Efficient QoS Routing

We consider the problem of routing in a network where QoS constraints are placed on network traffic. We provide two optimal algorithms that are based on determining the discontinuities of functions related to the optimization at hand. The proposed algorithms have pseudopolynomial worst case running time and for a wide variety of tested networks they have fairly satisfactory running times. They perform significantly better than the algorithm based on the direct application of the Dynamic Programming equations and can also be used in conjunction with known polynomial-time approximation algorithms to provide good average case behavior, in addition to guaranteeing polymonial worst-case running time

Replicated Server Placement with QoS constraints

The problem of placing replicated servers with QoS constraints is considered. Each server site may consist of multiple server types with varying capacities and each site can be placed in any location among those belonging to a given set. Each client can de served by more than one locationsaslongastherequestround-tripdelaysatisfies predetermined upper bounds. Our main focus is to minimize the cost of using the servers and utilizing the link bandwidth, while serving requests according to their delay constraint. This is an NP-hard problem. A pseudopolynomial and a polynomial algorithm that provide guaranteed approximation factors with respect to the optimal for the problem at hand are presented

RSSI-based maximum likelihood localization of passive RFID tags using a mobile cart

Summarization: In this paper a maximum likelihood estimator of the locations of passive RFID tags is presented, exploiting the Received Signal Strength Information (RSSI) collected at the reader. The reader-antenna is fixed on a moving cart and collects RFID data in the area of interest. Locations of the reader-antenna and of the target-objects are obtained by the RSSI of reference tags placed at known positions. The proposed method can be applied using commercial RFID equipment. Measurements were conducted in an office environment; mean error of 25cm with standard deviation equal to 12,4cm is recorded. Localization accuracy can be further improved by increasing the density of the reference tags and the number of reader antennas.Presented on

Introduction of dynamic virtual force vector in particle swarm optimization for automated deployment of RFID networks

Summarization: A scheme for automated planning of passive RFID network is proposed. The scheme comprises two parts. The first part creates a fast site-specific probabilistic propagation model for successful identification from the reader of any possible tag antenna. The materials of surrounding walls as well the tag antennas radiation pattern, the geometry and the polarization of both reader and tag are taken into account. In the second part, a hybrid form of particle swarm optimization (PSO) algorithm is applied. The proposed approach selects a subset of tag antenna configurations to be installed so that a given cost function is satisfied. By clustering problematic areas during each iteration and moving the swarms towards them, we imitate the acts of a human-planner. The combinatorial performance of all active readers is evaluated at each tag location; this reveals that good identification performance is recorded at overlapping regions, where no single reader- tag antenna operates adequately. The proposed clustering approach greatly improves the convergence-time of the standard PSO and greatly reduces equipment, cutting down the cost of the network accordingly. Comparison with standard PSO reveals that the overall equipment can be reduced by a factor of two, satisfying the same quality constraints.Παρουσιάστηκε στο: 13th European Conference on Antennas and Propagatio

Robotic inventorying and localization of RFID tags, exploiting phase-fingerprinting

Summarization: In this paper we investigate the performance of phase-based fingerprinting for the localization of RFID-tagged items in warehouses and large retail stores, by deploying ground and aerial RFID-equipped robots. The measured phases of the target RFID tags, collected along a given robot's trajectory, are compared to the corresponding phase-measurements of reference RFID tags; i.e. tags placed at known locations. The advantage of the method is that it doesn't need to estimate the robot's trajectory, since estimation is carried out by comparing phase measurements collected at neighboring time-intervals. This is of paramount importance for an RFID equipped drone, destined to fly indoors, since its weight should be kept as low as possible, in order to constrain its diameter correspondingly small. The phase measurements are initially unwrapped and then fingerprinting is applied. We compare the phase-fingerprinting with RSSI based fingerprinting. Phase-fingerprinting is significantly more accurate, because of the shape of the phase-function, which is typically U-shaped, with its minimum, measured at the point of the trajectory, when the robot-tag distance is minimised. Experimental accuracy of 15cm is typically achieved, depending on the density of the reference tags' grid.Presented on

Real-time 3D localization of RFID-tagged products by ground robots and drones with commercial off-the-shelf RFID equipment: challenges and solutions

Summarization: In this paper we investigate the problem of localizing passive RFID tags by ground robots and drones. We focus on autonomous robots, capable of entering a previously unknown environment, creating a 3D map of it, navigating safely in it, localizing themselves while moving, then localizing all RFID tagged objects and pinpointing their locations in the 3D map with cm accuracy. To the best of our knowledge, this is the first paper that presents the complex joint problem, including challenges from the field of robotics - i) sensors utilization, ii) local and global path planners, iii) navigation, iv) simultaneous localization of the robot and mapping - and from the field of RFIDs - vi) localization of the tags. We restrict our analysis to solutions, involving commercial UHF EPC Gen2 RFID tags, commercial off-the-self RFID readers and 3D real-time-only methods for tag-localization. We briefly present a new method, suitable for real-time 3D inventorying, and compare it with our two recent methods. Comparison is carried out on a new set of experiments, conducted in a multipath-rich indoor environment, where the actual problem is treated; i.e. our prototype robot constructs a 3D map, navigates in the environment, continuously estimates its poses as well as the locations of the surrounding tags. Localization results are given in a few seconds for 100 tags, parsing approximately 100000 measured samples from 4 antennas, collected within 4 minutes and achieving a mean 3D error of 25cm, which includes the error propagating from robotics and the uncertainty related to the "ground truth" of the tags' placement.Παρουσιάστηκε στο: 2020 IEEE International Conference on RFI