Bt Baseband Tricoli

7/29/2019 Bt Baseband Tricoli

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BluetoothBluetooth

Radio and baseband layers



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



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)



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)



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



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



ProtocolProtocol stackstackProtocols classifications

z Application group

z Middleware protocols

z Transport protocols

– Bluetooth Core Protocols

– Cable Replacement Protocols

– Telephony Control Protocols

– Adopted Protocols



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



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.



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



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



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))



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



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




– 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




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.




– 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.




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



– 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 Ph i l h l d li k tiPh i l h l d li k ti




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



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



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……



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



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……



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……



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……



– 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



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……



– HEC generation:

– CRC generation:




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)




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)




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)




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


z Retransmit filtering:



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


Fl hi l d



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



BB – Link controller z

Overview of states:(how a piconet/scatternet is estabilished and how devices can be added or

released from it)



ReferencesReferences

z Bluetooth Specification V1.2

Bt Baseband Tricoli

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