Originally posted by: merlocka
There are alot of "almost right" comments in this thread. Let me try to clear a few up.
What is Bluetooth?
Bluetooth is a wireless PAN (personal area network) protocol which operates in the 2.4GHz (ISM) band. The same band as 802.11b/g, many cordless phones, and a few other consumer gadgets. Bluetooth uses a spread-spectrum technology called FHSS (frequency hopping). There are 79 1MHz channels (2.402GHZ - 2.480GHz). The radio hops from channel to channel in a pseudo-random order (defined by the connection master device) at a rate of 1600 hops per second. Try to use a sniffer on that
What does it do?
The common verbage for Bluetooth is a "cable replacement" technology. That's pretty close, but you need to clarify what cables you want replaced.
There are a few main usage models for Bluetooth. These are referred to as "profiles" as they define how the connection between 2 devices behaves in the protocol stack.
1) Audio (handsfree, headset, cordless phone) - this type of connection will send mono voice quality audio in full-duplex between up to 3 devices.
Some typical applications here are
- Bluetooth headset for your cellphone (these are addicting)
- Handsfree car kits (that activate once your phone is in range and route the audio through the auto's handfree voice system)
- Cordless telephony (this isn't quite available yet, but you will soon be able to use your Bluetooth enabled phone as a cordless phone in your home and handoff to your carrier when you leave the house).
2) Data (serial port / USB port) - there are several profiles which basically use a serial port connection with a twist. This would be for sync'ing PDA's, transferring files amongst files, games, windows networking, etc.
Some typical applications here are
- PDA's can use Bluetooth to automatically sync with your desktop PC.
- Wireless keyboards and mice for Bluetooth enabled desktops/laptops.
- Printers
- Basic networking between portable devices (laptops, pda's etc)
There are many more applications, but those are the main ones.
How far away will it work?
That's a trick question. As with anything RF, YMMV. Some applications will have better radios/antennas than others.
There are 3 "classes" for the power of the Bluetooth radio transmitter. Class 1,2,3
Class 1 is a high power device (0dBm to 20dBm with power control). If two Class 1 devices are connected, range can be equal to or better than even the best WLAN connections.
Class 2 is what most typical consumer devices will be (-6dBm to +4dBm). Range can be expected to be between 10 to 20 meters.
Class 3 is a low power implementation ( > 0dBm). Range will be a couple of meters.
The throughput is only 1Mbps / 720kbps / too slow!!!
The symbol rate for Bluetooth is 1Mbps, just like the symbol rate for 802.11b is 11Mbps (max or 5.5,2,1). That doesn't mean you can use all 11Mbps. With a windows TCP/IP stack, you can generally expect about half that in TCP/IP throughput.
Bluetooth data connections are asymmetric, the max throughput depends on the connection (packet) type.
Here is a pretty good summary of the speeds in various modes. In summary, the max on-way throughput is 723.2kbps but when you get down to a file transfer or a practical test, you will see less than half that.
That is a typical "reason" why many people think Bluetooth "sucks". The reality is that it's a benchmark people are familiar with missapplied to Bluetooth. Who cares how fast Bluetooth does TCP/IP when just about every single laptop or PC which will have it embedded will also have WLAN. If you have WLAN, why the hell are you sending files with Bluetooth.
Bluetooth throughput rate is adequate for the things it does well. Keyboards, mice, voice-quality audio, sync-ing. As Bluetooth matures, the spec will provision for faster data rates, just like 802.11b allowed for the faster 5.5Mbps and 11Mbps rates from 802.11.
That's enough for now, hope my typo's weren't too bad. I'll add a few more items onto this if anyone cares. post a couple questions and I'll try my best to answer them.
Good info, so I was close.
I think bluetooth is a good idea. I figured I'd have no use for it at first, but I realized its pretty cool.
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