How does a bluetooth headset work near another one?
Posts: n/a What happens if two bluetooth headsets are in range of the base station (e.g. a cell phone)? Will both headsets be able to talk? Or, is there an association/authentication between the headset and the base station?  Responses to "How does a bluetooth headset work near another one?"
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Posts: n/a Re: How does a bluetooth headset work near another one? On Tue, 22 Jun 2004 09:29:54 +0100, Rob Shepherd wrote:> Usually the two headsets will be connected to different cellphones. The cellphones act as > the master for the network, headset as slave. > > Each network has a different frequency hopping routine and each mini-network or piconet as > it is termed, has a different access code. > > So if headset came into range of another it would not be aware of it, and because of > frequency hoppping (at 1600 times every second) the two networks would collide > > eg > > piconet A communicates on example channel sequence:- > > 10 48 34 27 58 1 9 30 18 52 14 25....... > > and piconet B communicates on example channel sequence:- > > 24 61 8 19 37 41 20 4 38 19 14 71....... > > Once a slave is connected to it's master it can predict the hopping sequence and thus know > the next channel to hop to, > > If two channels communicate on the same freq (see example above for hop 11, ch 14) then it > would not receive any valid data be cause the transmissions interfere with each other, In > this case the network hop to the next frequncy and retransmit the previuos packet... > > the Bluetooth specification version 1.2 has Adaptive frequncy hopping so if, for example, > the piconet is in range of a wireless LAN network they will interfere with each other also. > > However the lan equpment only uses a single channel in the entire range. The bluetooth > units in the piconet will notice they get interference every time they hop to this > particular channel and will negotiate that if they hop to this channel in the future they > will ignore it and just hop again. > > pretty clever huh... > > I'ts all to minimise interference and maximise the number of networks that can coexist in > the same physical space. What actually happens if two established Bluetooth piconets come into the range of each other, which are not LAN equipment. Say person-A is using a BT headset and paired phone at for example a railway station, and person-B is using the same, and person-B walks into range of person-A. Would the BT headsets and paired phones resequence themselves to avoid collisions ? -- Michael Turner Email (ROT13) zvxr.gheare1963@ivetva.arg
Posts: n/a Re: How does a bluetooth headset work near another one? Moin,Am Tue, 22 Jun 2004 16:40:49 +0100 schrieb michael turner: > Say person-A is using a BT headset and paired phone at for example a > railway station, and person-B is using the same, and person-B walks > into range of person-A. Would the BT headsets and paired phones > resequence themselves to avoid collisions ? No, they don't need to. The pseudorandom hopping sequence is determinded by the hardware addresse of the master, which means there is only a _really_ small chance that two piconets use the same hopping sequence. And even if they did, they would surely be at two different positions in the sequence. So there is a chance of 1 to 2^28 for two piconets to have the same hopping sequence times a chance of 1 to 2^27 for two piconets with the same hopping sequence to be at the same position in it. All taken together the probability for two different piconets to follow exactly the same sequence is pretty close to non-existent, so all there is is a chance of about 1 to 79 (or 23 in France) for two piconets to collide _in one timeslot_ only. Then after 625us both will use a different frequency and the packet is retransmitted. -- Henryk Plötz Grüße aus Berlin ~~~~~~~ Un-CDs, nein danke! http://www.heise.de/ct/cd-register/ ~~~~~~~ ~ Help Microsoft fight software piracy: Give Linux to a friend today! ~
Posts: n/a Re: How does a bluetooth headset work near another one? On Wed, 23 Jun 2004 09:19:10 +0100, Peter wrote:> I don't know about headsets but making a pile of devices like GPS > receivers, BT-USB adapters, BT access points, BT PDAs, communicate > concurrently is very unreliable. I suppose it's not so much an issue with BT headsets, given their typical usage. Which usually no more than a couple of feet from the paired phone. So unless another BT headset user stood or sat right next to the first headset user, the BT data packets wouldn't get stomped-on if collisions did occur. -- Michael Turner Email (ROT13) zvxr.gheare1963@ivetva.arg
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