ABSTRACT
Contents 3.1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
3.1.1 OFDM in Wireless Broadband Communication Systems. . . . . . . . . . . . . . . . . . . . . . . . . 42 3.1.2 OFDM Challenges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
3.1.2.1 Spectrum Efficiency in Wireless Broadband Communication Systems. 43 3.1.2.2 Nonlinearity in RF Power Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
3.2 IEEE 802.11a Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 3.3 Nonlinearity of RF Amplifier in WLAN OFDM Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.4 Model Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3.4.1 802.11a OFDM Signal Equivalent Mathematical Model . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.4.2 High-Power Amplifier’s Mathematical Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.5 PSD of Amplified 802.11a OFDM Signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.6 Design Example and Comparison with Simulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
3.1 Introduction Marconi’s innovative perception of the electromagnetic waves for radio transmission in 1897 was the first milestone on the important road to shared use of the radio spectrum. But only after almost a century did mobile wireless communication start to take off. The communication world in the
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late 1980s was rapidly becoming more mobile for a much broader segment of communication, users than ever before. Today, the spectacular growth of video, voice, and data communications over the Internet and the equally rapid growth of mobile telephony justify great expectations for mobile multimedia. Research and development are taking place all over the world to define the next generation of wireless broadband communication systems. These may create a “global information village,” which consists of various components at different scales ranging from global to cellular. Present communication systems are primarily designed for one specific application such as speech on a mobile telephone or high-rate data in a wireless local area network (WLAN). Supporting such large data rates with sufficient robustness against radio channel impairments requires careful choosing of modulation techniques. The most suitable modulation choice seems to be orthogonal frequency division multiplexing (OFDM).
