TAILIEUCHUNG - Digital communication receivers P13

Receiver Structures for Fading Channels In this chapter,realizablereceiverstructures synchronized for detectionon flat and selective fading channelsare derived and the interaction betweensynchronizationand detectionpathsat a minimum results in receiversof low complexity. As motivated below, we shall concentrate the so-calledinner on receiver, its components,and the necessary synchronizationtasks. Outer and Inner Receiver for Fading Channels In compliancewith Shannon’sthird lessonlearnedfrom information theory: “make the channel look like a Gaussianchannel” [ 11, we have distinguished between an outer and inner receiver [2] in the introduction of this book. The sole - yet by no meanstrivial - task of the inner. | Digital Communication Receivers Synchronization Channel Estimation and Signal Processing Heinrich Meyr Marc Moeneclaey Stefan A. Fechtel Copyright 1998 John Wiley Sons Inc. Print ISBN 0-471-50275-8 Online ISBN 0-471-20057-3 Chapter 13 Receiver Structures for Fading Channels In this chapter realizable receiver structures for synchronized detection on flat and selective fading channels are derived and discussed. Keeping the interaction between synchronization and detection paths at a minimum results in receivers of low complexity. As motivated below we shall concentrate on the so-called inner receiver its components and the necessary synchronization tasks. Outer and Inner Receiver for Fading Channels In compliance with Shannon s third lesson learned from information theory make the channel look like a Gaussian channel 1 we have distinguished between an outer and inner receiver 2 in the introduction of this book. The sole - yet by no means trivial - task of the inner receiver has been identified as attempting to provide the decoder with a symbol sequence that is essentially corrupted by white Gaussian noise only. If this can be accomplished the inner transmission system serves as a good channel for the outer transmission system . the source and possibly channel decoding system. If the channel is nonfading and Gaussian the inner receiver aims at delivering an optimally preprocessed and synchronized signal typically the matched filter output sequence àk ak mk serving as an estimate of the symbol sequence and sometimes termed soft decision . If the inner receiver were perfect . perfect frequency timing and phase synchronization matched filtering and decimation to symbol rate no loss of information would entail. In practice the imperfections sync errors word-length effects etc. translate into a slight increase of the noise power as seen by the outer receiver . a small SNR loss. In the case of fading channels the situation is more intriguing since .

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