Orthogonal frequency division multiplexing (OFDM)
Orthogonal frequency division multiplexing (OFDM) is one of the multi-carrier modulation (MCM) techniques that transmit signals through multiple carriers. These carriers (subcarriers) have different frequencies and they are orthogonal to each other. Orthogonal frequency division multiplexing techniques have been applied in both wired and wireless communications, such as the asymmetric digital subscriber line (ADSL) and the IEEE 802.11 standard.
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OFDM could be considered either a modulation or multiplexing technique; its hierarchy corresponds to the physical and medium access layer. A basic OFDM system consists of a QAM or PSK modulator/demodulator. The iterative nature of the FFT and its computational order makes OFDM ideal for a dedicated architecture outside or parallel to the main processor.
It is well known that Chang proposed the original OFDM principles in 1966, and successfully achieved a patent in January of 1970. Later on, Saltzberg analyzed the OFDM performance and observed that the crosstalk was the severe problem in this system. Although each subcarrier in the principal OFDM systems overlapped with the neighborhood subcarriers.
Using FPGA instead of an ASIC gives also flexibility for reconfiguration, which is a need for the Software Defined Radio (SDR) concept. Nowadays, wireless mobile communications have expanded dramatically all over the world, leading to a need to increase their bandwidth capacity. One way to increase the capacity of a wireless mobile communication system is to improve the communication technology. Orthogonal Frequency Division Multiplexing (OFDM) is considered the technology for the next-generation broadband wireless systems. As a matter of fact, it has been adopted for many standards.