bt baseband tricoli
TRANSCRIPT
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BluetoothBluetooth
Radio and baseband layers
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Table of contentsTable of contentsz Historyz General description
z Communication topology
z Protocol stack
z Radio layer
z Baseband layer: – BB - Physical channels and links
– BB - Logical channels and links
– BB - Packets – BB - Bitstream processing
– BB - Link controller
z References
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HistoryHistoryz 910(?)-987(?): Harald Blåtand
z 1994: Ericsson Mobile Communications initiated a
study to investigate the feasibility of a low-power low-cost radio interface between mobile phones and their accessories
z Feb. 1998: Bluetooth Special Interest Group (SIG) wasfounded by Ericsson, IBM, Intel, Nokia and Toshiba, todevelop an open specification for short-range wireless
connectivityz May 1998: BT publicly anounced
z July 1999: BT specification v 1.0
z Nov. 2003: BT specification v 1.2 (core)
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General descriptionGeneral descriptionz Bluetooth: “BT wireless technology is a short-range communications
system intended to replace the cable(s) connecting portable and/or fixedelectronic devices. Key features are robustness, low power and low cost. ”
– Core system: RF transceiver, baseband and protocol stack
z Overview of operation:
– Unlicensed ISM band at 2.4GHz
– FHSSs (Freq. Hopping Synchro. Sequences): to combat fadingand interferenceÆ AFH (Adaptive FH): improves BT co-existence withstatic ISM systems (e.g. 802.11)
– GFSK modulation: to minimize transceiver complexity
– Gross bit rate: 1Mb/s
– Piconet: devices synchronized to a common clock and FH pattern (amaster and more slaves)
– Scatternet: formed interconnecting multiple piconets (bridge nodes)
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General description continueGeneral description continue…………
– Physical channel sub-divided into time slotsÆfull
duplex transm. with TDD (Time Division Duplex)scheme
– Data transmitted in packets
– Hierarchy of channels and links (from physical channelupwards): physical channel, physical link, logical transport,logical link and L2CAP channel
– LMP (Link Manager Protocol): control protocol for the
baseband and physical layer
– Default ACL (Asynchronous Connection-oriented) and broadcast logical transport used to transport the LMP protocol signalling
– L2CAP layer for channel-based abstraction toapplications and services: segmentation and reassembly of application data and multiplexing and de-multiplexing of multiple
channels over a shared logical link
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Communication topologyCommunication topology
z
Piconet topologyz Operational procedures and modes:
– Inquiry (Discovering) procedure
– Paging (Connecting) procedure
– Connected mode
– Hold mode
– Sniff mode
– Parked mode
– Role switch procedure
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ProtocolProtocol stackstackProtocols classifications
z Application group
z Middleware protocols
z Transport protocols
– Bluetooth Core Protocols
– Cable Replacement Protocols
– Telephony Control Protocols
– Adopted Protocols
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Radio layer Radio layer
z Frequency bands and channel arrangement: – 2.400-2483.5GHz, f=2402 MHz+k, k=0,…,78
– Lower (2MHz) and upper (3.5MHz) guard bands
z Transmitter:
– Power classes:
(optional power control capability with LMP commands)
z Class 1: long range (~100m) devices, Poutmax=20dBm (100mW)
z Class 2: ordinary range (~10m) devices, Poutmax=4dBm (2.5mW)
z Class 3: short range (~10cm) devices, Poutmax=0dBm (1mW)
– GFSK modulation:
z BT=0.5, 0.28 < m < 0.35
z 1Æ positive freq. deviation, 0Ænegative freq. deviation: f min>=115kHz
– More: spurious emissions, RF tolerance
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Radio layer continueRadio layer continue……
z Receiver: – Sensitivity level:
z Reference: -70dBm
z Actual: “input level for which a raw BER of 0.1% is met”
z Receiver : -70dBm or better with any BT transmitter
– More: interference performance, out-of-band blocking,intermodulation characteristics, etc.
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BasebandBaseband layer layer z Piconets and scatternets:
– Up to 7 active slaves per piconet
– Up to 255 parked (synchronized) slaves per
piconet – Each piconet in a scatternet with its own
hopping sequence
a: point-to-point connection
b: point-to-multipoint conn.
c: scatternet
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BasebandBaseband layer continuelayer continue……
zPackets:
z Clock: – Native (CLKN), master (CLK), estimated (CLKE):
different appearances of the same clock – May be implemented with a counter
General packet format
BT clock
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BasebandBaseband layer continuelayer continue……
zDevice addressing:
– Unique 48-bit BD_ADDR from IEEE RegistrationAuthority
– 64 reserved LAP for general and dedicated inquiryoperations
z Access codes:(derived from LAP of device or inquiry address and usedalso for timing synchronization and offset compensation)
– DAC (Device AC): page, page scan and page response (pageddevice’s BD_ADDR)
– CAC (Channel AC): connection (master’s BD_ADDR)
– IAC (Inquiry AC): inquiry (GIAC (General IAC) and DIAC(Dedicated IAC))
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BBBB -- Physical channels and linksPhysical channels and links
z Ch types: inquiry scan (for discovering), page scan (for connecting) and basic piconet and adapted piconet (for communication)
z Each ch characterized by a combination of a pseudo-random
FHS (more for each type), the spec. slot timing of transmissions,
the access code and packet header encoding
z Hop-ratemax: 1600hops/s (connection) or 3200hops/s (page, inquiry)
z Each ch divided into time-slots, each slot (group) corresponds toa reception/transmission and an RF frequency (selected by hop
selection kernel)
z Each device in a piconet is time-synchronized and hop-synchronized to the ch
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BBBB – – Physical channels and links continuePhysical channels and links continue……
z Basic piconet:
– Default in connection
– Defined by the master : HS, unique for each piconet, determined by the
BD_ADDR (UAP and LAP) of the master; phase in the hopping determined
by master’s clock
– Traffic controlled by the master (device that initiates a
connection by paging) by a polling scheme
– Piconet clocks
– Master clock used for all timing and scheduling activities
– Offsets must be regularly updated
– Time slots:
z Length: 625µs
z Number: k from CLK 27-1
of master
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BBBB – – Physical channels and links continuePhysical channels and links continue……
– Master starts transmission always at even
numbered slots, slaves always at odd slots
– Packet start aligned with slot start
– Packet extended over up to 5 slots
– RF hop frequency fixed for the duration of a
packet – FH-TDD
Single- and multi-slot
packets
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BBBB – – Physical channels and links continuePhysical channels and links continue……
zHop selection: – 6 types of HS:
z Page HS: 32/79 freq., period length=32
z Page response HS: in one-to-one correspondenceto current page HS
z
Inquiry HS:32/79 freq., period length=32
z Inquiry response HS: in one-to-onecorrespondence to current inquiry HS
z
Basic ch HS: 79/79 freq. in a short time interval,very long period length
zAdapted ch HS: idem, may use fewer than 79/79
freq.
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BBBB – – Physical channels and links continuePhysical channels and links continue……
– General selection scheme:
z Selecting a sequence: page scan, inquiry scan,
page, inquiry, master page response, slave page
response, inquiry response, basic ch, adapted ch(Æsame ch mechanism)
zMapping this sequence onto the hop
frequencies
pseudo-random
sequence mapped to RF
ch freq.
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BBBB – – Physical channels and links continuePhysical channels and links continue……
z Hop selection scheme in connection state:
– 32 hop frequencies spanning about 64 MHz visited in a pseudo-random order
– Next, a different 32-hop segment is chosen, etc.
z In page/inquiry, page/inquiry scan or page/inquiryresponse substates, the same 32-hop segment is used all
the time (the segment is selected by the address)
BB Ph i l h l d li k ti
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– Basic hop selection kernel:
z X determines the phase in the 32-hop segment
z Y1 and Y2 selects between master-to-slave andslave-to-master transmission
z A to D determine the ordering within the segment
z E and F determine the mapping onto the hopfrequencies
BBBB – – Physical channels and links continuePhysical channels and links continue……
BBBB Ph i l h l d li k tiPh i l h l d li k ti
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BBBB – – Physical channels and links continuePhysical channels and links continue……
z Physical links: baseband connections between
devices (one associated to one phy ch)
– Common properties that apply to all logical
transports on a phy link:z Power control
z Link supervision: LS timer (Tsupervision) on master and slave,
supervisionTO
z Encryption
z Channel quality-driven data rate change
z Multi-slot packet control
BBBB Logical transports and linksLogical transports and links
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BBBB – – Logical transports and linksLogical transports and linksz Five LT types: SCO (Synchronous Connection-Oriented), eSCO (extended SCO),
ACL (Async. CO), ASB (Active Slave Broadcast), PSB (Parked SB)
– SCO:z Point-to-point LTs
z Up to 3 LTs for master, up to 3 for slave from the same master or 2 from different masters
z Voice or general sync. data
z SCO packets sent regularly at Tsco (counted in slots) interval in reserved M-to-S slots(circuit-switched connection)
z Never retransmitted
– eSCO:
z Like SCO with possible retransmission window after reserved slots
– ACL:z Point-to-point LTs
z Packet-switched connection between master and active slaves (also already engaged in async. LT)
z One ACL LT per slave
z Retransmission for assuring data integrity (for most ACL packets)
– ASB, PSB:z Point-to-multi-point LTs
z More addresses: PM_ADDR (Parked Member, 8bits), AR_ADDR (Access Request,assigned to parked slaves, not unique)
BBBB –– Logical transports and links continueLogical transports and links continue
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BBBB Logical transports and links continueLogical transports and links continue……
z TX/RX routines (informative only):
z Separately for each async. and sync. link
z In the master an async. buffer and one or
more sync. buffers for each slave
z Each buffer 2 FIFO: current and next regs
(current r. accessed and read by Link Controller to compose packets and next r.
by BB Resource Manager to load new info
z Switches controlled by Link Controller
(flush command)
z Separately for ACL LT and sync. LTs
z Single async.buffer shared among all slaves,
one or more sync. buffers for each slave
z Each buffer 2 FIFO: one r. accessed and loaded
by Link Controller with the last RX payload
and the other r. by BB Resource Manager to
read the previous payload
z TYPE field in the header permits the packet de-
comp. to auto. direct the traffic to the proper
buffers
BBBB –– Logical transports and links continueLogical transports and links continue……
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BBBB Logical transports and links continueLogical transports and links continue……
– Flow control: RX ACL buffer can be full while a new payloadarrivesÆFLOW field in the header to control the tx of new data (STOP,GO)
z Destination control
z Source control
z LT_ADDR: – Assigned by the master
– 3 bits for primary LT_ADDR, in packet header
– Only for active slaves – 000 for broadcast messages
– Secondary LT_ADDR for eSCO
– Valid for as long as a slave is in active modez Five LL types: LC (Link Control), ACL-C (Control), ACL-U
(User), SCO-S (Synchronous), eSCO-S (Sync.)
BBBB P k tP k t
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BBBB -- PacketsPackets
z General packet format: – Little Endian format: b0 is the LSB and the first bit sent over air
z Access code format:
– Shortened AC if no header follows (used in paging, inquiry and park) – For synchronization, DC offset compensation and identification
– Access code identifies all packets exchanged on a phy channel
– AC types: already seen
– Preamble for DC compen.
– Sync. word: derived from 24-bit LAP
– Trailer, with the 3 MSBsof sync. word, for DC compen.
BBBB – – Packets continuePackets continue……
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z Header format:
– LT_ADDR: indicates source or destination slave
– Type
– Flow: for flow control over the
ACL LT (Flow=0ÆSTOP transm.
indication, =1ÆGO)
– ARQN: ACK or NAK of a transfer
of payload data with CRC
– SEQN: to order the data packet stream(inverted for each new packet)
– HEC: to check header integrity;
in negative case the packet is discarded
– 1/3 FEC (18Æ54 bits)
Link ControlBBBB – – Packets continuePackets continue……
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z Packet types:
– ID: DAC or IAC, 68 bits, veryrobust
– NULL: CAC+header, 126 bits,
used to return link informationto the source (ARQN or FLOW),
does not have to be
acknowledged – POLL: very similar to NULL
but requires a confirmation,
used by the master to poll the
slaves, which must respond
– FHS: used for frequency hop sync
ACL
SCO, eSCO
FHS payload format
BBBB – – Packets continuePackets continue……
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– SCO packets:
z
HV: do not include a CRC, never retransmittedz DV: CRC on data section (which is retransm.), voice and data treated
separately
z Typically used for 64kb/s speech
z Payload format: body
– eSCO packets:z CRC and retransmission
z Used for 64kb/s speech as well as data at 64kb/s and other rates
z Payload format: body+CRC
– ACL packets:
z For user or control data
z
Payload format: body+header+possibly CRC
payload header for single slot ACL
payload header for multi-slot ACL
DV packet format
BB Bitstream processing
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BB - Bitstream processing
z Header bit processes:
z Payload bit processes:
z Error checking:
– Checking for errors or wrong delivery using channelaccess code, HEC and CRC in the payload
BBBB – – BitstreamBitstream processing continueprocessing continue……
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– HEC generation:
– CRC generation:
BBBB – – BitstreamBitstream processing continueprocessing continue……
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z Data whitening:
– Scrambling with a data whitening word to randomize the datafrom highly redundant patterns and to minimize DC bias in
the packet
– Whitening word generator:
– Initialization with CLK 6-1 of the master and MSB=1
(for FHS packet during inquiry or page response use of X
input and 2 MSBs of value 1)
– Header and payload XORed with the WW
– InitializationÆheader whiteningÆ payload whitening (no re-
initialization)
BBBB – – BitstreamBitstream processing continueprocessing continue……
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z Error correction:
– 3 schemes:z 1/3 rate FEC
z 2/3 rate FEC
z ARQ scheme for the data
– To reduce the number of retransmissions – In a error-free environment FEC unnecessarily reduces the throughput
rateÆ packet types without FEC
– Always 1/3FEC for packet header: contains valuable link information and is
designed to resist more bit errors
– 1/3FEC:
– 2/3FEC:
z (15,10) shortened Hamming code
z Initial value=0
z Can correct all single errors and detect
all double errors
z Tail bits (zeros) after the CRC to bring the total number to a multiple of 10(the encoder works with segments of 10 bits)
BBBB – – BitstreamBitstream processing continueprocessing continue……
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z ARQ scheme:
– Automatic repeat request scheme
– DM, DH, the data field of DV and EV are transmitted until
acknowledgement of a successful reception is returned by the
destination (or timeout is exceeded) – Acknow. information in the header of the return packet
– ARQ scheme used only for payload and on packets with
CRC
– Fast, unnumbered acknow. scheme:
z ACK (ARQN=1) or NAK (ARQN=0)
z Slave response: in the next s-to-m slot
z Master response: at the next event addressing the same slave
z For a successful reception at least the HEC must pass (also the CRC
if present)
BBBB – – BitstreamBitstream processing continueprocessing continue……
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z Receive protocol:
– ARQN in FHS not
meaningful and not
checked
– Broadcast packets checked on errors using CRC, but not ARQscheme
Retransmitted
data payload?
ACL
BBBB – – BitstreamBitstream processing continueprocessing continue……
z Retransmit filtering:
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Retransmit filtering:
– Data payload is transmitted until positive acknow. is received or timeout is exceeded
– Causes of retransmission :
• Packet transm. failure
• Acknowledgement, in return packet, failure (less probable because the header is more heavily coded):
the destination keep receiving the same payloadover and over againÆSEQN alternated for every new CRC data
payload (not for retransmission)
– SEQN set to 1 at start of new connection
– For ACL and SCO:(just DM, DH, DV
and EV affect SEQN)
– For eSCO: SEQN
toggled every time
and initial value=0
– For FHS: SEQN not
meaningful and not
checked
– For packet without CRC:
SEQN not modified
BBBB – – BitstreamBitstream processing continueprocessing continue……
Fl hi l d
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zFlushing payload:
– For ACL:• Variable delay in the traffic caused byretransm.
• Limited amount of delay allowed for certaincomm. linksÆisochronous traffic (abort of the retransmit scheme, flush of the old dataand link controller forced to take the next
data) – For eSCO: automatic at the end of eSCO
window
zA master carries out the ARQ protocolindepentently on each LT of a piconet
BB – Link controller
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BB – Link controller z
Overview of states:(how a piconet/scatternet is estabilished and how devices can be added or
released from it)
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ReferencesReferences
z Bluetooth Specification V1.2