OFDMA_Part5 - (called an OFDM block/symbol to achieve high...

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5 (called an OFDM block/symbol) to achieve high data rates and the symbol time for an OFDM symbol is much larger than the channel’s delay spread to combat ISI. The evolution of OFDM began in the 1960s when Chang proposed the concept of multicarrier transmission in [2]. Weinstein and Ebert’s work in [3] laid the foundations of OFDM in the 1970s by proposing time-limited multicarrier transmission and the use of Discrete Fourier Transform (DFT) for OFDM. At the time they published their paper, Digital Signal Processors (DSPs) were slow, expensive, and experimental; however, today wireless devices have fast, small, power-efficient and cheap DSPs that can easily perform Fast Fourier Transform (FFT) calculations in software. In the 1980s, work was done in [4] [5] [6] [7] to reduce the effects of frequency offset and phase jitter in OFDM using frequency domain equalization. In 1985, Cimini’s insights and simulations in [8] brought the world closer to implementing OFDM for mobile wireless devices. In [8], Cimini discussed the use of pilot-based correction to account for distortion in a wireless channel.
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