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A Cyclic Quorum based multi-channel MAC protocol with layered approach for mobile ad-hoc networks

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The IEEE 802.11 MAC layer protocol is designed for single channel. The improvement of network throughput can be done through the enhancement of spatial reuse and the reduction of transmission collusions by the utilization of multiple channels is
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  A Cyclic Quorum based Multi-channel MAC Protocol with Layered Approach for Mobile Ad-hoc Networks Md.Mosaddek Khan, Md. Tanvir Hamid † , Syed Kutub Uddin Ahmed ‡   Computer Science and Engineering, University of Dhaka, Dhaka, Bangladesh. †  Computer Science and Engineering, University of Dhaka, Dhaka, Bangladesh. ‡  Computer Science and Engineering, University of Dhaka, Dhaka, Bangladesh. mosaddek_sajeeb@yahoo.com, tanvir_cse062@yahoo.com, syed.kutubahmed@yahoo.com Abstract The IEEE 802.11 MAC layer protocol is designed for  single channel. The improvement of network throughput can be done through the enhancement of spatial reuse and the reduction of transmission collusions by the utilization of multiple channels is important. Channel allocation can exploit the multi-channel missing receiver problem besides there are other problems such as the primordial hidden terminal and exposed terminal problem. Existing multi-channel MAC protocols experience either higher hardware cost (because of applying multiple transceivers) or lower channel utilization (due to limited transmission opportunity). Previous approaches that use RTS/CTS or other modified ideas sometimes are not enough to meet the demands. In this paper, a fully distributed channel hopping solution has been discussed as, The Modified Cyclic-Quorum-based Multichannel (M-CQM) MAC  protocol. Cyclic quorum is used here in an efficient way. The proposed protocol has several attractive features. Sender is guaranteed to meet its receiver in a short time.  Each node’s channel hopping sequence is derived from its node ID and the layer it belongs. This proposed idea also tries to divide the physical location into three basic zones which removes the load of RTS/CTS or other similar approaches. We have evaluated our proposed approach (M-CQM) in network simulator (ns-2.34) and it outperforms existing proposals.   Keywords:  IEEE 802.11, MANET, Modified CQM (M-CQM) and Quorum Systems. I.   I NTRODUCTION   The IEEE 802.11 standard [2] has been broadly accepted as a single channel MAC mechanism for mobile ad hoc networks [4], [11]. The hidden terminal problem is solved  by the fundamental mechanism which is used to access the shared medium know as the Distributed Coordination Function (DCF) (IEEE 802.11 standard), that utilizes the RTS/CTS/DATA/ACK four-way handshake mechanism. A heavy-loaded network with single channel suffers from many collisions. This problem can be resolved by utilizing multiple channels, which helps to share the traffic loads among different channels. The total throughput can be increased by allowing users to use multiple channels which can also increase spatial reuse of the network. Designing a multi-channel MAC protocol is reasonable and desirable in IEEE 802.11-based mobile ad hoc networks as IEEE 802.1b and IEEE 802.11a support 3 and 13 non-overlapping channels, respectively. In fact there are many design challenges in multi-channel MAC  protocols while an imperative concern is how and which channel should be selected for data transmission. Solutions to this problem can be categorized as Single-/multi-transceiver; whether a user can utilize multiple transceivers or not and Single-/multi-rendezvous; whether multiple transmission pairs can accomplish handshaking simultaneously or not. There are many protocols [7], [10], [15], [16], [17], [18] that uses multiple transceivers to handle the channel allocation job. Nodes running these  protocols are prepared with at least two transceivers. In some protocols [15], [16], [17], [18], one transceiver is tuned to a common control channel which is dedicated for negotiating the channel to be used next. These protocols are referred to as the single-rendezvous solutions. An undesirable feature of the multi-transceiver, single-rendezvous category is that the dedicated control transceiver is a bottleneck. Without using a dedicated control channel, in [7], [10], each node has been fixed one of its transceivers to its own channel, waiting to accept transmission requests, and the other transceivers are free to switch to any channel to initiate a transmission of data. We call such solutions multi-rendezvous. The crisis of using multiple transceivers is high hardware cost. To reduce such cost, a number of studies [3], [8], [12], [13], [14], [19] utilize only one transceiver to solve the channel allocation problem. Some of them [8], [12], [19] used a dedicated control channel for exchanging control messages. In such a method, the dedicated control channel will be either over-loaded or under-utilized if the capacity of the dedicated control channel and the data channels is not distributed properly. Another proposal [14] uses a common control period, similar to the ATIM window concept in IEEE 802.11 power saving mode (PSM) [6], for nodes to negotiate the data channels. This scheme Proceedings of 13th International Conference on Computer and Information Technology (ICCIT 2010) 23-25 December, 2010, Dhaka, Bangladesh978-1-4244-8494-2/10/$26.00 ©2010 IEEE527  suffers from the same problem as those uses a dedicated control channel. Since the single-transceiver and multi-rendezvous are attractive features, we focus on designing a multi-channel MAC protocol in this class. In this paper, we propose a modified cyclic-quorum-based multi-channel MAC protocol (M-CQM) which overcomes the limitations of existing solutions in this class. The idea is to use one transceiver to emulate the multi-transceiver, multi-rendezvous solutions. The cyclic quorum system has the intersection property. Based on an extension of this  property and clever allocations of channels, the CQM  protocol can utilize any number of channels and guarantees that any sender can meet its intended receiver in a short time. The rest of the paper is organized as follows. In Section II, we describe previous related works. In Section III,  proposed layer architecture has been described. In section IV and V, the CQM and M-CQM protocol has been described in detail respectively. Simulations are provided in Section VI. Finally, in Section VII, we conclude the  paper. II. LITERATURE REVIEW & RELATED WORKS There are some other problems must be taken under consideration. First, is the multichannel hidden terminal  problem. Second, is the missing receiver problem. These  problems are resolved in the multi-transceiver and in single-rendezvous solutions. However, for the multi-transceiver, multi-rendezvous category, the missing receiver problem is solved but the multi-channel hidden terminal problem may still remain. For the single transceiver, single-rendezvous category, these two  problems occur if a dedicated control channel is used. For the single transceiver, multi-rendezvous class, only the missing receiver is a problem. We have evaluated our approach (M-CQM) in network simulator (ns-2.34) [1]. We focus on designing a multi-channel MAC protocol in the single-transceiver, multi-rendezvous class. Solutions in this class take channel hopping as the basic mechanism. We consider there are three design issues for a single transceiver, multi-rendezvous multi-channel MAC  protocol. First, we have to guarantee a sender and its intended receiver are able to communicate, i.e., they are guaranteed to hop to the same channel simultaneously. Second, this guarantee should be done with the least controlling overhead. The third design issue is that the  proposed solution has to avoid the missing receiver  problem. To achieve these requirements, we investigate the possibility of utilizing quorum systems to design a multi-channel MAC protocol. The hopping sequences of each node’s intended receivers can easily be obtained if their MAC addresses are known. When a node has data to send, it follows the intended receiver’s channel hopping sequence to enable the transmission. The channel hopping sequences have been designed such that nodes will overlap with each other at least once in a cycle. Specifically, each node’s hopping schedule can be determined by a set of (channel, seed)    pairs. However, the number of channels is limited to be a prime number. Maintain each node’s schedule correctly is also an overhead, especially in a high mobility environment. Moreover, allowing a node changing its schedule may produce the missing receiver  problem since the intended receiver’s schedule may also vary. 2.1 Quorum Concept We use the following definitions of quorum system. Given a cycle length n, let U = {0, 1… n-1} be a universal set. Definition 1:  A quorum system Q under U is a collection of non-empty subsets of U, each called a quorum, which  satisfies the intersection property: If ∀ G, H  ∈ Q: G ∩ H 6 ≠ Ø.   Definition 2:   Given an integer i ≥0 and quorum G in a quorum system Q under U, we define; G + i = {(x + i) mod n: x ∈ G}.   Definition 3:    A quorum system Q under U is said to have the rotation closure property if ∀ G, H  ∈ Q, i 2 {0, 1 … n -1}: G ∩ (H + i) ≠ Ø. Theorem 1:   Q is a solution to the QPS problem if Q is a quorum system satisfying the rotation closure property. There are two kinds of quorum systems, grid quorum system and cyclic quorum system, which satisfy the rotation closure property and can be applied for asynchronous wakeup in wireless sensor networks.   Cyclic Quorum System [5]:  A cyclic quorum system is  based on the ideas of cyclic block design and cyclic difference sets in combinatorial theory [7]. The solution set can be strictly symmetric for arbitrary n. For example, {1, 2, 4} is a quorum from the cyclic quorum system with cycle length= 7. Figure 1 illustrates three quorums from a cyclic quorum system with cycle length 7. Theorem 2:    Both grid-quorum systems and cyclic quorum  systems satisfy the rotation closure property and can be applied for QPS in wireless sensor networks.  The rotation closure property is as follows If ∀ G, H ∈ Q, i ∈ {0... n − 1}: G ∩ rotate (H, i) ≠Ø. For instance, the quorum system Q = {{1, 2},{1, 3},{2,3}} under {0, 1, 2, 3} has the rotation closure property, while the quorum system Q_ = {{0, 1},{0, 2},{0, 3},{1, 2,3}} under {0, 1, 2, 3} does not  process the rotation closure property because {0, 1} ∩ rotate({0, 3}, 3) = Ø. 528  Theorem 3:   The bound of quorum size k for a quorum  system Q over N is k ≥  n . Proofs of Theorems 1, 2, and 3 can be found in [3]. Generally, two quorums G and H from a cyclic quorum system or a grid quorum system are homogenous with each other since they have the same quorum size and G = H + i which shows a rotation  property. Although grid-quorum systems and cyclic quorum systems can be applied as a solution for QPS  problem, it is not necessary meaning that they can be a solution to the h-QPS problem. The definitions of difference set and cyclic quorum system are as follows. Definition 4:    A subset D = { ,.., } of Zn is called a difference set under Zn if for eve ry e ≠0 (mod n) there exists at least two different elements and ∈   D such that − = e (mod n). Definition 5:   Given any difference set D = { ,.., } under , the cyclic quorum system defined by D is; Q = { ,.., }, where = { ,.., }(mod n), i = 0..., n−1. For instance, D = {0, 1, 3} is a difference set under . The set Q = { , , ..., }, where = D, ={1, 2, 4}, = {2, 3, 5}, = {3, 4, 0}, = {4, 5, 1}, and = {5, 0, 2}, is a cyclic quorum system under . And , i = {0, ...,5} is a cyclic quorum. It can  be verified that the cyclic quorum system also satisfies the intersection property and rotation closure property. We also list a cyclic quorum system under here: Q’ = {{0, 1, 2, 4},{1, 2, 3,5},{2, 3, 4, 6},{3, 4, 5, 7},{4, 5, 6, 0},{5, 6, 7, 1},{6, 7, 0,2},{7, 0, 1, 3}}. The minimal difference set under for n= 4 to 111 can be found in [9].   Definition 6: For a given difference set  D = { ,.., } under , the complement set of  D ,  D’  , is defined as  − D . That is,  D’ = { , ..., } , where k + m = n , for   i = 1  , ..., k  ,  j = 1  , ...,m , ≠   .   For example,  D = {  0  , 1  , 3  } is a difference set under with complement set  D’ = {  2, 4, 5  } .   Theorem 4: Given a cyclic quorum system Q = { , ... } under , for i, j = {0, ..., n-1}, then ∩ ≠  Ø  if and only if ≠   . Proof: In the forward direction, we prove it by contraposition. If = , ∩ = Ø This proves the forward direction.   In the backward Figure 1:  The idea of an area divided by three basic zones. direction, we also prove it by contraposition. If ∩ = Ø, according to definition 5, =   . This proves the  backward direction. Theorem 4 verifies the feasibility of CQM. It is guaranteed that a sender’s switching slots and its receiver’s default slots intersect. The missing receiver  problem is solved accordingly.   III. PROPOSED LAYERED ARCHITECTURE The geographic area which is representative for the ad-hoc network can be divided by three zones in the basis of existence of obstacles. Figure 2 shows a sample of that  proposal where upper right zone reflects no obstacle and nodes communications are visible to each other. Lower zone resides limited amount of obstacles and some communications are visible to each other. Upper left zone inhere huge amount of obstacles and most of the nodes communications are invisible to each other. Although RTS/ CTS exchange can help reduce collisions, it also introduces delay and consumes channel resources. In the upper right zone of an area (see figure.2) it is not very useful to use those constraints to protect from hidden terminal, exposed terminal problem. It will accelerate the data communication rate on average in that particular geographic region. The other two regions need to provide some shorts of mechanisms or constraints to overcome those problems. Now a day through the use of Global Positioning System it is not very much difficult to find the geographic position of a particular node or its one hop neighbours with its environmental situation in respect to its surrounding obstacle for wireless communication. But to define the zone number in respect to the obstacle is NP-Hard problem. So to provide a heuristic solution for this  problem needs further research. IV. THE CQM PROTOCOL & ITS PROBLEMS In CQM[20] to enable a communication, a transmission  pair must tune to the same channel at the same time. When 529  Figure 2:  An example of CQM operation under with 3 channel [20]. they meet each other, the four-way handshake can be applied to fulfill data transfer. In essence, the most critical task is the joint allocation of channel/time for all the nodes in the network. In CQM, time is divided into a series of cycles. Each cycle consists of n time slots, numbered from 0 to n − 1. For each cycle, time slots are partitioned into default slots and switching slots. At default slots, a node will stay on its default channel, waiting for transmission requests. At switching slots, a node may switch to its intended receiver’s default channel. Each node’s default channel is selected from its node ID. Specifically, a node i ’s default channel (denoted as  DCi ) and default slots (denoted as  DSi ) are chosen as follows.  DCi = node IDi (mod m )  ,    DSi = Gj , j=node IDi (mod n ) ; where node IDi is the ID of node i . Figure 2 is an example of CQM operation under Z6 with 3 channels (numbered from 0 to 2). Nodes A and B, with IDs 0 and 1, respectively, are within each other’s transmission range. Each node’s default channel and default slots are shown in Figure 2, supposing that we choose the difference set {0, 1, 3} under Z6 as G0. The marked time slots are default slots. The number in each slot is the channel that should be switched to. When node A has packets pending for node B, node A switches to node B’s default channel (channel 1) at its switching slots. In this example, node A can send some packets to B at time slots 2 and 4 of each cycle. Similarly, if node B has  packets to A, the transmission can be done in time slots 0 and 3 by switching B’s transceiver to channel 0. So the main problem is that they may never meet each other if their default channels are different. It can never be guaranteed in cyclic quorum based system. So if this  problem needs to be solved to use this approach more effectively. V. PROPOSED M-CQM PROTOCOL To overcome the main drawback proposed in CQM  protocol which is used in multichannel MAC protocol, need to handle the non-overlapping of default and switching slots. It can never be guaranteed in cyclic quorum based system that any two nodes always have the suitable values for their corresponding slots. So M-CQM  provide a new idea of coordinator to handle this superfluous condition. So in M-CQM approach the transmission pairs continue their operation without being disturbed if there is overlapping slots available. On the other hand if the critical situations occur then related nodes accordingly report their scenario to the coordinator. After that the coordinator is responsible for breaking the deadlock. The action taken by the coordinator is so simple. Coordinator keeps the information of available channels in  particular slots of a cycle. So sender then needs to break the normal procedure by transmitting in the channel allocated by the coordinator from the available channel lists in that particular time slots. By adding these schemes the no overlapping problem can easily be handled. Coordinator handles the nodes transmissions by dividing them in three major types. The first type here is one to one communication with some problems in overlapping scenario. In the second type is many to one in case of receiver to sender. The third type is A  B  C type scenario where A sends to B and B sends to C at a time. Difficulty levels of those approaches are raising in one to third accordingly. VI. SIMULATION RESULTS For comparison purpose both M-CQM and CQM [20]  protocols are implemented under Z6 in network simulator. 100 nodes are uniformly placed in an area of 800 m × 800 m. Each node may act as a sender where the destination is randomly chosen from its one-hop neighbors. The flow length which is defined as the number of packets per flow is 500. The packet size is set to 512 bytes and nodes are supplied with constant bit rate traffic of 20,000 packets per second. This means the traffic load is about 80 Mbps. The transmission range of a node is 250 meter. Figure 3:  Handling Non-Overlapping of default and switching slots 530    Figure 4:  (a) Aggregate throughput in channels and pairs [top left]; (b) Average packet delay in all channels ad pairs [top right]; (c) Aggregate throughput vs. No. of nodes [down left]; (d) Average packet delay vs. No. of nodes [down right] Time slot duration is 10 ms long. The capacity for each channel is 54 Mbps. The channel switching delay is ignored in our simulations. The two metrics used in our simulation are Aggregate Throughput and Average Packet Delay. Here in figure 4(a) and 4(c) this is clear that as number of channels increased, average throughput is increased as well. But the impact of modification is clearly shown here. Metrics, which need to be considered carefully, is packet delay. Because of modification sometimes delay may be increased but 4(b) and 4(d) shows that despite some rare case on average condition M-CQM provides better results than CQM. VII. CONCLUSION In this paper, we proposed a layered approach and an important modification of a channel hopping MAC  protocol [CQM] for mobile ad hoc networks. The  proposed M-CQM protocol contains all amenities  provided by CQM [20] as well as it overcomes some key  problems in case of switching. This is obvious that by layering the geographic area of ad-hoc nodes it is possible to dramatically improve the overall overhead that was needed to restrict the popular problems like hidden-exposed terminal problem and so on. This solves the missing receiver problem in more efficient way. Simulation results verified that M-CQM has better  performance in that it achieves higher throughput and keeps the transmission delay low. So this is clear to all that the proposed scheme achieves a great improvement over existing multi-channel MAC protocols. REFERENCES  [1] The Network Simulator - ns-2. http://www.isi.edu/nsnam/ns [2] IEEE 802.11 Working Group, ”Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications”. 1997. [3] P. Bahl, R. Chandra, and J. Dunagan. ”SSCH: Slotted Seeded Channel Hopping for Capacity Improvement in IEEE 802.11 Ad-Hoc Wireless Networks”.  ACM MOBICOM  , pages 216–230, September 2004. [4] P. Camarda and O. Fiume. ”Collision Free MAC Protocol for Wireless Ad Hoc Networks based on BIBD Architecture”.  Journal of Communications , 2(7):1–8. [5] C.-M. Chao, J.-P. Sheu, and I.-C. Chou. ”An Adaptive Quorum-Based Energy Conserving Protocol for IEEE 802.11 Ad Hoc Networks”.  IEEE Transactions on Mobile Computing  , 5(5):560–570, Sept.-Oct. 2006. [6] J.-R. Jiang, Y.-C. Tseng, C.-S. Hsu, and T. H. Lai. ”Quorum-Based Asynchronous Power-Saving Protocols for IEEE 802.11 Ad Hoc Networks”. 10(1-2):169–181, Feb. 2005. [7] P. Kyasanur and N. H. Vaidya. ”Routing and Link-layer Protocols for Multi-Channel Multi-Interface Ad Hoc Wireless Networks”.  ACM SIGMOBILE Mobile Computing and Communications Review , Jan. [8] C.-S. Lin, M.-C. Wueng, T.-H. Chiu, and S.-I. Hwang. ”Concurrent Multi-Channel Transmission (CMCT) MAC 531
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