Wireless personal area networks and free-space optical links

This thesis is concerned with the link layer design of indoor (IrDA) and outdoor infrared links, as well as the performance of the higher layers of two major Wireless Personal Area Network (WPAN) technologies: IrDA and Bluetooth. Recent advancesin wireless technology have made it possible to put networking technology into small portable devices. During the past few years, WPAN technologies have been the subject of a tremendous growth both in research and development. Although many studies have been conducted on wireless links to address different issues on physical and link layers, wireless communications are still characterised by high error rates becauseof the frequently changing medium. On the other hand, performance studies of the higher layers are also very important. In this thesis, for the first time, a comprehensivestudy of the interactions betweenthe higher and the lower protocol layers of IrDA and Bluetooth has been carried out to improve the overall system performance. Mathematical models for the link layers are introduced for the infrared systems: infrared data association (IrDA) and free space optics (FSO). A model for the IrDA (indoor infrared) link layer is developed by considering the presence of bit errors. Based on this model, the effect of propagation delay on the link through put is investigated. An optimization study is also carried out to maximize the link throughput. FSO (outdoor infrared) links are often characterized by high speed and long link distance. A mathematical model for the FSO link layer is also developed. Significant improvement of the link throughput is achieved by optimizing the link parameters. Based on the link layer model, the performance of the IrDA higher layers (transport, session and application layers) is investigated. First, a mathematical model of TinyTP (transport protocol) is elaborated and subsequently verified by simulations. The effects of multiple connections and available buffer size are investigated. The throughput at the TinyTP level is optimized for different buffer sizes. Subsequently, the session layer, including Object Exchange (OBEX) and IrDA Burst (IrBurst) protocols, is studied and modelled. The derived mathematical model is verified by simulation results. A set of protocol parameters and hardware selection guidelines is proposed to optimize the overall system performance while also keeping the hardware requirementto a minimum. Finally, two rapidly developing IrDA applications, IrDA financial messaging(IrFM) and IrDA simple connection (IrSC), are studied. IrFM is investigated by comparison to other digital payment technologies, while the performance of IrSC is compared in two different technical approaches. In order to improve the throughput and minimize the transmission delay for the Bluetooth data applications, a systematic analysis is carried out for the Bluetooth Logical Link Control and Adaptation Layer Protocol (L2CAP). L2CAP is layered above the Bluetooth link layer (Baseband) and is essential to Bluetooth data applications. A simple and intuitive mathematical model is developed to derive simple equations for the L2CAP throughput and the average packet delay. The derived throughput equation, which is validated by simulations, takes into account bit errors as well as packet retry limits. Finally, a number of easy-to-implement performance enhancement schemes are proposed, including the optimum use of the protocol parameters

Koshinrai kokoritsu deta densoyo kinkyori hikari musen tsushin hoshiki ni kansuru kenkyu

制度:新 ; 報告番号:甲2917号 ; 学位の種類:博士(国際情報通信学) ; 授与年月日:2009/9/15 ; 早大学位記番号:新514

Wireless personal area networks and free-space optical links

This thesis is concerned with the link layer design of indoor (IrDA) and outdoor infrared links, as well as the performance of the higher layers of two major Wireless Personal Area Network (WPAN) technologies: IrDA and Bluetooth. Recent advancesin wireless technology have made it possible to put networking technology into small portable devices. During the past few years, WPAN technologies have been the subject of a tremendous growth both in research and development. Although many studies have been conducted on wireless links to address different issues on physical and link layers, wireless communications are still characterised by high error rates becauseof the frequently changing medium. On the other hand, performance studies of the higher layers are also very important. In this thesis, for the first time, a comprehensivestudy of the interactions betweenthe higher and the lower protocol layers of IrDA and Bluetooth has been carried out to improve the overall system performance. Mathematical models for the link layers are introduced for the infrared systems: infrared data association (IrDA) and free space optics (FSO). A model for the IrDA (indoor infrared) link layer is developed by considering the presence of bit errors. Based on this model, the effect of propagation delay on the link through put is investigated. An optimization study is also carried out to maximize the link throughput. FSO (outdoor infrared) links are often characterized by high speed and long link distance. A mathematical model for the FSO link layer is also developed. Significant improvement of the link throughput is achieved by optimizing the link parameters. Based on the link layer model, the performance of the IrDA higher layers (transport, session and application layers) is investigated. First, a mathematical model of TinyTP (transport protocol) is elaborated and subsequently verified by simulations. The effects of multiple connections and available buffer size are investigated. The throughput at the TinyTP level is optimized for different buffer sizes. Subsequently, the session layer, including Object Exchange (OBEX) and IrDA Burst (IrBurst) protocols, is studied and modelled. The derived mathematical model is verified by simulation results. A set of protocol parameters and hardware selection guidelines is proposed to optimize the overall system performance while also keeping the hardware requirementto a minimum. Finally, two rapidly developing IrDA applications, IrDA financial messaging(IrFM) and IrDA simple connection (IrSC), are studied. IrFM is investigated by comparison to other digital payment technologies, while the performance of IrSC is compared in two different technical approaches. In order to improve the throughput and minimize the transmission delay for the Bluetooth data applications, a systematic analysis is carried out for the Bluetooth Logical Link Control and Adaptation Layer Protocol (L2CAP). L2CAP is layered above the Bluetooth link layer (Baseband) and is essential to Bluetooth data applications. A simple and intuitive mathematical model is developed to derive simple equations for the L2CAP throughput and the average packet delay. The derived throughput equation, which is validated by simulations, takes into account bit errors as well as packet retry limits. Finally, a number of easy-to-implement performance enhancement schemes are proposed, including the optimum use of the protocol parameters.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

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

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