International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 1– Jan 2014
Maximizing Network Capacity in MANETs through Cooperative Communications P.Phani Kumar1, P.Anil Kumar2 1
(Department of CSE, Malla Reddy College of Engineering & Technology/ JNTU Hyderabad, India) (Department of CSE, Malla Reddy College of Engineering & Technology/ JNTU Hyderabad, India)
2
Abstract --Mobile Ad Hoc Networks are for many practical scenarios in the real world as it does not need any pre-established infrastructure. Nodes in the MANET are resource constrained. Communications over network consume energy resources of the network gradually. Therefore it is essential to have mechanisms that consume fewer resources over network. Cooperative communication is the strategy that can improve the life of MANET as it can save resources of the network. Many existing techniques that focused on cooperative communications gave importance to the issues related to link level physical layer. They mostly ignored the problems pertaining to upper layer like topology control, routing and network capacity. To overcome this problem, recently GUAN et al. came up with a scheme that ensures cooperative communications by controlling topology of the network. In this paper we implement that scheme practically using a prototype application that simulates the proof of concept. The empirical results revealed that in upper layer topology control can improve network capacity of MANET. Index Terms – Mobile Ad Hoc Network, cooperative communications, physical layer, topology control
I.
INTRODUCTION
Mobile devices are increasingly participating in communication network due to their increased power and bandwidth. More over the mobile users are expecting sufficient speed in the networks. There are many challenges thrown by wireless media. Besides having limited resources, the mobile networks are vulnerable to various kinds of attacks as there is mobility in the network that causes the nodes to connect and disconnect from networks. In this context, cooperative wireless communications have become very useful strategies in order to improve energy efficient communications in MANET. These strategies also support multiple antennas [1]. The mobile channel is of broadcast nature whose feature is exploited for cooperative communications in MANETs. With a single physical antenna, multiple virtual antennas can be used in order to improve
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performance. This kind of support is with IEEE 802.16j [2]. The prior works focused on the issues present in the physical layer such as outage probability and outage capacity [3], [4]. Moreover they ignored problems related to upper layer like topology control, routing and network capacity. Many wireless networks operate on point to point non-cooperative nature of the network. Though they are complex the technologies make them flexible and useful when compared with traditional techniques. The problems in the MANET such as collision resolution, and routing are resolved using cooperative communications [5]. For in-depth investigation of the problem, it is imperative to consider the topology control of MANET in order to increase network capacity. As MANETs have no centralized control, they need cooperation among the nodes for energy efficient communication. The nodes play many roles in the network such as topology organization, neighbor discovery, and topology reorganization. Choosing neighbors is possible in network with topology control which results in reduced energy usage and the increased throughput [6]. Recent research in topology control in MANET is done by Guan et al. [7] where the author controls topology using cooperative communications strategy. Their study revealed that the cooperative communications in Mobile Ad Hoc Networks can have its impact on the network capacity of the MANET the remainder of this paper is organized as follows. Section II provides details of proposed work that focuses on the network capacity improvement in MANETs. Section III presents the prototype application. Section IV presents experimental results while section V concludes the paper.
II.
PROPSOED APPROACH FOR NETWORK
CAPACITY
IMPROVEMENT In this section we provide information about our approach used to improve the network capacity in MANETs. The focus is on topology control using
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International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 1– Jan 2014
cooperative communications in MANETs those results in increasing the network capacity. Cooperative Communications Cooperative communications is the strategy used in MANET where the nodes cooperate each other in order to complete communication among the nodes. For this every node will act as a router who can forward data to other nodes. This will improve quality of communications resulting in network capacity. Here we generalize relay communications. When the strategy of cooperative communication is used, it results in reduced energy consumption, and improved quality in data transmission. The types of protocols that are used in MANET are shown in Figure 1.
topology changes from time to time, this feature has to be exploited in order to bring about improvements in throughput and energy consumption. It is possible to increase network capacity by controlling topology. The process of deploying links dynamically in order to improve the energy consumption, throughput and network capacity is known as topology control. Network Capacity of MANETs Network capacity in MANET is the ability of network that can deliver information. Earlier problems related to network capacity were explored by Gupta and Kumar [8]. These researchers introduced two kinds of capacities of network. They are known as throughput capacity and transport capacity. The former relays on channel’s information capacity while the latter considers distance and resembles one-hop capacity. Network Capacity Improvement Topology control can help in improving network capacity in MANETs. This is achieved by implementing cooperative communications. The network capacity is set as an objective function that can be represented as follows. G* = arg max f(G), s.t.network connectivity
Fig. 1 – Three types of communications (excerpt from [7]) As shown in Figure 1, it is evident that there are three types of protocols that can be used in MANET for efficient communications. The one denoted as (a) reflects direct communication by making use of conventional link in point to point fashion. The second one which is denoted by (b) works in two-hop fashion using two time-slots. The third one is denoted by (c) that supports cooperative communications and occupies two side by side slots. To decode the content, at the designation, the symbols are combined. Topology Control The physical arrangement of nodes in the network is called topology in MANET. However, the position of nodes in MANET is not static. The nodes have mobility and the network topology changes. As the
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There is network topology denoted by that is formed using multiple links and nodes in the network. With respect to objective function, the topology is constructed in order to excel in energy consumption and improving network capacity. The construction of topology is done as follows.
In order to derive network capacity, interference and network capacity are considered. When data is transmitted between the sender and receiver, it is possible to calculate outage link capacity provided the outage probability. In this context it is possible to use two-hop transmission for achieving multi-hop transmission. For achieving this, two time-slots are consumed. For transmitting messages from source to relay node, the first time slot is used while the second one is used to ensure that messages correctly reach the destination. In each hop the recording of interference is done as messages are transmitted over network. As simultaneous communication is not possible, usage of two time slots are to be considered with end to end interference. At each transmission, the outage of transmission is computed and finally
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International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 1– Jan 2014
the outage of two-hop transmission is computed. Interference occurs in every hop and there needs to be two time slots to have effective communication successfully. For the purpose of cooperative transmission of data in MANET, selection of proactive best relay is used. Decode and forward scheme is used to have communication between the source and destination nodes. The source node uses first slot in order to send messages to destination node. While receiving data, the receiver decodes it and then re-encodes when data is being forwarded to destination. At destination there is decoding of signals of source. Then the computation of outage capacity and probability take place [3]. In the broadcast period, successful transmission of data is made using neighbors involved in cooperative communication. Using link capacity and interference models, the network capacity can be derived [9]. Thus the value that has been derived can be used as an objective function that focuses on controlling topology. From the link – level perspective, the schemes that have been proposed can use physical layer for cooperative communications. Best type of transmission is taken care of using the objective function. Two conditions are used in the proposed scheme. They are path length and network connectivity in order to derive network capacity. The fundamental requirement of the network is path length. Network connectivity is guaranteed when the computation of objective function is done. In the network each node can act as in charge that takes responsibility for connections of other nodes in the neighborhood. When neighbors are involved in the communication, this results in end-to-end connectivity.
III.
PROTOTYPE IMPLEMENTATION
We built a prototype application that can simulate the concept of cooperative communication in MANET that results in increased network capacity and throughput while reducing the energy consumption in the network. There are multiple nodes in MANET and communication takes place between the source and destination nodes using intermediate nodes for cooperative communication. When a node fails in the process of communication, the relay nodes take the responsibility of data transmission in order to ensure the successful communication between the sender and receiver.
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Fig. 2 – Simulation of Cooperative Communications and Topology Control As shown in Figure 2, the cooperative approach is used for successful communication between the nodes where the communication process is carried out by source and relay nodes. In case of any failure in the network, the nodes cover this failure and continue communication between the source and destination nodes.
IV.
EXPERIMENTAL RESULTS
We made experiments without prototype application that demonstrates cooperative communication in MANET. We used .NET platform to build the application. We built a custom simulator prototype for simulating the MANET with cooperative communications that can improve the network capacity. The implementation is done using Microsoft .NET platform. C# programming language is used to achieve this. The environment used for the application and experiments is a PC with 4 GB RAM, Core 2 dual processor running Windows 7 operating system. The experimental results are compared with LLISE [10] which is one of the well known schemes that do not use cooperative communications. We also considered worst network capacity for evaluating the performance of the proposed system and also the LLISE. By changing different number of node s in MANET various experiments are made.
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Network capacity per node(bitd/Hz)
International Journal of Computer Trends and Technology (IJCTT) – volume 7 number 1– Jan 2014
[6] P. Santi, “Topology Control in Wireless Ad Hoc and Sensor Networks,” ACM Computing Surveys, vol. 37, no. 2, 2005, pp. 164–94. [7] QUANSHENG GUAN, F. RICHARD, SHENGMING JIANG, and VICTOR C. M. LEUNG, “TOPOLOGY CONTROL IN MOBILE AD HOC NETWORKS WITH COOPERATIVE COMMUNICATIONS”, IEEE, pp. 74-80. [8] P. Gupta and P. Kumar, “The Capacity of Wireless Networks,” IEEE Trans. Info. Theory, vol. 46, no. 2, 2000, pp. 388–404. [9] Q. Guan et al., “Impact of Topology Control on Capacity of Wireless Ad Hoc Networks,” Proc. IEEE ICCS, Guangzhou, P. R. China, Nov. 2008. [10] M. Burkhart et al., “Does Topology Control Reduce Interference?,” Proc. 5th ACM Int’l. Symp. Mobile Ad Hoc Networking and Computing, Tokyo, Japan, May 2004, pp. 9–19.
2 Propose d
1.5 1 0.5
LLISE
0 15
20 25 30 35 Number of Nodes
Fig. 2 – Number of nodes vs. network capacity As seen in figure 2, the comparison of network capacity is made using many nodes. The comparison is done as per the topology control scheme that has been implemented in this paper. Afterwards, the results are compared with other scheme named “LLISE” that do not use cooperative communications in the worst case scenario. The proposed approach yielded high network capacity and low energy consumption which is ideal for MANET. V.
CONCLUSION
In this paper we studied the cooperative communications in MANET. The paper considers physical layer for cooperative communications. Recently Guan et al. [7] presented a scheme is which is based on the topology control of the moving mobile nodes in the MANET. It has been observed that the topology control scheme in the physical layer can increase network capacity with the help of cooperative communications. We built a prototype application in order to implement cooperative communications in MANET. Our empirical results revealed that the proposed scheme is effective and is able to reduce energy consumption while increasing the network capacity.
REFERENCES [1] J. Laneman, D. Tse, and G. Wornell, “Cooperative Diversity in Wireless Networks: Efficient protocols and Outage Behavior,” IEEE Trans. Info. Theory, vol. 50, no. 12, 2004, pp. 3062–80. [2] P. H. J. Chong et al., “Technologies in Multihop Cellular Network,” IEEE Commun. Mag., vol. 45, Sept. 2007, pp. 64–65. [3] K. Woraditet al., “Outage Behavior of Selective Relaying Schemes,” IEEE Trans. Wireless Commun., vol. 8, no. 8, 2009, pp. 3890–95. [4] Y. Wei, F. R. Yu, and M. Song, “Distributed Optimal Relay Selection in Wireless Cooperative Networks with Finite-State Markov Channels,” IEEE Trans. Vehic.Tech., vol. 59, June 2010, pp. 2149–58. [5] Q. Guan et al., “Capacity-Optimized Topology Control for MANETs with Cooperative Communications,” IEEE Trans. Wireless Commun., vol. 10, July 2011, pp. 2162–70.
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