Module 2: Wireless Personal Area Networks

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Module 2: Wireless Personal Area Networks

Kaustubh S. PhanseDepartment of Computer Science and Electrical Engineering

Luleå University of Technology

SMD161 Wireless Mobile Networks

SMD161 Wireless Mobile Networks 2

Lecture objectivesDefine wireless personal area networks (WPAN)

Study various WPAN radio technologiesDesign goalsCharacteristicsTrade-offsServices/applications

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ReferencesH. Schiller, Mobile Communications, 2nd ed., Addison-Wesley, 2004

J. Haartsen, ”The Bluetooth Radio System,” IEEE Personal Communications, pp. 28-36, February 2000.

E. Callaway, et al., ”Home Networking with IEEE 802.15.4: A Developing Standard for Low-Rate Wireless Personal Area Networks,” IEEE Communications Magazine, pp. 70-77, August 2002.

T. Cooklev, Wirless Communication Standards: A Study Of IEEE 802.11, 802.15, And 802.16, IEEE Press.


Wireless personal area network (WPAN)

Network between devices carried or worn by or near a personWireless communication within a personal operating space (POS): defined as a radius of 10m around a person

IEEE 802.15 WPAN Working GroupInitiated as a study group from within the IEEE 802.11 WLAN working group (March 1998)Formally established in March 1999

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WPAN

Range

Data

rate

(Mbp

s)

Personal area Local area Metropolitan area Wide area

0.1

1

10

100

1000

UWBUWB

BluetoothBluetooth

ZigBeeZigBeeRange

Data

rate

(Mbp

s)

Personal area Local area Metropolitan area Wide area

0.1

1

10

100

1000

UWBUWB

BluetoothBluetooth

ZigBeeZigBee

UWBUWB

BluetoothBluetooth

ZigBeeZigBee

TechnologiesIEEE 802.15.1 medium-rate (MR-WPAN) Bluetooth

IEEE 802.15.4 low-rate (LR-WPAN) ZigBee

IEEE 802.15.3/ 802.15.3a high-rate (HR-WPAN)WiMedia


Bluetooth: history

Special interest group (SIG)Founders: Ericsson, Intel, IBM, Nokia and Toshiba

GoalsDevelop a single-chip, low-cost, low-power, radio-based technology for cable replacementEmbed in existing portable devices and inspire new devices and applicationsEnable ad-hoc networking of devices without operator intervention and without explicit human intervention

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Bluetooth: envisioned usage models

Cordless computer

Ultimate headset


Bluetooth: historyName origin: “Blåtand”

Harald Gormsen, King of DenmarkWas named “Blåtand” because of his dark complexion (and not because he had a blue tooth!)

1999 (Lund, Sweden)10th century (Jelling, Denmark)

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Bluetooth: characteristicsRadio spectrum

Unlicensed 2.4 GHz ISM frequency band, 79 channels (2400-2483.5 MHz in most countries), 1 MHz carrier spacing

Radio layerGaussian frequency shift keying (G-FSK) modulationTransmit power (1-100mW); typical range: 10-100 m without obstacles

Multiple accessInterference immunity throughspreadingFrequency hopping (FH-CDMA)Uncoordinated pseudo-random hopping sequence (1,600 hops/s)Time division duplexing (TDD)


Bluetooth: characteristicsCapacity

1 Mbps per channelTheoretical capacity of 79 Mbps cannot be reached due to non-orthogonal hopping sequences

Link typesSynchronous connection-oriented link (SCO)Asynchronous connectionless link (ACL)

Topology and medium access controlMaster-slave architecture

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Bluetooth: piconetCollection of bluetooth devices synchronized to the same frequency-hopping sequence

A device that establishes the piconet and determines the hopping sequence becomes the master (M)Other devices participating in the piconet act as slaves (S) and sychronize to thehopping sequenceNumber of simultaneously active devicesis limited to 8: exactly 1 master and a maximum of 7 slavesEach active device has a 3-bit active member address (AMA)

MS

PSB

S

S

P

P

SB

SBP


Bluetooth: piconet (contd.)

Master implements a centralized controlControls the medium access via polling

Any two or more Bluetooth devices can form a piconetA device acts as a master and sends its clock and device IDHopping sequence determined by device ID (48 bit, unique worldwide)Phase determined by the master’s clock

SBSB

SB

SB

SB

SB

SB

SB

SB

MS

PSB

S

S

P

P

SB

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Bluetooth: hop selectionThe first block determines the ”ordering” of the 32-hop subsequence (output is 5 bits, i.e., decimal 0-31)

The second block determines the ”mapping” onto the 79-hop carrier list


Bluetooth: hop selectionPseudo-random frequency hopping sequence

Determined by the master’s clock and identityCycle repeats after about 23 hours

32 hop consecutive sequence covers about 64 MHz spectrumFrequencing spreading over a short time interval

On average, all frequencies are visited with equal probability

Changing the clock and/or identity changes the clock sequence instantaneously

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Bluetooth: power management modesStand-by (SB) or idle

Devices not connected in a piconetExtremely low duty cycle (less than one percent): scan for 10 ms every 1.28-3.84 seconds

Parked (P)Devices are part of a piconet, but not activeDevices periodically scan the channel to resychronize the clocksAssigned an 8-bit parked member address (PMA)

Hold (H)Similar to parked mode, but devices keep AMAOften used to interconnect different piconets

Sniff (Sn)Used only by slave devices for power conservationDevice is active, but listens to channel at a reduced rate


Bluetooth: scatternetInterconnection of multiple piconets

Feasible due to slotted nature of medium accessEvery piconet defined by the frequency hopping sequence of the masterAt any instant of time, a device can communicate only in one piconetDevice can jump from one piconet to another by adjusting parameters (master identity and clock)

M

S

P

SB

S

S

P

P

SB

M

S

S

P

SB

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Bluetooth: scatternetDevice participation in a scatternet

Device can be a slave in different piconetsDevice can switch roles when jumping between piconets: slave in a piconet and master in another piconetBy definition, a device cannot act as a master in different piconets


Bluetooth: operational states

standby

inquiry page

connectedAMA

transmitAMA

parkPMA

holdAMA

sniffAMA

unconnected

connecting

active

low power

detach

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Bluetooth: packet based communicationAll packets have same format

Only one packet can be transmitted in a slot

Access codePseudo-random and derived from the piconet masterRecepient accepts a packet only if the access code matches that of the master -- prevents ”cross-piconet” packet transmission

Packet header18 information bits + FEC coding

access code packet header payload68(72) 54 0-2745 bits

AM address type flow ARQN SEQN HEC3 4 1 1 1 8 bits

preamble sync. (trailer)

4 64 (4)


Bluetooth: packet based communicationTypes of packets

4 control packets12 types of synchronous and asynchronous data packets, further divided into three segmentsSegment 1: Packets that fit into a single slotSegment 2: Packets that require 3 slots for transmissionSegment 3: Packets that require 5 slots for transmission

Packet transmissionMulti-slot packets are sent using the same carrierAfter the packet has been sent, the hop carrier specified by themaster’s hopping sequence is used

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Bluetooth: packet based communication

S

fk

625 µs

fk+1 fk+2 fk+3 fk+4

fk+3 fk+4fk

fk

fk+5

fk+5

fk+1 fk+6

fk+6

fk+6

MM M M

M

M M

M M

t

t

t

S S

S S

S

Single-slot packets

Three-slot packet

Five-slot packet


Bluetooth: physical linksSynchronous connection-oriented link (SCO)

Circuit-switched, point-to-point, 64 kbps duplex, optional forward error correction (FEC)For voice (maximum of 3 simultaneous connections)Master reserves periodic slotsSingle-slot packets

Asynchronous connectionless link (ACL)Packet-switched, point-to-multipoint (including broadcast), upto 433.9 kbps symmetric or 723.2/57.6 kbps asymmetricSlots remaining after SCO reservation are usedVariable packet size (1-, 3-, 5-slot packets)

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Bluetooth: physical links

MASTER

SLAVE 1

SLAVE 2

f6f0

f1 f7

f12

f13 f19

f18

SCO SCO SCO SCOACL

f5 f21

f4 f20

ACLACLf8

f9

f17

f14

ACL


Bluetooth: error recoveryRetransmission

ACL only, fast-ARQ (with 1-bit sequencing number)

Forward Error CorrectionSCO and ACL

MASTER

SLAVE 1

SLAVE 2

A C C HF

G G

B D E

NAK ACK

Error in payload(not header!)

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Bluetooth: security

E3

E2

link key (128 bit)

encryption key (128 bit)

payload key

Keystream generator

Data DataCipher data

Authentication key generation(possibly permanent storage)

Encryption key generation(temporary storage)

PIN (1-16 byte)User input (initialization)

Pairing

Authentication

Encryption

Ciphering

E3

E2

link key (128 bit)

encryption key (128 bit)

payload key

Keystream generator

PIN (1-16 byte)


Bluetooth: protocol stack

Radio

Baseband

Link Manager

Control

HostControllerInterface

Logical Link Control and Adaptation Protocol (L2CAP)Audio

TCS BIN SDP

OBEX

vCal/vCard

IP

NW apps.

TCP/UDP

BNEP

RFCOMM (serial line interface)

AT modemcommands

telephony apps.audio apps. mgmnt. apps.

AT: attention sequenceOBEX: object exchangeTCS BIN: telephony control protocol specification – binaryBNEP: Bluetooth network encapsulation protocol

SDP: service discovery protocolRFCOMM: radio frequency comm.

PPP

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Bluetooth: profilesAssociated with specific applications or usage models

Specify which protocol elements are mandatory in certain applicationsPrevents devices (e.g., headset, mouse) with little memory and processing power and tailored for specific application from implementing entire Bluetooth protocol stackNew profiles can be added to the Bluetooth specification

Basic profilesGeneric access; service discovery; cordless telephony, serial port, headset, dial up networking, fax, file transfer, etc.

Additional profilesAudio distribution; audio/video remote control; hands-free operation


IEEE 802.15.3 (HR-WPAN): backgroundGoal

Provide a WPAN solution with high data rates (up to 55 Mbps)...more than currently supported by BluetoothQuality of service (QoS) enabled multimedia communicationbetween portable consumer devicesLow cost, low complexity solutionSmall form factor (embed into portable devices)

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IEEE 802.15.3: characteristicsRange and data rates

At least 10 meters (up to 70 meters possible)11, 22, 33, 44, 55 Mbps; 802.15.3a: 100-400 Mbps

Dynamic topologyBased on the “piconet” conceptAd-hoc peer-to-peer connectivityShort time to connect (<1s)

Quality of service (QoS) for multimedia applicationsTDMA for streams with time based allocations

Multiple power management modesDesigned to support low power portable devices


IEEE 802.15.3: characteristicsSecure network

Support for authenticationKey distribution and managementShared key encryption and integrity

Ease of useDynamic coordinator selection and handover

Designed for a relatively benign multipath environmentPersonal or home space

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IEEE 802.15.3: usage modelsAudio/Video distribution

Home theater, interactive gaming, camcorder to TV, PC to LCD projector or other HD displays

High speed data transferPersonal storage, digital imaging: camera to PC/kiosk, scanner to PC or printer

Piconet

Piconet Coordinator (PNC)

Piconet

Piconet Coordinator (PNC)


IEEE 802.15.3: reference model

802.15.3 Medium Access Control (MAC)

802.15.3 PHY11, 22, 33, 44, 55 Mbit/s

802.15.3a PHYUltra-Wideband (UWB)

IEEE 802.2 Logical Link Control

(LLC)

TCP/IP

802.2 FCSL (mandatory)

IEEE 1394 FCSL (optional)

USB FCSL (optional)

Wireless FireWire

Wireless USB

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IEEE 802.15.3: piconetPiconet: a set of devices in the POS (~10m range) and controlledby a piconet controller or coordinator (PNC)

PNC provides basic timing reference for the piconetPNC manages the QoS for the piconetMaximum of 256 devices in a piconetPiconet Identifier (PiconetID) used for identifying the piconetsPeer-to-peer data communication

Parent Piconet ControllerPiconet DeviceChild/Neighbor Piconet ControllerPiconet RelationshipPeer to Peer Data TransmissionIndependent Piconet Controller


IEEE 802.15.3: piconetIf there are no free channels, a device may create a dependent piconet

Dependent piconetIf two piconets operate in the same channel, one is parent piconet and other is dependent piconetDependent piconets are autonomous and have distinct PiconetIDsThey use a dedicated time slot from the parent PNC called Channel Time Assignment (CTA) to share the time between piconets

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IEEE 802.15.3: piconetChild piconet

PNC belongs as a device in the parent piconetExtends the coverage area of the piconet

Neighbor piconetDoes not extend the coverage area


IEEE 802.15.3: piconet controller/coordinator (PNC)

PNC periodically sends beacon frames containing necessary information for piconet operations

Supplies timing with the beaconManages QoS, power save modes, and access controlAssigns time slots to each device and distributes payload protection keysAll devices are not required to be able to act as PNC

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IEEE 802.15.3: piconet creationDevice must make sure that there are no existing piconets using the same channel

Passive scanning is used to detect existing piconetsDevice goes through all the channels supported by the physical layerDevice listens the beacon frames from PNCs

A device creating a piconet becomes PNCSelects the channelStarts to transmit beacon frames


IEEE 802.15.3: joining a piconetPiconets are discovered using passive scanning

To join a piconetDevice authenticates with PNCDevice exchanges capability information with PNC (PHY data rates supported, power management status, buffer space, capability to act as PNC etc.)Device sends association request to join the piconet

PNC sends association response

After joining to the piconet, the device information is broadcasted with the beacon

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IEEE 802.15.3: PNC handoverChanging PNC during the operation

When active PNC leaves the network or runs out of battery, another device may take over PNC responsibilitiesNew device joining the piconet is more capable, then the currentPNC has the option to hand over PNC role to the devicePNC selects the best device among those that have the “PNC Capable” bit set

PNC handover maintains all existing time allocations so that there is no interruption in the delivery of data in the piconet


IEEE 802.15.3: superframe structure

BeaconTransmits control information to the entire piconet, allocates resources (GTS) per stream ID for the current superframe and provides time synchronization

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IEEE 802.15.3: superframe structureOptional Contention Access Period (CAP) (CSMA/CA):

Used for authentication/association request/response, stream parameters negotiation, … (command frames)PNC can replace the CAP with MTS slots using slotted Aloha access

Contention Free Period made of:Unidirectional Guaranteed Time Slots (GTS) assigned by the PNC for isochronous or asynchronous data streamsOptional Management Time Slots (MTS) in lieu of the CAP for command frames


IEEE 802.15.3: quality of service (QoS)IEEE 802.15.3 supports both synchronous and asynchronous data

CAP offers only best-effort

The PNC will allocate resources in the CFP through admission control

After performing admission control, GTSs may be allocatedSynchronous data: Based on number of time slots per superframe, duration of slot, priority and GTS typeAsynchronous data: Based on total data and priority

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IEEE 802.15.3: physical layer5 selectable data rates

11, 22, 33, 44, 55 Mb/sModulation formats: BPSK, QPSK (no coding), 16, 32, 64-QAM (8-state Trellis code)

15 MHz channel bandwidth

3 or 4 non-overlapping channels3 channel mode aligns with 802.11b for coexistence

Transmit Power: approximately 8 dBm


IEEE 802.15.3: physical layerCoexistence

Causes less interference as compared to 802.11: since it occupies a smaller bandwidth and transmits at lower power levelsProvides for dynamic channel selectionPer link dynamic power controlDetects and monitors for active channels and moves

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IEEE 802.15.3a: physical layer802.15.3 has created a Study Group to investigate the creation of an alternate PHY to address very high data rate applications

Uses ultra-wideband (UWB)Goal of very high-rate (VHR) WPAN (> 110Mbps @ 10 m, > 400 Mbps @ 5 m)

Applications Wireless video projection, image transfer, high-speed cable replacement (e.g., wireless USB)


IEEE 802.15.3a: ultra-wideband (UWB)UWB is a form of extremely wide spread spectrum where RF energy is spread over gigahertz of spectrum

Wider than any narrowband system by orders of magnitudeUWB signals can be designed to look like imperceptible random noise to conventional radios

Pulse width Inter-pulse spacing: uniform or variable

Narrowband (30kHz)

Wideband CDMA (5 MHz)

UWB (Several GHz)

Frequency

Part 15 Limit

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IEEE 802.15.3a: ultra-wideband (UWB)FCC limits ensure that UWB emission levels are exceedingly small

At or below spurious emission limits for all radiosAt or below unintentional emitter limitsLowest limits ever applied by FCC to any system

Total emissions over several gigahertz of bandwidth are a small fraction of a milliwatt


IEEE 802.15.3a: advantagesSimultaneously low power, low cost high data-rate wireless communications

Attractive for high multipath environments

Excellent range-rate scalabilityEspecially promising for high rates ( >100 Mbps)

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IEEE 802.15.4 (LR-WPAN): backgroundWhy another wireless standard?

Focus of previous wireless standards has been high data throughput, low delay applicationsExisting wireless standards (including Bluetooth!) are complexNeed an enabling technology for applications that do not need orcannot use higher-end wireless technologies

Newer embedded systems applications (home networking, industrial automation, medical, vehicular, ...) require:

Simple wireless connectivity Relaxed throughput and latency requirementsLow costExtremely low power consumption


IEEE 802.15.4: historyIEEE 802.15.4 (LR-WPAN) working group set up in December 2000

Cooperation between ZigBee and IEEE 802.15 standard groups

Goal: provide a wireless standard withUltra-low complexityUltra-low costUltra-low power (battery operation for several months/years)Low data rate (few bits per day to few kilobits per second)

ZigBee specification Set of high-level communication protocols based on the IEEE 802.15.4 LR-WPAN radio

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IEEE 802.15.4: physical layerMultiband, multirate

Two physical layer options across three frequency bands with different transmission rate

2.4 GHz ISM frequency bandTransmission rate: 250 kbpsWorldwide mobility, larger market, lower manufacturing costs

868/915 MHz frequency band868 MHz in Europe and 915 MHz ISM in the United StatesRespectively offer 20 kbps and 40 kbpsAlternative to growing congestion/interference in the 2.4 GHz band, and longer transmission range for a given link budget


IEEE 802.15.4: physical layerChannelization

27 frequency channels across the three frequency bandsDynamic channel selection possible: using receiver energy detection, link quality, channel switching

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IEEE 802.15.4: physical layerPacket format

Preamble (4 bytes) – used for synchronizationStart-of-packet delimiter (1 byte) – end of preamblePHY header (1 byte) – length of PSDUPSDU (up to 127 bytes) – payload


IEEE 802.15.4: physical layerModulation

868 MHz band: BPSK modulation and DSSS (chip rate: 0.3 Mchips/sec)915 MHz band: BPSK modulation and DSSS (chip rate: 0.6 Mchips/sec)2.4 GHz band: 16-ary orthogonal modulation and DSSS (chip rate: 2.0 Mchips/sec)

Sensitivity and rangeRecommended transmit power 1 mW (10-20 m range)

InterferenceUltra-low-duty cylce makes it among the best neighbor in the 2.4 GHz band

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IEEE 802.15.4: data link layer

Data link layer divided into two sublayersLogical link control (LLC) layer standardized by IEEE 802.2IEEE 802.15.4 Medium access control (MAC)


IEEE 802.15.4: data link layerIEEE 802.15.4 MAC layer

Provide services to the LLC via the service-specific convergence sublayer (SSCS)Provide services directly to proprietory LLCInterface between SSCS or LLC and the physical layer using service access points (SAPs)Low complexity and less features (compared to other wireless technologies)

Contention-based medium accessSlotted CSMA/CA for networks with beaconsUnslotted CSMA/CA for networks without beacons

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IEEE 802.15.4: data link layer

Frame controlType of MAC frame (data, acknowledgement, MAC control, beacon) and format of the address field

Sequence numberReliable delivery using acknowledgements


IEEE 802.15.4: data link layerAddress field is flexible (0-20 bytes)

Data frame may contain both source and destination addressesAcknowledgement frame contains no address informationBeacon frame only contains source addressSupport for short 8-bit device address and 64-bit IEEE device address

Payload is variable sizeTotal MAC frame cannot exceed 127 bytesContent depends on the type of frame

Frame check sequence (FCS)CRC

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IEEE 802.15.4: topologiesStar network topology

Single hop communication between PAN coordinator and devicesLow latency, dedicated bandwidth

Peer-to-peer network topologyDevices can communicate over multiple hopsLarge area coverage (wireless sensor networks)

PAN coordinator

Device

Device capable of routing


IEEE 802.15.4: topologiesHybrid topology (star + peer-to-peer)

PAN coordinator Device Device capable of routing

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IEEE 802.15.4: Superframe modeTo accomodate applications with dedicated bandwidth requirements

Superframe structurePAN coordinator transmits superframe beacons in predetermined intervals (15 ms – 245 s)The time between two beacons is divided into 16 equal time slots(independent of the superframe interval)

Guaranteed time slots (GTS)

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Module 2: Wireless Personal Area Networks