Bluetooth can be used to communicate between computers, computers and computer peripherals, cellphones, and lately audio/video devices.
Bluetooth has two purposes, one is to replace the cable that runs between two electronic units with a wireless connection and the other is to define a protocol to communicate on this connection. The replacement for a cable consists of a transceiver on each end that performs the signal connection at 2.4 GHz. This is a very low powered transmitter that is in an unlicensed band.
There are two classes of service. Class one provides a connection of two devices up to 330 feet away. Class two requires that the two devices be within 32 feet of each other. The connection between a class one and a class two device is not defined but it is generally less that between two class one devices and more than between two class two.
While class two says the devices can be up to 32 feet (10 meters) apart the reality is often much less than that. In some cases they will need to be with 5 or 6 feet for good reception. The power consumption and power output for class two is really low. More on this later.
Profiles are used to define the kind of connection you have. In the world of cables this is often defined by using a different kind of cable, such as an audio cable or an Ethernet cable. In Bluetooth this is done using profiles. There are many profiles defined for Bluetooth use and more are being added every time a new version is released.
While profiles define the kind of communication between two devices some are intended for bi-directional data flow and some are intended strictly to send information in one direction. For example a stereo system might want to send audio output to a stereo headset. In this case the headphones could be thought of as a recipient of the data initiated by the stereo system. The stereo would be the output device while the headphones would be the input device. A device used to adapt a Stereo system to Bluetooth would be called a Gateway. Profiles (as of version 5) include:
- GAP Generic Access Profile - basis for all access.
- GATT Generic Attribute Profile - basis for all attributes.
- GAVDP Generic Audio Video Distribution Profile
- GOEP Generic Object Exchange Profile (OBEX)
- A2DP Advanced Audio Distribution Profile
- AIOP Automation IO Profile
- AIOS Automation IO Service
- ANP Alert Notification Profile
- ANS Alert Notification Service
- AVCTP Audio Video Control Transport
- AVDTP Audio Video Distribution Transport
- AVRCP Audio Video Remote Control Profile (v1.3) w/ 4.0
- BAS Battery Service
- BCS Body Composition Service
- BIP Basic Imaging Profile
- BLE Basic Low Energy Profile (see Beacon)
- BLP Blood Pressure Profile
- BLS Blood Pressure Service
- BMS Bond Management Service
- BNEP Bluetooth Network Encapsulation Protocol
- BPP Basic Printing Profile
- CGMP Continuous Glucose Monitoring Profile
- CGMS Continuous Glucose Monitoring Service
- CIP Common ISDN Access Profile
- CPP Cycling Power Profile
- CPS Cycling Power Service
- CSCP Cycling Speed and Cadence Profile
- CSCS Cycling Speed and Cadence Service
- CTP Cordless Telephony Profile
- CTS Current Time Service
- DIS Device Information Service
- DNP (aka DUN) Dial Up Networking
- ESDP Extended Service Discovery Profile
- ESP Environmental Sensing Profile
- ESS Environmental Sensing Service
- FMP Find Me Profile
- FP Fax Profile
- FTMP Fitness Machine Profile
- FTMS Fitness Machine Service
- FTP File Transfer Profile
- GLP Glucose Profile
- GLS Glucose Service
- HCRP Hardcopy Cable Replacement Profile
- HFP Hands-free profile
- HFR Hands-Free Profile
- HID Human Interface Device Profile (Keyboard, Mouse, etc.)
- HIDS HID Service
- HOGP HID over GATT Profile
- HPS HTTP Proxy Service
- HRP Heart Rate Profile
- HRS Heart Rate Service
- HSP Headset Profile
- HTP Health Thermometer Profile
- HTS Health Thermometer Service
- IAS Immediate Alert Service
- IP Intercom Profile
- IPS Indoor Positioning Service
- IPSP Internet Protocol Support Profile
- IrDA IrDA Interoperability
- LAP LAN (Local Area Network) Access Profile
- LLS Link Loss Service
- LNP Location and Navigation Profile
- LNS Location and Navigation Service
- MAP Message Access Profile
- MCAP Multi-Channel Adaptation Protocol
- NDCS Next DST Change Service
- OPP Object Push Profile
- OTP Object Transfer Profile
- OTS Object Transfer Service
- PAN PAN (Personal Area Networking) Profile
- PASP Phone Alert Status Profile
- PASS Phone Alert Status Service
- PBAP Phone Book Access Profile
- PXP Proximity Profile
- PLXP Pulse Oximeter Profile
- PLXS Pulse Oximeter Service
- RFCOMM RFCOMM
- RSCP Running Speed and Cadence Profile
- RSCS Running Speed and Cadence Service
- RTUS Reference Time Update Service
- SAP SIM Access Profile
- ScPP Scan Parameters Profile
- ScPS Scan Parameters Service
- SDAP Service Discovery Application Profile
- SP Synchronization Profile
- SPP Serial Port Profile
- TDS Transport Discovery Service
- TIP Time Profile
- TPS Tx Power Service
- UDS User Data Service
- VDP Video Distribution Profile
- WSP Weight Scale Profile
- WSS Weight Scale Service
A particular device will likely only support a very small subset of the available profiles, perhaps only one. A smartphone might support a set like:
- Advanced Audio Distribution Profile (A2DP) 1.2,
- Audio/Video Remote Control Profile (AVRCP) 1.4,
- Generic Attribute Profile (GATT),
- Hands-free profile (HFP) 1.6,
- Object Push profile (OPP) 1.1,
- Phone Book Access Profile (PBAP) 1.1
This list was taken from a Nokia Lumia 520.
V1.0 Bluetooth release only supported a few profiles, most notably the cellphone headset profile, and did not last very long in the industry. It was pretty hard to use. It had a maximum data rate of 768Kbps. It was amended to V1.0B pretty quickly.
V1.1 improved the usability, added lots of profiles, and provide a way to access the signal strength of the connection. The data rate didn't change. The usable data rate was often less than the maximum due to interference from other devices in the same 2.4 GHz band.
V1.2 did not change the data rate but added FHSP, frequency hopping spread spectrum. The 2.4 GHz band used by Bluetooth is pretty crowded with unlicensed transmitting devices and interference is likely. Frequency hopping provided the ability to switch frequencies in the band to avoid interference. Thus the full data rate was much more likely to be achieved. A few new profiles were added that took advantage of this better throughput. Stereo headsets (A2DP) were first supported in this version.
V2.0 + EDR (Extended Data Rate) jumped the transfer rate by 3 times to about 2.5 Meg providing for transfers that would not have been attempted at the lower rate. For example video was now possible. New profiles are constantly being proposed and added to the available capabilities. Some implementations claim a 3 Meg rate. V2.0 was released in 2004 while V2.1 added some improvements in 2007.
V 3.0 + HS. The v3.0 (2009) Specification enables the use of a Generic Alternate MAC/PHY, allowing well known Bluetooth protocols, profiles, security, and pairing to be used in consumer devices while achieving faster throughput by momentary use of a secondary radio, such as WiFi, already present in the device. It also features enhanced power control for fewer dropouts and lower latency rates.
V4.0 (2010) adds Bluetooth Smart Devices with low energy (LE) requirements with battery life in the months or even years and with enhanced range. These kinds of devices are typically for wireless exercise or environment monitoring. The unit can switch radios from low power mode to high speed mode dynamically as needed. Mixed mode requirements are also defined to permit reliable operation between devices using different specifications.
V4.1 (Dec 2013) Software only to improve user experience and compatibility with mixed versions.
V4.2 (Dec 2014) Key improvement include improved privacy, increased speed, and new IP connectivity. It also lowers power consumption and builds upon the government-grade security features. It increases the speed and reliability of data transfers between Bluetooth Smart devices. By increasing the capacity of Bluetooth Smart packets, devices transfer data up to 2.5 times faster than with previous versions.
V5.0 (Fall 2016) quadruple the range and double the speed of 4.2 available. You can stream two sets of headphones simultaneously. It has the ability to broadcast a much richer set of information. Bluetooth 5 will make beacons, location awareness, and other connectionless services an even more relevant part of an effortless and seamless IoT experience. That richer set of information is thanks to what is perhaps Bluetooth 5.0's most important feature: connectionless data transfers. Long the bane of consumers trying to set up wireless keyboards and connect portable speakers to their smartphones, the Bluetooth pairing process could soon be a thing of the past.
 eBook Readers
Bluetooth has the ability to improve the experience of your eBook Reader depending on what profiles the particular implementation supports. Among the features could be:
- Keyboard support to provide entering a search argument for locating content in an eBook or a Title you are interested in.
- Headphone support would provide access to the audio capabilities of your eBook Reader including audio books, music, and TTS.
- DUN (Dial up network) could provide access to the Internet using the data facilities of your cell phone. With appropriate firmware you could even purchase eBooks and download them directly to your device.
- FTP or peer to peer personal LAN service could allow you to download eBooks from your Bluetooth equipped PC or even exchange eBooks with another user directly to their eBook Reader.
- Dual screen on some cell-phones where the second screen is E Ink. Bluetooth is the connection for displaying the data on the second screen.
- A Bluetooth stylus could be used to take notes right on the screen.
Beginning with the addition of Low Energy in version 4.0 the door has opened to BLE Beacons, or as Apple calls them iBeacons. Tile Mate also uses Beacons. The idea is that Bluetooth can use other Bluetooth Low Energy (BLE) devices to pass location information, hopscotching or piggybacking on to Wi-Fi. A Beacon device can not only provide its location triangulating with other beacons but can offer a dual role as the target and the enabler to pass data along. The location data works inside buildings where GPS won't and can be used to locate a person or lost hardware. It can also be used for local proximity advertising.
 For more information
http://www.bluetooth.com/ - the official Bluetooth site