362 research outputs found
Link layer protocol performance of indoor infrared wireless communications
The increasing deployment of portable computers and mobile devices leads to an increasing demand for wireless connections. Infrared presentsseveral advantagesover
radio for indoor wireless connectivity but infrared link quality is affected by ambient infrared noise and by low power transmission levels due to eye safety limitations. The Infrared Data Association (IrDA) has developed the widely used IrDA 1.x protocol standard for short range, narrow beam, point to point connections.IrDA addressedthe
requirement for indoor multipoint connectivity with the development of the Advanced Infrared (AIr) protocol stack.
This work analyses infrared link layer design based on IrDA proposals for addressing link layer topics and suggests implementation issues and protocol modifications that improve the operation of short range infrared connections. The performance of optical wireless links is measuredby the utilization, which can be drawn at the data link layer. A new mathematical model is developed that reaches a simple
equation that calculates IrDA 1.x utilization. The model is validated by comparing its outcome with simulation results obtained using the OPNET modeler. The mathematical
model is employed to study the effectiveness on utilization of physical and link layer parameters.The simple equation gives insights for the optimum control of the infrared
link for maximum utilization. By differentiating the utilization equation, simple formulas are derived for optimum values of the window and frame size parameters.
Analytical results indicate that significant utilization increase is observed if the optimum values are implemented, especially for high error rate links. A protocolimprovement that utilizes special Supervisory frames (S-frames) to pass transmission control is proposed to deal with delays introduced by F-timer expiration. Results indicate that employing the special S-frame highly improves utilization when optimum window and frame size values are implemented. The achieved practical utilization increase for optimum parameter implementation is confirmed by meansof simulation. AIr protocol trades speedfor range by employing Repetition Rate (RR) coding to achieve the increased transmission range required for wireless LAN connectivity. AIr employs the RTS/CTS medium reservation scheme to cope with hidden stations and CSMA/CA techniques with linear contention window (CW) adjustment for medium
access. A mathematical model is developed for the AIr collision avoidance (CA) procedures and validated by comparing analysis with simulation results. The model is
employed to examine the effectiveness of the CA parameters on utilization. By differentiating the utilization equation, the optimum CW size that maximises utilization
as a function of the number of the transmitting stations is derived. The proposed linear CW adjustment is very effective in implementing CW values close to optimum and thus minimizing CA delays. AIr implements a Go-Back-N retransmission scheme at high or low level to cope with transmission errors. AIr optionally implements a Stop-and-Wait retransmission scheme to efficiently implement RR coding. Analytical models for the AIr retransmission schemes are developed and employed to compare protocol utilization for different link parametervalues. Finally, the effectiveness of the proposedRR coding on utilization for different retransmission schemes is explored
Performance modelling and enhancement of wireless communication protocols
In recent years, Wireless Local Area Networks(WLANs) play a key role in the data communications and networking areas, having witnessed significant research and development. WLANs are extremely popular being almost everywhere including business,office and home deployments.In order to deal with the modem Wireless connectivity needs,the Institute of Electrical and Electronics Engineers(IEEE) has
developed the 802.11 standard family utilizing mainly radio transmission techniques, whereas the Infrared Data Association (IrDA) addressed the requirement for multipoint
connectivity with the development of the Advanced Infrared(Alr) protocol stack. This work studies the collision avoidance procedures of the IEEE 802.11 Distributed
Coordination Function (DCF) protocol and suggests certain protocol enhancements aiming at maximising performance. A new, elegant and accurate analysis based on Markov chain modelling is developed for the idealistic assumption of unlimited packet retransmissions as well as for the case of finite packet retry limits. Simple equations are derived for the through put efficiency, the average packet delay, the probability of a packet being discarded when it reaches the maximum retransmission limit, the average time to drop such a packet and the packet inter-arrival time for both basic access and RTS/CTS medium access schemes.The accuracy of the mathematical model is validated by comparing analytical with OPNET simulation results. An extensive and
detailed study is carried out on the influence of performance of physical layer, data rate, packet payload size and several backoff parameters for both medium access
mechanisms. The previous mathematical model is extended to take into account transmission errors that can occur either independently with fixed Bit Error Rate(BER) or in bursts. The dependency of the protocol performance on BER and other factors related to independent and burst transmission errors is explored. Furthermore, a simple-implement appropriate tuning of the back off algorithm for maximizing IEEE 802-11 protocol performance is proposed depending on the specific communication requirements. The effectiveness of the RTS/CTS scheme in reducing collision duration at high data rates is studied and an all-purpose expression for the optimal use of the RTS/CTS reservation scheme is derived. Moreover, an easy-to-implement backoff algorithm that significantly enhances performance is introduced and an alternative derivation is developed based on elementary conditional probability arguments rather than bi-dimensional Markov chains. Finally, an additional performance improvement scheme is proposed by employing packet bursting in order to reduce overhead costs such as contention time and RTS/CTSex changes. Fairness is explored in short-time and long-time scales for both the legacy DCF and packet bursting cases. AIr protocol employs the RTS/CTS medium reservation scheme to cope with hidden stations and CSMA/CA techniques with linear contention window (CW) adjustment for medium access. A 1-dimensional Markov chain model is constructed instead of the bi-dimensional model in order to obtain simple mathematical equations of the average packet delay.This new approach greatly simplifies previous analyses and can be applied to any CSMA/CA protocol.The derived mathematical model is validated by comparing analytical with simulation results and an extensive Alr packet delay evaluation is carried out by taking into account all the factors and parameters that affect protocol performance. Finally, suitable values for both backoff and protocol parameters are proposed that reduce average packet delay and, thus, maximize performance
WIRELESS LAN IN UTP CAMPUS AREA
In the world nowadays, more and more organizations and learning institute are deploying
the Wireless Local Area Network or WLAN to be used together or to replace with the
wired LAN. WLAN is wireless networks between computers within one building or a
group of buildings. The frequently used protocol in WLAN is the Wi-Fi (IEEE 802.11
standards. The objective of the project is to develop a conceptual design of a Wireless
LAN for UTP campus area. The literature review and case study touch on what is WLAN
and its pros such as mobility and the contras such as, the slow network speed and
interference. The methodology or steps used to complete the project are project
preliminary study, project requirements, project research and analysis, network design
and development stage, and lastly the evaluation stage. Though WLAN has some of its
downside, it is convenient because of mobility, lower cost to deploy and provide security
to its user
Performance modelling of fairness in IEEE 802.11 wireless LAN protocols
PhD ThesisWireless communication has become a key technology in the modern world, allowing network
services to be delivered in almost any environment, without the need for potentially expensive
and invasive fixed cable solutions. However, the level of performance experienced by wireless
devices varies tremendously on location and time. Understanding the factors which can cause
variability of service is therefore of clear practical and theoretical interest.
In this thesis we explore the performance of the IEEE 802.11 family of wireless protocols,
which have become the de facto standard for Wireless Local Area Networks (WLANs). The
specific performance issue which is investigated is the unfairness which can arise due to the
spatial position of nodes in the network. In this work we characterise unfairness in terms of the
difference in performance (e.g. throughput) experienced by different pairs of communicating
nodes within a network. Models are presented using the Markovian process algebra PEPA which
depict different scenarios with three of the main protocols, IEEE 802.11b, IEEE 802.11g and
IEEE 802.11n. The analysis shows that performance is affected by the presence of other nodes
(including in the well-known hidden node case), by the speed of data and the size of the frames
being transmitted.
The collection of models and analysis in this thesis collectively provides not only an insight
into fairness in IEEE 802.11 networks, but it also represents a significant use case in modelling
network protocols using PEPA. PEPA and other stochastic process algebra are extremely powerful
tools for efficiently specifying models which might be very complex to study using conventional
simulation approaches. Furthermore the tool support for PEPA facilitates the rapid solution of
models to derive key metrics which enable the modeller to gain an understanding of the network
behaviour across a wide range of operating conditions.
From the results we can see that short frames promote a greater fairness due to the more
frequent spaces between frames allowing other senders to transmit. An interesting consequence
of these findings is the observation that varying frame length can play a role in addressing
topological unfairness, which leads to the analysis of a novel model of IEEE 802.11g with
variable frame lengths. While varying frame lengths might not always be practically possible, as
frames need to be long enough for collisions to be detected, IEEE 802.11n supports a number of
mechanisms for frame aggregation, where successive frames may be sent in series with little
or no delay between them. We therefore present a novel model of IEEE 802.11n with frame
aggregation to explore how this approach affects fairness and, potentially, can be used to address
unfairness by allowing affected nodes to transmit longer frame bursts.Kurdistan Region Government of Iraq
(KRG) sponso
Performance modelling and enhancement of wireless communication protocols
In recent years, Wireless Local Area Networks(WLANs) play a key role in the data communications and networking areas, having witnessed significant research and development. WLANs are extremely popular being almost everywhere including business,office and home deployments.In order to deal with the modem Wireless connectivity needs,the Institute of Electrical and Electronics Engineers(IEEE) has developed the 802.11 standard family utilizing mainly radio transmission techniques, whereas the Infrared Data Association (IrDA) addressed the requirement for multipoint connectivity with the development of the Advanced Infrared(Alr) protocol stack. This work studies the collision avoidance procedures of the IEEE 802.11 Distributed Coordination Function (DCF) protocol and suggests certain protocol enhancements aiming at maximising performance. A new, elegant and accurate analysis based on Markov chain modelling is developed for the idealistic assumption of unlimited packet retransmissions as well as for the case of finite packet retry limits. Simple equations are derived for the through put efficiency, the average packet delay, the probability of a packet being discarded when it reaches the maximum retransmission limit, the average time to drop such a packet and the packet inter-arrival time for both basic access and RTS/CTS medium access schemes.The accuracy of the mathematical model is validated by comparing analytical with OPNET simulation results. An extensive and detailed study is carried out on the influence of performance of physical layer, data rate, packet payload size and several backoff parameters for both medium access mechanisms. The previous mathematical model is extended to take into account transmission errors that can occur either independently with fixed Bit Error Rate(BER) or in bursts. The dependency of the protocol performance on BER and other factors related to independent and burst transmission errors is explored. Furthermore, a simple-implement appropriate tuning of the back off algorithm for maximizing IEEE 802-11 protocol performance is proposed depending on the specific communication requirements. The effectiveness of the RTS/CTS scheme in reducing collision duration at high data rates is studied and an all-purpose expression for the optimal use of the RTS/CTS reservation scheme is derived. Moreover, an easy-to-implement backoff algorithm that significantly enhances performance is introduced and an alternative derivation is developed based on elementary conditional probability arguments rather than bi-dimensional Markov chains. Finally, an additional performance improvement scheme is proposed by employing packet bursting in order to reduce overhead costs such as contention time and RTS/CTSex changes. Fairness is explored in short-time and long-time scales for both the legacy DCF and packet bursting cases. AIr protocol employs the RTS/CTS medium reservation scheme to cope with hidden stations and CSMA/CA techniques with linear contention window (CW) adjustment for medium access. A 1-dimensional Markov chain model is constructed instead of the bi-dimensional model in order to obtain simple mathematical equations of the average packet delay.This new approach greatly simplifies previous analyses and can be applied to any CSMA/CA protocol.The derived mathematical model is validated by comparing analytical with simulation results and an extensive Alr packet delay evaluation is carried out by taking into account all the factors and parameters that affect protocol performance. Finally, suitable values for both backoff and protocol parameters are proposed that reduce average packet delay and, thus, maximize performance.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Bluetooth User-Driven Cooperative Gallery Using Pull-based Technology
The Dissertation ispart ofthe compulsory requirement upon completion ofthe Final
Year Project (Part A) and also tofulfill the requirement ofgraduating in Bachelor of
Technology (Hons) Information Communication and Technology (ICT). The topic
chosen for the project is Bluetooth User-Driven Cooperative Gallery Using Pullbased
Technology. The purpose ofthe report isto have an overview ofthe project. It
will discuss and clarify all the findings and information which are relevant to the
objectives ofthe project. Students will have the opportunity to exercise their writing
skills and to clearly communicate their idea and suggestions. Advance in wireless
technology are becoming more and more popular throughout the world. In a world
of increasing mobility, there is a growing needforpeople to have timely access to
information regardless of the location of the individuals or the information.
Introduction will cover the background of the project under study, problem
statement, and the objectives of the project. The objective is to implement Bluetooth
as a suitable wireless transmission technology that is appropriate to be usedfor the
Universiti Teknologi PETRONAS Gallery. Literature review is the analytical, critical
and objective review of the written materials on the chosen topic. It contains all
relevant theories, hypotheses, facts, and data which are relevant to the objective and
findings of the project. Methodology will be discussing the identification of the
procedure that will be using in the development of the project. This part will also
discuss all the tools needed in developing the product in terms of hardware and
software needed. Results and conclusion will discuss about the results from the
questionnaires made to the students and the clarifications of the design and
implementation phase. Lastly, the conclusion is to clarify whether the project has
been a success, where all the objectives had been achieved or otherwise as well as
therecommendationfor future wor
Performance Investigation of Wireless LAN with Variable Channel Width
Today, mostly the wireless LAN is based on preset static channel widths. Considering unique benefits of adapting channel width, which is a fundamental yet under-explored facet in wireless communication, We carried out investigations on the performance of suggested scenario, which are based on IEEE 802.11 and composed of different number of nodes with different channel width (10MHz, 20 MHz and 40 MHz) associated to one AP. This research work makes a strong case for wireless systems that adapt channel width in WLAN. Adapting channel width offers rich possibilities for improving system performance. This thesis provides an outlook of the aforementioned issues associated with wireless communication for instance, fairness problem among users associated to same AP and hidden terminal problem. Some issues are investigated and analyzed with Matlab tool. We found that the variable channel width increases the range of communication, providing the users with the required spectrum, which offers a natural way to both improve flow fairness and balance the load across the APs. Also the increase in channel width increases the throughput of suggested scenario compare to the fixed channel width. In our future work, we also provide possible solutions to the new problems in WLAN with variable channel width
Advanced Wireless LAN
The past two decades have witnessed starling advances in wireless LAN technologies that were stimulated by its increasing popularity in the home due to ease of installation, and in commercial complexes offering wireless access to their customers. This book presents some of the latest development status of wireless LAN, covering the topics on physical layer, MAC layer, QoS and systems. It provides an opportunity for both practitioners and researchers to explore the problems that arise in the rapidly developed technologies in wireless LAN
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Security problems in 802.11 wireless networks standard due to the inefficiency of wired equivalent privacy protocol.
Due to the rapid growth of wireless networking, the fallible security issues of the 802.11 standard have come under close scrutiny. Nowadays most of the organizations are eager to setup wireless local area networks to reduce the hassles of limited mobility provided by conventional wired network. There are serious security issues that need to be sorted out before everyone is willing to transmit valuable corporate information on a wireless network. This report documents the inherent flaws in wired equivalent privacy protocol used by the 802.11 standard and the ensuing security breaches that can occur to a wireless network due to these flaws. The solutions suggested in this report might not actually make the 802.11 standard secure, but will surely help in the lead up to a secure wireless network standard
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