Post on 31-Dec-2015
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Wireless# Guide to Wireless Communications 2
Objectives
• Define a high rate wireless personal area network (HR WPAN)
• List the different HR WPAN standards and their applications
• Explain how WiMedia and UWB work
• Outline the issues facing WPAN technologies
• Describe the security features of each HR WPAN technology
Wireless# Guide to Wireless Communications 3
High Rate WPAN Standards
• IEEE is currently working on two standards– IEEE 802.15.3 and 802.15.5
• IEEE 802.15.3 standard– Defines the specifications for HR WPANs supporting
speeds of 11, 22, 33, and up to 55 Mbps• In the 2.4 GHz ISM band
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802.15.3 High Rate WPANs
• IEEE standard defines the MAC and PHY layers
• WiMedia Alliance– Formed to support the development of any necessary
higher-layer protocols• And software specifications for 802.15.3
• Potential applications– Connecting digital cameras to printers and kiosks– Connecting laptops to multimedia projectors and
sound systems
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802.15.3 High Rate WPANs (continued)
• Application characteristics– Require high throughput– Transceiver should be low-power– Cost should be low– Require quality-of-service (QOS) capabilities– Connections should be simple and automatic– Devices should be able to connect to multiple other
devices– Security features should be included
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WiMedia Protocol Stack
• WiMedia group defined two different architectures– For the upper layers of the protocol stack– One is used for multimedia audio/visual applications
and the other for data transfer applications
• The lower two layers of the stack (MAC and PHY)– Are implemented in hardware
• 802.15.3 PHY layer– Converts data bits into a modulated RF signal– 802.15.3 standard uses the ISM 2.4 GHz band
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WiMedia Protocol Stack (continued)
• 802.15.3 PHY layer (continued)– Supports two different channel plans
• A coexistence channel plan• A high-density channel plan
– Channels are limited to 15 MHz bandwidth– IEEE 802.15.3 standard specifies five data rates
• 11 Mbps, 22 Mbps, 33 Mbps, 44 Mbps, and 55 Mbps– Trellis code modulation (TCM)
• Encodes the digital signal so single bit errors can be detected and corrected
– Also called error correction (FEC)
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WiMedia Protocol Stack (continued)
• Modulation– See Table 6-2 for modulation techniques– Enhancements
• Passive scanning• Dynamic channel selection• Ability to request channel quality information• Link quality and received signal strength indication• Transmit power control• An 802.11 coexistence channel plan• Lower transmit power• Neighbor piconet capability
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802.15.3 Network Topology
• Piconet coordinator (PNC)– Role assumed by the first device in the area– Provides all of the basic communications timing in a
piconet– PNC sends a beacon
• The piconet is peer-to-peer– Devices can transmit data directly to each other
• The PNC is also responsible for managing QoS
• Devices can form a dependent piconet
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802.15.3 Network Topology (continued)
• Types of dependent piconets– Child piconets
• Useful for extending the coverage of a piconet
– Neighbor piconets• Allow coexistence with other piconets in the same area
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Additional MAC Layer Functionality
• The IEEE 802.15.3 MAC layer functionality– Connection time (association) is fast– Devices associated with the piconet can use a short,
one-octet device ID– Devices can obtain information about the capabilities
of other devices– Peer-to-peer (ad hoc) networking– Data transport with QoS– Security– Efficient data transfer using superframes
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Additional MAC Layer Functionality (continued)
• IEEE 802.15.3 superframe structure– A beacon– An optional contention access period (CAP)– The channel time allocation period (CTAP)
• Communication in an 802.15.3 piconet– Beacon frame sent by the PNC includes a variable
indicating the end of the CAP– Devices can send asynchronous data in the CAP– Devices can request channel time on a regular basis
• Requested channel time is called isochronous time
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Additional MAC Layer Functionality (continued)
• Communication in an 802.15.3 piconet– Devices can also request channel time for
asynchronous communications in the CTAP• Communications use a time division multiple access
(TDMA) scheme
• Power management– 802.15.3 devices can turn off completely for long
periods of time• Without losing their association with the piconet
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Additional MAC Layer Functionality (continued)
• Power management (continued)– 802.15.3 power-saving methods
• Device synchronized power save (DSPS) mode
• Piconet synchronized power save (PSPS) mode
• Asynchronous power save (APS) mode
– Wake superframe• Superframe designated by the PNC
• Devices that are in power save mode wake up and listen for frames addressed to them
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Additional MAC Layer Functionality (continued)
• Power management (continued)– Additional power-saving methods
• PNC can set a maximum transmit power level
• Devices request a reduction or an increase in their own transmit power
• General MAC frame format– All MAC frames include a set of fields that are present
in the same order in every frame
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Mesh Networking (802.15.5)
• Mesh networking– Each device connects to all other devices within range– Effectively creating multiple paths for transmission– Enable WiMedia networks to span an entire building
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Ultra Wide Band (UWB)
• Allows new transmission techniques based on UWB to coexist with other RF systems– With minimal or no interference
• Characteristics– It transmits low-power, short-range signals– It transmits using extremely short low-power pulses
lasting only about 1 nanosecond– It transmits over a band that is at least 500 MHz wide– UWB can send data at speeds of up to 2 Gbps
Wireless# Guide to Wireless Communications 28
How UWB Works
• UWB PHY– Digital signals need to be spread over a wide band
• Using techniques such as FHSS or DSSS
– UWB uses short analog pulses for signaling• Does not rely on traditional modulation methods
• This technique is called impulse modulation
– Biphase modulation• Most common modulation technique used by UWB
• Uses a half-cycle positive analog pulse to represent a 1
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How UWB Works (continued)
• UWB PHY (continued)– Direct-sequence UWB (DS-UWB)
• When transmitting pulses that are a nanosecond long
– Signal spreads over a very wide frequency band
• In the UWB case, the signal spreads over a band that is at least 500 MHz wide
– Orthogonal frequency division multiplexing (OFDM)• Commonly referred to as MB-OFDM
• Frequency band is divided into five groups containing a total of 14 frequency bands
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How UWB Works (continued)
• UWB PHY (continued)– Orthogonal frequency division multiplexing (OFDM)
(continued)• Each frequency band is 528 MHz wide
– Further divided into 128 frequency channels
• Channels are orthogonal
– They do not interfere with each another
• Data bits are sent simultaneously (in parallel)
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IEEE 802.15.3a
• Proposed enhancement to 802.15.3
• Uses UWB technology to support higher data rates– For multimedia and imaging applications
• Protocol Adaptation Layer (PAL)– Enables wireless FireWire at 400 Mbps– Based on an 802.15.3a/WiMedia platform
• Wireless USB (WUSB) version 2– Based on the WiMedia specifications– Transmits at 480 Mbps at a distance of up to 2 meters
Wireless# Guide to Wireless Communications 35
WPAN Challenges
• Challenges– Competition Among WPAN Standards– HR WPAN Security– Cost of WPAN Components– Industry Support for WPAN Technologies– Protocol Functionality Limitations– Spectrum Conflict
Wireless# Guide to Wireless Communications 36
Competition Among WPAN Standards
• IEEE 802.15.3 and .3a are positioned to compete with Bluetooth for market share– It will take a few years before 802.15.3 products begin
to appear on the market
• Wireless USB and wireless 1394 (FireWire) have the potential to quickly outpace Bluetooth
Wireless# Guide to Wireless Communications 37
HR WPAN Security
• Bluetooth security– Bluejacking
• Exploits a Bluetooth device’s ability to discover nearby devices and send unsolicited messages
– Bluesnarfing• Accesses contact lists and other information without the
user’s knowledge
– Denial-of-service (DoS) attacks• Flood a Bluetooth device with so many frames that it is
unable to communicate
Wireless# Guide to Wireless Communications 38
HR WPAN Security (continued)
• Security for IEEE 802.15.3 HR WPANs– Based on the Advanced Encryption Standard (AES)– Defines how any two devices can establish a secure
communications session• To protect both the information and the integrity of
communications at the MAC and PHY layers
– 802.15.3 also supports message integrity verification at the MAC layer
• Prevents a man-in-the-middle attack
Wireless# Guide to Wireless Communications 39
Cost of WPAN Components
• Bluetooth currently supports more devices than other WPAN technologies– Industry experts believe that price must be reduced to
reach competitive advantage
• Does not make economic sense to use a chip that costs $15 to replace a cable that costs $7
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Industry Support for WPAN Technologies
• IrDA has had strong industry support for many years
• Bluetooth’s support in the networking industry has been, at best, spotty
• Industry experts predict that new technologies will be more quickly embraced by manufacturers– Such as 802.15.3 and ZigBee
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Protocol Functionality Limitations
• Bluetooth protocol suffers from its lack of hand-off capability between piconets
• Hand-off– Ability to move from one master or PNC to another
• Without getting disconnected from the network
• In infrared, roaming is a limitation but not a concern – Since this technology is designed for peer-to-peer
communications
Wireless# Guide to Wireless Communications 42
Spectrum Conflict
• Spectrum conflict– Potential for technologies using the same frequency
bands to interfere with each other
• Applying UWB technology may significantly reduce or eliminate this issue
• UWB can interfere with 802.11a networks
• ZigBee and WiMedia products should be able to coexist with 802.11b/g without any serious problems
Wireless# Guide to Wireless Communications 43
Summary
• IEEE 802.15.3-2003 is a WPAN technology – Optimized for multimedia voice and video signals
• The WiMedia protocol stack has two upper layers– One for audio/video and one for data transfer
applications
• The PHY layer supports two different channel plans– Works in the same ISM band as 802.11b WLANs
• 802.15.3 supports peer-to-peer or ad hoc networks
• 802.15.3 piconets support child and neighbor piconets
Wireless# Guide to Wireless Communications 44
Summary (continued)
• Efficient data transmission is accomplished by use of the superframe concept
• In 802.15.3, devices can be in one of several power-saving modes
• 802.15.5 mesh networking standard extends the capabilities of 802.15.3 networks
• Ultra Wide Band is a digital transmission technology – Will soon support very high-speed transmissions at up
to 100+ Mbps
• UWB transmissions: bandwidth of at least 500 MHz
Wireless# Guide to Wireless Communications 45
Summary (continued)
• UWB transmits using very short pulses
• Challenges for WPANs include speed, security, cost, industry support, interference, and protocol limitations
• WPAN devices that are designed to be small and consume very little power have limited processing capabilities and storage