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Multi hop connections using 802.11

Multi hop connections using 802.11. Guido R. Hiertz , Yunpeng Zang ComNets Chair of Communication Networks Aachen University (RWTH) Germany Jörg Habetha Philips Research Aachen Germany. Advantages of multi frequency mesh networks Less interference Exclusive channels Reuse patterns ….

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Multi hop connections using 802.11

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  1. Multi hop connections using 802.11 Guido R. Hiertz, Yunpeng Zang ComNets Chair of Communication Networks Aachen University (RWTH) Germany Jörg Habetha Philips Research Aachen Germany Guido R. Hiertz, ComNets, Aachen University (RWTH)

  2. Advantages of multi frequency mesh networks Less interference Exclusive channels Reuse patterns … Disadvantages of multi frequency mesh networks Frequency planning Frequency coordination Multiple transceivers … COST (!) Multi frequency Mesh Guido R. Hiertz, ComNets, Aachen University (RWTH)

  3. E.g. Consumer Electronics Mass production Limited power Limited computing power Ease of use … Cost sensitive (!) Even 50¢ extra might be too much Single transceiver solutions Easy to implement Available Well known … Single frequency Mesh Solutions for single frequency mesh needed, too Guido R. Hiertz, ComNets, Aachen University (RWTH)

  4. Assumption TDMA channel Equal transmission duration Equal transmission power Equal distance between stations No errors on wireless medium Simplex connection Interference range limited to neighboring station Reception limited to neighboring station Best case Spatial frequency reuse (1) Guido R. Hiertz, ComNets, Aachen University (RWTH)

  5. Reuse limited by neighbor Reuse distance min. 4 hops Spatial frequency reuse (2) Guido R. Hiertz, ComNets, Aachen University (RWTH)

  6. Packet forwarding in 802.11 Guido R. Hiertz, ComNets, Aachen University (RWTH)

  7. Packet forwarding in 802.11 (2) Guido R. Hiertz, ComNets, Aachen University (RWTH)

  8. 802.11 forwarding in detail Guido R. Hiertz, ComNets, Aachen University (RWTH)

  9. 802.11 = Single hop MAC • Distributed Coordination Function • Coordinates single hop • Local BSS only • No Coordination for Multi Hop • Independent process in each STA • Network Allocation Vector (NAV) reserves single only • No priority to forwarding Guido R. Hiertz, ComNets, Aachen University (RWTH)

  10. Infrastructure based BSS Multi hop connection via AP Hops to/from AP wireless Wired backbone Four address format Independent BSS All stations in reception range No forwarding procedure defined No Multi Hop concept in 802.11 Guido R. Hiertz, ComNets, Aachen University (RWTH)

  11. 802.11 duplex route in detail Guido R. Hiertz, ComNets, Aachen University (RWTH)

  12. Much worse than simplex connection Forwarding stations = Bottleneck “Neighborhood capture” (11-01/596r1) For system level, intra BSS Here: For multi hop between stations No equal channel access probability Un-proportional reduced for forwarding nodes Steady collisions with neighbors No priority to forwarding Uncoordinated access Duplex multi hop Guido R. Hiertz, ComNets, Aachen University (RWTH)

  13. Conclusion • 802.11 MAC is not sufficient for multi hop • 802.11 leaves information unused for multi hop • Multi hop is key element to mesh networks Without useful protocol for multi hop in core network, mesh will fail Guido R. Hiertz, ComNets, Aachen University (RWTH)

  14. Thank you for you attention hiertz@ieee.org zangyp@ieee.org Guido R. Hiertz, ComNets, Aachen University (RWTH)

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