Bluetooth Part-17

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TECHVILL
A

BLUETOOTH

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Bluetooth Origins• Study by Ericsson Mobile Communications in 1994.
• Alternatives to cables connecting mobile phones to
accessories.
• Use of radio links instead of infrared.
• Why?
• Transmission of data and voice.
• Result: Bluetooth spec.
• Named after Harald Blatand (Danish for Bluetooth).
• 10th
century Viking king who united Denmark and
Norway.

Bluetooth SIG History
• Early 1998: Bluetooth SIG is formed.
• Promoter company group: Ericsson, IBM, Intel, Nokia,
Toshiba.
• Goal: develop license-free technology for universal
wireless connectivity.
• Target: handheld market.
• Bluetooth spec: defines RF wireless communication
interface and protocols.

Bluetooth SIG History
• May 1998: Public announcement of Bluetooth SIG.
• July 1999: 1.0A spec (>1,500 pages) published.
• December 1999: version 1.0B released.
• December 1999: promoters increases to 9.
• 3Com, Lucent, Microsoft, Motorola
• February 2000: 1,800+ adopters.
• February 2001: version 1.1 out.

Goals• Open spec.
• Low cost.
• In order to replace cables, should have similar cost.
• Cell phone cable is ~ $10.
• Power efficiency.
• Lightweight and small form factor.
• Easy to use.
• Reliable and resilient to failures.

The Bluetooth Standard
• Defines a protocol stack to enable heterogeneous devices to
communicate.
• The Bluetooth stack includes protocols for the radio layer all the way
up to device discovery, service discovery, etc.

Bluetooth Protocol Stack
RF
Baseband
Link Manager
L2CAP
RFCOMM/SDP
Applications
Link Controller
Host Controller Interface
PHY
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application
OSI/ISO

Bluetooth Layers
• Radio: physically transmits/receives data.
• Baseband/Link Controller: controls PHY.
• Link Manager: controls links to other devices.
• Host Controller:e2e communication.
• Logical Link Control: multiplexes/demultiplexes data from higher
layers.
• RFCOMM: RS323-like serial interface.
• SDP: allows service discovery among Bluetooth devices.

The Bluetooth PHY

Radio Band
• 2.4 GHz license-free ISM band.
• Available worldwide.
• Industrial, Scientific, Medical (ISM) band.
• Unlicensed, globally available.
• Centered around 2.4 GHz.
• Resilient to interference.
• Frequency hopping.
• Range: 10, 20, and 100m.
• 1MB/s.

Unlicensed Radio Spectrum
902 Mhz
928 Mhz
26 Mhz 83.5 Mhz 125 Mhz
2.4 Ghz
2.4835 Ghz
5.725 Ghz
5.785 Ghz
cordless phones
baby monitors
Wireless LANs
802.11
Bluetooth
Microwave oven
unused
λ 33cm 12cm 5cm

Bluetooth Radio Link
• MA scheme: Frequency hopping spread spectrum.
• 2.402 GHz + k MHz, k=0, …, 78
• 1,600 hops per second.
• 1 Mb/s data rate.
. . .
1Mhz
1 2 3 79
83.5 Mhz

BT Radio Link (Cont’d)
• Time-division duplex (TDD)
• Separation of Xmission and reception in time.
• Units alternate transmits and receives.
• Gaussian Frequency Shift Keying (G-FSK) modulation.
• ‘1’s as positive frequency deviations from carrier frequency; ‘0’s as negative
deviations.

Multiple Access
• BT targets large number of independent communications
active in the same area at the same time.
• Single FH channel: 1 Mb/s.
• Each 1Mb/s channel shared by limited number of participants.
• In target user scenarios, it’s unlikely that all units in-range will
share data among all of them.
• 1 MB/s is reasonable. (is it?)
• Theoretically, total bandwidth is 79 Mb/s.
• In practice, < 79 Mb/s since codes are non-orthogonal.

Baseband
Carries out MAC
functions.
RF
Baseband
Link Manager
L2CAP
RFCOMM/SDP
Applications
Link Controller
Control end of baseband
+link controller=
Data link layer

Master and Slaves
• Communicating devices must agree on hopping sequence.
• BT devices can operate as masters or slaves.
• Master node defines sequence to be used.
• Slave units use master id to pick sequence.
• Master also controls when devices are allowed to transmit.
• Master allocates slots to slaves.
• Allocates total available bandwidth among slaves.

Piconets
• BT communication takes place over piconets.
• Piconet formation initiated by master.
• All other participants are slaves.
• Number of participants limited to 8 (1 master and 7 slaves).
• Channel capacity and addressing overhead.
• Each slave assigned a locally unique ID.
• Master/slave roles last for the duration of the piconet.

More on Piconets
• On a piconet, slaves only have direct links to master.
• Point-to-point or point-to-multipoint connections.

Piconets: Considerations
• Most target applications involve local communication among small
group of devices.
• Piconets with up to 8 nodes match well.
• If many groups of devices active simultaneously, each group as
separate piconet.
• Overlapping piconets can coexist.

Contention-Free MA
• Master and slaves.
• Master performs medium access control.
• Schedules traffic through polling.
• Time slots alternate between master and slave transmission.
• Master-slave: master includes slave address.
• Slave-master: only slave chosen by master in previous master-slave slot allowed to
transmit.
• If master has data to send to a slave, slave polled implicitly; otherwise, explicit poll.

BT States
Standby
Inquiry Page
Transmit Connected
Park Hold Sniff
Unconnected
Connecting
Active
Low power
. Initially, all nodes in
standby.
. Node (master) can begin
inquiry to find nearby
devices.
. Piconet is then formed.
. Devices join by paging.

Inquiry
• Device discovery
•Listeners respond with
their address.

Paging Master
Active Slave
Parked Slave
Standby
• Device enters paging to invite
others to join its piconet.
• Establishes links with nodes in
proximity.
• Paging message unicast to
selected receiver.
• Receiver sends ACK.
• Sender becomes master,
receiver slave.

Piconet New Node Admission
• Master can actively try to discover new nodes or wait (in scan/listen
mode) to be discovered.
• Communication in the current piconet suspended.
• Admission latency versus piconet capacity tradeoff.

Bluetooth Link Formation
• Point-to-point link:
• Master-slave relationship.
m s
s
s
m
s
• Piconet:
– 8 units: channel capacity.
– Master (establishes piconet) can
connect to up to 7 slaves.
– Master/slave relationship lasts while
link/piconet lasts.
– No slave-to-slave communication.

Link Types
• 2 types of links:
• Synchronous (SCO) links:
• Point-to-point between master and slave.
• Link established by reserving slots in either direction periodically.
• Used to carry real-time traffic (voice).
• Asynchronous (ACL) links:
• Point-to-multipoint between master and slaves.
• Use remaining slots on channel.
• Traffic scheduled by master.

Error Control
• Supports both FEC and retransmission.
• FEC for SCO packets.
• ARQ for ACL traffic.
• If no ACKs, retransmit.
• Stop-and-wait ARQ.
• Fast-ARQ: ACK included in RX slot immediately following the TX slot in which packet was
sent.
• CRC to check for errors.

Packet Format
72 bits 54 bits 0 - 2744 bits
Access
code
Header Payload
DataVoice CRC
No CRC
No retries
625 µs
master
slave
header
ARQ
FEC (optional)
FEC (optional)

Access Code
• Address of piconet master.
Access
code
Header Payload
72 bits

Packet Header
• Addressing (3)
• Packet type (4)
• Flow control (1)
• 1-bit ARQ (1)
• Sequencing (1)
• HEC (8)
Access
code
Header Payload
54 bits
Purpose
Broadcast packets are not ACKed
For filtering retransmitted packets
18 bitstotal
s
s
m
s
16 packet types (some unused)
Max 7 active slaves
Verify header integrity

Multiple Piconets
• Piconets may overlap in space and time.
• They can work independently.
• Each with its own hopping sequence.
• Packets with different access codes.
• Or they can overlap, i.e., nodes can participate in more than 1 piconet.
• “Time sharing”.

Scatternets
• Interconnection of multiple piconets.
Master
Slave

Scatternets (cont’d…)
• Interconnection by bridge nodes.
• Bridge nodes are members of piconets they interconnect.
• Bridge node “stay” in a piconet for some time, then switch to another piconet
by changing hop sequence.
• Do this for all member piconets.
• Send and receive in each piconet.
• Forward from one piconet to another.

Link Controller and Link Manager
RF
Baseband
Link Manager
L2CAP
RFCOMM/SDP
Applications
Link Controller
Carries out inquiry and paging
operations; manages multiple
links and different piconets.
Attaching/detaching slaves from
piconet; power management; security.

Power Management
• Low-power modes: prolong battery life.
• Devices can be turned-off when idle.
• Devices wake up periodically to send/receive data.

Low-Power Operation
• 3 modes:
• Hold: node sleeps for specified interval.
• Master can put slaves in hold while searching for new members, attending another piconet, etc.
• No ACL packets.
• Sniff: slave low-duty cycle mode.
• Slave wakes up periodically to talk to master.
• Fixed “sniff” intervals.
• Park:
• Very low power state.
• Used to admit more than 7 slaves in piconet.
• Slave gives up its active member address.
• Receives “parked” member address.
• Wakes up periodically listening for broadcasts which can be used to “unpark” node.

Security
• Authentication and encryption.
• LMP provides mechanisms for negotiation of encryption modes, keys,
etc.

RF
Baseband
Link Manager
L2CAP
RFCOMM/SDP
Applications
Link Controller
Optional interface layer
between higher and lower
layers of the BT stack.
E.g., when lower- and higher
BT layers run on different
Devices: PCMCIA card and
PC’s processor.

L2CAP
Logical Link Control and
Adaptation Protocol=
Session Layer.
L2CAP provides
• Protocol multiplexing
• Quality of service negotiationRF
Baseband
Link Manager
L2CAP
RFCOMM/SDP
Applications
Link Controller

RFCOMM/SDP
RF
Baseband
Link Manager
L2CAP
RFCOMM/SDP
Applications
Link Controller
Service discovery, serial port
interface.

42
Features Cost
20 dBm (~100 m)
Point-to-multipoint
No Scatternet
Applications
File Transfer,
Dial-Up Networking
LAN access, Fax, …
169 $
---
200 $
0 dBm (~10 m)
Point-to-multipoint
No Scatternet
File Transfer,
Dial-Up Networking
LAN access, Fax, …
169 $
---
Company
Toshiba,
Motorola,
Digianswer
IBM, TDK
3COM
10 m user-user;
100 m user-Base Station
Point-to-multipoint
SW- & FW-upgradeable
File Transfer,
Dial-Up Networking
LAN access, Fax, E-mail
Unconscious connection
149 $
Nokia
10 m user-user;
Point-to-point
Connectivity Battery
for the cell phone
File Transfer,
Dial-Up Networking
LAN access, Fax, E-mail
Unconscious connection
149 $
Ericsson,
Sigma
10 m user-user;
Point-to-point;
ARM processor;
USB; RFCOMM ports
Basic BT Radio stack
Embedded or Host stack
Programmable
500 $
1500$
Bluetooth on the market:Bluetooth on the market:
PC cards, Cell phones, Head sets, Chip sets,…

HC-05 Bluetooth Module

HC-05 BLUETOOTH MODULE

HC-05 working
• HC-05 embedded Bluetooth serial communication module has two
work modes:
• order-response work mode and automatic connection work mode.
• there are three work roles (Master, Slave and Loopback) at the
automatic connection work mode.
• When the module is at the automatic connection work mode, it will
follow the default way set lastly to transmit the data automatically.

• When the module is at the order-response work mode, user can send
the AT command to the module to set the control parameters and
sent control order.
• The work mode of module can be switched by controlling the module
PIN (PIO11) input level.

Bluetooth Part-17

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Bluetooth Part-17

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