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Future Personal Area NetworksZigBee and UWB ?

Low

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ZigBee

BlueTooth

802.11b 802.11a

802.11g

UWB

Low Data Rate High Data Rate

GSM GPRS/2½G UMTS/3G

Text Graphics Internet Audio VideoMulti-channel

Video

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ZigBee

•Low data rate, low power consumption, low cost wireless networking

•Target Applications :

–Home Automation

»security, remote control of domestic appliances, heating/ventilation/air conditioning (HVAC), lighting, curtains etc.

–Consumer Electronics

»TV, VCR, DVD, CD, toys, games etc.

–PC peripherals

»mouse, keyboard, joystick, gamepad etc.

–Personal healthcare

»monitors, diagnostics, sensors etc.

–Industrial & Commercial

»monitors, sensors, automation, control etc.

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•ZigBee Alliance :

–promoted by Philips, Mitsubishi, Motorola, Invensys

–many others also developing the technology and products

•Physical & MAC protocol layers just now standardised as IEEE 802.15.4

–Alliance members still developing upper protocol layers, profiles etc.

•Characteristics :

–data rates :»250kbps in 2.4GHz ISM band

»20kbps in 868MHz band (Europe)

»40kbps in 915MHz band (USA)

–low power consumption»battery life of 6months to 2 years on 2 AA batteries – 0.1% duty cycle

–low cost : $2 - $3 expected»claimed to be significantly lower than other technologies and standards

–range : 10m to 30m nominally, perhaps up to 75m»depending on power output required for a given application

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–star topology

»one full function master and up to 254 reduced function clients full function device (FFD) network coordinator capable, talks to any other device

reduced function device (RFD) limited to star topology, only talks to master

»virtual peer-to-peer defined

–clustered stars

»master communicates with other masters, each with their own clients

»up to 100 co-located networks

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–network coordinator/master

»transmits network beacons

»sets up a network

»manages network nodes

»stores network node information

»receives constantly

–network client

»generally battery powered

»searches for available networks

»transfers data from its application as necessary

»determines whether data is pending

»requests data from the network coordinator

»can sleep for extended periods

–8-bit micro-controller adequate for both master and client

»full protocol stack <32Kb, reduced function stack <4Kb

»coordinator may require extra RAM for node database, transaction table etc.

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–operating frequency bands

»868MHz/915MHz channel 0 :

channels 1-10 :

Binary Phase Shift Keying (BPSK) modulation

»2.4GHz channels 11-26 :

Quadrature Phase Shift Keying (O-QPSK)

868.3MHz

902MHz 928MHz

2MHz

2.4GHz 2.4835GHz

5MHz

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–CSMA-CA channel access

–fully handshaked protocol for transfer reliability - ACK/NAK return packets

–optional guaranteed time slots

–typical intended traffic types :

»periodic data application definded rate e.g. sensors

»intermittent data application/external stimulus defined rate e.g. light switch

»repetitive low latency data allocated time slots e.g. mouse

–devices can hibernate until an external event triggers an interrupt

–security

»data integrity and authentication using IEEE defined protocols

–all devices have unique 64 bit IEEE addresses

–addressing modes:

»network + device identifier (star)

»source/destination identifier (peer-to-peer)

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•Protocol architecture :

Application

Application Interface

Network Layer

Data Link Layer

MAC Layer

MAC Layer

Physical Layer

Cu

stom

er

IEE

E

Zig

Be

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Silicon ZigBee Stack Application

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–Physical frame structure :

–MAC frame structure :

»data frame

»beacon frame network information

frame structure

notification of pending node messages

»acknowledgment frame

»command frame status, network association, device synchronisation, beacon management etc.

synch.preamble

start of packetdelimiter

PSDUlength

Physical Service Data Unit (PSDU)

32 bits 8 bits 8 bits 0-127 octets

MAC header MAC Service Data Unit (MSDU) MAC footer

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–optional superframe structure :

Network beacon transmitted by network master

Contention period : access by any node using CSMA-CA

Reserved for nodes requiring guaranteed bandwidth

slot 1 slot 2 slot 23

15ms

Space reserved for beacon growth due to pending node messages

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Master Slave

Permit connectionBeacon

Connect

Connect

ACK

ACK

Connect confirm

New device Connect confirm

Tx

Rx

– Master/Slave network connection :

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MasterDestn.node

RTS

Query

Sourcenode

ACKRTS reply

Query response

CTS

Data

ACK

– Mediation device operation for peer-to-peer connection:

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•Comparison with Bluetooth

–ultra low power consumption

–255 devices per network instead of 7 per piconet

–data rate 250kbps instead of 1Mbps

–aimed at industrial control applications and home automation, not audio

»not expected to be incorporated in cellphones and headsets

–probably cheaper than Bluetooth

»protocol stack implementation ~32kb instead of 256kb

–Bluetooth better for audio, graphics, FTP, ad hoc networks

–ZigBee better for static networks, lots of devices, small data packets and infrequent use

–typical timing values :

»new slave connection : 30ms (ZigBee) versus >3s (Bluetooth)

»changing from sleeping to active : 15ms versus 3s

»active slave access time : 15ms versus 2ms

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Ultra Wide Band (UWB)

•Recent headlines :

–“UWB Communications may be in your future”

–“Ultrawideband renews high-speed wireless hopes”

–“Ultrawideband radio set to redefine wireless signalling”

–“Ultrawideband wants to rule wireless networking”

–“A Technology to Consider : Ultrawideband”

–“Ultra Wideband Technology – The Wave of the Future?”

–“Ultra-Wideband : Multimedia Unplugged”

–“Ultrawideband : an electronic free lunch?”

–but also sadly :

»“UWB in Limbo”

»“MBOA Falls Short Again” Multiband OFDM Alliance – set up to define UWB standards

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•What is UWB?

–transmissions consist of very narrow individual square wave pulses

»widths typically range from 100psec to 1.5nsec

–emitted at precisely timed nanosecond intervals

–Fourier Analysis applied against time duration of the pulse width

»shows that the bandwidth occupied is proportional to narrowness of pulse

»a 200psec pulse occupies more than 5GHz around a 2GHz centre frequency

–transmitted energy is divided across the wide range of frequencies

»at any individual frequency, energy measured is at extremely low levels

–hence pulses are within the noise floor of the electromagnetic environment

–to extract a UWB transmission, the receiver must correlate the RF signal with an expected waveform

»i.e. it must know exactly when the pulse may be expected

–each individual bit spread over several pulses

»received signal at expected pulse times then integrated to raise the signal above the noise level

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–a variety of methods possible to modulate information onto the pulse stream

»e.g. relative to a fixed repetition rate, an early pulse = 0, a late pulse = 1

»varying amplitude or pulse width also

»arguments still in progress as to best method

•Properties

–original Marconi spark gap transmitters were ultra-wideband

–so-called Baseband radio since there is no carrier frequency to be modulated

»though the pulse repetition rate is the equivalent

–reinvented in the military in the 1960s for Radar and secure transmissions

–becoming prominent again now because of technology developments

»only the latest CMOS processes are fast enough to handle the narrow pulses and controlled high repetition rates required

at 0.25 micron and smaller feature sizes

»only CMOS promises the low fabrication costs required for mass market applications

»should always be cheaper than carrier-based technologies no such circuitry required

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–just four essential components:

»the UWB transmit/receive chip

»the antenna

»a digital baseband processor to handle packetising, error correction etc,

»embedded firmware and protocols that drive the processor

–signal below the noise level

»should not interfere with other transmissions above the noise floor in theory!

–inherently longer range than carrier-modulated systems

»only pulse detection required

»maintaining integrity of modulation not involved

–almost impossible to intercept

»need to know the exact timing of the transmitted pulses

»this would be made private for security e.g. a pseudo-random sequence with secure key

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–multi-path fading can almost be eliminated

»caused by reflections from adjacent surfaces e.g. nearby buildings

»UWB pulses so narrow that any reflected pulse will be out of the expected receive-time window and therefore ignored

–not line-of-sight

»signals propagate through walls and other obstacles

»UWB has been used for ground-penetrating radar

–also used for through-the-wall imaging

»pulses received at a time indicating that they have been reflected from a nearby wall can be ignored

»pulses reflections received later will be from objects beyond the wall the inverse of removing multi-path signals

–UWB chipsets have already reached 40Mbps at ranges of 60m

»using 50 to 70 milliwatts of power

»(802.11 sends at 11/54Mbps using 100 milliwatts over 30m)

»PulseLink Inc. have demonstrated 400Mbps

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•Applications:

–wireless audio, video and data over LANs for home and office

»cable replacement - the Bluetooth and ZigBee market?

»802.11 also?

–geo-position location to centimetre accuracy

»a by-product of sending and receiving data between multiple UWB devices

»and precise timing of pulse arrivals

–car and home security radars

–also possible to use UWB over cable

»to coexist with cable frequency bands

»up to 1.2Gigabit downstream and 120MBps upstream transmission rates demonstrated by Pulse-Link

»HDTV, interactive services etc.

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•Regulation and Licensing issues

–UWB sidesteps the need for allocation of dedicated frequency bands

»may avoid any upcoming crunch in allocations

–should be able to co-exist with other radio transmissions

–other users still concerned however

»e.g. hospital equipment might be affected

»GPS transmissions may be affected

–too many co-existing UWB transmissions will eventually raise the noise floor

»and degrade effectiveness of 802.11, Bluetooth etc.

–Federal Communications Commission (FCC) in USA allowed experimental UWB transmissions to start in 2000

»according to FCC, UWB is any signal occupying at least 500MHz, and in the frequency band from 3.1GHz to 10.6GHz

»strict limits on radiated power

»formal rule changes permit UWB from Feb. 2002

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•IEEE standardisation effort

–rival groups competing for a 802.15.3a standard to be established

»MBOA : Intel, Philips, Mitsubishi, Texas Instruments, General Atomics et al.

»versus Motorola, XtremeSpectrum Inc., Partus-Cerva et al.

–consensus is that a multi-band system of some sort would be best

»i.e. several separate GHz-wide bands

»neither quite a simple as the baseband system first envisaged going back to carrier-based systems and using OFDM and frequency-hopping

–suggested that transmission bands should be above 3.1GHz

»to avoid GPS interference

–as of September 2003, no agreement has been reached

»the 75% majority needed not achieved

–European regulators still holding fire