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									July 2002                                  doc.: IEEE 802.15-02/312r0




             Cluster-based Multihop
                Networking with
               High-Rate WPANs
                          Oliver Mülhens
               Philips Research, Aachen, Germany

              Contact: oliver.muelhens@philips.com



Submission                   Slide 1          O. Muelhens, Philips Research
July 2002                              doc.: IEEE 802.15-02/312r0




                       Outline

     I.      The Need for Multihop in HR-WPAN
     II.     Evolution of Wireless Networks
     III.    HR-WPAN Multihop Concepts
     IV.     Conclusions, Work Items, Next Steps




Submission                 Slide 2        O. Muelhens, Philips Research
July 2002                                  doc.: IEEE 802.15-02/312r0




                        Preface
• Multi-hop wireless networking…
     – is not just a particular improvement of a WPAN
       parameter or single implementation aspect
     – but adds a new dimension to WPANs
     – includes, but is not limited to, 802.15.3
• Our mission is to
     – Create awareness of the Multihop concept and its
       potential
     – Start a persistent discussion thread

Submission                   Slide 3          O. Muelhens, Philips Research
July 2002                 doc.: IEEE 802.15-02/312r0




I. The Need for Multihop in HR-WPAN




Submission      Slide 4      O. Muelhens, Philips Research
July 2002                                 doc.: IEEE 802.15-02/312r0



                Top Requirements
•   High Data Rate (HDR) and scaleability
•   Mobility: Roaming between piconets
•   Dynamic QoS mgmt. incl. rate, delay, jitter
•   RF sense: Efficient spectrum usage
•   Effective range: Complete home, plus garden, …
•   Automated setup and changes in NW topology
•   Support for low latency and interactive data
•   Intelligent power (drain) management




Submission                  Slide 5          O. Muelhens, Philips Research
July 2002                                     doc.: IEEE 802.15-02/312r0



                  Top Requirements
•   High Data Rate (HDR) and scaleability
•   Mobility: Roaming between piconets
•   Dynamic QoS mgmt. incl. rate, delay, jitter
•   RF sense: Efficient spectrum usage
•   Effective range: Complete home, plus garden, …
•   Automated setup and changes in NW topology
•   Support for low latency and interactive data
•   Intelligent power (drain) management


         Go naturally with Multihop      Need 2nd thought
Submission                     Slide 6           O. Muelhens, Philips Research
July 2002                                               doc.: IEEE 802.15-02/312r0



  Top Requirement: High Data Rate...
• The pretty face of high data rates
     – Most prominent requirement of modern WPANs
       and WLANs, aiming at high-quality A/V streaming
       and high-speed computing, is high throughput
     – Striving to achieve hundreds of Mbit/s PHY rate
             • 802.15.3a:
               – 110 Mbit/s at 10 m
               – 200 Mbit/s at 4 m
               – 500 Mbit/s at <<4 m (USB 2.0 / IEEE 1394 cable replacement)
             • 802.11 HTSG and beyond
               – 100+ Mbit/s
               – Range not yet specified

Submission                             Slide 7             O. Muelhens, Philips Research
July 2002                                        doc.: IEEE 802.15-02/312r0



  Top Requirement: High Data Rate...
• The ugly face of high data rates
     – Alas, TX power is limited
             • Either by regulations, or
             • Battery power
             • Device cost

      As PHY rates go up, coverage ranges decrease!
      Wireless networks = pico cells
      Contrasts effective range requirements



Submission                             Slide 8      O. Muelhens, Philips Research
July 2002                          doc.: IEEE 802.15-02/312r0



  Top Requirement: High Data Rate...
• Solution to data rate dilemma:

   Multihop communication to increase range!




Submission             Slide 9        O. Muelhens, Philips Research
July 2002                    doc.: IEEE 802.15-02/312r0




  II. Evolution of Wireless Networks




Submission        Slide 10      O. Muelhens, Philips Research
July 2002                                doc.: IEEE 802.15-02/312r0




        Evolution of Wireless Networks
• Today: Infrastructure-based wireless networks
• Next step: Multihop WLANs/WPANs
      – Range extension
      – Locally centrally-controlled
      – Infrastructure based
• Ultimate goal: Ad-hoc multihop WLANs/WPANs
      – Auto configuration
      – Distributed control


Submission                    Slide 11      O. Muelhens, Philips Research
July 2002                          doc.: IEEE 802.15-02/312r0




             Ad-hoc WLANs/WPANs
• Devices communicate without necessarily
  using a given network infrastructure
• Self-configuring
• Terminals can communicate with each
  other when they are out of range, because
  some, if not all, nodes are capable of assuming
  router functionality when needed.
• The network topology can change
  constantly because nodes move

Submission             Slide 12       O. Muelhens, Philips Research
July 2002                                        doc.: IEEE 802.15-02/312r0




                  Impact of Multihop
•     First logical step towards the goal to have ad-hoc
      multihop wireless networks
•     Beside static coverage extension, multihop offers
      scalability and free node placement
      – E.g. include garden house into wireless home network. With
        multihop, it can easily be reached by an automatically
        assigned forwarding node (FN) in the home.
•     Decreased power by reducing average Tx distances
      – E.g. bridging 2x5 m needs less power than 1x10 m


      – Less max. Tx power can also reduce device cost
      – Smart power management assigns forwarder functionality
        primarily to stationary devices
Submission                      Slide 13            O. Muelhens, Philips Research
July 2002                                            doc.: IEEE 802.15-02/312r0


                     Properties of
             Clustered Wireless Networks
 • The smaller the pclusters (piconets), the more
   channels can be used in a given area (re-use)
       – Advantage: offered traffic per channel decreases
       – Option: spatial diversity improves re-use factor
 • The smaller the piconet, ...
       – ... the higher modulation/coding can be used
         => Advantage: increased channel capacity
       – ... the more hops are needed
         => Dynamic clustering helps to maintain efficiency
 • Applicable diversity techniques
       – Frequency (channel), space, possibly code


Submission                        Slide 14              O. Muelhens, Philips Research
July 2002                   doc.: IEEE 802.15-02/312r0




   III. HR-WPAN Multihop Concepts




Submission       Slide 15      O. Muelhens, Philips Research
July 2002                                              doc.: IEEE 802.15-02/312r0


             Multi-Channel Cluster Bridges
              (Forwarding in Frequency)
 • A Cluster Bridge (CB) associates with overlapping
   clusters operating in different channels
       –     Selection and hand-off of CB
       –     Part-time presence of CB in either of the two piconets
       –     QoS is guaranteed
       –     Requires some buffer space for transportation of packets
             from one piconet into the other


 • Special case Forwarding Node (FN)
       – Extends piconet by a single remote device


Submission                           Slide 16             O. Muelhens, Philips Research
July 2002                                              doc.: IEEE 802.15-02/312r0


  Multi-Channel Forwarding Example
• PNCs operate on different frequencies
     – FN/CB switches from one frequency to the other
     – FN/CB synchronizes to new beacon
     – Switching Times TS and Waiting Times TW will occur

             Freq 1

             Freq 2

             FN/CB    Freq 1   Frq 2          Freq 1

                           TS TW       TS TW
Submission                         Slide 17               O. Muelhens, Philips Research
 July 2002                                    doc.: IEEE 802.15-02/312r0



Example 1: QoS-enabled In-home Appl.
    Den                              Living room
(Piconet 1 @                         (Piconet 2 @
 channel 1)                           channel 2)




Cellar piconet

Photo Jukebox
                 • No new wires
Dig. Cable Rx    • Mobility and freedom of device placement
 Submission               Slide 18                  O. Muelhens, Philips Research
July 2002                              doc.: IEEE 802.15-02/312r0




                 Multihop Example 2
Home scenario
 FN: Forwarding Node
 CB: Cluster Bridge                         PNC
                                            PNC + FN
                                            CB
                                            PNC + CB

                                         Yard




     Lines: Possible hops
Submission                  Slide 19      O. Muelhens, Philips Research
 July 2002                                             doc.: IEEE 802.15-02/312r0



Support for low Latency and high Throughput
 • Latency often seen as a disadvantage of
   multihop networks
      – Example: A forwarder switches between 2 channels
        and transfers data from channel 1 to channel 2
      – The shorter the period...
              • … the lower the latency, but
              • … the higher the overhead (re-synchronize to new channel)
    Possible solution
      – Multi-frequency forwarding
      – Can be split on 2 stations (see next slide)
      – Maximum throughput will not be halved per hop

 Submission                           Slide 20            O. Muelhens, Philips Research
July 2002                                      doc.: IEEE 802.15-02/312r0



        Split Multi-Channel Forwarding




   • 2 Cluster Bridges that work alternatingly on 2 channels
   • Useful to sustain near-maximum throughput between clusters
Submission                     Slide 21           O. Muelhens, Philips Research
July 2002                                   doc.: IEEE 802.15-02/312r0


    Single-Channel Multihop Example
          (Forwarding in Time)
 • A Cluster Bridge associates with overlapping
   piconets (different Net IDs) in the same
   channel
       – CB is present in both piconets
       – CB copies data between piconets

 • A Forwarding Node could generate a
   substitute superframe for the remote device
       – The forwarding device is a transparent
         representative of the PNC
Submission                   Slide 22          O. Muelhens, Philips Research
July 2002                                           doc.: IEEE 802.15-02/312r0



                Smart Power Management
• Multihop tansmission means
     – Increased number of transmissions, but…
     – Due to decreased transmission distances,
       multihop does not need more power than
       traditional wireless networks
     – Smart power management assigns forwarder
       functionality primarily to stationary devices
             • E.g. VCR, TV set or PC in the home




Submission                           Slide 23          O. Muelhens, Philips Research
 July 2002                   doc.: IEEE 802.15-02/312r0




IV. Conclusions, Work Items, Next Steps




 Submission       Slide 24      O. Muelhens, Philips Research
July 2002                                doc.: IEEE 802.15-02/312r0



                      Conclusions
 • Ever increasing PHY rates lead to decreased coverage
   range => QoS-enabled Multihop becomes
   indispensable for HR-WPANs to compensate for that
 • In the home, QoS-enabled multihop WPANs allow for
   NW scalability, device mobility and freedom of
   placement
 • Capacity increase possible by smart clustering
 • Throughput, latency and battery power issues have
   been addressed
 • MH can be built upon existing 802.15.3 features
       – Child/parent piconets
       – Low-latency TDMA scheme (GTS)
Submission                    Slide 25      O. Muelhens, Philips Research
 July 2002                                                    doc.: IEEE 802.15-02/312r0




              T4
                          Technical Items to be tackled
      T5
                                  •   Dynamic clustering
T6      PNC1          T3              – Signalling procedures
                                      – Membership management
                     T2
   T1          T7
                                  •   Interconnection of clusters
        T8      PNC2         T9       – Forwarding procedure
                                      – Choice of forwarding stations
               T10          T11       – Cluster bridge installation and hand-off
  T12
                                  •   Routing of packets
        PNC3          T16
T13                                   – Type of algorithm
                    T15               – Address resolution
              T14                 •   Smooth integration into 802.15.3
 Submission                                 Slide 26             O. Muelhens, Philips Research
July 2002                                   doc.: IEEE 802.15-02/312r0



                     Next Steps...
 • Multihop should be on the agenda of the
   802.15.3 Task Group
       – Address technical details in short term
       – Transfer existing valuable expertise from WLAN
         Multihop simulations to WPAN
 • Prove that multihop fits well into current
   HR-WPAN concepts
 • Let’s do the first steps now!

                                        Thank you!
Submission                   Slide 27          O. Muelhens, Philips Research

								
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