**5.2. Network topologies**

Three types of topologies are used in the evaluation. Each topology consists of 36 mesh nodes distributed in an area of 500x500 meters.

Topology 1 is a grid topology; Topology 2 is a randomly generated topology while in Topology 3, called controlled random, the physical terrain is divided into a number of cells and a mesh node is placed randomly within each cell.

**Figure 7.** Failure Recovery Mechanism of TICA

channel assignment schemes is also given.

**5.1. Simulation environment** 

interfere with each other.

the MPSPT.

Assignment" (CCA) scheme for multi-radio mesh nodes. The detailed results of simulations for performance evaluation of TICA based on throughput analysis of a 36-node network are presented, and analyzed. The features' comparison of TICA with related well known

For the performance evaluation via throughput analysis, NS2 (version 2.30) [26] simulation tool is used. However, MATLAB [27] is used to generate the power controlled topology, the MPSPT graph, the link ranking of the MPSPT and the channel assignment for the links of

Multi-interface wireless mesh nodes are created in NS2 by modifying the built-in IEEE 802.11 node model in NS2, using the procedure given in [28]. Based on the channel assignment by the gateway, the radio interfaces are configured for each node and the transmission power for each radio of each mesh node is set accordingly. All the mesh nodes at the periphery of the network send traffic to the gateway. Each of these nodes generates an 8 Mbps Constant Bit Rate (CBR) traffic stream consisting of 1024 byte packets, and sends data to the gateway node at the same time. They do not stop transmitting until the end of the simulation. So, this is a scenario in which multiple flows within the mesh network

All radios are IEEE 802.11a radios and support 12 channels. The first 11 non-overlapping channels are used by the data radios, whereas the 12th channel is used by the control radio on each node. If the distance between the nodes is less than the cross-over distance, free space propagation model is used; if the distance between the nodes is greater than the crossover distance, two-ray propagation model is used. As per [4], the minimum receiver sensitivity (*RxThresh*) is set to -65 dBm ( -10 3.16227 10 Watts) in order to achieve a

In order to achieve a strongly connected topology, the maximum transmission power for all the radios is set to 27 dBm. The maximum power transmission range is 164 meters and the maximum power interference range is 328 meters. RTS/CTS is disabled. Note that in the CCA and SRSC schemes, the mesh nodes do not control their power, transmit with the same maximum power (27 dBm) and use AODV (Ad hoc On-Demand Distance Vector) [29]

Three types of topologies are used in the evaluation. Each topology consists of 36 mesh

Topology 1 is a grid topology; Topology 2 is a randomly generated topology while in Topology 3, called controlled random, the physical terrain is divided into a number of cells

maximum data rate of 54 Mbps supported by IEEE 802.11a.

routing protocol as their routing agent.

nodes distributed in an area of 500x500 meters.

and a mesh node is placed randomly within each cell.

**5.2. Network topologies** 

Grid Topology (GT) is used to evaluate TICA in a densely populated topology. Random Topology (RT) is used to evaluate TICA in an unplanned deployment of randomly and uniformly distributed mesh nodes. Controlled Random Topology (CRT) is used to reflect realworld deployments where mesh routers are uniformly distributed for maximum coverage.

Channel Assignment Using Topology Control Based on Power Control in Wireless Mesh Networks 69

6

(7)

All the mesh nodes at the periphery of the network send traffic to the gateway. Each of these nodes generates an 8 Mbps Constant Bit Rate (CBR) traffic stream consisting of 1024 byte packets and sends data to the gateway node at the same time. They do not stop transmitting

The Average Throughput (AT) in Mega bits per second at the gateway node is calculated

8 1024

( ) 1 10

*TrafficStopTime TrafficStartTime* 

Figure 8 shows a graphical comparison of the average throughput of all schemes for ten random topologies. The results in this figure clearly indicate that the proposed algorithm

Figure 9 shows a graphical comparison of average throughput of all schemes for ten controlled random topologies. The results in this figure clearly indicate that the proposed algorithm TICA

The placement of the nodes and hence, the length of links in the MPSPT of a topology affects the interference range and hence, the channel assignment. In random and controlled random topologies, the random placement of nodes results in variation in the length of links in the MPSPT. This results in LICs, which may cause significant interference in the network

Figure 10 shows the comparison of average throughput of all schemes for the three

Note that for random and controlled random topologies in Figure 10, the average throughput is the average over ten different random and controlled random topologies, respectively. Figure 10 shows that as compared to the CCA scheme, the throughput improvement with TICA is 3 times for random topology, 11 times for controlled random topology and 12 times for grid topology. In comparison to the SRSC scheme, the throughput improvement with TICA is 8 times for random topology, 95 times for controlled random

The results in this figure clearly indicate that the proposed algorithm, TICA, significantly

topologies (random, controlled random and grid) for a network of 36 nodes.

TICA significantly outperforms other schemes for all different random topologies.

significantly outperforms other schemes for all different controlled random topologies.

until the end of the simulation, which is 600 seconds (10 minutes).

*TPR AT*

Note that *TPR* is the Total Packets Received in (7).

*5.3.2. Simulation results* 

**a. Random Topology** 

**b. Controlled Random Topology** 

and degrade the overall throughput.

topology and 133 times for grid topology.

outperforms other schemes for the three topologies.

**c. Throughput Comparison for the three topologies** 

using the following formula:

### **5.3. Simulation results based on throughput analysis**

#### *5.3.1. Simulation parameters*

The physical layer and MAC layer settings of the node which are used during the simulation are shown in Tables 1 and 2, respectively. Note that out of the 12 available nonoverlapping 802.11a channels, 11 channels are used for data traffic and channel 12 is used for control. Based on the channel assignment by the gateway node, IEEE 802.11a channels are assigned to the links between the mesh nodes and transmission power for each radio of each mesh node is set accordingly.


**Table 1.** Physical layer node configuration in NS2

As mentioned earlier, the maximum transmission power for all the radios is 27 dBm. In the CCA and SRSC schemes, MRs do not control their power, transmit with the same maximum power (27 dBm), and use AODV (Ad hoc On-Demand Distance Vector) routing protocol as their routing agent.


**Table 2.** MAC layer node configuration in NS2

All the mesh nodes at the periphery of the network send traffic to the gateway. Each of these nodes generates an 8 Mbps Constant Bit Rate (CBR) traffic stream consisting of 1024 byte packets and sends data to the gateway node at the same time. They do not stop transmitting until the end of the simulation, which is 600 seconds (10 minutes).
