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 NoAnother wireless LAN
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
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.
Applications 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
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
2. Technical Overview
a. Design considerations Noise, interference power spectrum Recovered data signal Data signal x(t) cost Goal: • high bandwidth • conserve battery power • cost < $10
EM Spectrum ISM band ISM band 902 – 928 MHz 2.4 – 2.4835 GHz 5.725 – 5.785 GHz VHF UHF SHF EHF LF MF HF 300MHz 30MHz 30GHz 300GHz 3GHz 3MHz 30kHz 300kHz 100mm 10cm 10m 1cm 1m 100m 10km 1km FM radio S/W radio TV TV AM radio cellular ISM band X rays Gamma rays visible UV infrared 1 MHz 1 GHz 1 kHz 1 THz 1 EHz 1 PHz
Unlicensed Radio Spectrum 12cm 5cm 33cm 26 Mhz 83.5 Mhz 125 Mhz 902 Mhz 2.4 Ghz 5.725 Ghz 2.4835 Ghz 5.785 Ghz 928 Mhz 802.11a HyperLan 802.11 Cell. 802.15 Bluetooth, Microwave oven cordless phones, baby monitors, Wireless LANs
b. Bluetooth radio link 1MHz . . . 79 1 2 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
3. Review of basic concepts
Radio propagation: path loss r3.3 r2 near field path loss in 2.4 Ghz band Pr r 8m r > 8m Pt far field near field r Pr path loss=10 log (4r2/)r 8m = 58.3 + 10 log (r3.3 /8)r > 8m
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)
Bandwidth of digital data Fourier transform Frequency domain Time domain Signal amplitude f MHz 0.5 MHz 1 MHz 1.5 MHz baseband signal (1 Mb/s) • 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
Channel coding and modulation demodulation modulation channel decoding channel coding baseband signal baseband signal Challenges • Modulation of 1MHzbaseband signal into 2.4GHz band is difficult to achieve in one step.
Radio architecture: typical design Intermediate Frequency Intermediate Frequency mixing mixing modulation demodulation channel coding channel decoding baseband signal baseband signal
Power consumption Transmit Receive Receive Transmit Radio Radio • Single chip radio (minimize external components • Time division duplex Baseband Baseband Vcc = 3 V Vcc = 3 V 802.15 Bluetooth 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.
Bluetooth Radio • Low Power • Standby modes: Sniff, Hold, Park. • Low voltage RF • Low Cost • Single chip radio (minimize external components) • Today’s technology • Time division duplex
b) a) c) a. Wireless Positioning a)Cellular radio systems with squares representing stationary BS; b)Bluetooth systems; c)Ad hoc systems.
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 Wireless Positioning
4. Bluetooth Architecture, Piconets and Scatternets • 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. Sb S M P S P S M=Master; S=Slave; P=Parked; Sb=Standby
m s m s s • Piconet • Each Piconet has max capacity = 1 Mbps s a. Bluetooth Physical link • Point-to-point link • master - slave relationship Fast frequency hopping 1600 hops/sec • 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 algorithmwhich can calculate a frequency hop sequencefrom a Bluetooth device address and a Bluetooth clock.
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. Communication in a Scatternet Master node Slave node Bridge node
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)
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.
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 2500MHz 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.
c. Piconet channels FH/TDD f5 f1 f4 f3 f2 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.
d. Multiple Access Scheme Single-slave communication 259 Multiple-slave communication
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.
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 GFSKwith 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.
FHSS FHSS is an ideal for a WLAN in a noisy frequency band ! 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
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.
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. • Mschedules the traffic in both the uplink and downlink. • The M control prevents collisions between the channels. • Slotted ALOHA is applied: information is transmitted withoutlisten-before-talk. If the information is received incorrectly, it is retransmitted at the next transmission (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/Sswitch 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 Ssending its FHS packet to the M; M takes on a CLKoffset 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.
How to schedule presence in two piconets? Forwarding delay ? Missed traffic? Scatternet scenario 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 Ssending its FHS packet to the M; M takes on a CLKoffset to match the S’s CLK, while the S switches to using its own CLK.
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.
SCO ACL SCO ACL ACL SCO M S1 S2 S3 Mixing of synchronous SCO links and asynchronous ACL links on a single piconet channel.
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.
7. Data Packet Types DM1 DH1 DM3 DH3 DM5 DH5 Symmetric Asymmetric 2/3 FEC Asymmetric Symmetric No FEC DM-Data Medium, with Forward Error Control DH-Data High, no Forward Error Control
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-mentbit 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
Identifies the master and slaves within radio range of two masters can tell which traffic is for them. Packet Format For a single time slot the data field is 240 bits. 54 bits 72 bits 0 - 2744 bits Access code Header Payload Containing typical MAC sublayer fields Voice Data header CRC No CRC No retries ARQ FEC (optional) FEC Forward error coding (optional) 625 µs master slave
a. Access Code Types • Channel Access Code (CAC) • Device Access Code (DAC) • Inquiry Access Code (IAC) 72 bits Access code Payload Header Purpose • Synchronization • DC offset compensation • Identification • Signaling X
b. Packet Header m Max 7 active slaves s s s 54 bits Access code Payload Header Purpose • Addressing (3) • Packet type (4) • Flow control (1) • 1-bit ARQ (1) • Sequencing (1) • HEC(8) 16 packet types (some unused) Broadcast packets are not ACKed For filtering retransmitted packets Verify header integrity (Header Error Control) total 18 bits Encode with 1/3 FEC (Forward Error Correction) to get 54 bits
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
8. Voice Packets (HV1, HV2, HV3) 3.75ms (HV3) 2.5ms (HV2) 1.25ms (HV1) HV-High Voice 240 bits 54 bits 72 bits = 366 bits Access code Header 30 bytes Payload HV1 + 1/3 FEC 10 bytes 20 bytes HV2 + 2/3 FEC HV3 30 bytes
Multi slot packets FH/TDD f1 f5 f4 f6 m s1 s2 625 µsec Data rate depends on type of packet
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) f(k+3) f(k+4) f(k+5) TX RX TX RX f(k) f(k+5) TX RX The frequency and timing characteristicsof:single-slot, three-slot and five-slot packets
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 define16 different payload types (4 control Packets and 12 type of codes),