bluetooth vs. 802.11: state-of-the-art and research challenges · bluetooth vs. 802.11: market...

10/29/2001 Pravin Bhagwat 1

Bluetooth Vs. 802.11: state-of-the-art and research challenges

Pravin BhagwatReefEdge, Inc.

[email protected] or [email protected]://www.cs.umd.edu/~pravin

WINLAB, RutgersOct 28, 2001

mailto:[email protected]

mailto:[email protected]


Emerging Landscape

Licensed spectrumVoice continues to be the main revenue generator application Data services are trying to find a foothold

Unlicensed spectrumEnterprise environmentsIndustry verticalsPublic spacesPersonal area wireless networks

voicedataPotentialfor wirelesscarrier entry

Who will be the winner – 802.11 or Bluetooth ?


Short Range Wireless: Emerging Landscape

Bluetooth802.11

Cordlessheadset

LAN AP

802.11b for PDAsBluetooth for LAN access

New developments areblurring the distinction

Designed for wiredEthernet replacement

Designed for cablereplacement

Which option is technically superior ?What market forces are at play ?What can be said about the future ?


Bluetooth Specifications

Data

RFCOMMIP

Single chip with RS-232,USB, or PC card interface

HCI

ProfilesApplications

SDP

L2CAPAudio

Link Manager

RFBaseband

A hardware/software/protocol descriptionAn application framework


802.11 Specifications

MAC

MIB

Cont

rol

DSSS FH IR OFDMPHY

WEP

LLC

MAC Mgmt

Specification of layers below LLCAssociated management/control interfaces

Applications


Bluetooth Vs. 802.11

Audio Link Manager

L2CAPData

RFCOMMIP

HCI

ProfilesApplications

SDP

RFBaseband

Bluetooth is a (top down) market driven consortiumBusiness interests take precedence over other considerationsDesigned primarily for voice; data an afterthought

802.11 is a (bottom up) open standard effortDesigned primarily for data; voice an afterthoughtGood piece of engineering except for WEP

MIB

DSSS FH IR OFDMPHY

WEP MAC MgmtMAC


Comparison Axes

Business

Application

Network

Link

Radio

Spectrum


Unlicensed Radio Spectrum

12cm 5cmλ26 Mhz

33cm

83.5 Mhz 125 Mhz

902 Mhz

928 Mhz

2.4 Ghz

2.4835 Ghz5.725 Ghz

5.850 Ghz

802.11a802.11bBluetoothMicrowave oven

cordless phonesbaby monitorsWireless LANs

Spectrum is free, but the right of way is not free


CMU’s spectrum sharing policy

“Computing Services will approach the shared use of the 2.4 GHz radio frequency in the same way that it manages the shared use of the wired network. While we will not actively monitor use of the airspace for potential interfering devices, we will seek out the user of a specific device if we find that it is actually causing interference and disrupting the campus network. In these cases, Computing Services reserves the right to restrict the use of all 2.4 GHz radio devices in university-owned buildings and all outdoor spaces on the Carnegie Mellon Campus”.

http://www.cmu.edu/computing/wireless/airspace.html


Spectrum War: Status today

Enterprise 802.11Network

Wireless Carrier Public 802.11


Spectrum War: Next phase of evolution



Market consolidationEntry of Wireless CarriersEntry of new playersFootprint growth


Spectrum War: Eventual Steady State



Virtual Carrier

Emergence of virtual carriersRoaming agreements


Comparison Axes

Business

Application

Network

Link

Radio

Spectrum


Design considerations

• high bandwidth• conserve battery power• cost < $10

Data signal x(t)

power

spectrum

Noise, interference

Recovereddata signal

cost

Goal


Radio: cost, power, range tradeoff

α dn dtransmit power

α 1dn_

α 1d2_

battery life

access points (N)

Tradeoff between battery life & the cost of the overall system

battery life N 0.5 n α

for n = 4 4x 2x


Bluetooth Radio

Low CostSingle chip radio (minimize external components)Today’s technologyTime division duplex

Low PowerStandby modes Sniff, Hold, ParkLow voltage RF


Radio architecture: 802.11b

channel coding

mixingD/A

basebandsignal

modulation

IF

CMOS

Typically SiGe or GaAs

demodulation

channel decoding

mixingA/D

basebandsignal

IF

oscillators, PAfilters

Analog oscillators, LNAfilters

DSP


Radio architecture: Bluetooth

demodulation

channel decoding

mixingA/D

baseband signal

IF

channel coding

mixingD/A

basebandsignal

modulation

IF

CMOS

Analog CMOS oscillators,LNA, filters

DSP


Transmit power & receiver sensitivity

Tx power0 dBm

Rx power @ 10 cm-20

Rx power @ 10m-70

C/I = 21 dB-91 Noise floor


Comparison Axes

Business

Application

Network

Link

Radio

Spectrum


Bluetooth Physical link

Point to point linkmaster - slave relationshipradios can function as masters or slaves m s

ss

m

s

PiconetMaster can connect to 7 slavesEach piconet has max capacity (1 Mbps)hopping pattern is determined by the master


Scatternet

Cell phone Cordlessheadset

Cordlessheadset

Cell phone

Cordlessheadset

Cell phone

mouse


802.11 ArchitectureBasic Service Set (BSS): a set of stations which communicate

with one another

Infrastructure Basic Service Set (BSS)

• AP provides • connection to wired network• relay function

• stations not allowed to communicate directly

Independent Basic Service Set (IBSS)

• only direct communication possible

• no relay function


Extended Service SetESS: a set of BSSs interconnected by a distribution system (DS)

• ESS and all of its stations appear to be a single MAC layer• AP communicate among themselves to forward traffic • Station mobility within an ESS is invisible to the higher layers


Bluetooth MAC LayerFH/TDD

m

s1

s2

625 λsec

f1 f2 f3 f4 f5 f6

1600 hops/sec


Physical Link Types

Synchronous Connection Oriented (SCO) Link slot reservation at fixed intervals

Asynchronous Connection-less (ACL) LinkPolling access method

SCO SCO SCOSCO SCO SCOACL ACL ACLACL ACL ACL

m

s1

s2


802.11 - MAC layer

Prioritiesdefined through different inter frame spacesno guaranteed, hard prioritiesSIFS (Short Inter Frame Spacing)

highest priority, for ACK, CTS, polling responsePIFS (PCF IFS)

medium priority, for time-bounded service using PCFDIFS (DCF, Distributed Coordination Function IFS)

lowest priority, for asynchronous data service

t

medium busy

DIFS DIFS

SIFSPIFS

contention next frame

direct access if medium is free ≥ DIFS


Comparison Axes

Business

Application

Network

Link

Radio

Spectrum


The Connectivity Problem

The same problem is beingFaced by all market segmentsand many solutions have been tried

• PoE• L2TP, PPTP• GSM – smart card auth.• EAP + 802.1x• Mobile IP• AAA• IPSEC• MS passport – Web sign on

WLANBluetoooth

3GCable/DSL

Internet


Basic network access issuesAccountingAccess ControlAuthentication

Anonymity Confidentiality Audit trails

User concerns

No red tape No queues No fraud

ScalabilityEfficiencyLow cost

Equipment vendor’s concerns

Prevent masquerading,modification, and unauthorized access

Protect identity theft Accurate usage monitoring

Service Provider’sconcerns


Connection establishment & Security

GoalsAuthenticated access

Only accept connections from trusted devices

Privacy of communicationprevent eavesdropping

ConstraintsProcessing and memory limitations

$10 headsets, joysticksCannot rely on PKISimple user experience

LMP_host_conn_req

LMP Accepted

Security procedure

Paging

Master

Slave

LMP_setup_complete

LMP_setup_complete


Authentication

Authentication is based on link key (128 bit shared secret between two devices)How can link keys be distributed securely ?

Verifier

Claimant

challenge

response

accepted

Link keyLink key


Pairing (key distribution)

Pairing is a process of establishing a trusted secret channel between two devices (construction of initialization key Kinit)Kinit is then used to distribute unit keys or combination keys

Random number

Kinit

PIN + Claimant address

Randomnumber

Verifier Claimant

Kinit

challenge

response

accepted

PIN + Claimantaddress

Randomnumber


Wired Equivalent Privacy (WEP)

Design ObjectivesConfidentiality

Prevent others from eavesdropping trafficData Integrity

Prevent others from modifying traffic Access Control

Prevent unauthorized network access

Unfortunately, WEP fails on all three counts


Comparison Axes

Spectrum

Radio

Link

Network

Business

Application


Synchronization and Push

More bits over the airUtilization of unused capacity during non-busy periodsHigher barrier for switching service providers


Cell phone as an IP gateway

More bits over the airEnhanced user experience

Palmpilot has a better UI than a cell phoneGrowth into other vertical markets


Voice Call Handoff

Cordless base

Threat or

opportunity?

More attractive calling plansAlleviate system load during peak periodsServe more users with fewer resources


Bluetooth Value chain

Conspicuously

missingWirelessCarriers

Stackproviders

SoftwarevendorsIntegrators

Radio

Silicon


Biggest challenges facing Bluetooth

InteroperabilityAlways a challenge for any new technology

Hyped up expectationsOut of the box ease of use Cost target $5Critical massRF in silicon


802.11 current status

MAC

MIB

DSSS FH IRPHY

WEP

LLC

MAC Mgmt

802.11b5,11 Mbps

802.11g20+ Mbps

802.11a6,9,12,18,24

36,48,54 Mbps

OFDM

802.11isecurity

802.11fInter Access Point Protocol

802.11eQoS enhancements


Bluetooth Vs. 802.11: MAC issues

Possible, but not yet defined

PossiblePaging

YesNot sureFuture safe?

Stable at high loadsLimitedScalability

Not possiblePossiblePower Control

YesYesPower Management

RTS/CTSNot an issueHidden nodes

ARQARQRobustness to interference

CSMAGood for data, but difficult for voice

TDDGood for voice, but difficult for data

Access Method

802.11Bluetooth


Bluetooth Vs. 802.11: Market issues

TCP/IPStill looking for a killer app.Applications

802.11 is a more mature technology

The biggest problem of Bluetooth at present

Interoperability

Will reduce in the futureLower due to low power transmitter and tight integration

Power consumption

Multi chip solutionSmaller due to single chip integration

Form factor

It is unlikely that 802.11 will penetrate the cosumer electronic device market in the near future

Potentially huge if every consumer electronic device is Bluetooth enabled

Market size

Technology advances and market growth can reduce cost, even if tight single integration is not achieved in the near term

Potential for low cost implementation exists but the market size will eventually determine the price point

Cost

802.11Bluetooth


Concluding remarksFuture of Bluetooth

Bluetooth is ideal for cable replacementInitial applications of Bluetooth will exploit its point-to-point or point-to-multipoint connectivity featureAttempts to turn it into a LAN technology will face very tough competition from 802.11Multi-hop over Bluetooth is a challenging research problemHigher chance of success in Europe and Asia

802.11Will continue to grow in

Public spaces, home, industry vertical, and enterprise market802.11 will provide a viable alternative to 3G in public places


ThankYou

bluetooth vs. 802.11: state-of-the-art and research challenges · bluetooth vs. 802.11: market...

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