In passive RFID systems, how to reduce the collision among tags is an important issue at the medium access control layer. The Framed Slotted ALOHA and its variations are well-known anti-collision algorithms for RFID systems. However, when the Framed Slotted ALOHA is used, the system efficiency and the average time delay deteriorate rapidly when the total number of tags increases. On the other hand, the total number of slots in a frame can¡¦t be infinity. In this thesis, we first compare existing anti-collision protocols and then propose a novel algorithm based on the Enhanced Dynamic Framed Slotted ALOHA (EDFSA) and the Progressing Scanning (PS) algorithm. The proposed algorithm is called Dynamic Grouping (DG). The DG algorithm partitions the RFID tags according to the distances from tags to the reader in order to avoid using too many slots in a frame. Inparticular, the DG algorithm estimates the spatial distribution of tags based on previous scanning results and then adjusts the partition accordingly. Unlike PS algorithm, the DG algorithm is applicable when the RFID tags are uniformly distributed or normally distributed.

In this thesis, We propose two power saving strategy in wireless sensor networks with multi-packet reception and slotted ALOHA is as a systematic model. We concentrate on the case in which the packet arrival process is Bernoulli and the maximum queue is 1.This thesis first simulate results and to compare with the analytical results of pervious thesis. Traditional slotted ALOHA only have transmit and idle state. In this thesis, add a sleep state to decrease the energy consumption, and according to different strategy propose two different methods. This two methods decide to the sleep time and the retransmission probability to achieve the energy-efficient. At last we will use the simulation result to show the performance of our power saving strategy.

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We design, analyze, and optimize distributed detection and estimation algorithms in a large, shared-channel, single-hop wireless sensor network (WSN). The fusion center (FC) is allocated a shared transmission channel to collect local decisions/estimates but cannot collect all of them because of limited energy, bandwidth, or time. We propose a strategy called reliability-based splitting algorithm that enables the FC to collect local decisions/estimates in descending order of their reliabilities through a shared collision channel. The algorithm divides the transmission channel into time frames and the sensor nodes into groups based on their observation reliabilities. Only nodes with a specified range of reliabilities compete for the channel using slotted ALOHA within each frame. Nodes with the most reliable decisions/estimates attempt transmission in the first frame; nodes with the next most reliable set of decisions/estimates attempt in the next frame; etc. The reliability-based splitting algorithm is applied in three scenarios: time-constrained distributed detection; sequential distributed detection; and time-constrained estimation. Performance measures of interest - including detection error probability, efficacy, asymptotic relative efficiency, and estimator variance - are derived. In addition, we propose and analyze algorithms that exploit information from the occurrence of collisions to improve the performance of both time-constrained distributed detection and sequential distributed detection.

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The thesis deals with the issue of possible chlorine leakage from the Aqua Park in the town of Uherské Hradiště. Chlorine is a toxic substance, widely used in industry. The amount of chlorine used in the aqua park does not comply with the values stipulated under the Major Accident Prevention Act, as it is under the limits set in the act and the object therefore cannot be classified into either group A or group B. Since the aqua park falls between unclassified sources, it is not subject to any obligations under this act, including processing documentation for cases of emergency. Despite that it is necessary to ensure the safety of persons in the aqua park area, as well as in its immediate vicinity in case of leakage of large quantities of the substance. The aim of the thesis is to determine whether the aqua park can ensure preparedness for emergencies, especially for chlorine leakage. Chlorine is a moderately toxic substance which irritates particularly the respiratory system, eyes and mucous membranes, and in high concentrations, it can cause pulmonary edema and death. The thesis defines its basic physical and chemical properties, the method of using and providing first aid in case of exposure to the substance. Furthermore, it presents basic concepts related to emergencies and leakages of hazardous substances as well as basic legislation dealing with the issue. Such legislation includes primarily the Act on Integrated Rescue System, Act on Chemical Substances and Mixtures, as well as the Fire Protection Act. The thesis further includes risk assessment and analysis carried out using the Cause-Consequence Analysis or cause-effect analysis. This method is used for a better understanding of failures which can occur in an enterprise. It tries to deal mainly with the evaluation of the probability of system failures and looks for the causes of such failures. Using the Aloha and Terex software programs, a chlorine leak was simulated into the surrounding areas during the summer and winter seasons. Both programs simulated a chlorine leak in the total amount of 975 kg, under the same meteorological conditions for both seasons. Based on the specified input information, endangered zones in which it is necessary to evacuate the people were determined.

Radio frequency identification (RFID) systems are increasingly used for a wide range of applications from supply chain management to mobile payment systems. In a typical RFID system, there is a reader/interrogator and multiple tags/transponders, which can communicate with the reader. If more than one tag tries to communicate with the reader at the same time, a collision occurs resulting in failed communications, which becomes a significantly more important challenge as the number of tags in the environment increases. Collision reduction has been studied extensively in the literature with a variety of algorithm designs specifically tailored for low-power RFID systems. In this study, we provide an extensive review of existing state-of-the-art time domain anti-collision protocols which can generally be divided into two main categories: 1) aloha based and 2) tree based. We explore the maximum theoretical gain in efficiency with a 2-fold frequency division in the ultra-high frequency (UHF) band of 902-928 MHz used for RFID systems in the United States. We analyze how such a modification would change the total number of collisions and improve efficiency for two different anti-collision algorithms in the literature: a relatively basic framed-slotted aloha and a more advanced reservation slot with multi-bits aloha. We also explore how a 2-fold frequency division can be implemented using analog filters for semi-passive RFID tags. Our results indicate significant gains in efficiency for both aloha algorithms especially for midsize populations of tags up to 50. Finally, we propose two modifications to the Q-algorithm, which is currently used as part of the industry standard EPC Class 1 Generation 2 (Gen 2) protocol. The Q-Slot-Collision-Counter (QSCC) and Q-Frame-Collision-Counter (QFCC) algorithms change the size of the frame more dynamically depending on the number of colliding tags in each time slot with the help of radar cross section technique whereas the standard Q-algorithm uses a fixed parameter for frame adjustment. In fact, QFCC algorithm is completely independent of the variable "C" which is used in the standard protocol for modifying the frame size. Through computer simulations, we show that the QFCC algorithm is more robust and provide an average efficiency gain of more than 6% on large populations of tags compared to the existing standard.