Adaptación de la comunicación y el diseño en el libro

1.1 ADAPTIVE COMMUNICATIONS AND THE BOOK LAYOUT

In order to justify the content of the book and to make suggestions on how the book should be studied, we start with the generic block diagram of a digital communication system shown in Figure 1.1.

The standard building blocks, information source, source encoder, encryptor, channel encoder and data modulator are used to produce a narrowband signal, for example, binary phase shift keying (BPSK), quaternary phase shift keying (QPSK) or M-ary quadrature amplitude modulation MQAM carrying information content. The spreading of the sig- nal spectra is obtained by real or complex multiplication of the narrowband signal by a code. After power amplification, the signal will be transmitted by one antenna or by multiple antennae (transmit diversity). After multipath propagation, multiple replica of the transmitted signal will reach the receiver. In a number of parallel processors (RAKE), the receiver will try to independently demodulate a number of signal replicas. The first step is signal despreading of the number of multipath components. To do so a channel estimator is needed to estimate the delays and amplitudes of these components in order to be opti- mally combined in coherent RAKE combiner. Prior to combining, cancelation of multiple access and multipath interference (MPI) may be performed in order to improve system performance. After signal combining, the remaining signal processing, including channel decoder, decryptor and source decoder, is performed. Separate block ‘channel + network’ characterizes the impact of fading, noise, network design and information broadcast from the network for control purposes.

On the basis of side information obtained either from the network or channel estimator, the receiver configuration control block from Figure 1.1 will put together the best possible receiver/transmitter parameters or even change the system configuration.

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