tailieunhanh - Adaptive thu phát không dây P1

In recent years the concept of intelligent multi-mode, multimedia transceivers (IMMT) has emerged in the context of wireless systems [l-61. The range of various existing solutions that have found favour in already operational standard systems was summarised in the excellent overview by Nanda et al. [3]. The aim of these adaptive transceivers is to provide mobile users with the best possible compromise amongst a number of contradicting design factors, such as the power consumption of the hand-held portable station (PS), robustness against transmission errors, spectral eficiency, teletrafic capacity, audiohideo quality and so forth [2] | Adaptive Wireless Tranceivers L. Hanzo . Wong . Yee Copyright 2002 John Wiley Sons Ltd ISBNs 0-470-84689-5 Hardback 0-470-84776-X Electronic Chapter Prologue Motivation of the Book In recent years the concept of intelligent multi-mode multimedia transceivers IMMT has emerged in the context of wireless systems 1-6 . The range of various existing solutions that have found favour in already operational standard systems was summarised in the excellent overview by Nanda et al. 3 . The aim of these adaptive transceivers is to provide mobile users with the best possible compromise amongst a number of contradicting design factors such as the power consumption of the hand-held portable station PS robustness against transmission errors spectral efficiency teletraffic capacity audio video quality and so forth 2 The fundamental limitation of wireless systems is constituted by their time- and frequencydomain channel fading as illustrated in Figure in terms of the Signal-to-Noise Ratio SNR fluctuations experienced by a modem over a dispersive channel. The violent SNR fluctuations observed both versus time and versus frequency suggest that over these channels no fixed-mode transceiver can be expected to provide an attractive performance complexity and delay trade-off. Motivated by the above mentioned performance limitations of fixed-mode transceivers IMMTs have attracted considerable research interest in the past decade 1-6 . Some of these research results are collated in this monograph. In Figure we show the instantaneous channel SNR experienced by the 512-subcarrier OFDM symbols for a single-transmitter single-receiver scheme and for the space-time block code G2 7 using one two and six receivers over the shortened WATM channel. The average channel SNR is 10 dB. We can see in Figure that the variation of the instantaneous channel SNR for a single transmitter and single receiver is severe. The instantaneous channel SNR may become as low as 4 dB due to deep