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Adaptive Wireless Tranceivers P10

In this chapter, the wideband AQAM scheme explored in the previous chapter is extended to incorporate the benefits of channel coding. Channel coding, with its error correction and detection capability, is capable of improving the BER and throughput performance of the wideband AQAM scheme. Since the wideband AQAM scheme always attempts to invoke the appropriate modulation mode in order to combat the wideband channel effects, probabilthe ity of encountering a received transmitted burst with a high instantaneous BER is low, when is advantageous, compared to the constituent fixed modulation modes | Adaptive Wireless Tranceivers L. Hanzo C.H. Wong M.S. Yee Copyright 2002 John Wiley Sons Ltd ISBNs 0-470-84689-5 Hardback 0-470-84776-X Electronic Chapter 10 RBF Equalization Using Turbo Codes In this chapter the wideband AQAM scheme explored in the previous chapter is extended to incorporate the benefits of channel coding. Channel coding with its error correction and detection capability is capable of improving the BER and throughput performance of the wideband AQAM scheme. Since the wideband AQAM scheme always attempts to invoke the appropriate modulation mode in order to combat the wideband channel effects the probability of encountering a received transmitted burst with a high instantaneous BER is low when compared to the constituent fixed modulation modes. This characteristic is advantageous since due to the less bursty error distribution a coded wideband AQAM scheme can be implemented successfully without the utilization of long-delay channel interleavers. Therefore we can exploit the error detection capability of the channel codes near-instantaneously at the receiver for every received transmission burst. Turbo coding 152 155 is invoked in conjunction with the RBF assisted AQAM scheme in a wideband channel scenario in this chapter. We will first introduce the novel concept of Jacobian RBF equalizer which is a reduced-complexity logarithmic version of the RBF equalizer. The Jacobian logarithmic RBF equalizer generates its output in the logarithmic domain and hence it can be used to provide soft outputs for the turbo decoder. We will investigate different channel quality measures - namely the short-term BER and average burst log-likelihood ratio magnitude of the bits in the received burst before and after channel decoding - for controlling the mode-switching regime of our adaptive scheme. We will now briefly review the concept of turbo coding. 10.1 Introduction to Turbo Codes Turbo codes were introduced in 1993 by Berrou Glavieux and Thitimajshima 152 155 . .