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Hybrid Multi-Channel Assignment for Heterogonous Wireless Mesh Network

P.Kanaga valli1, Mrs.S.Muthu Lakshmi, M.E.,(Ph.D.).,2
  1. Department of Electrical Electronics Engineering, Syed Ammal Engineering College, Ramanathapuram, India
  2. Assistant Professor, Department of EEE, Syed Ammal Engineering College, Ramanathapuram, India.
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Wireless mesh networks offer many advantages in terms of connectivity and reliability. Traditionally, Wireless mesh networks based on either purely static or dynamic channel allocation approaches in wireless mesh network. However, there are limitations in wireless mesh networks, such as lower through-put and delay in the channel allocation scheme. This paper is focus on the hybrid multichannel multiradio wireless mesh networking architecture, where each mesh node has both static and dynamic interfaces which efficiently utilizes multiple wireless interfaces to achieve better throughput. Adaptive Dynamic Channel Allocation protocol (ADCA), will considers optimization for both throughput and delay in the channel assignment. Our simulation result show that compared to MMAC, ADCA reduces the packet delay considerably without degrading the throughput.


wireless Mesh Network, multiradio, multichannel, channel allocation.


WIRELESS MESH NETWORKS [1] are promising technology for next generation wireless networking ,the backbone of wireless mesh network’s provide good solution for user to access the internet anywhere anytime. WMNs facing one major problem are the capacity reduction due to wireless interference. In recently wireless mesh network equip with multiple radios, which can be configured to different channel, and thus reduce the network interference. The major challenges in multiradio multichannel Wireless mesh networks are assignment of channel to interface of mesh routers so that network throughput can be maximized.
The current two channel allocation approaches are static channel allocation and dynamic channel allocation approach. In static channel allocation, [2] a channel assigned permanently to each interface of every mesh router. In dynamic channel allocation [3], an interface is allowed to frequently switch from one channel to another channel. Both strategies have their relative strengths and weaknesses.
In this paper focus on hybrid architecture, this combines the advantages of static and dynamic allocation approaches. In this architecture, one interface from each router uses the static channel allocation strategy, while the other interfaces use the dynamic channel allocation strategy. The links working on dynamic channel enhance the network connectivity and network’s adaptivity the changing traffic while the links working on the static channels provide high throughput paths from end-users to the gateway. Therefore, this hybrid architecture can achieve better adaptivity compared to the pure static architecture without much increase of overhead compared to the pure dynamic architectu re.
In this paper, we discuss many important issues in the hybrid wireless mesh network. 1) The system architecture, where one radio works as static interface and the other radios work as dynamic interfaces in each node. 2) The channel allocation for dynamic interfaces: multichannel medium access control protocol MMAC [4] is currently one of the most efficient dynamic channel allocation protocols. However, the channel assignment in MultichannelMAC protocol is considered for network throughput but delay is high in this protocol. Adaptive Dynamic Channel Allocation protocol (ADCA) was proposed, which considers both throughput and delay in the channel assignment. Compared with MMAC protocol, ADCA protocol is able to reduce the packet delay without degrading the network throug hput.
The remainder of the paper is organized as follows. Section II describes the network model. Section III discusses analytical model. Section IV discusses dynamic channel allocation protocol. Section V Performance Evaluation and Section VI conclude the paper.


In this paper, we propose to use the hybrid architecture to achieve both adaptively to changing traffic and low channel switching overhead. Let G (V, E) be the network topology, where V is the set of mesh routers and E represents pairs of mesh routers that are within radio communication range. Assume each mesh node has multiple interfaces. In the hybrid mesh architecture, one interface of each mesh router work on fixed channels, and let the other interfaces of mesh router be able to switch channel frequently.
Fig.1 illustrates a hybrid multiradio multichannel wireless mesh network. Most mesh router including the gateway has 3 interfaces, and a some boundary mesh router {N3; N7; N9; N6} have 2 interfaces. For each mesh router, one interface works as static interface, and the others work as dynamic interf aces.
The static channel allocation interfaces will constitutes a major portion of the traffic in the network while maximizing the network throughput from end-users to gateways. The proposed algorithm, construct a load balanced tree for each gateway. The main goal of the tree construction is to allocate bandwidth fairly to each mesh node with regard to the user-gateway throughput. aims at maximizing the network throughput from end-users to gateways. Each link can assign channels, after the topology have been constructed. The links closer to the gateways are given first priority to be allocated with less congested channels. The tree topology with thick lines is shown in fig.1 and we call the se links as static links. Dynamic interfaces work in an on-demand fashion. The data transmission in Two dynamic interfaces that are within radio transmission range of each other will able to communicate by switching to a same channel.
Multichannel MAC improves the network throughput at the cost of increasing packet delivery delay. When the traffic load is below saturation level, Multichannel MAC may cause unnecessary packet delay, which can be shown by the examples in Fig.2. In Fig.2 (a), assume node N1 has some data to send to N3. Let the maximum bit rate of each interface be R, and assume the traffic rate is less than R=2. According to MMAC, in the first time interval S1, the packets are transmitted from N1 to N2, and then in the second interval S2, the packets are transmitted from N2 to N3. Therefore, the packet delay is around two intervals. On the other hand, if we assign N1, N2 and N3 with the same channel, and use 802.11 to resolve contention in this sub network, the packets can be transmitted from N1 to N3 within one interval. In Fig.2 (b), assume N1 has some data to both N2 and N3, with the aggregate traffic rate of less than R. We can see that MMAC still needs two intervals to complete the transmission, while it can actually be done in one interval by assigning the same channel to all the three nodes. N1 just needs to alternatively data to be transmitting N2 and N3 to avoid collision.
The reason why Multichannel MAC causes unnecessary packet delay in the above cases is that only set of nodes negotiate common channels in each interval, and thus each packet can be transmitted at most one hop away in one interval. If more than two nodes enable to negotiate a common channel, the transmission packet delay can be reduced dramatically. For example, in both cases of Fig.2 (b), if N1, N2, and N3 can negotiate a common channel together, then all the transmissions can be completed in one time slot. Next, discusses the design of Adaptive Dynamic Channel Allocation protocol (ADCA).
ADCA uses the similar framework with Multichannel MAC. It divides time into permanent length intervals. Each interval is further separate into control interval and data interval. Let Sc, Sd be the length of control interval and data interval respectively (Obviously, we have S = Sc + Sd) and S be the interval length. In the control interval, all the nodes are switch to the negotiate channels and same default channel. In the data interval, the nodes working on the same channel transmit and receive data among each other. In MMAC, S is set to 100ms, and Sc is set to 20ms, which is long enough for nodes to negotiate channels when network traffic is saturated level. Our proposed protocol uses the same parameter settings (S and Sc), but is different in the channel allocation scheme du ring control interval.
In Adaptive Dynamic Channel Allocation protocol, each dynamic mesh interface maintains multiple queues in the link layer with one queue for each neighbor. The data to be transmitted to each neighbor are buffered in the corresponding queue. The first step of channel negotiation in Adaptive Dynamic Channel Allocation protocol is similar to Multichannel MAC protocol. For each dynamic mesh interface, if it has data to be sent, it selects a neighbor that it needs to communicate with and tries to negotiate a common channel with the neighbor. There are more criteria for sel ecting neighbors.
Multichannel MAC consider only throughput, we may select the neighbor with the longest queue. However, this method may cause starvation. Therefore, we augment it with some fairness considerations, that is, we evaluate a neighbor’s priority by considering both its how long the queue and queue has not been served. As a result, during this step, pair of nodes has negotiated common channels with each other such as the example in Fig.3 (a).
Fig 3: Adaptive Dynamic Channel Allocation
Different from MMAC, ADCA enables further channel negotiation among nodes. The example in Fig.3 illustrates how our protocol works. Assume the network traffic is below saturation. In Fig.3 (a), set of nodes negotiate channels according to MMAC. Then further channel negotiations are performed as illustrated in Fig.3 (b). There are three cases illustrated in the figure. 1) N1 has some data to send to N3 through N2. N1 and N2 got the right to transmit data on a common channel, whileN2 and N3 did not. In this case, N2 can further negotiate with N3 so that N3 works on the same channel with N1 and N2. 2) N4 has some data to both N5 and N6. N4 and N5 got the right to transmit data on a common channel, while N4 and N6 did not. In this case, N4 can further negotiate with N6 so that N6 works on the same channel with N4 and N5. 3) N7 has some data to N9 through N8. N7 and N8 got the right to transmit data on a common channel, while N9 got the right to transmit data to N10 on a common channel. In this case, N8 can negotiate with N9 so that N7, N8, N9, and N10 w ork on the same channel.
Compared with Multichannel MAC, Adaptive Dynamic Channel Allocation protocol can negotiate common channels among more than two nodes in each interval when network traffic is not saturated. As a result, ADCA protocol has the potential to reduce packet delay while satisfying the imposing traffic. When the traffic is near saturated, ADCA will behave similar to Multichannel MAC. Multichannel MAC is only optimized for maximizing the network capacity. In contrast, Adaptive Dynamic Channel Allocation protocol optimizes for both throughput and delay with regard to the imposing traffic load. Therefore, ADCA is adaptive to the network traffic.


Fig. 5 shows the packet delay for both MMAC and ADCA protocols. In comparison with MMAC, ADCA dramatically decrease network interference. From the simulation results, finally conclude that ADCA is able to achieve lower delay than MMAC.


In this paper, the channel allocation problem in multichannel wireless mesh network where each mesh node equipped with multiple radios have been formulated and addressed. An Adaptive dynamic channel allocation protocol was presented in this paper that assigns the channels to communication links in the hybrid wireless mesh network with the objective of maximizing the network throughput and reduce the packet delay. The simulation results have shown that, the effectiveness of the above approaches will improve the network throughput and reduce the packet delay.


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