Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> 2) BLUETOOTH <s> Video-on-demand (VOD) service requires balanced use of system resources, such as disk bandwidth and buffer, to accommodate more clients. The data retrieval size and data rates of video streams directly affect the utilization of these resources. Given the data rates which vary widely in multi-resolution video servers, we need to determine the appropriate data retrieval size to balance the buffer with the disk bandwidth. Otherwise, the server may be unable to admit new clients even though one of the resources is available for use. To address this problem, we propose the following new schemes that work together: (1) A replication scheme called Splitting Striping units by Replication (SSR). To increase the number of admitted clients, SSR defines two sizes of striping unit, which allow data to be stored on the primary and backup copies in different ways. (2) A retrieval scheduling method which combines the merits of existing SCAN and grouped sweeping scheme (GSS) algorithms to balance the buffer and disk bandwidth usage. (3) Admission control algorithms which decide whether to read data from the primary or the backup copy. The effectiveness of the proposed schemes is demonstrated through simulations. Results show that our schemes are able to cope with various workloads efficiently and thus enable the server to admit a much larger number of clients. <s> BIB001 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> 2) BLUETOOTH <s> We study carefully the IEEE 802.11ah draft standard published in July 2014.We overview use cases of .11ah, especially related to smart cities scenarios.We describe in details novel mechanisms and explain why they are needed in .11ah. Smart technologies play a key role in sustainable economic growth. They transform houses, offices, factories, and even cities into autonomic, self-controlled systems acting often without human intervention and thus sparing people routine connected with information collecting and processing. The paper gives an overview of a novel Wi-Fi technology, currently under development, which aims to organize communication between various devices used in such applications as smart grids, smart meters, smart houses, smart healthcare systems, smart industry, etc. <s> BIB002 </s> Low Power Wide Area Networks: A Survey of Enabling Technologies, Applications and Interoperability Needs <s> 2) BLUETOOTH <s> Internet of Things (IoT) technology has attracted much attention in recent years for its potential to alleviate the strain on healthcare systems caused by an aging population and a rise in chronic illness. Standardization is a key issue limiting progress in this area, and thus this paper proposes a standard model for application in future IoT healthcare systems. This survey paper then presents the state-of-the-art research relating to each area of the model, evaluating their strengths, weaknesses, and overall suitability for a wearable IoT healthcare system. Challenges that healthcare IoT faces including security, privacy, wearability, and low-power operation are presented, and recommendations are made for future research directions. <s> BIB003
Portable devices can also be connected using a wireless technology standard called Bluetooth [28] . Bluetooth is an industry specification currently managed by the Bluetooth special interest group (SIG). It sends small packets over multiple 1 MHz channels of bandwidth and uses short-range radio frequency (RF) from 2.402 to 2.480 GHz of the industrial, scientific and medical (ISM) band. The IEEE standard for Bluetooth is 802.15.1  , in which the radio for the physical layer and logical link control and adaptation protocol (L2CAP), link manager protocol (LMP) and baseband for the MAC layer are defined. Bluetooth has been mainly used for connecting wireless devices distributed in a small area (maximum of 30 m). Multiple radios allow a number of different applications such as streaming audio between a smartphone and speaker, controlling medical devices from a tablet or exchanging messages between nodes. On the one hand, the Bluetooth low energy (BLE) radio is designed for ultra low power and reliable and secure operations of continuous data streaming applications. The data are transmitted over 40 channels using a robust frequencyhopping spread spectrum (FHSS) to provide ranges for data rates (between 125 kbps and 2 Mbps), power levels (from 1 mW to 100 mW) and security options. The Bluetooth basic rate/enhanced data rate (BR/EDR) radio on the other hand, which is typical for burst data transmission, can support data rates from 1-3 Mbps and similar power and security levels of the LE radio [28] . Bluetooth has been adopted by a number of use-cases including control and monitoring of smart building and industry and automation of heating, air conditioning, security, lighting and location services such as indoor navigation, asset and item tracking, space utilization and point of interest information [28] . BLE was identified as the most suitable short-range communications solution in healthcare BIB003 . 3) WiFi IEEE 802.11 (also called WiFi) is another short-range technology that enables communication between wireless devices within a limited distance. WiFi is commonly used for closed environments such as homes and offices. It uses 5 GHz and 2.4 GHz in the ISM band. In addition to the IEEE 802.11, there are 802.11a/b/e/g/h/i/k/n/p/r/ac/ad/ax standards  . Additional features were added to 802.11ac to improve the performance and speed and better manage the interference. It achieves these features through more channel bounding and MIMO and denser modulation. WiFi has advantages over ZigBee and Bluetooth in terms of the data rate and coverage distance. New generations of WiFi allow nodes to communicate at very high data rates (e.g., 802.11ad has a data rate up to 7 Gbps) and, compared with ZigBee and Bluetooth, have much lower latency and higher power consumption. WiFi has managed to extend the communication distance and decrease delay (at the expense of power consumption), but the number of supported devices has remained a challenge BIB001 , BIB002 . The WiFi improvements, therefore, do not meet the requirements of the IoT applications. The technical features of the discussed short-range M2M wireless technologies are summarized in Table 1 . Although, ZigBee, Bluetooth and WiFi have been used for connecting various wireless devices, they are not able to address the demands of current IoT applications in terms of network range, capacity and power efficiency. This necessitates the design of other technologies that maintain the good features of available technologies and enhance their limitations. Furthermore, they should allow M2M communications while meeting the requirements of different IoT applications and can be deployed in all environments.