Page 431 - Complete Wireless Design

Wireless Issues

430 Chapter Ten

with the software completely controlling and changing the functions of the
radio (expected in about 2006).
As software-defined radio (SDR) exists today, albeit in a limited manner, we
will concentrate on this technology. A majority of SDRs consist of a transmitter
with an analog filter, SSPA, frequency conversion stage, and the digital stages
(Fig. 10.14). The receiver is constructed of an analog filter, LNA, frequency con-
version stage, and digital IF and baseband functions incorporating signal pro-
cessing hardware algorithms (Fig. 10.15). SDR architectures must be low-cost,
small, and easily configurable to different bands, protocols, bandwidths, and
modulation schemes in order to become pervasive.
There are two different kinds of software-defined radios.

Heterodyne SDR. As shown in Fig. 10.15, the antenna receives the RF signal,
which is then filtered, amplified, and converted to the IF by these analog
stages. A very fast ADC then converts the analog IF into a digital signal, where
the receive signal processor (RSP) filters and tunes the signal to the required
channel as required to provide baseband I and Q outputs to the DSP (digital
signal processor). This allows various channels, frequencies, and standards to
be placed within one radio. In fact, the RSP is where the SDR has its tuning
and selectivity, data rate, channel bandwidth, and even channel-shaping abil-

Figure 10.14 A software-defined radio transmitter.

Figure 10.15 A software-defined radio receiver.

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