To support simulation in CR wireless network, several new
frameworks and functions are added in NS-3 for the functionality provided in
section 2. These frameworks and
functions are summarized as follows.
·
Design Overview of
CR MAC/PHY
·
Design Overview of
Spectrum Database
·
Design Overview of
Attack Model
·
Design
Overview of Coexistence (under construction)
·
Interaction
between the core of CRCN simulator and GUI (under
construction)
This
simulator provides simulation support for CR MAC/PHY. The functionalities
provided are listed as follow.
·
CR
multi-channel simulation environment
·
Interface
for channel decision
·
Able
to differentiate the common control channel and data channel
·
Interface
for transmission power decision
·
Interference
information
·
Traffic
information
The
supported functionalities for CR MAC/PHY in this simulator are shown in the
following diagrams.
1)
Contention based CR
MAC/PHY
Figure 2 depicts
contention based CR MAC and PHY implementation. For simplicity, the
developments of MAC/PHY in this version are based on the WIFI MAC/PHY implemented
in the original NS-3 packet. The components of WIFI MAC/PHY implementation shown
with dark boxes in figure 2 are modified to realize the cognitive features such
as spectrum sensing and the spectrum mobility. Later, we will provide a
specific CR MAC implementation (Game-theory based CR MAC [21]) as an example to
show how to integrate user defined CR MAC into our simulator. The descriptions
of modifications of each module are shown below:
a.
DCF
Manager
The
spectrum sensing notification is added in this module in order to invoke the
spectrum sensing function periodically triggered by the scheduler.
b.
MAC
Layer
The
packet queue and packet transmission are managed in the MAC Layer. Thus, once
the spectrum sensing is notified, the network node will transfer to the
spectrum sensing state, and the MAC layer will push the new packet into the
queue and hold the transmission.
c.
PHY
Layer
The
spectrum sensing is implemented in this module. In the current version, we
implemented the energy detection based spectrum sensing scheme wherein the CRCN
nodes periodically check the received signal energy over a specified channel
band
Figure 2. Data flow for contention based CR MAC/PHY
2)
Contention free CR
MAC/PHY
Following figure depicts the contention free CR MAC/PHY
implementation. In this implementation, the Dynamic Spectrum Allocation (DSA)
mechanisms are involved. Within the CRCN, DSA function calculates the optimal
transmission power for each user and assigns the channel bands to the users
targeting on maximizing the overall network performance. The available channel
bands are obtained from Spectrum Database. Considering the simple
implementation of the infrastructure based network, we consider the DSA module is
installed in the base station. Thus the spectrum sensing reports and other
information from users will be fed back to the DSA module. The utilization
status of channel bands will be updated in the spectrum database.
Figure 3. Data flow for contention free CR MAC/PHY
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