Radio Engineering: From Software Radio to Cognitive Radio

Chapter 8Transmitter/Receiver Digital Front End¹

The contents of this chapter are principally dedicated to the digital signal processing carried out between the antenna and the classical baseband signal processing. This corresponds to the function called digital front end (DFE) depicted in Figure 6.5. Even if the content is applicable to all software-defined radio (SDR) architectures presented in Chapter 6, it is much more easily apprehendable in the context of low intermediate frequency (IF) SDR architecture, as shown in Figure 6.9. Therefore, the sampled wideband signal includes a large number of channels that may go up to a complete standard for a base station that simultaneously processes all the channels. Among these, the channel of interest may lie anywhere in the band on an arbitrary carrier frequency. This concept of DFE was originally proposed by Tim Hentschel and Gerhard Fettweis in several papers and in Chapter 6 of [TUT 02]. The boundary between the functions of the analog front end (AFE) (Chapter 7) and DFE (Chapter 8) depends only on the performance of the converters, and hence, on the sampling frequency. Depending on the functions performed by the AFE, the DFE will differ and will have more or less strong constraints to be respected. Figure 8.1 shows the three functions that must be realized by DFE. Note that the order of the functions is not necessarily as follows:

– modulation/demodulation or transposition on in-phase and quadrature phase channel (I/Q), often called ...