@article {4519,
	title = {A Comparative Study of Machine Learning Models for Spreading Factor Selection in LoRa Networks},
	journal = {Journal of Wireless Networks and Broadband Technologies (IJWNBT), IGI Global},
	volume = {10},
	year = {2021},
	pages = {100-121},
	abstract = {Low Power Wide Area Networks (LPWAN) technologies offer reasonably priced connectivity to a large number of low-power devices spread over great geographical ranges. Long Range (LoRa) is a LPWAN technology that empowers energy-efficient communication. In LoRaWAN networks collisions are strongly correlated with Spreading Factor (SF) assignment of end-nodes which affects network performance. In this work, SF assignment using Machine Learning models in simulation environment is presented. This work examines three approaches for the selection of the SF during LoRa transmissions a) random SF assignment b) Adaptive Data Rate (ADR) and c) SF selection through Machine Learning (ML). The main target is to study and determine the most efficient approach as well as to investigate the benefits of using ML techniques in the context of LoRa networks. In this research a library that enables the communication between ML libraries and OMNeT++ simulator was created. The performance of the approaches is evaluated for different scenarios, using the delivery ratio and energy consumption metrics.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris and Nikolaos Papachristos}
}
@article {4510,
	title = {Energy efficient mechanism for LoRa networks},
	journal = {Internet of Things: Engineering Cyber Physical Human Systems, Elsevier Science, 2021},
	volume = {13},
	year = {2021},
	pages = {1-13},
	abstract = {Internet of Things (IoT) is the ability of communication between objects and refers to a wide range of applications, such as the Search and Rescue (SAR) operations. SAR applications need long distance connectivity, thus can be benefited by Low Power Wide Area Networks (LPWAN). One LPWAN technology is called LoRa (Long Range). In this context, the WeSAR project has been created that provides a system for locating and rescuing people, especially those who belong to population groups with a very high probability of getting lost. The energy consumption of the wearable devices is important factor in the SAR operations, as the battery should last more than 45 50 hours. Therefore, the proposed system is based on LoRa technology, the user localization is based on LoRa using trilateration and Time Difference of Arrival (TDoA) instead of Geolocation Positioning System (GPS), as GPS increases the energy consumption, and we created an energy-efficient mechanism to tackle the problem of energy consumption. In this paper, an energy efficient mechanism for LoRa networks is presented, that is based on the user{\textquoteright}s state and the battery level of the wearable device. Realistic simulations have been conducted to evaluate the system for both one wearable device, and multiple wearable devices, using different mobility models. The results from the simulations have shown a decrease in the energy consumption in various node mobility models that were tested, without compromising the delivery ratio of the network, something important as the LoRa packets are used for the localization of the lost person.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris}
}
@conference {4526,
	title = {Energy Efficient Mechanism over LoRa for Search and Reuse operations},
	booktitle = {The 2021 IEEE International Symposium on Networks, Computers and Communications (ISNCC 2021): Smart Cities and the Internet of Everything, October 31 {\textendash} November 2, Dubai - UAE},
	year = {2021},
	abstract = {Search and Rescue (SAR) operations can be vastly benefited by the use of IoT and especially by Low Power Wide Area Networks (LPWAN) technologies, such as Long Range (LoRa). In this framework, the wearable device-based Search And Rescue system (WeSAR) project has been created. The main goals that WeSAR tries to improve are the localization accuracy and the energy efficiency of the wearable device. In this paper, the authors propose an energy-efficient mechanism for LoRa networks, taking into consideration the energy of a real wearable device, containing multiple sensors in a SAR scenario. In this work, we simulate the LoRa network, taking into consideration the various states of a wearable device and the impact of the sensors on the energy consumption, in order to have insights into the mechanism{\textquoteright}s efficiency with multiple nodes, up to 500 nodes. The experiment results reveal significant reductions in the energy consumption of the wearable device and improvement of battery life, in urban and suburban conditions, and in stationary and no stationary node mobility models.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris}
}
@conference {4523,
	title = {Exploring the energy efficiency for Search and Rescue operations over LoRa},
	booktitle = {11th IFIP International Conference on New Technologies, Mobility and Security (NTMS{\textquoteright} 2021), April 19 - 21, 2021, Paris, France },
	year = {2021},
	month = {April 19 - 21},
	abstract = {The Internet of Things (IoT) is one of the pioneering domains of Computer Science and Engineering, that comes to solve a plethora of real-life problems. One of the most promising technologies that aim to provide long-distance transmission while retaining energy consumption at low levels, is Long Range (LoRa). In this paper, a thorough study of the energy efficiency in LoRa based Search and Rescue (SAR) project for people with special needs, called Wearable based Search And Rescue system (WeSAR) is presented. After research the authors propose a LoRa based system, taking into consideration the energy efficiency. The results of the proposed mechanism are encouraging in terms of energy consumption, and the battery can last enough for the majority of the SAR operations, even when the battery is not fully charged. Also, there is no deterioration in terms of the delivery ratio of the network which is important for localization algorithms.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris}
}
@conference {4536,
	title = {GuideMe: A system for Indoor Orientation and Guidance},
	booktitle = {The Seventh International Conference on Smart Portable, Wearable, Implantable and Disability - oriented Devices and Systems (SPWID 2021), May 30 - June 3, 2021, Valencia, Spain},
	year = {2021},
	abstract = {The interest for indoor navigational systems is expanding daily, and concerns among others visually impaired people that cannot navigate safely indoors. The main goal of such systems is to localize and direct the individual that has a wearable device and provide voice commands to navigate indoor buildings. This paper{\textquoteright}s aims to present the design and the implementation of the GuideMe project. GuideMe project{\textquoteright}s goal is the design, implementation and evaluation of a navigation system focused on people that face troubles in indoor moving, utilizing a wearable device. Specifically, the focus group is people suffering from visual impairment. The person carrying the wearable device takes guidelines about the location from indoor UltraWide Band (UWB) anchors. The commands provided are about indoor direction through voice commands, assisting him to avoid obstacles in his route. We present the architecture and the details of the various modules which consist of the proposed indoor navigation system, and finally, some initial evaluations of the proposed system yield promising results.},
	author = {Eirini Barri and Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris}
}
@conference {4528,
	title = {GuideMe: A system for Indoor Orientation and Guidance},
	booktitle = {The Seventh International Conference on Smart Portable, Wearable, Implantable and Disability - oriented Devices and Systems (SPWID 2021), May 30 - June 3, 2021, Valencia, Spain },
	year = {2021},
	abstract = {The demand for indoor navigational systems is increasing daily. The use of navigational systems is ranging from smart cities and robots to visually impaired people support to navigate safely. The GuideMe Project aims to provide guidance and security for people suffering from blindness, and in the time being it is in the final development stage. This paper presents GuideMe Project goals GuideMe Project architecture and GuideMe final prototype. GuideMe Project architecture consists of the wearable device curried the user has, the anchors with which the wearable device works to determine the position of the user, the smartphone that is informed by the system for the route the user must follow and converts the message into audio information through the user{\textquoteright}s headset. The headset in order to guide the user in indoor places and the local server who controls the protocols, and the information are the last parts of the architecture. It is clear that the system is quite complex, it consists of several entities and requires them to work together harmoniously to provide the prescribed functionality, in real-time. All the technologies developed to this final system, each of which has multiple sub-entities as mentioned, handle the required functionality that is the provision orientation of users who are located and moving indoors.},
	author = {Eirini Barri and Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris}
}
@conference {4572,
	title = {HCI preliminary study and implementation for a LoRa based SAR system},
	booktitle = {The 12th International Conference on Sensor Device Technologies and Applications (SENSORDEVICES 2021), November 14 {\textendash} 18, 2021, Athens, Greece },
	year = {2021},
	abstract = {The subject of this paper is the study and implementation of a Long Range (LoRa) based Search and Rescue system that can help in the localization of people having a high risk of going missing. These people may suffer from dementia, attention disturbance, and distraction, or disease in the autism spectrum, and it is of great importance to be found in a specific time frame, as their life can be in danger. The system is based on LoRa network architecture that enables both long-range communication and low energy consumption. In this paper aspects of the human-computer interaction were taken into consideration in contrast to the majority of the related papers, and is the proposed system is evaluated using heuristic evaluation and questionnaires.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris}
}
@conference {4507,
	title = {Spreading Factor Analysis for LoRa networks: A supervised learning approach},
	booktitle = {9th World Conference on Information Systems and Technologies (WorldCIST{\textquoteright}21), March 30 - 31 and 1-2 April 1 - 2, 2021, Azores, Portugal},
	year = {2021},
	abstract = {Today, the Internet of Things (IoT) has been introduced in our lives, giving a variety of solutions and applications. The critical requirements for de-vices connected to the IoT are long battery life, long coverage, and low de-ployment cost. Some applications require the transmission of data over long distances, thus Low Power Wide Area Networks (LPWAN) have emerged, with LoRa being one of the most popular players of the market. In order, to improve energy consumption and connectivity problems, machine learning can be used in LoRa networks. In this paper, we intend to improve the energy consumption of end nodes by using machine learning models. For this reason, we present a comparison of classification algorithms, specifically, the k-NN, the Na{\"\i}ve Bayes, and Support Vector Machines (SVM), for the Spreading Factor (SF) as-signment in LoRa networks. The simulation results indicate that, both energy efficiency and reliability in IoT communications could be significantly im-proved using the proposed learning approach. These promising results, which are achieved using lightweight learning, make our solution favorable in many low-cost low-power IoT applications.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris and Nikolaos Papachristos}
}
@conference {4531,
	title = {Spreading Factor Selection Mechanism for Transmission over LoRa Networks},
	booktitle = {28th International Conference on Telecommunications (ICT 2021), June 1 - 3, 2021, London, UK },
	year = {2021},
	pages = {344-353},
	abstract = {This paper presents a mechanism for Spreading Factor (SF) prediction in LoRa networks for more optimized data transmissions. The proposed mechanism is based on Machine Learning (ML) algorithms and assigns the node{\textquoteright}s SF value based on prior transmission data. This paper examines three different approaches for the selection of the SF during LoRa transmissions a) Random SF assignment b) Adaptive Data Rate (ADR) and c) ML based SF selection. The main target is to study and determine the most efficient approach, as well as to investigate the exploitation of ML techniques in the context of LoRa networks. We created a simple library based on ML libraries, such as Scikit Learn that can be used with the FLoRa an OMNeT++ based LoRa simulator. With the use of this library, it is possible to predict the node{\textquoteright}s SF using ML techniques. Two classification algorithms were tested, the k Nearest Neighbors (k-NN) and Na{\"\i}ve Bayes classifier. Finally, we compared the ML mechanisms with two variants of the ADR mechanism. The approaches performance is evaluated for different scenarios, using the delivery ratio and energy consumption metrics.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris and Nikolaos Papachristos}
}
@article {4567,
	title = {GuideMe: A Complete System for Indoor Orientation and Guidance},
	journal = {International Journal of Smart Sensor Technologies and Applications (IJSSTA), IGI Global},
	volume = {1},
	year = {2020},
	pages = {36-53},
	abstract = {The interest for indoor navigational systems is expanding daily with concerns among visually impaired people who cannot navigate safely indoors. The main goal of such systems is the localization and direction of the individual who has a wearable device that provides voice commands to navigate indoor buildings. This paper aims to present the design and the implementation of the GuideMe project. The GuideMe project{\textquoteright}s goal is the design, implementation, and evaluation of a navigation system focused on people who face troubles in indoor moving utilizing a wearable device. Specifically, the focus group is people suffering from visual impairment. The person carrying the wearable device takes guidelines about the location from indoor ultrawide band (UWB) anchors. The commands provided are about indoor direction through voice commands, assisting him to avoid obstacles in his route. The authors present the architecture and the details of the various modules, which consist of the proposed indoor navigation system, and some initial evaluations of the proposed system yielding promising results.},
	author = {Eirini Barri and Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris}
}
@conference {4500,
	title = {GuideMe: A Networked Application for Indoor Orientation and Guidance},
	booktitle = {The Sixteenth International Conference on Networking and Services (ICNS 2020), September 27, 2020 - October 01, 2020, Lisbon, Portugal },
	year = {2020},
	abstract = {Today{\textquoteright}s indoor navigational systems are more and more in demand, commonly used for applications such as smart cities, robots and visually impaired people. As far as outdoor navigation is concerned, the Global Positioning System (GPS) technology is still one of the most (if not the most) commonly used approaches. Even though it is still considered an ideal solution for navigating in outdoor areas, challenges and problems arise when GPS is considered for navigation inside buildings due to obstacles (e.g., shopping malls, hospitals, etc.) and because signals cannot be absorbed by the building walls. To tackle the aforementioned issue, other technologies have emerged aimed at indoor navigation, such as Wireless-Fidelity (Wi-Fi), Bluetooth and sensors. This paper{\textquoteright}s contribution is towards indoor navigation and, more specifically, it targets designing and developing a tracking and navigation system aimed at people that experience difficulties in indoor orientation using a wearable device. The user takes direction from the wearable device for the indoor orientation through voice commands helping him to avoid obstacles. The central part of the system is a device that provides the ability to navigate and find a route by voice commands, based on the device{\textquoteright}s location and orientation capabilities.},
	author = {Christos Bouras and Eirini Barri and Apostolos Gkamas and Christina Koulouri and Evangelos Michos and Spyridon Katsampiris}
}
@conference {4462,
	title = {GuideMe: A Networked Application for Indoor Orientation and Guidance},
	booktitle = {The Sixteenth International Conference on Networking and Services (ICNS 2020), September 27, 2020 - October 01, 2020 , Lisbon, Portugal (to appear)},
	year = {2020},
	abstract = {Today{\textquoteright}s indoor navigational systems are more and more in demand, commonly used for applications such as smart cities, robots and visually impaired people. As far as outdoor navigation is consider, the Global Positioning System (GPS) technology is still one of the most (if not the most) commonly used approaches. Even though it is still considered an ideal solution for navigating in outdoor areas, challenges and problems arise when GPS is considered for navigation inside buildings due to obstacles (e.g., shopping malls, hospitals, etc.) and because signals cannot be absorbed by the building walls. To tackle the aforementioned issue, other technologies have emerged aimed at indoor navigation, such as Wireless-Fidelity (Wi-Fi), Bluetooth and sensors. This paper{\textquoteright}s contribution is towards indoor navigation and more specifically, it targets at designing and developing a tracking and navigation system aimed at people that experience difficulties in indoor orientation using a wearable device. The user takes direction from the wearable device for the indoor orientation through voice commands helping him to avoid obstacles. The central part of the system is a device that provides the ability to navigate and route by voice commands, based on the device{\textquoteright}s location and orientation capabilities.},
	author = {Eirini Barri and Christos Bouras and Apostolos Gkamas and Christina Koulouri and Evangelos Michos and Spyridon Katsampiris}
}
@inbook {4496,
	title = {Search and Rescue System Based on NB-IoT Wearable Device},
	booktitle = {Principles and Applications of Narrowband Internet of Things (NBIoT), IGI Global},
	year = {2020},
	pages = {195-222},
	chapter = {9},
	abstract = {This chapter presents the design and development of a search and rescue (SAR) system, for the location and provision of aid to people who are missing or in imminent danger, especially those belonging to population groups with a particularly high probability of getting lost. With the use of Low-Power Wide Area Network (LPWAN) technology, such as Narrow Band Internet of Things (NB-IoΤ), authors are able to provide search and rescue solutions for individuals, especially those belonging to groups of people who are more likely to get lost. The central part of the system is a modular {\textquotedblleft}wearable (portable){\textquotedblright} device, while in the framework of the implementation of this system authors have seriously taken into consideration the aspects of energy efficiency in order to provide better battery life.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris and Nikolaos Papachristos}
}
@conference {4459,
	title = {Text to Speech through Bluetooth for People with Special Needs Navigation},
	booktitle = {The Sixteenth International Conference on Networking and Services (ICNS 2020), September 27, 2020 - October 01, 2020 , Lisbon, Portugal},
	year = {2020},
	abstract = {As far as outdoor navigation is considered, the Global Positioning System (GPS) technology is still one of the most (if not the most) commonly used approaches. Even though it is still considered an ideal solution for navigating in outdoor areas, challenges and problems arise when GPS is considered for navigation inside buildings due to the fact that GPS signals cannot penetrate walls/ceilings (e.g., shopping malls, hospitals, etc.) and because signals can be absorbed by the building walls. This paper{\textquoteright}s contribution is navigation system that assists people with special needs using an audio guidance system that incorporates input from a voice recognition system. The central part of the system is a device that is able to identify the position and orientation of the person that carries it and provide the ability to navigate and route by voice commands. The suggested voice synthesis system is used, so as to guide the user through obstacles in indoor locations. The information of the precise location and.orientation of the device is made available to the whole system, through the building{\textquoteright}s network infrastructure, so that the user{\textquoteright}s mobile phone, been connected to the same network and also to the user{\textquoteright}s headset through BLE, is able to send audio commands. For the voice commands, Google Cloud Text-ToSpeech (TTS) will be used, supposed that an online connection is active on the user{\textquoteright}s device.},
	author = {Eirini Barri and Christos Bouras and Apostolos Gkamas and Christina Koulouri and Evangelos Michos and Spyridon Katsampiris}
}
@conference {4414,
	title = {Comparison of LoRa Simulation Environments},
	booktitle = {The 14th International Conference on Broad - Band Wireless Computing, Communication and Applications (BWCCA - 2019), Antwerp, Belgium},
	year = {2019},
	month = {November 7 - 9},
	pages = {374-385},
	abstract = {Internet of Things (IoT) is used more and more in our everyday life, connecting different wireless devices, and their distance can vary from some centimeters to many kilometers. New IoT technologies such as Long Range (LoRa) are emerging enabling power efficient wireless communication over very long distances. Simulation of LoRa networks is quite important, because can be used for the design and the evaluation of LoRa based application without the need of costly implementations or before to proceed to the actual implementation of the system. Choosing the right parameters of the systems like spreading factor can improve the energy consumption of the wireless devices. This paper presents the most important LoRa simulation environments available in the literature and after that, we present a comparative evaluation of LoRa simulation environments. The benefits, the disadvantages and the highlights of each LoRa simulation environment is presented.},
	author = {Christos Bouras and Apostolos Gkamas and Spyridon Katsampiris and Vasileios Kokkinos}
}
