drop-offs tardily, to establish the spectrum drop-off quicker; windowing is applied to the OFDM signal.
The proposed OFDM wireless system and its algorithm are described in section III.
OFDM also has no interference between users in the same cell, and interference from users from adjacent cells is averaged effectively via hopping patterns (see Figure).