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ith a qr code or transmitted using nfc this allows users to directly select a specific audio stream in applications such as audio guides in a museum simultaneous translations in multiple languages silent tv screens in a bar or community center public events or music performances at conference halls sports venues houses of worship station and service announcements in public transport and flight announcements in airports 52 midi edit developed by the midi manufacturers association mma working group now the midi association there is a formalized bluetooth le midi ble midi specification 53 a wireless protocol designed to transmit midi data over bluetooth low energy it focuses on power efficient wireless midi communication for devices such as midi controllers keyboards pedals etc that don t continuously stream data and without significant latency operating systems that support it include windows 10 version 1607 macos and android contact tracing and notification edit main articles digital contact tracing bluetooth proximity tracing contact tracing mobile phones and exposure notification in december 2020 the bluetooth sig released a draft specification for a wearable exposure notification service this service allows exposure notification services on wearable devices to communicate with and be controlled by client devices such as smartphones 54 implementation edit chip edit starting in late 2009 bluetooth low energy integrated circuits were announced by a number of manufacturers these ics commonly use software radio so updates to the specification can be accommodated through a firmware upgrade hardware edit current mobile devices are commonly released with hardware and software support for both classic bluetooth and bluetooth low energy operating systems edit ios 5 and later 55 windows phone 8 1 56 windows 8 and later 57 windows 7 and earlier requires drivers from bluetooth radio manufacturer supporting ble stack as it has no built in generic ble drivers 58 android 4 3 and later 59 android 6 or later requires location permission to connect to ble blackberry os 10 60 linux 3 4 and later through bluez 5 0 61 unison os 5 2 62 macos 10 10 zephyr os technical details edit radio interface edit bluetooth low energy technology operates in the same spectrum range the 2 400 2 4835 ghz ism band as classic bluetooth technology but uses a different set of channels instead of the classic bluetooth 79 1 mhz channels bluetooth low energy has 40 2 mhz channels within a channel data is transmitted using gaussian frequency shift modulation similar to classic bluetooth s basic rate scheme the bit rate is 1 mbit s with an option of 2 mbit s in bluetooth 5 and the maximum transmit power is 10 mw 100 mw in bluetooth 5 further details are given in volume 6 part a physical layer specification of the bluetooth core specification v4 0 bluetooth low energy uses frequency hopping to counteract narrowband interference problems classic bluetooth also uses frequency hopping but the details are different as a result while both fcc and etsi classify bluetooth technology as an fhss scheme bluetooth low energy is classified as a system using digital modulation techniques or a direct sequence spread spectrum 63 specification basic enhanced data rate low energy nominal max range 100 m 330 ft 100 m 330 ft over the air data rate clarification needed 1 3 mbit s 125 kbit s 500 kbit s 1 mbit s 2 mbit s application throughput or goodput 0 7 2 1 mbit s 0 27 1 37 mbit s 64 active slaves 7 not defined implementation dependent security 56 128 bit and application layer user defined 128 bit aes in ccm mode and application layer user defined robustness adaptive fast frequency hopping fec fast ack adaptive frequency hopping lazy acknowledgement 24 bit crc 32 bit message integrity check wake latency from a non connected state typically 100 ms 6 ms minimum total time to send data det battery life 0 625 ms 3 ms 65 voice capable yes yes 66 network topology scatternet scatternet power consumption 1 w as the reference 0 01 0 50 w depending on use case peak current consumption 30 ma 15 ma primary use cases mobile phones gaming headsets stereo audio streaming smart homes wearables automotive pcs security proximity healthcare sports fitness etc mobile phones gaming smart homes wearables automotive pcs security proximity healthcare sports fitness industrial etc more technical details may be obtained from official specification as published by the bluetooth sig note that power consumption is not part of the bluetooth specification advertising and discovery edit ble devices are detected through a procedure based on broadcasting advertising packets this is done using 3 separate channels frequencies in order to reduce interference the advertising device sends a packet on at least one of these three channels with a repetition period called the advertising interval for reducing the chance of multiple consecutive collisions a random delay of up to 10 milliseconds is added to each advertising interval the scanner listens to the channel for a duration called the scan window which is periodically repeated every scan interval the discovery latency is therefore determined by a probabilistic process and depends on the three parameters viz the advertising interval the scan interval and the scan window the discovery scheme of ble adopts a periodic interval based technique for which upper bounds on the discovery latency can be inferred for most parametrizations while the discovery latencies of ble can be approximated by models 67 for purely periodic interval based protocols the random delay added to each advertising interval and the three channel discovery can cause deviations from these predictions or potentially lead to unbounded latencies for certain parametrizations 68 security edit bluetooth low energy has security instances such as the encrypted advertising data ead feature allowing some or all of the application data payload that is transmitted in advertising packets to be encrypted a standard mechanism for the sharing of key material between a broadcasting device and the observers that are intended to receive this data is also defined so that the data may be decrypted when received 69 all transmitted bluetooth le pdus include a cyclic redundancy check crc that is recalculated and checked by the receiving device for the possibility of the pdu having been changed in flight 69 software model edit all bluetooth low energy devices use the generic attribute profile gatt the application programming interface offered by a bluetooth low energy aware operating system will typically be based around gatt concepts 70 gatt has the following terminology client a device that initiates gatt commands and requests and accepts responses for example a computer or smartphone server a device that receives gatt commands and requests and returns responses for example a temperature sensor characteristic a data value transferred between client and server for example the current battery voltage service a collection of related characteristics which operate together to perform a particular function for instance the health thermometer service includes characteristics for a temperature measurement value and a time interval between measurements descriptor a descriptor provides additional information about a characteristic for instance a temperature value characteristic may have an indication of its units e g celsius and the maximum and minimum values which the sensor can measure descriptors are optional each characteristic can have any number of descriptors some service and characteristic values are used for administrative purposes for instance the model name and serial number can be read as standard characteristics within the generic access service services may also include other services as sub functions the main functions of the device are so called primary services and the auxiliary functions they refer to are secondary services identifiers edit services characteristics and descriptors are collectively referred to as attributes and identified by universally unique identifiers uuids any implementer may pick a random or pseudorandom uuid for proprietary uses but the bluetooth sig have reserved a range of uuids of the form xxxxxxxx 0000 1000 8000 00805f9b34fb 71 for standard attributes for efficiency these identifiers are represented as 16 bit or 32 bit values in the protocol rather than the 128 bits required for a full uuid for example the device information service has the short code 0x180a rather than 0000180a 0000 1000 the full list is kept in the bluetooth assigned numbers document online gatt operations edit the gatt protocol provides a number of commands for the client to discover information about the server these include discover uuids for all primary services find a service with a given uuid find secondary services for a given primary service discover all characteristics for a given service find characteristics matching a given uuid read all descriptors for a particular characteristic commands are also provided to read data transfer from server to client and write from client to server the values of characteristics a value may be read either by specifying the characteristic s uuid or by a handle value which is returned by the information discovery commands above write operations always identify the characteristic by handle but have a choice of whether or not a response from the server is required long read and long write operations can be used when the length of the characteristic s data exceeds the mtu of the radio link finally gatt offers notifications and indications the client may request a notification for a particular characteristic from the server the server can then send the value to the client whenever it becomes available for instance a temperature sensor server may notify its client every time it takes a measurement this avoids the need for the client to poll the server which would require the server s radio circuitry to be constantly operational an indication is similar to a notification except that it requires a response from the client as confirmation that it has received the message battery impact edit bluetooth low energy chipset power consumption when acting as a beacon as per the hitchhikers guide to ibeacon hardware by aislelabs 72 bluetooth low energy is designed to enable devices to have very low power consumption several chipmakers including cambridge silicon radio dialog semiconductor nordic semiconductor stmicroelectronics cypress semiconductor silicon labs and texas instruments had introduced bluetooth low energy optimized chipsets by 2014 devices with peripheral and central roles have different power requirements a study by beacon software company aislelabs reported that peripherals such as proximity beacons usually function for 1 2 years powered by a 1 000 mah coin cell battery 73 this is possible because of the power efficiency of bluetooth low energy protocol which only transmits small packets as compared to bluetooth classic which is also suitable for audio and high bandwidth data in contrast a continuous scan for the same beacons in central role can consume 1 000 mah in a few hours android and ios devices also have very different battery impact depending on type of scans and the number of bluetooth low energy devices in the vicinity 74 with newer chipsets and advances in software by 2014 both android and ios phones had negligible power consumption in real life bluetooth low energy use 75 2m phy edit bluetooth 5 has introduced a new transmission mode with a doubled symbol rate bluetooth le has been traditionally transmitting 1 bit per symbol so that theoretically the data rate doubles as well however the new mode doubles the bandwidth from about 1 mhz to about 2 mhz which makes for more interferences on the edge regions the partitioning of the ism frequency band has not changed being still 40 channels spaced at a distance of 2 mhz 76 this is an essential difference over bluetooth 2 edr which also doubled the data rate but was doing that by employing a π 4 dqpsk or 8 dpsk phase modulation on a 1 mhz channel while bluetooth 5 continues to use just frequency shift keying the traditional transmission of 1 mbit in the bluetooth basic rate was renamed 1m phy in bluetooth 5 the new mode at a doubled symbol speed was introduced as the 2m phy in bluetooth low energy every transmission starts on the 1m phy leaving it to the application to initiate a switch to the 2m phy in that case both sender and receiver will switch to the 2m phy for transmissions this is designed to facilitate firmware updates where the application can switch back to a traditional 1m phy in case of errors in reality the target device should be close to the programming station at a few meters le coded edit bluetooth 5 has introduced two new modes with lower data rate the symbol rate of the new coded phy is the same as the base rate 1m phy but in mode s 2 there are two symbols transmitted per data bit in mode s 2 only a simple pattern mapping p 1 is used which simply produces the same stuffing bit for each input data bit in mode s 8 there are eight symbols per data bit with a pattern mapping p 4 producing contrasting symbol sequences a 0 bit is encoded as binary 0011 and a 1 bit is encoded as binary 1100 77 in mode s 2 using p 1 the range doubles approximately while in mode s 8 using p 4 it does quadruple 78 the le coded transmissions have not only changed the error correction scheme but it uses a fundamentally new packet format each le coded burst consists of three blocks the switch block extended preamble is transmitted on the le 1m phy but it only consists of 10 times a binary 00111100 pattern these 80 bits are not fec encoded as usual but they are sent directly to the radio channel it is followed by a header block fec block 1 which is always transmitted in s 8 mode the header block only contains the destination address access address 32 bit and an encoding flag coding indicator 2 bit the coding indicator defines the pattern mapping used for the following payload block fec block 2 where s 2 is possible 79 the new packet format of bluetooth 5 allows transmitting from 2 up to 256 bytes as the payload in a single burst this is a lot more than the maximum of 31 bytes in bluetooth 4 along with reach measurements this should allow for localisation functions as a whole the quadrupled range at the same transmission power is achieved at the expense of a lower data being at an eighth with 125 kbit the old transmission packet format as it continues to be used in the 1m phy and 2m phy modes has been named uncoded in bluetooth 5 the intermediate le coded s 2 mode allows for a 500 kbit data rate in the payload which is both beneficial for shorter latencies as well lower power consumption as the burst time itself is shorter see also edit ant ant bluetooth low energy denial of service attacks dash7 eddystone ieee 802 15 ieee 802 15 4...
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