BLE Beacons in the Smart City: Applications, Challenges, and Research Opportunities
11 BLE Beacons in the Smart City: Applications,Challenges, and Research Opportunities
Petros Spachos,
Senior Member, IEEE, and Konstantinos Plataniotis,
Fellow, IEEE
Abstract —Internet of Things (IoT) helps to have every individual interconnected with their surroundings and to interact with themthrough smart devices. In recent years, Bluetooth Low Energy (BLE) technology has become very popular in the smart infrastructures,the medical and retail industry, and many more, due to its availability in a plethora of wireless devices. BLE is widely used in IoTdevices, such as smartphones, smartwatches, and BLE beacons. Beacons are small, low cost and low power, wireless transmittersthat bring attention to their location by broadcasting a signal with a unique identifier at regular intervals. BLE beacons are a promisingsolution for many smart city applications: from proximity marketing to indoor navigation. However, they do pose security and privacychallenges. This work discusses the characteristics of BLE beacons, the applications that can benefit from them, and the challengesthey pose while try to identify research opportunities and future directions. (cid:70) I NTRODUCTION B LUETOOTH
Low Energy (BLE) beacons, commonlyknown as beacons, are devices growing in popularityand research potential. Their deployment is projected toreach 400 million deployed devices globally by the year2020 [1]. They can help with the next step from IoT devicesto smart and social objects that interact with the users [2],[3]. Beacons broadcast signals at certain intervals and withintheir transmission range. An analogy of the beacon’s opera-tion is with the operation of a lighthouse, which representsa known location that can be uniquely identified by itslight. Every ship that sees the light, they know about theexistence of the lighthouse. However, the lighthouse neithercommunicates with the ships nor does it know how manyships see its light. Similarly, a beacon is broadcasting a radiosignal to advertise to BLE-enabled devices its presence inthe area. It is not able to communicate with the devices norto identify how many devices are receiving its signal.Beacons operation is shown in Fig. 1. Several beaconsin an area, they broadcast their signals. BLE-enabled de-vices, such as smartphones, smartwatches and single-boardcomputers like Raspberry Pis can listen to the signal andthrough applications, they can trigger some actions. Theseapplications are running on the hosting device, while thebeacons are not aware of them nor of the number of nearbybeacon devices.They are wireless devices that use Bluetooth Low Energy(BLE) technology, which was developed for the purposesof low power consumption for applications that requireminimal data throughput. Their small size, low cost, andrelatively long battery life increase their popularity. Theybroadcast packets that identify the particular beacon, alongwith possible telemetry data collected from sensors that mayhave been included by the beacon manufacturer.Beacons are attractive solutions for several Internet ofThings (IoT) applications [4]. Their small size and lowcost provide a means of increased scalability and theirBLE functionality establishes simple integration with smart-phone devices, making them a highly versatile device. Theycan be used in a plethora of smart city applications, fromadvertisement and Location Based Services (LBS) to indoor
BLE
Beacon
BLE
Beacon
BLE Beacon BLE
Beacon
Fig. 1: BLE beacons deployed in a city and broadcasting theirsignals to nearby devices. A device can listen signals fromseveral beacons and take some actions in response.localization [5], positioning, and tracking [6].
Wireless Technologies for Smart City Applications
For wireless data transmission, smart city applications andIoT devices can take advantage of traditional wireless in-frastructure, to minimize the additional deployment cost,or use some of the wireless technologies that are designedspecifically for IoT devices and smart cities. The uniquecharacteristics of each application should always be consid-ered before the selection of the proper technology [7].Among the technologies that have been used success-fully in the past for general purpose devices and they arepopular for IoT systems as well, is the IEEE 802.11 standard,commonly known as Wi-Fi. A popular technology due tothe great distribution of access points and signal availabilityin different environments. Zigbee is another popular com-munication protocol based on the IEEE 802.15.4 standard,known for its low-power and secure networking. Zigbeeis intended to be simpler and less expensive than generalwireless networking. LoRaWAN is a long-range, low powerconsumption wireless technology while Near Fields Com-munication (NFC) allows wireless data transfer between a r X i v : . [ c s . N I] F e b two portable devices in close proximity. Radio FrequencyIdentification Device (RFID) was primarily designed fordata transferring and storing, and it can be passive (tags),where the electromagnetic field of the reader powers thedevice, or active (reader), where the RFID device has its ownpower source. Another popular technology is cellular IoTwhich connects IoT devices using existing cellular networks.Technologies such as NB-IoT and LTE-M will be a keypart of 5G, which is a promising solution for future IoTapplications with ultra-low latency and wide range services.There are also technologies that are specifically designedfor IoT devices such as the IEEE 802.11ah (Wi-Fi HaLow)and the Bluetooth Low Energy (BLE) that were designed tosupport the concept of IoT and smart cities.A popular wireless technology for short range commu-nication is Bluetooth [8]. The standard is managed by theBluetooth Special Interest Group (SIG) and can be foundin several devices from mobile phones to robotic systemsand laptops. Usually, it is used in symmetric connectionsbetween two devices. Bluetooth 4.0 aimed at novel applica-tions in the healthcare, fitness, beacons and Bluetooth LowEnergy (BLE) which is part of Bluetooth 4.0, is the popularbeacon technology. In comparison with traditional Wi-Fi, ithas low energy requirements and extended range. BLE wasdesigned specifically for IoT and smart cities application [9].It has low power requirements and good data transfer rates.BLE 4.0 can reach 25 Mbit/s at a distance of 60 meters. Asa competitor of Wi-Fi HaLow among IoT devices, Bluetooth5.0 was introduced recently. This latest version is claimedto have four times longer transmission range, exchangedata eight times faster, while it has twice the speed of theprevious version. BLE B
EACONS C HARACTERISTICS
BLE beacons have received a lot of attention due to theirunique characteristics that made them ideal for severalapplications. They are wireless devices with the main goal ofbringing attention to their location. Beacons are very smallsize, very low power, and especially low-cost devices thatbroadcast a wireless signal to all nearby devices. There isa wide variety of BLE beacon devices available from manyvendors with different hardware, firmware, and protocol.
Hardware
Beacon hardware is compact and simple. The hardwarecomponents dictate important factors, such as the cost, thepower consumption, the performance, the on-chip memory,and the size. Similar to other wireless device hardware,beacon hardware has three components: the radio chip, themicrocontroller, and the power source. Additionally, thereare beacons that have some sensors and general peripherals.Texas Instruments, Nordic Semiconductors, Dialog Semi-conductors, and Cypress are leading the beacon radio chipdevelopment process. Table 1, shows some representativepopular BLE chipsets. The availability of an integratedprocessor, the flash and RAM capacity and the current con-sumption are important factors for the proper chip selection.The processor in some of these chipsets is on-chip whilesome of them come without a processor. The 8051, and Manufacture SoC Integrated CurrentProcessor Cons. (RX/TX)Texas CC2541 8051 18.2 mACC256x External -Instruments CC26xx Cortex-M3 5.9 mANordic nRF51822 Cortex-M0 9.7/ 8Semiconductors nRF8001 External 14.6/12.7 mADialog DA14580 Cortex-M0 3.6 mASemiconductorCypress PRoC Cortex-M0 15.6/ 16.4 mASemiconductorTABLE 1: Chipset and their characteristics.the ARM Cortex-M0 and Cortex-M3 are popular choices.For many smart city applications, this should be sufficient,however, when more performance is required, standalonedevices should be selected, that can work with an externalmicrocontroller. The flash capacity starts from 32 kB andgoes up to 256 kB and the RAM capacity is between 8 kB and64 kB. It is important to note that all the chipsets supportBLE v4.1 or v.4.2 which is the most common today.The power source is another critical internal component.Coin cell batteries are popular among beacons. Dependingon the size of the hardware, the battery size varies. There arecoin cell batteries of 240 mAh allowing the beacon device tohave very small dimensions, at the cost of reduced batterylife. On the other hand, standard AA batteries of 2,000 mAhcan be used to drastically improve battery life, at the cost ofa far larger dimension. There are also beacons with build-in Li-ion battery as well as solar-powered beacons. Whenexternal power is required, power outlet and USB outlet arepopular choices.
Firmware
Each beacon has a specific firmware that makes use ofthe available hardware. A critical characteristic of beacon-based applications is the lifespan of the beacon nodes. Thefirmware controls several characteristics that impact thetotal power consumption. Two are the main configurationparameters that greatly affect the power consumption: thetransmission power, and the advertising interval.Transmission power is the strength of the signal beingbroadcast, often represented as decibels with reference to1 mW, i.e. dBm. As the signal travels in the air, its receivedsignal strength decreases. This is a trade-off. High trans-mission power levels can achieve long distances with morepower consumption requirements, while low transmissionpower achieves small ranges but less power is required.At the same time, long transmission range can increase theinterference between beacons, while short ranges might notfit the application needs.The second configuration parameter is the advertisinginterval. This is the frequency in which packet transmissionsoccur, often expressed in milliseconds. This is another trade-off. A high advertising interval of 100 ms (i.e. 10 times in asecond) will lead to a faster battery drain, but the receivercan get more signals and perform tasks with high accuracy,such as micro localization [5]. On the other hand, a low
Transmission Power (dBm) A v e r age P o w e r C on s u m p t i on ( m W ) Advertising Interval100 ms500 ms1000 ms
Fig. 2: Average power consumption under different adver-tising intervals and transmission power levels.advertising interval of 1,000 ms (i.e. 1 time in a second) willlead to an extended lifespan of the beacon, but it shouldbe preferred in applications that can cope with this latency,such as in proximity-based applications. Fig. 2 depicts howthe energy consumption changes over three transmissionpower levels and three advertising intervals for a BLE bea-con. It is clear that the power consumption is proportionalto the transmission power and inversely proportional to theadvertising interval.
Protocol structure
BLE has 40 physical channels in the 2.4GHz ISM band, eachseparated by 2MHz. BLE defines two types of transmissions,advertising and data transmission. Out of the 40 channels,three channels, 37, 38 and 39 are used for advertising andthe rest for data transmission [8]. The three channels wereselected to avoid conflict with Wi-Fi traffic in the area. It isimportant to note that beacons are connectionless devices,hence no device pairing is required. BLE defines a packerformat for transmission. This format has four components:preamble, access address, Protocol Data Unit (PDU) andCyclic Redundancy Check (CRC).Beacons need a protocol that facilitates the integrationof manufacturing, programming, transmission, and generalfunctionality. Bluetooth SIG has not defined an official bea-coning standard, however, among the most commonly usedprotocols is the iBeacon by Apple [10], the Eddystone byGoogle [11], the AltBeacon by Radius Network [12], andthe GeoBeacon by Tecno-World [13]. The structure of eachprotocol is shown in Fig. 3. Among the different fields,the beacon ID is crucial, the Major and Minor fields canbe used to identify different areas and applications whilethe RSSI and the coordinates provide useful information forpositioning and tracking.Each approach has advantages and for every smart cityapplication, the protocol should be carefully selected. For in-stance, iBeacon and AltBeacon offer more space to forwardinformation. Although iBeacon uses specific manufacturer
Preamble(1 Byte) Access Address(4 Bytes) CRC(3 Bytes)PDU(2-39 Bytes)Header (2 Bytes)
MAC address (6 Bytes)
Data (28 Bytes)
UUID(16 Bytes) Major (2 Bytes) Minor (2 Bytes) TX Power(1 Byte)Adv. Header(2 Bytes) Company ID(2 Bytes) iBeacon Type (1 Byte) iBeacon Length (1 Byte)
BLE Advertising PDU
Flags (3 Bytes) iBeacon
Eddystone Frame(20 Bytes)Services(4 Bytes)
AltBeacon
Beacon ID(20 Bytes) Ref RSSI (1 Byte)
MFG
RSVD(1 Byte)
GeoBeacon
NAC Coord. Long. (6 Bytes)
User Data(8 Bytes)NAC Coord. Lat. (6 Bytes)AD
Type(1 Byte) AD Length(1 Byte) MFG ID(2 Bytes) Beacon Code(2 Bytes)EID Length (1 Byte)
EID Type (1 Byte)
MFG ID(2 Bytes)
Beacon
Code(2 Bytes) Ref RSSI(1 Byte) Voltage(1 Byte)Length, Type, UUID(4 Bytes)
Fig. 3: Structure of four BLE protocols.ID for every chipset, in AltBeacon, which is open sourceprotocol, the manufacturer ID can be defined by the user.On the other hand, Eddystone broadcasts three differenttypes of packets: UID, URL, and TLM which can help totransfer different data, while GeoBeacon has a very compactdata storage and can provide high resolution coordinates,especially for location-based applications.
Additional Sensing Capabilities (Peripherals)
BLE beacons often include a variety of additional low powersensors such as temperature and humidity sensors, luxome-ter, barometer, accelerometer, gyroscope, microphone, etc.The sensors enable the beacons to provide useful infor-mation about the environmental conditions in which it isdeployed. At the same time, they can be used for manyunique applications, such as micro-climate data collectionand acoustic monitoring level prediction. S MART C ITY A PPLICATIONS
Several smart city applications can take advantage of theunique characteristics of beacons. They can be placed inmany environments, both indoor and outdoor and convertthem into smart areas, by providing interaction with theusers. Most of the applications are context-aware servicesand they fall into two general categories: Proximity-BasedServices (PBS), and Location-Based Services (LBS). In bothservices, beacons can be placed in a static position or at-tached to moving objects.
Proximity-Based Services
PBS delivers information according to the proximity of thereceiver node from the transmitter node.
Point of Interest
When the beacons are static, they can be used as Pointof Interest (PoI) solutions and enhance interactivity in asmart museum or for proximity marketing. In a smart mu-seum [14], they can be placed beside the exhibits, shown inFig. 4a, and when the visitors are close to them, they can for-ward to the visitor’s smartphone, useful information about (a) Beacon beside an exhibit. (b) Beacon inside a luggage.
Fig. 4: Proximity-Based Services: Beacon (a) besides Point ofInterest and (b) attached to a moving object.the exhibit. In a shopping mall, offers can be provided to theusers when they are about to enter a store or a restaurant, aslong as they have their smartphone Bluetooth active and usethe proper mobile application. Beacons can offer many moreopportunities to deliver context and enhance interactivity atthe right time and place. However, the proper placement ofthe beacons and their advertising interval are crucial. Theusers might end up getting notifications from every beaconin the area which can lead to too many notifications andinformation that might not be useful.
Moving objects
Beacons can be attached to moving objects such as luggage,bicycles or even cars. Mobile applications can be imple-mented in order to collect beacon signals and notify theusers when they are close to them. For instance, beacons canbe placed inside a luggage, shown in Fig. 4b, and when theluggage in a crowded airport is close to their owner, theirsmartphone can send them a notification. The advantagesof using beacons in such applications are the low cost andthe ease of deployment. At the same time, the broadcastingnature of beacon signals poses some security concerns. Thelocation of valuable assets can be revealed to eavesdroppersthrough the beacon signals.
Location-Based Services
LBS delivers information according to the location of theuser.
Indoor Positioning Systems
In Indoor Positioning System (IPS), beacons can be deployedat static positions, shown in Fig. 5a, in a complex indoor
Beacon
RECEIVERRECEIVER RECEIVERRECEIVERRECEIVERRECEIVER (a) Indoor Positioning System.
Beacon
RECEIVERRECEIVER RECEIVERRECEIVERRECEIVERRECEIVER (b) Real Time Location System.
Fig. 5: Location-Based Services: Beacon used (a) at an IPSand (b) at a RTLS.environment, such as an office or a University. A usercan position in the area by performing localization on aBLE-enabled device such as a smartphone, according tothe received signals. The beacons keep broadcasting whilethe users collect these signals with their smartphone andnavigate in the area. However, several factors, such as thenumber of the transmitting beacons and their transmissionpower can greatly affect the accuracy of the system. Thesefactors should always be selected after extensive experimen-tation in the area. The placement of the beacons would be achallenge, due to the fact the beacons performance decreaseswhen the interference increases. Hence, beacons cannot beplaced too close to each other. At the same time, techniquessuch as fingerprinting, which records the signal strengthfrom several beacons in range and store this information in adatabase along with the known coordinates of each beacon,can be used to improve the overall system accuracy.
Real Time Locating Systems
In Real Time Locating System (RTLS), beacons can be at-tached to valuable moving assets, shown in Fig. 5b, in ahospital or a warehouse. RTLS works in the opposite wayof the IPS: the moving beacon transmits the signal to edgedevices, which performs the localization. A hospital canintegrate beacon technology in order to maximize informa-tion exchange. Beacons can be placed on critical medicalassets and devices. They can report the location of theassets in real time in a general management system. Thebeacon will transmit the signal to nearby collecting devices,such as Raspberry Pi. Then, the beacon location can beestimated. There are many techniques that can be used tofind the location of the beacon, such as trilateration from theReceived Signal Strength of the beacons [5]. As the beacon ismoving in the area, its location can be tracked based on theinformation it transmits to nearby devices. When needed,the exact location of each device in a large hospital can befound. In such applications, the advertising interval of thebeacon should be carefully selected to meet the expectedmoving speed of the object. At the same time, factors suchas the number of the collecting devices and their placement can also affect the performance of the system. Advancefiltering approaches should be implemented to improve thelocalization accuracy of the system. With further processing,beacons on nearby devices can also navigate the user to therequired device. S ECURITY AND P RIVACY C HALLENGES
The high deployment of beacons in smart city applicationshas also raised several security issues and privacy con-cerns [15]. Some of these concerns are more challenges tocope with, depending on the application and the nature ofthe information.
Security issues
There are some security issues regarding beacons. Somemore challenging to cope with. • Cracking:
Due to their small size, beacons can beplaced in many locations. Usually, beacons are “hid-den” in different spots to cover an area. An importantsecurity attack on beacons is their physical removal.An attacker can remove the beacon from a wall, openit up and have straight access to its hardware and anystored information.A real time monitoring of the beacon status canalleviate this problem along with the decrease ofthe information that is stored inside the beaconmemory. Information such as user passwords oruser preferences should not be stored locally in thebeacon. At the same time, when an interruption ofthe communication between the control system andthe beacon happens, an alert should be sent to thesystem administrator. However, an increase in thecommunication between the beacon and the controlsystem may affect the lifespan of the beacons dra-matically. Therefore, there must be a balance betweenmonitoring frequency and energy management. • Spoofing:
Spoofing is when an attacker detects andclones a beacon. Beacons do not come with advancedencryption mechanisms. Hence, most of the timethey broadcast their ID. An attacker who wants toattack the beacon and consequently, the users usingthis beacon, can use the same ID at another areaand create a clone beacon. With the use of the clonebeacon, the attacker can forward false information tothe user. For instance, in a smart museum with bea-cons in the building, one beacon can send welcomemessages to the visitors when they use the museumapplication and enter the building. An attacker cancopy the beacon ID and replay the welcome messagein another location, far away from the museum,leading the visitors to remove the application.A technique to minimize the issue of spoofing is bydynamically changing the ID of the beacons periodi-cally. Beacons can create random IDs periodically tominimize spoofing. However, the user has to accepta connection to the new beacon ID every time. • Piggybacking:
Piggybacking is when an attacker lis-tens to a beacon and captures the UUIDs, Majors,and Minors and adds them to another application without consent. The attacker can then even clonethe first application. For instance, in a shopping mall,Store A can offer a BLE-based mobile application thatsends promotion codes to customers, when they areclose. Store B can clone the beacon and the mobileapplication for its customers. In this way, when thecustomers that have the application of Store B, entersStore A, they will receive promotions for Store B. • Hijacking:
In the communication with the beacons,there is no encryption techniques. Passwords or im-portant information that is broadcasted from the bea-con can be hijacked by an eavesdropper. Advancedencryption mechanisms can be applied to alleviatesome of the security issues. However, this may ad-versely affect the lifespan of the beacon.
Privacy concerns
Privacy is important, especially when it comes to interactionwith everyday objects and can reveal private patterns andhabits. The following privacy concerns should be consideredfor BLE beacon applications. • Static IP.
Most BLE beacons have a static IP. Thisstatic IP is broadcasted so everyone in the transmis-sion area can receive it. Hence, an attacker can mimica trusted beacon, by using the same trusted IP andhave access to private information.Many vendors have started research on dynamic IPassignment. This would require extra energy thatmay have varying effects on the lifespan of thebeacon. • Risk of unlawful surveillance.
Another importantprivacy concern comes from unlawful surveillance.Most of the beacon applications are based on lo-calization. By using location services offered frombeacons, the users share their location with them.Any attack on the beacons can reveal behaviouralpatterns about the user. Hence a user can be undersurveillance without permission or their behaviouraland location patterns can be shared with unautho-rized personnel through the beacons. • Risk of undesired advertisement.
Beacons are useda lot for advertisement. For more targeted adver-tisements, information about the user can be sharedwith the beacon applications. This information canbe used by third parties for further undesired adver-tisements. F UTURE D IRECTIONS
Although some of the challenges remain, their unique char-acteristics will increase the BLE beacons deployment insmart city applications. Since beacons can transmit a lotinformation over seconds, providing in this way a largeamount of data, machine learning techniques can be usedto improve their usage. It is important to have smart dataprocessing for smart city applications. For instance, deeplearning approaches can be applied to improve the local-ization accuracy of the deployed systems. The availabilityand the low cost of the BLE signals can help towardsthis direction. At the same time, general machine learning approaches can be applied to alleviate some of the currentsecurity and privacy challenged. The integration of machinelearning approaches that can enhance security and privacy,into content aware location-based services along can open anew and promising research area. Similarly, social learningusing BLE beacons can be used to promote wellness.The new BLE v.5.0 can improve the accuracy of currentnavigation applications and lead to the development ofseveral more. The addition of the direction finding capa-bility can be used along with techniques such as Angle ofArrival (AoA) and Angle of Departure (AoD) to improvethe performance of the BLE-based systems. C ONCLUSION
BLE beacons are a promising, low cost and energy-efficientIoT solution, mainly for location application. The selectionof the proper beacon and the optimal configuration ofthe beacon parameters are important factors for successfulapplication deployment. Experiments should be conductedto examine the performance of different beacons in differentareas while security and privacy should always be a con-cern. At the same time, the unique characteristics of BLEbeacon make them an attractive solution for several smartcity applications. R EFERENCES
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Petros Spachos (M’14–SM’18) received theDiploma degree in Electronic and Computer En-gineering from the Technical University of Crete,Greece, in 2008, and the M.A.Sc. degree in 2010and the Ph.D. degree in 2014, both in Electricaland Computer Engineering from the Universityof Toronto, Canada. He was a post-doctoral re-searcher at University of Toronto from Septem-ber 2014 to July 2015. He is currently an As-sistant Professor in the School of Engineering,University of Guelph, Canada. His research in-terests include experimental wireless networking and mobile computingwith a focus on wireless sensor networks, smart cities, and the Internetof Things. He is a Senior Member of the IEEE.