Nicolae Tapus

Home automation design using 6LoWPAN wireless sensor networks

Wireless sensor and actuator networks (WS&ANs) are a new technology based on networks of small radio-enabled embedded devices that are being deployed in areas such as environmental monitoring, vehicle tracking, building management, body monitoring and other applications. Power sources for network nodes are often limited, which imposes restrictions on hardware resources and their use by the underlying embedded software. We propose a new wireless sensor network architecture that is especially designed for the task of home automation. Our system relies on a low power WS&AN that employs energy harvesting techniques to maximize node lifetime and an embedded residential gateway that offers user interaction and secure connectivity to the outside world. The advantages of our system are its scalability, low power, self sufficiency and versatility.

Enabling Mobile Devices for Home Automation Using ZigBee

Home automation systems are collections of interconnected devices for controlling various functions within a house, such as light control, heating, air conditioning, etc. Mobile devices are ideal in providing a user interface in a home automation system, due to their portability and their wide range of capabilities. They can communicate with a home automation network through an Internet gateway, but cannot directly communicate with devices in the network, as these devices usually implement low power communication protocols, such as ZigBee. We investigate several methods to equip an Android device with a dongle capable of ZigBee communication. We propose a scalable architecture, with three abstraction layers, that scales over multiple communication channels, such as the TCP channel, for communication with the gateway, and the USB channel, for direct communication with devices through the dongle. We test the application with two client devices running Android 4.0 and a mock home automation network consisting of a couple of ZigBee devices and a PC as gateway. We estimate the energy consumption of WiFi transfers over several typical use cases and we conclude that using ZigBee can prove beneficial in some cases, both in terms of functionality and performance.

Efficient Data Structures for Online QoS-Constrained Data Transfer Scheduling

Distributed applications and services requiring the transfer of large amounts of data have been developed and deployed all around the world. The best effort behavior of the Internet cannot offer to these applications the necessary quality of service (QoS) guarantees, making the development of data transfer scheduling techniques a necessity. In this paper we propose novel methods of efficiently using some well-known data structures (e.g. the segment tree and the block partition), which can be implemented in a resource manager (e.g. grid job scheduler, bandwidth broker) in order to serve quickly large numbers of advance resource reservation and allocation requests.

Mobile sensors in air pollution measurement

In this paper we present a mobile system for air quality and pollution measurement suited for the urban environment. We designed, tested and built a reliable measurement device that can acquire information about the air quality of its surroundings, store it in a temporary memory buffer and periodically relay it to a central on-line repository. Real-time gathered data can be freely accessed by the public through an on-line web interface. Users can select and view different gases and concentrations overlapped on a map of the city.

Fault-Tolerant Flooding Time Synchronization Protocol for Wireless Sensor Networks

Time synchronization is one of the basic middleware services in Wireless Sensor Networks. It is required in various applications such as target tracking, sensor event ordering, sound delay measurements and time-division multiplexing. Fault-tolerance in needed in order to perform correctly in the presence of faulty nodes. We extended Flooding Time Synchronization Protocol to support fault-tolerance in the case of malicious nodes that lie about their global time. The proposed algorithm will detect inconsistent global time and start asking the neighbors about their received global time. After it gathers sufficient information from its neighbors so that it can compute a new time value, it decides if the initially received global time was correct or not. If it was incorrect, the new computed value is stored. Otherwise, it permits the initial global time to be stored on the sensor device.

Task Scheduling in Wireless Sensor Networks

This paper discusses a scheduling algorithm for the sub-tasks of an application in a Wireless Sensor Network. With the next generation of sensor networks, task-based systems are needed to provide services to entities outside the network. Allocation of tasks on different wireless nodes must take into account energy constraints, compatibility of tasks to a given node or topology and must be in agreement with the purpose of the network. The problem described in this paper requires maximizing network lifetime and satisfying these allocation constraints. The solution proves to be correct though in some cases it can lead to algorithmic complexity, such that further work on an approximation algorithm might be indicated.

Maximum reliability k-hop multicast strategy in tree networks

In this paper we consider directed tree networks, for which the reliability of each edge (a real number between 0 and 1) is known. For these networks, we investigate the problem of finding a k-hop multicast strategy of maximum reliability. This problem is equivalent to the k-station placement problem, which was previously solved in polynomial time for trees. We present here O(kldrn2) and O(kldrn3) dynamic programming algorithms for the problem, which improve upon the previous best known solution, which is O(kldrn2ldrlog(n)) and rather complicated to implement. We then extend the algorithms to general directed graphs and also present some new algorithms for this case.

Optimal Offline TCP Sender Buffer Management Strategy

The transmission control protocol (TCP) uses a sliding window in order to enforce flow control. The receiver advertises its available buffer space to the sender, which cannot transmit more data than the advertised space. Transmitted data is first copied from application buffers into TCP buffers and from there it is sent through the network. In this paper we propose a model which characterizes the senderpsilas behavior throughout the duration of a TCP conversation. The model is suitable in the case of powerful, but variably loaded senders, slow receivers, fast connections and moderate amounts of data transmitted. For this model we present an O(nldrlog2n) algorithm which computes the minimum processing time spent by the sender, if the window sizes advertised by the receiver and the senderpsilas load are known in advance. The solution is based on an algorithmic framework for the segment tree data structure, which we introduce in this paper.

Performance evaluation of a Python implementation of the new LEDBAT congestion control algorithm

LEDBAT is a new congestion control algorithm which was proposed in an IETF draft in March 2009. LEDBATs goal is to provide a less-than-best-effort data transport service, i.e. a LEDBAT flow should back-off in the presence of other competing flows (TCP flows in particular). Because of its intended friendliness to competing flows, LEDBAT has already been implemented in the popular Bittorrent client uTorrent. In this paper we present performance evaluation results for our Python implementation of LEDBAT. We ran tests both in emulated networks as well as in real world networks. One of the tests involved approximately 300 volunteers spread throughout the world.

A fault-tolerant peer-to-peer object storage architecture with multidimensional range search capabilities and adaptive topology

In this paper we present a fault-tolerant, collaborative peer-to-peer object storage architecture with adaptive topology and efficient multidimensional range search capabilities. Every stored object has a fixed set of index properties, whose ranges of values form a multidimensional geometric property space. The architecture efficiently supports multidimensional range queries by mapping the peer identifiers into the property space of the stored objects. The potential disadvantage of not balancing the load on the peers which may be caused by this approach in the case of a static topology is addressed by introducing a dynamic topology, which attempts to balance the storage load. The architecture seamlessly supports dynamic node arrivals and departures.