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Reliability of Bluetooth System
Bluetooth technology is a wireless communications system. In poor RF environments, this system should be considered inherently unreliable. To counteract this the system provides levels of protection at each layer.
The baseband packet header uses forward error correcting (FEC) coding to allow error correction by the receiver and a header error check (HEC) to detect errors remaining after correction. Certain Baseband packet types include FEC for the payload. Furthermore, some baseband packet types include a cyclic redundancy error check (CRC).
On ACL logical transports the results of the error detection algorithm are used to drive a simple Automatic Repeat-reQuest (ARQ) protocol. This provides an enhanced reliability by re-transmitting packets that do not pass the receiver's error checking algorithm. It is possible to modify this scheme to support latency-sensitive packets by discarding an unsuccessfully transmitted packet at the transmitter if the packet's useful life has expired.
The L2CAP layer provides an additional level of error control that is designed to detect the occasional undetected errors in the baseband layer and request retransmission of the affected data. This provides the level of reliability required by typical Bluetooth applications.
Broadcast links have no feedback route, and are unable to use the ARQ scheme (although the receiver is still able to detect errors in received packets). Instead each packet is transmitted several times in the hope that the receiver is able to receive at least one of the copies successfully. Despite this approach there are still no guarantees of successful receipt, and so these links are considered unreliable.
In summary, if a link or channel is characterized as reliable this means that the receiver is capable of detecting errors in received packets and requesting retransmission until the errors are removed. Due to the error detection system used some residual (undetected) errors may still remain in the received data. For L2CAP channels the level of these is comparable to other communication systems, although for logical links the residual error level is somewhat higher.
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