Page 478 - From GMS to LTE

464 From GSM to LTE-Advanced Pro and 5G

modulation techniques allow the encoding of several bits per transmission step. Thus,
it is possible to increase the datarate while the total channel bandwidth of 1 MHz and
the slot time of 625 microseconds remain constant. To be backward‐compatible, the
headers of the new packets are still encoded using standard GFSK modulation. Thus,
the system becomes backward‐compatible as legacy devices can at least decode the
header of an EDR packet and thus become aware that they are not the recipient of the
packet. The same approach is used by WLAN (see Chapter 4) to ensure backward
compatibility of 802.11n and 11 g networks with older 802.11b devices. Furthermore, a
coding scheme for the packet‐type field was devised that enables non‐EDR devices to
recognize multislot EDR packets which are sent by a master to another slave device in
order to be able to power down the receiver and thus save energy for the time the packet
is sent. Table 7.4 gives an overview of all possible ACL packet types and the maximum
datarate that can be achieved in an asynchronous connection. In this example, five‐slot
packets are used in one direction and one‐slot only packets in the reverse direction. The
first part of the table lists the basic ACL packet types which can be decoded by all
Bluetooth devices. The second and third parts of the table contain an overview of the
EDR ACL packet types. Types 2‐DH1, 2‐DH3 and 2‐DH5 are modulated using DQPSK,
while 3‐DH1, 3‐DH3 and 3‐DH5 are modulated using 8DPSK. The numbers 1, 3 and 5
at the end of the packet‐type name describe the number of slots used by that packet type.
Owing to the number of EDR packet types, it is no longer possible to identify all
packet types using the 4‐bit packet‐type field of the ACL header (see Figure 7.5). Since
it was not possible to extend the field because of the need for backward‐compatibility,
the Bluetooth specifications had to go a different way. EDR is always activated during
connection establishment. If master and slave recognize that they are EDR capable, the
link managers of both devices (see Section 7.4.3) can activate the EDR functionality,
which implicitly changes the allocation of the packet‐type field bit combinations to
point to 2‐DHx and 3‐DHx types instead of the standard packet types. While the

Table 7.4 ACL packet types.

Uplink datarate Downlink datarate
Type Payload (bytes) (kbit/s) (kbit/s)

DM1 0–17 108.8 108.8
DH1 0–27 172.8 172.8
DM3 0–121 387.2 54.4
DH3 0–183 585.6 86.4
DM5 0–224 477.8 36.3
DH5 0–339 723.2 57.6
2‐DH1 0–54 345.6 345.6
2‐DH3 0–367 1174.4 172.8
2‐DH5 0–679 1448.5 115.2
3‐DH1 0–83 531.2 531.2
3‐DH3 0–552 1766.4 265.6
3‐DH5 0–1021 2178.1 177.1