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Generic MAC for Coordinated Topology

This presentation introduces a novel MAC protocol for 802.15.13, focusing on macro-diversity in coordinated topologies. Suitable for high-reliability industrial applications with low latency needs. Highlights various MAC functions, distributed MIMO setup, results, and requirements for industrial wireless networks.

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Generic MAC for Coordinated Topology

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  1. November 2017 Generic MAC for Coordinated Topology Date: 2017-11-04 Authors: Volker Jungnickel (Fraunhofer HHI)

  2. Abstract This presentation proposes a generic MAC for the coordinated topology in 802.15.13 featuring macro-diversity with mobility support between coordinators supervised by a master coordinator. The proposed MAC is suitable for industrial applications which require high link availability and very low latency. Volker Jungnickel (Fraunhofer HHI)

  3. Content • Introduction: OWC for Industrial Wireless • Coordinatedtopology • GenericMAC forcoordinatedtopology • MAC procedures • Howtobuild MAC frames • Implementation • Removalof DME • Whatfunctionalsplit? • Summary Volker Jungnickel (Fraunhofer HHI)

  4. Introduction • Li-Fi: Every light bulbbecomesa mobile accesspoint • Li-Fihaschallengingcost, energy, form factor • High volumesmakeitdifficulttointroduceLi-Fiin general • Introduce intermediate steps • Start withusecasesthat relax someoftheserequirements • Promising usecasesfor Li-Fi • Leverageuniquesellingpointsof light comparedradio • Mobile backhaulingofsmallradiocells simple P2P • OWC for Industrial Wireless • Secure wirelessaccess in conferencerooms, classrooms etc. Volker Jungnickel (Fraunhofer HHI)

  5. OWC for Industrial Wireless Industrial OWC: high availability, low latency  use MIMO! Use omni-directional Tx at robot and distributed Rxs Build first Li-Fi channel sounder (200 MHz BW, 8x8 MIMO) Take 6x8 MIMO measurements in real robotics environment Volker Jungnickel (Fraunhofer HHI)

  6. Distributed MIMO Setup • 6 Tx at robots arm pointingto all directions • 8 Rx at thefenceofmanufacturingcell • 48 channelsbetween all Txand all Rxmeasuredalong mobile robotstrajectory • Observations • SNR islow in wide-beam setups • Design maydifferfrom high SNR scenariotypicalfor Li-Fi • Few MHz bandwidth, SC modulation • Diversity-oriented MIMO Volker Jungnickel (Fraunhofer HHI)

  7. Results • High availabilityreachedwithmacro-diversityconcepts • Fit welltoow SNR and moderate data rate raterequirements MIMO measured along robots trajectory Fast time variance due to blocked LOS Spatial diversity creates robust OWC link Volker Jungnickel (Fraunhofer HHI)

  8. Requirements for Industrial Wireless • High reliability (almost 100% link availability) • spatiallydistributedOWC frontends • mobile deviceswithomni-directionalbeam characteristics • Low latency (< 5 ms) • Conventionalhandoveristooslowforindustrialwireless • Move mobilitysupportfromnetworklayerintothe MAC layer! • Proposal:Usethenewcoordinated MAC topologyin 802.15.13 • distributed OWC frontendsareconsideredascoordinators (CO) • Macro-diversityrealizedwithcentralizedmastercoordinator (MC) • protocolsfordistributed multi-user MIMO • suitablefunctionalsplitbetween MC and CO inside MAC or PHY Volker Jungnickel (Fraunhofer HHI)

  9. Coordinated Topology • Central controlunit: mastercoordinator (MC) • Distributed accesspoints at fixedlocations: coordinators (COs) • Mobile deviceswithomni-directionalcharacteristics = devices (DEVs) Volker Jungnickel (Fraunhofer HHI)

  10. Generic MAC for coordinated topology • CAPs areonlyusedfornetworkaccess / joining • High reliabilityrequirescontention-freemedium access: GTSs in CFP • Connectivity matrix in wavelength-division (WDD) and time-division duplex (TDD) modes WDD: downlinkWDD: uplink TDD: • WDD: VLC is not alwaysreciprocal • TDD: Additional direct links between COs and DEVs Volker Jungnickel (Fraunhofer HHI)

  11. Generic MAC functions • Network joining • At anylocationwherethe mobile deviceissituated • TDD withfixed, network-widesplitbetweendown- and uplink • CAP foradmission / join-request / connectivityestimation • Beaconframemulticellchannelestimation feedbackin CAP  superframespecification • Macrodiversity • Multiple COs actasonecluster i.e. transmitorreceivejointly • All COs aresynchronized e.g. using PTP + SynchE • Flexible clustersdepending on UL/DL connectivitymatrix • Data forwardedfrom/to MC to/fromclusteroverinfrastructurenetwork Volker Jungnickel (Fraunhofer HHI)

  12. Generic MAC frames: Overview • Classical frame structure • Applicable to 802.15.13 • Global transmissions e.g. for network access • synchronously transmitted by all COs • Regional transmissions e.g. for macro-diversity • transmitted by individual CO or clusters of COs synchronously • same time slot is reused by distant clusters (disjoint connectivity) • different time slots are used in case of overlaping clusters • Local transmissions e.g. for identification and connectivity estimation • transmitted by individual COs in parallel  interference-limited • an appropriate frequency reuse scheme may be implemented here Volker Jungnickel (Fraunhofer HHI)

  13. Global and local frames • Global frames • All COs send the same signal • Needs full synchronization • Local frames • Frames are orthogonal • Use orthogonal resources for adjacent COs • Use non-orthogonal resources for distant COs • Operated in interference-limited scenario Volker Jungnickel (Fraunhofer HHI)

  14. Regional frames • Used for macro-diversity • All COs in a cluster jointly transmit or receive the same signal on the same resource • Distant clusters (with no connectivity) transmit or receive different signals on the same resources • Overlapping clusters do the same but use different time slots or frequencies to avoid interference Volker Jungnickel (Fraunhofer HHI)

  15. What frame is local/regional/global? • Beacon frameis global • Allow DEVs to synchronize to the whole network • Contains e.g. macOWPANId, MAC address of MC, feedback mode field, reduced superframe spec to advertise CAPs for network access • Medium access frame is typically regional • Transmitted as part of the data in a scheduled cluster • Spatial reuse is supervised by the MC based on connectivity • Multicell channel estimation frame is local • Contains orthogonal sequences to identify adjacent COs • Local information about the specific CO such as MAC address, reuse factor and optional sequence index • Sequences are reused by distant Cos Volker Jungnickel (Fraunhofer HHI)

  16. What frame is local/regional/global? (2) • Feedback frame is global or regional • As a global frame, FB is used for joining the network • Then it contains connectivity information and is transmitted in CAP • More complex feedback can be provided for scheduling/joint processing (applicable feedback mode is signaled in the beacon frame) • As a regional frame, it is used in a cluster to limit feedback overhead • Simultaneous transmissions take place in distant clusters • In overlapping clusters, transmissions take different time slots Volker Jungnickel (Fraunhofer HHI)

  17. Generic MAC procedures • Beacon transmission • Beacon allows mobile devices to synchronize to the network • Moreover, it informs the device where CAPs are availabe for network access • Information is extracted from globalsuperframe specification Volker Jungnickel (Fraunhofer HHI)

  18. Generic MAC procedures (2) Multicellchannelestimation • Enablesmeasuringall channelsfrom all COs • Doneby all COs in dedicatedresources • Overhead isreducedbyspatialreuse • Pulsed Modulation PHY • Code-division multiplex (energyefficincy): different orthogonal code at each CO • Code length, codes+reuseassignedbyMC • OFDM PHYs • Frequency-division multiplex: Combofsubcarriers, anothercombshiftforeach CO • Carrier spacing, shift+reuseassignedby MC Volker Jungnickel (Fraunhofer HHI)

  19. Generic MAC procedures (3) • Feedback delivery • Mobile DEVs • Connectivity varies over time • Detected by the device by observing i) the regular beacon frame ii) the multi-cell channel estimation frame • In idle mode, the DEV sends a feedback frame during next CAP. • Before a DEV can start uplink transmission, it has to send a feedback frame, even ifdownlink connectivity was unchanged. • For continuous transmissions, feedback delivery happens in a CFP. • The feedback packet is fed forward by the CO(s) to the MC. Volker Jungnickel (Fraunhofer HHI)

  20. Generic MAC procedures (4) • Superframe Specification in parallel clusters • MC knows global connectivity and broadcasts global Superframe Spec • Regional Superframe Spec for the cluster is filtered out at the CO • Only the regional SF Specification is forwarded to the DEVs • This allows spatial reuse for both, control information and data Volker Jungnickel (Fraunhofer HHI)

  21. Generic MAC procedures (5) • Superframe Specification in parallel clusters • MC knows global connectivity and broadcasts global Superframe Spec • Regional Superframe Spec for the cluster is filtered out at the CO • Only the regional SF Specification is forwarded to the DEVs • This allows spatial reuse for both, control information and data Volker Jungnickel (Fraunhofer HHI)

  22. Available mechanisms in G.hn/TG13 D1 • Many mechanisms can be reused or mobile OWC operation, some t.b.d. • Selected examples Volker Jungnickel (Fraunhofer HHI)

  23. How to build generic frames • Beacon frame • Global transmission for synch, advertisement of the whole network • Bitwise equal for all COs at a specific time • Contains the assignment of CAPs for network access • Use very robust modulation and coding • Multicell channel estimation frame • Local transmission using orthogonal ressources • HCM can be used as orthogonal codes in Pulsed Modulation PHY • Subcarrier masks can be used in HB OFDM PHY to define comb • Channel between subcarriers in the comb is obtained by interpolation • Channel information can be used for precise localization by triangulation (additional protocol like ranging a.k.a. timing advance) Volker Jungnickel (Fraunhofer HHI)

  24. How to build generic frames (2) • Feedback frame • Transmitted by OWC DEVs in uplink direction • Using a „general purpose“ MLME frame with new primitive in a reserved GTS which contains management message • Uplink channel estimation can be part of the feedback frame, by adding orthogonal channel estimation sequence • Medium access frame / superframe specification frame • Informs devices about CAPs and GTSs • Contains regional information only, not the global superframe spec. • Transmitted on orthogonal ressource, to avoid interference with other clusters Volker Jungnickel (Fraunhofer HHI)

  25. How to build generic frames (3) • Macro diversity data frame • Macro diversity = signals transmitted/received by multiple COs („cluster“) • Clusters are preconfigured e.g. by using dedicated VLAN IDs for each cluster and dynamically selected using an appropriate control message protocol • MAC layer has the same data available at all COs: Data is classified and queued at MC and then broadcast to all COs in the cluster via the infrastructure network • Acknowledgements and retransmissions are also processed at the MC • This approach avoids/repairs packet losses during MAC-internal „handover“  high robustness, low latency for industrial wireless Volker Jungnickel (Fraunhofer HHI)

  26. DME in 802.15.7-2011 • DME in 802.15.7-2011 is used for dimming control • Should be removed in 802.15.13 Volker Jungnickel (Fraunhofer HHI)

  27. What functional split in 802.15.13? • Optical SAP/PHY switch • Not defined as digital or analog? • Switch is part of PHY and so far controlled by PLME • Should become part of the MAC and (remotely?) controlled by MC • Concept should be revised in 802.15.13, needs more detailled substructure of MAC and PHY • Leverage previous work from • IEEE 1904.3 Radio over Ethernet (RoE) • IEEE 1914 on Next Generation Fronthaul Interface (NGFI) Master Coordinator Coordinator Analog or digital Fronthaul? Volker Jungnickel (Fraunhofer HHI)

  28. Summary • A generic MAC layer is proposed for the coordinated topology. • It is designed for the use of OWC in industrial wireless applications where high availability and low latency are required. • A distributed multiuser MIMO featuring macrodiversity and mobility support inside the MAC has been proposed. • MAC functions have been classified into global, regional and local ones, together with the associated frame structures. • Generic MAC procedures have been highlighted and explained how to build the corresponding frames. • TG13 needs a clearer view what MAC functions shall be centralized and what distributed, i.e. find a good functional split btw. MC and COs. Volker Jungnickel (Fraunhofer HHI)

  29. Possible functional splits NRT-RT split PHY-MAC split Volker Jungnickel (Fraunhofer HHI)

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