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Inside Bluetooth Low Energy EXCLUSIVE


The operational mode of Bluetooth low-energy technology ideally suits transmission of data from compact wireless sensors (exchanging data every half second) or other peripherals like remote controls where fully asynchronous communication can be used. These devices send low volumes of data (i.e. a few bytes) infrequently (for example, a few times per second to once every minute or more seldom).




Inside bluetooth low energy



Dual-Mode Chips will be used anywhere a Classic Bluetooth chip is used today. The consequence is that cell phones, PCs, Personal Navigation Devices (PNDs) or other applications fitted with a dual-mode chip will be capable of communicating with all the legacy Classic Bluetooth devices already on the market as well as all future Bluetooth low energy devices. However, because they are required to perform Classic Bluetooth and Bluetooth low energy duties, dual-mode chips are not optimized for ULP operation to the same degree as single-mode devices.


Single-mode chips can operate for long periods (months or even years) from a coin cell battery such as a 3V, 220mAh CR2032. In contrast, Classic Bluetooth technology (and Bluetooth low energy dual mode devices) typically requires the capacity of at least two AAA cells (which have 10 to 12 times the capacity of a coin cell and much higher peak current tolerance), and often more, to power them for days or weeks at most (depending on the application). (Note: There are some highly specialized Classic Bluetooth applications that can run on batteries with a lower capacity than AAA cells.)There are three characteristics of Bluetooth low-energy technology that underlie its ULP performance: maximized standby time, fast connection, and low peak transmit/receive power.


Once connected, Bluetooth low-energy technology switches to one of its 37 data channels. During the short data transmission period the radio switches between channels in a pseudo-random pattern using the Adaptive Frequency Hopping (AFH) technology pioneered by Classic Bluetooth technology (although Classic Bluetooth technology uses 79 data channels).


A clue to some of the likely early applications is provided by the Bluetooth SIG's intention to follow up the December 2009 publication of Bluetooth Version 4.0 Core Specification (which includes Bluetooth low energy) with the release of the first Profiles: these Profiles optimize a generic Bluetooth low energy chip for a specific application such as Personal User Interface Devices (PUID) (such as watches), Remote Control, Proximity Alarm, Battery Status and Heart Rate Monitor. Other health and fitness monitoring profiles such as blood-glucose and -pressure, cycle cadence, and cycle crank power will follow. (See figure 3.)


The low cost and low maintenance (because batteries require only infrequent changes) of Bluetooth low energy sensors will encourage widespread use in public places. One key application could be indoor location (where there is no GPS signal) whereby sensors around a large public building (such as an airport or rail station) constantly broadcast information about their location. A Bluetooth low energy equipped cell phone passing within range could then display that information to its owner. Sensors could transmit other information such as flight times and gates, location of amenities, or special offers from nearby shops. (See figure 4.)


Once the fully qualified silicon reaches the market, expect a tsunami of Bluetooth low energy products to follow. Analyst IMS estimates that by 2013, a billion Bluetooth low energy devices will be sold every year. That represents the fastest adoption of any wireless technology by far.


About the Author: Kjartan Furset is Senior Applications Engineer with Nordic Semiconductor. Nordic Semiconductor is a leading manufacturer of proprietary 2.4GHz ULP silicon solutions and a member of the group that developed the Bluetooth low energy wireless specification. The company expects to be among the first to market single mode devices meeting the specification. For more information on these products, go to www.nordicsemi.com. For more on Bluetooth low-energy technology, go to _Energy.aspx.


The Low Energy part in Bluetooth Low Energy is there for a reason. Bluetooth Low Energy is usually selected as a wireless technology in a product for two main reasons: the proliferation of Bluetooth low energy in smartphones and the low energy consumption that comes with it (allowing you to design devices that can last for years on tiny batteries).


Nowadays, when satellite navigation systems such as GPS, GLONASS, or Galileo are available for everyone, it is usually not a problem to locate a person or a mobile device outside. A situation can get more complicated in high-density urban areas with rare line-of-sight to the satellites of the corresponding system. The situation is most complicated inside buildings with no line-of-sight. In such cases, other solutions are employed, usually those based on radio networks (e.g., IEEE 802.11-WiFi) and fingerprints of signal strengths of individual WiFi devices which transmit their signals inside a building [1]. Localization accuracy is influenced by a number of circumstances, for example, by characteristics of transmitters and receivers and characteristics of the environment which influence the radio signal propagation. Another factor which can be adjusted quite easily is the number of radio transmitters and their positions. A typical situation is that there already are some WiFi access points in the building which more or less cover the building with the radio signal which can be used for localization. To increase the accuracy of the localization, it is possible to install more transmitters which would enrich the individual fingerprints or cover the places which are poorly covered by the existing WiFi network.


The rest of this paper is organized as follows. We discuss related work in Section 2. Section 3 describes the technology of BLE beacons (iBeacons) and deals with support of Bluetooth Low Energy with the Google Android platform. Section 4 summarizes the use of BLE beacons in indoor navigation. Section 5 describes the architecture of our indoor localization system based on BLE beacons and the localization method. Section 6 is focused on the arrangement of BLE beacons inside the building. Section 7 describes the results of the evaluation. In Section 8, we summarize, discuss, and interpret the achieved results. Section 9 concludes the paper.


Methods based on triangulation can be further divided into lateration and angulation [2]. These methods use estimation of the distance from several transmitters based on signal attenuation [3], time characteristics of the signal propagation (TOA: Time Of Arrival [4]; TDOA: Time Difference of Arrival [5]), or the direction of the received signal (AOA: Angle of Arrival [6]) when using directional antennas or antenna arrays. All these methods achieve good performance in an open space with line-of-sight propagation between the transmitter and the receiver. Unfortunately, they have weak results inside buildings where the measured variables are highly influenced by the environment. The radio signal may be reflected and attenuated by several obstacles such as walls making the estimation of distance more difficult.


Bluetooth-based indoor localization is not a novel idea [14, 15]. Due to the limitation of the original Bluetooth specification (now called Bluetooth Classic), this approach has not been widely used. The time required for obtaining a sufficient number of nearby Bluetooth devices was not satisfactory due to the lengthy process of discovery. Likewise, energy and economic demands of Bluetooth infrastructure were high compared to WiFi-based infrastructure, which also served other purposes.


The most important function for BLE indoor localization is scanning of the available BLE devices in the neighborhood. For this purpose, API level 18 offers startLeScan() and stopLeScan() methods of the BluetoothManager class. The scanning process is asynchronous and every device found is reported to an instance of the LeScanCallback callback class. The scanned device is represented by the BluetoothDevice class which includes its MAC address, byte-array scan record (containing UUID, etc.), and RSSI. API level 21 moves the process of low energy scanning into the separate BluetoothLeScanner class. Its instance is obtained by calling the getBluetoothLeScanner() method of the BluetoothAdapter class. In contrast to API level 18, it is possible to specify even more detailed parameters of scanning. Unfortunately, implementation of the above mentioned classes and underlying system libraries can vary across different vendors. The most common issue is that BLE devices are not reported repeatedly during the scanning process which is a condition necessary for localization. For this reason it is necessary to implement a mechanism which starts and stops scanning repeatedly in a given time interval. It is also possible to use available libraries, for example, Android Beacon Library ( -beacon-library/), which provides CycledLeScanner class that encapsulates this mechanism.


WiFi networks are commonly being used for localization inside buildings. A building is usually a complicated system regarding WiFi signal propagation due to the materials used. That is why areas with no WiFi signal may appear in the buildings despite high concentration of efficient WiFi access points. In such areas it is not possible to collect fingerprints because they would contain no signals measured from the surrounding WiFi networks. These areas can additionally be covered by other transmitters. For this purpose, BLE beacons can be used. They transmit a Bluetooth signal instead of a WiFi signal. While powered by batteries, they can be placed in less accessible places where there are no power sockets or other forms of supply, such as ethernet cables, allowing to use power-over-ethernet. When placing the beacons it is necessary to care about the radiation pattern of a given device and also about possible attenuation elements in the environment. Reference [22] deals with this topic in detail. 041b061a72


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