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					ELEC 5508 – Wireless Networks
Part 2 – Data services
Zainab Zaidi
Network Systems Group
NICTA

Zainab.Zaidi@nicta.com.au
Consultation Time: Wednesday 4-6 pm
Lab 730 EE
Contents

• IEEE 802.15 Wireless Personal Area Networks (WPANs)
   – Bluetooth IEEE 802.15.1
   – Ultra-wideband (UWB) IEEE 802.15.3a
   – Zigbees IEEE 802.15.4
• Radio Frequency Identification (RFID)
Bluetooth

• Idea
    – Universal radio interface for ad-hoc wireless connectivity
    – Interconnecting computer and peripherals, handheld devices, PDAs, cell
      phones – replacement of IrDA
    – Embedded in other devices, goal: 5€/device (2005: 40€/USB bluetooth)
    – Short range (10 m), low power consumption, license-free 2.45 GHz ISM
    – Voice and data transmission, approx. 1 Mbit/s gross data rate




One of the first modules (Ericsson).
Characteristics

• 2.4 GHz ISM band, 79 RF channels, 1 MHz carrier spacing
   – Channel 0: 2402 MHz … channel 78: 2480 MHz
   – G-FSK modulation, 1-100 mW transmit power
• FHSS and TDD
   – Frequency hopping with 1600 hops/s
   – Hopping sequence in a pseudo random fashion, determined by a master
   – Time division duplex for send/receive separation
• Voice link – SCO (Synchronous Connection Oriented)
   – FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-
     point, circuit switched
• Data link – ACL (Asynchronous ConnectionLess)
   – Asynchronous, fast acknowledge, point-to-multipoint, up to 433.9 kbit/s
     symmetric or 723.2/57.6 kbit/s asymmetric, packet switched
• Topology
   – Overlapping piconets (stars) forming a scatternet
Piconet

• Collection of devices connected in an ad hoc                 P
  fashion                                                                S

• One unit acts as master and the others as          S
  slaves for the lifetime of the piconet                       M             P

• Master determines hopping pattern, slaves         SB
  have to synchronize                                                    S
                                                           P        SB
• Each piconet has a unique hopping pattern

• Participation in a piconet = synchronization to
  hopping sequence
                                                    M=Master       P=Parked
                                                    S=Slave        SB=Standby
• Each piconet has one master and up to 7
  simultaneous slaves (> 200 could be parked)
Forming a piconet
• All devices in a piconet hop together
    – Master gives slaves its clock and device ID
        • Hopping pattern: determined by device ID (48 bit, unique worldwide)
        • Phase in hopping pattern determined by clock
• Addressing
    – Active Member Address (AMA, 3 bit)
    – Parked Member Address (PMA, 8 bit)
                                                                P 
                                                                  S
          SB
             SB                                       S
                                                                M             P
 SB
                    
           SB         SB
                                                                         S
SB               
                                                      SB
                                                              P 
                   SB
        
        SB
                                                                  SB
                SB
 Scatternet
 • Linking of multiple co-located piconets through the sharing of common
   master or slave devices
     – Devices can be slave in one piconet and master of another
 • Communication between piconets
     – Devices jumping back and forth between the piconets         Piconets
                                                                   (each with a
                                                                   capacity of
                           P
                                    S           S                  720 kbit/s)

                S
                                                             P
                                            P
                           M
                                                        M
              SB                        S
M=Master               P       SB                           SB
S=Slave
P=Parked                                            S
SB=Standby
 Bluetooth protocol stack
audio apps.     NW apps.       vCal/vCard          telephony apps.         mgmnt. apps.

                TCP/UDP           OBEX
                                                AT modem
                    IP
                                                commands
                                                               TCS BIN     SDP
              BNEP PPP                                                             Control

                         RFCOMM (serial line interface)

  Audio           Logical Link Control and Adaptation Protocol (L2CAP)                         Host
                                                                                               Controller
                                                                       Link Manager            Interface

                                         Baseband

                                           Radio

AT: attention sequence                                       SDP: service discovery protocol
OBEX: object exchange                                        RFCOMM: radio frequency comm.
TCS BIN: telephony control protocol specification – binary
BNEP: Bluetooth network encapsulation protocol
Frequency selection during data transmission
625 µs

 fk      fk+1   fk+2   fk+3   fk+4   fk+5      fk+6

M        S      M        S    M       S        M
                                                      t

         fk            fk+3   fk+4   fk+5      fk+6

         M               S    M       S        M
                                                      t

 fk                    fk+1                    fk+6

M                       S                      M
                                                      t
 Baseband

 • Piconet/channel definition
 • Low-level packet definition
        – Access code
            • Channel, device access, e.g., derived from master
        – Packet header
            • 1/3-FEC, active member address (broadcast + 7 slaves), link type, alternating bit
              ARQ/SEQ, checksum

                         68(72)          54          0-2745            bits
                    access code packet header          payload



    4         64       (4)         3            4         1        1           1       8      bits
preamble    sync.   (trailer) AM address      type      flow      ARQN        SEQN   HEC
 Baseband data rates
                   Payload User                        Symmetric Asymmetric
                   Header Payload                      max. Rate max. Rate [kbit/s]
ACL       Type     [byte]  [byte]       FEC    CRC     [kbit/s]  Forward     Reverse
          DM1      1         0-17       2/3    yes     108.8         108.8   108.8
 1 slot
          DH1      1         0-27       no     yes     172.8         172.8   172.8
          DM3      2         0-121      2/3    yes     258.1         387.2   54.4
 3 slot
          DH3      2         0-183      no     yes     390.4         585.6   86.4
          DM5      2         0-224      2/3    yes     286.7         477.8   36.3
 5 slot
          DH5      2         0-339      no     yes     433.9         723.2   57.6
          AUX1     1         0-29       no     no      185.6         185.6   185.6
          HV1      na        10         1/3    no      64.0
          HV2      na        20         2/3    no      64.0
SCO
          HV3      na        30         no     no      64.0
          DV       1D        10+(0-9) D 2/3 D yes D    64.0+57.6 D

               Data Medium/High rate, High-quality Voice, Data and Voice
SCO payload types
                                  payload (30)

HV1     audio (10)                               FEC (20)

HV2                  audio (20)                             FEC (10)

HV3                                audio (30)


DV      audio (10)        header (1)    payload (0-9)   2/3 FEC   CRC (2)

                                                                       (bytes)
ACL Payload types
                                         payload (0-343)


         header (1/2)                        payload (0-339)                   CRC (2)


DM1 header (1)          payload (0-17)         2/3 FEC     CRC (2)

DH1 header (1)              payload (0-27)                 CRC (2)               (bytes)


DM3      header (2)           payload (0-121)        2/3 FEC         CRC (2)

DH3      header (2)                 payload (0-183)                  CRC (2)

DM5      header (2)              payload (0-224)               2/3 FEC         CRC (2)

DH5      header (2)                          payload (0-339)                   CRC (2)

AUX1 header (1)             payload (0-29)
   Baseband link types
  • Polling-based TDD packet transmission
      – 625µs slots, master polls slaves
  • SCO (Synchronous Connection Oriented) – Voice
      – Periodic single slot packet assignment, 64 kbit/s full-duplex, point-to-point
  • ACL (Asynchronous ConnectionLess) – Data
      – Variable packet size (1,3,5 slots), asymmetric bandwidth, point-to-multipoint
           SCO           ACL        SCO        ACL        SCO          ACL         SCO           ACL
MASTER      f0            f4         f6        f8          f12         f14          f18          f20




SLAVE 1
                 f1                       f7         f9          f13                      f 19


SLAVE 2
                               f5                                            f17                       f21
   Robustness

   • Slow frequency hopping with hopping patterns determined by a master
          – Protection from interference on certain frequencies
          – Separation from other piconets (FH-CDMA)
   • Retransmission                              Error in payload
          – ACL only, very fast
                                                 (not header!)
   • Forward Error Correction
          – SCO and ACL                                                   NAK       ACK


MASTER              A             C          C            F           H




SLAVE 1                   B            D            E



SLAVE 2                                                           G             G
L2CAP - Logical Link Control and Adaptation
Protocol
• Simple data link protocol on top of baseband

• Connection oriented, connectionless, and signaling channels

• Protocol multiplexing
    – RFCOMM, SDP, telephony control

• Segmentation & reassembly
    – Up to 64kbyte user data, 16 bit CRC used from baseband

• QoS flow specification per channel
    – Follows RFC 1363, specifies delay, jitter, bursts, bandwidth

• Group abstraction
    – Create/close group, add/remove member
L2CAP logical channels



        Slave                          Master                      Slave

L2CAP                         L2CAP                       L2CAP
           2    d   1                    1 d d d d 1                  1      d   d   2
baseband                      baseband                    baseband




  signalling            ACL           connectionless   connection-oriented
L2CAP packet formats
  Connectionless PDU
     2          2             2                0-65533          bytes
   length     CID=2         PSM                 payload


  Connection-oriented PDU
     2          2                        0-65535                 bytes
   length      CID                       payload



  Signalling command PDU
     2          2                                                bytes
   length     CID=1                One or more commands


                        1          1        2             0
                       code        ID     length          data
   Security
                              User input (initialization)
       PIN (1-16 byte)                 Pairing                  PIN (1-16 byte)

                            Authentication key generation
              E2                                                      E2
                            (possibly permanent storage)

       link key (128 bit)          Authentication              link key (128 bit)

                             Encryption key generation
              E3                                                      E3
                             (temporary storage)

 encryption key (128 bit)            Encryption             encryption key (128 bit)


  Keystream generator                                        Keystream generator


         payload key                  Ciphering                  payload key
                                     Cipher data
Data                                                                                Data
   802.11 vs. 802.15/Bluetooth

   • Bluetooth may act like a rogue member of the 802.11 network
          – Does not know anything about gaps, inter frame spacing etc.
f [MHz]
   2480                                                                                                                           802.11b




                                                                                          SIFS

                                                                                                  DIFS
                         DIFS




                                                                                          ACK
                                                      1000 byte                                                                   3 channels
                                                                                                                                  (separated by
                                                                                                                                  installation)
          DIFS




                                                                                           DIFS
                                               DIFS




                                                                                  SIFS
                                       SIFS
                                       ACK




                                                                                  ACK
                  500 byte                                   500 byte                                    500 byte
                                                                                                                                  802.15.1
                                                                                                                                  79 channels




                                                                                   DIFS




                                                                                                         DIFS
                  DIFS




                                        DIFS




                                                             DIFS




                                                                                                                       SIFS
                                SIFS




                                                      SIFS




                                                                           SIFS




                                                                                                  SIFS
                                ACK




                                                      ACK




                                                                           ACK




                                                                                                  ACK




                                                                                                                       ACK
                         100                   100                  100                    100                  100
                         byte                  byte                 byte                   byte                 byte              (separated by
 2402                                                                                                                             hopping pattern)
                                                                                                                              t
   • IEEE 802.15-2 discusses these problems
          – Proposal: Adaptive Frequency Hopping
                 • a non-collaborative Coexistence Mechanism
   • Real effects? Many different opinions, publications, tests, formulae, …
          – Results from complete breakdown to almost no effect
          – Bluetooth (FHSS) seems more robust than 802.11b (DSSS)
WPAN: IEEE 802.15-1 – Bluetooth

• Data rate                                    • Connection set-up time
    – Synchronous, connection-oriented: 64         – Depends on power-mode
      kbit/s                                       – Max. 2.56s, avg. 0.64s
    – Asynchronous, connectionless             • Quality of Service
         • 433.9 kbit/s symmetric
                                                   – Guarantees, ARQ/FEC
         • 723.2 / 57.6 kbit/s asymmetric
• Transmission range                           • Manageability
                                                   – Public/private keys needed, key
    – POS (Personal Operating Space) up to           management not specified, simple
      10 m                                           system integration
    – with special transceivers up to 100 m
                                               • Special Advantages/Disadvantages
• Frequency                                        – Advantage: already integrated into
    – Free 2.4 GHz ISM-band                          several products, available
• Security                                           worldwide, free ISM-band, several
    – Challenge/response (SAFER+), hopping           vendors, simple system, simple ad-
      sequence                                       hoc networking, peer to peer,
                                                     scatternets
• Availability                                     – Disadvantage: interference on ISM-
    – Integrated into many products, several         band, limited range, max. 8
      vendors                                        devices/network&master, high set-
                                                     up latency
WPAN: IEEE 802.15

• 802.15-2: Coexistance
   – Coexistence of Wireless Personal Area Networks (802.15) and Wireless Local
     Area Networks (802.11), quantify the mutual interference
• 802.15-3: High-Rate
   – Standard for high-rate (20Mbit/s or greater) WPANs, while still low-
     power/low-cost
   – Data Rates: 11, 22, 33, 44, 55 Mbit/s
   – Quality of Service isochronous protocol
   – Ad hoc peer-to-peer networking
   – Security
   – Low power consumption
   – Low cost
   – Designed to meet the demanding requirements of portable consumer
     imaging and multimedia applications
UWB – IEEE 802.15.3

• 802.15.3a:
    – Alternative PHY with higher data rate as extension to 802.15.3
    – Applications: multimedia, picture transmission


• 802.15.3b:
    – Enhanced interoperability of MAC
    – Correction of errors and ambiguities in the standard


• 802.15.3c:
    – Alternative PHY at 57-64 GHz
    – Goal: data rates above 2 Gbit/s


• Not all these working groups really create a standard, not all standards
  will be found in products later …
 UWB in the Digital Home

    Local high
throughput delivery                                                                  Wired /Wireless
                        Wired / Wireless

                                               Broadband


           Wired / Wireless




                                                       Long range delivery
                                                   wired & wireless (Backbone)




          Wired / Wireless
                                                                                          Wired / Wireless




  UWB defines high spatial capacity and effortless interconnectivity
 Courtesy:http://download.microsoft.com/download/9/8/f/98f3fe47-dfc3-4e74-92a3-088782200fe7/TWMO05003_WinHEC05.ppt
Qualities of the 802.15.3 MAC

• Centralized and connection-oriented ad-hoc networking topology:
     – The coordinator (PNC) maintains network synchronization timing, performs
       admission control, assigns time for connection between 802.15.3 devices
       (DEV), manages PS requests,…
• Communication is peer to peer
• Support for multimedia QoS:
     – TDMA superframe architecture with Guaranteed Time Slots (GTS)
• Authentication, encryption and integrity
• Multiple power saving modes (asynchronous and synchronous)
• Robustness:
     – Dynamic channel selection, TX power control per link
     – PNC handover




Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
Scalable Security Capabilities


• Mode 0 is no security
• Mode 1 allows the user to restrict access to the piconet
     – User externally specifies which devices (MAC address) are in ACL
     – Can be done with simple open enrollment modes using common
       button push
• Mode 2 provides cryptographic authentication, payload
  protection and command integrity.
• Mode 3 provides payload protection, command and data
  integrity as well as cryptographic authentication using digital
  certificates.

• The security modes above mode 0 are optional


Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
Superframe Structure



        Beacon
          #m
       From PNC



 Time-slotted superframe structure consists of 3 sections:
 • Beacon:
       – transmits control information to the entire piconet, allocates resources (GTS) per
         stream ID for the current superframe and provides time synchronization
 • Optional 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
 • CFP made of:
       – Unidirectional Guaranteed Time Slots (GTS) assigned by the PNC for isochronous or
         asynchronous data streams
       – Optional Management Time Slots (MTS) in lieu of the CAP for command frames


Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
GTS and MTS Slots
  • GTSs may have different persistence
       – Dynamic GTS: position in superframe may change from superframe to
         superframe (Beacon CTA IE or broadcast channel time Grant command)
       – Pseudo-static GTS (isochronous streams): PNC may change the GTS
         positions, but needs to communicate and confirm with both Tx and Rx
         DEVs
       – Variable guard times between adjacent slots to prevent collision (clock
         drift)




  • MTS
       – Open & dedicated MTS: Used for PNC/DEV communication
       – Association MTS
       – Number of MTS per superframe is controlled by the PNC

Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
Quality of Service (QoS)

• QoS typically defined as the latency required to bound jitter
  of a continuous data stream at a desired rate.
     – Latency can be used to buffer data stream so that effects of non-
       deterministic transmission times can be reduced.
     – Very small amounts of jitter can be handled by the presentation
       device.
     – Use of latency to reduce jitter requires higher channel bit rates to
       “catch up”.
• Additional requirements placed on systems where multiple
  data streams must be synchronized.
     – Home theater audio distribution to multiple speakers
• Allocation of channel time (TDMA) the best solution.



Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
2.4GHz PHY (802.15.3)


    • 5 selectable data rates:
          – 11, 22, 33, 44, 55 Mb/s
          – 11 Msymbol/s
          – Modulation formats: BPSK, QPSK (no coding), 16, 32, 64-QAM (8-
            state Trellis code)
    • 15 MHz channel bandwidth
    • 3 or 4 non-overlapping channels
          – 3 channel mode aligns with 802.11b for coexistence
    • Transmit Power: approximately 8 dBm
    • Coexistence:
          – Compared to 802.11, an 802.15.3 2.4GHz PHY system causes less
            interference since it occupies a smaller bandwidth and transmits at
            lower power levels
          – Provides for dynamic channel selection
          – Per link dynamic power control
          – Detects and monitors for active channels and moves


Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
Alternate PHY Study Group (802.15.3a)


    • 802.15.3 has created a Study Group to investigate the
      creation of an alternate PHY to address very high data
      rate applications
          – Goal of > 110Mbps @ 10 m, > 400 Mbps @ 5 m
          – 1394a, USB2.0 HS cable replacement
          – DV50, DV100, HD DVD, High resolution printer and scanner,
            fast download speed for MP3 players, digital still cameras
    • Currently reviewing Application Presentations and
      developing requirements documents
    • UWB is a potential candidate for these VHR WPAN
      applications



Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
UWB Throughput




  Courtesy:http://download.microsoft.com/download/9/8/f/98f3fe47-dfc3-4e74-92a3-088782200fe7/TWMO05003_WinHEC05.ppt
UWB Signals


   • UWB signals are typically modulated pulse trains
        – Very short pulse duration (<1 ns)
        – Uniform or non-uniform inter-pulse spacing
   • Pulse repetition frequency (PRF) can range from hundreds of thousands to
     billions of pulses/second
   • Modulation techniques include pulse-position modulation, binary phase-
     shift keying and others




        Pulse width       Inter-pulse spacing: uniform or variable




Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
        What is Ultra Wideband?
           Radio technology that modulates impulse based waveforms instead of continuous carrier
            waves


                                   Time-domain behavior                          Frequency-domain behavior
Communication
Ultrawideband




                                   1            0           1
                Impulse
                Modulation

                                                                    time             3        frequency         10 GHz

                                                                                          (FCC Min=500Mhz)
  Narrowband
Communication




                                   0        1         0         1

                Frequency
                Modulation
                                                                                    2.4                             GHz




      Courtesy:http://www.cse.ohio-state.edu/siefast/presentations/ultra-wide-band-kimyoung-2003/ultra-wide-band-kimyoung-2003.ppt
Information Modulation

     Pulse length ~ 200ps; Energy concentrated in 2-6GHz band;
     Voltage swing ~100mV; Power ~ 10uW

     •    Pulse Position Modulation (PPM)

     •    Pulse Amplitude Modulation (PAM)

     •    On-Off Keying (OOK)



     •    Bi-Phase Modulation (BPSK)




Courtesy:http://www.cse.ohio-state.edu/siefast/presentations/ultra-wide-band-kimyoung-2003/ultra-wide-band-kimyoung-2003.ppt
Large Relative (and Absolute) Bandwidth

               Narrowband (30kHz)



                  Wideband CDMA (5 MHz)                                      Part 15 Limit

                                                   UWB (Several GHz)

                                                                                   Frequency

   • 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 magnitude
        – Power seen by a narrowband system is a fraction of the total
        – UWB signals can be designed to look like imperceptible random noise to
          conventional radios




Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
Large Fractional Bandwidth

  • Original FCC UWB definition (NPRM) is 25% or more
    fractional bandwidth
        – Fractional Bandwidth is the ratio of signal bandwidth (10 dB) to
          center frequency: Bf = B / FC = 2(Fh-Fl) / (Fh+Fl)
  • Preliminary FCC rules enable in excess of 100% fractional
    bandwidths
        – 7.5 GHz maximum bandwidth at –10 dB points
  • Large fractional bandwidth leads to
        – High processing gain
        – Multipath resolution and low signal fading




Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
   Multipath Performance

   • Ultra-wide bandwidth provides robust performance in
     multipath environments
        – Less severe signal fading due to multipath propagation means fade
          margin of only a few dB
        – Extremely short pulses enable resolution and constructive use of
          multipath energy using RAKE receiver techniques




Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
   Implications for Applications

  • UWB characteristics:
     – Simultaneously low power, low cost high data-rate wireless
       communications
     – Attractive for high multipath environments
            • Enables the use of powerful RAKE receiver techniques
            • Low fading margin
       – Excellent range-rate scalability
          • Especially promising for high rates ( >100 Mbps)

  • Candidate Applications:
     – Wireless Video Projection, Image Transfer, High-speed Cable
       Replacement




Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
 Challenges for UWB

• Wide RF Bandwidth Implementation
• In-Band Interference
• Signal Processing Beyond Current DSP (today requires
  analog processing)
• Global Standardization
• Broadband Non-resonant Antennas




 Courtesy: http://www.fcc.gov/realaudio/presentations/2002/042602/IEEE_802-15.ppt
The 802 Wireless Space




                                    Source: http://www.zigbee.org/en/resources/



Courtesy: http://homepage.uab.edu/cdiamond/ZigBee.ppt
IEEE 802.15.4 & ZigBee In Context

         Application                            Customer

                                                                                 – “the software”
               API
                                                                                 – Network, Security &
             Security                                                              Application layers
      32- / 64- / 128-bit encryption             ZigBee
                                                 Alliance                        – Brand management
            Network                                                            IEEE 802.15.4
      Star / Mesh / Cluster-Tree
                                                                                 – “the hardware”
                MAC                                                              – Physical & Media Access
                                                  IEEE                             Control layers
                  PHY                            802.15.4
     868MHz / 915MHz / 2.4GHz


        Silicon          Stack           App


          Source: http://www.zigbee.org/resources/documents/IWAS_presentation_Mar04_Designing_with_802154_and_zigbee.ppt



Courtesy: http://homepage.uab.edu/cdiamond/ZigBee.ppt
Applications


• Designed for wireless
  controls and sensors
      – Environmental
        Monitoring
      – Agricultural Monitoring
      – Home Automation Still
        on Horizon
      – Control of lights,
        switches, thermostats,
        appliances, etc.
• Connectivity between
  small packet devices

                                                        Source: ZigBee Specification Document




Courtesy: http://homepage.uab.edu/cdiamond/ZigBee.ppt
ZigBee/802.15.4 Technology: General
Characteristics


• Data rates of 250 kbps , 20 kbps and 40kpbs.
• Star or Peer-to-Peer operation.
• Support for low latency devices.
• CSMA-CA channel access.
• Dynamic device addressing.
• Fully handshaked protocol for transfer reliability.
• Low power consumption.
• 16 channels in the 2.4GHz ISM band, 10 channels in the
  915MHz ISM band and one channel in the European
  868MHz band.
• Extremely low duty-cycle (<0.1%)


Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
IEEE 802.15.4 Basics

• 802.15.4 is a simple packet data protocol for lightweight
  wireless networks
     – Channel Access is via Carrier Sense Multiple Access with collision
       avoidance and optional time slotting
     – Message acknowledgement and an optional beacon structure
     – Multi-level security
     – Works well for
          • Long battery life, selectable latency for controllers, sensors, remote
            monitoring and portable electronics
     – Configured for maximum battery life, has the potential to last as long
       as the shelf life of most batteries




Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
IEEE 802.15.4 PHY Overview

• PHY functionalities:
     –   Activation and deactivation of the radio transceiver
     –   Energy detection within the current channel
     –   Link quality indication for received packets
     –   Clear channel assessment for CSMA-CA
     –   Channel frequency selection
     –   Data transmission and reception




Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
Channel Access Mechanism

• Two type channel access mechanism, based on the network
  configuration:
     – In non-beacon-enabled networks  unslotted CSMA/CA channel
       access mechanism
     – In beacon-enabled networks  slotted CSMA/CA channel access
       mechanism
          • The superframe structure will be used.


• GTS mechanism




Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
Superframe Structure




• A superframe is divided into two parts
     – Inactive: all stations sleep
     – Active:
          • Active period will be divided into 16 slots
          • 16 slots can further divided into two parts
                     »   Contention access period
                     »   Contention free period
                     »   (These slots are “MACRO” slots.)




Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
GTS Concepts

• A guaranteed time slot (GTS) allows a device to operate on
  the channel within a portion of the superframe.
• A GTS shall only be allocated by the PAN coordinator.
     – … and is announced in the beacon.
• The PAN coordinator can allocated up to seven GTSs at the
  same time
• The PAN coordinator decides whether to allocate GTS based
  on:
     – Requirements of the GTS request
     – The current available capacity in the superframe




Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
  Battery Life Extension
                                       2560 us
                                     160 symbols
                                      80 octets
                                                          First Five Full Backoff Periods after the Beacon IFS period


                        Backoff   Backoff      Backoff    Backoff     Backoff      Backoff      Backoff      Backoff
                        Period    Period       Period     Period      Period       Period       Period       Period


                           Minimum                                       Listen Interval
Beaconing Device
                           Beacon                                   (when no frame detected)

                                            SIFS
                             576 us                                               1792 us
                           36 symbols                                           112 symbols
                            18 octets                                            56 octets




                                                                                  CCA



                                                                                               CCA
                                                                                                              Transmit Frame

                           Always at least
                            three backoff

                                                                     CCA



                                                                                  CCA
                          periods available                                                            Transmit Frame
                               to start
                            transmission
                                                         CCA



                                                                     CCA


                                                                                                 Transmit Frame




  Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
Comparison Between WPAN




Courtesy: http://www.centronsolutions.co.uk/docs/zigbee-802.15.4%5B1%5D.ppt
RFID – Radio Frequency Identification (1)

•   Data rate                                           • Connection set-up time
     –     Transmission of ID only (e.g., 48 bit,
           64kbit, 1 Mbit)                                  – Depends on product/medium
     –     9.6 – 115 kbit/s                                   access scheme (typ. 2 ms per
•   Transmission range                                        device)
     –     Passive: up to 3 m                           • Quality of Service
     –     Active: up to 30-100 m                           – none
     –     Simultaneous detection of up to, e.g., 256
           tags, scanning of, e.g., 40 tags/s           • Manageability
•   Frequency                                               – Very simple, same as serial interface
     –     125 kHz, 13.56 MHz, 433 MHz, 2.4 GHz,        • Special Advantages/Disadvantages
           5.8 GHz and many others
•   Security                                                – Advantage: extremely low cost, large
     –     Application dependent, typ. no crypt. on           experience, high volume available,
           RFID device                                        no power for passive RFIDs needed,
•   Cost                                                      large variety of products, relative
     –     Very cheap tags, down to 1€ (passive)              speeds up to 300 km/h, broad
•   Availability                                              temp. range
     –     Many products, many vendors                      – Disadvantage: no QoS, simple denial
                                                              of service, crowded ISM bands, typ.
                                                              one-way (activation/ transmission of
                                                              ID)
RFID – Radio Frequency Identification (2)

• Function
   – Standard: In response to a radio interrogation signal from a reader
     (base station) the RFID tags transmit their ID
   – Enhanced: additionally data can be sent to the tags, different media
     access schemes (collision avoidance)
• Features
   – No line-of sight required (compared to, e.g., laser scanners)
   – RFID tags withstand difficult environmental conditions (sunlight, cold,
     frost, dirt etc.)
   – Products available with read/write memory, smart-card capabilities
• Categories
   – Passive RFID: operating power comes from the reader over the air
     which is feasible up to distances of 3 m, low price (1€)
   – Active RFID: battery powered, distances up to 100 m
RFID – Radio Frequency Identification (3)

• Applications
   – Total asset visibility: tracking of goods during manufacturing,
     localization of pallets, goods etc.
   – Loyalty cards: customers use RFID tags for payment at, e.g., gas
     stations, collection of buying patterns
   – Automated toll collection: RFIDs mounted in windshields allow
     commuters to drive through toll plazas without stopping
   – Others: access control, animal identification, tracking of hazardous
     material, inventory control, warehouse management, ...


• Local Positioning Systems
   – GPS useless indoors or underground, problematic in cities with high
     buildings
   – RFID tags transmit signals, receivers estimate the tag location by
     measuring the signal„s time of flight
RFID – Radio Frequency Identification (4)

• Security
   – Denial-of-Service attacks are always possible
       • Interference of the wireless transmission, shielding of transceivers
   – IDs via manufacturing or one time programming
   – Key exchange via, e.g., RSA possible, encryption via, e.g., AES


• Future Trends
   – RTLS: Real-Time Locating System – big efforts to make total asset
     visibility come true
   – Integration of RFID technology into the manufacturing, distribution
     and logistics chain
   – Creation of „electronic manifests“ at item or package level
     (embedded inexpensive passive RFID tags)
   – 3D tracking of children, patients

				
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