Page 472 - From GMS to LTE

458 From GSM to LTE-Advanced Pro and 5G

Data frames of piconet 1

Frequency 1
Frequency 2
Frequency 3
Frequency 4
…
Frequency 77
Frequency 78
Frequency 79
t
Data frames of piconet 2

Figure 7.2 By using different hopping sequences, many piconets can coexist in the same area.

limit is sufficient for most applications. Even if Bluetooth is used with a personal com-
puter (PC) to connect with a keyboard and a mouse, five more devices can still join the
PC’s piconet at any time.
Each device can be a master or a slave of a piconet. Per definition, the device that initi-
ates a new piconet becomes the master device, as described in the following scenario.
Consider a user who has a Bluetooth‐enabled mobile phone and headset. After initial
pairing (see Section 7.5.1), the two devices can establish contact with each other at any
time and thus form a piconet for the duration of a phone call. At the end of a phone call,
the Bluetooth connection ends as well, and the piconet thus ceases to exist. In the case
of an incoming call, the mobile phone establishes contact with the headset and thus
becomes the master of the connection. In the reverse case, the user establishes an out-
going phone call by pressing a button on the headset and by using the voice‐dialing
feature of the mobile phone. In this case, it is the headset and not the mobile phone that
establishes the connection and thus the headset becomes the master of the newly estab-
lished piconet. If another person in the vicinity also uses a Bluetooth‐enabled mobile
phone and headset, the two piconets overlap. As each piconet uses a different hopping
sequence, the two connections do not interfere with each other. Because of the initial
pairing of the headset and the mobile phone, it is ensured that each headset finds its
own mobile phone and thus always establishes a connection for a new phone call with
the correct mobile phone.
The master of a piconet controls the order and the duration of slave data transfers over
the piconet channel. To grant the channel to a slave device for a certain period of time,
the master sends a data packet to the slave. The slave is identified by a 3‐bit address in the
header of the data packet, which has been assigned to the device at connection establish-
ment. The data packet of the master can have a length of one to five slots depending on
the amount of data that has to be sent to the slave. If no data needs to be sent to the slave,
an empty one‐slot packet is used. Sending a packet to a slave device implicitly assigns the
next slot to the slave, regardless of whether the packet contains user data. The slave can
then use the next one to five slots of the channel to return a packet. With Bluetooth 1.1,