Design Overview for CR Routing

Users create the TCL script to configure the number of radios and channels needed for simulations. The basic idea is to create multiple radios or channels through the TCL library according to user’s script, which invokes the creation of several copies of LL, queue, MAC, NetIf, and channels for each radio in C++ library. The design overviews are shown through the following figures. The blocks with darker color are modified by CRCN to provide a complete solution.

A. Equal number of Radios and channels

Figure 2(a) shows the design for routing when the radio and channel are equals. In this design, the channel is created for each radio.

B. Single radio multi-channel

Figure 2 (b) shows the design structure for single-radio, multi-channel structures. Multiple channel copies are created for this structure. Although routing algorithms can still use the same design as shown in figure 2 (a) for single-radio multi-channel by checking the radios being used, existing MAC protocols in NS-2 need to be modified to support this checking. On the contrast, by adopting the design shown in figure 2 (b), new introduced routing algorithms for multi-channel, single-radio can use the existing MACs in NS-2 protocol stack, which is convenient to users.

C. Unequal number of radios and channels

Figure 2 (c) shows the design structure for multi-radio, multi-channel design with unequal number of radios and channels.

Due to the limitation of NS-2 design structure, the interface for routing and MAC algorithms to use the above structures are slightly different. Users can refer to the next following sections for more details.

There are some existing works [6][7][9] to enhance the NS-2 to support multi-radio multi-channel based on the design as shown in figure 2. However, there are several disadvantages for this kind of design if we only adopt them for CR simulation, which are listed as follows.

· MAC layer is not aware of multiple channels created for each radio. Channel selection must be made in routing layer instead of MAC layer, which is conflict with most current MAC protocol designs. Thus, additional work is required in MAC to support multiple channels in MAC, which can be found in next section 12.

· MAC layer address confliction is introduced by the related works.

· Since channels are created in the same way, these radios and channels have the same radio and spectrum characteristic, which is not sufficient to support the simulation in heterogeneous CR network.

· The radio and channel number are equal. Some routing and MAC algorithms simulations such as common control channel based algorithms are not supported if we only adopt the previous contribution work alone.

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