Bluetooth
From MobileRead
Bluetooth can be used to communicate between computers, computers and computer peripherals, cellphones, and lately audio/video devices.
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[edit] Overview
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.
[edit] Profiles
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 include:
- GAP Generic Access Profile - basis for all access.
- SDAP Service Discovery Application Profile
- CTP Cordless Telephony Profile
- IP Intercom Profile
- SPP Serial Port Profile
- HSP Headset Profile
- DNP (aka DUN) Dial Up Networking
- FP Fax Profile
- LAP LAN (Local Area Network) Access Profile
- GOEP Generic Object Exchange Profile (OBEX)
- OPP Object Push Profile
- FTP File Transfer Profile
- SP Synchronization Profile
- PAN PAN (Personal Area Networking) Profile
- ESDP Extended Service Discovery Profile
- GAVDP Generic Audio Video Distribution Profile
- A2DP Advanced Audio Distribution Profile
- VDP Video Distribution Profile
- AVRCP Audio Video Remote Control Profile
- BIP Basic Imaging Profile
- BPP Basic Printing Profile
- CIP Common ISDN Access Profile
- HFR Hands-Free Profile
- HCRP Hardcopy Cable Replacement Profile
- HID Human Interface Device Profile (Keyboard, Mouse, etc.)
- SAP SIM Access Profile
A particular device will likely only support a very small subset of the available profiles, perhaps only one.
[edit] History
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 MHz band.
V1.2 did not change the data rate but added FHSP, frequency hopping spread spectrum. The 2.4 MHz 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 capablities. Some implementations claim a 3 Meg rate.
[edit] 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.
[edit] For more information
http://www.bluetooth.com/ - the official Bluetooth site
