2.3 Design Overview 1

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 Coexistence (under construction)

· Interaction between the core of CRCN simulator and GUI (under construction)

2.3.1 CR MAC/PHY

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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