Wireless Local and Wireless Personal Area Network Communication in Industrial Environments - Networked Embedded Systems - page 633

Cellular Ad hoc

FIGURE . Closest next co-channel interferer in cellular and ad hoc networks. (From Matheus, K. Industrial
Information Technology Handbook . Ed. R. Zurawski, CRC Press, Boca Raton, FL, . With permission.)

for frequency licensing. Nevertheless, it requires complying to the respective sharing rules. ∗ As a
consequence, Bluetooth performs a rather fast frequency hopping (FH) over  carriers of  MHz
bandwidth each, such that every Bluetooth packet is transmitted on a newly chosen frequency (which
results in a nominal hop rate of  hops/s). To further reduce cost and support the distribution of
the Bluetooth technology, the Bluetooth specification is an open standard that can be used without
needing to pay for the use of its key patents, on the term that the strict qualification procedure is
passed. †
The latter is to ensure the acceptance of the technology. For the same purpose, the specifica-
tion contains application profiles he profiles ensure compatibility up to the application layer, thus
enabling units of different manufactures to interoperate. The most important characteristics of the
physical layer are as follows: The data is GFSK modulated at  Mbps and organized in packets con-
sisting of access code, header, and payload. he employment of forward error correction (FEC) for
the payload is optional. Interpacket interleaving is not performed. his allows for lower chip prices,
because memory can be saved.
Bluetooth uses a master-slave concept in which the unit that initiates a connection is temporarily
assigned “master” status (for as long as the connection is up). he master organizes the traffic of up to
seven other active units, called “slaves” of this “piconet.” From the master's device address the identity
of each piconet and with it the FH sequence are derived. he header of a packet contains the actual
addressee, the length of the packet, and other control information. Note that within one piconet the
slave can only communicate with the master (and not directly with the other slaves) and this—in case
of data connections—only after having been asked (i.e., “polled”). ‡
The channel is organized in a TDMA/TDD [GL] scheme (see Figure .). It is partitioned into
 µs time slots. Within this slot grid the master can only start transmission in the odd-numbered
slotswhiletheslavescanonlyrespondineven-numberedones.Whenaunitisnotalreadyinoneof
thespeciicpowersavemodes(snif,hold,park),theslottingispower-consumptionfriendly,because

∗ For the United States [Fed,Part ] for Europe [Eura], for Japan [Min].
† The Bluetooth specification has also been adopted by the IEEE as IEEE ...
‡ Every BT unit can simultaneously be a member of up to four piconets (though it can be master in only one of them).
A formation in which several piconets are interlinked in that manner is called “scatternet.” Aspects like routing, which
play an important role in scatternets, are not covered in this chapter. he chapter focuses on the properties of a single or
multiple independent piconets.