3b. Bluetooth Communications (01/21)
1. Introduction
2. Technical Overview
a. Design considerations
b. Bluetooth radio link
3. Review of basic concepts
4. Bluetooth Architecture
a. Wireless Positioning
5. Medium Access Control
6. Voice and Data Links
7. Data Packet Types
a. Master-to-Slave Role Switching
8. Voice Packets
9. Communication Scenario
a. Data rate calculation
a. Bluetooth Physical link
b. Piconet formation
c. Piconet channels
d. Multiple Access Scheme
e. The Modulation Scheme
a. Physical Link Definition
a. Access Code
b. Packet Header
c. Addressing
a. Connection Establishment
b. Inquiry on time axis
d. Piconet Management
1
Bluetooth Communications. 802.15
Bluetooth is considered
as a secure short-range
wireless network.
•
•
•
•
A cable replacement technology
1 Mb/s symbol rate
Range 10+ meters
Single chip radio
– at low power & low price ($5)
Why not use Wireless LANs?
- power
- cost
No Another wireless LAN
2
802.11
• Replacement for Ethernet
• Supported data rates
– 11, 5.5, 2, 1 Mbps; and recently up to >20 Mbps in
2.4 GHz
– up to 54 Mbps in 5.7 GHz band (802.11 a)
• Range
– Indoor 20 - 25 meters
– Outdoor: 50 – 100 meters
• Transmit power up to 100 mW
• Cost:
– Chipsets $ 35 – 50
– AP $200 - $1000
3
Bluetooth working group history
• February 1998: The Bluetooth Special Interest
Group promoter: Ericsson, IBM, Intel, Nokia, Toshiba.
• May 1998:
• July 1999: version 1.0A is released.
• December 1999: version 1.0B is released.
• March 2001: version 1.1 is released
• Where Did the Name Come From?
• Herald Blatant “Bluetooth II ”–King of
Denmark 940-981 AC.
• Noted for unifying Denmark and Sweden.
4
User benefits
• Multiple device access
(phone, music)
• Cordless phone benefits
• Hands free operation
• Conference Table
• Cordless Computer
• Business Card Exchange
• Instant Postcard
• Computer Speakerphone
Cordless
headset
5
•
•
•
•
•
•
•
•
•
•
•
•
•
Generic Access
Service Discovery
Cordless Telephone
Intercom
Serial Port
Headset
Dial-up Networking
Fax
LAN Access
Generic Object Exchange
Object Push
File Transfer
Synchronization
6
2. Technical
Overview
7
a. Design considerations
Noise, interference
power
spectrum
Data signal x(t)
Recovered
data signal
cost
Goal:
• high bandwidth
• conserve battery power
• cost < $10
8
EM Spectrum ISM band
ISM band
902 – 928 MHz
2.4 – 2.4835 GHz
5.725 – 5.785 GHz
LF
30kHz
10km

MF
300kHz
1km
VHF
HF
3MHz
30MHz
100m
10m
ISM
band
1 kHz
1 MHz
1 GHz
UHF
300MHz
1m
SHF
3GHz
EHF
30GHz
300GHz
1cm
100mm
10cm


X rays
infrared visible UV
1 THz
1 PHz
Gamma rays
1 EHz
9
Unlicensed Radio Spectrum

33cm
26 Mhz
902 Mhz
12cm
83.5 Mhz
2.4 Ghz
928 Mhz
cordless phones,
baby monitors,
Wireless LANs
2.4835 Ghz
802.11 Cell.
802.15 Bluetooth,
Microwave oven
5cm
125 Mhz
5.725 Ghz
5.785 Ghz
802.11a
HyperLan
10
b. Bluetooth radio link
1MHz
. . .
79
12 3
83.5 MHz
• frequency hopping spread spectrum
– 2.402 GHz + k x1MHz, k=0, …, 78=79
– 1,600 hops per second (1:1600=625 μs)
• GFSK modulation - 1 Mb/s symbol rate
• transmit power - 0 dBm (up to 20dBm with power control)
FHSS/TDD channel applied in Bluetooth.
Multiple Ad hoc links will make use of different hopping channels
with different hopping sequences and have misaligned slot timing
11
3. Review of basic
concepts
12
Radio propagation: path loss
near field
path loss in 2.4 Ghz band
Pr
r  8m
Pt
near field
r
Pr
 r2
path loss = 10 log (4r2/)
= 58.3 + 10 log (r3.3 /8)
r > 8m
far field
 r3.3
r  8m
r > 8m
13
Fading and multipath
Fading: rapid fluctuation of the amplitude of a radio signal over a
short period of time or travel distance
Tx
Rx
Effects of multipath
• Fading
• Varying Doppler shifts on different multipath signals
• Time dispersion (causing inter symbol interference)
14
Bandwidth of digital data
Time domain
baseband signal (1 Mb/s)
Signal amplitude
Fourier transform
Frequency domain
0.5 MHz
1 MHz
1.5 MHz
f MHz
• Baseband signal cannot directly be transmitted on
the wireless medium
• Need to translate the baseband signal to a new
frequency, so that it can be transmitted and
received accurately over a communication channel
15
Channel coding and modulation
modulation
channel coding
baseband signal
demodulation
channel decoding
baseband signal
Challenges
• Modulation of 1MHz baseband signal into 2.4GHz band is
difficult to achieve in one step.
16
Radio architecture: typical design
Intermediate
mixing
Frequency
modulation
channel coding
baseband
signal
Intermediate
mixing Frequency
demodulation
channel decoding
baseband
signal
17
Power consumption
Radio
Baseband
Transmit
Receive
50 mA
45 mA
25 mA
Vcc = 3 V
802.15 Bluetooth
Transmit
Radio
Receive
450 mA 300 mA
Baseband
Vcc = 3 V
802.11
Class 1, with power 1mW (0dBm) for distance 10 m.
Class 2, with power 2.5 mW (4dBm) for distance 20 m.
Class 3, with 100mW (20dBm) for distance100 m.
– Single chip radio (minimize external components
– Time division duplex
18
Bluetooth Radio
• Low Power
– Standby modes:
– Low voltage RF
Sniff, Hold, Park.
Power
Class
Transmit Power
1
100 mW (20 dBm)
Nominal
Range
100 m
2
2.5 mW ( 4 dBm)
20 m
3
1 m W ( 0 dBm)
10 m
Low Cost
Single chip radio (minimize external components)
Today’s technology
Time division duplex
19
a. Wireless Positioning
a) Cellular radio systems with squares representing stationary BS;
b) Bluetooth systems;
c) Ad hoc systems.
b)
a)
c)
20
Wireless Positioning
Wireless LAN
• On-campus:
Office, School, Airport,
Hotel, Home
Cellular
• Off-Campus:
Global Coverage
Bluetooth
• Person Space:
Office, Room, Briefcase,
Pocket, Car
• Short Range/Low Power
• Voice and Data
• Low-cost
• Small form factor,
• Many Co-located Notes
• Universal Bridge
21
4. Bluetooth Architecture, Piconets and Scatternets
A Piconet is collection of devices connected to
the Master.
Sb
• One unit will act as a Master (the device, which
initiates an exchange of data) and the others as
Slaves (the device, which responds to the Master)
S
• Master sets the clock, dwell time, hopping
pattern.
P
• Each Piconet has a unique hopping pattern/ID
• Each master can connect to 7 (specification
limits) simultaneous or 255 inactive (parked)
slaves per Piconet
A Scatternet is collection of the Piconets
connected in an Ad Hoc fashion.
M
S
S
P
M=Master;
S=Slave;
P=Parked;
Sb=Standby
22
Scatternet
23
a. Bluetooth Physical link
• Point-to-point link
m
s
– master - slave relationship
m
• Piconet
– Each Piconet has max capacity
= 1 Mbps
s
s
s
•All devices in a Piconet hop together. To form Piconet: master gives
slaves its clock and device ID; Hopping pattern (48-bit); determined
by device ID; Hopping pattern determined by Clock.
•A Piconet is centralized TDD system, with the master controlling the
clock and determined which device gets to communicate in which
time slot.
•The baseband part of the Bluetooth specification describes an
algorithm which can calculate a frequency hop sequence from24a
Bluetooth device address and a Bluetooth clock.
Communication in a Scatternet
If there are many independent piconets: there could be a collision on a particular
channel, these packets will be lost and retransmitted, or if voice signals, it will be
ignored.
Master node
Bridge node
Slave node
25
b. Piconet formation
• Page - scan protocol
– to establish links
with nodes in
proximity
Master
Active Slave
Parked Slave
Standby
Direct, slave-to-slave
communication is not
possible.
Piconet Addressing:
Active Member Address (AMA, 3-bits);
Parked Members Address (PMA, 8-bits)
26
Characteristics
• Operates in the 2.4 GHz band at a data rate of 720 Kb/s
• Uses FHSS: Number of channels (2.402-2.480 GHz = 79 channels).
• Radio transceivers hop from one channel to another in a
pseudorandom fashion, determined by the master.
Topology
Supports up to 7
simultaneous links
Each link requires another
cable
Flexibility Goes through walls, bodies.
Line of sight
Rate
1Mb/s, 720 Kb/s
Varies with use and cost
Power
0.1 Watts active power
0.05 Watts or higher
Range
10 meters or less
Typically 1-2 meters
Universal Work anywhere in the world
Cables vary with local customs
Security
Secure (it’s a cable)
link layer security
27
a. Radio Spectrum:
• In the USA, the band: from 2400 to 2483.5 MHz. In most
parts of Europe, in Japan the band from 2400 to 2500
MHz has been allowed for commercial applications and
has been harmonized with the rest of the world.
• In most countries of the world, free spectrum is available
from 2400 MHz to 2483.5 MHz.
b. Interference Immunity:
• Interference Suppression can be obtained by coding or
direct sequence spreading.
• Interference Avoidance obtained by filtering in the
frequency domain. It provides the suppression of the
interferers at other parts of the radio band.
The filter suppression can arrive at 50 dB.
28
c. Piconet channels
FH/TDD
f1
f2
f3
f4
f5
f6
M
S1
S2
625 μsec
1600 hops/sec
devices hop once per packet, which will be:
every slot, every 3 slots, or every 5 slots.
29
d. Multiple Access Scheme
Single-slave communication
259
Multiple-slave communication
30
Multiple Access Scheme (cont)
Operating modes
• Two modes: 1. As a Master, or 2. As a Slave. If it is Master that sets
the frequency hopping sequences. Slaves synchronize to the Master
in time and frequency by following the Master’s hopping sequence.
• Every Bluetooth device has a unique address, and a clock. The
baseband part of the Bluetooth specification describes an algorithm
which can calculate a frequency hop sequence from a Bluetooth
device address and a Bluetooth clock.
• When Slaves connect to a Master, they are told the Bluetooth device
address and clock of the Master. They then use this to calculate the
frequency hop sequence. Because all Slaves use the Master’s clock
and address, all are synchronized to the Master’s frequency hop
sequence.
• In addition to controlling the frequency hop sequence, the Master
controls when devices are allowed to transmit.
• The Master allows Slaves to transmit by allocating slots for voice
traffic or data traffic. In data traffic slots, Slaves are only allowed
to transmit when replying to a transmission to the by the Master.31
e. The Modulation Scheme
• The operating band is divided into 1 MHz-spaced channels,
each signaling data at 1 Mega-symbol per second = 1 MB/s.
• With the chosen modulation scheme of GFSK with Kf= 0.3.
• Binary 1 gives Fc +Δf , while a binary 0 gives Fc -Δf.
• Simply Modulation and Demodulation schemes allows the
implementation of low-cost radio units.
• After each packet, both Tx & Rx retune their radio to a
different frequency, hopping from channel to channel.
• Bluetooth devices use the whole of the available band and if
a interference occurred on one channel, the retransmission
will always be on a different (hopefully clear) channel.
• Each Bluetooth time slot lasts 625 μs, and devices hop once
per packet: every slot, every 3 slots, or every 5 slots. 32
Transient noise
may impair
transmission
during one hop
FHSS is an
ideal for a
WLAN
in a noisy
frequency
band !
Time
Power
FHSS
Frequency
Signal will hop
from one
channel to
another
During any one hop, the signal is vulnerable to noise in that
frequency band, but it will soon move to another frequency
with less noise. This new band will be sufficiently removed
f
33
rom the previous noisy band
5. Medium Access Control
• Bluetooth with 79 channels can support 79 Mb/s.
• When a Piconet is established, the slaves add offsets to
their native clocks to synchronize to the master. These
offsets are released again when the Piconet is cancelled, but
can be stored. Channels have a different hopping
sequences.
• Each unit can become a master or slave. By definition, the
unit that establishes the Piconet becomes the master.
• Access is completely contention free.
• The master implements centralized control;
• The time slots are alternately used for master transmission
and slave transmission.
34
Medium Access Control (cont)
• In M transmission, the M includes a S address.
• To prevent collisions due to multiple S transmissions, the
M applies a polling technique: for each S-to-M slot, the
M decides which S is allowed to transmit. Only the S
addressed in the M-to-S slot directly preceding the S-to-M
slot is allowed to transmit.
• If the M has information to send to a specific S, this S is
polled and can return information.
• M schedules the traffic in both the uplink and downlink.
• The M control prevents collisions between the channels.
• Slotted ALOHA is applied: information is transmitted
without listen-before-talk. If the information is received
incorrectly, it is retransmitted at the next transmission
35
(opportunity for data only).
a. Master-to-Slave Role Switching
• M in an existing Piconet might allow itself to be paged and
connected to a new device and then switch between S/M.
• This is accomplished with M/S switch and is particularly
useful in situation where a connection has just been
established by a device which normally wishes to be a S.
• Mechanism involves the S sending its FHS packet to the
M; M takes on a CLK offset to match the S’s CLK, while
the S switches to using its own CLK.
• The new M also sends an Link Manager Packet massage,
which contains the lower part of the Bluetooth CLK
contained in the FHS together with the sub-slot offset
information to allow the new S fully synchronize its timing.
36
Scatternet scenario
How to schedule presence
in two piconets?
Forwarding delay ?
Missed traffic?
M in an existing Piconet might allow
itself to be paged and connected to a
new device and then switch between
S/M .
This M/S switch is useful in situation
where a connection has just been
established by a device which normally
wishes to be a S.
Mechanism involves the S sending its
FHS packet to the M; M takes on a
CLK offset to match the S’s CLK,
while the S switches to using its own
CLK.
37
6. Voice and Data Links
• Bluetooth allows both time sensitive communication: voice or
audio, and time insensitive packet: data communication.
• So, two different types of links are defined:
• Synchronous Connection Oriented (SCO) links
for voice communication
• Asynchronous Connectionless (ACL) links
for data communication.
• ACL data packets are: a 72-bit access code, a 54-bit packet header
and a 16-bit CRC code, in addition to the payload data.
• Different types of packets allow different amounts of data to be
sent: The largest packet data payload is a DH5 (Data High) packet,
with 5 slots. A DH5 packet carry 339 bytes, or 2712 bits of data.
So, 2858 bits are sent for 2712 bits of information, and the
minimum length reply is one slot.
• Thus, the maximum baseband data rate in one direction is 723.2
kb/s.
• With 5-slot packet sent in one direction, the 1-slot packet sent in the
38
other direction, so this would be an asymmetric link.
Mixing of synchronous SCO links and asynchronous
ACL links on a single piconet channel.
SCO
ACL
SCO
ACL
ACL
SCO
M
S1
S2
S3
39
a. Physical Link Definition
1. SCO link (voice traffic)
2. ACL link (data traffic)
• The SCO link is a point-to-point link between the M and a
single S. The link is established by reservation of duplex
slots at regular intervals. For SCO links only single-slot
packets have been defined and supports a full-duplex link
with a user rate 64 kbps in both directions.
• The ACL link is a point-to-multipoint link between the M
and all the slaves on the Piconet. The ACL link can use all
of the remaining slots on the channel not used for SCO
links. The traffic over the ACL link is scheduled by the M.
The maximum user rate is 723.2 kbps. In that case, a
return link of 57.6 kbps can be supported.
40
7. Data Packet Types
Symmetric
Asymmetric
DM1
108.8
108.8
108.8
DM3
258.1
387.2
54.4
DM5
286.7
477.8
36.3
2/3 FEC
Symmetric
No FEC
Asymmetric
DH1
172.8
172.8
172.8
DH3
390.4
585.6
86.4
433.9
723.2
57.6
DH5
DM-Data Medium, with Forward Error Control
DH-Data High, no Forward Error Control
41
Frame format types
(3 x 18)
The Address - identifies which of the 8
active devices the frame is intended for.
The Type - frame type (ACL, SCO)
The Flow - is asserted by a slave when
its buffer is full and cannot receive any
more data
The Ack-ment bit is used for ACK
The Sequence - is used to number
the frames for retransmissions.
The protocol is stop-and-wait.
Checksum The 18-bit header is
repeated 3 times for a total of 54
bits Header
42
Packet Format
Identifies the
master and
slaves within
radio range of
two masters
can tell which
traffic is for
72 bits 54 bits
Access
code
them.
Containing
typical
MAC
sublayer
fields
FEC
Header
0 - 2744 bits
Payload
Voice
Data
No CRC
No retries
ARQ
Forward error coding
For a single
time slot
the data
field is 240
bits.
(optional)
CRC
FEC (optional)
625 µs
master
slave
43
a. Access Code
72 bits
Access
code
Header
Purpose
•
•
•
•
Synchronization
DC offset compensation
Identification
Signaling
Payload
Types
 Channel Access Code (CAC)
 Device Access Code (DAC)
 Inquiry Access Code (IAC)
X
44
b. Packet Header
54 bits
Access
code
Header
s
Purpose
•
•
•
•
•
•
Addressing (3)
Packet type (4)
Flow control (1)
1-bit ARQ
(1)
Sequencing (1)
HEC
(8)
total
m
Payload
18 bits
s
s
Max 7 active slaves
16 packet types (some unused)
Broadcast packets are not ACKed
For filtering retransmitted packets
Verify header integrity (Header
Error Control)
Encode with 1/3 FEC (Forward Error Correction) to get 54 bits
45
c. Addressing
• Active Member address (AM_ADDR)
– 3 bits active slave address
– all zero broadcast address
• Bluetooth device address (BD_ADDR)
– 48 bit IEEE MAC address
• Parked Member address (PM_ADDR)
– 8 bit parked slave address
46
8. Voice Packets (HV1, HV2, HV3)
HV-High Voice
240 bits
72 bits 54 bits
Access
Header
code
= 366 bits
30 bytes
Payload
HV1
HV2
10 bytes
20 bytes
HV3
2.5ms
1.25ms (HV1)
+ 1/3 FEC
+ 2/3 FEC
30 bytes
3.75ms
(HV2)
(HV3)
47
Multi slot packets
FH/TDD
f1
f4
f5
f6
m
s1
s2
625 µsec
Data rate depends on type of packet
48
The frequency and timing characteristics of:
single-slot, three-slot and five-slot packets
0.625 msec
f(k)
f(k+1)
f(k+2)
f(k+3)
f(k+4)
f(k+5)
TX
RX
TX
RX
TX
RX
f(k+3)
f(k+4)
RX
TX
f(k)
TX
f(k)
TX
f(k+5)
RX
f(k+5)
RX
49
Packed-Based Communication
• Information stream is fragmented into packets. In each time slot,
only a single packet can be sent, all with the same format.
• The access code is used as a DS code in certain access operations.
The access code includes the identity of the Piconet master.
• All packets exchanged on the channel are identified by this master
identity. Only if the packet access code matches to the Piconet
master access code the packet will be accepted by the recipient.
• The packet header contains link control information (address,
ACK, ACK/NACK for the Automatic Repeat reQuest (ARQ)
scheme, packet type code, Header Error Check (HEC).
• The header is further protected by Forward Error Correction (FEC)
coding.
• Packet type code define 16 different payload types
(4 control Packets and 12 type of codes),
50
Packed-Based Communication (cont)
1. The ID or identification packet: Only consists of the access code,
used for signaling.
2. The NULL packet: Only has an access code and a packet header,
used if link control information carried by the packet header has
to be conveyed.
3. The POLL packet. Similar to the NULL packet, used by the master
to force slaves to return a response.
4. The FHS packet. An FH-synchronization packet, used to exchange
real-time clock and identity between the units, contains all
information to get hop synchronized between two units.
• The remaining 12 type codes are used to define packets for
synchronous and asynchronous services.
• These 12 types of packets are divided into three segments:
segment 1 specifies 1-slot; segment 2 specifies 3-slot packets, and
segment 3 specifies 5-slot packet.
• Multislot packets are sent on a single-hop carrier
51
a. Data rate calculation: DM1 & DH1
625 µs
72 bits 54 bits
Access
Header
code
240 bits
= 366 bits
30 bytes
Dir Size
Payload
DM1 1
DH1 1
17
2
27
2/3
FEC
2
Freq Rate


17
17
108.8


27
172.8
27
172.8
1600/2
108.8
625 µs
1
2
52
Data rate calculation: DM3 and DH3
1875 µs
54
72
bits bits
= 1626 bits
1500 bits
Access Header
code
187 bytes
Dir Size Freq Rate
Payload
DM3 2
121
DH3 2
183
1875 µs
1
2
3
2
2/3
FEC
2


121
17
54.4


183
585.6
27
86.4
1600/4
387.2
4
53
Data rate calculation: DM5 and DH5
3125 µs
54
72
bits bits
= 2870 bits
2744 bits
Access
Header
Code
343 bytes
Payload
DM5 2
224
DH5 2
339
625 µs
3125 µs
1
2
3
2
4
5
Dir Size Freq
2/3
FEC
2
Rate


224
17
36.3


339
723.2
27
57.6
1600/6
477.8
6
54
9. Communication Scenario
55
a. Connection Establishment
•How to find each other? how do they make connections?
Scan, page, and inquiry support connection establishment:
In idle mode (sniff): the unit periodically listens if other units want
to connect. The scan window is about than 10 ms.
At every wake up, it scans at a different hop carrier. The Bluetooth
wake up hop sequence is only 32 hops in length and is cyclic. All
32 hops in the wake up sequence are unique, and they scan at least
64 MHz of the 80 MHz available.
Scan duration
10 ms
Sniff offset
Slave
Master
Sniff period
56
The unit that wants to connect it does not know when the idle unit will
wake-up and on which frequency. Solving is placed at the paging unit.
Assume: 1. the paging unit knows the identity of the unit to connect.
2. it knows the wake-up sequence. 3. can generate the access code.
The paging unit then transmits the access code repeatedly at different
frequencies every 1.25 ms; the paging unit transmits two access codes
and listens twice for a response. The paging unit transmits the access
code on these 16 frequencies cyclically. If the idle unit wakes up in
any of these 16 frequencies, it will receive connection setup procedure
follows. The paging unit and the idle unit establish a piconet
TX1
TX2
f(k)
f(k+1)
RX1
f(k+2)
RX2
f(k+3)
TX3
f(k+4)
TX4
f(k+5)
t
1250 μs
57
Standby
Standby
ID
Inquiry
Inquiry
FHS
Inquiry
response
Standby
Standby
Access cod
Page
Page
FHS
Idle units listens the inquiry, returns
the inquiry and FHS packet which
includes identity & clock information.
During page & inquiry, 32 hop used
& access code is used for signaling
Slave ACKs the paging massage,
switches to the Master’s CLK & moves to
Master’s frequency hop and timing sequence
ID
Master
response
To make a connection unit broadcasts
inquiry message with return address
& clock information.
Slave
response
Connection
Connection
(M)
(S)
M enters the M response with its
FHS packets.
During connection state, various data
exchange & logical channels are possible.
58
From time to time, device changes state.
b. Inquiry on time axis
Slave1
f1
f2
Inquiry hopping
sequence
Master
Slave2
59
c. Error Correction
On the ACL link, an ARQ scheme applied: packet retransmission is
carried out if the reception of the packet is not ACKed.
Payload contains a CRC. Several ARQ schemes have been considered:
stop-and-wait ARQ, go-back-N ARQ, & selective-repeat ARQ.
Bluetooth has implemented a fast-ARQ (is similar to the stop-andwait ARQ) scheme where the sender is notified of the packet reception
in the RX slot directly following the TX slot in which the packet was
sent.
0.625 msec
f(k+3)
t
A1
B1
ACK A1
Crash
f(k+2)
ACK B1
B
f(k+1)
NAK A1
A
f(k)
A1
t
B2
60
d. Piconet Management
Attach and detach slaves
Master-slave switch
Establishing SCO links
Handling of low power modes
( Sniff, Hold, Park)
Transmit power in
Bluetooth applications
for short-range
connectivity is 0 dBm.
allow up to 20 dBm
Paging
s
s
s
req
response
Slave
m
Master
•
•
•
•
•
61
Power Management:
Low power mode (hold)
Duty cycle is well below 1 %
Hold offset
Slave
Hold duration
Master
62
Power Management: (Sniff)
In SNIFF mode, the slave does not scan at every
M-to-S slot, but has a larger interval between scans.
Sniff duration
Sniff offset
Slave
Master
Sniff period
• Traffic reduced to periodic sniff slots
63
Power Management: (Park)
PARK mode can only be applied after the Piconet has
126 μs been established. Duty cycle can be reduced < 1%
Slave
Beacon instant
Master
Beacon interval
• Power saving + keep more than 7 slaves in a
Piconet
• Give up active member address, maintain
synchronization
• Communication via broadcast LMP messages
64
Appendix
65
Bluetooth protocol stack
Application layer
Middleware layer
Applications
IP
SDP
RFCOMM
Data
Data link layer
Audio
Physical layer
L2CAP
Link Manager
Baseband
RF
Single chip with
RS-232,USB, or
PC card interface
Allocations of The Bluetooth protocol stack is a series of layers,
through there are some features which cross several layers. 66
The Bluetooth Protocol Architecture
Application
layer
Application/Profiles
Other
Audio
LLC
RFcomm Telephony Service
cont. pr. discovery
Logical link control adaptation protocol
(L2CAP)
(LLC)
Link manager
Baseband (MAC)
Physical radio
Host
Control
Middleware
layer
Data link
layer
Physical
layer
1. The Physical Layer is responsible for: electrical interface media,
modulation & channel coding. It covers the radio and part of baseband
and corresponds to the physical layer in the OSI and 802 models.
2. The Baseband Layer is analogous to the MAC sublayer + elements
of the physical layer. It deals with how the master controls time slots
and how these slots are grouped into frames.
67
3. L2CAP: analogous to the standard 802 LLC sublayer, but different.
The Bluetooth Protocols
Application
layer
Application/Profiles
Other
Audio
LLC
RFcomm Telephony Service
cont. pr. discovery
Logical link control adaptation protocol
Link manager
Host
Control
Middleware
layer
Data link
layer
Baseband
Physical radio
Physical
layer
a. Telephony (TCS Telephony Control Protocol Specification) provides
telephony services. Bluetooth’s TCS defines how telephone calls should be
sent across a Bluetooth link. It gives guidelines for the signaling needed to set
up both point-to-point, and point-to-multipoint calls.
b. SDP (Service Discovery Protocol) lets Bluetooth devices to discover what
services other Bluetooth devices support. In LAN, you find a connection to a
printer, and once found, it stays in place. Bluetooth is designed to allow to68
walk into an area and find a printer, without having to pre-configure settings.
The Bluetooth Protocols (Cont)
Application
layer
Application/Profiles
Other
Audio
LLC
RFcomm Telephony Service
cont. pr. discovery
Logical link control adaptation protocol
Link manager
Host
Control
Middleware
layer
Data link
layer
Baseband
Physical radio
Physical
layer
c. RFCOMM is protocol for RS-232 serial cable. RS-232 serial ports have nine
circuits, which can be used for transforming data and signaling. It provides
multiple concurrent connections by relying on L2CAP to handle multiplexing
over single connections, and to provide connections to multiple devices.
d. L2CAP (Logical Link Control and Adaptation Protocol). This provides
segmentation and re-assembly services to allow large packets to pass across
Bluetooth links, also takes data from higher layer of the Bluetooth stack
and
69
from applications and sends it over the lower layers of the stack.
The L2CAP layer has three major
functions:
• First, it accepts packets of up to 64 Kb from the upper layers
and breaks them into frames for transmission. At the far end, the
frames are reassembled into packets again.
• Second, it handles the multiplexing and demultiplexing of
multiple packets sources. When a packet has been reassembled,
the L2CAP layer determines which upper-layer protocol to hand it
to, for example, RFcomm or telephony.
• Third, L2CAP handles the quality of service requirement, both
when links are established and during normal operation. Also
negotiating at setup time is the maximum payload size allowed, to
prevent a large-packet device from droving a small-packet device.
This future is needed because not all devices can handle the 64-Kb
maximum packet. This layer corresponds with 802 Data Link
Layer, that usually is responsible for transmission, framing, and
error control over a particular link.
70
L2CAP
Applications
IP
SDP
Logical Link Control and
Adaptation Protocol
RFCOMM
Data
Audio
L2CAP
Link Manager
Baseband
RF
L2CAP provides
• Protocol multiplexing
• Segmentation and Re-assembly
• Quality of service negotiation
71
The Bluetooth Protocols (Cont)
Application
layer
Application/Profiles
Audio
Other RFcomm Telephony Service
cont. pr. discovery
LLC
Logical link control adaptation protocol
Link manager
Host
Control
Middleware
layer
Data link
layer
Baseband
Physical radio
Physical
layer
e. HCI (The Host Controller Interface) handles communications between a
separate hosts and Bluetooth module.
f. LM (The Link Manager) controls & configures links to other devices. The LM
translates commands into operations at the baseband level. following operations:
 Attaching Slaves to a piconet, and allocating their active member addresses
 Breaking connection to detach Slaves from a piconet.
 Configuring the link including controlling Master/Slave switches.
 Establishing ACL (data) and SCO (voice) links.
72
 Putting connections into low-power modes: Hold, Sniff, and Park.
 Controlling test modes.
Link Manager Protocol
Applications
IP
SDP
RFCOMM
Data
Audio
Setup and management
of Baseband connections
L2CAP
Link Manager
Baseband
RF
LMP
• Piconet Management
• Link Configuration
• Security
73
Link Manager Protocol Summary
Device 1
Device 2
L2CAP
L2CAP
LMP
Data link
LMP
Baseband
Baseband
Physical
• Piconet management
• Link configuration
– Low power modes
– Packet type selection
• Security: authentication and encryption
74
The Bluetooth Protocols (Cont)
Application
layer
Application/Profiles
Audio
Other RFcomm Telephony Service
cont. sp. discovery
LLC
Logical link control adaptation protocol
Link manager
Host
Control
Middleware
layer
Data link
layer
Baseband
Physical radio
Physical
layer
g. The Baseband & Link Controller (LC) Controls radio links, assembling packets
and controlling FH. The is responsible for DLL operations in response to
commands from Link Manager. The baseband is responsible for channel coding
and decoding & low level timing control and management within the single data
packet transfer. Bluetooth is a TDM system, where the basic unit of operation is
slot of 625  s duration. 1. In connection (transferring), all transmit or receive
operation occur in 1, 3, or 5 slots (a packet). 2. In pre-connection operation (the
scanning, paging, inquiry which precedes a connection), The packets are joined
together in transmit and receive pairs. In connection, a packet-pair can be 2,4,6,8,
or 10 slots long.
75
Baseband Link Types (Cont)
• Polling-based (TDD) packet transmissions
-1 slot: 0.625 msec (max 1600 slots/sec)
-master/slave slots (odd/even-numbered slots
-polling: master always “pools” slaves
• Synchronous connection-oriented (SCO) link
-”circuit-switched” (periodic single-slot packet
assignment)
-symmetric 64 Kb/s full-duplex
• Asynchronous connection-less (ACL) link
-packet switching
-asymmetric bandwidth (variable packet size, 1-5 slots,
max. 721 kb/s, 57.6 kb/s return channel, 108.8-432.6 76kb/s,
symmetric
Baseband: Summary
Device 1
Device 2
L2CAP
L2CAP
LMP
Data link
LMP
Baseband
Baseband
Physical
•
•
•
•
TDD, frequency hopping physical layer
Device inquiry and paging
Two types of links: SCO and ACL links
Multiple packet types (multiple data
rates)
77
Physical Layer
Link-level and
Medium access
Management
Packet-level
Channel
Access
Control
Packet-level
Channel
Processing
And Timing
Link
Manager
Link
Controller
Baseband
Radio
Physical Layer
h. The Radio modulates and
demodulates data.
Bluetooth operate at 2.4 GHz.
The operating band of 83.5 MHz
is divided into 1 MHz spaced
channels, each signaling data at 1
Mb/s. with modulation scheme of
GFSK. “1”= rise to a frequency
from the normal carrier “0” =
reduce frequency.
Noise: car security, cordless head phones, standardized Wireless
LAN, microwave ovens and sodium vapor street lamps, so the 2.4
GHz band is not a stable or reliable medium.
78
Physical Link Types
Synchronous Connection Oriented (SCO) Link
for real-time data, such as telephony connections. This
type of channel allocates a fixed slot in each direction.
Due to the nature of SCO links, frames sent over them are
never retransmitted. Instead, forward error correction can
be used to provide high reliability. A S may have up to
three SCO links with its M. Each SCO link can transmit
one 64,000 bps PCM channel.
Asynchronous Connection-less (ACL) Link used for
packet-switching data, available at irregular intervals.
These data come from the L2CAP layer on the sending
side and are delivered to the L2CAP layer on the
receiving side.
79