Introductory Material on Bluetooth
Links
Sigma Comtec ID29t4q245p9r73
Bluetooth Protocol Stacks for Linux
Projects
Bernhards Stauffer and Thomas Jörg have estabished some first projects to set up bluetooth infrastructure at TIK. Their focus is a wireless home, with basestations and possible multihop propagation. (completed)
The BTnode Project
Local Documents
Apps
Knowledgebase - here I collect various insights and things i keep forgetting. a loose collection of thoughts...
Serial Connections (it is even better to check out Horowitz: "The Art of Electronics" on page 720ff.)
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Asymmetric Asynchronous channels (732.2 kbps and return 57.6 kbps) are not equal to symmetric asynchronous channels (two way 433.9 kbps)?
To
achieve maximum asymmetric transfer rate (723.2 / 57.6) the packet length is
five and one time-slots, respectively, in the different directions. To achieve
maximum symmetric transfer rate (433.9) the packet length is five time-slots
in both directions. The two devices send every other packet. Each packet contains
overhead such as the head and the at least 220us dead time that allow the devices
to switch from transmitting to receiving. These overheads occur more frequently
using short packets. The total transfer rate is therefore higher in symmetric
traffic where all packets are five time-slots in length.
The difference between asymmetric and symmetric transfer rates is to be found
in the packet types used. In symmetric transfer mode the same packet type, e.g.
DM5 or DH5, is used in both forward and reverse direction. When sending asymmetric,
different packet types are used in respective direction, e.g. DH5 forward and
DH1 reverse.
Every second is divided into 1600 timeslots. The different packet types use
different amount of these timeslots. The DH5/DM5 packets uses 5 timeslots, DH3/DM3
uses 3 slots and DH1/DM1 uses 1. Thanks to smaller headercost, etc, the bigger
packets transfer more useful information per time unit. For example, a DH5 package
is able to transfer up to 339 bytes of information while DH1 transfers only
27 bytes. Please see the specification for more details.
To put this together we can look at an asymmetric DH5/DH1 connection and compare
it with the symmetric DH5/DH5 connection.
DH5/DH1:
Forward transfer rate is found by 339*8*(1600/5)*(5/6) = 723,2 kb/s
where 339 equals the number of information bytes in DH5 package,
1600/5 equals the number of DH5 packets/second,
5/6 equals the part of time used by forward direction
Reverse) transfer rate is equal to 27*8*1600*(1/6) = 57,6 kb/s
where 27 equals the number of information bytes in the DH1 package,
1600 equals the number of DH1 packets/second,
1/6 equals the part used for transferring in reverse direction
DH5/DH5:
Here the forward transfer rate equals the reverse and is found by 339*8*(1600/5)*(1/2)
= 433,9 kb/s
where 339 equals the number of information bytes in the DH5 packet,
1600/5 equals the number of DH5 packets/second,
1/2 equals the part of time used by forward/reverse direction.
HCI Layer
Baseband
Set up of piconets according to hopping sequence issued by the master to the slaves (max. 7 active channels and n synced parked slaves)
Overlapping piconets form a scatternet. A masteror slave of one piconet can be slave of another piconet using a different hopping sequence.
The BD_ADDR Bluetooth device address is 48 Bit (IEEE802).
The AM_ADDR (active member address) is 3 Bit long to identify the temporarily active nodes. Parked slaves give up the AM_ADDR and are reassigned an AM_ADDR upon reentry. In parked state they can be identified by the BD_ADDR or an 8 Bit PM_ADDR (255 units or 2^48 units). The master has no AM_ADDR but can be identified by the timing relative to the slave. AM_ADDR all zero is a broadcast.
79 channels can support up to 10 piconets with up to 8 nodes each. 1 Mbit/sec gross data rate includes headers and error correction (1 Msymbols/sec), thus 10 Mbit/sec aggregate bandwidth.
Physical Layer
Bluetooth specs 3 power classes:
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