Information Technology Reference
block. This code corrects all single bit errors and detects all two-bit errors in a code word. All
ACL packets will be followed immediately by a return packet and therefore the effective
number of slots used is 2, 4, or 6. Though the data payloads of DH packets are greater than
those of DM packets, the latter packets may achieve higher throughputs in noisy channel
since FEC protection can significantly reduce retransmission events. While ACL packets
support various transmission rates, only one fixed packet type is used during the whole
Bluetooth transmission period. Since it cannot adapt the transmit packets to the dynamic
channel conditions, only limited data throughput is expected. To overcome this difficulty,
several packet type selection schemes based on channel conditions have been suggested [7,
11, 15, 18].
Figure 1. Basic rate packet format.
Figure 2. Enhanced data rate packet format.
Whereas the packets defined by the Bluetooth standard (Table 1) have fixed error control
schemes, a custom coding can be implemented by making use of the AUX1 packet. With the
AUX1 packet the Bluetooth device delivers the received bits independently whether they are
correct or not. While the former asynchronous packets with ARQ maintain a reliable link with
random delay (which approaches infinity for low values of SNR), the AUX1 packet may
alternatively provide an unreliable link with delay of only one time slot.
Valenti and Robert  have proposed the use of BCH codes with the CRC code for
error detection. As the ARQ is turned off, it must be implemented at the application layer.
The coder is implemented by inserting a (232, k) BCH code in the payload of the AUX1
packet. The inputs of the BCH coder are the data and two CRC bytes, resulting in a packet
with K=k-16 data bits. The code then considered was a (232, 156) binary BCH code with a
correction capability of up to t =10 errors. In this work five novel modifications in the AUX1
packet are analyzed: (1) BCH code without ARQ; (2) BCH code without ARQ and CRC; (3)
Hamming code without ARQ; (4) Hamming code without ARQ and CRC; (5) AUX1 packet
The same BCH code of  can be applied, but without retransmission (BCH2 and
BCH3 packets). Although this strategy can decrease the reliability of transmitted packets, in
terms of energy consumption it may be very useful, for it is not necessary to send a return
packet to indicate the success of the transmission. The BCH2 packet utilizes the CRC code
for error detection, without asking retransmission. A packet is discarded if the CRC detects
any errors. The BCH3 packet does not use either retransmission or CRC. The difference
between BCH2 and BCH3 is that in the latter the packets are transmitted to the next node (in