京都大学 / 新制・課程博士 / 博士(情報学) / 甲第23328号 / 情博第764号 / 新制||情||130(附属図書館) / 京都大学大学院情報学研究科通信情報システム専攻 / (主査)教授 原田 博司, 教授 守倉 正博, 教授 大木 英司 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

In modern society, security has become an increasingly important subject, as technologyhas become an integrated part of everyday life. The security of a system can be tested withthe help of fuzzing, where incoming messages to the system are altered. In this thesis, afuzzer was developed targeting an E-UTRAN Node B (eNB) in the Long-Term Evolution(LTE) landscape. The eNB is current prototype and is from the company Ericsson. Thefuzzer is particularly designed for testing the Medium Access Control (MAC) layer of theeNB. The fuzzer uses a genetic method where all of the fuzzer’s flags (the R, F2, E, LCID, Fand L flags) are triggered during the fuzzing period. Depending on the output of the firstgeneration of fuzzed values, new values are generated either by choosing a value close tothe original value, or by choosing a value that belong to the same subgroup as the originalvalue. Four test cases are made, where first test case is the base line of the program and theother three test cases fuzzes the eNB, using different parts of the fuzzer. The results show that depending on which parts of the fuzzer are used, the connectionbecomes different. For test two and three, the connection became increasingly unstable andmore data was present in the connection. Test case four did not however deviate so muchfrom the baseline, if compared to test two and three.

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Recent accomplishments in link-level and radio technologies have significantly improved the performance of wireless links. Wireless mobile ad hoc networks, however, typically only take limited advantage of these enhancements. In this research, the medium access control protocol and ad hoc routing protocol are extended to take advantage of radios offering multi-user interference cancellation and direct-sequence spread-spectrum functionality, by encouraging multiple simultaneous connections and adaptively changing communication parameters on a per-packet basis. Through its environment characterization techniques, the adaptive direct sequence spread spectrum MAC protocol for non-broadcast multiple access networks (ADIM-NB) improves several aspects of the wireless mobile ad hoc network performance, including throughput, delay, stability, and power consumption, through its use of spread-spectrum multiple access and four different adaptive algorithms. The four adaptive algorithms change processing gain, forward error correction coding rate, transmit power, and number of simultaneous connections. In addition, the ad hoc routing protocol is extended with the clustering algorithm for mobile ad hoc network (CAMEN). With ADIM-NB in mind, CAMEN discourages the use of broadcast messages, supplements ADIM-NB's functionality at the network level, and improves the network scalability by aggregating nodes into clusters. Both protocols are intended to lead to more powerful and flexible communication capabilities for wireless nodes. Simulation models have been developed and simulated to verify the performance improvements of both protocols at the network-level as well as provide a means to perform trade-off analysis. Results indicate that the network capacity is increased between 50% in a moderately loaded network to 100% in a heavily loaded network over a non-adaptive MAC protocol. The delay also improve significantly in most scenarios of interest. / Ph. D.

Even if 3rd and 4th generation wireless systems aim to achieve multimedia services at high speed, it is rather difficult to have full-fledged multimedia services due to insufficient capacity of the systems. There are many technical challenges placed on us in order to realize the real multimedia services. One of those challenges is how efficiently to allocate resources to traffic as the wireless systems evolve. The review of the literature shows that strategic manipulation of traffic can lead to an efficient use of resources in both wire-line and wireless networks. This aspect brings our attention to the role of link layer protocols, which is to orchestrate the transmission of packets in an efficient way using given resources. Therefore, the Media Access Control (MAC) layer plays a very important role in this context. In this research, we investigate technical challenges involving resource control and management in the design of MAC protocols based on the characteristics of traffic, and provide some strategies to solve those challenges. The first and foremost matter in wireless MAC protocol research is to choose the type of multiple access schemes. Each scheme has advantages and disadvantages. We choose Wireless Code Division Multiple Access/Time Division Duplexing (WCDMA/TDD) systems since they are known to be efficient for bursty traffic. Most existing MAC protocols developed for WCDMA/TDD systems are interested in the performance of a unidirectional link, in particular in the uplink, assuming that the number of slots for each link is fixed a priori. That ignores the dynamic aspect of TDD systems. We believe that adaptive dynamic slot allocation can bring further benefits in terms of efficient resource management. Meanwhile, this adaptive slot allocation issue has been dealt with from a completely different angle. Related research works are focused on the adaptive slot allocation to minimize inter-cell interference under multi-cell environments. We believe that these two issues need to be handled together in order to enhance the performance of MAC protocols, and thus embark upon a study on the adaptive dynamic slot allocation for the MAC protocol. This research starts from the examination of key factors that affect the adaptive allocation strategy. Through the review of the literature, we conclude that traffic characterization can be an essential component for this research to achieve efficient resource control and management. So we identify appropriate traffic characteristics and metrics. The volume and burstiness of traffic are chosen as the characteristics for our adaptive dynamic slot allocation. Based on this examination, we propose four major adaptive dynamic slot allocation strategies: (i) a strategy based on the estimation of burstiness of traffic, (ii) a strategy based on the estimation of volume and burstiness of traffic, (iii) a strategy based on the parameter estimation of a distribution of traffic, and (iv) a strategy based on the exploitation of physical layer information. The first method estimates the burstiness in both links and assigns the number of slots for each link according to a ratio of these two estimates. The second method estimates the burstiness and volume of traffic in both links and assigns the number of slots for each link according to a ratio of weighted volumes in each link, where the weights are driven by the estimated burstiness in each link. For the estimation of burstiness, we propose a new burstiness measure that is based on a ratio between peak and median volume of traffic. This burstiness measure requires the determination of an observation window, with which the median and the peak are measured. We propose a dynamic method for the selection of the observation window, making use of statistical characteristics of traffic: Autocorrelation Function (ACF) and Partial ACF (PACF). For the third method, we develop several estimators to estimate the parameters of a traffic distribution and suggest two new slot allocation methods based on the estimated parameters. The last method exploits physical layer information as another way of allocating slot to enhance the performance of the system. The performance of our proposed strategies is evaluated in various scenarios. Major simulations are categorized as: simulation on data traffic, simulation on combined voice and data traffic, simulation on real trace data. The performance of each strategy is evaluated in terms of throughput and packet drop ratio. In addition, we consider the frequency of slot changes to assess the performance in terms of control overhead. We expect that this research work will add to the state of the knowledge in the field of link-layer protocol research for WCDMA/TDD systems. / Ph. D.

Clock synchronization in a wireless sensor network (WSN) is essential as it provides a consistent and a coherent time frame for all the nodes across the network. Typically, clock synchronization is achieved by message passing using carrier sense multiple access (CSMA) for media access. The nodes try to synchronize with each other, by sending synchronization request messages. If many nodes try to send messages simultaneously, contention-based schemes cannot efficiently avoid collisions which results in message losses and affects the synchronization accuracy. Since the nodes in a WSN have limited energy, it is required that the energy consumed by the clock synchronization protocols is as minimum as possible. This can be achieved by reducing the duration for which the clock synchronization protocols execute. Synchronous clock synchronization protocols in WSNs execute the clock synchronization process at each node, roughly during the same real-time interval, called synchronization phase. The duration when there is no synchronization activity is called the synchronization interval. Synchronization phases are divided into synchronization rounds. The energy consumed by these protocols depends on the duration of the synchronization phase and how frequently the synchronization phase is executed. Hence, to minimize the energy consumption by each node, the duration of synchronization phase should be as small as possible. Due to different drift rates of the clocks, the synchronization phases at different nodes drift apart and special techniques are required to keep them in sync. An existing protocol, called improved weighted-average based clock synchronization (IWICS) uses a pullback technique to achieve this. If a message from (i + 1)th synchronization round is received by a node still executing the ith synchronization round, the receiving node reduces its next synchronization interval to ensure greater overlap in the synchronization rounds. The reduction in overlap is a gradual and continuous phenomenon, and so, it can be detected and dealt with continuously. In this thesis, first, we make use of TDMA-based MAC protocols, instead of CSMA, to deal with the problem of message losses. We discuss the challenges of using TDMA-based MAC protocols for clock synchronization and how to overcome these challenges. Second, The IWICS protocol calculates the virtual drift rate which we use to modify the duration of the synchronization interval so that there is more overlap between the synchronization phases of neighbouring nodes. We refer to this technique as drift rate correction. Finally, we propose a different pullback technique where the pullback detection is carried out in each of the synchronization phase as opposed to the old pullback mechanism where it would be detected only when an out-of-round synchronization message is received. The proposed pullback technique when applied to the current synchronization interval ensures that the synchronization phases, that follow the current synchronization interval, are better synchronized with each other. As a result of this, we are able to reduce the duration of synchronization phases further. The IWICS protocol with all these modifications incorporated is termed as the TIWICS (TDMA-based IWICS) protocol. Simulation and experimental results confirm that the TIWICS protocol performs better in comparison to the existing protocols.

Recent research has shown that several spectrum bands are mostly underutilised. To resolve the issue of underutilisation of spectrum bands across the networks, the concept of Cognitive Radio (CR) technology was envisaged. The CR technology allows Secondary Users (SUs) to acquire opportunistic access to large parts of the underutilised spectrum bands on wireless networks. In CR networks, SUs may scan and identify the vacant channels in the wireless spectrum bands and then dynamically tune their receivers to identify vacant channels and transmitters, and commence communication among themselves without causing interference to Primary/Licensed Users (PUs). Despite the developments in the eld of CR technology, recent research shows that still there are many challenges unaddressed in the eld. Thus, there is a need to reduce additional handshaking over control and data channels, to minimise large sized control frames and to introduce reliable channel selection process and maintenance of SUs' communication when PUs return to a licensed channel. A fundamental challenge a ecting this technology is the identi cation of reliable Data Channels (DCHs) for SUs communication among available channels and the continuation of communication when the PU returns. This doctoral research investigates in detail how to resolve issues related to the protocol design for Cognitive Radio Networks (CRNs) on Medium Access Layers (MAC) for Ad-Hoc networks. As a result, a novel Reliable and Energy e cient Cognitive Radio multi-channel MAC protocol (RECR-MAC) for Ad-Hoc networks is proposed to overcome the shortcomings mentioned. After discussing the background, operation and architecture of CR technology, this research proposes numerous platforms and testbeds for the deployment of personal and commercial applications of the CRNs. Side by side, optimised control frames and a reduced number of handshakes over the CCH are suggested to extend the transmitting time for data communication. In addition, the reliable channel selection process is introduced instead of random selection of DCHs for successful data communication among the SUs. In RECR-MAC, the objective of every SU is to select reliable DCHs, thereby ensuring high connectivity and exchanging the successful data frames across the cognitive network. Moreover, the selection criteria of the DCHs are based on multiple factors, such as an initial selection based on the maximum free time recorded by the SUs over the DCH channel ranking, which is proportional to the number of positive/negative acknowledgements, and the past history of DCHs. If more than two DCHs have an equal value during the second, third and following iterations, then the DCHs are selected based upon the maximum free time. The priorities of the DCHs are then assigned based on Reliable Data Channels, that is, RDCH 1, RDCH 2, RDCH 3, and RDCH 4 respectively (where RDCH 1 and RDCH 2 have the highest priority, DRCH 3 and RDCH 4 have the next priority, and so on). The impacts of channel selection process and Backup Data Channel (BDC) over the proposed RECR-MAC protocol are analysed in combination with comparative benchmark CR-MAC protocols based on the timing diagrams proposed. Finally, the RECR-MAC protocol is validated by using a MATLAB simulator with PU impact over the DCHs, both with and without BDC, and by comparing results, such as communication time, transmitting energy and throughput, with benchmark CR-MAC protocols.

Dans cette thèse, il s'agit de proposer un protocole MAC qui prend en compte certaines spécificités des réseaux de capteurs sans fil linéaires. Ce protocole MAC est basé sur des jetons circulants qui donnent aux noeuds le droit d’accès au canal de transmission. Nous évaluons à partir de ce protocole l’impact des interférences et de la connectivité sur un réseau linéaire. Cette évaluation nous permet de proposer des techniques de clustering dans un réseau de capteurs sans fil linéaire. Nous supposons d’abord un clustering basé sur une exploitation logique du voisinage des noeuds capteurs. Nous considérons dans ce cas, un modèle de propagation déterministe qui ne tient pas en compte la complexité du milieu. Ensuite, nous considérons une technique de clustering dans laquelle le modèle de propagation prend en compte les fluctuations qui rendent le milieu complexe. / In this thesis, we propose a MAC protocol that takes into account the specific characteristics of LSNs. This MAC protocol is based on tokens circulating that give the right to nodes to access to the transmission channel. We evaluate from this protocol the impact of interference and connectivity in the LSN. This evaluation allows us to propose clustering techniques in a LSN. We assume first a clustering based on a logical exploitation of the vicinity of the sensor nodes. In this case, we assume that a deterministic propagation model that does not take into account the complexity of the environment. Next, we consider a clustering technique wherein the propagation model takes into account the fluctuations that make complex the medium.

Esta tesis tiene como objetivo final la propuesta de un protocolo de acceso al medio imbricado con los parámetros de nivel físico que dan soporte a dicho protocolo. Puesto que la propuesta se basa en un esquema TDMA, se eligen como base del análisis los sistemas de segunda generación GSM, TETRA y DECT, a partir de los cuales se extrapolan determinados parámetros a fin de sintonizarlos con los sistemas de tercera generación en su especificación TDMA. Se evalúan dichos sistemas a nivel físico sobre diferentes modelos de canal de propagación y distintas técnicas de compensación implementadas en el receptor: ecualizadores implementados sobre filtros transversales y antenas adaptativas. Además, se implementan y evalúan algoritmos de ecualización sencillos como LMS o RLS y más complejos como algoritmos bidireccionales sobre ecualizadores DFE. La elección de una u otra opción condicionará fuertemente el diseño del protocolo de acceso propuesto en el subnivel MAC. / This thesis has as final aim the proposal of a medium access protocol (MAC) closely related to the physical layer parameters that support such protocol. As the proposal is based on a TDMA scheme, three representative systems belonging to the second generation of mobile communication systems have been chosen: GSM, TETRA and DECT, which are employed to extract some parameters in order to tune them with the third generation systems in its TDMA specification. Such systems are evaluated at physical layer over different propagation channel models with several compensation techniques implemented on the receiver. As well, equalizers based on digital filters and adaptive antennas are utilized. The equalization algorithms evaluated include from the simplest ones like LMS or RLS to bidirectional algorithms over DFE structure. Choosing one or another option will strongly condition the design of the proposed access protocol within the MAC sublayer.

L'utilisation des canaux multiples améliore significativement les performances globales des réseaux de capteurs sans fil (RCSF) en permettant des transmissions parallèles sur plusieurs canaux. Cependant, la mise en place d’un protocole MAC multi-canal dans un réseau multisauts nécessite une méthode efficace d’allocation des canaux pour permettre une coordination entre les nœuds afin de partager les canaux disponibles. Dans cette thèse, nous nous intéressons à la conception d’un protocole MAC multi-canal qui répond aux exigences des applications de collecte de données à haut débit dans un réseau multi-saut. Pour ce faire, nous abordons d’abord les principales façons d’utiliser plusieurs canaux pour réaliser le partage du médium. Ensuite, nous proposons un protocole MAC multi-canal, répondant aux exigences des RCSF à haut débit, qui combine les trois techniques TDMA, CSMA et FDMA. En effet, nous utilisons une nouvelle méthode d’allocation des canaux qui permet aux nœuds de choisir le canal de réception le plus convenable dans leurs voisinages jusqu’à 3-sauts d’une façon distribuée afin de minimiser les effets des interférences et des collisions. Enfin, nous évaluons par simulation les performances de notre protocole et nous le comparons à d’autres protocoles proposés dans la littérature. Les résultats obtenus montrent l’efficacité de notre proposition dans les différents scénarios étudiés. / The use of multi-channel significantly improves the overall network performance of wireless sensor networks (WSNs) by allowing parallel transmissions over multiple channels. However, the design of a multi-channel MAC protocol in a multi-hop network requires an efficient channel allocation method that allows the coordination between the nodes in order to share available channels. In this thesis, we focus on the conception of a multi-channel MAC protocol that meets the requirements of high data collection applications in a multi-hop network. In order to achieve this goal, we first present the main techniques to use multiple channels to realize medium access sharing. Then, we propose a multi-channel MAC protocol that meets the requirements of high data rate WSNs, which combines three techniques TDMA, FDMA and CSMA. Indeed, we use a new channel assignment method that enables nodes to choose the most convenient channel in their 3-hop neighborhood in a distributed manner in order to minimize the effects of interferences and collisions. Finally, we evaluate by simulation the performance of our protocol and we compare it to other protocols proposed in the literature. The results show the efficiency of our proposition in the different studied scenarios.