Friday, August 19, 2016

Orthogonal Frequency Division Multiplexing (OFDM) Overview


Orthogonal Frequency Division Multiplexing (OFDM) OverviewIn the recent years, the demand for higher data rate services such as multimedia, voice, and data traffic over both wired and wireless links increased tremendously with the advancement of information and communication technology. To transfer large amount of data required new modulation techniques which were not supported by theexisting 3rd generation (3G) schemes such as CDMA 2000 and Wideband Code Division Multiple Access (WCDMA). Meanwhile, a form of multi-carrier modulation called Orthogonal Frequency Division Multiplexing (OFDM) received significant attention.

Orthogonal Frequency Division Multiplexing (OFDM) OverviewSome unique features offered by OFDM like its resistance to frequency selective fading make it comparable to single carrier systems. Usually, the data rate is increased by the single carrier systems with the expense of increased occupied bandwidth and decreased symbol duration. Therefore, wideband channels require complex equalizers to recover the original transmitted signal at the receiver side because these channels are very sensitive to frequency selective fading. OFDM splits the wide-band channel into a sequence of narrow-band channels that experience flat fading. Such arrangements then demands only single tap equalizers at the receiver side, reducing complexity significantly. Although, OFDM has many advantages over single carrier systems; however, it still suffers from many issues, i.e. sensitivity to carrier frequency offset and large Peak to Average Power Ratio(PAPR). The superposition of “N” independent equally spaced subcarriers at the Inverse FastFourier Transform (IFFT) at transmitter side produces large PAPR in time domain signal. If large PAPR is retained at transmitter side, it saturates High Power Amplifier (HPA) which in turn
produces undesirable distortion and out-of-band radiation and also degrades the Bit Error Rate
(BER) performance at the receiver side. Therefore, it is essential to find a way of reducing large
PAPR that allows for a more efficient HPA.

© Muhammad Shahab Shah -Thesis page no 1 -- COMPARATIVE PERFORMANCE ANALYSIS OF COMPLEX AND NON-COMPLEX VERSIONS OF SLM AND PTS PAPR REDUCTION SCHEMES IN OFDM SYSTEMS

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