Performance Enhancement of 802.11 based wireless Mesh Network by using Multi- Radio Multi-Channel

Er. Navneet Kaur CSE/IT Department

Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib

Punjab, India

Er. Jatinder Singh Saini CSE/IT department

Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib

Punjab, India

Abstract— Classical WMNs work in single-radio single-channel (SR-SC) architecture in which one network interface card (NIC) is deployed in each router and one common radio channel is shared by every mesh router. In this architecture, network endures from low capacity and throughput due to frequent back offs and packet collisions, hence single-radio multiple-channels (SR-MC) had been designed to enhance the WMNs performance. In SR-MC architecture every mesh router has to switch between channels dynamically with varying traffic load in the network, while integrating with adjoining mesh nodes to assure exchange of information for some period of time through a common channel but such coordination can be achieved by tight time synchronism among mesh nodes, but in a multihop WMNs it is difficult to achieve such synchronization among nodes. An adequate solution to reduce the high latency and simultaneously enhance throughput, reduce jitter and packet drop ratio of WMNs is to use Multi-Radio Multi-Channel (MR-MC) architecture. In MR-MC WMNs architecture, numerous communications can happen at the same time, and different channels assigned to adjoining links can carry data packets without interference. After implementing SR-MC WMNs and MR-MC WMNs in Qualnet simulator, results are evaluated based on parameters like throughput, jitter and packet receive ratio. Results show the significant difference between these two scenarios. MR-MC WMN provides the better result as compare to the SR-MC WMN. MR-MC WMN is much more suitable for the disaster management in the broadband internet application.

Keywords— WMN (Wireless Mesh Network), SR-SC (Single radio-Single Channel), SR-MC (Single radio-Multi Channel), MR-MC (Multi radio-Multi Channel).

I. INTRODUCTION Mesh topology and multiple hops in WMNs, has been excogitated as a fundamental technology for many applications in addition to community and neighborhood

networking, broadband home networking, metropolitan area networking and enterprise networking [2]. As shown in Fig. 1[1], the common WMNs framework consists of three different elements of wireless network: Mesh Clients (mobile or others), mesh gateway (mesh routers with gateway/bridge functionalities) and Mesh access points (router). Mesh clients connect to mesh routers with wireless or wired link. All mesh router broadcast data for rest of the mesh routers and some mesh routers have supplementary efficiency of being network gateways. These gateway routers are mostly connected via wired links which transmits the data from internet to the mesh routers.

Figure 1: Wireless mesh network architecture having basic network component Various bewitching advantages of WMNs are self-configuration, self-healing, enabling quick deployment, self-organization, cost effectiveness and easy maintenance. Many characteristics of wireless adhoc networks are inherited by WMNs but mesh routers are mostly fixed as compared to the. adhoc nodes. Thus, ad hoc networks are generally energy-strained, and energy proficiency is the main design objective whereas there is no energy constraint in mesh routers.

Classical WMNs work in single-radio single-channel (SR-SC) architecture in which one network interface card (NIC) is deployed in each router and one common radio channel is shared by every mesh router. In this architecture, network endures from low capacity and throughput due to frequent back offs and packet collisions, mostly for real-time applications such as CBR, VBR, VoIP transmission in multihop WMNs [3, 4]. In fact, the IEEE 802.11a and the IEEE 802.11b/g band yield 12 and 3 non-overlapping

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channels, respectively. Though there exist a great extent of interference in these non-overlapping channels in the current asset IEEE 802.11 hardware, by using improved frequency filters in hardware for multi-channel this problem can be solved. Hence, to enhance the performance of WMNs SR-MC WMN has been designed [5, 6]. On comparison with the SR-SC WMNs, the SR-MC WMNs helps to mitigate the interference, reduce the latency and network throughput is increased. In SR-MC architecture every mesh router has to switch between channels dynamically with varying traffic load in the network, while integrating with adjoining mesh nodes to assure exchange of information for some period of time through a common channel but such coordination can be achieved by tight time synchronism among mesh nodes, but in a multihop WMNs it is difficult to achieve such synchronization among nodes. Moreover, commodity hardware is not yet available with fast channel switching efficiency (in the order of 100 s). It is described that the delay in switching the channels by using the commodity hardware NICs of 802.11 can be 100 ms [7, 8].

An adequate solution to reduce the high latency and simultaneously enhance throughput, reduce jitter and packet drop ratio of WMNs is to use Multi-Radio Multi-Channel (MR-MC) architecture. In MR-MC WMNs architecture, numerous communications can happen at the same time, and different channels assigned to adjoining links can carry data packets without interference but with the use of MR-MC architecture there exist many channel assignment issues. When channels are assigned appropriately, it can upgrade the working of WMNs on interference reduction, connectivity, network capacity increase, energy efficiency, mobility resilience, etc.

A. Multi-radio multi-channel (MR-MC) WMNS

In MR-MC WMNs, every mesh router is deployed with multiple network interface cards and all NICs can work on multiple frequency channels. An example of MR-MC WMN with six wireless mesh routers (access points), five frequency channels and three NICs per router is shown in Fig 2. The number shows the designated channels that are reused spatially.

Figure 2: MR-MC WMN example

The MR-MC architecture has attracted attention of the researchers due to mitigated interference, high throughput and packet receive ratio and reduced jitter in wireless mesh networks. As specified earlier, available channels within the IEEE 802.11a and IEEE 802.11b/g frequency bands is limited

to 12 and 3 respectively. This signifies that same channels can be assigned to some logical links but the channel should be assigned properly so that the logical links having same channel should not be close to each other, otherwise it will increase the interference rate and thus the interfering links will not be active simultaneously. Moreover, the NICs accessible are bounded and hence NIC to transmit/receive the data packets have to share some logical links in a router. When the same NIC is used by two logical links in a router for communication, they require same frequency channel but they will not be active at the same time. Thus, it extremely mitigates their effective capacity. The capacity of active links can be increased by discarding some logical topology links. However, when some links are deactivated, it may increase the number of hops through some routing paths and may be some topological links are not connected properly. Therefore, many factors need to be examined in MR-MC like allocation of channels and interfaces, the number of logical links which should be assigned among the neighboring routers, and through which logical link the data packets should be forwarded.

Moreover, four important issues that should be considered in various constraints of MR-MC WMNs and physical topology of the routers are summarized in [11], i.e., interface assignment, formation of logical topology, routing and allocation of channels. Network connectivity and set of logical links is determined by the logical topology. Assignment of logical links to the NICs in every mesh router is decided by interface assignment. Active channel for every logical link is selected by the channel allocation algorithm. Lastly, the transmission of data packets should be done over which logical link is determined by routing.

After analyzing the issues mentioned above in the MR-MC architecture, current communication protocols designed need to be improved.

In WMNs the MAC protocols can be divided into two different groups: single-channel and multi-channel MAC protocols [13, 14]. Designing an adequate distributed multi-channel MAC protocol is challenging task in MR-MC WMNs. Although a lot of channel assignment algorithms already exists in MR-MC WMNs but still efficient channel assignment must be designed for maintaining the targeted topology and efficient spectrum utilization.

In routing layer, the routing protocols which are designed for ad hoc networks can be used in WMNs, but still designing efficient routing protocols for WMNs is an active area of research. In WMN routing algorithm needs to consider network topology to select interference free routing path and the routing path selection is intertwined with rate adaptation, avoidance of interference and resource allocation in multiple hops. An MR-MC routing protocols not only have to select a path among different mesh nodes [14], but it also needs to select the most appropriate channel or NIC in the network. The algorithms designed for routing should not only select the high-throughput logical links with less jitter, but also provide

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mitigated interference among adjoining nodes. Hence, MAC/routing joint optimization and efficient design of cross-layer are essential for MR-MC WMN [15].

II. RELATED WORK Several proposals have been made to modify the MAC layer to support multi-channel networks. The approach taken by most of this body of research is to and an optimal channel for a single packet transmission, essentially avoiding interference and enabling multiple parallel transmissions in a neighborhood in contrast to all these previous proposals, our architecture does not perform channel switching on a packet by-packet basis; our channel assignment lasts for a longer duration, such as several minutes or hours, and hence does not require re-synchronization of communicating network cards on a different channel for every packet. This property of our architecture makes it feasible to implement using commodity hardware of 802.11 standard. According to [18] Anan Prabhu Subramanian, Himanshu Gupta, Sanur R.Das, Jing Cao. Compares plots for dense and sparse networks and brings out interesting features. The fractional interference mitigates with increase in number of radios per node, however this trend permeate beyond a certain number of radios. This saturation point is reached smaller number of radios for sparse networks than for dense network for the same number of channels. This is because the denser network can potentially support more concurrent transmissions than the sparse network. According to [7] Ashish Raniwala, Tzi-Cker Chiuch purposed Multi-channel wireless mesh network architecture (called Hyacinth) is that equips each mesh network node with multiple 802.11 network interface cards (NIC’s). Comparison between the distributed and centralized channel assignment algorithms show that centralized channel assignment algorithm does not perform much better than the distributed ,this shows that the performance loss due to distribution of intelligence is very small. According to [6] P.Kyasanur and N.H. Vadiya mentioned that frequent channel switching in wireless mesh networks adversely affects the end-to-end delay performance. According to [5] A.Raniwala, K.Gopalan and T. Chiuch mentioned that with only one radio per node, channel switching is required. This switching delay grows as the number of channels is increased. For example the switching delay for the present 802.11 hardware ranges from a few milliseconds to a few hundred milliseconds.

III. PROBLEM FORMULATION Wireless mesh networking (WMN) is an emerging technology that enables multi-hop wireless connectivity to different areas where installing cables is expensive or difficult. Multicast is a form of communication that delivers information from a source to a group of destinations at the same time in an adequate manner. In a single-channel WMNs, all nodes share and communicate with each other through same channel. In such type of network, the throughput of multicast degrades

significantly as the network size increases. A node with a single half-duplex radio is restricted to access one channel at a time and thus cannot transmit and receive simultaneously. The use of single, half-duplex radio per node contributes to the rapid degradation of bandwidth and throughput in single-channel WMNs. One of the most effective approaches to achieve high throughput and packet receive ratio and to reduce jitter in WMNs is to use systems with multiple channels and multiple radios (MC-MR) per node. An MC-MR node may transmit and receive on different channels at the same time using two different radios, and thus increase the throughput and packet receive ratio and reduce the jitter. As Multi-channel Multi-radio overcome the problems of single channel wireless mesh network but still the channel interference problem is faced in this network so appropriate channel assignment techniques will used to overcome this channel interference problem to achieve the desirable outputs.

IV. EXPERIMENTAL SETUP The simulator used for the analysis is Qualnet. The terrain dimension is set to 1500 x 1500. Then 9 mesh nodes and two wireless subnets are placed on the canvas. One subnet is set to 802.11a radio type and this subnet is linked with 3 mesh nodes (node 1, 2 and 3) and other subnet is at 802.11b radio type and this subnet is linked with all the 9 nodes. Node 1, 2 and 3 are made as the mesh access points. Rest of the nodes is mesh points. The IEEE 802.11a and IEEE 802.11b/g standard provide 12 and 3 non-overlapping frequency channels respectively so the nodes attached with the 802.11a subnet are assigned three different non-overlapping channels of 802.11a band and the nodes attached with the 802.11b subnet are assigned three non-overlapping channels of 802.11b band. The CBR traffic is sent from node 7 to node 8 where node 7 is in the range of node 3 access point and node 8 is in the range of node 2 access point.

Figure 3 : Senario of MR-MC WMN

A. Simulation parameter The network designed contains basic network entities presented in table:-

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V. EXPERIMENTAL RESULT AND DISCUSSION After implementing SR-MC WMNs and MR-MC WMNs in Qualnet simulator various parameters like throughput, jitter and packet receive ratio was analyzed and the results obtained are shown below:

A) Throughput

a) Single-Radio Multi-Channel WMNs

Figure 4 : CBR Server Throughput (bits/s)

b) Multi-Radio Multi-Channel WMNs

Figure 5 : CBR Server Throughput (bits/s)

With the use of multi-radio multi-channel in WMNs the throughput is increased by 0.37 bits/s as compared to the use of single-radio multi-channel in WMNs because with the use of the multiple radio networks are able to make use of most frequencies available from the radio spectrum. This would give opportunity to do multi transmission at high speeds without clogging. . B) Jitter

a) Single-Radio Multi-Channel WMNs

Figure 6 : CBR Server Average Jitter (s)

Parameters Values

Area 1500*1500 m

Propagation channel

frequency

2.4 GHz

Propagation Model Statistical

Path loss Model Selection Two Ray

Shadowing Model Constant

Radio Type 802.11a,802.11b

Simulation Time 500 sec

Data Traffic Type CBR

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b) Multi-Radio Multi-Channel WMNS

Figure 7 : CBR Server Average Jitter (s)

In MR-MC due to the presence of multiple radios different channels can communicate simultaneously and with this the jitter in the network can be reduced. This is proved by the above graphs because in above graphs jitter in multi-radio multi-channel is reduced by 5.02 sec as compared to single-radio multi-channel WMNs due to multiple transmissions at the same time with less interference. C) Packet received Total packet sent in both the cases are 100 and the received packets are: a) Single-Radio Multi-Channel WMNs

Figure 8: CBR Server Total Packet Received

b) Multi-Radio Multi-Channel WMNs

Figure 9: CBR Server Total Packet Received

In multi-radio multi-channel the packet receive ratio is increased by 15% as compared to single-radio multi-channel WMNs because in MR-MC WMNs the access points and the client work on multiple radios so frequent channel switching is not required in this case as SR-MC WMNs which makes the network more reliable.

VI. CONCLUSION In this paper we have investigated different approaches and the possibilities for implementation of 802.11 based WMN to enhance performance in wireless multi-hop mesh networks. After analyzing a set of proposed solutions, a multi-radio multi-channel was chosen. This approach has many advantages as compared to single-radio multi-channel. Not only did it have to work, but optimizations had to be done to get a significant increase in performance compared to the classical single-radio single-channel setup. The various parameters like throughput, jitter and packet receive ratio of the wireless mesh networks can be upgraded extremely by using multi-radio multi-channel approach instead of using single-radio multi-channel approach with different data traffics like CBR, VBR, VoIP etc. Further this work can be extended by evaluating the performance of multi-radio multi-channel on scalability factor or by implementing any attack.

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