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Phil Edholm of Nortel Networks laid down the law where wireline, nomadic, and wireless networks improve like the all-pervasive Moore’s law (Cherry, 2004). Figure 1 depicts that data rates increase against the timeline, at the same exponential rate for all three network modes. From the figure, it can be inferred that the wireless data rates have doubled every 18 months over the last three decades. To meet the demands on data rates for broadband communication systems, orthogonal frequency division multiplexing(OFDM) has proven to be a disruptive technology (Frederiksen et al.,2002). OFDM is essentially a multicarrier modulation(MCM) technique, where long symbol time results in greater immunity to noise and fading (J Bingham, 1990). Thus, it converts a high rate data stream into a set of parallel low data rate streams which can be quickly equalized (Molisch, 2005). Owing to its efficient algorithm, it combats Inter-Symbol Interference(ISI), which is a major impediment in the wireless channel with minimal complexity (Schmiter, 2004). By transforming a wideband channel into a set of parallel narrowband channel, it increases the symbol time (
) of the signal such that it exceeds the maximum channel delay spread (
). The unanimous choice of OFDM as multiple access technique is due to its inherent ability to convert a wideband frequency selective channel into many parallel flat fading channels. OFDM enjoys numerous advantages over its counterpart technologies like Time Division Multiple access(TDMA) and Code Division Multiple access(CDMA). Amongst its many benefits, high spectral efficiency and adaptability for broadband data transmission, resistance to ISI caused by multipath fading, natural support for Multiple Input Multiple Output(MIMO) are the key ones (Zarrinkoub, 2014).
Evolution of OFDM: The principle of orthogonal multiplexing for transmitting multiple data messages simultaneously through a linear band-limited transmission medium at a maximum data rate without inter-channel and inter-symbol interferences was first proposed by Robert W Chang (1966). Saltzberg (1967) analyzed the performance of parallel data stream for orthogonal Quadrature Amplitude Modulation (QAM). By this method of data transmission, Saltzberg demonstrated that speeds very close to the Nyquist rate of bandlimited channels could be realized without the use of sharp cut-off filters. Moreover, the use of a vast number of parallel narrowband channels was able to combat the deleterious effects of delay and amplitude distortion of the transmission medium.