Internetworking third generation (3G) technologies with wireless LAN (WLAN) technologies such as Universal Mobile Telecommunication Systems (UMTS) and IEEE 802.11, respectively, is an emerging trend in the wireless domain. Its development was aimed at increasing the UMTS network'­s capacity and optimizing performance. The increase in the number of wireless users requires an increase in the number of smaller WLAN cells in order to maintain an acceptable level of QoS. Deploying smaller cells in areas of higher mobility (e.g., campuses, subway stations, city blocks, malls, etc.) results in the user only spending a short period of time in each cell, which significantly increases the rate of handoff. If the user does not spend sufficient time in the discovered WLAN's coverage area, the application cannot benefit from the higher data rates. Therefore, the data interruption and performance degradation associated with the handoff cannot be compensated for. This counters the initial objective for integrating heterogeneous technologies, thus only handoffs that are followed by a sufficient visit to the discovered WLAN should be triggered. The conventional RF-based handoff decision method does not have the necessary means for making an accurate decision in the type of environments described above. Therefore, a location-aided handoff decision algorithm was developed to prevent the triggering of handoffs that result from short visits to discovered WLAN's ­ coverage area. The algorithm includes a location-based evaluation that runs on the network side and utilizes a user's location, speed, and direction as well as handoff-delay values to compute the minimum required visit duration and the user'­s trajectory. A WLAN coverage database is queried to determine whether the trajectory's end point falls within the boundaries of the discovered WLAN's coverage area. If so, the mobile node is notified by the UMTS network to trigger the handoff. Otherwise, the location-based evaluation reiterates until the estimated trajectory falls within the boundaries of the discovered WLAN'­s coverage area, or the user exits the coverage area. By taking into consideration more then merely RF-measurements, the proposed algorithm is able to predict whether the user'­s visit to the WLAN will exceed the minimum requirements and make the decision accordingly. This allows the algorithm to prevent the performance degradation and cost associated with unbeneficial/unnecessary handoffs. / Master of Science

One of the major challenges of Cognitive Radio (CRNs) is the spectrum handoff issue. Spectrum handoff happens when a Primary Users (PUs) appears in a spectrum band that is occupied by a Secondary User (SU). In such a case, SU should empty this spectrum band and perform a handoff procedure and search for an available free one. This process will be continued until the SU completes its data transmission. To avoid multiple spectrum handoffs, the spectrum handoff procedure should be performed in the unlicensed channels rather than the licensed channels. Thus, the number of handoffs can be reduced as no more spectrum handoffs will occur since all users have priority in this type of spectrum channel. This technique will help secondary users' QoS from degradation. This paper proposes a prioritized spectrum handoff decision scheme in a mixture spectrum environment of unlicensed and licensed channels, in order to reduce the handoff delay. The licensed channels in the proposed scheme have been modelled using a pre-emptive resume priority (PRP) M/M/C queue. In contrast, the unlicensed channels have been modelled using an M/M/C retrial priority queue. In order to examine the performance of the implemented model, the handoff and new SUs are considered with equal and different priorities. Experimental results show that the prioritized handoff scheme outperforms the other scheme in terms of average handoff delay under various traffic arrival rates as well as the number of licensed and unlicensed channels used.

Handoff is a call handling mechanism that is invoked when a mobile node moves from one cell to another. Such movement may lead to degradation in performance for wireless networks as a result of packet losses. A promising technique proposed in this thesis is to apply multicasting techniques aided by mobility prediction in order to improve handoff performance. In this thesis, we present a method that uses a Grey model for mobility prediction and a fuzzy logic controller that has been fine-tuned using evolutionary algorithms in order to improve prediction accuracy. We also compare the self-tuning algorithm with two evolutionary algorithms in terms of accuracy and their convergence times. Our proposed method takes into account signal strengths from the base stations and predicts the signal strength of the next candidate base station in order to provide improved handover performance. The primary decision for mobility prediction is the accurate prediction of signal strengths obtained from the base stations and remove any unwanted errors in the prediction using suitable optimisation techniques. Furthermore, the model includes the procedures of fine-tuning the predicted data using fuzzy parameters. We also propose suitable multicasting algorithms to minimise the reservation of overall network resource requirements during handoff with the mobility prediction information. To be able to efficiently solve the problem, the situation is modelled using a multicast tree that is defined to maintain connectivity with the mobile node, whilst ensuring bandwidth guarantees and a minimum hop-count. In this approach, we have tried to solve the problem by balancing two objectives through putting a weight on each of two costs. We provide a detailed description of an algorithm to implement join and prune mechanisms, which will help to build an optimal multicast tree with QoS requirements during handoff as well as incorporating dynamic changes in the positions of mobile nodes. An analysis of how mobility prediction helps in the selection of potential Access Routers (AR) with QoS requirements - which affects the multicast group size and bandwidth cost of the multicast tree -- is presented. The proposed technique tries to minimise the number of multicast tree join and prune operations. Our results show that the expected size of the multicast group increases linearly with an increase in the number of selected destination AR's for multicast during handoff. We observe that the expected number of joins and prunes from the multicast tree increases with group size. A special simulation model was developed to demonstrate both homogeneous and heterogeneous handoff which is an emerging requirement for fourth generation mobile networks. The model incorporates our mobility prediction model for heterogeneous handoff between the Wireless LAN and a cellular network. The results presented in this thesis for mobility prediction, multicasting techniques and heterogeneous handoff include proposed algorithms and models which aid in the understanding, analysing and reducing of overheads during handoff.

Made available in DSpace on 2014-12-17T14:55:42Z (GMT). No. of bitstreams: 1 patriciaAC_DISSERT.pdf: 1727038 bytes, checksum: 6d92b0a685d31e2550d0b963726e444f (MD5) Previous issue date: 2010-02-19 / This work deals with experimental studies about VoIP conections into WiFi 802.11b networks with handoff. Indoor and outdoor network experiments are realised to take measurements for the QoS parameters delay, throughput, jitter and packt loss. The performance parameters are obtained through the use of software tools Ekiga, Iperf and Wimanager that assure, respectvely, VoIP conection simulation, trafic network generator and metric parameters acquisition for, throughput, jitter and packt loss. The avarage delay is obtained from the measured throughput and the concept of packt virtual transmition time. The experimental data are validated based on de QoS level for each metric parameter accepted as adequated by the specialized literature / Este trabalho trata de estudos experimentais a respeito de conex?es VoIP em redes WiFi 802.11b com mobilidade de um dos usu?rios envolvidos na conex?o de voz e, por conseguinte, na presen?a de handoff. Os experimentos s?o realizados em ambientes indoor e outdoor com foco na medi??o dos ar?metros de desempenho usualmente tidos como indicadores da qualidade de servi?o - QoS em aplica??es VoIP: atraso, vaz?o, jitter, e perda de pacotes. Os par?metros de desempenho s?o obtidos com o aux?lio das ferramentas Ekiga, Iperf e Wimanager que possibilitam, respectivamente, simular uma conex?o VoIP, injetar tr?fego controlado em um ambiente de rede WiFi e medir a vaz?o, o jitter e a perda de pacotes. O atraso m?dio ? obtido analiticamente a partir da vaz?o medida e do uso do conceito de tempo de transmiss?o virtual m?dio de um pacote de voz. A aferi??o da aceita??o dos resultados ? feita com base nos n?veis de servi?os tidos como adequados na literatura para cada uma das m?tricas obtidas nos experimentos

[pt] Esta tese apresenta novos algoritmos para controle de admissão de usuários em redes móveis celulares. É utilizada a técnica de reserva de recursos, também conhecida por uso de canais de guarda, para atingir os graus de qualidade de serviço desejados para cada tipo de usuário. São propostos algoritmos dinâmicos, capazes de se adaptar ao perfil de tráfego presente na rede e que possuem diferentes filosofias de projeto. Inicialmente, foi considerado o caso de uma classe que resulta em dois tipos de usuários: chamadas novas e chamadas em handoff. Os algoritmos propostos são testados em condições de tráfego representadas por diversas distribuições para o tempo de permanência do usuário na célula. Foi desenvolvido um novo simulador em linguagem C que é capaz de verificar o desempenho dos algoritmos propostos. Resultados analíticos para desempenho dos algoritmos de uma classe e um número fixo de recursos reservados são apresentados empregando uma modelagem por Cadeia de Markov. Foi desenvolvido um método que permite calcular a intensidade de tráfego máxima a qual o sistema pode ser submetido, e a quantidade de recursos a ser reservada assumindo que o objetivo é maximizar a utilização do sistema atendendo os valores de qualidade de serviço estabelecidos, no caso de tempo de retenção do recurso de rádio modelado por uma chamada com distribuição exponencial. Foi proposto um algoritmo simples, dinâmico e distribuído, baseado em medidas em tempo real, cuja meta é acompanhar a curva ótima de número de recursos reservados. Posteriormente, os resultados analíticos empregando Cadeia de Markov são generalizados para M classes. Alguns dos algoritmos definidos para o caso de uma classe são estendidos para o caso de duas classes e seu desempenho é avaliado, utilizando o simulador desenvolvido neste trabalho. O método para calcular a intensidade máxima de recursos que o sistema comporta, sem violar os requisitos de qualidade de serviço, é estendido para o caso de duas classes. Finalmente, são definidos parâmetros que permitem comparar o desempenho dos algoritmos com 2M classes, considerando uma distribuição genérica para o tempo de permanência do usuário na célula. / [en] This thesis presents new algorithms for Channel Admission Control in wireless communications systems. We investigate techniques based in resource reservation, also known as guard channel, to achieve the quality of service desired for each class of users. We propose dynamic schemes based in the cell traffic. Each algorithm has a different goal, some try to minimize the probability of handoff fail, others try to maximize the traffic intensity when the limit imposed by QoS is being approached. First, we considered one class (M = 1) divided in two classes: new users and handoff users. In order to test the new schemes we developed a simulator in C that uses different distributions for the dwell-time. During the simulation, the measures of channel solicitations and the result of their allocation are used to decide whether new calls will be admitted. We also obtained analytic results using a Markov Chain model. We developed a method to calculate the maximum traffic intensity that the system supports without violating the established quality of service constraints, assuming one class of users and the dwell-time modelled by a exponential distribution. This method allows to identify the maximum traffic intensity supported by the system and also the exact number of resources to be reserved for each value of traffic intensity. We proposed a new, dynamic and distributed algorithm based on real time measures which targets to follow the optimum number of reserved curve obtained from our procedure. We generalized the analytic results using M-dimensional Markov Chains to 2M classes of users. Some of the algorithms defined to two classes (M = 1) were extended to the case of four classes (M = 2) and their performances are evaluated using the simulator developed in this work. The method to evaluate the maximum intensity of traffic within the limits of QoS is also extended to the case of four classes. Finally we define new parameters that allow the performance comparison among 2M class algorithms, considering any dwell- time distribution.

<p>The objective of the thesis research is to design such vertical handoff decision algorithms in order for mobile field workers and other mobile users equipped with contemporary multimode mobile devices to communicate seamlessly in the NGWN. In order to tackle this research objective, we used fuzzy logic and fuzzy inference systems to design a suitable handoff initiation algorithm that can handle imprecision and uncertainties in data and process multiple vertical handoff initiation parameters (criteria) / used the fuzzy multiple attributes decision making method and context awareness to design a suitable access network selection function that can handle a tradeoff among many handoff metrics including quality of service requirements (such as network conditions and system performance), mobile terminal conditions, power requirements, application types, user preferences, and a price model / used genetic algorithms and simulated annealing to optimise the access network selection function in order to dynamically select the optimal available access network for handoff / and we focused in particular on an interesting use case: vertical handoff decision between mobile WiMAX and UMTS access networks. The implementation of our handoff decision algorithm will provide a network selection mechanism to help mobile users select the best wireless access network among all available wireless access networks, that is, one that provides always best connected services to users.</p>

<p>The objective of the thesis research is to design such vertical handoff decision algorithms in order for mobile field workers and other mobile users equipped with contemporary multimode mobile devices to communicate seamlessly in the NGWN. In order to tackle this research objective, we used fuzzy logic and fuzzy inference systems to design a suitable handoff initiation algorithm that can handle imprecision and uncertainties in data and process multiple vertical handoff initiation parameters (criteria) / used the fuzzy multiple attributes decision making method and context awareness to design a suitable access network selection function that can handle a tradeoff among many handoff metrics including quality of service requirements (such as network conditions and system performance), mobile terminal conditions, power requirements, application types, user preferences, and a price model / used genetic algorithms and simulated annealing to optimise the access network selection function in order to dynamically select the optimal available access network for handoff / and we focused in particular on an interesting use case: vertical handoff decision between mobile WiMAX and UMTS access networks. The implementation of our handoff decision algorithm will provide a network selection mechanism to help mobile users select the best wireless access network among all available wireless access networks, that is, one that provides always best connected services to users.</p>

Philosophiae Doctor - PhD / The objective of the thesis research is to design such vertical handoff decision algorithms in order for mobile field workers and other mobile users equipped with contemporary multimode mobile devices to communicate seamlessly in the NGWN. In order to tackle this research objective, we used fuzzy logic and fuzzy inference systems to design a suitable handoff initiation algorithm that can handle imprecision and uncertainties in data and process multiple vertical handoff initiation parameters (criteria); used the fuzzy multiple attributes decision making method and context awareness to design a suitable access network selection function that can handle a tradeoff among many handoff metrics including quality of service requirements (such as network conditions and system performance), mobile terminal conditions, power requirements, application types, user preferences, and a price model; used genetic algorithms and simulated annealing to optimise the access network selection function in order to dynamically select the optimal available access network for handoff; and we focused in particular on an interesting use case: vertical handoff decision between mobile WiMAX and UMTS access networks. The implementation of our handoff decision algorithm will provide a network selection mechanism to help mobile users select the best wireless access network among all available wireless access networks, that is, one that provides always best connected services to users. / South Africa

Philosophiae Doctor - PhD / Seamless mobility is the missing ingredient needed to address the inefficient communication problems faced by the field workforces of service companies that are using field workforce automation solutions to streamline and optimise the operations of their field workforces in an increasingly competitive market place. The key enabling function for achieving seamless mobility and seamless service continuity is seamless handoffs across heterogeneous wireless access networks. A challenging issue in the multi-service next generation wireless network (NGWN) is to design intelligent and optimal vertical handoff decision algorithms, beyond traditional ones that are based on only signal strength, to determine when to perform a handoff and to provide optimal choice of access network technology among all available access networks for users equipped with multimode mobile terminals. The objective of the thesis research is to design such vertical handoff decision algorithms in order for mobile field workers and other mobile users equipped with contemporary multimode mobile devices to communicate seamlessly in the NGWN. In order to tackle this research objective, we used fuzzy logic and fuzzy inference systems to design a suitable handoff initiation algorithm that can handle imprecision and uncertainties in data and process multiple vertical handoff initiation parameters (criteria); used the fuzzy multiple attributes decision making method and context awareness to design a suitable access network selection function that can handle a tradeoff among many handoff metrics including quality of service requirements (such as network conditions and system performance), mobile terminal conditions, power requirements, application types, user preferences, and a price model; used genetic algorithms and simulated annealing to optimise the access network selection function in order to dynamically select the optimal available access network for handoff; and we focused in particular on an interesting use case: vertical handoff decision between mobile WiMAX and UMTS access networks. The implementation of our handoff decision algorithm will provide a network selection mechanism to help mobile users select the best wireless access network among all available wireless access networks, that is, one that provides always best connected services to users

There is a growing range of IP-based data and voice applications using mobile devices (e.g. 3rd , 4th generation mobile phones and PDAs) and new access technologies (e.g. Bluetooth, 802.11, GPRS, ADSL). This growth is driving a desire to support mobility at the IP level � in other words, allowing an IP host to keep on communicating with other hosts while roaming between different IP subnetworks. Mobile IPv6 allows hosts to move their physical and topological attachment points around an IPv6 network while retaining connectivity through a single, well-known Home Address. Although Mobile IPv6 has been the subject of simulation studies, the real-world dynamic behavior of Mobile IPv6 is only gradually being experimentally characterised and analysed. This thesis reviews the use of Mobile IPv6 to support mobility between independent 802.11b-attached IPv6 subnets, and experimentally measures and critically evaluates how long an end to end IP path is disrupted when a Mobile IPv6 node shifts from one subnetwork to another (handoff time). The thesis describes the development of an experimental testbed suitable for gathering real-world Mobile IPv6 handoff data using publicly available, standards compliant implementations of Mobile IPv6. (An open-source Mobile IPv6 stack (the KAME release under FreeBSD) was deployed). The component of handoff time due to 802.11b link layer handoff is measured separately to assess its impact on the overall Mobile IPv6 handoff time. Using Mobile IPv6 handoff results, the likely performance impact of Mobile IPv6 handoff on a common webcam application and a bulk TCP data transfer is also evaluated. The impact of handoff on these applications clearly shows that a default Mobile IPv6 environment would be highly disruptive to real-time and interactive applications during handoff events, even if the underlying link-layer handoff was instantaneous.