bluetooth vs. 802.11: state-of-the-art and research challenges · bluetooth vs. 802.11: market...
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10/29/2001 Pravin Bhagwat 1
Bluetooth Vs. 802.11: state-of-the-art and research challenges
Pravin BhagwatReefEdge, Inc.
pravin@reefedge.com or pravin@acm.orghttp://www.cs.umd.edu/~pravin
WINLAB, RutgersOct 28, 2001
10/29/2001 Pravin Bhagwat 2
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 ?
10/29/2001 Pravin Bhagwat 3
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 ?
10/29/2001 Pravin Bhagwat 4
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
10/29/2001 Pravin Bhagwat 5
802.11 Specifications
MAC
MIB
Cont
rol
DSSS FH IR OFDMPHY
WEP
LLC
MAC Mgmt
Specification of layers below LLCAssociated management/control interfaces
Applications
10/29/2001 Pravin Bhagwat 6
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
10/29/2001 Pravin Bhagwat 7
Comparison Axes
Business
Application
Network
Link
Radio
Spectrum
10/29/2001 Pravin Bhagwat 8
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
10/29/2001 Pravin Bhagwat 9
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
10/29/2001 Pravin Bhagwat 10
Spectrum War: Status today
Enterprise 802.11Network
Wireless Carrier Public 802.11
10/29/2001 Pravin Bhagwat 11
Spectrum War: Next phase of evolution
Enterprise 802.11Network
Wireless Carrier Public 802.11
Market consolidationEntry of Wireless CarriersEntry of new playersFootprint growth
10/29/2001 Pravin Bhagwat 12
Spectrum War: Eventual Steady State
Enterprise 802.11Network
Wireless Carrier Public 802.11
Virtual Carrier
Emergence of virtual carriersRoaming agreements
10/29/2001 Pravin Bhagwat 13
Comparison Axes
Business
Application
Network
Link
Radio
Spectrum
10/29/2001 Pravin Bhagwat 14
Design considerations
• high bandwidth• conserve battery power• cost < $10
Data signal x(t)
power
spectrum
Noise, interference
Recovereddata signal
cost
Goal
10/29/2001 Pravin Bhagwat 15
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
10/29/2001 Pravin Bhagwat 16
Bluetooth Radio
Low CostSingle chip radio (minimize external components)Today’s technologyTime division duplex
Low PowerStandby modes Sniff, Hold, ParkLow voltage RF
10/29/2001 Pravin Bhagwat 17
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
10/29/2001 Pravin Bhagwat 18
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
10/29/2001 Pravin Bhagwat 19
Transmit power & receiver sensitivity
Tx power0 dBm
Rx power @ 10 cm-20
Rx power @ 10m-70
C/I = 21 dB-91 Noise floor
10/29/2001 Pravin Bhagwat 20
Comparison Axes
Business
Application
Network
Link
Radio
Spectrum
10/29/2001 Pravin Bhagwat 21
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
10/29/2001 Pravin Bhagwat 22
Scatternet
Cell phone Cordlessheadset
Cordlessheadset
Cell phone
Cordlessheadset
Cell phone
mouse
10/29/2001 Pravin Bhagwat 23
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
10/29/2001 Pravin Bhagwat 24
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
10/29/2001 Pravin Bhagwat 25
Bluetooth MAC LayerFH/TDD
m
s1
s2
625 λsec
f1 f2 f3 f4 f5 f6
1600 hops/sec
10/29/2001 Pravin Bhagwat 26
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
10/29/2001 Pravin Bhagwat 27
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
10/29/2001 Pravin Bhagwat 28
Comparison Axes
Business
Application
Network
Link
Radio
Spectrum
10/29/2001 Pravin Bhagwat 29
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
10/29/2001 Pravin Bhagwat 30
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
10/29/2001 Pravin Bhagwat 31
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
10/29/2001 Pravin Bhagwat 32
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
10/29/2001 Pravin Bhagwat 33
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
10/29/2001 Pravin Bhagwat 34
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
10/29/2001 Pravin Bhagwat 35
Comparison Axes
Spectrum
Radio
Link
Network
Business
Application
10/29/2001 Pravin Bhagwat 36
Synchronization and Push
More bits over the airUtilization of unused capacity during non-busy periodsHigher barrier for switching service providers
10/29/2001 Pravin Bhagwat 37
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
10/29/2001 Pravin Bhagwat 38
Voice Call Handoff
Cordless base
Threat or
opportunity?
More attractive calling plansAlleviate system load during peak periodsServe more users with fewer resources
10/29/2001 Pravin Bhagwat 39
Bluetooth Value chain
Conspicuously
missingWirelessCarriers
Stackproviders
SoftwarevendorsIntegrators
Radio
Silicon
10/29/2001 Pravin Bhagwat 40
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
10/29/2001 Pravin Bhagwat 41
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
10/29/2001 Pravin Bhagwat 42
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
10/29/2001 Pravin Bhagwat 43
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
10/29/2001 Pravin Bhagwat 44
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
10/29/2001 Pravin Bhagwat 45
ThankYou
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