3b. Bluetooth Communications (01/21). 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? - PowerPoint PPT Presentation
1 3b. Bluetooth Communications (01/21) 1. Introduction 2. Technical Overview a. Design considerations b. Bluetooth radio link 3. Review of basic concepts a. Wireless Positioning 4. Bluetooth Architecture a. Bluetooth Physical link b. Piconet formation c. Piconet channels d. Multiple Access Scheme e. The Modulation Scheme 5. Medium Access Control a. Master-to-Slave Role Switching 6. Voice and Data Links a. Physical Link Definition 7. Data Packet Types a. Access Code b. Packet Header c. Addressing 8. Voice Packets a. Data rate calculation
Transcript
1
3b. Bluetooth Communications (01/21) 1. Introduction
2. Technical Overview a. Design considerationsb. Bluetooth radio link
3. Review of basic concepts a. Wireless Positioning
4. Bluetooth Architecture a. Bluetooth Physical linkb. Piconet formationc. Piconet channelsd. Multiple Access Scheme e. The Modulation Scheme
5. Medium Access Control a. Master-to-Slave Role Switching
6. Voice and Data Links a. Physical Link Definition
7. Data Packet Types a. Access Codeb. Packet Headerc. Addressing
8. Voice Packets a. Data rate calculation
9. Communication Scenario a. Connection Establishment b. Inquiry on time axisd. Piconet Management
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Bluetooth Communications. 802.15
• A cable replacement technology• 1 Mb/s symbol rate• Range 10+ meters
• Single chip radio – at low power & low price ($5)
Bluetooth is considered as a secure short-range wireless network.
Why not use Wireless LANs?- power- cost
No Another wireless LAN
3
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
4
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.
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ApplicationsUser benefits
• Multiple device access (phone, music)
• Cordless phone benefits
• Hands free operation
• Conference Table
• Cordless Computer
• Business Card Exchange
• Instant Postcard
• Computer Speakerphone
Cordlessheadset
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Bluetooth Profiles• Generic Access
• Service Discovery
• Cordless Telephone
• Intercom
• Serial Port
• Headset
• Dial-up Networking
• Fax
• LAN Access
• Generic Object Exchange
• Object Push
• File Transfer
• Synchronization
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2. TechnicalOverview
8
a. Design considerations
• high bandwidth• conserve battery power• cost < $10
Data signal x(t) Recovereddata signal
Goal:
cost
power
spectrum
Noise, interference
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EM Spectrum ISM band
LF HF VHF UHF SHF EHFMF
AM ra
dio
UV
S/W ra
dio
FM ra
dio
TV TV cellu
lar
1 MHz1 kHz 1 GHz 1 THz 1 PHz 1 EHz
infrared visible
X raysGamma rays
902 – 928 MHz
2.4 – 2.4835 GHz
5.725 – 5.785 GHz
ISM band
30kHz 300kHz 3MHz 30MHz 300MHz 30GHz 300GHz
10km 1km 100m 10m 1m 10cm 1cm 100mm
3GHz
ISM band
10
Unlicensed Radio Spectrum
902 Mhz
928 Mhz
26 Mhz 83.5 Mhz 125 Mhz
2.4 Ghz
2.4835 Ghz5.725 Ghz
5.785 Ghz
cordless phones,baby monitors,Wireless LANs
802.11 Cell.802.15 Bluetooth,Microwave oven
802.11aHyperLan
33cm 12cm 5cm
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b. Bluetooth radio link
• 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)
. . .
1MHz
1 2 3 7983.5 MHz
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
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3. Review of basic concepts
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Radio propagation: path loss
Pt
Pr
Pr
near field
path loss = 10 log (4r2/) r 8m
= 58.3 + 10 log (r3.3 /8) r > 8m
r
path loss in 2.4 Ghz band
near field far field
r2
r 8m r > 8m
r3.3
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Fading and multipath
Tx
Rx
Fading: rapid fluctuation of the amplitude of a radio signal over a short period of time or travel distance
• Fading• Varying Doppler shifts on different multipath signals• Time dispersion (causing inter symbol interference)
Effects of multipath
15
Bandwidth of digital data
• 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
Time domain Frequency domain
1 MHz 1.5 MHz0.5 MHz
Sig
nal
am
pli
tud
e
Fourier transform
baseband signal (1 Mb/s)
f MHz
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Channel coding and modulation
• Modulation of 1MHz baseband signal into 2.4GHz band is difficult to achieve in one step.
channel coding
demodulation
channel decoding
baseband signal
modulation
baseband signal
Challenges
17
Radio architecture: typical design
channel coding
demodulation
channel decoding
mixing mixing
basebandsignal
baseband signal
modulation
IntermediateFrequency
IntermediateFrequency
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Power consumption
50 mA 45 mA
25 mA
Transmit Receive
Radio
Vcc = 3 V
Baseband
450 mA 300 mA
Transmit Receive
Radio
Vcc = 3 V
Baseband
802.15 Bluetooth 802.11Class 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
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Bluetooth Radio• Low Power
– Standby modes: Sniff, Hold, Park.– Low voltage RF
Power Class
Transmit Power Nominal
Range
1 100 mW (20 dBm) 100 m
2 2.5 mW ( 4 dBm) 20 m
3 1 m W ( 0 dBm) 10 m
Low CostSingle chip radio (minimize external components)Today’s technologyTime division duplex
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a) Cellular radio systems with squares representing stationary BS; b) Bluetooth systems; c) Ad hoc systems.
a)
b)
c)
a. Wireless Positioning
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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
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4. Bluetooth Architecture, Piconets and Scatternets
MS
P
S P
S
Sb
A Piconet is collection of devices connected to the Master.
• 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)
• Master sets the clock, dwell time, hopping pattern.
• 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.
•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 from a Bluetooth device address and a Bluetooth clock.
Fast frequency hopping 1600 hops/se
c
25
Communication in a Scatternet
Master node
Slave nodeBridge node
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.
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b. Piconet formation
Master
Active Slave
Parked Slave
Standby
• Page - scan protocol– to establish links
with nodes in proximity
Direct, slave-to-slave communication is not possible.
Piconet Addressing: Active Member Address (AMA, 3-bits); Parked Members Address (PMA, 8-bits)
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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 link layer security Secure (it’s a cable)
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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.
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c. Piconet channels
M
S1
S2
625 μsec
f1 f2 f3 f4
1600 hops/sec
f5 f6
FH/TDD
devices hop once per packet, which will be:
every slot, every 3 slots, or every 5 slots.
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d. Multiple Access Scheme
Multiple-slave communication
Single-slave communication259
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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.
Multiple Access Scheme (cont)
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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.
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Frequency
Power
Signal will hop from one channel to another
Transient noise may impair transmission during one hop
Time
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 from the previous noisy band
FHSS is an ideal for a WLAN in a noisy frequency band !
FHSS
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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.
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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 (opportunity for data only).
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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.
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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.
38
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 other direction, so this would be an asymmetric link.
39
S1
S2
S3
M
SCO ACL SCO ACL ACL SCO
Mixing of synchronous SCO links and asynchronous ACL links on a single piconet channel.
40
a. Physical Link Definition1. 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.
41
7. Data Packet Types
DM1
DM3
DM5
DH1
DH3
DH5
2/3 FEC
No FEC
Symmetric Asymmetric
108.8 108.8 108.8
258.1 387.2 54.4
286.7 477.8 36.3
Symmetric Asymmetric
172.8 172.8 172.8
390.4 585.6 86.4
433.9 723.2 57.6
DH-Data High, no Forward Error Control
DM-Data Medium, with Forward Error Control
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Frame format types
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
• Addressing (3)• Packet type (4)• Flow control (1)• 1-bit ARQ (1)• Sequencing (1)• HEC (8)
Access code
Header Payload
54 bits
Purpose
Encode with 1/3 FEC (Forward Error Correction) to get 54 bits
Broadcast packets are not ACKed
For filtering retransmitted packets
18 bitstotal
ss
m
s
16 packet types (some unused)
Max 7 active slaves
Verify header integrity (Header Error Control)
46
c. Addressing
• Bluetooth device address (BD_ADDR)– 48 bit IEEE MAC address
• Active Member address (AM_ADDR)– 3 bits active slave address– all zero broadcast address
• Parked Member address (PM_ADDR)– 8 bit parked slave address
47
8. Voice Packets (HV1, HV2, HV3)
Access code Header
Payload
72 bits 54 bits 240 bits
30 bytes
= 366 bits
10 bytes
+ 2/3 FEC
+ 1/3 FEC
20 bytes
30 bytesHV3
HV2
HV1
3.75ms (HV3)2.5ms (HV2)
1.25ms (HV1)
HV-High Voice
48
Multi slot packets
m
s1
s2
625 µsec
f1
FH/TDD
Data rate depends on type of packet
f4 f5 f6
49
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
TX RX TX RX
TX RX
f(k) f(k+3) f(k+4)f(k+5)
f(k+5)f(k)
50
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),
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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
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a. Data rate calculation: DM1 & DH1
Payload
Accesscode Header
72 bits 54 bits 240 bits
30 bytes
= 366 bits
2/3 FEC
1 17 2DM1
1 27 2DH1
625 µs
625 µs
1 2
Dir Size Freq Rate
17 1600/2 108.8
17 108.8
27 172.8
27 172.8
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Data rate calculation: DM3 and DH3
Payload
Access code
Header
72 bits
54 bits
1500 bits
187 bytes
= 1626 bits
2/3 FEC
2 121 2DM3
2 183 2DH3
1875 µs
1875 µs
Dir Size Freq Rate
121 1600/4 387.2
17 54.4
183 585.6
27 86.4
1 2 3 4
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Data rate calculation: DM5 and DH5
Payload
AccessCode Header
72 bits
54 bits
2744 bits
343 bytes
= 2870 bits
2/3 FEC
2 224 2DM5
2 339 2DH5
3125 µs
3125 µs 625 µs
1 2 3 4 5 6
Dir Size Freq Rate
224 1600/6 477.8
17 36.3
339 723.2
27 57.6
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9. Communication Scenario
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a. Connection Establishment
At every wake up, it scans at a different hop carrier. The Bluetoothwake up hop sequence is only 32 hops in length and is cyclic. All32 hops in the wake up sequence are unique, and they scan at least64 MHz of the 80 MHz available.
•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.
Master
Slave
Sniff period
Sniff offsetScan duration
10 ms
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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
To make a connection unit broadcasts inquiry message with return address & clock information.
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
M enters the M response with its FHS packets.During connection state, various data exchange & logical channels are possible. From time to time, device changes state.
Access cod
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b. Inquiry on time axis
Slave1
Slave2
Master
Inquiry hoppingsequence
f1 f2
60
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-and-wait 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.
c. Error Correction
0.625 msec
f(k) f(k+1) f(k+2) f(k+3)t
Crash
A1 A1
B1 B2t
A
B
NA
K
A1 AC
K
A1
AC
K
B1
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d. Piconet Management• Attach and detach slaves• Master-slave switch• Establishing SCO links• Handling of low power modes • ( Sniff, Hold, Park)
req
response
Paging
Master
Slaves
s
m
s
Transmit power in Bluetooth applications for short-range connectivity is 0 dBm. allow up to 20 dBm
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Power Management: Low power mode (hold)
Slave
Hold duration
Hold offset
Master
Duty cycle is well below 1 %
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Power Management: (Sniff)
Master
Slave
Sniff period
Sniff offsetSniff duration
• Traffic reduced to periodic sniff slots
In SNIFF mode, the slave does not scan at every M-to-S slot, but has a larger interval between scans.
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Power Management: (Park)
Master
Slave
Beacon interval
Beacon instant
• Power saving + keep more than 7 slaves in a Piconet
• Give up active member address, maintain synchronization
• Communication via broadcast LMP messages
PARK mode can only be applied after the Piconet has been established. Duty cycle can be reduced < 1% 126 μs
65
Appendix
66
Bluetooth protocol stack
RF
Baseband
AudioLink Manager
L2CAP
Data
SDP RFCOMM
IP
Single chip with RS-232,USB, or PC card interface
HC
I
ApplicationsApplication layer
Middleware layer
Data link layer
Physical layer
Allocations of The Bluetooth protocol stack is a series of layers, through there are some features which cross several layers.
67
The Bluetooth Protocol Architecture
Physical radio
Baseband (MAC)
Logical link control adaptation protocol(L2CAP)
(LLC)Link manager
Other RFcomm Telephony Service cont. pr. discovery
Audio LLC
Application/Profiles
HostControl
Application layer 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.3. L2CAP: analogous to the standard 802 LLC sublayer, but different.
68
The Bluetooth Protocols
Physical radio
Baseband
Logical link control adaptation protocol
Link manager
Other RFcomm Telephony Service cont. pr. discovery
Audio LLC
Application/Profiles
HostControl
Application layer Middleware layer
Data link layer
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 to walk into an area and find a printer, without having to pre-configure settings.
69
The Bluetooth Protocols (Cont)
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 from applications and sends it over the lower layers of the stack.
Physical radio
Baseband
Logical link control adaptation protocol
Link manager
Other RFcomm Telephony Service cont. pr. discoveryAudio LLC
Application/Profiles
HostControl
Application layer Middleware layer
Data link layer
Physical layer
70
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.
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L2CAP
Logical Link Control andAdaptation Protocol
L2CAP provides• Protocol multiplexing• Segmentation and Re-assembly• Quality of service negotiation
RF
Baseband
AudioLink Manager
L2CAP
Data
SDP RFCOMM
IP
Applications
72
The Bluetooth Protocols (Cont)
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 addressesBreaking connection to detach Slaves from a piconet. Configuring the link including controlling Master/Slave switches. Establishing ACL (data) and SCO (voice) links. Putting connections into low-power modes: Hold, Sniff, and Park. Controlling test modes.
Physical radio
Baseband
Logical link control adaptation protocol
Link manager
Other RFcomm Telephony Service cont. pr. discoveryAudio LLC
Application/Profiles
HostControl
Application layer Middleware layer
Data link layer
Physical layer
73
Link Manager Protocol
Setup and management of Baseband connections
• Piconet Management• Link Configuration• Security
LMP
RF
Baseband
AudioLink Manager
L2CAP
Data Con
trolSDP RFCOMM
IP
Applications
74
Link Manager Protocol Summary
• Piconet management• Link configuration
– Low power modes– Packet type selection
• Security: authentication and encryption
Baseband Baseband
L2CAPL2CAPLMPLMP
Physical
Data link
Device 2Device 1
75
The Bluetooth Protocols (Cont)
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.
Physical radio
Baseband
Logical link control adaptation protocolLink manager
Other RFcomm Telephony Service cont. sp. discovery
Audio LLC
Application/Profiles
HostControl
Application layer Middleware layer
Data link layer
Physical layer
76
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
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.
79
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.
