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Bluetooth Technology

Bluetooth Technology. David Treharne Ford Amateur Radio League February 21, 2013. Introduction.

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Bluetooth Technology

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  1. Bluetooth Technology David Treharne Ford Amateur Radio League February 21, 2013

  2. Introduction • Bluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength radio transmissions in the ISM band from 2400–2480 MHz) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Created by telecom vendor Ericsson in 1994,[2] it was originally conceived as a wireless alternative to RS-232 data cables. It can connect several devices, overcoming problems of synchronization

  3. Who was Harold Bluetooth? • Harald "Bluetooth" Gormsson (Old Norse: HaraldrblátǫnnGormsson, Danish: HaraldBlåtandGormsen) (probably born c. 935) was the son of King Gorm the Old and of ThyraDannebod. He died in 985 or 986 having ruled as King of Denmark from c. 958 and King of Norway for a few years probably around 970. Some sources state that his son SweynForkbeard forcibly deposed him as King. • The Bluetooth communications protocol in these devices is named after this king, ostensibly due to his abilities to make diverse factions communicate with each other. According to legend, he gained the nickname "Bluetooth" due to his love of blueberries, which stained his teeth. The Bluetooth logo is a bind rune merging the Younger Futharkrunes  (Hagall) (ᚼ) and  (Bjarkan) (ᛒ), Harald's initials.

  4. Frequencies of Operation • Bluetooth uses a radio technology called frequency-hopping spread spectrum, which chops up the data being sent and transmits chunks of it on up to 79 bands (1 MHz each; centered from 2402 to 2480 MHz) in the range 2,400–2,483.5 MHz (allowing for guard bands). This range is in the globally unlicensed Industrial, Scientific and Medical (ISM) 2.4 GHz short-range radio frequency band. It usually performs 800 hops per second, with Adaptive Frequency-Hopping (AFH) enabled • In the US, FCC part 15 on unlicensed system in the 900 MHz and 2.4 GHz bands permits more power than non-spread spectrum systems. Both frequency hopping and direct sequence systems can transmit at 1 Watt. The limit is increased from 1 milliwatt to 1 watt or a thousand times increase.

  5. Antennas • Savvi Bluetooth 8x3 antenna • BT Antenna 2.4—2.5 GHz • Peak Gain 1.39 dBi • Average Efficiency 78% • VSWR Match 2.0:1 max • Feed Point Impedance 50 ohms unbalanced • Power Handling .5 Watt cw • Polarization Linear • Isolated magnetic dipole

  6. Polar Plots • Antenna is directional in one direction, pretty isotropic in others. Designed for the top of a cell phone to be strong toward a headset.

  7. Spread Spectrum • Bluetooth can connect up to eight devices simultaneously in a 10 m radius. • Bluetooth uses a technique called spread-spectrum frequency hopping that makes it rare for more than one device to be transmitting on the same frequency at the same time. In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. • One of the challenges of frequency-hopping systems is to synchronize the transmitter and receiver. One approach is to have a guarantee that the transmitter will use all the channels in a fixed period of time. The receiver can then find the transmitter by picking a random channel and listening for valid data on that channel. The transmitter's data is identified by a special sequence of data that is unlikely to occur over the segment of data for this channel and the segment can have a checksum for integrity and further identification. The transmitter and receiver can use fixed tables of channel sequences so that once synchronized they can maintain communication by following the table. On each channel segment, the transmitter can send its current location in the table.

  8. Speed of Data • The older Bluetooth 1.0 standard has a maximum transfer speed of 1 megabit per second (Mbps), while Bluetooth 2.0 can manage up to 3 Mbps. Bluetooth 2.0 is backward-compatible with 1.0 devices. • Net throughput: Bluetooth can send data at more than 64 kilobits per second (Kbps) in a full-duplex link -- a rate high enough to support several voice conversations. If a particular use calls for a half-duplex link -- connecting to a computer printer, for example -- Bluetooth can transmit up to 721 Kbps in one direction, with 57.6 Kbps in the other. If the use calls for the same speed in both directions, Bluetooth can establish a link with 432.6-Kbps capacity in each direction.

  9. Typical Applications • Headsets for phones • Streaming audio to a vehicle stereo or home speaker system • PC mouse, keyboard, and printer • Replacment for RS-232 (its original intent) for PCs, GPS units, and medical devices • Replacement for infared controls, since it does not have to be strict line of sight. • Game controllers, such as Nintendo Wii • “Man Overboard” alarm when the device leaves a defined area.

  10. Protocol • Bluetooth has a wide variety of protocols available. Maybe too many, since it is not possible for all devices to talk to one another. • L2CAP The Logical Link Control and Adaptation Protocol (L2CAP) • In Basic mode, L2CAP provides packets with a payload configurable up to 64 kB, with 672 bytes as the default MTU, and 48 bytes as the minimum mandatory supported MTU. • In Retransmission and Flow Control modes, L2CAP can be configured either for isochronous data or reliable data per channel by performing retransmissions and CRC checks. • Streaming Mode (SM): This is a very simple mode, with no retransmission or flow control. • SDP The Service Discovery Protocol (SDP) allows a device to discover services offered by other devices • RFCOMM: Radio Frequency Communications is a cable replacement protocol used to create a virtual serial data stream. RFCOMM provides for binary data transport and emulates EIA-232 (formerly RS-232) control signals over the Bluetooth baseband layer, i.e. it is a serial port emulation • And more!

  11. Security • Original versions could be hacked within 24 hours. • Newer versions in 2.0 and beyond improve that. • Pairing also prevents unknown devices from connecting to systems • There has been problems, and they have been addressed by newer devices.

  12. What is Next? • Bluetooth had a slow start, but is now gaining great popularity. • Protocols were a problem, dropouts and directivity of the radio signal, body shielding (2.4 GHz is microwave band) • Faster speeds are coming available, capable of video and higher data transmissions. • Medical devices worn outside or inside the body can send data to a smart phone to record data and notify personnel of an emergency. • Canada is experimenting using Bluetooth from cars to the roadside to gain information on vehicle congestion. • Will not replace WiFi, but is great for local communication.

  13. Credits and Sources • http://en.wikipedia.org/wiki/Bluetooth • http://www.bluetooth.com/Pages/Bluetooth-Home.aspx • http://www.howstuffworks.com/bluetooth.htm • https://www.bluetooth.org/apps/content/ • http://en.wikipedia.org/wiki/Harald_Bluetooth • http://www.ethertronics.com/products/bluetooth/ • http://www.bluetooth.com/Pages/Product-Directory.aspx

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