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Wireless communication systems were initially designed primarily for voice services. First generation cellular systems were analog in nature, thus unsuitable for data transmission. The driving force for the second (digital) cellular generation was increased capacity to accommodate the high demand for new customers. The explosion of Internet usage, with the ever increasing demand for the downloading of large bulks of data in multimedia services, on the one hand, and the gradual predominance of wireless communication over the wired one, on the other hand, made second generation cellular systems fully inadequate. For this reason, third and even more fourth generation were designed focusing on multimedia Internet, rather than voice services. The resulting, high data rates that are needed to satisfy the users' requests, together with the severe limitations in the available bandwidth devoted to cellular services, force wireless communication systems to face ever increasing challenges on severe bandwidth and energy constraints. The present and future of wireless communications is then dependent on the possibility of fully exploiting the available bandwidth by increasing as much as possible the efficiency of its use. Moreover, the time-varying characteristics of the wireless channel, and its frequency selectivity induced by the multipath fading, pose severe challenges to the system designer in order to cope with the high quality of service required for multimedia applications. Very recent tools like adaptive coding and modulation, multi-antenna transmitter and receiver (MIMO), turbo and LDPC codes, iterative co-decoding and reception techniques based on the turbo principle are revolutionizing the theory and practice of digital communication.
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