Cluster-based Multihop Networking with High-Rate WPANs

1. Cluster-based Multihop Networking withHigh-Rate WPANs Oliver Mülhens Philips Research, Aachen, Germany Contact: oliver.muelhens@philips.com

2. 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

3. 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

4. I. The Need for Multihop in HR-WPAN

5. 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

6. 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

7. Top Requirement: High Data Rate... • The pretty face of high data rates • Most prominent requirement of modern WPANsand 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

8. 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

9. Top Requirement: High Data Rate... • Solution to data rate dilemma: Multihop communication to increase range!

10. II. Evolution of Wireless Networks

11. 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

12. 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

13. 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

14. 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

15. III. HR-WPAN Multihop Concepts

16. 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

17. 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 Frq 2 Freq 1 Freq 1 FN/CB T T T T S W S W

18. Example 1: QoS-enabled In-home Appl. Den(Piconet 1 @ channel 1) Living room (Piconet 2 @ channel 2) Cellar piconet Photo Jukebox • No new wires • Mobility and freedom of device placement Dig. Cable Rx

19. Multihop Example 2 Home scenario FN: Forwarding NodeCB: Cluster Bridge PNC PNC + FN CB PNC + CB Yard Lines: Possible hops

20. 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

21. Split Multi-Channel Forwarding • 2 Cluster Bridges that work alternatingly on 2 channels • Useful to sustain near-maximum throughput between clusters

22. 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

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

24. IV. Conclusions, Work Items, Next Steps

25. 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)

26. T7 T8 T9 T11 T10 T12 T13 T16 T15 T14 Technical Items to be tackled T4 T5 T6 PNC1 T3 • Dynamicclustering • Signalling procedures • Membership management • Interconnection of clusters • Forwarding procedure • Choice of forwarding stations • Cluster bridge installation and hand-off • Routing of packets • Type of algorithm • Address resolution • Smooth integration into 802.15.3 T2 T1 PNC2 PNC3

27. Next Steps... • Multihop should be on the agenda of the802.15.3 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!