Software Defined Radio: Enabling Technologies

6

The Digital Front End – Bridge Between RF and Baseband Processing

Tim Hentschel and Gerhard Fettweis

Technische Universität Dresden

6.1 Introduction

6.1.1 The Front End of a Digital Transceiver

The first question that might arise is: What is the digital front end? The notion of the digital front end (DFE) has been introduced by the author in several publications (e.g. [13]). Nonetheless it is useful to introduce the concept of the DFE at the beginning of this chapter.

Several candidate receiver and transmitter schemes have been presented by Beach et al. in Chapter 2. They all have in common that they are different from the so-called ideal software radio insofar as the signal has to undergo some signal processing steps before the baseband processing is performed on a software programmable digital signal processor (DSP). These signal processing stages between antenna and DSP can be grouped and called the front end of the transceiver.

Historically, the notion of a front end was applied to the very part of a receiver that was mounted at or near the antenna. It delivered a signal at an intermediate frequency which was carried along a wire to the back end. The back end was possibly placed apart from the antenna. In the current context the notion of the front end has been undermined a bit and moreover extended to the transmitter part of a transceiver. The functionality of the front end can be derived from the characteristics of the signals at its input and output. Figure 6.1 shows the ...