Information Technology Reference
In-Depth Information
E RROR C ONTROL S TRATEGIES FOR B LUETOOTH
Table 1 shows the main characteristics of different ACL packet types provided by
Bluetooth v2.0+EDR for asynchronous data transmission [2, 3].
An ACL packet may occupy 1, 3, or 5 consecutive time slots where each slot is assigned
625 u s . Bluetooth employs stop and wait ARQ (Automatic Repeat Request), CRC (Cyclic
Redundancy Check) and FEC (Forward Error Correction) to achieve high reliability on the
hostile wireless links. Bluetooth uses a stop-and-wait ARQ for ACL error control. The
receiver will respectively send a positive acknowledgment, ACK (ARQN=1), or negative
acknowledgment, NACK (ARQN=0), back to the transmitter for successful or failed packet
transmission. Unless the transmitter receives a valid ACK or the retransmission timeout is
reached, the packet will be retransmitted during the next transmission [6, 9, 11]. All ACL
packet types are composed of three fields, namely access code (AC), packet header and
payload. Figure 1 shows the packet format for the basic rate and Figure 2 presents the packet
format for the enhanced data rate [1, 2, 3].
Table 1. Asynchronous packet types
Payload
Header
(bytes)
User
Payload
(bytes)
CRC
and
ARQ
Symmetric
Max. Rate
(kbps)
Asymmetric Max.
Rate (kbps)
Forward
Packet
FEC
Reverse
DM1
1
0-17
Hamming
(15,10)
Yes
108.8
108.8
108.8
DH1
1
0-27
No
Yes
172.8
172.8
172.8
DM3
2
0-121
Hamming
(15,10)
Yes
258.1
387.2
54.4
DH3
2
0-183
No
Yes
390.4
585.6
86.4
DM5
2
0-224
Hamming
(15,10)
Yes
286.7
477.8
36.3
DH5
2
0-339
No
Yes
433.9
723.2
57.6
AUX1
1
0-29
No
No
185.6
185.6
185.6
2-DH1
2
0-54
No
Yes
345.6
345.6
345.6
2-DH3
2
0-367
No
Yes
782.9
1174.4
172.8
2-DH5
2
0-679
No
Yes
869.1
1448.5
115.2
3-DH1
2
0-83
No
Yes
531.2
531.2
531.2
3-DH3
2
0-552
No
Yes
1177.6
1766.4
235.6
3-DH5
2
0-1021
No
Yes
1306.9
2178.1
177.1
The AC field is used for synchronization, DC offset compensation and piconet
identification. The access code is error robust, because the coded synchronization words have
a large Hamming distance ( d min = 14). The packet header field contains link control
information, which includes packet type, destination address, sequence number and
acknowledgment flag (ARQN). The header contains a ( n,k )=(3,1) repetition code for error
verification. A header checksum field (HEC) is used to verify the integrity of the decoded
packet header field. The payload field contains a header of 1 or 2 bytes and a 2-byte cyclic
redundancy code (CRC) for checking the integrity of the field after decoding. In DM (Data-
Medium rate) packets the payload is 2/3 FEC encoded while the DH (Data-High rate) packets
do not incorporate any FEC encoding. The FEC scheme employed in DM packets is a (15,
10) shortened Hamming code, which encodes each 10-bit information into a 15-bit codeword
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