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(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. OFDM is also used in land-based ADSL Internet service (see DSL).

OFDM Uses Subcarriers
Although frequency division multiplexing (FDM) by itself implies multiple data streams, OFDM carries only one data stream broken up into multiple signals. Hundreds of carriers are used; each one a "subcarrier" 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 OFDMA, carrier, bandwidth, CCK/OFDM and 8-VSB.
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References in periodicals archive ?
Tellambura, "Analysis of clipping noise and tone-reservation algorithms for peak reduction in OFDM systems," IEEE Transactions on Vehicular Technology, vol.
Zwick, "MIMO OFDM radar with communication and interference cancellation features," in Proceedings of the 2014 IEEE Radar Conference, RadarCon 2014, pp.
Finally, this continuous time domain OFDM signal is transmitted through power amplifier after filtering.
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 main function of the PTS method is that it divides the input OFDM signal into many sub-signals, each sub-signal is then multiplied by a specific, deferent weight, and this function is repeated until the needed value is reached.
[11] Kang S G, Kim J G, Joo E K, "A novel subblock partition scheme for partial transmit sequence OFDM," IEEE Transactions on Broadcasting, vol.
(2013) to mitigate the impulsive noise in the frequency domain through detection and sharing approach for OFDM demodulation.
Under narrow-band circumstance and for arbitrary target signal in space, the downconverted echoes of the OFDM array radar can be written as
where [S.sub.B](t) denotes the baseband OFDM signal, [N.sub.sc] denotes the number of subcarriers, [C.sub.k] denotes the information symbol or pilot symbol of the [k.sub.th] subcarrier, and [f.sub.k] is the frequency of the subcarrier.
To improve the data rate and range resolution, OFDM linear frequency modulation (LFM) signals based on fractional Fourier transform (FRFT) [11] and a random stepped-frequency (SF) OFDM signal based on correlation processing [12] have been given.