DESIGN AND IMPLEMENTATION OF A WIRELESS LOCAL AREA NETWORK (WLAN)

DESIGN AND IMPLEMENTATION OF A WIRELESS LOCAL AREA NETWORK (WLAN)

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ABSTRACT

Wireless networks provide communications to fixed, portable and mobile users and offer substantial flexibility to both end-users and service providers. Current cellular/PCS networks do not offer cost effective high data rate services for applications, such as, telematics, traffic surveillance and rescue operations. This research, studies the feasibility and behavior of outdoor implementation of low-cost wireless LANs used for high mobility telematics and traffic surveillance. A multi-hop experimental wireless data network is designed and tested for this purpose. Outdoor field measurements show the wireless coverage and throughput patterns for static and mobile users. The results suggest that multi-hop wireless LANs can be used for high mobility applications if some protocols are improved.

CHAPTER ONE

GENERAL INTRODUCTION

1.0            PREAMBLES

Recently wireless local area networks (WLANs) have emerged as flexible communication systems, which have been implemented as an extension or alternative to a wired LAN within buildings. Using electromagnetic waves WLANs transmit and receive data over air interface, minimizing need for wired connection; thereby it enables user mobility in covered area without losing connectivity from the backbone network. The system implementations vary from simple peer-to-peer connection between two computers to cover entire buildings by many transmitter/receiver devices - access points (AP), which are connected to the wired network.

Most of the recently used WLAN systems are specified in IEEE 802.11 standard. The IEEE 802.11 standard is divided into two main layers: the Medium Access Control layer (MAC) and the Physical Layer (PHY). These two layers allow a functional separation of the standard and, more importantly allow a single data protocol to be used with several different RF transmission techniques.

WLAN systems mainly work based on these standards:

• 802.11b (802.11HR) - DSSS at 2.4 GHz with 1, 2, 5.5, and 11 Mbps data rates,

• 802.11g - OFDM at 2.4 GHz with 1, 2, 5.5, 11, and 22 Mbps data rates,

• 802.11a - OFDM in 5 GHz band with 6, 12, 18, 24, 36, 48, and 54 Mbps data rates, and

• HiperLAN2 – OFDM in 5.15-5.35 GHz and 5.725-5.825 GHz bands, similar to the 802.11a PHY (with varying convolution codes).

The indoor signal propagation differs from an outdoor case particularly in distances and in variability of the environment. Due to the multipath propagation (multiple reflections, diffractions and scatterings of electromagnetic waves from surrounding objects) the radio signal distortions and propagation losses (fading) occur.

For a small network in a limited area, only manufacturer’s information on the coverage range is sufficient to deploy the APs. For a larger network, a more accurate deployment procedure is required to ensure sufficient coverage and network functionality (bit rate, capacity, interference, etc.). Basically there are two approaches. The first is based on a site survey with a lot of measurements and experimental decisions. The second method comprises of software planning using propagation models.

1.1   STATEMENT OF THE PROBLEM

The basic issue addressed in this project is to study the feasibility and characteristics of wireless local area networks. The success of current wireless LANs under these conditions will lead us to use them as high rate outdoor wireless data networks.

Wireless networks can provide communications to both fixed and mobile users without any need of using data cables and can provide substantial flexibility to both end-user and service provider.

The use of current cellular/PCS high data rate services for data networking is not economically feasible due to high usage costs. Wireless local area networks have been designed and used for mostly indoor applications. The possible use of these wireless LANs for high mobility outdoor applications, such as, telemetry, traffic surveillance, rescue operations, and outdoor data networking can provide reasonably high data rates at minimal operational costs. These attractions led us to investigate the feasibility and operational characteristics of current wireless LAN standards in high mobility outdoor environments

1.2 OBJECTIVES OF THE STUDY

          This project is focused on WLANs and associated wireless technology. When addressing key aspects of technology such as WLANs, a comprehensive and holistic approach is required in order to truly derive an overall understanding of the complex, integrated and inter-dependent aspects.

The objectives of the study include the following:-

       i.            To analyze the architectural and operational structure of the IEEE 802.11b standard.

     ii.            To recommend appropriately measures that would ensure improvements to the standard.

1.3 SCOPE OF THE STUDY

This study will cover the WLANs and associated wireless technology. When addressing key aspects of technology such as WLANs, a comprehensive and holistic approach is required in order to truly derive an overall understanding of the complex, integrated and inter-dependent aspects of it. Hence, further to wireless technology, the guide also delves into security issues. This area should be further addressed in order to gain a comprehensive understanding and view of wireless technology’s role within your district’s overall strategy.

And also focuses on the IEEE 802.11b standard, which is one of the most commonly deployed and commercially available wireless LANs around the world. The success of 802.11b lies in the use of license-free 2.4GHz band, reasonable high available data rates (up to 11mbps), and commercially available product around the world. The investigation enables us to study the throughput and delay performance of an experimental multi-hop outdoor wireless network with increasing number of hops and speed.

1.4 LIMITATION OF THE STUDY

All area of human endeavors is usually characterized by some limits factors. The peculiar constraints encountered in carrying out this project are as follows:-

              i.            Constraint of time: the study was carried out with a given terminal data for submission due to the shortness in the semester.

           ii.            Unavailability of language compiler for use such as the language that would have enabled the development of more sophisticated work.

         iii.            Virus attack during programming design, there was virus attack which indicated start from scratch.

1.5 SIGNIFICANT OF THE STUDY

In the design of this project it will assure that the computer scientist should have conversant with the use of computer hardware system, computer network and computer software.

1.6 DEFINITIONS OF KEY TERMS

Access Point: An entity that has station functionality and provides access to the destination services, via the wireless medium for associated stations.

Ad hoc Network: A network composed solely of stations within mutual communication range of each other via the wireless medium.

Bridge: A device that forwards link-level frames from one physical network to another, sometimes called a LAN switch.

Channel: An instance of medium use for the purpose of passing protocol data units (PDUs) that may be used simultaneously, in the same volume of space, with other instances of medium use (on other channels) by other instances of the same physical layer (PHY), with an acceptably low frame error ratio due to mutual interference.

Client: The requester of a service in a distributed system.

Congestion: A state resulting from too many packets contending for limited resources, which may force the router (switch) to discard packets.

Congestion Control: Any network resource management strategy that has, as its goal, the alleviation or avoidance of congestion.

Connectionless Protocol: A protocol in which data may be sent without any advance setup.

CSMA/CD: Carrier Sense Multiple Access with Collision Detect. CSMA/CD is a functionality of network hardware. “Carrier sense multiple access” means that multiple stations can listen to the link and detect when it is in use or idle; “collision detect” indicates that if two or more stations are transmitting on the link simultaneously, they will detect the collision of their signals.

Ethernet: A popular local area network technology that uses CSMA/CD and has a bandwidth of 10 Mbps.

Host: A computer attached to one or more networks that supports users and runs application programs.

Internet: The global internet based on the Internet (TCP/IP) architecture, connecting millions of hosts worldwide.

Interoperability: The ability of heterogeneous hardware and multivendor software to communicate by correctly exchanging messages.

IP: Internet Protocol, A network layer protocol that provides a connectionless, best-effort delivery service of Datagrams across the Internet.

Latency: A measure of how long it takes a single bit to propagate from one end of a link or channel to the other. Latency is measured strictly in terms o


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