Author Topic: An Efficient Shortest-Path Aided Back-Pressure Routing over Multihop Wireless Ne  (Read 3022 times)

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Author : T. Antony Thobias, P. Vijayananth, S. Manikandan
International Journal of Scientific & Engineering Research Volume 3, Issue 1, January-2012
ISSN 2229-5518
Download Full Paper : PDF

Abstract—This project proposes a new optimal routing/scheduling back-pressure algorithm that not only guarantees network stability (throughput optimality), but also adaptively selects a set of optimal routes based on shortest-path information in order to minimize average path lengths between each source and destination pair. Our results indicate that under the traditional back-pressure algorithm, the end-to-end packet delay first decreases and then increases as a function of the network load (arrival rate). The proposed particle swarm optimization based back pressure algorithm adaptively selects a set of routes according to the traffic load and energy efficiency so that long paths are used only when necessary, thus resulting in much smaller end-to-end packet delays as compared to the traditional back-pressure algorithm.

Index Terms – Back-pressure, PSO Algorithm, Multihop, Throughput Optimal
 
1   INTRODUCTION
Due to the scarcity of wireless bandwidth resources, it is important to efficiently utilize resource to support high throughput, high-quality communications over multihop wireless networks. In this context, good routing and scheduling algorithms are needed to dynamically allocate wireless resources to maximize the network throughput region. To address this throughput-optimal routing and scheduling, first developed in the seminal work, has been extensively studied. While these algorithms maximize the network throughput region, additional issues need to be considered for practical deployment. With the significant increase of real-time traffic, end-to-end delay becomes very important in network algorithm design. The traditional back-pressure algorithm stabilizes the network by exploiting all possible paths between source–destination pairs (thus load balancing over the entire network). While this might be needed in a heavily loaded network, this seems unnecessary in a light or moderate load regime. Exploring all paths is in fact detrimental-it leads to packets traversing excessively long paths between sources and destinations, leading to large end-to-end packet delays.

Back-pressure-type algorithms have recently received much attention for jointly routing and scheduling over multihop wireless networks. Good routing and scheduling algorithms are needed to dynamically allocate wireless resources to maximize the network throughput region. While this extensive exploration is essential in order to maintain stability when the network is heavily loaded, under light or moderate loads, packets may be sent over unnecessarily long routes, and the algorithm could be very inefficient in terms of end-to-end delay and routing convergence times. This project presents a routing/scheduling back-pressure algorithm that not only guarantees network stability (throughput optimality), but also adaptively selects a set of optimal routes based on shortest-path information in order to minimize average path lengths between each source and destination pair. The disadvantages of this system are End to end delay, routing convergence time.

Wireless access points are also often close to humans, but the drop off in power over distance is fast, following the inverse-square law. The HPA's position is that “...radio frequency (RF) exposures from WiFi are likely to be lower than those from mobile phones.” It also saw “...no reason why schools and others should not use WiFi equipment.” In October 2007, the HPA launched a new “systematic” study into the effects of WiFi networks on behalf of the UK government, in order to calm fears that had appeared in the media in a recent period up to that time". Dr Michael Clark, of the HPA, says published research on mobile phones and masts does not add up to an indictment of WiFi

2   WIRELESS NETWORK
Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a method by which homes, telecommunications networks and enterprise (business) installations avoid the costly process of introducing cables into a building, or as a connection between various equipment locations. Wireless telecommunications networks are generally implemented and administered using a transmission system called radio waves. This implementation takes place at the physical level (layer) of the network structure.
The term refers to any kind of networking that does not involve cables. It is a technique that helps entrepreneurs and telecommunications networks to save the cost of cables for networking in specific premises in their installations. The transmission system is usually implemented and administrated via radio waves where the implementation takes place at physical level. The types of networks are defined on the bases of their size (that is the number of machines), their range and the speed of data transfer.

Wireless PAN - Personal area network Wireless Personal Area Networks. Such networks interconnect devices in small premises usually within the reach of a person for example invisible infra-red light and Bluetooth radio interconnects a headphone to a laptop by the virtue of WPAN. With the installation of Wi-Fi into customer electronic devices the Wi-Fi PANs are commonly encountered.

Wireless LAN - Local Area Network The simplest wireless distribution method that is used for interlinking two or more devices providing a connection to wider internet through an access point. OFDM or spread-spectrum technologies give clients freedom to move within a local coverage area while remaining connected to the LAN. LAN’s data transfer speed is typically 10 Mbps for Ethernet and 1 Gbps for Gigabit Ethernet. Such networks could accommodate as many as hundred or even one thousand users.

Wireless MAN - Metropolitan Area Networks, The wireless network that is used to connect at high speed multiple wireless LANs that are geographically close (situates anywhere in a few dozen kilometers). The network allows two or more nodes to communicate with each other as if they belong to the same LAN. The set up makes use of routers or switches for connecting with high-speed links such as fiber optic cables. WiMAX described as 802.16 standard by the IEEE is a type of WMAN.

Wireless WAN is the wireless network that usually covers large outdoor areas. The speed on such network depends on the cost of connection that increases with increasing distance. The technology could be used for interconnecting the branch offices of a business or public internet access system. Developed on 2.4GHz band these systems usually contain access points, base station gateways and wireless bridging relays. Their connectivity with renewable source of energy makes them stand alone systems. The most commonly available WAN is internet.   Mobile devices networks the advent of smart phones have added a new dimension in telecommunications; today’s telephones are not meant to converse only but to carry data.

GSM - Global System for Mobile Communications Global System for Mobile Communications is categorized as the base station system, the operation and support system and the switching system. The mobile phone is initially connected to the base system station that establishes a connection with the operation and support station that later on connects to the switching station where the call is made to the specific user.

PCS - Personal Communications Service is a radio band that is employed in South Asia and North America; the first PCS service was triggered by Sprint. D-AMPS Digital Advanced Mobile Phone Service is the upgraded version of AMPS that is faded away due to technological advancements. TAN - Tiny Area Network and CANs - Campus Area Networks are two other types of networks. TAN is similar to LAN but comparatively smaller (two to three machines) where CAN resemble MAN (with limited bandwidth between each LAN network). 

The Utility of Wireless Networks the development of wireless networks is still in progress as the usage is rapidly growing. Personal communications are made easy with the advent of cell phones where radio satellites are used for networking between continents. Whether small or big, businesses uses wireless networks for fast data sharing with economical means. Sometimes compatibility issues with new devices might arise in these extremely vulnerable networks but the technology has made the uploading and the downloading of huge data a piece of cake with least maintenance cost.

3    MULTI-HOP NETWORKING
Multi-hop or ad hoc, wireless networks use two or more wireless hops to convey information from a source to a destination. There are two distinct applications of multi-hop communication, with common features, but different applications.

Mobile ad hoc networks (MANETS) A mobile ad hoc network consists of a group of mobile nodes that communicate without requiring a fixed wireless infrastructure. In contrast to conventional cellular systems, there is no master-slave relationship between nodes such as Ňbase station to mobile usersÓ in ad hoc networks. Communication between nodes is performed by direct connection or through multiple hop relays. Mobile ad hoc networks have several practical applications including battlefield communication, emergency first response, and public safety systems. Despite extensive research in networking, many challenges remain in the study of mobile ad hoc networks including development of multiple access protocols that exploit advanced physical layer technologies like MIMO, OFDM, and interference cancellation, analysis of the fundamental limits of mobile ad hoc network capacity, practical characterization of achievable throughputs taking into account network overheads.

Multi-hop cellular networks Cellular systems conventionally employ single hops between mobile units and the base station. As cellular systems evolve from voice centric to data centric communication, edge-of-cell throughput is becoming a significant concern. This problem is accentuated in systems with higher carrier frequencies (more path loss) and larger bandwidth (larger noise power). A promising solution to the problem of improving coverage and throughput is the use of relays. Several different relay technologies are under intensive investigation including fixed, mobile relays (other users opportunistically agree to relay each other’s' packets), as well as mobile fixed relays (fixed relays that are mounted on buses or trains and thus moving). There has been extensive research on multi-hop cellular networks the last few years under the guise of relay networks or cooperative diversity. The use of relays, though, impacts almost every aspect of cellular system design and optimization including: scheduling, handoff, adaptive modulation, ARQ, and interference management. These topics are under intense investigation.

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