Cluster-based Multihop Networking with Controlled Quality of Service March 2002 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

March 2002 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

The need for multi-cluster multi-hop QoS-controlled WLANs March 2002 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!

Preface Multi-hop wireless networking… Our mission is to March 2002 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

Synopsis: Benefits of Multi-Cluster Multi-Hop QoS-controlled WLANs March 2002 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

Problem I: Limited coverage area of QBSSs March 2002 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

Solution: Extension of Coverage Area by means of Forwarding March 2002 Solution: Extension of Coverage Area by means of Forwarding Coverage area of HC’s QoS management increased through forwarding of control information City scenario: HC FN QBSS coverage area increased through forwarding of user traffic FN: Forwarding Node (FQSTA)

Problem II: Interconnection of QBSSs March 2002 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

Solution: Multi-Channel Cluster Bridges March 2002 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

Properties of Clustered Wireless Networks March 2002 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

Ex.: Capacity Increase over # Clusters March 2002 Ex.: Capacity Increase over # Clusters = Number of Clusters

Clustering in 802.11 Applicable diversity techniques March 2002 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)

March 2002 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

II. Wireless Interconnection of BSSs March 2002 II. Wireless Interconnection of BSSs Cluster 1 (frequency 1) HC CB HC Cluster 2 (frequency 2) CB: Cluster Bridge HC: Hybrid Coordinator

III. Multi-Freq. Forwarding Example March 2002 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 FQSTA/CB Freq 1 Frq 2 Freq 1 T T T T S W S W

Work Items to be tackled March 2002 Work Items to be tackled T4 T5 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 T6 HC1 T3 T2 T1 T7 T8 HC2 T9 T11 T10 T12 HC3 T16 T13 T15 T14

March 2002 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

Next Steps... Discussion and standardization has to be started now March 2002 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!