Cluster-based Multihop Networking with Controlled Quality of Service

1. Cluster-based Multihop Networking with Controlled Quality of Service Oliver Mülhens , Jörg Habetha, Wolfgang O. Budde Philips Research, Aachen, Germany Contact: oliver.muelhens@philips.com

2. Outline • The need for multi-cluster multi-hop communication in QoS-supporting BSSs (QBSSs) • Coverage area extension of a QBSS: Forwarding mechanisms • Interconnection of QBSSs Multi-hop ad hoc networking • Conclusions • Next steps

3. The need for multi-cluster multi-hop QoS-controlled WLANs • Wireless QoS usually achieved through centrally-controlled clusters, e.g. 802.11e QBSS • But QBSSs’ coverage area is limited to the radio range of the Hybrid Coordinator (HC) • Overall capacity for QoS-controlled traffic is given by the capacity of a single channel • Multi-cluster multi-hop communication is a necessity for QoS-enhanced wireless networks • Standardization needs to be started now!

4. Preface • Multi-hop wireless networking… • is not just a particular improvement of a WLAN parameter or single implementation aspect • but adds a new dimension to next-gen WLANs • includes, but is not limited to, 802.11a/e/h • Our mission is to • Create awareness of the Multi-hop concept and its potential • Start a persistent discussion thread

5. Synopsis: Benefits of Multi-Cluster Multi-Hop QoS-controlled WLANs • Coverage extension of QBSSs • Capacity increase due to smart clustering • E.g. different from single-channel IBSS • Wireless interconnection of QBSSs • More efficient use of spectrum in case of multi-hop connections (no collisions) • Can be built upon existing 802.11 extensions • 802.11e: QoS enhancements • 802.11h: Frequency agility

6. Problem I: Limited coverage area of QBSSs • The higher the radio frequency, ... • the more line-of-sight the propagation, • the higher the free-space loss, • the higher the attenuation due to walls and other obstacles, • thus, the smaller the coverage area

7. FN FN HC Solution: Extension of CoverageArea by means of Forwarding • Coverage area of HC’sQoS management increased through forwarding of control information City scenario: • QBSS coverage area increased through forwarding of user traffic FN: Forwarding Node (FQSTA)

8. Problem II: Interconnection of QBSSs • As of today, QBSSs can only be interconnected through wired infrastructure • A-priori network planning required • Rather limited ad-hoc capabilities • No multi-hop mode defined for QBSSs

9. Solution: Multi-Channel Cluster Bridges • A cluster bridge (CB) associates with overlapping QBSSs operating in different channels • Part-time presence in either of the two BSSs • Throughput optimization by predefined medium access opportunities • Requires some buffer space for transportation of packets from one BSS into the other

10. Properties of Clustered Wireless Networks • The smaller the clusters, 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 cluster, the higher modulation/coding can be used • Advantage: increased channel capacity • The smaller the cluster, the more hops needed • Dynamic clustering helps to maintain efficiency

11. Ex.: Capacity Increase over # Clusters = Number of Clusters

12. Clustering in 802.11 • Applicable diversity techniques • Frequency (channel) • Space • Code • Compliant with latest 802.11 extensions • 802.11h: frequency agility • 802.11e: QoS enhancements (periodic beacons, reserved TXOPs)

13. I. Coverage Extension • The forwarding QSTA (FQSTA) is a transparent representative of the HC • Selection and hand-off of FQSTA and HC. • QoS is guaranteed • Bandwidth-efficient FQSTA HC

14. II. Wireless Interconnection of BSSs Cluster 1 (frequency 1) HC CB HC Cluster 2 (frequency 2) CB: Cluster Bridge HC: Hybrid Coordinator

15. III. Multi-Freq. Forwarding Example • PCs/HCs operate on different frequencies • FQSTAs/CBs switch from one frequency to the other • FQSTAs/CBs switch during (E)DCF-phase • Switching Times TS and Waiting Times TW will occur Freq 1 Freq 2 Frq 2 Freq 1 Freq 1 FQSTA/CB T T T T S W S W

16. T7 T8 T9 T11 T10 T12 T13 T16 T15 T14 Work Items to be tackled T4 T5 T6 HC1 T3 • Dynamic clustering • Signalling procedures • Membership management • Interconnection of clusters • Forwarding procedure • Choice of forwarding stations • CB-installation and hand-off • Routing of packets • Type of algorithm • Address resolution T2 T1 HC2 HC3

17. Conclusions • Multi-cluster multi-hop communication is indispensable for QoS-enhanced wireless networks • Centralized solutions based on 802.11 PC/HC and Forwarding Stations / Cluster Bridges have been roughly sketched • Compliance with current 802.11 features and extensions shown • Coverage extension and capacity increase for QoS-controlled networks is feasible

18. Next Steps... • Discussion and standardization has to be started now • 802.11a is in initial deployment • 802.11e/h are settling these days • The road towards coverage extension and capacity increase must be presented in short term • Experience from simulation exists • Join forces!