Typically, we use Iris together with an off-the-shelf
highly flexible radio frequency front-end known as the Universal
Software Radio Peripheral (USRP), which depending
on the selected daughterboard can operate in transmitter/
receiver/transceiver mode on a multitude of radio frequencies
(see www.ettus.com). In such a configuration, baseband
in-phase and quadrature (IQ) signal samples are passed between
the USRP and the host PC, where Iris is running as
an application, using either Ethernet or USB connection. An
example radio constructed for the purpose of the experiment
is depicted in Figure 3. The radio consists of a single USRP
device connected over Ethernet to a host PC where Iris is
running. The constructed Iris radio is divided into two signal
paths: receiver and transmitter, which are responsible for
interactions with the USRP driver on the host PC and baseband
modulation/demodulation processes. Demodulated OFDM signal
samples are passed to the cyclostationary signature detector
and to the Whitespace MAC (WS-MAC) layer. The former
informs the Dynamic Spectrum Access (DSA) Controller about
the detection of a signature, and the latter reads the MAC
header of the received data to check whether the received
packet data unit (PDU) belongs to the control or the data
plane. All data packets are passed to an application, which
translates them to user readable format, for example a text
file or a video stream. All the components of the radio are
monitored by the Dynamic Spectrum Access Controller, which
collects reconfiguration events (e.g. signature detected) and
issues reconfiguration commands to specific components, e.g.
to Read/Write USRP - change the carrier frequency to N
GHz. For the purpose of the experiment we have implemented
two new Iris modules: the WS-MAC protocol and the DSA
Controller.