BLUETOOTH (I)
• Bluetooth technology aims at so-called ad hoc
piconets, which are local area networks with a
very limited coverage and without the need for an
infrastructure.
• Needed to connect different small devices with
wireless infrastructure.
• Represents a single-chip, low-cost, radio-based
wireless network technology.
1
BLUETOOTH (II)
• Bluetooth uses the license-free frequency band at
2.4GHz allowing for worldwide operation.
2
BLUETOOTH (III)
• Physical layer:
– A frequency-hopping\time-division duplex scheme is used for
transmission with a fast hopping rate of 1,600 hops per second.
The time between two hops is called a slot, which is an interval
of 625μs, thus each slot uses a different frequency.
– On average, the frequency-hopping sequence ´visits´ each hop
carrier with an equal probability.
– All devices using the same hopping sequence with the same
phase form a Bluetooth piconet.
3
BLUETOOTH (IV)
– With transmitting power of up to 100 m, Bluetooth
devices have a range of up to 10m (or even up to 100m
with special transceivers).
– Having this power and relying on battery power, a
Bluetooth device cannot be in an active transmit mode
all the time.
– Bluetooth defines several low-power states for the
device.
4
BLUETOOTH (V)
– States of a possible Bluetooth device and possible
transitions:
• Standby mode: Every device which is currently not
participating in a piconet (and not switched off)
– In this mode, a device listens for paging messages.
• Connections can be initiated by any device which becomes
the master.
– This is done by sending page messages if the device already knows
the address of the receiver, or inquiry messages followed by a page
message if the receiver’s address is unknown.
5
BLUETOOTH (VI)
• To save battery power, a Bluetoth device can go into one of
three low power states if no data is ready to be sent:
– PARK state: The device has the lowest duty cycle, and thus the
lowest power consumption. The device releases its MAC address, but
remains synchronized with the piconet. The device occasionally
listens to the traffic of the master device to resynchronize and check
for broadcast messages.
– HOLD state: The power consumption of this state is a little higher.
The device does not release its MAC address and can resume
sending at once after transition out of the HOLD state.
– SNIFF state: It has the highest power consumption of the low-power
states. The device listens to the piconet at a reduced rate.
6
BLUETOOTH (VII)
unconnected
STANDBY
inquiry
transmit
PARK
page
connected
HOLD
SNIFF
connecting
active
low power
7
BLUETOOTH (VIII)
• MAC layer:
– Several mechanisms control medium access in a Bluetooth
system.
– First of all, one device within a piconet acts as a master, all other
devices (up to seven) act as slaves.
– The master determines the hopping sequence as well as the
phase of the sequence.
– All Bluetooth devices have the same networking capabilities,
i.e., they can be master or slave. The unit establishing the
piconet automatically becomes the master and controls medium
access; all other devices will be slaves.
8
Bluetooth Topology
• Piconet
– Two or more Bluetooth devices
– One master
• regulates traffic between devices
– Remainder termed slaves
• Scatternet
– Two or more piconets
• Note that a device can be a member of more
than one piconet at a given time.
Comparative Network Speeds
CDMA
1xEV/DO
2400
W-CDMA
stationary
W-CDMA
moving
2000
384
CDMA
1xRTT
144
GPRS
114
CDMA
64
PDC-P
28.8
GSM/PDC
9.6
Theoretical
data
transmission
speed
kbps
Source: ITU.
CDMA BASICS
• CDMA (Code Division Multiple Access) splits calls
into fragments and send them over different
frequencies simultaneously
• The use of multiple frequencies gives CDMA
effective protection against interference and lost
calls
• CDMA supports true packet switching and does
not use time slots, therefore is more bandwidth
efficient than TDMA -- also a more direct path to
3G
• Current CDMA penetration in the world market is
about 27%
3G CDMA Architecture
CDMA System Architecture (Basic)
• BTS: Base Station, which creates a single cell
• BSC: Base Station Controller, which controls roaming and channel
allocations amongst various BSTs and is also referred to as a Radio Network
Controller (RNC).
• MSC: Mobile Switching Center, which performs the telephony switching
functions and is usually connected to an SS7 network.
• PDSN: Packet Data Serving Node, maintains IP communications between all
MNs and the Packet Data Network (PDN), which in this diagram is the
Internet.