After more than two decades’ development, modern mobile cellular networks now have almost approached to the commercial level of fourth generation communication networks. For each of the mobile solutions, there are special attributes but also similarities compared to the other competitive solutions. We can also find relationships between the old generation solutions and the inheritors or innovations. During the communicating session using any kind of existing mobile handset, the handover procedure is a very important one that may effect connection quality and also the phone call continuity. Nowadays, the mobile cellular networks have a trend to interact with LAN networks. They will co-exist and work together to support higher data rate over a wider coverage. Seamless handover proposals like Unlicensed Mobile Access (UMA) can support the heterogeneous handover between Global System for Mobile Communications (GSM) and Wireless (Wi-Fi) Network. Several Media Independent Handover (MIH) proposals can handle the vertical handover in the hybrid mobile data network environment such like between wireless local area network (WLAN) and Universal Mobile Telecommunications System (UMTS) by different solutions.

Vystantis technologijoms, prieš apytiksliai aštuonerius metus buvo už patentuota nauja tinklo rūšis - bevielis tinklas. Pastebėjus jų privalumus buvo pradėti sparčiai vystyti . Sparčiai jiems populiarėjant išryškėjo kolizijos problema.Siekiant daugiau apie tai sužinoti buvo iškeltas darbo tikslas - išnagrinėti kolizines situacijas, pateikiant jų pasekmes, vengimo galimybes.Siekiant šio tikslo išnagrinėti populiariausi tinklų tipai. Eksperimentiškai įvykdytos dvi populiariausios kolizinės situacijos. Apžvelgti jau taikomi, bei taikytini, kolizinių situacijų vengimo būdai. Atlikus visas išsikeltas užduotis prieita prie išvados: Norint sumažinti kolizijų kiekį, pagerinti tinklo pralaidumą, pratęsti mobilaus prietaiso energijos šaltinio gyvavimo laiką (energijos suvartojimo kiekį) siūlau „paskleisti“ vartotojus (sudarinėti kiek į manoma mažiau vartotojų turinčius tinklus).Pvz. nagrinėtame WLAN centralizuotos tipologijos koliziniame atvejyje, reikia išdėstyti daugiau kreipties taškų AP. Taip būtų mažinamas vartotojų kiekis vienam AP. Bluetooth „ad hoc“ tipologijai, turint kitokią struktūrą , šis pasiūlymas tiktų turint ne mažiau kaip tris vienu laiko momentu aktyvius prietaisus. / By developing the technologies, approximately eight ears ago a new way of network where found and patented – wireless network. After seeing the advantages of these networks, they started fast development. As wireless network started to be more and more popular a problem of collisions in it started to give more concern. In order to know more about collisions and the way of collision appearance, the task of thesis was to – inspect the situations of collision, bring out the consequences, possible avoidance of it. Seeing this goal most of popular wireless networks where investigated. Reasons of collisions, experimentally explored situations for collisions, possibilities of resolving it where reviewed. After doing all this work, it can be concluded: To lower possible collision rate, ensure better throughput, make longer life time to mobile station (save energy) spreading of users (make smaller networks, with lower quantity of mobile users) might be a way. For example: in case of collision in analyzed WLAN central topology, we would need to add extra access points. That‘s would lower quantity of users per AP. Bluetooth „ad hoc“ topology is different in structure so this proposal would be valid just when minimum three active devices are in a range.

The 4th generation wireless communication systems aim to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. To achieve this goal, the support of vertical handoff is important in mobility management. This thesis focuses on the vertical handoff decision algorithm, which determines the criteria under which vertical handoff should be performed. The problem is formulated as a constrained Markov decision process. The objective is to maximize the expected total reward of a connection subject to the expected total access cost constraint. In our model, a benefit function is used to assess the quality of the connection, and a penalty function is used to model the signaling incurred and call dropping. The user's velocity and location information are also considered when making the handoff decisions. The policy iteration and Q-learning algorithms are employed to determine the optimal policy. Structural results on the optimal vertical handoff policy are derived by using the concept of supermodularity. We show that the optimal policy is a threshold policy in bandwidth, delay, and velocity. Numerical results show that our proposed vertical handoff decision algorithm outperforms other decision schemes in a wide range of conditions such as variations on connection duration, user's velocity, user's budget, traffic type, signaling cost, and monetary access cost.

Šis darbas tiria objetų vietos nustatymo paklaidų problemą bevieliuose tinkluose ir leidžia jas įvertinti įvairiais aspektais. Įvertinimo rezultatas pateikiamas kaip sugeneruotas geografinis žemėlapis bei tekstinės reikšmės. Sistema sukurta taip, kad nepriklausytų nuo bevielių ryšių technologijos, o duomenų analizės rezulate sistema leidžia juos peržiūrėti valdant geografinę padėtį bei tikslumą. Ši sistema naudojama realiose aplikacijose, pavyzdžiui, MSC MPS R5 LBS, MPS112 platformoje, taip pat „Bitės tinklo padengimo žemėlapiai“ sprendime. Sistemos veikimas yra universalus ir ji gali būti naudojama įvairiose komercinėse tinklų planavimo ar LBS platformose. Sistema nepriklauso nuo bevielės technologijos ypatumų ir bus tinkama naudoti ateities bevielių tinklų įvertinimui. / This work investigates problem of positioning calculation error in mobile cellular networks and provides means to evaluate the errors in variuos aspects. Evaluation results are presented as generated geographical maps and values. The positioning calculation error evaluation is then used to extract requirements for engineered system. System is engineered in a way that it is cellular technology independand and is not limited by generations or carrier technologies of particular investigated networks. Resulting system allows users to select geographical area and precision of analysis to be carried on positioning calculation error. Radio signal propagation and coverage estimation algorithms are used to interpret input data and GIS data is used together to provide visual interpretation for positioning calculation error. This system is beeing used in real word aplications. At the time the system is used in MSC MPS R5 LBS, MPS112 platforms, also in solution „Bitės tinklo padengimo žemėlapiai“. Solution is universal, it can be used in variuos commercial network planning and LBS platforms. The system is cellular network technology neutral and it will be possible to evaluate future cellular or wireless networks as well.

Visas pasaulinis interneto tinklas, dauguma duomenų perdavimo įrenginių naudojasi materialiomis jungtimis. Populiariausia plačiajuosčio interneto prieigos galiniams vartotojams perdavimo priemonė – vario kabeliai, kur informacija perduodama vario gyslomis tekančios srovės impulsais. Paskutiniu metu pradėta naudoti ir spartesnė bei brangesnė duomenų perdavimo terpė – optiniai kabeliai. Šiuose kabeliuose informacija perduodama šviesos impulsų pagalba, siunčiant ją optinio pluošto gyslomis. Deja, laidinės komunikacijos priemonių pagrindinis trūkumas – įrenginių stacionarumas. Vartotojai negali naudotis internetu keisdami savo vietą (ribotai, trumpais atstumais). Beveik nėra galimybių keisti vietos nenutraukus ryšio. Dėl šios priežasties tarp vartotojų labai paplito belaidės ryšio priemones. Šiuo metu egzistuojantys tinklų standartai remiasi centralizuotu paslaugos teikimu (pav. 1). Tai belaidžių tinklų architektūra naudojama mobiliojo ryšio operatorių bei namų belaidžiuose tinkluose, kai visi vartotojų srautai pirmiausiai turi eiti per centrinę stotį. Šiuo metu atsiranda naujų siūlymų, kaip galima patobulinti komunikaciją bei gerinti belaidžio ryšio paslaugos kokybę, pritaikant ją pagal poreikius. Belaidis ryšys gali būti panaudojamas tiesioginei komunikacijai tarp įrenginių, apeinant bazinę stotį, bei panaudojant kitus abonentus kaip tarpininkus, norint užmegzti tolimesnius ryšius. Daugiašuolių tinklų veikimas vis dar kelia daug problemų, bet aiškiai matoma perspektyva... [toliau žr. visą tekstą] / During last year there was high emphasis on mobile networking and access to the internet everywhere and any time. This was achieved by using wireless networks, like GSM or Wi-Fi family. New standards are emerging, like WiMax. This is centralized architecture networks, where central base station or access point is the essential part of the network. During down-time of this network part, whole network remains down. Other drawback this architecture – closely positioned users cannot communicate directly. Their communication is routed by some base station which is located at greater distance. This affects not optimal usage of wireless resources. New generation of wireless networks uses multihop architecture. This architecture does not include central base station in it. Users can directly communicate with each other. This affects smaller area where radio resources are used. It can lead to higher channel reuse. Linear and plane topology multihop networks were analyzed. Instant network capacity can reach up to λ/w=0.5 with line topology and up to λ/w=0.33 with plane topology. This achieved with lowest possible density when nodes can still communicate. When network density increases there is exponential drop of capacity heading towards λ/w=1/n value. It shows negative relation of network size and capacity. Experiment shows that there is some density, when wireless network can operate at maximum capacity. We call it optimal density. This can be used as a recommendation for deploying... [to full text]

Technologies such as WiFi and WiMAX, can be a powerful driving force for increasing rural / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2007.

We first present a non-cooperative auction game to solve the bandwidth allocation problem for non-cooperative channel access in a wireless network. The Nash equilibrium is obtained as a solution of the game. To address this problem of bandwidth sharing under unknown information, we further develop a Bayesian auction game model and then Bayesian Nash equilibrium is then obtained. Next, we present a framework based on coalitional game for cooperative channel access for carry-and-forward-based data delivery. Each mobile node helps others to carry and then forward their data. A coalitional game is proposed to find a stable coalition structure for this cooperative data delivery. We next present static and dynamic coalitional games for carry-and-forward-based data delivery when the behavior of each mobile node is unknown by others. In the dynamic game, each mobile node can update its beliefs about other mobile nodes’ types when the static coalitional game is played repeatedly.

Modern industrial control systems use a multitude of spatially distributed sensors and actuators to continuously monitor and control physical processes. Information exchange among control system components is traditionally done through physical wires. The need to physically wire sensors and actuators limits flexibility, scalability and reliability, since the cabling cost is high, cable connectors are prone to wear and tear, and connector failures can be hard to isolate. By replacing some of the cables with wireless communication networks, costs and risks of connector failures can be decreased, resulting in a more cost-efficient and reliable system. Integrating wireless communication into industrial control systems is challenging, since wireless communication channels introduce imperfections such as stochastic delays and information losses. These imperfections deteriorate the closed-loop control performance, and may even cause instability. In this thesis, we aim at developing design frameworks that take these imperfections into account and improve the performance of closed-loop control systems. The thesis first considers the joint design of packet forwarding policies and controllers for wireless control loops where sensor measurements are sent to the controller over an unreliable and energy-constrained multi-hop wireless network. For a fixed sampling rate of the sensor, the co-design problem separates into two well-defined and independent subproblems: transmission scheduling for maximizing the deadline-constrained reliability and optimal control under packet losses. We develop optimal and implementable solutions for these subproblems and show that the optimally co-designed system can be obtained efficiently. The thesis continues by examining event-triggered control systems that can help to reduce the energy consumption of the network by transmitting data less frequently. To this end, we consider a stochastic system where the communication between the controller and the actuator is triggered by a threshold-based rule. The communication is performed across an unreliable link that stochastically erases transmitted packets. As a partial protection against dropped packets, the controller sends a sequence of control commands to the actuator in each packet. These commands are stored in a buffer and applied sequentially until the next control packet arrives. We derive analytical expressions that quantify the trade-off between the communication cost and the control performance for this class of event-triggered control systems. The thesis finally proposes a supervisory control structure for wireless control systems with time-varying delays. The supervisor has access to a crude indicator of the overall network state, and we assume that individual upper and lower bounds on network time-delays can be associated to each value of the indicator. Based on this information, the supervisor triggers the most appropriate controller from a multi-controller unit. The performance of such a supervisory controller allows for improving the performance over a single robust controller. As the granularity of the network state measurements increases, the performance of the supervisory controller improves at the expense of increased computational complexity. / <p>QC 20150504</p>

In wireless networks, devices (nodes) are connected by wireless links. An important issue is to set up high quality (high bandwidth) and efficient routing paths when one node wants to send packets to other nodes. Resource allocation is the foundation to guarantee high quality connections. In addition, it is critical to handle void areas in order to set up detour-free paths. Moreover, fast message broadcasting is essential in mobile wireless networks. Thus, my research includes dynamic channel allocation in wireless mesh networks, geographic routing in Ad Hoc networks, and message broadcasting in vehicular networks. The quality of connections in a wireless mesh network can be improved by equip- ping mesh nodes with multi-radios capable of tuning to non-overlapping channels. The essential problem is how to allocate channels to these multi-radio nodes. We develop a new bipartite-graph based channel allocation algorithm, which can improve bandwidth utilization and lower the possibility of starvation. Geographic routing in Ad Hoc networks is scalable and normally loop-free. However, traditional routing protocols often result in long detour paths when holes exist. We propose a routing protocol-Intermediate Target based Geographic Routing (ITGR) to solve this problem. The novelty is that a single forwarding path can be used to reduce the lengths of many future routing paths. We also develop a protocol called Hole Detection and Adaptive Geographic Routing, which identifies the holes efficiently by comparing the length of a routing path with the Euclidean distance between a pair of nodes. We then set up the shortest path based on it. Vehicles play an important role in our daily life. During inter-vehicle communication, it is essential that emergency information can be broadcast to surrounding vehicles quickly. We devise an approach that can find the best re-broadcasting node and propagate the message as fast as possible.

Communication by wireless technologies has seen a tremendous growth in the last decades. Mobile phone technology and wireless broadband solutions are rapidly replacing the last-hop wireline connectivity for telephones and Internet access.  Research has, however, shown that Internet traffic can experience a performance degradation over wireless compared to wired networks.  The inherent properties of radio communication lead to a higher degree of unreliability, compared to communication by wire or fiber.  This can result in an increased amount of transmission errors, packet loss, delay and delay variations, which in turn affect the performance of the main Internet transport protocols TCP and UDP.  This dissertation examines the cross-layer relationship between wireless transmission and the resulting performance on the transport layer. To this end, experimental evaluations of TCP and UDP over a wireless 4G downlink system proposal are performed.  The experiment results show, in a holistic scenario, that link-level adaptive modulation, channel prediction, fast persistent link retransmissions, and channel scheduling, enables the transport protocols TCP and UDP to perform well and utilize the wireless link efficiently.  Further, a novel approach is proposed where a modified TCP receiver can choose to accept packets that are corrupted by bit errors. Results from network emulation experiments indicate that by accepting and acknowledging even small amounts of corrupted data, a much higher throughput can be maintained compared to standard TCP.